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post #271 of 10416 Old 12-22-2004, 08:57 AM
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Andy,

Acoustic correction should always be attempted first, if at all possible. The problem with EQ is that it can only improve a localized area. Very low frequency absorption will improve the entire room, so there will not be seating issues.

While bass traps will improve a room and are advisable, a room with serious low frequency problems cannot be completely corrected without Herculean measures -- devoting a very major portion of the space to bass trapping. While possible for a studio, this is generally not a practical alternative for a home theater due to space, aesthetic, and/or budgetary considerations.

EQ is the next step after acoustical correction. In many cases, though, it can fix a room which is simply too problematic for completely effective very low frequency acoustic treatment. Unfortunately, the latter is the rule rather than the exception.

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post #272 of 10416 Old 12-22-2004, 11:50 AM
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Bob,

> I thought there were several types of phase shift (time delay > 1ms) <<br />
It's important to distinguish between straight delay and phase shift. If you add straight delay to some channels more than others, the phase shift will be different for different frequencies. So the arrival time differences create peaks and nulls in the air where the waves combine. Likewise for phase shift if it's not the same in all speakers. The key point is that the response errors occur only as a result of identical content arriving from two different sources and combining. Without the combining, the frequency response is not harmed. Any phase shift or delay that's common to all channels is benign.

> c) different delay for different freqeuencies - caused by bad EQ electronics, or bad crossover electronics, or bad bass management electronics, or a bad filter. <<br />
Phase shift caused by "bad" electronics is not an issue because presumably the same shift will be applied to all channels. Not counting a subwoofer which is a different issue. To be clear, electronics adding phase shift is neither bad nor undesirable. It occurs all the time, especially in equalizers, and is a fundamental part of how EQ works. If you haven't seen it yet, HERE is a short article I wrote that explains the role of phase shift in EQ circuits.

> subwoofer phase shift control knob <<br />
That's a little different. The phase shift knob on a subwoofer is used to better align the two different sources - the subwoofer and mains - around the crossover frequency so both signals arrive at your ears in phase to avoid peaks and nulls.

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post #273 of 10416 Old 12-22-2004, 11:55 AM
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Andy,

> I've always always read that EQ causes phase distortions which lead to a 'smearing' of the sound. <<br />
This is a huge problem. Misinformed magazine writers (and even some pro recording engineers) have repeated that so many times it's now accepted as fact. Nothing could be further from the truth. The whole notion of phase shift causing "smearing" is based on fantasy. Room echoes can "smear" imaging, but that's not related to phase shift. See the article I linked above about how phase shift is inherent in EQ, and why some people wrongly believe phase shift is an audible problem.

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post #274 of 10416 Old 12-25-2004, 07:14 AM
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Hi-

How kid and pet friendly are these materials? Do you need to cover them? Do they pull apart if messed with? Is one better than the other?

I am concerned with the stuff you put on the walls (versus in the walls).

Thanks,
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post #275 of 10416 Old 12-25-2004, 12:17 PM
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Jeff over in another new HT suggested I repost this here.

I'm hoping to start my HT early in January and am quite excited but know very little about acoustics, but no doubt after reading through and following this thread I hope to be up and running


Just wondering:

Would it be possible not the mud and finish the sheet rock especially as the CertainTeed UltraDuct Gold covers the walls??? I can certainly do the framing and sheet rock but would Never dare do the mud and tape work - lol

Thanks so much for your advice.

Cheers,

Geoffrey
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post #276 of 10416 Old 12-25-2004, 05:05 PM
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You really should do the joints with tape and at least a rough mud job even if it is going to be covered. You wouldn't have to sand it though or worry too much, just seal up the joints.

Good luck.

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post #277 of 10416 Old 12-25-2004, 07:14 PM
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Thanks bpape:

I'll certainly take your advise and thanks again.

Cheers,

Geoffrey
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post #278 of 10416 Old 12-26-2004, 06:31 AM
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I recently bought some Owens Corning 2 inch 703 from a roofing wholeseller for about 50 cents a sq. ft. They carried OC shingles and were able to get all OC products.
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post #279 of 10416 Old 12-28-2004, 06:51 AM
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Man around here they are charging over $1 a sq. ft for any rigid fiberglass. I have called about 30 places and only 2 carry it so far. Ordering online would be more expensive do to shipping. This stinks.

Mark-
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post #280 of 10416 Old 12-28-2004, 06:59 AM
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Sorry, it was over 1 per sq ft. I just thru it out there as an option for getting the stuff. If you can just have it thrown on a load that is already coming in, the shipping isn't much.
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post #281 of 10416 Old 12-28-2004, 09:28 AM
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marjen:
Quote:


Man around here they are charging over $1 a sq. ft for any rigid fiberglass.

