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HT/dedicated listening room sizes


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On 3/10/2004 12:23:45 AM formica wrote:

Even optimising your dimensions before building will help reduce the need for treatment... but real life performance rarely matches design predictions. Wall rigidity plays a role in the defining the apparent acoustic dimension of the room, but it is rarely factored in. (pliable walls will make the room appear acoustically larger versus it’s actual measured dimensions)

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Indeed - which is why thin panel walls will perform better than 1/2" sheetrock, for example. Back them with plenty of the soft stuff, and you'll have a huge sounding room.

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Indeed - which is why thin panel walls will perform better than 1/2" sheetrock, for example. Back them with plenty of the soft stuff, and you'll have a huge sounding room.

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This sounds contradictory to what the Ethan Winer and Iso-Walls sites say? Or not? I was of the mind that the stiffer the walls, the better?

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On 3/10/2004 9:47:37 AM Champagne taste beer budget wrote:

This sounds contradictory to what the Ethan Winer and Iso-Walls sites say? Or not? I was of the mind that the stiffer the walls, the better?

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I'm not 100% in agreement with Ethan about that. A thin wall will pass more audio, where a more rigid wall will reflect it. To create a larger-sounding space, one needs to pass as much signal through the wall as possible, then absorb it on the other side.

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On 3/9/2004 8:38:17 PM Griffinator wrote:

That's what bass traps are for. Bass traps make up lack of width via depth and airspace.

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Wrong Griff. Bass traps do not make up for lack of width. And they will not make the room seem 'bigger'. They primarily affect the frequency response. And not as low as most people seem to think.

Frequency response is not how we determine a room's size. That domain belongs to the specular distribution of the sound waves as it relates to direct sound verses the first early reflections and reverberation time/decay. Even here, it's primarily the middle and upper frequencies that our ears/brain uses to interprete the sound.

Scattering some random placement of hanging rigid fiberglass panels (or other absorption material) across the back walls, ceiling or whatever, is not going to create much of a bass trap. They simply don't go down low enough. And its not where you would make the best use of it. In order to make efficient use of bass traps, the traps still have to be large, deep, and most importantly, placed where they can be put to their best use, which is in the vertical, then horizontal, corners of the room which is where most of the low frequencies tend to pile up.

Somehow, recently this idea of 'virtual' room size has come into play as if the sound can 'see' the walls beyond the walls. It's simply an excuse for someone's ego to justify in their mind that their room is somehow larger than it really is and that they can benefit from it. It's BS. And its not what you want anyway. In fact, its something to be avoided. Auditoriums & recording studios alike are often built as a 'room inside a room'. But this is done to isolate the interior structure from noise transmission, structural and airborne, not to make it seem acoustically larger.

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good advice so far...

artto-my hero.you really did it right.

i'll throw my .02 in.

i guess i lucked out w/my ht room. it needed remodeling when we bought the house. it used to be a rear porch,so the interior walls are brick on the sides,with paneling behind the speakers/equipment/screen which are on a 3ft.deep 'stage'.it is 12' wide by 23' deep(less the 3ft.stage=20ft.)there is a 6'W x 10'D area to the left(opening in the middle of the left wall). the former homeowner installed fiberglas ceiling tiles(covered by thin plastic)in a 7ft. suspended ceiling,and the rear wall is covered with the same tiles.they are about 2ft.by 4ft.in the ceiling and 4 x 4 on the back wall. i have some 'movie themed' carpet on the floor.a large double door opens on the right to the house,just behind the seating area. i sit 13ft.back from my screen.

after playing w/toe-in/out on my KLF-30's i achieved a SOLID center to my soundstage, WITH sounds coming from BEYOND the left and right walls that they are next to.my ksp-s6's are about 2ft.above my head and about 3ft.behind my couch,and about 2ft.in front of the rear wall.this places the front horn/woofer pointing at my sweet spot,with the rear array reflecting off the rear wall. my RSW-15 is in the back right corner.

IT SOUNDS GREAT!!

the only thing i may do is try to absorb some first reflections off the brick,but i'm not in a hurry as it really works well for me.

hope this helps.

avman.

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On 3/10/2004 10:20:41 AM artto wrote:

Wrong Griff. Bass traps do not make up for lack of width. And they will not make the room seem 'bigger'. They primarily affect the frequency response. And not as low as most people seem to think.

