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Acoustical Treatments Master Thread - Page 309

post #9241 of 10191
Quote:
Originally Posted by Dennis Erskine View Post

Do not place a subwoofer such that the driver is aimed into the seating locations (in a residential sized room). If you do, you should place a 1" thick piece of 1.5 PCF fiberglass in front of the driver. Sometimes it requires 2".

+1

Needing to do that myself, as my subwoofers are triangular, was looking to use 70mm even... which is close to 3". ( I like overkill. biggrin.gif )
post #9242 of 10191
Quote:
Originally Posted by Dennis Erskine View Post

Do not place a subwoofer such that the driver is aimed into the seating locations (in a residential sized room). If you do, you should place a 1" thick piece of 1.5 PCF fiberglass in front of the driver. Sometimes it requires 2".
What's wrong with having the driver aimed into the listening position?
post #9243 of 10191
Quote:
Originally Posted by Skylinestar View Post

What's wrong with having the driver aimed into the listening position?

You may bounce other sound too early towards listener as well.
post #9244 of 10191
Quote:
Originally Posted by Dennis Erskine View Post

FOH...let's avoid this terminology. Perhaps better as where the x.x wave length is longer than the room dimension. There is too much misunderstanding about "bass not fitting into a room".


"as any freq with half a wavelength bigger than will fit into the room"



I'm guessing many understood, but you're right, I'm sure there's those that misunderstand. I certainly didn't want to muddy up the waters. Many savvy enthusiast don't get it, muct too much confusion and the whole point is clarity.

Typically, I'm more clear (read verbose) with regard to PVG, like I did in this excerpted post;

"Pressure Vessel Gain (PVG), or room gain, is the scenario whereby the longest dimension of the room can no longer support full propagation of the waveform. At this point, the acoustic propagation transitions to acoustic pressurization. A typical myth is a small cabin cannot support the lowest frequencies.... nothing could be further from the truth. The manner in which the sound is reproduced into the space changes from a normal cyclic propagation, to pressurization because the wavelengths are too big for the space. The frequency at which this occurs is approximately the point whereby half the wavelength of a given frequency is equal to the rooms longest dimension. So, a 20 hz frequency has a wavelength 56.5 feet. So half of that, 28.25 feet, is the point of transition. Any frequency below that point pressurizes the room, and any frequency above that point propagates freely. So in this room that's approximately 28 feet in the longest dimension, from 20 hz downward, the room gives back acoustically. This is room gain, cabin gain, or more specifically PVG...Pressure Vessel Gain.

At this frequency, the results are a gain in acoustic pressures in the room that grows as the frequency decreases. This acoustic support reciprocity, is theoretically 12db per octave. The percentage of the 12 db/octave gain one achieves, entirely depends on the integrity of the boundary walls and surfaces. If it was the theoretical concrete bunker, a full 12db/octave boost would occur. Typically, somewhere between 6-10 db octave could result. Also, in addition to the walls and surfaces flexing, other aspects may affect the point at which room gain begins. Furniture, cabinets etc, anything that consumes a certain measure of cubic feet, may slightly alter the transition frequency merely because the items take up space.

This acoustic pressurization, room gain, is the proverbial free lunch. It is essentially headroom that's thrown back into the system. And unlike horn subs, the distortions and non-linearities are not magnified. An IB sub system is a sealed alignment. Sealed alignments roll off second order. Room gain also is second order. So one can see how integrating a sealed alignment may offer substantial benefit when attempting to integrate the system to the room via time and frequency equalization. The -3db point of the IB, may typically be deeper than the transition point where room gain begins. Properly adjusted, this would result in substantial headroom added back in for significant capability for the big LFE effects."

Thanks
post #9245 of 10191
Right. This is when rubber seals around doors starts to get interesting. The stiffer and the better sealed, the better the pressurization. That's why my livingroom stereo could never yield the ULF response that the system itself had capability of, but it is one of the things I really hope to achieve with "The Larch" theater.
post #9246 of 10191
Quote:
Originally Posted by Nightlord View Post

Right. This is when rubber seals around doors starts to get interesting. The stiffer and the better sealed, the better the pressurization. That's why my livingroom stereo could never yield the ULF response that the system itself had capability of, but it is one of the things I really hope to achieve with "The Larch" theater.