Some people have been successful bartering over the price, offering to pick it up, etc. For example, one guy in england bartered from $1.50 per square foot down to $0.30 a square foot.

An amateur built the Ark. Titanic was built by professionals. Of course Noah took a little advice.
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post #282 of 10416 Old 01-04-2005, 09:08 AM
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Help:

I can not find INSUL-Shield but I have found Owens Corning SelectSound Black in blanket form for about $216.00 for a 48"X100' roll.

Can I get a couple of quick opinions on using this instead of the INSUL-Shield?

Thank you,

Dave
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post #283 of 10416 Old 01-05-2005, 05:46 PM
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My room is 20 by 14 by 7.5 I'm going to try and find some of the material listed at the very beginning of this thread.

If I'm able to find THIS in the rigid form would it look OK to leave it uncovered?

My system will be 7.1, 6 of the speakers will be floor standing towers.

I must admit that this is all very confusing (figuring out which method of treatment to use).

I intend to use the room approximately 90 percent of the time for home theater.

So this is what I plan on doing (correct/stop me if I'm wrong)

Cover the entire front wall with 1 inch and the other three walls to match the height of my speakers.

Cover the bottom of the soffit with 1 inch as well.

HH
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post #284 of 10416 Old 01-06-2005, 04:43 AM
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I guess you could leave it uncovered - it seems to be designed for that.

The perimeter of the room should be done to ear level - not to the top of the speakers necessarily.

Don't forget to do the first reflection points.

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post #285 of 10416 Old 01-06-2005, 07:26 AM
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Quote:


Originally posted by bpape
I guess you could leave it uncovered - it seems to be designed for that.

The perimeter of the room should be done to ear level - not to the top of the speakers necessarily.

Don't forget to do the first reflection points.

I would like to cover with fabric but I don't have the skills to do it right and haven't found a GOOD tutorial on DIY with pictures.

I will do ear level.

Doesn't ear level on three walls take care of the First reflection points?

HH
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post #286 of 10416 Old 01-06-2005, 07:29 AM
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Quote:


Originally posted by HuskerHarley
My room is 20 by 14 by 7.5 I'm going to try and find some of the material listed at the very beginning of this thread. If I'm able to find THIS in the rigid form would it look OK to leave it uncovered?

I intend to use the room approximately 90 percent of the time for home theater.

So this is what I plan on doing (correct/stop me if I'm wrong)

Cover the entire front wall with 1 inch and the other three walls to match the height of my speakers. Cover the bottom of the soffit with 1 inch as well.

I'm in the exact same situation. Today, I will have 60 of the 2 ft x 4 ft black acoustic panels delivered. I will be applying them to the front wall, primary reflection pionts, around the perimeter at and below ear level, and on the bottom of the soffit. I'm not sure if it looks acceptable without a fabric covering but I hope so. I'll let you know after I see it tonight.
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post #287 of 10416 Old 01-06-2005, 07:36 AM
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Quote:


Originally posted by Carlton Bale
I will have 60 of the 2 ft x 4 ft black acoustic panels delivered.

I'll let you know after I see it tonight.

How much do they cost?

Please post a picture if you can.

HH
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post #288 of 10416 Old 01-06-2005, 09:06 AM
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The insulation up to ear level gets the majority. Don't forget the ceiling though.

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post #289 of 10416 Old 01-06-2005, 10:27 AM
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Quote:


Originally posted by bpape
The insulation up to ear level gets the majority. Don't forget the ceiling though.

Please tell me what I should do so I get it somewhat correct the first time.

HH
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post #290 of 10416 Old 01-06-2005, 10:36 AM
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You'll be fine on the walls. Some do the ceiling, some don't. If you want to calculate where to put them (mirrors are a lot harder on the ceiling! ), draw it out. If you measure from the mid/tweeter center to the ceiling and then draw a phantom ABOVE the ceiling the same distance, then draw a line from that point to your ears, you have the hypotenuse (sp?) of a triangle. The other sides of it are the straightline distance from the real speaker to your ears and double the distance from mid/tweet to the ceiling.

Once you get that triangle trigged out, then you know the angles. From there, calc the triangle (phantom) above the ceiling and use the base for the distance from the speaker front out toward you. From side to side, put it in a straight line between you and the speaker.

This seems like a lot of math to some but to me it's easier than trying to get someone else to hold a mirror of decent enough size that I can actually see anything flat on a ceiling and move it around without being in the way.

