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MAS...


Coytee

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or anyone that might have a thought/fact/opinion...

In the world of diffusers & absorbers, most people are mounting them ONTO the walls I presume? (meaning on top of something like drywall in typical home)

My basement is in open studs right now and the thought hit me...

Could I ...how to word this clearly... Prior to installing drywall, could I take some spots that might seem like obvious places to put some absorbers and plan on NOT putting drywall in that specific location.(or will that NOT be obvious until drywall is up?)

Meaning... if an absorber went "here" (as I point to a 2x3' section of the wall in my office) and I attached a 2x3 aborber there... would/could I not get BETTER absorbtion if I removed the drywall behind it and allowed the insulation inside the walls to help aid to the panel on top?

Now, before you think I've got holes all over my walls with insulation showing, that's not my thought.

My thought would be to mount the absorber OVER the hole in the wall so you'd actually have say, a 4" thick absorber mounted on top of 3 1/2" of insulation that is inside the wall, giving you 7 1/2" inches of absorbtion, yet only 4" intrusion into the room. The absorber would then cover the otherwise unsightly pink insulation underneith.

So, I guess I'm trying to ask... is there some way you can use some of the materials already inside the walls to better enhance any room issues by selectively (and hopefully decoratively) allowing the sound to pass INTO the walls instead of bouncing off them?

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Richard,

Generally speaking, what you are suggesting is possible.

Considerations
would include being aware that any lack of sealing, mass, and air space
will result
in a potential increase in the flanking paths increasing sound
transmission through the walls and a potential decrease in thermal
efficiency. Additionally, any covering of loose fill insulation other
than the material of the absorber itself will need to be evaluated for
its sonic transparency and reflective characteristics.

That
aside, you could potentially use the insulation in the wall to augment
absorption. The impedance of the insulation would sum with any
additional absorption.

In general, such applications would be
most effective used in conjunction with bass traps that will benefit
greatest from the added mass and depth. Such wall space could also be
effectively used for Helmholtz resonators as well.

Additionally, most mid-range absorbers are typically relatively thin materials averaging ~2 inches and may not benefit as much from such a treatment,

If you have a specific situation, PM me and I will be glad to attempt to lend a hand with any advice...

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  • 2 weeks later...

I would offer caution about this idea.

Eventually everything in life changes. Someday you may want to change the location of things in your room and discover that the holes need to be in a different place on the walls, then what?

Also, until the room is finished you are really only guessing as to exactly where you need the room treatments. What if you guess wrong? It will only be after the room is finished that you can correctly determine where and what treatments you need.

The holes you are referring to are going to be fixed and not flexible unless later, if things change, you repair the holes and make new ones. Just something to consider.

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Hey Roc...

I think that's an excellent point. Meaning, if I want to do it ONCE, then install the drywall, figure out where my reflection points are and (perhaps) deal with some cuts in the drywall. Sure makes more sense than as you said, THINKING I know where they might be, make holes...decide I'm wrong (figure THEM odds!! [:o]) FIX said holes and make more of them...

I can see the wife now...arms folded... foot tapping... "that look" on her face as I sheepishly try to patch said holes and then THINK I'm going to put more into "her" walls??

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Unfortunately as I have traveled through life, most everything that I do, I wind up doing twice or sometimes three or more times before I get it right. And this occurs eventhough I try to always measure twice and cut once.

That plan could wind up with a lot of pictures covering a lot of holes.

Lots of holes are good for Swiss Cheese but not for listening rooms.

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We still must stop and examine and understand the roles of the walls and treatment. If we fail to distinguish and understand the issues of sound transmission between spaces, and the treatment of sound within a space, we beg disaster.

Any consideration of incorporating absorption or diffusion into the walls begs a potential blurring of this distinction, and the integrity of the separate functions.

Again, generally speaking, mid-frequency absorption gains little from the added mass/thickness of the absorption. If the 1/2 inch of drywall and the say, 2" of absorptive material is felt to be an overwhelming impediment, this could certainly be eliminated. Fortunately, drywall is an extremely easy material to work with, both from the perspective of economy and labor.

If this were to be a room whose use could vary over time, it would be prudent and most reasonable to use simple panel based absorptive and diffusive treatments. This approach is further recommended by the relative lack of advantage to built in treatment for these issues.

A more advantageous use of the space would be from the perspective of corner bass traps and panels, as well as in the implementation of cavity based Helmholtz resonators. And as the room modes for which these would be an effective treatment are determined by room geometry, room orientation would have little effect upon them.

Again, the caveat being that sound transmission through the walls would tend to increase and the thermal efficiency would tend to decrease, rendering this approach less desirable for exterior walls and near spaces where sound transmission will be an issue.

As with most things in life, planning would be an important consideration.

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If it matters, this room has a bathroom/utility room on one side, garage on other side and the other two sides are block walls to outdoors

So, no other room will really be terribly affected by this space. Kitchen is above but I can live with that :)

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Unfortunately as I have traveled through life, most everything that I do, I wind up doing twice or sometimes three or more times before I get it right.

