Ceiling: drywall vs. panel

[formica]

a few room measurements would render this entire

debate moot, as then you would know what would be the optimal need....

But before any treatment is proposed, it sure would be nice to know

what aspects of the acoustical room response SHOULD be amended in order

to optimize the acoustics rather than simply running about suggesting

whatever treatments come to mind.

As an additional note, Damon's room isn't actually built yet (well,

it's in the middle of getting built) so it makes actual measurement

difficult. Room mode calculators is all he's got to go with for

the moment... but once the sheet rock is in, I don't doubt he'll

take some measurements before and after treatment.

Without sophisticated software, pre-construction predictions are... well.... generalized approximations.

ROb

[PrestonTom]

..... however I can only find measurements of its effectiveness down to 125hz (Ethan Winer's page) and I would like to know if its going to do any good at 41hz. This is going to be an ongoing project lasting at least a year I'm sure but initially I'm shooting for a reflection free zone at the primary listening position only and some bass traps in the front of the room.

Trying to tame the very low bass requires more heroic measures. First, as mentioned already, I would try and do some acoustic measures ahead of time to identify what the specific problems might be.

Typically it is bass ringing and room modes (an uneven freq response). Simply using absorption will probably not work (the wavelengths are simply too large); however, bass trapping may be effective. Again, measurements ahead of time are important, otherwise your treatment (which can be expensive) may not be on target.

Good luck,

-Tom

[mas]

As you have already made some decisions, I certainly don't want run around kicking anyone's dog...

But a few considerations. Especially as you mention the goal of a RFZ. Without a room plot, it sounds like you are attempting to absorb your way to this goal. The problem with this apporach is that too often the overall result is what plagued the very first generation of LEDE, whose goal was the same. It WAS dead!

If you want what amounts to a step by step implimentation of an LEDE room that employs a RFZ, please PM me. It also explains in depth exactly what, and more importantly, WHY they are doing the various steps. Additionally, it is one of the best 'all in one' tutorials providing insight into the role of time based measurements as they apply to a room. They do use some measurements, but the concepts can easily be employed for general use. Only the commercially available treatments have changed since it was printed.

Lacking the precise measurements, my suggestion is to use diffusion rather than absorption. For the low frequencies and standing waves please forget standard wall treatments! They lack sufficient mass to be effective. For LF, the way to go is via the use of traps. And if you have the means and the wherewithall to build the offset 'integrated' wall bass traps, it would still be easier to simply splay one long wall (front to back) by 1 foot(& ideally, both walls! And then combined with corner placement of the speakers, life becomes very easy). And if you did that you could even employ the cavity to make part of that wall into an effective bass trap/Helmholtz resonator(s).

And pardon me for focusing on the potential to use that ceiling space as a coupled space! Since Russ Berger has decided to make some of his private tricks available commercially through his sideline PartScience and distributed by Auralex, the commercial tools are available (for a price!!!!!! But still half the cost of RPG!) But with a router and several sheets of luan and a weekend, you would be set with both diffraction grating for a ceiling and for side wall treatments. And if you chose to 'stuff' the grating, you would have a terrific treatment for the back wall.

I apologize for rambling, as there are lots of effective paths and options, and I do enjoy debating the pros and cons of each. And this area is one discipline that even when it is incredibly frustrating, is still actually quite enjoyable!

I won't bore you further here, but if I can answer any questions, or if it will make you feel better to tell me how crazy I am (the line forms here...), please feel free to PM or call me.

Best of luck and have fun!

[colterphoto1]

I think one problem with drywall at evenly spaced stud intervals (16" or 24") is that you have a whole bunch of equally sized panels that will vibrate sympathetically at the same frequency. Think of the 14" x however many feet sections as invidual drum 'heads'.

A lot of people thing my Gallery room would sound very live and ringy, being that it is all hard surfaces, Brazilian Cherry (a very hard wood) on the floor, no drapes or carpeting. Yet clap your hands and there is barely the first distinct echo. None of the pingy fluttery echo that a drywall room would normally have. Why? Because my gallery is 2 sheets of 1/2 PLASTERboard that is very very dense. So it just kills the sound.

My idea in drywalling a basement room would be to put blocking between the stud spaces at very random heights, divide one section in two, the next in three, so on. This would make the drum 'heads' different sizes and perhaps break up some of the liveness from within the wall.

