[spag_bace]

anyone know STC for LL/LLP over the frequency, especially below 125hz? I already searched this forum and google but couldn't find anything.

I'm trying to weigh LL/LLP over alternatives.

 

[braves6117]

I doubt you'll find that info. If I recall, it hasn't been released nor independently tested. Sorry

 

[capnxtreme]

About the same as any 1/8" (1lb/sq.ft.) MLV, I would think.

What do you mean by alternatives?

 

[Rudeboy]

Should be around 13-14 for the 100-125 Hz range - same as any 1 lb/ft² MLV. The foam doesn't really come into play until 1 kHz and up. Here's a test I did. The top (purple) line is untreated 22 gauge steel only. The next (orange) is plain 1 lb/ft² MLV. Next (green) is LLP. You can see that the foam makes a big difference between 1 kHz and 5 kHz.

 

[FoxPro5]

Transmission loss (frequency: dB)
100: 14
125: 16
160: 13
200: 16
250: 18
315: 19
400: 19
500: 21
630: 23
800: 26
1K: 28
1.25k: 29
1.6k: 31
2K: 33
2.5k: 35
3.15k: 37
4K: 40
5k: 42
STC = 29

Predictions based on Mass Law as STC standard testing doesn't look lower....
80: 6
63: 4
50: 2
40: .1

 

[spag_bace]

thanks Rudeboy & Foxpro!! Exactly what I want to see.

Rudeboy, what happens from 400-900hz. Looks like there's no coverage at all. The vinyl layer of LLP can block sound <400hz? Or could it be your system/rig resonance frequency? From Foxpro's numbers, it should a steady rise in Loss at frequency increases.

The foam makes a huge difference from 1khz and up!

 

[Rudeboy]

The fundamental resonant frequency is around 80 Hz, but it could be a harmonic or even a secondary fundamental from a different component of the system. I didn't include the data with nothing in the aperture, but it is far from a straight line. This is pretty primitive and I just rely on it for relative data and general trends. Next time I set it up I'll measure without the 22 gauge steel in place to see how that looks, but steel then barrier is really more representative of what we are doing.

thanks Rudeboy & Foxpro!! Exactly what I want to see.

Rudeboy, what happens from 400-900hz. Looks like there's no coverage at all. The vinyl layer of LLP can block sound <400hz? Or could it be your system/rig resonance frequency? From Foxpro's numbers, it should a steady rise in Loss at frequency increases.

The foam makes a huge difference from 1khz and up!

 

[FoxPro5]

Something like LLP is technically a double wall barrier. As I'm sure you understand, the foam is there to keep the barrier from becoming resonant by decoupling it from the surface. Not sure what Don is doing in his test rig, but in our car the substrate the barrier's sitting over might be resonant. In this case, you can get better overall STC numbers by damping it first (outside of "mass loading" the surface.)

What that graph shows is the importance of decoupling the barrier (ie making a double wall barrier) and damping the substrate to push the RF down as low as possible. If it's 80 hz then you'll see that coincidence drop and then the TL go way up (theoretically at 18 db/oct). Below 80 hz (the RF of the barrier system) a double wall is no better than a single wall (ex just some MLV thrown down on the floor) but above it you see what happens.

Not sure if any of that made sense. :surprised:

Also, LLP isn't straight up 1 lb/sqft. It's more like 1.3#. The PVC foam used is pretty dense and heavy as far as foam is concerned. It's no Ensoheavy, but it's aaaite (inside joke).

 

[Rudeboy]

Something like LLP is technically a double wall barrier.

Not to take this too far in a direction that seems to piss a lot of people off, but the barrier/foam composite isn't itself a double wall barrier. If you put the layer of MLV in direct contact with the sheet metal substrate you are basically doubling the mass of the first barrier - the steel substrate. The foam layer makes it a double wall because there is space between wall 1 - the substrate and wall 2 - the MLV.

The best way to visualize what's happening around the resonant frequency of the system is to realize that when it resonates, the thing is basically acting like a speaker cone. The sound that is striking it from the outside is exciting whatever we've put in its way and what we are hearing is actually coming from the front surface of the vibrating system. This is why, no matter what else we do, we should treat the sheet metal with enough vibration damper to minimize its reaction to sound around its resonant frequency.

 

[FoxPro5]

Yea, stop pissing people off with all this tech talk razzamataz rigamarow babble smabble and whatnot. Spoons...big spoons with A LOT of brainless info and a lot of them. Feed them.