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Discussion Starter · #1 ·
This evening I was reading through some of my archived information on HT construction and came across a multi-part article from Audio/Video interiors from summer 2000. The author is Russ Herschelmann, also published monthly in SGHT and Project Designer for the "Ultimate Home Theater Experience" at Epcot, etc., etc..


Regarding construction of walls and ceilings, Mr. Herscelmann states, "If the wall surface inside your theater is too rigid, the sound in the room will be problematic-boomy in spots and wimpy in others. Walls made out of multiple layers of sheetrock are much too stiff. Use one layer of standard 1/2-inch gypsum board...; Soft walls inside your theater are good, but you need stronger, stiffer stuff on the other side of the wall, outside the theater. Two layers of gypsum board do a great job of stopping outside noises from getting inside your theater, and vice versa. For the two layers, use different thicknesses, such as 5/8-inch and 1/2-inch." and also, "Like the interior walls, ceilings should be soft too, so make sure to use a single layer of 1/2-inch sheetrock - no more!"


He also does not recommend a slab floor, but instead says to construct a "completely sealed" wooden platform which will act like a drum and vibrate when pressurized by the bass in the room.


I don't mean to open a hornet's nest here, but this certainly flies in the face of much of what is posted on this site. Anyone have any thoughts?
 

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The problem is that with rigid walls you can "fix" the modes that are problematic. You can't fix your wall structure once it is contructed without major efforts.


After struggling with this when I was in my construction phase I chose the safer route and love the results. I agree with Dennis Erskine on this one. You can use known methods that are much cheaper AFTER your room structure is done.


There is just too many varibles with "flexible" walls. Of course Russ does recommend 3 subs in all his installs :)


Greg
 

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Quote:
" As luck would have it, conventional home construction, gypsum board on 2"x4" studs, is an effective low frequency absorber - play some loud music and feel the walls. Double glazed windows are quite similar in their absorption properties, so we are off to a good start. The worst possible rooms are those built in basements with concrete floor and walls. Such rooms need to have false walls built inside them. To improve on normal construction, I suggest two layers of gypsum board on some (but not necessary all) surfaces, possibly with a layer of 1/2" "sound board" between (glue the three layers together using nails or screws to hold will the adhesive sets.)"


--- Dr. Floyd Toole

Vice President Acoustic Engineering

Harmon International


Dr. Toole is noted for his research on the acoustics and psychoacoustics of sound reproduction, conducted during his 25 year tenure at Canada's National Research Council.
There...now a third opinion. I suppose throwing fuel on the fire is not a good idea in Colorado at the moment. :)


Subs: RH wants three. Toole will use one or two. Holman is typically uses one or two. I believe Mr. Subwoofer (Tom Nousaine) is in the one or two camp. I'm in the one camp (using two different size woofers crossed over in their optimal performace range is really my preference.) Toole has also retorically stated "why are we putting all this acoustic power into rooms just to absorb it at the boundaries later?" This statement however was not in the context of subwoofers but rather in a discussion in favor of disperson controlled speakers.


Isn't life easy when everyone is in such wild agreement. :D
 

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Discussion Starter · #4 ·
Dennis,


The quote from Dr. Toole seems to suggest that screws are used to hold the layers together only until the adhesive has cured, does one then remove all mechanical fasteners? This would certainly seem to provide more effective isolation.
 

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I don't believe there was any suggestion one go back and remove the mechanical fasteners. Further, a good adhesive would not be mechically decoupling the wall from the framing. Use of staggered framing would be the better plan. Glue is also necessary since it will prevent the drywall from creating rattles between layers and the studs.
 

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Discussion Starter · #6 ·
My mistake, I was evidently reading too much into the last paranthetical sentence; "glue the three layers together using nails or screws to hold WHILE the adhesive sets" (emphasis added).
 

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I don't think your room would be up to code if you were to go through and start removing screws. Could you imagine the inspectors face when you tell him there are no screws, just glue?
 

