Downunder Theatre MKII

Originally Posted by Dennis Erskine

...also, watch the defaults on the input and output "pots" and filters. They are down considerably.

Helpful hint. On the input side, insert a mixer with your source on one input and the signal generator on the other. With that, you can test the full channel chain plus you then have white, pink and sine noise available from each channel.

A secret QSC feature ... regardless of the number of filters and other do-dads you insert into a chain, the latency for all channels will be exactly the same.

Have a blast.

Originally Posted by Dennis Erskine

Elill - 7 to 15 degrees is what is used along with an AR coated optical glass. OTOH, if you have a cheap projector with cheap plastic lenses ... how much worse can it get?

The issue is not damage to the projector. It is:
1. Light reflection off the glass surface back into the projector lens reducing contrast;
2. Loss of image sharpness, uneven focus, color banding or rainbowing as a result of poor optics ... or, degrading the quality of the lens the manufacturer went to a lot of trouble to avoid.

Originally Posted by Dennis Erskine

The "need" or lack of "need" for a curved screen is a combination of factors:

1. Throw distance between screen and lens (short throws, wide screens = problems);
2. Width of the screen with respect to the width of the room (the closer the screen to the room's width, the more points in favor of curved)
3. Relationship between screen width and distance of primary row (or front row) from the screen.

All of the above need be considered. My experience suggests, corner to corner focus need not be a problem. OTOH, I also find in most installations of curved screens the radius of the screen is way too small ... generally by about half of what it ought to be.

Originally Posted by Dennis Erskine

My general suggestion is to consider the tallest reasonable 1.78:1 format your room and seating distances will tolerate. Then take that height and calculate screen width for a 2.35 or 2.40 aspect.

Originally Posted by Dennis Erskine

There you go. Here's a suggestion. Draw a rectangle showing the largest possible size of your room. Inside that rectangle, draw seats, rows. Now, draw lines 3' out from each seating row on the sides ... at least that behind the back row (5' is better). Now, from the center of the front row draw two lines toward the front of the room tha will form a 45 degree angle from the front center seat. From the end seats on the front row, draw a straight line to the front of the room. Where your two straight lines intersect your two angled lines from the center seat, draw a line between these two points. There you have your screen width and distance to the screen from the front row. Allow approximately three feet of space behind the screen.

Ok, now you have working dimensions to use to begin determining actual room dimensions, room entry, platform locations, where you can install equipment (not in the room). In other words, you have defined your maximum and minimum dimensions available, so play in that sand box. For your walls, ceiling consider that your finished wall surfaces willl be 5" to 6" inside your framing. You can now tweak ... screen aspect vs seating distance, 3D or not 3D, speaker locations, your preferences and so forth.

Originally Posted by Dennis Erskine

I'm not going to agree entirely with Roger, nor entirely disagree. Each has their place and proper application. Certainly monopoles can be made to work in a small room with a single (maybe two) listening positions. They aren't going to be timbre matched unless they are the same distance as the mains from all boundaries and at the same height. (The timbre, as heard in the listening position, will change with height on a monopole design.) Once you have a small room with, say, two rows of seats and three to four seats in each row, monopoles can easily create a bigger problem than they solve. Other than timbre, you now have a situation where those on the ends of the rows are overwhelmed with that nearest side surround ... in other words, ears are soooo close to their respective side surround speaker, that speaker will over power the rears and opposite side speakers.

In larger rooms, with multiple rows, a relatively respectable distance between the end seats and the walls and the luxury of surrounds for each row, now you can create something really stunning with an array of monopole surrounds.

In the end, saying one is better than the other without context is not entirely correct. That's, of course, my opinion. Take it, leave it, or roll your own.

Originally Posted by Dennis Erskine

Memories of SRS.

I don't want to leave the impression timbre isn't important; but, it is only one of "billions and billions" (to quote Carl Sagan) of combinations and permutations which need be considered when putting together a high performance (acoustic) space. When we consider the challenges of 6 to 8 seats in a small residential space, timbre matching surrounds will not necessarily be the biggest elephant in the room.

Larry, a doubling of the distance from the source will result (in round numbers) in a 6dB decrease in SPL. If you want to determine the SPL difference from surround speaker "A" between seats located at R1 and R2, here's a reasonable means to estimate that difference. SPL2 = SPL1 − 20 log10 (R2 / R1 ) With side surrounds you'd want the delta in SPL between the closest seat to the speaker to be not more than 3dBSPL higher than at the furthest seat from the speaker. You'd want to achieve the same with the rear surrounds and, of course, the front speakers as well. (Note ... you have to account for the radiation pattern of the speaker.) If you look at two rows of seating and a monopole speaker, from a timbre AND SPL perspective, you also need to recognize that one, if not both, rows will be off axis from the speaker. Since the distances (from side surrounds particularly) are much shorter than from the LCR's, listeners will be more off axis with respect to the side speakers than the front. More off axis equates to not only SPL differences but timbre as well.

Referring back to ITU specifications (and those configurations suggested by other sources), we generally see the ideal is that all speakers are equidistant from the (single) listening position. The impossibility of equidistant in most rooms was solved by receivers/pro-pros allowing you to set that distance in the speaker set-up menus. Or, did it really solve the problem? Not exactly. It solved a path, or phase, difference problem to a single seat. It certainly does not resolve a timbre difference in a room with multiple rows of multiple seats due to off axis response. How do you resolve that? Simple (maybe). You need to be careful of the off axis response characteristics of the speakers you select for *your* specific physical environment. The low hanging fruit may not be timbre.

Originally Posted by Ted White

For proper expectations, please keep in mind that the ultra-low frequencies will still get into your framing. This is simply a function of the resonance point of your walls and ceiling. If the walls have a resonance point of 40Hz, sound from 60Hz on down will get progressively transmitted out of the theater better. This is why we layer as much mass as we can on the walls and ceiling. It's the most direct means to lower that resonance point even lower.

If we add a third sheet of drywall, for example, we can drop that resonance point quite a bit. So instead of 40Hz, you might have 30Hz, which gives you better low frequency isolation from 45Hz on up. The 30Hz and 40Hz figures are examples only.

Originally Posted by Dennis Erskine

Here's the best you can do (why am I telling people this? geeze, it takes money out of my pocket. Hey buddy, you got a buck for a cup of coffee?)

Where the conduit enters the room (through the drywall), maker certain the conduit does not touch the drywall. You can use a flexible caulk (Ted has some acoustic caulk that will work well) to seal the gap between the conduit and drywall.

Where the conduit passes through framing, cut the hole bigger than the conduit and do exactly the same thing ... don't let it touch the framing...use caulk to seal the gap.

Where the conduit runs through a wall, make certain it cannot contact either side of the walls (back side of the drywall) or any framing ... you don't want rattles. Where you use clamps or attaching brackets to secure the conduit inside the walls, get slightly oversized and use pipe wrap between the bracket and the conduit.

If you want to go "over the top", wrap the entire conduit run.

At each end, once your wires are pulled, plug the ends with fiberglass but make sure you can pull that fiberglass out in case you run a new wire in the future.

Originally Posted by Dennis Erskine

The typical method is to install 2x2's on the wall and ceiling using screws and a construction adhesive. The screws through the 2x2's should anchor into your HAT channel (if that's what you are using). The soffits (preconstructed) are then raised into place and screwed into the 2x2 runners without construction adhesive. This provides a more secure anchorage and allows for easy future removal of the soffit if required.

Originally Posted by Dennis Erskine

There are two standards, or recommended best practices, for sound isolation depending upon the objective:

1. In room ambient noise level. This is defined as NR or NC 21 or lower (STC does not count since it ignores sub 125Hz frequencies and was never intended for this application in the first place ... so don't use it). In simple terms, with all environmental elements (HVAC, fans, equipment, etc.) running the ambient noise level in the room should be NC/NR 21 or lower. Using dBSPL as an example, if the ambient noise level is 32dB in room, you must lower that to 21dBSPL. 30 to 35 is typical of a residence. Basically, you need to lower the noise floor by 11dB. [NOTE: you cannot use dBSPL for accurate measurement against the NC/NR curves; but, you will get close.] Thus, your isolation strategy is to reduce noise entering the room, or noise from stuff YOU put in the room.

2. Avoid noise contamination outside the space. The generally accepted metric here is that you will not increase ambient noise levels outside the room by more than 3dB. Let's put this in simple context: the dynamic range is from 22dB to 105dB ... 115dB for low frequency. Thus, if your ambient noise level in an adjacent room (or neighbor's apartment) is 33dB, your sound isolation strategy needs to address a requirement to reduce noise transfer by 79dB. Once again, using dBSPL will get you close; but, that is not the method used to determine NR/NC. For reference, a baby screaming or crying loudly is on the order of 130dB ... I'm sure OSHA will try to regulate that level of noise pollution at some point.

Neither of these goals is easily achieved and likely not by anyone other than very skilled and experienced individuals and contractors. One can, however, see the effort to prevent noise pollution in adjacent spaces is a much different challenge than keeping in room ambient to NR21!

Originally Posted by Dennis Erskine

"There are two sides to this coin. The outside in and inside out views. The inside out perspective is the more common: "I want to listen to my stuff loud and not raise the ire of spouse, children, neighbors and environmentalists". The outside in perspective says you want to listen to the entire dynamic range of a recording (22dB SPL to 105dbSPL at the listening position) without clipping, distortion, or permanent hearing loss.

Let's look at both of these and use, as a starting point, the value of 35 dBSPL as the typical ambient noise level in a quiet suburban home. Also the recommended best practice which says the objective is you do not want to raise the noise level in an adjacent space more than 3dB (a doubling of loudness).

So from the inside out view, if your ambient noise level is 35dB, we add 3dB to that and say our goal is 37dB. Taking the top of the dynamic range of 105dB and substracting 37dB from that, we come up with 68dB. In the simpliest form, your isolation efforts need to reduce sound transmission through the walls/floor/ceiling by 68dB. Again, in its most simple form, you're looking for an STC of 68dB. That's pretty substantial. [NOTE: STC is a poor metric in this case since STC only considers the 1/3 octaves centered at 125Hz through 4000Hz and further is a single weighted number representing that entire range. But, for simplicity's sake, it's what we have for now.]

The ouside in view, says we have an ambient noise floor of 35dB, the softest sound recorded on a sound track is 22dB. You need to achieve a >13dB reduction in ambient noise inside the room. By comparison, that looks pretty easy to do until you start to consider noise being transmitted into the room by HVAC system, equipment fans, projector fans, etc. When we look to certification bodies ... THX for example ... the concern is less on noise sources you can control (dishwasher, children bouncing balls off the floor above) and more directed to environmental noises you cannot control (airplanes, traffic, trains, etc.). These noises by the way are loud by comparison to ambient and therefore the >13dB number is very minimal. OK, so what happens if you don't get the noise floor in the room to <22dB?. Let's assume your speakers will produce 22dB at the listening position using 15 watts. To produce 25dB would require 30 watts, to produce 27dB would require 60 watts, to produce 30dB would require 120 watts, to produce 33dB would be 240 watts ... you can see where this is going. Do the same calculation at 105dB (top of dynamic range) and you'll see you need some really large amps and some very, very loud speakers ... you'll be chasing the volume control forever or facing discomfort and permanent hearing loss. Remember the inside out piece? Your STC requirements are no longer in the 70 range; but, way, way beyond that.