These are the little details that when building HT many don't know about, including me 5+ years ago. Completely sealed means no path for sound to leak out.
I've got can lights in the ceiling, those "leak" into the space above since I did not build backer boxes around them, so even when I put a door on my basement HT I'll never get the full effect of PV gain.
post #9247 of 10191
Those mammoth wavelengths are so long, the leaks you're discussing would be much more detrimental to sound egress/sound proofing, than diminishing the benefits of PVG.
post #9248 of 10191
Quote:
Originally Posted by FOH View Post

Those mammoth wavelengths are so long, the leaks you're discussing would be much more detrimental to sound egress/sound proofing, than diminishing the benefits of PVG.

There's no need to compete in the "what's worse" game, one can discuss each issue seperately even if there are larger gains to be made. After all, people discuss different DACs...
post #9249 of 10191
Quote:
Originally Posted by Nightlord View Post

There's no need to compete in the "what's worse" game, one can discuss each issueseparatelyy even if there are larger gains to be made. After all, people discuss different DACs...


No "what's worse" game here, but I do understand your point.

We can discuss themseparatelyrately, however that doesn't change the accuracy of my contention.


If one can enjoy ~9dB/octave PVG below the 1, 0, 0 mode, in a typical 2x4 wood stud/sheetrock space (a space that's diaphragmatic and quite lossy), ... I'd recommend focusing one's energy elsewhere. That's my opinion based on my experiments/ measurements. Sealing a room tightly is something I've no experience with in my home, so I can't speak to any details in that realm.

I currently have no "within the home" isolation needs. Also, my home is a brick ranch, with side-to-side neighbors about 100 feet either direction of my listening room. Neighbors front to back are several hundred feet away, so I'd characterize my external iso needs as minimal as well. With (4)18s, (4)15s, plus dual 12" LCRs, the LF/ULF can travel however. During cold, calm nights, while out with our dog, I have certainly contemplated a fully iso'd HT build(out) at some time.

Thanks
post #9250 of 10191
Quote:
Originally Posted by FOH View Post

"as any freq with half a wavelength bigger than will fit into the room"
I'm guessing many understood, but you're right, I'm sure there's those that misunderstand. I certainly didn't want to muddy up the waters. Many savvy enthusiast don't get it, muct too much confusion and the whole point is clarity.
Typically, I'm more clear (read verbose) with regard to PVG, like I did in this excerpted post;
"Pressure Vessel Gain (PVG), or room gain, is the scenario whereby the longest dimension of the room can no longer support full propagation of the waveform. At this point, the acoustic propagation transitions to acoustic pressurization. A typical myth is a small cabin cannot support the lowest frequencies.... nothing could be further from the truth. The manner in which the sound is reproduced into the space changes from a normal cyclic propagation, to pressurization because the wavelengths are too big for the space. The frequency at which this occurs is approximately the point whereby half the wavelength of a given frequency is equal to the rooms longest dimension. So, a 20 hz frequency has a wavelength 56.5 feet. So half of that, 28.25 feet, is the point of transition. Any frequency below that point pressurizes the room, and any frequency above that point propagates freely. So in this room that's approximately 28 feet in the longest dimension, from 20 hz downward, the room gives back acoustically. This is room gain, cabin gain, or more specifically PVG...Pressure Vessel Gain.
At this frequency, the results are a gain in acoustic pressures in the room that grows as the frequency decreases. This acoustic support reciprocity, is theoretically 12db per octave. The percentage of the 12 db/octave gain one achieves, entirely depends on the integrity of the boundary walls and surfaces. If it was the theoretical concrete bunker, a full 12db/octave boost would occur. Typically, somewhere between 6-10 db octave could result. Also, in addition to the walls and surfaces flexing, other aspects may affect the point at which room gain begins. Furniture, cabinets etc, anything that consumes a certain measure of cubic feet, may slightly alter the transition frequency merely because the items take up space.
This acoustic pressurization, room gain, is the proverbial free lunch. It is essentially headroom that's thrown back into the system. And unlike horn subs, the distortions and non-linearities are not magnified. An IB sub system is a sealed alignment. Sealed alignments roll off second order. Room gain also is second order. So one can see how integrating a sealed alignment may offer substantial benefit when attempting to integrate the system to the room via time and frequency equalization. The -3db point of the IB, may typically be deeper than the transition point where room gain begins. Properly adjusted, this would result in substantial headroom added back in for significant capability for the big LFE effects."
Thanks

Interesting.