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It's amazing how many different camps there are when it comes to home theater and acoustics. Everyone can argue, and even pull out complex equations to reinforce their views. There are times when I'll pull back from answering a question, just because I don't feel like getting beaten up on my response then having to defend my position. I remember one person questioning one of my recommendations in a forum, and I ended up spending a week trying to find the text to support my words. I've seen Dennis point this out many times, and I agree wholeheartedly, that a lot of the information that people have is based on two-channel audio, and are not specific to "small" room multichannel residential construction which is the primary focus of what we discuss in this forum. Most acoustic principles will cross over to the small residential room, but experience is still an important factor. I know my company has altered design after the fact just to improve on something that looked good in theory, but in practical application couldn't keep up. We adjust our designs based on our experience whether or not it conflicts with someone else's theory. Different people will have different ideas, a lot of it is based on where or how they're educated, and what their background is.


And by the way, Dennis is wrong about the one sub thing ;), or is that we have a different way of accomplishing a goal?





Boy, did I ramble and not say anything useful or what :)
 

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I was told by a person whom I trust greatly on such matters that you want the walls to absorb as much as possible. When you clap in a room, all you should hear is the clap, not the echo. He recommended the best way to build a room is to put 3/4" medium density fiberboard on each side of the 2x4 studs and fill the wall with sand. He built a studio in the UK for about 1000 Pounds (I can't find the $ for pounds). Another company who spent 100,000 came and heard theirs, tore theirs apart and built it like his. It was that good, according to him. After seeing his house and audio system, I am certain that he is not the hard up for money type, so there must be something to this.


I know that sand is used to absorb vibrations in many high end component racks, tables, stands and also in platforms and risers. I also know that almost all speakers are built out of medium density fiberboard. Shouldn't it then be a logical step that these same things we do for the risers work for the walls?


My current plan for my construction is to do this very thing, assuming that my concrete floor can support the weight of the sand. I will have to re-engineer the ceiling to support a large load of sand - only 1 inch thick, but still a lot of weight.


A good idea, or am I on crack? (I have a poll running, but I would like another opinion)


Mike Poindexter
 

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Unless you feel like experimenting it is a good idea to duplicate successful methods used by others.


Most of the members of this forum prefer using two layers of gypsum board for walls and ceilings. They usually coat the walls and ceilings with materials that absorb sound to cut down on reflections.


However the question of if you want a completely dead room or not is a matter of personal preference. If you have ever been in a chamber designed to limit sound reflections, it sounds very odd. There is no perceptible echo which feels unnatural. I think most people expect a small amount of echo. So I don't recommend going overboard and striving for a totally dead room. On the other extreme, if the walls and ceiling are hard surfaces like gypsum board or wood you may have too much echo, which is also annoying.


While the weight of sand will help minimize sound transmission to other rooms, I don't recommend putting it in the ceiling for two reasons:

(1) the great weight requires very sturdy walls and joists

(2) the sand may tend to fall down into the walls and room as it is vibrated by the sound below.


If you are really intent on putting a large mass between the ceiling and floor above, I think you would be better to use concrete ceiling and walls for the home theater room. That would provide structural strength as well as a large mass which would help limit sound transmission. Using concrete probably requires professional builders and an architect or structural engineer.
 

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As I understand it MDF will NOT pass code in the US as a building material.


If you are going this route better eat your wheaties! A 96x54 MDF sheet is O N E H E A V Y mofo. My goodness I can't imagine using MDF. Cuting it? ugh, and how do you hide the seems? Fabric?


I am tired just thinking about it.


Greg
 

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Correct me if I am wrong, but aren't the sheets 96x48? I don't know how I will hide the seams, unless I can use some kind of spackle over them. Other than that, I can attempt to have the visible walls (inside the room) have their seams at one height and run a chair rail along it. That would cover the horizontal seams. For the vertical seams, I could run a wooden beam from floor to top, similar to the pillars others run around the perimeter. Of course, sand wouldn't be able to leak out of those seams, as they are going to happen on a 2x4. The horizontal ones would just have to be taped/glued/spackled or something and that should take care of them.