Keeping the room quiet not only improves the audio experience but also reduces what you need to do to avoid wasting all your wattage energizing the entire house."

Originally Posted by Dennis Erskine

You're going to "fill that room up" with sound. You're going to fill an aquarium full of water. It doesn't matter which wall (floor, side, etc) you build from plastic wrap, when that water comes pouring out of the aquarium, it's getting everywhere in the house. So you treat a common wall ... the vibrations get to the roof joists, which rest on the outside wall of the bedroom, and, you have sound in the bedroom ... through the floors, ceiling, attic, places you would not expect. A one or two sided aquarium is rather worthless.

Sound in or sound out. In the overall scheme of things, it doesn't make much of a difference. The isolation techniques used in typical construction are not one-way devices. On the other hand, isolation to reduce sound transmission out of the room is harder to do than the isolation required to prevent environmental sounds into the room (unless you live next to Hobby, Sugarland Airport, etc.)

A traditional metric is you don't want to raise the noise level in an adjacent space by more than 3dB. So if the ambient noise level in your room is 33dB (not unusual), then outside your room, you don't want the noise level to get above 36dB when you're playing your system. The usual sound track is recorded with a dynamic range from 22dB to 105dB (115dB for LFE). By that metric you have 105dB - 36dB is 69dB ... good luck. Even with GG, DD, Clips, Isolation, careful HVAC work, etc, etc, you're not going to get there from here unless the crew building that shell is expert in building isolated rooms. (Just as a reference ... going from 33dB SPL to 36dB SPL is a doubling of SPL.)

Let's go the other way ... ideally, you'd want the noise floor in your room (equipment and HVAC running) to be 21dB (just below the softest sound recorded on a CD, DVD, BD) so you can hear the softest sound without turning up the volume (and making your sound isolation problem even harder). If the ambient noise level in your home is 33dB, then your isolation requirements are 33dB - 21dB = 12dB ... a much easier problem to solve...but, even at that, it isn't going to be solved by half way measures.

Does sound isolation affect in room acoustics. Yes; but, indirectly. You have comfortable listening levels, enhanced dialog intelligibility, you're not running your system at levels upwards of 8 times intended volume (to raise the quietest sound above the background level), running your equipment to distortion and you don't have to buy as many bass traps from Ethan.

"Acoustically, a concrete floor under good pad and carpet is not going to affect your overall sound to the point of concern. Remember, there are 5 other walls in which to absorb low frequency sound (depending on how much flexure you give these walls). Concrete floors combined with rigid walls (double dry wall, green glue adhered to closely spaced studs) will increase bass reflection due to the reduced flexure of the walls. More importantly than the concrete floor, and this is where most people make mistakes, is positioning of seats and subs, poor riser design, integrating the subs improperly into the system, and not using correction. These factors will be far more harmful than any concrete floor."

Originally Posted by Dennis Erskine

I have never been particularily fond of the "leave a gap, fill it with caulk" approach to ceiling/wall intersections.

Presuming the ceiling and walls are decoupled using isolation clips and channel, then anything else attached to the wall/channel is also decoupled. My preference is to adopt a construction method which is less prone to leaving air gaps (now or in the future). Therefore, what I prefer be done, is the ceiling drywall (first layer) be installed followed by the first layer on the walls. Caulk any gaps. Now install the second layer on the ceiling followed by the second layer on the walls. By default that will make all wall/wall and wall/ceiling intersections lap seams not butt joints. The lap seams are less likely to allow open gaps and air leakage than a butt joint. To the crown question, the crown is then installed as one would in any other room.

This method may reduce the springiness at the intersections but will not adversely affect the flex, or vibration, required for a CLD material (like Green Glue) to do its job properly. In the overall scheme of things, an air gap will go further to degrade wall performance than any loss of flex at the joints.

Originally Posted by Dennis Erskine

I started this sticky some while ago because this forum is a beehive of individuals building DIY home theater projects. I thought it would be useful for those who are starting on such projects to discuss the errors, omissions and "oh oops" that have been made by others to avoid making the same mistakes. Hopefully this has helped.

Our firm is a design/build/install organization with the ability to completely turnkey a project. Clearly, our business doesn't fit the profile of a DIY forum (with the exception of the designs we produce which many DIYers have utilized). Because we can turnkey an entire project, we have a view of the total project and can control the entire process...which is why we prefer turnkey engagements (but don't insist on them). Today, I thought I'd add just a few "errors" I've encountered with "disjointed" projects (the designer, builder, installer are different groups) and those where the lack of experience has resulted in some hair pulling.

1. Projector Mounting:
---- throw distances incorrect for projector/screen combination
---- projector mounted outside the range of it's vertical offset resulting in picture distortion
---- projector mounted higher than the top of the image area on the screen (a real problem with masking screens)

2. Seating
---- Radius seating (curved rows) where the seating radius is smaller than the radius of the seating platform.
---- Radius seating where the radius of the seats has the viewers on the ends of the rows looking straight ahead to the opposite side of the screen (most manufacturers will custom make the radii)
---- Front row viewing angle has the viewer looking upward more than 10-12 degrees to the center of the screen (uncomfortable).
---- Second/third rows don't have an unobstructed view of the entire screen area.
---- First row is too close to too large a screen, second row is too far for an immersive experience.
---- Elevated second row platform plopped on the floor as a island in the back of the room.
---- Attempts to put too many seats in the room, making it crowded, expensive, uncomfortable for "general" use and looking like you've tried to put 50lbs of potatoes in a 5lb sack.

3. HVAC
---- Even in Fargo, ND in the middle of the worst winter, you MUST consider the cooling and ventilation requirements of these rooms.

4. Room colors
---- I don't like black "man caves" any more than your wife; but, light colors (tans, off white) and bright colors WILL ruin your picture.

5. Screens
---- Screen too big for the room. Screen widths should never be more than 80% of the room width. Keep the screen at least 3' off the floor (if not more) and don't mount it within inches of the ceiling. Big is not always better.
---- Screen too large for your projector budget. A dim picture is not wanted and will result in low utilization of a room you put a bunch of money into.
---- With all the "arm waving" and "oh, my goodness, it will ruin your sound" I hear about AT screens, the FUD factor will result in the big non-AT screen and then the speakers end up stuffed in the corner of the room. If you want to argue about the "damage" an AT screen will do to your sound, here's news flash ... what an AT screen might, or might not do, won't even begin to compare with the damage the corner stuffing will do.

6. Sound Isolation
---- I've said it many, many times before. You can read all of Ted's goodies, buy all the right stuff, and have little to no sound isolation when you're done. This is really, really anal stuff. 1/2 way is zero results. Get help.
---- The primary object of sound isolation is to keep the room quiet...not to keep adjacent rooms quiet (if my wife isn't in the theater with me, let her eat cake...hope she doesn't read this). Once you've done this proud work, why is all the equipment in the room room?
---- Now that you have this very quiet room and you can watch movies really, really loud, tell me...will you hear the smoke alarms go off in your house? (and, you were wondering if you bought enough bass traps from Ethan).

Nuff for now.

Originally Posted by Dennis Erskine

Increasing the size of your "vents" and adding "vents" will decrease the air noise. As well, the design of the "vents" will make a significant difference in air flow noise. As you add supply "vents" you need to increase the size of the "return vent(s) as well.

Handler in closet.
Raise the air handler an inch or two and mechanically isolate the return duct from the air handler. Mechanically isolate the supply ducts from the handler. The air handler should be suspended using isolation hangers (www.kineticsnoise.com/hvac/suspended.html).
Install Dynamat sheets to the outside of the sheet metal panels of the air handler. Install another layer of drywall in the closet with Green Glue between the new layer and the existing drywall. Install a heavy solid core door with rubber gaskets, seals and sweeps (door becomes air tight). Line the walls and ceiling of the closet with duct board or linacoustic (if you use duct board, fiberglass side exposed to room, silver side to the wall).

Having fun yet?

Originally Posted by GRBoomer

250 feet per minute - this is the face velocity through the diffusers to minimize rushing air noise.

Cubic feet per minute is volumetric air flow, which is what you need to calculate the air changes per hour and the BTUs to remove from the room. Rule of thumb 6-9 ACH which is similar to the exchange rate for a kitchen. Once you get the air exchanges based on the volume of the room then you can calculate the airflow (CFM) requirements, then add enough diffuser face area to reduce the face velocity to 250 fpm.

Originally Posted by Dennis Erskine

http://www.nailor.com/digitalcatalog...WEB/CADBLD.pdf

You can look at the Bar registers.
One other point, the HVAC contractor will be determining CFM (cubic feet per minute). That's fine, let them have at it; however, YOU tell them that regardless of the CFM required per diffusor, you want no more than 250 FEET PER MINUTE velocity.

(8'' is apparently quieter, provides greater air flow velocity, etc).
Your HVAC contractor is concerned with volume. They will calculate room requirements as Cubic Feet per Minute (CFM). They will size the ducts according.

From a noise perspective, we are concerned with Feet Per Minute (FPM) or velocity. To keep your diffusors (registers) from creating a lot of air flow noise, you do not want more than 250 FPM through a slotted or bar type diffusor. Therefore, let the HVAC contractor size the system but you insist upon the velocity...which will mean larger ducts and larger diffusors.

From a capacity perspective, the HVAC contractor needs to look at the demand of the room to be on the same order as a kitchen (that's if you cannot calculate latent and sensible BTU requirements). For example, six people sitting in the room will require 3000 BTU's/hr. (exclusive of equipment, etc).

Originally Posted by Dennis Erskine

Here's a manufacturer's catalog http://www.nailor.com/OnlineCatalogs/CAD-06/CADBLD.pdf

Page 33 for slotted diffusors. I believe Ted at Soundproofingcompany.com can get these for you. You can get them in black (or spray paint 'em yourself). I'll use the 1/2" bar spacing 0 degree deflection (occasionally, 15 degree). You can line your soffit and use your soffit as the plenum. Once you get the velocity down to spec, they are very quiet (as measured by super duper, highly sensitive Sencore equipment).

Originally Posted by Dennis Erskine

The soffit's structural integrity is just as sound.

1. It is easier to seal and isolate a rectange than a polygon;
2. With the soffit internal to the room, it can be used as a wire chase without affecting the integrity of the isolation;
3. You must bring HVAC into the room. This requires very large holes through the barrier. With an internal soffit, you bring the supply/return ducts into the room behind the internal soffit using the soffit itself as a duct chase. This allows multiple 90 degree turns in the duct and between the opening in the barrier and the opening in the soffit for the return/supply (the soffit should be lined with an appropriate fiberglass liner).

Clips plus GG and DD ... nope not excessive and GAP for this kind of application.