I had been recently considering the addition of two tapped horn subwoofers to my setup, but decided additional research was required. I currently have four sealed Seaton SubMersive HP subwoofers in my basement theater, that is ~27 x 21 x 8; the room is not completely sealed, but I do feel some modest pressurization sensations occasionally. I am happy with the performance, but desire increased performance at lower frequencies. It would seem that sticking with sealed subs versus ported or tapped horns would be easier to integrate with respect to time and frequency equalization.

Did I understand that correctly?

Thanks.

Mark
post #9251 of 10191
Quote:
Originally Posted by FOH View Post

We can discuss themseparatelyrately

biggrin.gif funny! It's the iPad spacebar that sometimes don't register the fast taps. A regular keyboard is superior, but then I can't sit where I want to.
post #9252 of 10191
Quote:
Originally Posted by giomania View Post

I had been recently considering the addition of two tapped horn subwoofers to my setup, but decided additional research was required. I currently have four sealed Seaton SubMersive HP subwoofers in my basement theater, that is ~27 x 21 x 8; the room is not completely sealed, but I do feel some modest pressurization sensations occasionally. I am happy with the performance, but desire increased performance at lower frequencies. It would seem that sticking with sealed subs versus ported or tapped horns would be easier to integrate with respect to time and frequency equalization.

Did I understand that correctly?

Thanks.

Mark

Hi Mark,

If you are after more bass you need to first experiment with raising the sub level, and then probably just add a manual EQ for the subs of some form. I had measured the 4 combined SubMersives to be ~5dB down at 10Hz at the listening position after Audyssey's calibration, and the mic I had with is rolled off slightly by 10Hz itself. There was only about 2dB of peaking over the 20Hz level up past 100Hz. More capability only gives more impact if you ask it from the subs. An EQ with shelf filter capabilities make this sort of adjustment very simple and some even have presets you can select for those case you want to amp it up or even when you don't want to give anyone upstairs an unintended foot-massage. wink.gif
post #9253 of 10191
Quote:
Originally Posted by FOH View Post

In a typical room, proximity to the source is everything for both measurements and listening. Using the example that th OP inquired about, ... yes, the closer to the sub, one encounters less "room", and more sub. All the way to an inch off the cone for a nearfield measurment,....minimizing the room relative to the driver's direct sound.

FOH, I think you misunderstood why I was replying as such. Being 5 foot or 10 foot away from a speaker doesn't make it more or less prone to room problems. Yes, measuring from 2" is a different story than 10 feet, though the question wasn't posed in a way that made me believe he wasn't inquiring for measuring purposes. Obviously it is impractical to sit 2" away from a speaker as to get less of the "room" sound (and room resonance and SBIR still happens regardless of where you sit, so there still is those anomalies you'll have to deal with no matter where you sit). Yes, the relative SPL of resonance when compared with SPL of the sub will be different pending where you are sitting, but that doesn't mean those acoustic problems aren't happening, nor does it mean they can't destroy the response you hear. I hope that makes more sense!
post #9254 of 10191
Quote:
Originally Posted by Mark Seaton View Post

I had measured the 4 combined SubMersives to be ~5dB down at 10Hz at the listening position after Audyssey's calibration, and the mic I had with is rolled off slightly by 10Hz itself. There was only about 2dB of peaking over the 20Hz level up past 100Hz.