Frequency response is not how we determine a room's size. That domain belongs to the specular distribution of the sound waves as it relates to direct sound verses the first early reflections and reverberation time/decay. Even here, it's primarily the middle and upper frequencies that our ears/brain uses to interprete the sound.

Scattering some random placement of hanging rigid fiberglass panels (or other absorption material) across the back walls, ceiling or whatever, is not going to create much of a bass trap. They simply don't go down low enough. And its not where you would make the best use of it. In order to make efficient use of bass traps, the traps still have to be large, deep, and most importantly, placed where they can be put to their best use, which is in the vertical, then horizontal, corners of the room which is where most of the low frequencies tend to pile up.

Somehow, recently this idea of 'virtual' room size has come into play as if the sound can 'see' the walls beyond the walls. It's simply an excuse for someone's ego to justify in their mind that their room is somehow larger than it really is and that they can benefit from it. It's BS. And its not what you want anyway. In fact, its something to be avoided. Auditoriums & recording studios alike are often built as a 'room inside a room'. But this is done to isolate the interior structure from noise transmission, structural and airborne, not to make it seem acoustically larger.

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OK....

You're kinda misunderstanding me again.

I didn't say Bass traps would make the room sound bigger. All they'll do is break up the standing waves that live in the corners of your room.

And there are ways to make the room "sound" bigger. The ceiling cloud I laid out is one of them.

As far as Ethan's position on the false walls - he and I just got done chatting about this directly - here's how the conversation went:

Ethan: My logical mind tells me that, to reduce reflections in a room (and create a larger sense of space), using false walls with thinner wallboard material (1/8" plyboard paneling, for example), then packing absorption behind them would be more effective than using rigid (1/2" sheetrock, for example) wall materials.

What's wrong with this deduction?

Scott,

Nothing is wrong - you have it exactly right. For the best bass response in a room you'd like walls that pass or absorb the waves that strike them, rather than reflect.

--Ethan

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On 3/10/2004 10:20:41 AM artto wrote:

Somehow, recently this idea of 'virtual' room size has come into play as if the sound can 'see' the walls beyond the walls. It's simply an excuse for someone's ego to justify in their mind that their room is somehow larger than it really is and that they can benefit from it. It's BS. And its not what you want anyway. In fact, its something to be avoided. Auditoriums & recording studios alike are often built as a 'room inside a room'. But this is done to isolate the interior structure from noise transmission, structural and airborne, not to make it seem acoustically larger.

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I would have to disagree... although I'm not saying that the room behaves like a significantly larger one, it just won't act as predicted. This "virtual" room can actually be measured in certain circumstances, such as when there are 3 rigid walls and a single pliable one. In this case the placement of the low frequency nodes in the room will shift over toward the weak wall, as if it were further out. It makes optimizing the room on paper very difficult.

There are beneficial factors to weak walls that include their ability to absorb low frequency sounds and act somewhat like a bass trap (I'm talking about controlling sound within the room and not attenuation in adjacent rooms). Resilient furring can be quite effective when combined with an acoustically insulated wall. The bass will use it's energy to vibrate the sheeting, dissipating energy in the insulation, and reducing the reflected sound.

Yes, double stud walls are not a form of pliable wall, but are oriented towards isolating sound from other rooms. Sound studios usually use both these techniques, as well as several others.

Rob

PS: 1/2 gypsum on furring is pliable in my book, where-as 2 sheets of 5/8" is not... 2.gif

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I'm going to have to vehemently (& respectfully) disagree with the 'virtual' room & weak wall crap.

The main reason to have strong sturdy walls/floors/ceilings is so those surfaces DO NOT act as 'passive radiators', vibrating, and adding coloration to the sound. Its the wrong approach. And it does more potential harm than good.

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Just got of the phone with an OC rep in Minneapolis, very informed and friendly guy. He said the 703 would be $.82/sq ft in the 2", $1.70 for 4", both available for delivery today. At least I have a name and number for when the time comes to order some. He also brought up another idea, their "Hat Channel" product, used to offset the walls from the studs. Sounds like the product is fastened to the studs at 90 degrees, then the wall material is fastened to it instead of the studs, essentially isolating the wall from transfering sound. He thought that the same effect could be had by using furring strips as opposed to their special product. Any thoughts on this idea?