Originally Posted by Talented Amateur

This is sort of true. It really has more to do with the pressure drop created by the type of diffuser or grille. For example, the standard three-cone diffuser used in the commercial industry has been around for a long time and can be very quiet at a given duct velocity (as Dennis has mentioned 250 fpm is preferred and is what we have used for HVAC systems in lecture theaters - as well as duct liner, large radius elbows, acoustically lined air valves, and silencers). If you replaced a standard three-cone diffuser with a perforated face diffuser of the same size (which is often done for aesthetics), you would notice a difference in the noise level due to the increased pressure drop (more restrictive). Any diffuser or grille can be used depending on what suits your installation, but it must be sized and installed properly. The linear diffusers that Dennis has pointed to must use a plenum of adequate volume (factory plenum also shown) for proper air distribution and have a large enough supply duct to provide the low duct velocity. Often times the sheet metal contractor can fabricate these to suit site conditions as the factory plenums don't always fit. Duct liner will also help.

If you soffit is not large enough for a proper plenum you may want to avoid the linear slot diffusers. They sure look nice but can be quite noisy and are very unforgiving when installed improperly. The linear bar diffusers are a bit more flexible. Avoid tight spacing of the bars.

Originally Posted by Dennis Erskine

I doubt the mufflers will help. The issue is the "high velocity" which creates turbulence which creates noise. About all you can do is decrease the velocity by using larger ducts and larger diffusors OR more (meaning lots more) small ones.

Now to my soap box ....

I have a potential client that is very focused on specifying duct size, diffusor size, etc. Here's how it works when you're dealing with other trades (such as HVAC contractors). If your objective is to have a duct of size "x", then specify "x" if that's what is important to you. I'd suggest, that duct size is of no importance to you in an acoustic application. What is important is noise levels, etc. So if the noise level of the air leaving a diffusor is important to you then specify (as an example), the Noise Rating (or Noise Criteria) shall be not more than 21 when measured .5 meter from any diffusor.

Another example ... are you concerned that the HVAC will provide 18,000 BTU's of cooling. I'd suggest that's not what you're really interested in. Here's a better way: "The system shall maintain 70 degrees with an outside temperature range from -30 degrees to 110 degrees, humidity shall not be less than 25% nor greater than 35%...."

Let me explain one (not all) of the reasons for this. If you tell your HVAC contractor that he must meet a given temperature, humidity and NR, then if you don't get that, it is his problem to fix, at his expense, at his potential loss of license. On the other hand, if you tell him you want 10" dia. ducts, and he gives you 10" dia ducts but the air noise is outrageous and the room will get no cooler than 85, it's your problem, not his.

Think about it.

Originally Posted by Dennis Erskine

Bar diffusors. To size, you first determine how many CFM the HVAC contractor says he's giving you per diffusor. You then size to get velocity (not quantity) down to 200 to 250 FPM.

Originally Posted by Dennis Erskine

This will likely be long; but, first, there isn't anything wrong with the use of 1" dome tweeters. They are like any other "tool" ... they must be appropriate to the task. One other preface ... pro speaker companies publish the polar radiation plots of their speakers. Pros must know the radiation characteristics of any speaker so it can be used in an appropriate application for the specific speaker. Consumer speaker companies do not, will not, or simply have never done the measurements...scary thought eh? (I think they rely on marketing hype and a lack of consumer education to sell their stuff ... there are still some very excellent consumer speaker manufacturers who really do care.)

Here are some basic principles. Sound will decay in air. Generally, you can figure on a six dB loss for each doubling of the distance between the listener and the speaker. That being said, high frequencies decay faster than low frequencies...by a lot.

Given that, as you move further from the speaker, you'll experience a decrease in SPL. In addition, you'll experience a greater loss in the high frequencies than the mids and lows. What are then some of the practical considerations?

First, when you have multiple rows of seating, you want a greater distance between the first row and the speakers than with a single row of seating. The reason is that overall loss of 6dB for every doubling of the distance ... the purpose is to reduce, as much as possible the difference in SPL between each row. Second, we have the problem that as we move further from the source, the high frequency loss is greater than in the mid and low frequencies. For accurate reproduction we therefore need to increase the high frequency output of the speakers to compensate such that when given a flat 20Hz to 20kHz input signal, you get a flat response at the seating location.

Let's look at a fundamental difference between a true studio monitor and a typical consumer grade speaker. The designer of the studio monitor has very specifically designed that speaker with the expectation the listener (mix/sound engineer) will be listening in the near field of the speaker. If you were to measure the FR of a true studio monitor at 1 meter (maybe less for some monitors), you should see bascially a flat response to 20kHz. If you were to do the same with a speaker designed for consumer use, you should see not a flat response; but, a rise in output above 10kHz to 20kHz. The amount of this rise would tell you what the speaker designer thought would be the typical listening distance by consumers purchasing that speaker. Because of that rise in high frequency response, if you were seated closer than expected, the speaker would sound overly 'bright' and you're likely not going to like it.

So now, let's consider speakers designed for large rooms. You'll find they use any number of techniques to compensate for the HF rolloff in air. These would be in the form of wave guides, compression drivers, and horns. All of which have the singular purpose of increasing HF energy from the speaker. In this case, if you were seated closer to the speaker than its designed intent, you'd find it harsh and bright (this is one reason I suspect many dislike horns ... ala Klipsch and others ... simply because they are too close to the speaker). Have you ever had a consumer electronics sales person tell you not to buy the Klipsch speaker because your seating distance is six feet? Nah. In fact, they'll try and sell you the bigger one because it is totally awesome, dude.

So, how does this align with 1" dome tweeters? There are very, very good 1" dome tweeters on the market and they do an excellent job of accurately reproducing high frequencies; but, within the physical constraints of the tweeter and its engineering design. When over driven, they will distort, overheat, and blow out (as would any other driver when driven beyond its design limits). Unaided, they are not high output devices.

Once you get beyond 8 to 10 feet that tweeter cannot keep up with the mid/lf drivers, to overcome the in air decay over distance. Your solution ... turn up the volume. The response is distortion and blown drivers. It really isn't the 1" dome tweeter's problem, it's the problem with the sales person's lack of knowledge and the fact the speaker selected doesn't match the application it is being asked to accomplish.

In the end, with multiple rows we need:
1. more distance between the speakers and the first row to reduce row to row SPL differences;
2. we need to overcome the loss in energy over distance (which is now greater) to compensate for that greater distance; and,
3. we need even more HF energy to compensate for its high decay rate over distance.
We're talking about some serious output/amplification/speaker out put issues here.

The designed capabilities of the speaker(s) must be matched to the engineering requirements of the space and seating distances and once you get beyond about 10' and you have more than one row of seating, that 1" dome tweeter (and the speaker you were sold *before* the room was designed) simply won't cut it. There's nothing wrong with the tweeter. The problem is you (and/or your HT 'expert') are trying to move a ton of coal with a wooden tea spoon.

How many times have we seen: "Hey guys I just bought the following gear (list of "stuff") and will be building a home theater in my basement. I have two difference places I could put it ... need your help." At this point, he is likely beyond help. How many times have you seen an "experienced, we know our s**t" home theater company with here's the list of stuff, let's design and build this thing?.

Oh, well. There's more to this room design thing than dimensions, isolation clips, and fuzzy stuff on the walls.

[i]"with only 14" behind the last row you really only have 1 viable option which is for broadband absorption in the centre of the back wall. As a 14" clearance is not much room to play with, I'd suggest you consider the type of broadband bass trap called "membrane or diaphragmatic" which works on the principle of absorbing sound most efficiently when the sound wave's pressure is maximized, which is right at the point on impact with the wall - so diaphragmatic absorption traps hang on the wall and are usually thin enough to work with your 14" limitation. The other absorption option most seem to select is a "resistive" broadband bass trap which should be a minimum of 4" thick with the thicker the better. However, the resistive traps works best when the sound air partical speed is maximized (not its pressure) which is one-quarter of the wavelength's distance out from the wall. So a 100Hz has a wavelength of 11.3ft so one-quarter equals 34", clearly beyond your 14" distance. Your 14" distance equates to about one-quarter of a 250Hz frequency so the resistive trap type may still be acceptable and is typically less costly than the thinner diaphragmatic type.

You might consider diffusion on either side of the broadband absorption if the distance between it and the rear seats warrants it."

1.) LOW FREQUENCY OPERATING RANGE - as diffusers need to handle long wavelengths and should work down to your room's Schroeder or Transition frequency (typcially 300-500Hz), pick a design with the deepest cell/well depth as you can find or build yourself, with the limitation being distance from diffuser to listening chair (see point 2. below).

2.) DISTANCE BETWEEN BACK WALL & LISTENING CHAIR - should be 3 wavelengths of the lowest frequency that the diffuser will perform well at, so that the sound coalesceses before it reaches your ears and troublesome lobbing isn't heard. If you're considering the more popular QRD- or Skyline-types of diffusers, then a conservative calculation of the lowest frequency wavelength will be to multiply the deepest cell depth in inches by 2 to get the entire wavelength of the lowest freq that the diffuser will work well at and then express it in feet by dividing it by 12 and then divide it into the speed of sound of 1130. For example, a Skyline of max cell depth of 7.5" will perform well down to 904Hz [ 1130/((7.5*2)/12) ]. The diffuser will continue to perform to lower frequencies but with diminishing ability. Now calculate 3 wavelengths of 904Hz as follows: 1130/904 * 12 * 3 = 45inches. So you'd need to sit at least 45inches away from the rear wall with a diffuser of max depth equal to 7.5 inches.

3.) DIFFUSER PLACEMENT - be sure they are centered at ear level so 3/4 height may/may not fit the bill depending on seating height and of course your height! Also it should cover 2ft below and above your ear level so a minimum dimension of 4ft.

4.) WALL COVERAGE AREA - Prof Trevor Cox a diffusion expert, told me that some general diffusion principles exist, most relevant is the less periodicity the more diffuse the scattering. Dr Floyd Toole concurs saying "these designs get better as they get larger." So, to improve scattering efficiency over your desired wall area, choose a Skyline diffuser with the largest prime number or QRD diffuser with the largest number of wells to cover the desired area, and in both cases a max cell/well depth as calculated above. So it's better to have one large diffuser than several smaller ones put together. For a polyfuser pick one with at least a 12" radius however when combined with other polyfusers it loses its ability to diffuse low frequencies, so space them apart, change angles, and change their radius depths too if possible.

Originally Posted by Dennis Erskine

All of my comments below refer only to absorption of sound energy in air.

There are two commonly used mechanisms to absorb sound energy: (1) velocity type absorption; and, (2) diaphragmatic or pressure absorbers. For a velocity type absorber to function effectively, that device must be placed in a location where the velocity of the air molecules are at their maximum velocity. For a pressure type absorber to function effectively, that surface must be placed at a location where air molecule velocity is zero (or near zero) and pressure is at its maximum.

If we imagine an air molecule striking a wall, at the instant it strikes the wall, its velocity is zero and pressure is high. However, sound propagation is cyclic in nature and cycles through rarefication and compression. At maximum rarefication and maximum compression, velocity is zero and pressure at its maximum.

To achieve maximum effectiveness in a velocity absorber, that absorber should be placed such that it is located at the 1/4 wavelength of the frequency(ies) for which we wish to reduce energy. Velocity absorbers are characterized by fiberglass batts or fiberglass panels. At 80Hz, the wavelength is 14' and the quarter wavelength is therefore 3.5'. If a dimension in your room is any multiple of 14', then a velocity absorber would need to be placed 3.5' away from a wall surface to be effective at 80Hz.