So then you just need a boost circuit to lift you 10Hz by 20-30dB so you get some useful ULF. Preferrably one that can shape the boost curve, but I suppose they are rare unless people make them themselves.
post #9255 of 10191
Quote:
Originally Posted by Mark Seaton View Post

Hi Mark,
If you are after more bass you need to first experiment with raising the sub level, and then probably just add a manual EQ for the subs of some form. I had measured the 4 combined SubMersives to be ~5dB down at 10Hz at the listening position after Audyssey's calibration, and the mic I had with is rolled off slightly by 10Hz itself. There was only about 2dB of peaking over the 20Hz level up past 100Hz. More capability only gives more impact if you ask it from the subs. An EQ with shelf filter capabilities make this sort of adjustment very simple and some even have presets you can select for those case you want to amp it up or even when you don't want to give anyone upstairs an unintended foot-massage. wink.gif

Thanks for the input, Mark. Maybe I should just stay off the "the new master list of bass in movies with frequency charts" thread! eek.gif

Let me clarify that when "normal" bass (~30 Hz???) hits in movies, it brings a smile to my face; that is after I have landed from the sometimes inevitable jump out of my seat!

I shall experiment with the bass levels over the holidays, as I will be off. Funny story about subwoofer levels: We had a couple over to watch The Cabin In The Woods, and I was finding myself disappointed with the bass. It dawned on me to check the sub levels, and they had been reset to -12.0 dB (the Audyssey calibrated setting) from the -7.0 dB (Mark's adjusted setting). What a difference that made! This phenomenon occurs on my Denon AVR-4311 CI sometimes after a brief power outage.

Mark
post #9256 of 10191
Quote:
Originally Posted by GIK Acoustics View Post

FOH, I think you misunderstood why I was replying as such. Being 5 foot or 10 foot away from a speaker doesn't make it more or less prone to room problems. Yes, measuring from 2" is a different story than 10 feet, though the question wasn't posed in a way that made me believe he wasn't inquiring for measuring purposes.

I appreciate the added clarity.


The OP asked; ... "Does anyone sit close to their subs?"


You replied; .... "A speaker or sub being "nearfield" doesn't make it more or less prone to room problems. The room will equally effect a pair of mains, nearfield, or far field monitors/speakers."

I want to make clear that a speaker or sub nearfield is less prone to room problems. In my experience, even in your clarification statement above runs counter to my experiments/measurments. Being 5 feet away does lessen the significance of the ever present acoustic distortions. Yes, they never go away, however their relative significance is lessened in the nearfield.


A compartive example below.

There's black and white;
.. ie, opposite tri-corner measurements, stimulating every mode to it's maximum, compared to a mic measurement right up near the cone. The acoustic distortions still reside in the room, but they're rendered insignificant due to relative level. That's black and white.

There's shades of grey;
.. ie, relative far field typical LP in domestic living room, compared to relative nearfield in the same domestic setting. Again, the acoustic distortions don't change, however their significance due to relative level does.



Where am I wrong? Again, I merely wanted clarity for those following along, myself included.

Thank you
post #9257 of 10191
Quote:
Originally Posted by Nightlord View Post

biggrin.gif funny! It's the iPad spacebar that sometimes don't register the fast taps. A regular keyboard is superior, but then I can't sit where I want to.

smile.gif

It's my wife's laptop. Her "ieSpell" or whatever, is bizaare,....it corrects, but adds words, strings them together etc, weird and total junk. biggrin.gif

Never owned an ipad or similar. Hell, just traded in my flip phone recently for an Android Samsung. Being a photog for several decades, the best thing is having a decent camera w/me at all times.

btw; saw a Christmas card recently whereby all family members had the phones out and thumbing away .... quite funny really.



Thanks for the heads up
post #9258 of 10191
Quote:
Originally Posted by Nightlord View Post

Quote:
Originally Posted by Mark Seaton View Post

I had measured the 4 combined SubMersives to be ~5dB down at 10Hz at the listening position after Audyssey's calibration, and the mic I had with is rolled off slightly by 10Hz itself. There was only about 2dB of peaking over the 20Hz level up past 100Hz.

So then you just need a boost circuit to lift you 10Hz by 20-30dB so you get some useful ULF. Preferrably one that can shape the boost curve, but I suppose they are rare unless people make them themselves.

