KnoxVegas "Bang for the Buck" Theater - Page 2

Looking great. Looks to be an awesome upgrade over the previous space.

Shan

Looks great! The front wall construction idea pictures looked good earlier - gave you much thicker absorption at the front end which will be great for trapping bass. One thing I will say is that you may want to be prepared - building walls with a higher STC rating will likely cause some low frequency issues that weren't imminent prior to construction. A higher STC means more sound stays in the room, meaning low frequencies that once were transmitted out of the room before, now aren't. You may want to consider some thicker panels around the room.

Soundproofing treatments reduce the sound (vibration) passing through the wall or ceiling. I don't believe this translates to more rejection / reflection of soundwaves back into the room, but would love to be corrected on this.

A damped panel will not act as an absorber, however an improperly treated hollow cavity will resonate.

For the door, start with a 1 3/4" solid core interior door slab. I would laminate a sheet of 5/8" - 3/4" MDF to the door slab (theater side) with damping compound. I would bag the MLV.

^+1 about the door.

That's what I did and I've been very happy with it.

Yes, stuffing the riser should help in both those ways. You will prevent any inherent resonance the riser may introduce (which would act as a panel absorber of sorts - definitely welcomed) and it should help to alleviate some low frequency build-up in the room. You may end up needing additional bass trapping (perhaps in corners in the room, or on the wall), but it is hard to know without being able to test the room (or even have an account of how it sounds, since construction isn't finished yet)

Soundproofing removes leaks of sound that travel through flanking paths - walls, floors, HVAC, etc. When these sounds 'leak' outside of the room, they are being transmitted out of the room. When you reduce these flanking paths, those sounds do not travel outside of the room anymore, which can cause frequency buildups, usually evident in low frequencies inside the room. As an example, a concrete bunker is wonderful for isolation - but awful for acoustics.

Somewhat...if you research "Constrained Layer Dampening" you can see how it works. Pretty simple really, as sound vibrates the drywall, the drywall flexes in motion (of course, very little). The Green Glue will take those vibrations, and convert the energy into heat (similar to porous absorbers), and thus gives us a higher STC rating.

Exactly, so sound energy is changed to heat energy which therefore results in less sound being heard outside of the room. So soundproofing does not keep more sound in the room, it changes the sound that would normally leave into something that cannot be heard. Instead of sound leaving the room, more heat does.

I don't see how soundproofing results in more sound staying in the room.

I'm not trying to be confrontational by the way, just curious.

By the way Johnny, regarding your riser and insulation, I would do some more research about cutting vents into it to allow it to act as a bass trap. I've seen this done successfully in many builds, but I know that it takes some thought and calculations to get it "tuned" correctly.

That is only in constrained layer dampening and in the case of added insulation between the studs, but we know those are not the only pieces of the isolation system. These are small additions to the actual STC rating as a whole. Most of inherent isolation comes from mass, mass, and more mass. And the point is, low frequencies can penetrate thin partitions (thin in terms of low frequency waves) - but have a hard time penetrating hard, dense, heavy, thick material. I keep referring to concrete because its easy to imagine, but other materials can act similarly too. I remember Rod Gervais commenting on this previously with a good quote. I thought it may have been in his book, but I did a quick look through and couldn't find it. Perhaps he said it on another forum? Either way, I'll do some more digging and let you know if I do find it.

I suppose I should have been more specific: not every step of isolation will encourage sounds to stay in the room, but the main step of isolation - that is - mass, mass, mass...does encourage sound staying inside the room. Also in isolation, you try to remove any diffraction that could occur through vents, door frames, and other openings. When you create an air tight system, diffraction is not possible. Lastly, dampening flanking paths won't encourage any more sound to be inside the room than previously, but removing them could.

And I didn't find your posts to be unusually provocative - we all strive to learn - there is no problem there. I question other ideas similarly when I'm not sure.

Anywhoo, no point to dirty up this thread anymore with this. I'd be happy to chat with any of you over PM, perhaps we could find some cool links to share and learn more. I'm personally not an isolation expert - most of my knowledge when it comes to this is from books.

Of course! Those points you make above are all good for covering - its good you are able to make for some other functional use out of that riser. The space in the back does seem like it could contribute some problems, but it will be hard to know without listening. It is a great spot for trapping though - out of the way visually, and we tend to see lots of bass build ups in the back of the room.

I will keep an eye on the thread and pop in again when necessary. Good work so far - keep up the great build!
Edited by GIK Acoustics - 9/5/12 at 6:10pm

GIK, thanks for clearing that up. I understand your point now. It's always a good day when you learn something new!

Johnny,

I'm no expert when it comes to these types of things, but this thread has some good info.

http://www.avsforum.com/t/1103345/fixing-my-riser-broadband-bass-trap-and-from-56-to-7-deep#post_15441346

I know that properly built riser bass traps are something that Dennis Erskine and his design team incorporate into many theaters.

Congratulations on the carpet! I love mine and am looking forward to some pictures.

In 2006-2007 we ran various tests as time allowed at Orfield Labs in Minneapolis. We found that if a wall had a resonance frequency of 100Hz (just an example), then frequencies on or about 100Hz were most readily removed from the room. Partitions at resonance are like superconductors and allow the resonance frequency to pass much more easily. This is at the heart of why we look to build structures with as low a fundamental resonance as possible.

Looking great man. Can't wait to see what the before/after sound difference is.

Hey Johnny,

You can use Room EQ Wizard to test your room if you have a microphone handy. Here's a video we did explaining how to download, install, run, set up, and test with REW: http://www.gikacoustics.com/video_rew_room_eq_wizard_tutorial.html

An omnidirectional microphone would be best for showing accurate graphs, but it is not really necessary. Other mics might paint a prettier picture, but you can still see large resonances, nulls, and peaks regardless of the microphones you use.

You can run multiple tests for - if you wish - all the different seating positions. Or perhaps just the middle seat in each row. The graphs will show room resonances (modes), any cancellations that might be happening (nulls), standing waves, flutter echo, comb filtering...etc. When you know the problem frequencies of the room, a lot of the guesswork is taken out of how to treat and where to treat.

Let me know if you have any other questions!

Diffusers are wonderful but a little tricky to place. I would worry about getting the absorption in there first, with the diffusion as an after thought. It also depends on how far your rear speakers are from the back wall area. If it is within a couple feet, I wouldn't recommend diffusers. But if you're a good 5-6 foot away they could certainly be useful. Perhaps both diffusion and absorption could be beneficial here.

It really depends - if that area has a large boom to it - it would be a really great place for absorption. Considering too, that the wall is angled downwards it will throw a lot of reflections right back at listening position, so I would certainly add some sort of treatment there. Diffusion doesn't do much below ~600 Hz (depending on size of the diffuser) so, I would worry first about getting the bass in check and then adding diffusion later if it is wanted.

Looks good. I was going to go back to your plans and see what that weird cabinet was behind the seats . . . Then I saw the picture of teh riser.

Wow. That sucks

Man talk about bad luck. Sorry to hear about the car. At least your kids weren't in it.

Tim