A simple form of pressure absorber is a fiberglass batt with paper backing. If you imagine a trampoline, the paper backing is the surface of the trampoline and the fiberglass is the spring. Now, imagine jumping off the roof of your house onto your trampoline. The trampoline will indeed absorb some of the energy from your fall; but, the spring is going to release some of that energy back throwing you back into the air. The spring action is an issue in the design of diaphragmatic type absorbers since they can become "speakers".

One of the characteristics of modal frequencies is they, by definition, are always at their minimum velocity and at maximum pressure at the wall surface. In this situation, a pressure type absorber is more effective at the wall surface. A velocity type absorber would need to be placed at a 1/4 wave length distance from the wall surface. (At 80Hz, that's 3.5'.)

In the low frequency arena, the bigger (not only) sound quality problems are with modal frequencies (and some would argue that in a small room, it's the first three axial modes which are the real killers). [Note: in small rooms modal problems dominate from approximately 300Hz downward but generally present the biggest audible problems below 100Hz.]

The reason we typically find vendors suggesting their bass control devices be placed in room corners is because it is at the room corners where all the axial modes are at their highest pressure/lowest velocity.

The statement made by SMB is true in that general purpose bass traps/absorbers are not very effective below 100Hz. For them to work at the velocity level, they'd have to be 14' from a wall (assuming a 20Hz modal frequency). For them to be effective as pressure absorbers, they'd need to be at the wall surface (for modal frequencies). Neither is very practical. When placed any distance from a wall, their effectiveness would vary by frequency based almost entirely on their placement (a 6" difference can radically change the frequencies upon which you'd see the greatest effectiveness).

Multiple tools need be utilized to resolve low frequency sound quality issues in small rooms. These tools would include electrical as well as mechanical.

As to the question about nulls/peaks existing in multiple areas of the room, a couple of points. First, we don't give a tinker's damn about sound quality in areas of the room where no one is sitting. Secondly, when it comes to LF and modal issues, it is the amplitude of the peaks/nulls which are audible and cause us grief. As the energy to that frequency increases, the delta between the peak and null gets larger and more audible. The converse is true as well. As energy is absorbed, that delta decreases and you have more consistent response (I didn't say good, I said "more consistent"). The use of differential parametric EQ, is one means be which modal frequencies can be 'resolved' without sucking the life or energy out of a room.

Among the challenges for a well performing room is to have all frequencies not only decay at the same rate (in the seating locations), but all frequencies to have the same relative SPL. This is a significant challenge since any form of pressure, or velocity type absorber will affect different frequencies differently just based on their position in the room. Adding bass trapping devices to a small room is very helpful. It cannot, however, be a helter skelter placement nor simply putting fuzzy stuff in the corners. There will be a point at which the treatment ceases to be helpful and begins to work against your objective.

Originally Posted by Dennis Erskine

There is a plastic sheeting with an adhesive back...comes in rolls. It is used by contractors over carpet to prevent soiling the carpet during construction. This makes a good membrane. You can also use 3mil or 6mil plastic sheeting as well.

Originally Posted by Dennis Erskine

Here's an approach y'all can experiment with. Use a 1/4" thick sheet of masonite peg board. The hard surface formed into an arc provides difusion. The fiberglass behind along with the holes in the peg board provide lower frequency absorption. The number of holes in the peg board left open will determine the lower frequencies being absorbed. Due to the radius, the depth between the pegboard and the wall will vary the range of frequencies absorbed. There's enough calculus behind this that a computer model is the only brain blow out safety mechanism. (Of course, if your brain explodes, in room frequency response will no longer be an issue.)

Originally Posted by Dennis Erskine

Significantly less effective for low frequencies! Still effective for high frequencies. A general target is a frictional (velocity type) absorber needs to have a depth equal to, or greater than, a 1/4 wavelength. Some of these corner frictional absorbers have a vinyl barrier between a couple of layers of the fuzzy stuff...that creates a pressure type absorber. In fact if you take two layers of 1" fuzzy stuff and put it on a wall, you'll get absorption down to frequency "x". If you now put a very thin sheet of vinyl or plastic between those two layers, the absorber suddenly starts performing more like 4" of fuzzy stuff.

Let me give you a slightly better mental picture of pressure vs velocity. Find a very solid wall. Concrete for example. Stand 3 meters from the wall. Now run as fast as you can directly toward this wall. When you hit the wall, your velocity is zero but you're feeling a lot of pressure.

Originally Posted by Terry Montlick

Yes, 1-2" of 703 on the surface and lighter material like uncompressed fiberglass batts for the several inches of inside thickness gives somewhat more absorption below 200 Hz compared to solid 703 for the entire thickness. The difference is not huge, but gets more significant with greater thickness.

Originally Posted by Dennis Erskine

Behind the screen wall:
- Two 1" layers of coated InsulShield Black. Install 3mil poly sheeting between the layers.
- GOM is Guilford of Maine. Typically Guilford of Maine FR701 type fabric.
- "batting" refers to polyester batting, typically you'll find this used to make quilts.
- InsulShield is a Johns Manville insulation product which is (a) black and (b) coated to allow it to be exposed to free air.

Originally Posted by Dennis Erskine

If the platform extends the width of the room and goes to the rear wall, the platform is positioned to be within the areas where modal frequencies are peaking (low velocity/high pressure). With proper design of the seating platform, 4x24, 4x36 floor registers (bar diffusors) can be used. By properly designed I mean the following has been accounted for in the construction of the platform:

1. Fiberglass insulation has been installed in the cavities of the platform;
2. The areas (very near the wall) under the platform have been framed with sufficient volume to do some good.

Originally Posted by Dennis Erskine

Do the math to determine center frequency and Q. Frequency and Q are a function of port size and cavity size. Before you start down that road, determine your modal frequencies. Your openings along the back wall should have the greater impact on length modes, the openings at the corners should impact all modal frequencies and those on your side wall have an impact on width modes ... noting however your corner and side openings are coupled into a single cavity and may not perform as you expect.

The direction you're taking is providing the opportunity for a broad band absorber with the greatest impact on modal frequencies. The 'slits' as provide the opportunity to create more narrow bands of absorbtion.

Originally Posted by Dennis Erskine

What I use, where I use it all depends upon the engineering requirements of each room. "Stuff" will go over the PB. PB was used in the THX Certified project, but incorporated into panels so you never saw it.

Originally Posted by Dennis Erskine

As an FYI, there is a new product (a couple actually) from Quest Acoustical Interiors (www.questai.com), ... no I don't work for them.

Perf-Sorber is a combination absorber/diffuser in a single fiberglass panel. An excellent early reflection point product speakers with good off axis response. Also, a good choice around surround speakers. The other (I forget their trade name) is a product with very good absorption down to 150Hz.

Originally Posted by pepar

1. Speaker position.
2. Listener position.
3. Acoustical treatments.
4. Electronic correction.

Many/Most of us do not have the option of #2 as they are usually dictated by room size and layout, seats present, display size and location, etc. In other words ... other factors.

For #1, many times subs can be moved around, but the factors restricting #2 also many times limit #1.

More should be done with #3 but it sometimes runs afoul of aesthetics ... and even room space limitations. Nonetheless, acoustical treatments of room modes can make a HUGE improvement. Certainly moving a sub so as to not excite a particular room mode makes sense - and is free - but the mode is not eliminated .. and other modes are not addressed. Bass traps reduce the reflections that are the cause of room modes ... all of them. Install enough of the right traps and the room's LF response smooths out and sounds amazing. Unfortunately, most people are so unfamiliar with smooth, flat bass that they feel something is missing when they hear it. (But that's another subject entirely.)

Number four is the icing on the cake, but I would strongly recommend that something like the SVS AS-EQ1 (and multiple subs) be used to correct LF response. Simple equalizers don't come close to the improvements from this piece of gear. And it improves over all of the listening positions, not just one. And it works partly in the time domain so it can help with ringing. Electronic correction is not a substitute for acoustical treatments, but it will improve just about any room/system.

Just my $.02.

Originally Posted by kevinzoe

Pepar - here's the calculation for rever beration time: RT = 0.049V/A
V = the total volume in cubic feet
A = the total absorption in the room in Sabins, calculated by adding all of the boundary areas multiplied by their respective absorption coefficients. (e.g. square footage of drapes * its absorption coefficient + square footage of carpeting * its absorption coefficient etc etc)

Typical target RT's appear to range from .2 -> .4 +- and is pretty much an individual taste/preference.

Originally Posted by glaufman

A few points about reading REW graphs for everyone:
1: When posting a waterfall, make sure the frequency axis is in LOG mode. There is a known bug with the Freq axis in LIN mode that makes the plot unreliable.
2: Post an FR along with the waterfall with the same graph limits to make it easy to match up.
3: When posting your FR, before making the jpg, make sure to check the soundcard cal and mic cal buttons under the plot to display these traces on the plot. This allow people to see where in the very low or very high end your data becomes unreliable due to the effect of the cal files on your noise floor.
4: Don't sweat persistent noise very low, unless you absolutely have to and are absolutely sure your setup has a noise floor capable of these measurements.

Originally Posted by Dennis Erskine

Now that Bluesky has taken his obligatory pot shot, let's get back to bass management (I think this will be a long post).

Understand, at the start, we very rarely see "bass management" in use in large venues. It was developed specifically for use in the residential environment, or, let's say "small room acoustics". Low frequency modal issues in large rooms aren't the issue they are in smaller spaces.

In smaller rooms (whether you have two fronts, or three), one of the objectives is to create a wide and deep, 3-dimensional, if you will, sound stage. Problematic in residential spaces is it is very difficult to get any speaker sufficiently far away from any room boundary to not have an adverse impact from SBIR (Speaker Boundary Interference Response). To achieve an excellent sound stage, speakers are moved, twisted, raised, and/or tilted until that sound stage is as good as it can be. To further craft the sound stage, various forms of acoustic treatments are also common. This width and depth of the sound stage affected by the mid to high frequency range ... not by low frequencies.

So now comes the low frequency response (in the seating locations) problem. Ignoring for a moment that most "full range" speakers are not, the challenge is to create smooth bass response in the seating location(s). In the low frequency domain, modal response is the killer. Modal response issues can be addressed by careful subwoofer placement (that crawling on the floor thing), the use of some number of subwoofers (that number being between 4 and 5000) ala the Toole, Olive, Welti, Devantier method, or Gerry Lemay's "virtual" subwoofer method. Another, very rarely used method is to deliberately create constructive and destructive interference between multiple subwoofers to create smooth bass response (not commonly used because it is tricky and very, very time consuming). None-the-less, modal interaction within the seating area is highly dependent upon subwoofer positioning (moving the seats is often not an option because that sound stage gets corrupted in the process).

In the end, it is more often than not found that the best positions for the main speakers to craft an excellent sound stage are exactly the wrong positions for low frequency drivers to provide a manageable low frequency response at the seating locations.

Effectively, bass management allows low frequency content to be removed from the L/C/R (and surround) speakers and be redirected to one, or more, subwoofers. Once physically divorced from the main speaker, the low frequency drivers can be moved to those positions which provide a more optimal response at the seating locations.