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post #291 of 10416 Old 01-06-2005, 11:01 AM
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Quote:


Originally posted by bpape
You'll be fine on the walls. Some do the ceiling, some don't. If you want to calculate where to put them (mirrors are a lot harder on the ceiling! ), draw it out. If you measure from the mid/tweeter center to the ceiling and then draw a phantom ABOVE the ceiling the same distance, then draw a line from that point to your ears, you have the hypotenuse (sp?) of a triangle. The other sides of it are the straightline distance from the real speaker to your ears and double the distance from mid/tweet to the ceiling.

Once you get that triangle trigged out, then you know the angles. From there, calc the triangle (phantom) above the ceiling and use the base for the distance from the speaker front out toward you. From side to side, put it in a straight line between you and the speaker.

This seems like a lot of math to some but to me it's easier than trying to get someone else to hold a mirror of decent enough size that I can actually see anything flat on a ceiling and move it around without being in the way.

I grew up in the crayon age and I'm embarrassed to say but I don't understand most of what you instructed me to do.

HH
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post #292 of 10416 Old 01-06-2005, 11:10 AM
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Then get a stepladder, a decent sized mirror, a good patient friend, and some beer (not till after the mirrors are down ) and find them that way.

It's tough to describe a math problem for 2 - 2 dimensional triangles in a 3 dimensional space with just text.

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post #293 of 10416 Old 01-06-2005, 09:52 PM
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Quote:


Originally posted by HuskerHarley
How much do they cost?

Please post a picture if you can.

HH

Agreed, curious about looks (uncovered) and cost. Thanks!
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post #294 of 10416 Old 01-06-2005, 10:26 PM
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Couple of questions in the early planning stages of my theater.

What do you think of pre-made acoustic panels like these? Are they good performance-wise? My company can get them as a dealer, and I like the way a darker color GOM covered panel looks on a black lower wall. If I got some 4'x4' or 4'x longer, and did them across the bottom, would an inch or more of space in between each panel for aesthetics hurt performance much? I think butting them right up to each other might look strange, but spaced slightly apart, they kind of look like art. How about some idea on cost for the "right" way to do it, with GOM fabric stretched over the JM duct liner stuff? Any idea about how much it costs to do it that way for a room 14'x 18' to 4' high? I would prefer to just do a moulding at the top & paint above instead of fabric all the way up if I use the fabric method. I will be having a GC build the room. So I would need to factor cost of materials and understand if an average competent GC can install this stuff & how long it might take. The pre-made panels are in the range of $280 for 4' x 10' so that gives me an idea to compare against. Let's leave the front wall out of the equation for now as I will need to treat it either way. And that brings me to my next issue:

I will be moving a very nice family room projection system into a new dedicated room. More info & pics of current setup here Note I have not updated that thread yet, but I am now thinking of abandoning the dual front/ rear two sided projection. I will update that thread as to why. Still not 100% sure.

Regardless, I LOVE my rear projection image and deep blacks I get from the screen, and think I now want to use that in my new dedicated theater if I can swing it. The question is how will it impact the acoustics (I'm guessing not well) and what if anything can I do to help? The screen is 80"x45" and it is 1/2" thick optical rear projection glass (not plexi.) It will go into a wall that is probably about 14' wide. It will have a rear projection room behind it. Glass screen framed into that separator wall like a window. I can treat that wall (and the back side too, if necessary) with whatever will help. But of course, unlike most of you, I cannot treat the area behind the screen, as the screen is glass.

Other info: the room will probably be about 17' to 18' deep. I have two full range tower L/R speakers w/ 12" sub/10" passive radiator for mains. One additional 15" stand alone sub. Thinking two rows of 3-4 seats each, back row on small riser. Probably a modified stage with three decoupled sections, sides filled w/ sand & middle w/ insulation (this is not on ground level.) Ceiling height to be 8' range, with two small areas about 17" lower. Screen (if I go RP, or keep my original dual FP theater/ RP family room idea) will be on the lower side, about 29" AFF due to where the RP screen is now. Actually, if I build the RP room over I can make that higher if needed. So I could put the center above or below.

Any info or tips on these issues for planning my acoustics most appreciated. Also, are there any good room planning software programs out there that are free or close to it, so I can play around with ideal room dimensions and seat/speaker placement while in the planning stages?
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post #295 of 10416 Old 01-07-2005, 06:37 AM
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I've seen those from Acoustics First before. Unfortunately, they do not list individual absorbtion numbers at different frequencies. They also specify that they use 'high density fiberglass'. Generally, something around 3pcf is desirable. Higher densities can have issues with being too reflective at higher frequencies. Without knowing the specs, it would be almost impossible to determine what they will do in your application.