How many times you been married?

That's cute.

One time.

Coming up on 40 years in Novemebr.

The only thing in life that I got right the first time.

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Coytee now I do this, kinda like a skrim in the front or backs! What I did with 12" of insulation..all around the speakers... it totally made the fronts and backs reflections dead... but the space behind them was 3/4" drywall.. Of course..

The results were dramatic and wonderful..

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When the Ht stage curtains are pulled back to the side walls, it also made for a great deflection too with heavy red curtains... That might also help as another suggestion to make it look great and sound great too?

I had so many people at my house for the Klipsch Weekend, I am not sure if you made it by or not Coytee?

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Instead of putting drywall up and then cutting into it, can you make the acoustical treatment phase part of the building phase? By that I mean that you put speakers into the room before you mount the drywall. Put the drywall up only in areas that you know are going to need it, but leave 3-4 panels missing where you think the holes should go. Crank up the tunes and then find yourself a board to temporarily mount where the drywall would go and note the changes in sound. Heck, you could even measure the changes to see what works best.

Mark tells me this has been done, but I would try to take an approach of using the holes in the wall as an avenue for sound to travel into adjacent rooms...and then putting another hole elsewhere in your room to allow the sound in the adjacent rooms to come back into the main listening room. The idea here is that you force the sound to travel a further distance in hopes of improving your reverberant field. Basically, you want the sound energy to stay in your room, but you only want it to be there about 20ms after the initial direct sound. So basically, you want to get rid of the first 20ms of reflections, but somehow have them return after 20ms. The only way to achieve this is by forcing the reflections to travel a further distance. This is basically what diffusion does...it redirects the sound around the room so that it travels a further distance inside the room before arriving at the listening position. Absorption just eats up all the sound - which means there is no more sound left to add to the revererant field (and this is why overly absorbed rooms sound dead).

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Instead of putting drywall up and then cutting into it, can you make the acoustical treatment phase part of the building phase? By that I mean that you put speakers into the room before you mount the drywall. Put the drywall up only in areas that you know are going to need it, but leave 3-4 panels missing where you think the holes should go. Crank up the tunes and then find yourself a board to temporarily mount where the drywall would go and note the changes in sound. Heck, you could even measure the changes to see what works best.

Mark tells me this has been done, but I would try to take an approach of using the holes in the wall as an avenue for sound to travel into adjacent rooms...and then putting another hole elsewhere in your room to allow the sound in the adjacent rooms to come back into the main listening room. The idea here is that you force the sound to travel a further distance in hopes of improving your reverberant field. Basically, you want the sound energy to stay in your room, but you only want it to be there about 20ms after the initial direct sound. So basically, you want to get rid of the first 20ms of reflections, but somehow have them return after 20ms. The only way to achieve this is by forcing the reflections to travel a further distance. This is basically what diffusion does...it redirects the sound around the room so that it travels a further distance inside the room before arriving at the listening position. Absorption just eats up all the sound - which means there is no more sound left to add to the reverberant field (and this is why overly absorbed rooms sound dead).

Mike, a technique to do this is to use a phase grating in place of suspended ceiling tiles and or doorways into adjacent rooms such as he bathroom or utility room (assuming adequate noise levels (the lack thereof) in the rooms). Ths could also be done at the first reflection points as well IF such flexibility is possible (which is rarely the case!) This technique pioneered by Russ Berger and the basis behind is Phase Coupler product is that it allows signals at a particular incidence angle (near 90 degrees) to enter the space and bounce around and to then reenter the space only when they hit the grating at a near 90 degree incident angle, thus adding to longer diffuse tail to the sound field creating the sense of a much larger space.

A wonderfully elegant technique.

Also, if you have a renovator's supply nearby or a lot that sources used/recovered building materials or somewhere where you can get their damaged material cheap, you can skin the interior with the cheapest paneling (ie 1/8 inch luan) you can find with a very simple tacking (as the goal is not to create lots of extra labor) and then shoot the room. Various methods are available if one is creative and thinks ahead. Besides, many of the supply houses will almost give you the material as they will normally toss it.

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I think I understand the way the"space couplers" work to make the room

sound much bigger and more airy. But...I have a dumb

question. Why can't this effect be created just as convincingly

through some kind of DSP?? I suspect it has something to do with

it being very hard to fool the ear/brain combo? These types of

effects have been available on most receivers for some time now...I

guess if it was working well, we would all be using them...

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I believe sfogg mentioned that he has a Lexicon unit that does precisely that. It goes a step further too by introducing mics into the room so that the sounds you make (breathing, walking, talking, etc...) also sound like they're part of the larger acoustical space. So basically the approach is to make the room as anechoic as possible and then rely on the DSP to provide all the acoustical cues.

I believe the main reason active approaches are generally considered is because they are significantly more expensive.

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