One of the more common arguments against bass management have included, "I can hear the sub (localize it) and the positional disconnect from the mains is annoying." The fact of the matter is, you cannot localize low frequency sources (say 80Hz and below since that is a common crossover point). It is not the low frequencies which are being localized. Subwoofers can easily create higher frequency artifacts of their efforts to create the low frequency sounds. This includes mechanical sounds, the cone slapping the air, and so forth. These sounds can be easily eliminated. A further cause of distress can be linked directly to poor integration of the sub(s) to the mains. This integration cannot be done with just an SPL meter. If one "hears" the subwoofer(s), the calibration and integration is poor at best. In a properly calibrated room, the fact the surround speaker's low frequency content has been relocated to multiple subs is not going to be detected by the listener.

Now there are risks which can be introduced into the listening environment once you have excellent low frequency performance to 20Hz or below. These risks go back to the recording and production chain. Let me give an example: A Grammy winning recording artist produced a track where the 35Hz content would take your head off. It was very loud and horribly distracting (on the bright side most car stereos and all iPods couldn't reproduce 35Hz on a good day). This poor mix occurred because the mix engineer was sitting very close to the peak of the 35Hz null of the mix room! [EDIT: peak of the null ... near where the null was almost at its deepest point). There are other examples such as hearing the train passing through the London Tube below the recording studio ... the playback monitoring system wasn't capable of reproducing that particular low frequency range. It was on the release, most never heard it, but those with capable systems did, and, correctly, gave it a poor review. On the other hand, the Telarc 1812 (re-released as an SACD #60646) did have very deliberate way below 20Hz content. The Telarc Holst Planets with Fredrick Fennell (re-released as SACD) does as well. (These were both recorded on our Soundstream system and originally released for vinyl.) In any event, once you get a system which can accurately reproduce below 20Hz content, be prepared for some surprises (or disappointments as the case may be).

Originally Posted by Dennis Erskine

Multiple subs are used in multiple locations in the room to smooth bass response (provide consistent response) in the seating locations. No one cares what the bass is like where no one is seated. Typically, with two subs, one along the front wall and one along a side wall. When you have two subs (both set to the same phase) situated like that, they will behave as though you have one sub 1/2 between the two. Soooo, as many who've crawled around a room on their knees have discovered, the ideal location for a single sub is somewhere (inconveniently) out in the room. The two subs, working together, create a "virtual" sub in that inconvenient out in the middle of the room location.

Multiple subs have absolutely nothing to do with localization. With an 80Hz crossover, you're not going to localize the sub (you may be able to localize the higher frequency sounds from a sub which are related to the sub's mechanical actions and the drivers slapping the air).

A single sub (regardless of the number of drivers) is still and single sub. It is a misconception to think multiple subs will excite multiple modes in a room. That fact is a single sub will excite all the modes in the room...the degree to which each modal frequency is excited is dependent upon the location of the sub in the room.

A sub, in a corner, is generally a poor choice. All room modes peak in a right tricorner. Thus, placing a sub in a corner serves only to better excite all room modes which is something you'd want to avoid.

Using an 80Hz crossover, you'd want the center of the dust cover on the sub's driver to be closer than 3.5 feet from a wall boundary to avoid a notch in response.

Originally Posted by Dennis Erskine

Understand the Welti approach provides consistent bass response in the seating area ... not necessary smooth bass response. I've been using two primary subs in the front of the room and three smaller asymetrically placed smaller subs for the past 15 years. The positioning of the three smaller subs is determined by estimating the interaction of the subs (ala Gerry Lemay's Virtual Subwoofer process) within the planned seating area. Several of those rooms have not required EQ ... Jamin has experience in one of them.

Originally Posted by Dennis Erskine

Heck if I know ... made use of a big word though.

When you have multiple subs in the room, the first step in calibration is to have them all level matched and at the same phase. You can then calibrate in real time by adjusting phase, PEQ, and SPL of each sub (individually) to deliberately create constructive/destructive interference to further deal with modal issues. That is differential EQ. Currently (at least for me) this is pretty much trial and error along with knowing from experience what worked and what did not. Differential EQ would be an excellent PhD thesis for someone working toward a PhD in acoustics. (Hey, Todd. You busy? )

Example with two subs. We know when you have two subs in a room, the summed behavior of those two subs is identical to having a single sub mid-way between the two physical subs (virtual subwoofer). By tweaking the SPL of the physical subwoofer you can "move" the location of the virtual sub along that line between the two physical subs. You can do that with four subs (much more a challenge and time consuming). As well if some of those multiple subs are close to the ceiling you can manage the height of the "virtual sub" as well.

Originally Posted by SierraMikeBravo

A different and perhaps a more sightly and economical approach would be to use an appropriate parametric EQ. Also, you need to determine just what is causing the "dip" to occur? Is it modes (unlikely if it is that wide) or is it something in the room that is causing a suckout, or is it something else, SBIR, speaker/listener positioning? This should be determined first if you want to treat it correctly. Best wishes!

Originally Posted by SierraMikeBravo

Not quoting a site...but of my own volition...I hope you recognize that the description you provided is not entirely correct. Ring time is a function of the peak itself. The additional energy of the peak provides a longer ring time (check out a waterfall plot of your room if you don't believe me) due to the fact...well...it takes more time for that energy to decay to an inaudible level. By reducing the energy of a peak via a PEQ, you thereby also reduce the ring time. I certainly hope you did not come away with the idea that bass traps strung throughout the room can reduce a null by increasing that null's energy. Bass traps work the same way as a PEQ just less targeted (unless you are using a Hemholtz resonator)...they reduce the peaks...which thereby reduces the depth of the null. Believe it or not though, you can sometimes increase a null's energy via a PEQ (generally not a lot but you can) without causing audible damage or audible distortion...but I've never heard of a bass trap increasing a null's energy. I am not saying that I don't incorporate bass traps...I do through design...but I certainly do not rely on them to deal with frequency problems below 100 Hz. It's just not practical or the best method IMHO. Best wishes!

Originally Posted by erkq

Ring time's relation to peak energy is linear. Of course.
You seem to be a knowledgeable fellow, so your characterization of a null as absence of energy and insistence that it can't be treated successfully with a bass trap is puzzling. It all depends on how you define "energy". A null is in fact the meeting of two (or more) sound waves 180 degrees out of phase with each other. One large cause of this is a sound wave reflected off the back wall meeting incoming waves from the speaker. If bass traps can get rid of, or ameliorate, this reflection, the null can be reduced considerably. In this case "reduction" of a null equates to bringing the energy back up at the null's frequency.

But I'm sure you know this... that's why it's puzzling.

PS I don't quote what I don't understand.

Originally Posted by SierraMikeBravo

It's not really puzzling. It's just a relation of the surrounding frequencies to the null. If you drop the peaks...you eliminate the effects of the null, but what you are really eliminating is the harmful effects of the longer ring times. Yes, your analysis is correct, but in order to really effectively treat that peak....it would need to be approximately 1/4 the wavelength of that peak you are trying to reduce. In the case of 50 Hz...it would need to be 5-6 feet thick. 1/10 the wavelength is also possible provided certain specifics are adhered to...but the trap would still be 2.25 feet thick. Now, another factor to consider, bass traps as the main stream thinks of them, are made of fiberglass which is a frictional absorber. Frictional absorbers work best when something is moving against them. Along the walls...the velocity of the wave is near zero...but the pressure is much higher (boundary gain anyone) especially for low frequency waves that we are referring to. Now, since the velocity is near zero, the frictional absorber doesn't work as well as it would say at the point of lowest wave pressure and highest velocity of that wave...which is not along the walls but out in the room itself. So, I am not saying you can't use bass traps to deal with freqs below 100 Hz, but they would be impractical and obtrusive to be truely effective. Engineering and PEQ are the only way to go IMHO. BTW...you don't seem too shabby yourself in the knowledge department! Best wishes!

Originally Posted by penngray

You can go cheaper with this mic

http://www.parts-express.com/pe/show...number=390-801

download the free REW from here

http://www.hometheatershack.com/foru...ease-read.html

Use a PC, measuring your room and find a used DCX2496 for under $400. It has all you need and more.

Originally Posted by Terry Montlick

For auto-EQing multiple subs, a single-sub system like Audyssey is not optimal. Ideally, subs should have separate equalizers. EQ one sub, then leave those settings. EQ the second sub, with the first sub playing with its fixed EQ settings. Leave those second settings on the second sub. EQ the third sub, with the first two subs playing with their fixed EQ settings.

- Terry

Originally Posted by Dennis Erskine

To determine if that is a modal null, move the microphone at least 3 feet in a diagonal direction and measure again. If you have your cross over set to 80 hz, that could be because your sub is 180 degrees out of phase from your mains at 80 Hz.

Originally Posted by Roger Dressler

Between the Madagascar screen shot, and the fabulous 3D modeling, I'm hooked in this thread. Great design and planning.

A few ideas to offer, having just finished my first 7.1 room with two rows, I've come to some conclusions.

a) The most serious/critical listening or watching happens solo. In the money seat--front/center. When others join, the concerns over "template perfection" are relaxed. So I attached a diagram with the Dolby template shifted to the prime seat.

b) Having had the opportunity to do some serious seat time in both rows, I've come to appreciate the extra envelopment in the rear. As a result, if I had the chance, I'd move the surrounds from their current locations, 90-deg to the front row ears, to maybe 6"-12" forward.

c) The 140" screen width gives a 60-deg viewing angle. Serious widescreen effect. In that case, I'd recommend considering a 2.40 screen so that 16x9 images don't overwhelm. Unless maybe you're an Imax fan, then go for it!

This calculator spreadsheet is real useful for checking the math. It shows that a smaller screen can also work, but then you run into the issue of the frame blocking the L/R speakers. I made my screen small enough to fit between the speakers, so it's a 42-deg view.

d) Looks like several walls/floor are concrete, which are good at keeping bass inside the room. Should enhance the room modes. My prediction is that you’ll need and want more subs. Partly for peak output, but more for improved uniformity across the seats. Might consider planning for a total of 4 subs near the 4 corners. Have a look at Fig 19 of this paper by Dr. Toole. Could consider either something like in-wall Triad subs, or whatever powered subs would fit—and pre-wire accordingly. I had rather severe bass nulls in my room, and multiple “subs” and a BassQ processor fixed it. I didn’t try multiple subs until I had the BassQ, so can’t say if I could have gotten away with just the multiple subs used alone.

Originally Posted by Roger Dressler

Last point first. You may be right that dipole/tripole speakers ought not go in the room corners. So where they are currently positioned is just fine. (Mine are direct radiators, in the corners, angled into the room, and they sound as good as the side wall units.)

When I created those "speaker wedges" diagrams at Dolby, it was an attempt to allay concerns from folks who thought that the surrounds must be exactly at 110-deg, or the fronts exactly at 30-deg, no tolerance. Also, we also wanted to avoid giving the idea that if you switched between 5.1 and 7.1 playback mode, you'd need to physically move the surround speakers a foot forward. Lastly, we needed to accommodate THX, which likes dipoles at 90-deg, even for a 5.1 setup. So we stopped saying "this is the precisely optimal angle." The center of the speaker can go anywhere within the wedge and give decent results.

Having said that, there is no doubt in my mind that 90-deg is better for surrounds in a 7.1 system than 100 or 110 deg. That's been the consensus since 7.1 was introduced. As originally drawn, the surrounds in your room were slightly further back than optimal for the front row listeners.