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Yes, thats basically what Rob mentioned.....resilient channel. Its used for sound isolation & boosts the STC rating of the wall. I didn't use it for the reasons mentioned in my previous post. Especially with Khorns. You need a solid wall, not one that's going to be vibrating to dissipate the sound energy hitting it. Its for a different purpose.....to reduce airborne sound transmission, not to improve internal room acoustics.

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Although I would prefer the sound to be completly comtained in the room, I realize that's not possible. I don't mind if some escapes to the rooms on the sides, but I'd like to prevent it from traveling through the ceiling as much as possible. Would the channels be a good idea for the ceiling? I expect to caulk every nook and cranny in an attempt to stop sound transfer outside of the room, but how does one seal the door? Seems I read something about that somewhere, I don't think it was on this board though.

At the moment, I am thinking of double walls and ceiling with insulation bats between the walls to prevent as much sound transfer as possible. Using 2x2's or sideways 2x4's to seperate the inner and outer walls. How much of an effect will the type material used for the OUTER wall have? Could I get by with cheap paneling of some sort to save money, or would I be better off using sheetrock for both walls?

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I never felt comfortable with the resilient channels, for this application. Too much sound pressure. Its primarily intended to reduce noise transmission between 2 rooms. For instance, it might be beneficial to use it on the shop/workroom walls if such a room is adjacent to the listening room. Or the utility room side. Etc.

Insulation bats stuffed tightly between the ceiling joists is a good idea. IMO you would be better off using a high density sound barrier material between behind the drywall like ProSpec Noise Barrier made by Auralex. Its denser (& heavier) than Lead (which is what used to be used for these applications). I just recently installed it under new tile kitchen floor which is above part of my room. Cant hear any walking up there anymore even though the new floor is a harder surface than the old one. There are limits of course.

Another thing that often gets overlooked is installing stringers (or more of them) (the cross bracing you see between the joists) to reinforce the ceiling/floor joists & walls.

Regarding the outer walls, it depends on how much sound isolation you need. If youre building a dedicated room, quietness can add a great deal of quality to the sound reproduction. And remember, as you treat the room acoustically and IT becomes more quiet, other outside noises may become exposed.

Its best to try and isolate all potential noise sources from the building and room structure. And I mean EVERYTHING. Water pipes, vents, electrical conduit, anything that is linked to other parts of the building services.

Stay away from 2x2. Its not strong enough. And dont turn the 2x4s sideways. Instead use either staggered 2x4 studs on a 2x6 plate. Or preferably, 2 completely separate 2x4 plates essentially making 2 walls.

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artto, you're really helping my plans, but you're also really hurting my wallet. 2.gif I'm going to end up sinking more into just building the room than a nice vintage set of Khorns would set me back!!

I know, I know, an investment in my future listening enjoyment.

I'm gonna end up going to the lumberyard every other friday and buying half a dozen 2x4's and 2 sheets of drywall, but at least that way I can work on it for 2 hours every other weekend for 6 months instead of dedicating a week of vacation to getting the construction done. I'd rather have it "right" from the get go than be sorry I didn't do it right later.

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This is why I suggested the drop-ceiling system.

Get off the joists completely by using a drop-ceiling attached to free-standing walls, and use 703 or 705 as your ceiling panels, and stack up a double layer of pink on top, giving you a net of 2" of rigid fiberglass plus 8" of soft glass which, coupled with the isolation from the actual floor joists, will cure your sound leakage through the ceiling problem.

Whether you buy into the thin-wall+absorption material concept or not, the ceiling plan I laid out will totally isolate your HT from the upstairs.

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champaign.....thats exactly the point. The room is arguably far more important than any of the gear you're going to put in it. As far as I'm concerned its not even an arguable point. And yes, I did spend more on the room than the equipment. I figure it if it weren't for my 'sweat equity', my room would probably have cost me $15K in 1984 dollars. And thats for construction inside of an existing building, what would normally be a very generous size 'family room'.

The problem with drop ceilings is they don't do much to stop (block) sound transmission. You still need MASS and an air tight surface. Drop type ceilings do not accomplish this.

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Artto - I gotta apologize to you.

