lgl`s soundproof HT

[Ted White]

This can be calculated, but it's along the lines of a foor or two of airspace and 6-7 sheets of drywall on each side. Shocking, really

[patchesj]

Ted White wrote:

This can be calculated, but it's along the lines of a foor or two of airspace and 6-7 sheets of drywall on each side. Shocking, really

Interesting. Would using MDF, concrete board, or some other high density material be of benefit? I would think that creating a sandwich of materials with varying densities would broaden the absorption properties of the wall.

[Ted White]

Not really. The resonance of the system is defined by the whole system, not the parts. Mass is mass. If well damped, there's no advantage to using dissimilar densities of mass in a leaf.

The LF resonance point calculation looks at:

Decoupled leaves?

Total Mass added

Absorption in cavity?

Air cavity depth (which is related to absorption).

[patchesj]

I wonder how much depth lgl has at the rear wall of his room? In my case the rear of the room backs up to a storage area. Creating a high mass floating wall (2x4s with single drywall on both sides filled with some high density material like sand OR 3-4 layers of 1" MDF, not tied to the side walls or ceiling??) in front of a 2' filled cavity (fiberglass or cotton?), with the final isolated double drywall behind that would create this low frequency absorber?

[Ted White]

Absorber is a term generally used to describe a treatment of sound remaining in the room. The sound we're describing has sufficient energy to enter (and leave) the room.

The object is to build partitions with as low of a resonance point as is practical.

Decouple the framing with a double stud wall.

Have as large a gap as possible between the two frames

Add absorption with standard R13 iberglass.

Add mass, generally double 5/8" drywall

These are the factors that lower that resonance point. Keep in mind that we're only able to significantly affect frequencies at 1.5X the resonance point and up. So if a wall had a resonance point of 60Hz, we're going to start to see a drop in performance at 90Hz and below.

Also your earlier question about a 45 Hz wall would be more along the lines of a 1' air cavity and 3-4 sheets of drywall. That's a guesstimate this morning.

[patchesj]

Now that I think about it, trying to absorb frequencies that low would be very difficult. My original concept was to allow a mass in the room to be "moved" by the pressure waves and try to dampen/translate the energy (a tuned mass damper??). And this is why I'm not a professional...

[Ted White]

I admire your thoughts and questions patchesj

[lglura]

Hello again. Thanks for all the feedback in this thread,
have finally realized that it is not possible to build the room completely soundproof.
Thanks to all the feedback I now know how to build the room.
I will build it as solid as it is possible within the limited space I have, walls and ceiling get 2x 1/2 " drywall and 1x 1/2" MDF and green glue between the layers. I come back with pictures to describe the build

[patchesj]

Looking forward to the pictures!! Good luck and keep us informed. Out of curiosity (maybe I missed it in the thread), why 1/2" drywall, why 1 layer of MDF, and what will the sandwich look like (dry W, dry W, MDF? or MDF in the middle?).

Thanks

[lglura]

patchesj wrote:

Looking forward to the pictures!! Good luck and keep us informed. Out of curiosity (maybe I missed it in the thread), why 1/2" drywall, why 1 layer of MDF, and what will the sandwich look like (dry W, dry W, MDF? or MDF in the middle?).

Thanks

Hi patshesj. It is drywall/drywall and MDF as the inner wall plate and i`ll use 1/2 " because it is the cheapest solution, 5/8" comes only in fire-plate design.
This is the type of MDF wall plates I`ll use
lgl

[Ted White]

So this is a 1/2" total thickness product? If so, I really recommend to increase the mass by adding a thick sheet of drywall behind that finished material.

Are you planning to incorporate acoustic treatments on the walls? Often the walls are completely covered with treatments. In that case there's not much use in applying a finished panel like you're showing.

Just trying to fully understand what you're goals are.

Thanks,

[lglura]

Ted White wrote:

So this is a 1/2" total thickness product? If so, I really recommend to increase the mass by adding a thick sheet of drywall behind that finished material.

Are you planning to incorporate acoustic treatments on the walls? Often the walls are completely covered with treatments. In that case there's not much use in applying a finished panel like you're showing.

Just trying to fully understand what you're goals are.