The change I suggest will be immaterial to the back row. We're talking subtleties here, in the grand scheme, and once the D-Box is humming, no one will care! It's only an issue for your "solo flights."

Looks like you're well set for future subwoofer options!

Originally Posted by Roger Dressler

IMHO, Option 4. When you say mid level, let's refine that to mean the tweeters are roughly ear level for the "money" row--that's about 40". With a 10' ceiling, your screen can be as high as maybe 30" off the floor. That means the difference in height between L/R and center would be about 1 foot, whereas if the center speaker is above the screen, it would be 3-4' higher than L/R. It's much better if the heights L/C/R can be kept within 2' or less to promote smoother lateral panning.

The problem with horizontal center speakers is usually that they are 2-way designs, and it's not possible to obtain good off-axis response because the woofers run too high in freq and cause lobing. With a 3-way speaker, with a vertically stacked tweeter/midrange, this problem can be avoided. Yes, if you can use 3 identical speakers, great. But with careful selection, other options can work well, too. To see an example of the preferred driver config, see the Triad In-Room Gold LCR.

In either case, do tilt the C speaker up so it aims directly at the listener's heads. That will keep the drivers better aligned for best response.

Originally Posted by Dennis Erskine

No, that would adjust the volume at the speaker. What you want to do is minimize the the difference in SPL between each row of seats. To do that, you need to reduce the difference in distance between the speaker and each row, and/or, move the speakers further away from the seating area (approx 6dB decrease with each doubling of distance). For example, the difference in direct sound between rows at 5' and 10' would be 6dB, between 10' and 15' would be ~4dB but between 15' and 20' would be 2dB. (Direct sound intensity decreases inversely with the square of the distance, or I = 1/d**2 )

Thus minimizing the difference in distance from the speakers and/or increasing the distance from the speakers will minimize row to row variances in SPL. This comes significantly into play where the back row of seats is very close to the back wall (rear surround speakers) or you place seats too close to side walls (side surrounds). You now have the effects field completely overwhelming the L/C/R at the expense of intelligibility, clarity, focus, and sound stage width/depth.

Originally Posted by Dennis Erskine

Small rooms are problematic with such issues. Even multiple rows of seating and the LCR's. You can easily find a 6dB difference between the first and second rows (LCR) of many smaller rooms. Once you increase the distance between the speakers and the first/second row, this delta decreases; but, once you increase the distance high frequency roll off (in air) can be very significant...then to solve that issue you have to use either compression drivers or horns (which can be very bright if you're too close to them). Not easy. The key to the surrounds (poster's question) is to NOT use direct radiators when seats are close to the speakers (localization and "hot spot" issues) and, to raise the surrounds higher on the walls. Placing them higher on the walls (and aiming into the seating location) decreases the distance delta between the speakers and each row and hence SPL differences.

Originally Posted by Dennis Erskine

That, or, I'd suggest dipoles mounted in the soffit aimed face down to the floor (flame suit is on). Understand, with movies (music has NO standards for what they are doing with the "effects" channels) your enemy is localization with respect to the "effects" channels. Note, I used the term "effects channels" three times now while stamping my foot on the floor ... an indication that question will be on the test.

Originally Posted by Dennis Erskine

You want the sides and rears at the same height.
place the tweeters 1/2 the distance between the 42" mark off the riser to the bottom of the soffit/ceiling.

Originally Posted by appelz

Most of my clients will have a DSP 322ua or at least a DSP-30 dedicated to the subwoofers, so I am doing quite a bit more than kicking subs around and moving chairs! But not everyone reading this thread has that equipment, and many would not even have something like Audyssey, so quite often, the only tools available are a basic calibration of speaker levels and distances, and moving speaker and listeners to the proper position.

If the subwoofer is jammed in the corner, energizing all of the room modes, and the couch is up against the back wall, pushing the start button on the auto room correction is not going to be very effective. Yes, it will likely improve, but the goal is to make the experience the best possible.

A standard audio calibration goes like this.

1. Show up on time.
2. Drag 80lbs of test equipment into the cinema.
3. Sit and listen with the client to his reference material, explain the process.
4. Set up test equipment and take both physical and acoustical measurements.
5. Verify system. This includes checking polarity of every driver in the system, near field response of each speaker, off-axis response, menu settings on the AVR or Pre-Pro, impedance plots, checking distortion levels, etc. No sense calibrating broken gear.

From here, the structure is more fluid. From the acoustical and physical measurement of the room, we determine best seating location to avoid putting the listener in the middle of a null. We can determine subwoofer locations the same way. A basic calibration happens (distance and level matching), and I start listening in stereo. Toe-in, angles, distance from front wall, how much first reflection I want based on earlier off-axis response plots and client feedback. Hours later, once satisfied with stereo, the center channel is integrated. Surround speakers next. End of Day 1.

Second day is all about subs and creating a smooth transition between the mains by use of level matching and phase. Moving the subs into 1st and 2nd measured room modes will help smooth the response plot at the seating position. If I have DSP, then parametric EQ is also used. A "house curve" is added.

Listen, listen, listen to my reference material, tweaking until I am smiling. The client is then allowed back into the room, and we listen some more, and I explain the changes and why. Now that he is better educated, we listen some more, and make final changes based on his listening preferences.

I have started Day1 with the subs after all of the initial measurement and verification. All depends on the mood that day.

Originally Posted by Dennis Erskine

Fair question...method coming. But first, time vs frequency domains. Each has it's own set of pros and cons and with Fourier transforms, it's pretty easy to bounce back and forth betwixt the two. One of the points Audyssey makes, is their ability to examine room response to a higher level of resolution and apply corrections to this higher level of resolution (of course, without specifying exactly what that "level" is). That can be just as good as it can be bad. Applying a high resolution fix (avoiding the "Q" term here), can have very unfortunate down stream impacts on drivers and amplifiers. Another short coming is the Audyssey process considers only room response and does not provide a means to first measure speaker (near field) response in order to constrain its correction. Another example of a short coming, is a case where the user (or "pro" calibrator ... someone who paid to buy the kit) has placed the main free standing speakers within 3' of the front wall. This creates a notch and try as it may, Audyssey cannot correct this. Only a real pro will recognize this has to be addressed by physical means ... moving the speaker or very specialized treatment on the front wall. Attempts to correct this (time or frequency domain) can run the risk of serious problems. FIR filters, IIR filters...again each have their short comings; but, bless the evil marketing department. Real calibration still requires experienced human intervention and must encompass all means available, including, but not limited to, moving the *$(#$ speaker(s).

So now we come to your direct question (don't you just love "what if's"). To achieve the use of Dynamic volume, etc. the process would be to run Audyssey to the six or eight time limit of your pre-pro. Go back into the pre-pro's set up and modify the crossovers to those more correct for the room/equipment being used. Then you want to set Audyssey to default to "flat" rather some other curve. The next step, using conventional measurement equipment and name your poison signal processor (Lake, QSC, Symetrix, etc.) to address the full calibration and deal with issues your particular pre-pro/Audyssey combination cannot handle (like multiple side surrounds, four, five, six subs etc). However, in this case your test signals must be generated externally and passed through the pre-pro. (Many units, like the QSC 322, 922, etc. can generate internal test signals.) You cannot by pass the pre-pro with test signals since you're then bypassing not only your crossovers but whatever Audyssey did and you'll be chasing your tail down in the weeds forever.

Will that work? Yup, it will.

NOTE: if you are using multiple subs or multiple side/rear surrounds beyond what is native to your pre-pro (ie, you are splitting the Left Side Surround channel in three discrete channels external to the pre-pro), you will have to set this up within your external signal processor and set the levels before you run Audyssey. Here's a short, perhaps not complete, method using the pre-pros internal "set levels" test signal:

1. Use speaker set up to set up your speakers (large, small) as you expect to use them and set the crossovers.
2. (We'll use the left side surround as the example). In your external signal processor, mute all but one of the left side surrounds.
3. Set the level for that one side surround...that level MUST be set using the gain control within your external signal processor but using the pre-pro's internal test signal. Once set, mute that speaker and set the level of the next Left Side Surround speaker. Continue until you've done this for all speakers in your left side surround "array".

This process assures you that each of the speaker members of the Left Side Surround channel are set to the same level.

Now you can run your speaker level set up in the pre-pro as you would normally. You'll find your side surround will need some downward adjustment.

Originally Posted by Dennis Erskine

General Comments:
A pro would use something along the lines of a Quantum Data 780 or Sencore DAG to generate the audio test signals. These devices will output DD or DTS encoded test signals and allow the calibrator to specifically address a given channel. Should a QSC DSP be part of the output chain, each channel's output can be turned off making this process a bit easier.

Pre-Pro in the loop.
It is helpful to keep the pre-pro in the calibration loop. The decoding/processing delays can be noted (has an impact on ITDG and ETG results). As well, it allows the bass management function to be viewed. For example, Bass Management ON, Xover to (80Hz), and then overlay the front channel(s) response over the sub(s) response to view the actual crossover point and the crossover slopes. (Usually not a problem with a THX certified pre-pro. I have seen pre-pros where the slopes are dead wrong and an 80Hz setting is producing a 100Hz xover point.) The only way you can properly match the subwoofer levels with the mains is to do it this way or by a full range RTA live.

Near Field Measurements
Taking near field measurements of the speakers is the first step, always. The near field shows what the speakers are doing and if anything is broken ... like an Xover or a blown tweeter. In the general scheme of things, attempting to fix poor speaker response with an external EQ is not always successful and some response error correction shouldn't even be attempted. In the end, knowing the speaker's response allows you, during room calibration, to separate out what the speakers are doing vs room effects.

Dave, if I understand your circumstances correctly:

1. Your previous speakers in your previous (non dedicated) room did not cause you this hearing distress.

2. Your current speakers in your previous room did cause this distress.

3. Your current speakers in your current room also cause this distress.

From this, it is pretty safe to say the speakers are the culprit. With that in mind, the question is what are the speakers doing that might create this problem for you. You may have developed a sensitivity to distortion in narrow areas of the frequency spectrum. Looking at the near field plots, there are differences between the L, C and R speakers ... the signficance of these differences is difficult to tell without very precise level matching and then an over lay of the three plots. However, they all exhibit a very deep, narrow notch at just below 800Hz, your left is showing something going on at 2kHz (also apparent in the C and R but not as deep), and nasty peak at about 5.5kHz. The notch at 800Hz cannot be addressed by PEQ whilst the stuff at 5.5kHz can be fixed.

I'm rather suspicious of the "stuff" going on at 5.5kHz as being something you could be reacting to ... the 800Hz notch could also be contributing to the issue.

Next steps. I'd suggest you have friends over and see if they have the same issue(s) you have...if not, it could easily be a specific sensitivity in your hearing which has been exacerbated by these particular speakers ... an audiologist may be able to sort this out. As well, the problem you're experiencing could be resolved using different speakers. That's a tough approach because that means listening to other speakers in a geography where this is less than easy to do. I would vote for a visit to an audiologist just to verify your hearing and then listening tests.