Cutting the boards isn't too hard, is it? Sure, you can't use a knife, but you can use a handy little skillsaw. I suppose it would be a real bear to put the sheets up on the ceiling, though. I was thinking that there I would use a metal bracket to join the two pieces and cover them with crown moulding.


Concrete would be highly reflective, whereas MDF/sand will be highly absorptive. And sand from the ceiling won't fall down into the walls if the walls are already 100% full of sand. To prevent the sand from getting through the seams in the particle board on the ceiling, I was told to first put up a sheet of plastic. Thick plastic is easy is get, cheap and simple to install. I suppose I should put it up over the 2x4 frame prior to putting up the fiberboard.


Now, fiberboard will not pass code, but wafer board will?


As for duplicating what has been done, this has been done by another person who is not on this forum. Perhaps I should have another discussion with him and get some more info.


Mike
 

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>> When you clap in a room, all you should hear is the clap, not the echo. He recommended the best way to build a room is to put 3/4" medium density fiberboard on each side of the 2x4 studs and fill the wall with sand.



That's doesn't get rid of echoes in the room.



>> He built a studio in the UK for about 1000 Pounds


Filling the walls with sand, I'm sure it weighed much more than 1000 pounds (just kidding). Didn't I mention above about many people's experience being in the 2-channel (studio) realm?




dkramer3 - :)
 

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I don't know how much his studio used, but my calculations show about 15,000 pounds of sand. That number can change, according to the type of sand I am going to be using, of course.


I suppose that brings up another point. What kind of sand do people use in their risers and such? Coarse? Fine? I would guess coarse, but I don't know for certain yet...


I realize that 2 channel systems have different requirements than surround, but I listen to a God-awful amount of music. I would be amazed if my stereo wasn't on a minimum of 4 hours a day. Don't buy a used amp from me, man. I will put some serious hours on it under a large load.


I guess the next question is how much of a benefit is it to 2 channel audio and how much of a detriment is it to 5.1 or 7.1 audio using this system vs. the staggered stud/sheetrock, etc. system.


For a reference point, I don't even use home theater speakers, really, at the moment. My surrounds are 5'2" tall full range towers. At 140 lbs. a piece, I don't think mounting them anywhere is a possibility. My mains are old Infinity IRS Betas and if I can ever find them for sale, I will upgrade them to the full IRS V, or the Genesis 1.1 (if I can afford them, which I currently cannot). Clearly, I would like to get the maximum musical performance out of these speakers as possible.


Mike
 

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>>Concrete would be highly reflective, whereas MDF/sand will be highly absorptive.


True for a .45 caliber bullet, not accurate for sound.
 

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Well, could my theater at least double as a panic room?


So, John, are you saying that the sand filled MDF walls will not be accurate for sound?


Mike
 

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I'm strickly a .50 cal McPherson guy anyway.


There are a few points I'd like to throw on the table here. First, the acoustic requirements of a sound studio, mix room and/or sound stage are tremendously different than those of a playback environment (multi-channel or stereo).


Second, you have two issues in a playback room you must contend with. One is sound isolation ... the prevention of exterior sounds from raising the noise floor of your room and the prevention of really annoying your family when you're listening to something at obnoxious levels. The other are the acoustic properties within the room, including RT60. Sand in the walls may do well for sound isolation but won't do twit for the long, long list of in room acoustic issues you must resolve. Lastly, the in room acoustic requirements for two channel playback are considerably different than the requirements for multi-channel (more than two) play back.


You can go through all the structural considerations for sand filled walls and ceilings and end up with an absolutely horribly sounding room.
 

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>>So, John, are you saying that the sand filled MDF walls will not be accurate for sound?


Sorry for the confusion, I meant your statement was not accurate. You said that MDF/sand was highly absorptive, and that's not an accurate statement (again, unless we're talking about ballistics).


.50cal? Goodness!
 

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These walls are absorbing only at some frequencies. Not at the high and mid range ... the sound has to get through that MDF before the sand can do anything. If you're standing outside the room, you might say it is absorptive at all frequencies. One of those "it depends upon your vantage point" as covered by the Special Theory of Relativity.
 
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