Sound Transmission Loss- LL/LLP

[Aaron Clinton 2,372]

Great post Don.

[Dr Durden 0]

Don't get me wrong

Edited June 27, 2008 by FoxPro5

[Dr Durden 0]

I think some of the anger being expressed here is a little misplaced.

If you think the "anger" expressed by a few of us here has to do with....

Where to use vibration damper and where to use a barrier is a critical question when planning a project, but the swing toward barriers being the one true way is just as silly as claims that vibration damper alone is the solution to your problem

Edited June 28, 2008 by FoxPro5

[Rudeboy 152]

Really? How many have you made, Don? I have 3 of said composite barriers...using foam, lead, aluminum, galvanized sheet metal... in my car in addition to my own and Anthony's products. Blown away? Not to my ears.

Also, how about adhesives? All those materials need to be glued together. That's what ultimately kills the budget project when trying to beat a pre-fabbed (and tested) decoupled barrier. Well, in my experience anyway. For what it does, LLP is tough to beat.

I think you misunderstood me. I was talking about creating a single piece barrier shell with multiple layers and no gaps or breaks. I wasn't talking about the the cheapest approach, rather the ideal barrier configuration. I've built none of these because it would be completely over the top, IMO. I get all of the performance I need from the commercially available stuff. Describing the ideal gives people something to think about.

Diffusion

At what frequencies? Seems to me that the 1/4 wavelength rule is still going to apply. Even if one of these "diffusers" was 1/2" thick, it would only be effective at 6.8kHz and above.

[Dr Durden 0]

At what frequencies? Seems to me that the 1/4 wavelength rule is still going to apply. Even if one of these "diffusers" was 1/2" thick, it would only be effective at 6.8kHz and above.

Seems they work on the ITD (initial time delay) which helps "clean" up the sound due to the acoustical phenomenon of diffusion. So even if the troughs are not at least 1/4 of the lowest frequency wavelength, it seems they can cause a shifting great enough to cause an overall audible response. CAE has some data on the effects of their product, and to me that's what looks like is going on. Plus we all know what happens when sound is shifted and shaped due to the negative effects of early reflections and odd order harmonics all bouncing around in a small space (ie a car). Maybe these pads turn that negative into inaudible? I don't know.

Edited June 28, 2008 by FoxPro5

[Rudeboy 152]

At what frequencies? Seems to me that the 1/4 wavelength rule is still going to apply. Even if one of these "diffusers" was 1/2" thick, it would only be effective at 6.8kHz and above.

Seems they work on the ITD (initial time delay) which helps "clean" up the sound due to the acoustical phenomenon of diffusion. So even if the troughs are not at least 1/4 of the lowest frequency wavelength, it seems they can cause a shifting great enough to cause an overall audible response. CAE has some data on the effects of their product, and to me that's what looks like is going on. Plus we all know what happens when sound is shifted and shaped due to the negative effects of early reflections and odd order harmonics all bouncing around in a small space (ie a car). Maybe these pads turn that negative into inaudible? I don't know.

Our friend Abmolech has argued that the claimed benefits for these things are completely false and impossible (maybe going as far as calling for prison time for the people selling them I'm willing to argue some things with him, but on a topic like this I absolutely defer. There's plenty of anecdotal evidence showing improvement, but in each case, I think the added mass and possible VE damping account for it all.

[Dr Durden 0]

Our friend Abmolech has argued that the claimed benefits for these things are completely false and impossible (maybe going as far as calling for prison time for the people selling them I'm willing to argue some things with him, but on a topic like this I absolutely defer. There's plenty of anecdotal evidence showing improvement, but in each case, I think the added mass and possible VE damping account for it all.

That dude has done more acid than I could do in my entire lifetime.

I'm kidding and yes, I am familiar with his stance. I'm still on the fence, though.

Don't see how the mass accounts for anything substantial, personally. I'm willing to bet you will not see a major difference in results by gluing two pads two each other vs using just one. Hell, slip a sheet of lead in there to make yourself a Deflex pad sammich and I'd expect to see the same result on paper as using just one. Great experiment though right there.

Edited June 30, 2008 by FoxPro5

[///M5 2,833]

If the area behind the speaker is deadened well enough, most likely there is enough mass that adding the pad isn't substantial. Of course this would be easy to simulate by making an enclosure with a very massive back wall and testing it out.

[Rudeboy 152]

If the area behind the speaker is deadened well enough, most likely there is enough mass that adding the pad isn't substantial. Of course this would be easy to simulate by making an enclosure with a very massive back wall and testing it out.

I'm not endorsing the practice, but most of the reports I've seen of improvement came from people installing these products in minimally deadened or completely untreated doors. In that case, the difference may be noticeable.