Originally Posted by Dennis Erskine

Subwoofers -
EQ will be required plus your room design should allow the ability to move and relocated the subs during the calilbration process. Generally, you should avoid having the drivers point directly into the seating locations. If you do, an 1" of fiberglass board ( like OC703) can be placed in front of the sub's driver. These drivers create HF artifacts as a result of their operation. These artifacts can lead to subwoofer localization ... something you want to avoid.

Comb Filtering:
The audible impact of comb filtering is very unequal frequency response within critical frequency ranges. The same sound from two different speakers will cross paths, and, when they do, you'll have some frequencies cancelled (180 degrees out of phase) and other frequencies augmented (in phase) plus all the variations in between. These cancellations/augmentations will be inconsistent throughout the room.

Isolation:
Reducing noise entering a space and reducing noise leaving that space to adjoining rooms is NOT mutually exclusive, nor did I say that. My point is the REAL reason sound isolation should be employed in dedicated rooms is to reduce the noise floor IN the room. The fact those efforts assist in reducing noise levels OUTSIDE the room should be considered a bonus. There are some differences between the two efforts. First, a significant cause of high noise floors in a room are a result of the noise brought into the room by the A/V installer or home owner ... the equipment. Other in room sources of noise include HVAC noise. The remainder is noise entering the room from the outside which needs to be eliminated. Second, if the sound track is at 75dB in the room, and ambient noise levels outside the room are at 35dB, you have a 40dB problem to solve. If the ambient noise in the room (from outside sources) is 35dB, you have a 13dB problem to solve. Don't get excited ... that sounds easier than it is and when we say 'noise floor' the metric is either NC or NR which are weighted curves across a broad spectrum of frequencies.

The desired standard for noise transmission from inside a room to the adjoining spaces is the theater should not increase the ambient noise level outside the room by more than 3 dB SPL

Originally Posted by Dennis Erskine

Peter:

From a pure technical perspective, full range speakers should be 15' from anything; but, that isn't practical. Keeping speakers further from boundaries is more important in two channel rooms. In multi-channel applications, the speakers can be moved closer to walls; but, those walls need to be treated to avoid, among other things, the notch created by the boundary effect. The treatments need not be expensive.

PeterM is correct that the distance between the driver and the screen depends on the screen material.

Baffle mounting is another approach; but, without knowing the radiation characteristics of the speaker, it can be a bit dicey. Once in a built baffle, you're not going to move them a couple of inches (cm) one way or the other to snap the sound stage in place.

EDIT: The issues for the L/R are the same as for the center. The good news/bad news of this is the L/R are a different distance from the side walls than the center; but, again, doable.

Originally Posted by Dennis Erskine

In the most general of terms, "bookshelf" (which means not full range) speakers plus standalone subwoofers are preferred. Due to the way small rooms interact with speakers, the subs+bookshelf approach allows you to place the L/C/R speakers in a location for best imaging, clarity, etc. whilst the sub(s) are located in positions providing the better bass response in the seating locations. Further (assuming an 80Hz crossover between the mains/subs) you'd want your L/C/R's to be more than 3.5' from any wall (floor or ceiling) and your subs less than 3.5' from any wall. If you cannot get the mains more that 3.5' from a wall you'll need 4 or more inches of absorptive materials on all surfaces inside that 3.5' radius. (3.5' is approximately the 1/4 wavelength of the crossover frequency).

Originally Posted by Dennis Erskine

Running all your speakers at full range (assuming they really are full range), will either work wonderfully or fail horribly. The interaction between the LCR speakers and the room boundaries, the physical characteristics of those speakers, and your seating distance(s) are going to dictate the placement of the LCR in order to create the best in room response and provide your soundstage. Your low frequency drivers; however, have their own positioning needs in order to achieve the most consistent bass response at the seating locations. It is very, very rare you find a room where the location of the LCR speakers for the best sound stage and the location of the low frequency drivers to provide the smoothest bass response are the same.

Additionally, there is another issue. I'll use 80Hz as the example for the crossover frequency. At 80Hz, the wave length is 14' ... the 1/4 wave length is 3.5' feet. At 80Hz then, if the speaker is 3.5' from a wall, you'll have a phase cancellation, or notch, at 80Hz (3.5' + 3.5' = 7', or 1/2 wavelength, or 180 degrees out of phase). As a speaker moves closer to a wall, the notch frequency increases. So, with an 80Hz crossover, you move your subs closer than 3.5' from the wall, no notch ... the notch frequency is higher than the sub's highest frequency. As you move your LCR's further away from the wall, the notch frequency decreases ... thus, if your mains are more than 3.5' from a wall, you notch frequency is lower than the lowest frequency being produced by the main speakers.

One point that is missed and messes people up is that at the crossover frequency (80Hz, for example) you sub and main speaker must be in phase. The cross over frequency is the only frequency which is produced by the mains and the subs at the same time and same intensity. Getting that wrong is why many feel something isn't right. As demonstrated in our HAA classes, when it is right, you cannot tell if the sub is on or off.

Here's a teaser .... when you have two subs in a room, they do not behave as two independent speakers ... they behave as if there was only one sub located 1/2 way between the two actual subs.

Originally Posted by Dennis Erskine

Two channel uses the room as the surround processor. These environments need to have more reflections to provide that faux surround effect. Because of that, you cannot risk the notches and comb filtering. In multi-channel, we can push stuff closer to the wall and treat the problem. (Because they are full range, you also have the problem that the best location for smooth bass response is likely not the best positions for a great sound stage).

Some of the newer receiver based systems should not be overcome with this kind of situation ... certainly a standalone would provide a better result; but, we're splitting hairs here.

Maybe if the three of you can get your schedules together, I should slip down under.

Originally Posted by Dennis Erskine

Some how the point is being missed:

1. No speaker will be flat off axis.
2. The off axis plot should have the same shape and character as the angle increases. Note the good response ... the shape, is the same at all angles ... is just rolls off on the high end. Basically, the frequency response is exactly the same...just the SPL rolls off.
3. Look at the bad response ... the off axis picks up a notch. That is bad, bad, bad. When your off axis doesn't match your on axis, you want to absorb. When it does you want diffusion. In the case of the B&W plots, the FR of the on axis and off axis are very different. Not good.

Originally Posted by Dennis Erskine

You certainly do not want the back wall "dead" if you have surround speakers back there. The extent to which that wall is treated, and exactly with what, is dependent upon many factors ... distance from speakers, distance from nearest row, available height for rear speaker installation, overall decay rate by frequency in the room, where are the side surrounds (and type), etc.

Originally Posted by Dennis Erskine

Mark, I start with "A".
Center channel not withstanding, the sound stage can collapse when the speakers are too far apart. The depth and width of the sound stage is very much affected by the design of the specific speaker and the acoustic treatments used (as well as the geometry of the seating in relation to the speakers). Sucking out the side wall reflections can kill a sound stage.

A point to remember is (in residential sized rooms) as the speakers move further apart, they get closer to the side walls. The impact of wall proximity can be very significant and a contributor to sound stage failings.

If the speakers are on stands behind the screen you have the advantage of pushing, pulling and twisting the speakers after construction. If you're using a true baffle wall, you've got to start with full polar radiation plots of the speakers ... this is a real engineering problem because those speakers ain't moving once installed.

Lobing may or may not be a problem depending on the speakers being used. Elevating the speakers above the ears, above the ears and aiming downward, may or may not place one or more rows (seats) in a problem area. (An advantage with raising the speakers and aiming downward into the seating area is it will reduce the SPL delta between rows.) Elevating speakers above ear level (whose ears, which rows) will not inherently exacerbate lobing issues ... it is speaker dependent. On the other hand, lobing effects are generally not realized by casual listeners who are seated ... moving around the room can make lobing artifacts very apparent. Excellent speaker designs are making lobing less and less an issue ... in many cases, much less an issue than the difference in the high frequencies between the first, second, third, etc. rows of seats ... particularly in small residential rooms ... not a problem in two channel since two channel is so focused on one and only one seat.

The two channel boys have it easy. They can get by with horrid speaker designs (from ma lobing perspective) due to two inherent factors in 2-channel "audiophilia" rooms: (1) the sound has to be good in one, and only one spot approximately the size of a 10" cube which is a bunch easier to do than good sound in 16 seats; and, (2) 2-channel is so full of it's own inherent distortions from reality ... (well, I won't go there again).

Masking panels - The impact of the masking panels when closed to 1.78:1 will vary from non-audible to a higher roll off in the high frequency range. The non-impact could be a result of really good masking panels or the fact the roll off is in a frequency range we adults tend to have lower sensitivity. The audibility issue would largely stem from a timbre mismatch between the center and L/R speakers. This, however, can be easily compensated for by an EQ device which allow for multiple profiles to be saved and recalled.

Originally Posted by Dennis Erskine

Here is a reasonable approach ...

Make your diffusers from 1/4" peg board. Take a 4x8 sheet, cut it in half.

Starting on the room center line, from the ceiling down, orient your first diffuser vertically. Directly below that, install one oriented horizontally ... and so on down to the floor (you don't need to go all the way to the floor .... whatever works with the spacing.

Next, you do the same to the two rows to each side of the center; but, your first cylinder would be horizontal, not vertical. Carry on following that pattern and ideally your last row to each end would be a single, floor to ceiling cylinder straddling the corners.

You might want to cover the pegboard with fabric for appearance sake. Behind each cylinder install 3.5" of non-faced fiberglass. (Let the math wizards take a crack at that).

That is the simple way. The more complex way is to vary the radii (meaning for spacing you'd have to calculate the chords so they match), horizontally, you'd have three rows of cylinders and vertically, you'd have five or seven columns.

(Much more than a 2nd order differential equation.)

Originally Posted by Dennis Erskine

There is no reason to be equi-distant from the listener (which one) if you have variable phase control on each sub or a PEQ.

Three across the front is not a good idea at all...mid point side wall, midpoint back wall, midpoint front wall. Alternative, between the L and C, between the C and R and 1/3 the width of the back wall or 1/3 the length of the side wall.

Originally Posted by HDvids4all

Discs? We don't need no stinking discs!!

Put me in the 'Home Theater Computers' camp, although I don't stream right now, I run everything local (see my signature for details).

AnyDVD HD+MyMovies+TMT3+Windows 7 Media Center. With about 180 BDs and 400 DVDs, I've never had a problem with any titles playing incorrectly or displaying errors (after everything was configured correctly). Stacked together with a Harmony One, it's so easy even my girlfriend can do it.

Originally Posted by Dennis Erskine

You'll want two supplies (typically in the front of the room, high mounted) and two returns (high mounted) in the back of the room. You do not want air flow directly on any seating location. You do not want a velocity of more than 250 FPM through any vent (diffusor). You want the HVAC system to maintain a temperature of 70 degrees F with an outdoor temperature range of -30 to 100 degrees F and to maintain a relative humidity of not less than 25% nor greater than 50%. You want six air exhanges per hour and 15 CFM of fresh air per person

Originally Posted by Dennis Erskine

Peter:

That design could be improved ... all of those sharp 180 turns will create velocity and noise problems of their own.