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post #296 of 10416 Old 01-07-2005, 07:32 AM
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I received my Owens Corning SelectSound Black 2 ft x 4 ft panels yesterday; pictures are below. This is probably the best looking non-covered fiberglass panel there is, but I still don't think it is quite nice enough to hang on the wall uncovered, due mostly to the edges showing but also because the front isn't completely smooth and uniform. The front isn't too bad, but it's not as nice in appearance as a fabric covering would be. I'll probably cover mine with black grill cloth.

Front: Back:

Side:
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post #297 of 10416 Old 01-07-2005, 10:04 AM
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can anyone help with this scenerio?
I'm using the Danzian Celtic Cloth for an accoustically transparent screen (54"x96") with three in-walls for the LCR duties. The room is sorta large @ 24x24x8 and right now, the in-walls are pretty close with maybe a 1/4" gap between the screen fabric & front speaker baffle. Should i be concerned with treating the whole front wall or the area just behind the screen with a deadening material? Should i "float" the screen out and away from the speakers more than they are now even if i do/don't treat the area behind the screen?

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post #298 of 10416 Old 01-08-2005, 08:49 AM
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Rudee,

> The room is sorta large @ 24x24x8 ... Should i be concerned with treating the whole front wall <<br />
With dimensions like those you should by much more concerned about treating the lower frequencies. That room has a huge resonance at 71 Hz, and nearly as huge resonances at 24 and 47 Hz. All multiples of those frequencies are also resonating. The result is that all music will be very boomy sounding at those frequencies.

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post #299 of 10416 Old 01-09-2005, 03:10 PM
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Ethan, I have a couple of questions about your previous post to Rudee. Please forgive me if these questions sound like I'm a novice. I am.

First, does it matter that Rudee's room has a huge resonance specifically at 71 Hz, and also at 24 and 47 Hz, as compared to having resonances at some other frequency? Let me explain where I'm coming from with this question... I have done quite a bit of reading on your web site at realtraps.com about bass traps. (By the way, the educational information and videos you provide are amazing!) Based on my understanding of your video on "Non-modal peaks and nulls in small rooms", it really doesn't matter what the resonances are related to a room's dimensions. Your video seems to prove to me that all rooms need broadband bass trapping and not trapping at specific frequencies. So would Rudee's room be treated any differently than a room that had equally huge resonances at some other frequency?

My second question is this, Would you treat a room differently if it has "huge" resonances at some particular frequency (like Rudee's), vs. a room that has more moderate resonances? Again, let me explain where I'm coming from with this question... Your educational materials indicated to me that you believe most rooms need 8 to 10 broadband base traps placed in corners. Is this true regardless of the bass problems that a room has, or is this an average? Would a room like Rudee's need more panels, or would the recommended 8 - 10 be sufficient?

Finally, I know the broadband bass traps ideally should go in the corners. However, if I place 8 - 10 traps in my room, does it matter if they are equally disbursed? For example, if due to aesthetics or practicality, I can not put a trap in one particular corner, Can I double-up in another corner to compensate? (By "double-up", I mean stack the traps so they cover the entire 8 foot tall area in the corner.) Or even more drastically, could I put all eight in the corners behind the proscenium and get satisfactory results?
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post #300 of 10416 Old 01-09-2005, 06:03 PM
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wow - i hope all the questions above get answered b/c inquiring minds want to know! I have often thought what dreadful things were happening in here due to the square vs rectangle dimensions so often mentioned . The room doesn't sound half bad as is...
I am running a two tempest i/b located dead center between the mains in the front of the room and about 24" into the room and since it's an ib it's not going anywhere. Here's the very first frequency response i ran a few weeks ago.
Numbers below:
HZ r/s meter adjusted
17.5 80 87.3
20 88 94.2
22 88 93.4
25 88 84.4
28 80 79.6
32 72 75
36 80 82.5
40 80 82
45 92 93.7
50 102 103.3
56 102 103
63 104 104.8
71 106 106.7
80 102 102.5
89 106 106.4
100 112 112.3
112 91 91.25
126 95 95.2

sorry i don't know how to insert the graph but the numbers show a good dip from 25 to 45. These are the first numbers i have ever taken in this room and will be doing more testing as time permits. I'm thinking of doing a built in trap in each front corner as seen in some of the links on bobgolds site with oc 703 or equal. I didn't think the raw room numbers were too bad- i do have a bfd to help in the end but i wanted to address the room to some extent.
ethan, to the trained eye are my numbers relfecting the bad things you say are happening to the lower frequencies in this size space?


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