Any thoughts on a simple building technique such as this?

[IndyKlipschFan]

I would go for the drywall myself.. I stuffed with insulation a lot of it 12" thick up there... between the joists.. a sound barrier and then drywall. The results are very good. I think the "room within a room" idea I did.... where no side walls and no ceiling crossbeams touched the original frames of the house... helped me the most to keep the sound where it should stay.. Picky did a lot more than I did. I would listen to him very carefully, he appearantly really has a incredible room. And it shows too.

My 2 cents..

[DrWho]

Hey Mike, that's definetly an interesting idea. I think most of the resonations that occur are from the trapped hollow acoustics spaces between the studs - not so much the drywall itself vibrating like a drum head. I think the reason drywall sounds so pingy is because the material its made out of is extremely reflective over a narrow frequency and no so much at other frequencies. Your plaster walls have a much flatter reflection frequency response (loose way of thinking about it).

All that to say, I think you will notice bigger results by putting insulation between the studs. And wouldn't it be cheaper too?

[damonrpayne]

Yeah I think I've indicated before that all walls & ceiling are getting stuff with r-13 fiberglass.

[colterphoto1]

I would go for the drywall myself.. I stuffed with insulation a lot of it 12" thick up there... between the joists.. a sound barrier and then drywall. The results are very good. I think the "room within a room" idea I did.... where no side walls and no ceiling crossbeams touched the original frames of the house... helped me the most to keep the sound where it should stay.. Picky did a lot more than I did. I would listen to him very carefully, he appearantly really has a incredible room. And it shows too.

My 2 cents..

I wasn't aware that your framing met the 'isolated room within a room' design concept. It looks like standard finished basement framing to me. How is your framing isolated from the rest of the house???

M

[colterphoto1]

Hey Mike, that's definetly an interesting idea. I think most of the resonations that occur are from the trapped hollow acoustics spaces between the studs - not so much the drywall itself vibrating like a drum head. I think the reason drywall sounds so pingy is because the material its made out of is extremely reflective over a narrow frequency and no so much at other frequencies. Your plaster walls have a much flatter reflection frequency response (loose way of thinking about it).

All that to say, I think you will notice bigger results by putting insulation between the studs. And wouldn't it be cheaper too?

Doc,

I'm just talking about adding a simple 2x4 block of wood (formally known as fire-blocking), between wall studs at random intervals in addition to insulation, to keep the sizes of the resonant panels different. I think it would help, as would glueing and screwing the drywall.

Also using 5/8 fire-rated drywall is much stiffer because it contains fire-resistant fibres (just try to cut the stuff), so that would help also.

My plaster walls not only are 1" thick (2x 1/2") but have two fire blocks per stud section. Those are some super stiff walls- no wonder the Khorns sound so good!

M

[mas]

Actually, decoupling the drywall from the stud walls by using neoprene offsets and pliable adhesive is more effective as it prevents energy from being effectively coupled and transmitted to the stud wall frame and thus some energy is dissipated. This is also fundamental construction technique employed when utilizing double layers of drywall when sound transmission through the wall is a factor. Likewise the concept of a room within a room utilizes neoprene pucks to support and decouple the floor joists from the foundation floor, thus rendering the entire room 'floating' for the same purpose - to dissipate energy from being efficiently transfered. {But mid and high frequencies are not really an issue here.)

But I still think we are tending to mix problems and solutions. May I suggest clearly distinguishing between sound transmission issues through the wall to surrounding areas and reflective issues within the room - as the sources and solutions are not the same.

For sound transmission issues, tightly sealed (as in airtight) wall mass and loosely coupled components are the order of the day. While for internal room issues, wall mass has little effect upon the reflective characterisitics of the mid and high frequencies. And the low frequencies are effected both by wall mass and the use of various types of diaphragmatic resonant 'traps'.

[PrestonTom]

" ..........

But I still think we are tending to mix problems and solutions. May I suggest clearly distinguishing between sound transmission issues through the wall to surrounding areas and reflective issues within the room - as the sources and solutions are not the same.

......"

I think MAS has hit the nail on the head. These require very different solutions and trying to do both can be very expensive.

-Tom