Just talking (typing) aloud here:

I would not use flex duct (unless there's a local code issue). Basically, I'd keep the MDF baffles but make each chamber larger. Then, I'd line the entire inside of the muffler with two 1" layers of something like Johns-Manville insul-shield. Between those two layers I'd install a 3 to six mill poly sheeting. The first, fully exposed layer will latch on to the higher frequency noises. The poly sheeting turns the second layer into a diaphramatic absorber improving lower frequency performance. The whole thing is more efficient if the fan is located close to the exhaust (pulling air from the room). Pulling air is more efficient than pushing and the fan is further from the room.

Also, while you are creating an opportunity for sound leaving the room, your "real" objective is to eliminate outside sounds from getting into the room. To not affect the rest of the house, you need a 70dB reduction. For the house to not affect the theater, you need a 17dB reduction.

Originally Posted by Elill

Ted - just to clarrify this, what I had planned:

- Cut a hole in the wall depending on duct size
- Getting a PVC connector the same size and putting that through the hole, sealing with stuff
- connect the flex duct to the PVC connector on either side
- run the inside flex duct to where it needs to go via a soffit
- place a dead vent outside the room, hooked up to the flex duct on the outer side of the wall
- hook in line fans up to more flex duct coming out of the dead vent

If I read you correctly, you're saying the dead vent needs to be inside the room? crap if thats the case its going to take up HEAPS of room?

Originally Posted by Dennis Erskine

I cannot respond with respect to what Insteon can, or cannot dim. The entire issue boils down to the type of transformer used by the low voltage fixture. Virtually all dimmers have no problem dimming magnetic transformer loads. If the transformer is electronic, you'd need to go back to the manufacturer and ask if they will dim electronic transformers and if an interface is required for that purpose. ALSO, there are some electronic transformers which specifically state they cannot be dimmed. Ardee Varianti and Halo 1499 fixtures use magnetic transformers and can be easily dimmed.

NOTE:
Low voltage housings (or fixtures) are generally available in three variants:

1. Magnetic low voltage transformer located inside each housing (meaning the electrician wires standard 120V to each fixture;
2. Electronic low voltage transformer located inside each housing wired as above; or,
3 No transformer in the housing. These fixtures are wired with low voltage (Class 2) wiring back to a central transformer rated to handle the load of all fixtures on the transformer. (This is an option with, for example, Ardee and Seagull.)

Ok, so how do you get an answer from a supplier? First, understand the dimmer manufacturer (unless it's Lutron) isn't going to say they can, or cannot dim, any specific fixture. They are not about to be held liable for the performance of some other manufacturer's fixtures. The manufacturer, in the case of electronic low voltage transformers, is not going to say if any dimmer manufacturer's product will properly dim their transformer ... they don't want to be buying you new dimmers. The lighting fixture manufacturer can tell you if their ELV transformer can or cannot be dimmed.

You therefore have to ask the lighting manufacturer if the transformer is magnetic or electronic, if electronic, can it be dimmed (they should be able to email you the specifications). After you have this information, call Insteon (if they'll answer the phone and have someone who knows something about the product), if they can dim the Electronic Low Voltage transformers and under what conditions (interface, special dimmer, etc.)

Insteon does claim their Model #2476D dimmer can dim electronic low voltage and magnetic low voltage loads. I am not an Insteon fan and would direct you toward Lutron's RadioRA2 product...but, that's just my opinion.

Originally Posted by Dennis Erskine

The top is further out from the wall than the bottom. Reflections are directed into the carpet.

Originally Posted by Dennis Erskine

We do not use Planet Waves for speaker cable. For that we use a 12 AWG multi-stranded cable (typically from Liberty Wire & Cable). The electrical requirements are pretty straight forward ... the quality of the sheath (like for pulling through walls, however) is a different matter.

Originally Posted by Dennis Erskine

Let's see. You buy a $20,000 monoblock amplifier. You buy it because it is "good", transparent...whatever the manufacturer claims. You plug it into the power using the manufacturer's supplied power cable. Now, some yahoo (professional word crafter who likes free equipment) and claims this $1000 power cable will make your amp sound better. Come on!

1. If a better power cable would make the amp perform better, don't you think the guys who engineered the amp in the first place would have known that?
2. Do you really think the manufacturer would deliberately degrade the quality of their amp by using an inappropriate power cable?
3. If you upgrade power cables, does the manufacturer of the amp stand to make money on that?
4. Do you really believe your power cable to your amp should act as a tone control?
5. Do you really believe 3' of "super copper", "silver clad copper", etc. can clean up several miles of bad electrical transmission line (it takes a bit more than that).

Point of this ... it doesn't take a PhD in EE or Physics to see through this BS.

Originally Posted by CptnRandy

I'm afraid you've fallen in with a bad crowd here.

Here's my advice - leave here and don't log in again

Seriously. We're all maniacs. The advice you'll get here will not make your wife happy. It will cause you to spend much more than you though you'd ever spend.

I mean it. Log off. Have the builder run you some wires, drywall the room, and you can get a nice projector, maybe some new speakers at Best Buy.

There's no other way to put this: we're serious geeks about this. That means that no home builder will meet our standards and understand our obsession. We represent a very small niche market. And as I said, we're all pretty much nuts.

But if you really want to dig into it, you'll find some very nice, extremely helpful people here. We'll help you empty your bank account, too! We are the holders of some very interesting secrets, but as I said, learning about them will be expensive.

I spent over six months just planning, asking questions, and talking with people here online, then another eight months building. My wife doesn't want to know what I spent (it's a good thing she doesn't). And our family is very happy with our theater. It's an amazing space and we love to entertain and to use it ourselves almost every day. There's nothing like experiencing a movie in a well designed and executed home theater.

I'm sorry, but your builder can't do it. Even if he says he can. He just won't have the experience or the knowledge to design and build a proper acoustic environment. It's not as simple as putting up some drywall.

Most people are very happy with their simple home theaters without going to the lengths that we go to. But if you ever get a chance to visit one of our theaters, you'll know why we've gone slightly off kilter about the subject.

Good luck to you!

Randy

Originally Posted by Dennis Erskine

Elill ... can you raise the height of your entry door to extend your seating platform across the width of the room and place a landing outside the door? IOW, your step up to the rear platform would be outside the room. If you can do this, I'll tell you how to make your platform a bass trap for the modal frequencies.

Originally Posted by tlllava

You should really think about leaving these brick columns exposed. It would be a great look. It shouldn't mess up the sound so long as one isn't right at a primary reflection point from a speaker.

Good luck with your build.

Originally Posted by Roger Dressler

If my conversions are correct, it looks like your front row's ears will be about 12' from the screen wall in a 16.7' room. (In my 17.5' room that's 10'.)

Have you somehow determined that the 12' location gives ideal sound performance wrt room modes or other factors? If so, you may be right.

What made all the difference was going with multiple subs and a BassQ processor to tune them.

Originally Posted by Roger Dressler

With such rigid walls, I'm curious to see how the bass performance will come out. We can continue that discussion at your thread if you like.

Originally Posted by Elill

So I’ve built the other 3 walls of my room by “room in room” methodologies and now comes the last and most difficult (BTW these photos dont show the new walls). I’ve figured out how to get around these pipes so that’s not a problem.

They’re really loud when the ensuite above is “used”.

Question do I need to insulate them in anything?

Or by building around them (no flanking points) is that good enough? By way of information, they’ll have 45mm thick beams covering them on the theatre side and obviously nothing on the other.

Originally Posted by Mr.Tim

Well, changing them out for a heavier pipe like cast iron would be the dream solution, but I am pretty sure that is not an option.

Barring that, the next best thing would be to add mass to the piping. There have been a couple of threads from people on how they did this. Some people have used some sort of asphalt roll-roofing. Other people have used Dynamat or Dynamat-type materials to wrap the pipe.

Try searching the forum for "dynamat", it should pick up as few threads about it.

Good luck! Too bad that brick had to be covered, the room looks cool!

Originally Posted by NJ Jackals

Do this:

Originally Posted by Ted White

Elill, you'll need the insulation in any cavity. Mass + absorption.

Originally Posted by 3fingerbrown

Wrapping the pipe in acoustical pipe wrap would be a lot easier than replacing it with iron pipe. You can see in my build thread, I had a pipe behind my screen wall that I wrapped with this stuff, purchased from the Soundproofing company.

Originally Posted by Ted White

You never, ever want dense insulation within a closed air space.

Originally Posted by Intricate1

Cast iron and a repipe with thought process as to how water is going to fall in those pipes is the BEST solution.

The pipe he has here is a thin gauge compared to what we commonly use in the USA, which is even louder then what most of us are accustomed to. As much as I hate recomending CI pipe for anything it would cut your sound level by a HUGE margin. Leaving the biggest noise producer being the splashing water from under the concrete slab area.

Originally Posted by Intricate1

The insulators you are talking about are meant to reduce sound transmission between the supply piping and the framing members. When supply piping is attached directly to joists it transfers vibration to the framing members turning said framing into one big speaker.

His issue as far as I can see is mostly because of the way the piping was run, water is splashing with force into those pipes when they drain. Adding into the fact they are using a low density thin plastic pipe he is stuck in a pretty much worst case scenario.

And he is likely correct paying a pro to rework with CI is going to cost him a good chunk of change. No idea what it would cost in Australia. Here in Middle tn USA I would likely charge him $800-900 bucks to make it quiet.

Originally Posted by Elill

The cast iron pipe itself isn't that expensive - about $100 for 3m.

I've contacted a plumber to see what it'll cost to replace. I think it'll be worth the extra coin....unless he comes back at $100 an hour and 10hours work..

Just to clarify a point, there will be no contact between the pipes and the room in room structure of the theatre. I've devised a way around this. I haven't drawn it in sketchup yet but basically there will be a beam running on 90x90 posts which will sit inside the line of the wall. These will likely become columns...sorry that doesn't explain it very well.

Try again.

1. There will be 3 stud walls sitting in between the engaged brick peirs.
2. These will be connected by narrow (350mm x 2400mm x 19mm) strips of ply
3. Attached to the ply will be the 90x90 posts
4. The beam will sit on top of the posts and the studd walls (with rebates cut for the sections of the engaged peirs)
5. Sitting on top of that beam will be another beam at right angles that goes up round the pipe
6. The new ceiling joists will sit on this new beam. Basically the posts will support a beam that the new joists will sit on - as if I was building a very heigh (2400mm) deck

I'll them insulate the stud sections, put more ply in, then GG then DD. I'll probably DD and GG around the posts as well. My rear speakers and treaments will sit within the sectional studd walls and I'll cover that section in fabric frames and make the post section a column or feature (timbers, lights something)

Ok So I'll look into some sort of mass loaded vinyl perhaps [/quote[
Nope. Not appropriate for this kind of application. You want a damping agent that will physically adhere to the PVC pipe.

Originally Posted by Elill

I'll hopefully get the cast iron replacement, if that is still too loud there is a 25mm lagging product that looks good, you wrap it around the pipe and seal it off with aluminium tape.

Originally Posted by Mazlem

Any Dynamat is overpriced, but generally stuff with butyl instead of asphalt is better for adhesion and very high or low temps. Check out www.secondskinaudio.com and www.raamaudio.com. They also sell closed-cell foam there (same as linacoustic?) That stuff would stick to the pipe. Mass-loaded vinyl could be attached with spray adhesive, to the pipe or the damping material.

Originally Posted by Dingaling2004

...even shots of the kennel will be fine!