If you want 10Hz elevated by 15-20dB, that's certainly an option. As you approach reference level though, you want a more flat response. The point of my post was not that more 10Hz was needed, rather that there was plenty of extension and capability, and the desired effects would best be had by some "seasoning to taste" of the response. Audyssey's Dynamic EQ is another option to experiment with, especially if you dial back the amount of boost applied.
post #9259 of 10191
Quote:
Originally Posted by giomania View Post

Quote:
Originally Posted by Mark Seaton View Post

Hi Mark,
If you are after more bass you need to first experiment with raising the sub level, and then probably just add a manual EQ for the subs of some form. I had measured the 4 combined SubMersives to be ~5dB down at 10Hz at the listening position after Audyssey's calibration, and the mic I had with is rolled off slightly by 10Hz itself. There was only about 2dB of peaking over the 20Hz level up past 100Hz. More capability only gives more impact if you ask it from the subs. An EQ with shelf filter capabilities make this sort of adjustment very simple and some even have presets you can select for those case you want to amp it up or even when you don't want to give anyone upstairs an unintended foot-massage. wink.gif

Thanks for the input, Mark. Maybe I should just stay off the "the new master list of bass in movies with frequency charts" thread! eek.gif

Let me clarify that when "normal" bass (~30 Hz???) hits in movies, it brings a smile to my face; that is after I have landed from the sometimes inevitable jump out of my seat!

I shall experiment with the bass levels over the holidays, as I will be off. Funny story about subwoofer levels: We had a couple over to watch The Cabin In The Woods, and I was finding myself disappointed with the bass. It dawned on me to check the sub levels, and they had been reset to -12.0 dB (the Audyssey calibrated setting) from the -7.0 dB (Mark's adjusted setting). What a difference that made! This phenomenon occurs on my Denon AVR-4311 CI sometimes after a brief power outage.

Mark

Not a problem at all Mark. I just wanted to point out that extension wasn't a part of what you were hearing, and this really comes down to playback levels, low frequency room acoustics/decay times, and some seasoning to taste. Sometimes a little tweaking of the levels do the trick. An external EQ for the subs can be another good way to achieve this, just as you can also experiment with Audyssey's Dynamic EQ, especially if you dial back the effect.

While it's important to know where your starting point was and how to get back there if needed, you shouldn't be afraid of making some adjustments. While a narrow peak or dip of 2-4dB isn't very audible and we see that range of variation all the time, when you make such adjustments to a couple octaves at a time by changing the subwoofer level, it makes for very audible changes.

Circling this discussion detour back to acoustics, how long the sound lingers in the rooms of different size, construction and treatment, aka the decay times are the reason a similar measured frequency response can sound rather different in different spaces.
post #9260 of 10191
Quote:
Originally Posted by Mark Seaton View Post

If you want 10Hz elevated by 15-20dB, that's certainly an option. As you approach reference level though, you want a more flat response.

I haven't detail studied the fletcher-munson curves that much, but I have a feeling that also at ref you need a quite substantial lift. I can understant that one might want to level out to save cone excursion or neighbour irritation, but not from a reproduction point of view.
post #9261 of 10191
FOH,

I never stated you were wrong, nor did I join up in conversation to prove you wrong. The relative level of acoustic distortions due to rooms are of course due to your position relative to the speakers. We both agree smile.gif

Being 4 feet away from speakers is more than enough distance to inherit 'bad' acoustic distortions from what I've seen - regardless of a nearfield speaker or not. I'm not disagreeing that it might be worse at 10 or 20 feet, but I am saying that a typical minimum listening distance is a long enough distance that most acoustic distortions can impart their effects. Considering most of the work I've done is in studios where people sit one to two yards from their nearfield speakers, I can certainly say, the room's effects are still extensively problematic. It may be "worse" farther away, but that doesn't mean they are "better" closer to the speaker, only different in relative dB SPL.

Of course, I appreciate your response as well, and asking me to clarify my original statement was warranted as not to confuse others. Though now, I think we've both stated our points. We can continue over PM with some cool measurements to show each other our points in a more convincing manner. I'm not very articulate so data speaks better than words for me. smile.gif
post #9262 of 10191
Thanks, no prob
post #9263 of 10191
Has anyone discovers a fabric that can be had locally for covering OC 703? I want to pick some up tomorrow.
post #9264 of 10191
Quote:
Originally Posted by GIK Acoustics View Post

How thick are you building them? If 2-6" thick, OC703 would be 'better' - thicker than that, Safe'n'Sound would be 'better'. However, the differences are not immense and Safe'n'Sound is cheaper. If you can afford it - 6.5" (two batts of Roxul) thick traps of the Safe'n'Sound would produce some great results.