Seems I was misunderstanding the isolation aspect a bit.

Had some further discussion with Ethan and a couple of other guys on his forum

1) The concept I laid to soundproof is sound except - you still need the rigid inside surface on the decoupled walls in order to acheive the isolation. Therefore, the drop-ceiling/paneled walls isn't going to work the way I expected it to, no matter how much insulation you pack behind it.

2) Therefore, you still need to do your sheetrock on these decoupled walls (but only on the inside, not the outside, then pack the space between these inside walls and the adjacent and overhead walls. There will be your maximum absorption across the entire frequency spectrum.

FWIW, had the isolation aspect not been so crucial, my previous plan would have been ideal, simply because the standing waves would have been defeated by the absorption materials behind the false walls and in the drop ceiling.

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Griff, correct..now youre beginning to understand the whole picture a little better. You really need isolation to yield the best room performance. There are 3 main acoustical aspects, and each of those have their own sub-categories of implementation.

Isolation, Absorption and Diffusion. Just doing one, or two & not the other will not yield the desired results.

I do have one correction though, possibly its just a grammatical error. The decoupled wall(s) need to be on the outside walls. If the situation were such that high sound pressure levels, especially at low frequencies, were not going to be produced in the room, say something like a classroom bordering an adjacent washroom or utility room, then decoupling the walls on the inside or both sides makes sense. But for our purposes, flexing, vibrating walls, floors & ceiling surfaces just adds coloration & distortion to the sound.

Isolation is a very important aspect of acoustics because it has an impact on signal to noise ratio of the room which affects the intelligibility or articulation of sound in the room, especially at lower sound levels. Theres really quite a bit more noise infiltration into our domestic environments, especially in urban/suburban areas, than most people realize. Not to mention noise sources within the home. HVAC, refrigerators, running water, etc.

There are only two ways to get residual low frequency sound energy out of a room. The first and most common is leakage. Unlike the downtown recording studio, deep bass leaks out of most home and apartment construction. Leakage paths can be direct transmissions through the walls, ceiling, floor, doors and windows. The heavier the surface, the less leaky it becomes. Other leakage paths are through openings such as under the door. Air, like water, especially under pressure as it is in a listening room will find its way thru any crack or opening.

Absorption is the second method by which acoustic energy is removed from a room. Downtown recording studios are heavy-walled and sealed airtight to keep unwanted sound out. This is called isolation. If sound is kept out, its also kept in. And thats were large diffusers (ideally at least ¼ of the wavelength of the lowest frequencies) and various forms of absorption come into play.

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On 3/12/2004 12:39:11 PM artto wrote:

I do have one correction though, possibly it’s just a grammatical error. The decoupled wall(s) need to be on the outside walls. If the situation were such that high sound pressure levels, especially at low frequencies, were not going to be produced in the room, say something like a classroom bordering an adjacent washroom or utility room, then decoupling the walls on the inside or both sides makes sense. But for our purposes, flexing, vibrating walls, floors & ceiling surfaces just adds coloration & distortion to the sound.

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Here's a picture of various wall implementations and their absorption factors (from Ethan's website)

walls.gif

If you sheetrock the inside portion of this iso-wall (and the inside portion of the adjacent room wall), you gain more net absorption (17dB net increase) than if you sheetrock both sides of both walls.

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ok, DON'T LAUGH!!! I don't have any fun/fancy art/drawing programs, so I made a stick drawing of what I believe a top view of the wall should look like. You're looking down at the studs/walls. Seperate footers for both sets of studs, with an air gap between each footer. Question is, if I'm trying to prevent transmission/vibration to the ceiling joists, what do you attach the tops of the studs to?

Also, if I am reading this right, a solid ceiling of drywall with a drop ceiling under it of the 700 series panels would work well? The panels would help absorb the low frequencies, and what did get through would be more isolated from the upstairs by the solid ceiling above it? Figure two layers of bat type insulation, one over the drop ceiling and another over the drywall stuck into the floor joists. Or skip the drop ceiling altogether, make a second hard ceiling, although I'm not sure how that would be mounted without having some fairly stiff connections to the joists, which I assume would just transfer the sound through themselves to the upstairs?

p.s. STOP laughing at my stick drawing!!

post-13504-1381925318165_thumb.jpg

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