Thanks,

The total thickness in wall and ceiling is 1/2" DW+ 1/2" DW +1/2" MDF= 1.5".
This is what I have found out thanks to all posts in the thread, and because of limited space.
The acoustic treatment is the last thing I do, and I shall not cover the walls completely.
Grateful for your participation Ted
lgl

[Space]

Ted White wrote:

So this is a 1/2" total thickness product? If so, I really recommend to increase the mass by adding a thick sheet of drywall behind that finished material.

If I may ask, what would be the difference between 2: 1/2" and one thick sheet? I mean, what is the difference in terms that I can understand as a builder of rooms.

Granted I wouldn't put the MDF on the inside of the room, but it is treatable It would be better situated as the first layer, but that's just from what I know.

[Ted White]

Well, that's a really great question.

From a mass perspective it's a wash, let's just say. Two 1/2" pieces = the weight of one 1" panel. But splitting that mass up gives you the opportunity to damp the panels with a damping material.

If you were not going to damp, then having two dis-similar thicknesses of the material would break up resonance better.

Three layers of 1/2" mass (damped) is better than two 3/4" layers of (damped) mass, which is better than a single layer of 1.5" undamped mass. Why would three thin layers of damped mass be better than two thick layers of damped mass. Why?

Multiple dmping layers work better than a single layer. Even if the total amount of damping material remains the same.

Also, people use MDF on walls all the time, especially on the recording studio side of things. It's just an awfully expenside source of mass. We often recommend using a 7/16" OSB, then 5/8" or double 1/2". This gives you a nail base everywhere later when studs are hard to find

[Space]

If damped.

This report:
http://www.cmhc-schl.gc.ca/publicati...ch/02-108.html
that is the conclusion of this data:
http://irc.nrc-cnrc.gc.ca/pubs/ir/ir761/ir761.pdf
reads that, based on the research, 13mm fire rated is recommended....if available.

[Ted White]

That's a bit of a misleading recommendation they have and certainly not generally heeded advice. Otherwise we'd all be building our walls with lighter 1/2" board. But we don't (unless like lgl we use multiple 1/2" layers)

Mass law is a law, and 1/2" and 5/8" drywall are both sources of mass. Heavier 5/8" will outperform lighter 1/2" if we look at the larger sound spectrum.

One conclusion they derive is to use denser and thinner board. Technically, this is a great recommendation. The thinner panels allow more flex = more internal friction = more damping. Vibration is converted to heat. This is a good thing. And they pick up on the fact that 1/2" board is denser than 5/8" and thinner (flexible). However, 1/2 while more flexible and more dense is also lighter. And that it what swings the pendulum back in favor of the 5/8".

I also think they were considering the data produced from 16" OC wall tests, which are inherently stiffer frames (less flex, less internal damping) vs. the more flexible 24" OC framing. If a 16" stud wall is being used, the 1/2" gets closer in performance than 5/8" because it can flex better on a narrow 16" stud spacing than can the stiffer 5/8".

[Space]

Thanks for the verification. I think the National Research Council of Canada is a gold mine of information for audio related builds for people that choose to use it.

[patchesj]

Wow Ted, that is some good info. So if you were designing the "perfect" (but reasonable) wall, what would it be? 1/2 DW", green glue, 5/8" DW on a 24" OC frame? Would using different thicknesses out weigh additional mass of a 5/8" X 2 wall?

[Ted White]

Hi Patches,

I should mention that if you damp the system with a damping material, the whole 1/2" vs. 5/8" goes out the window. A damping material will damp far more efficiently than the board itself,

Given that, what I would recommend for a single stud wall (you mentioned) is 24" studs and double 5/8".

I would not recommend a single stud wall, however. A single stud wall is still coupled. I would recommend at least a staggered stud, and preferably a double stud wall to introduce decoupling.

[patchesj]

Ah yes, I was assuming an isolated wall. Another crazy question, what about using green glue between the studs and first layer of drywall as well as between sheets? Any benefit?

[Ted White]

Intuitively damping material would prove beneficial on the edges of studs and joists. There's insufficient surface area and little damping occurs there.

When used on a much larger surface area between sheets of drywall very efficiend damping can take place.

[Ted White]

So... any updates?

[lglura]

Ted White wrote:

So... any updates?

Hi Ted. There is no update, have been very concerned with maintaining the house exterior. Begin to build walls in two weeks.
lgl

[Ted White]

Better to do the exterior walls now

[lglura]

There was bad weather, so I worked a little inside. cut 1 inch of the roof beams in order to gain more headroom



To compensate for the weaker beams I glued on the reinforcement