I would be building them 12"x12". And would I be better off putting up an acoustical panel on the very back wall of the theater behind the seats or a diffuser? along with bass traps in the corners.
post #9265 of 10191
Quote:
Originally Posted by jbrown15 View Post

I would be building them 12"x12". And would I be better off putting up an acoustical panel on the very back wall of the theater behind the seats or a diffuser? along with bass traps in the corners.

The 12x12 corner ones will work well with Safe'n'Sound, though I would recommend doing 16" square if its possible. Roxul makes 16" wide batts so this might be an easy construction.

Also, it would really depend. Diffusion can really give a great sound to a room, but if your bass is out of control it is more important to get that controlled IMO. There's a few options you could do:

Build the corner bass traps and see how your bass response sounds. If all is well and you want to do diffusion, then go for it.
-OR-
Pick one and go with it
-OR-
Build diffusers with bass traps behind (or you can consider it bass traps with diffusion on the front)

Another option is to do something like our Scatter Plate (http://gikacoustics.com/product/gik-acoustics-scatter-plate/) to get high frequency scattering, coupled with absorption.
post #9266 of 10191
I received some fabric samples from GOM today. I Like the Anchorage Mulberry but I have read some post that say it is OK for panels and some say it is not. In my space I will have 2" material on the side walls and 4" in the rear. Will the Anchorage be OK in this application or will it significantly reduce the effectiveness of my treatments? The speakers will be in the columns and not covered by the Anchorage.

How about the false wall? I will have bass traps and 2" material in the front behind an AT screen. Is Anchorage OK here?

I have heard of people using triple velvet. Is this AT? Is this better or worse than FR701?
post #9267 of 10191


I am going to try some diffusion in my small theater room. I've already got bass traps on all the corners and I have 3 subs. Low end is awesome.

The room is 10 feet high, 15 feet long and 8.5 feet wide. Seating position is 7 feet from back wall.

The blue sofa is the sweet spot so I am thinking diffusion on the back wall and possibly on the side walls.

I have designs for 3 two foot n11 panels, or one 6 ft n31 panel for the back wall. I will be making panels out of gator board and stuffing back cavities with OC703.

I was going to buy commercial panels but I have access to an excellent local carpenter who needs the work.

The N11 panels would be 6" deep and the n31 would be 9" deep. I've read conflicting information about whether its better to go with one panel or with repeating panels.

So question 1 is what's best, 1 panel or 3 panels? The design of the n31 allows for deeper wells and better performance?

Question 2 is would it benefit to put diffusion on the back side walls and door?

And last question is the design I have is for 32" tall panels. The thinking is since a lot of sound would be caught by the sofa, the 32" panel height would give a thick enough horizontal plain of diffusion. say 1 foot below couch top and 20" above. Thoughts?




Edited by HaroldKumar - 12/18/12 at 9:41pm
post #9268 of 10191
With front speakers that close to the side walls, I'd suggest absorption/reflex prevention rather than diffusion. "Gills" aimed towards speakers stuffed with insulation would be my tip.

Here's an example of it:
post #9269 of 10191
Quote:
Originally Posted by colleycol View Post

Has anyone discovers a fabric that can be had locally for covering OC 703? I want to pick some up tomorrow.


Burlap, at any fabric store. Its flammable though so use at own discretion.
post #9270 of 10191
Quote:
Originally Posted by Nightlord View Post

With front speakers that close to the side walls, I'd suggest absorption/reflex prevention rather than diffusion. "Gills" aimed towards speakers stuffed with insulation would be my tip.
Here's an example of it:

Those gills are a good idea, I can see how that will keep the sound waves (rocks) from skipping off the water. I have experimented with different first reflection treatment, but have not thought of gills, I will try that!

But with this specificproject, I am talking about diffusion placed *behind* the seating position, primarily I've seen QRDs used on the back wall, and sometimes on the sides walls behind the first reflection points.
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