A comparison of the effectivity of various speaker damping materials

[cavedriver]

For the higher frequencies I would intuitively expect that a very lightweight (low density) material would be better at bringing them down- something with a mass low enough for 1k+ Hz sound waves to vibrate it. Or maybe something with a fine enough surface texture to "trap" waves of that short a wavelength. I guess I need to think about how sound is absorbed a little more to realize what would work best.

 

[ryanosaur]

There is a F13 felt pic on post #40. It is 75% wool as opposed to denim which is usually cotton. Do not have the denim-based Sonic Barrier but expect it is comparable to the cotton blanket I tested.

I know Dennis Murphy likes the Denim product. I didn't know that PE was carrying it as had seen it prior on the old Meniscus site. Good to know, @cavedriver , thank you.

I think though the blanket may be similar, any changes of density from folding and layering would give different results than a consistent layer of material like the Fiberglass or UltraTouch type stuff. Think along the lines of how they warn you not to compress fiberglass insulation when installing in a wall frame because it will alter its efficacy. Likewise, how the Transmission Line guys have arrived at a specific weight per cubic foot (or liter) when it comes to stuffing a Line with Acoustuff or PolyFill (much as you showed above with the two measurements you did).

Cool thread, BTW!

 

[Rick Sykora]

With the exception of the thinner Sonic Barrier (might need to retest), the damping for all materials tested is very comparable from 300 to 600 Hz.

Can see very similar results from the 600 to 1200 Hz with the major standouts being the thicker Sonic Barrier (red trace) and NoRez (yellow trace). Sonic Barrier does better from 1000-1200 Hz and NoRez does better from 1200-2000 Hz. Much above 2000 Hz the differences start to lessen as the early frontrunners show some variability. This view is pretty complex, so here is a simpler one that may help...

This is the baseline with NoRez and Sonic Barrier and the purple trace adds the cotton blanket. As I mentioned, doubt that much above 1200 Hz or so is audible with a rear port. So might argue that the cotton seems the best value. Will need to add some frontal measurements to see if there is some other difference. Before I do, will also look at some often-applied combinations to see if they yield any better results. Am not sure whether the denim advocates are lining the walls or shredding it as fill. If there is major interest, maybe will test the Sonic Barrier but is not inexpensive (although cost per square inch is much better).

 

[ryanosaur]

With the exception of the thinner Sonic Barrier (might need to retest), the damping for all materials tested is very comparable from 300 to 600 Hz.

View attachment 392871


Can see very similar results from the 600 to 1200 Hz with the major standouts being the thicker Sonic Barrier (red trace) and No Rez (yellow trace). Sonic Barrier does better from 100-1200 Hz and NoRez does better from 1200-2000 Hz. Much above 2000 Hz the differences start to lessen as the early frontrunners show some variability. This view is pretty complex, so here is a simpler one that may help...

View attachment 392879

This the baseline with NoRez and Sonic Barrier and the purple trace adds the cotton blanket. As I mentioned, doubt that much above 1200 Hz or so is audible with a rear port. So might argue that the cotton seems the best value. Will need to add some frontal measurements to see if there is some other difference. Before I do, will also look at some often-applied combinations to see if they yield any better results. Am not sure whether the denim advocates are lining the walls or shredding it as fill. If there is major interest, maybe will test the Sonic Barrier but is not inexpensive (although cost per square inch is much better).

Not shredding it. Using it as a cut piece inserted behind woofer. I can’t speak to how Dennis is stuffing his towers, but the stand mounts I’ve seen have a slightly oversized piece inserted in and held in place largely by friction. No treatment to the actual cabinet. And definitely not filling the cabinet.

While I would love to see measurements I wouldn’t ask you to spend on it just for a test.

 

[Rick Sykora]

I recently placed a PE order so might be a while before I get enough stuff to break the free shipping mark. I have denim that could be shredded but looking for materials that can be purchased readily by others. If I just order the Acousta-Blu pretty sure am going to pay hefty shipping premium.

So, it is on my list unless someone decides to send me some.

 

[kyuu]

So, it is on my list unless someone decides to send me some.

Are we talking the 1" sheet? So about $45 after shipping? I'd be happy to send a sheet. All I ask for in return is your advice in applying what we learn here to treating a wall cavity for in-wall speakers.

 

[Rick Sykora]

Tried my best to forget this commitment and had to steal some from the basement rafters but here is about 80g of Owens-Corning paper-backed R-19 fiberglass....

While difficult to place well inside (the upper portion of the cabinet could not be readily accessed (without cutting more pieces and more handling) in the small C-Note cabinet, fiberglass did a bit better than the cotton blanket at damping the major resonance and very comparably above that. So nothing exceptional enough to make me want to use regularly but useful if alternatives are difficult to acquire. Definitely best applied before the front baffle is attached so can be evenly placed.

 

[kyuu]

Looks like the fiberglass insulation that my cat regularly pulls out of my old Energy towers through the port is well chosen. And for wall cavities, buying a batt to stuff in there may be the easiest and best solution. Though common wisdom seems to be to keep it away from the drivers as the fiberglass may get into it and cause damage?

 

[ZolaIII]

Looks like the fiberglass insulation that my cat regularly pulls out of my old Energy towers through the port is well chosen. And for wall cavities, buying a batt to stuff in there may be the easiest and best solution. Though common wisdom seems to be to keep it away from the drivers as the fiberglass may get into it and cause damage?

I would keep glass out of my respiratory tract... similarly as it can cut into soft tissue it can stick in the rubber but it won't cut into paper. Fix those holes at least, won't even comment on cat's behalf.

 

[ryanosaur]

Though common wisdom seems to be to keep it away from the drivers as the fiberglass may get into it and cause damage?

Generally, it is highly recommended to not let your stuffing of choice be right up on the back of the drivers.

 

[terryforsythe]

Tried my best to forget this commitment and had to steal some from the basement rafters but here is about 80g of Owens-Coring paper-backed R-19 fiberglass....

View attachment 393080

While difficult to place well inside (the upper portion of the cabinet could not be readily accessed without cutting more pieces and more handling) the small C-Note cabinet, fiberglass did a bit better than the cotton blanket at damping the major resonance and very comparably above that. So nothing exceptional enough to make me want to use regularly but useful if alternatives are difficult to acquire. Definitely best applied before the front baffle is attached so can be evenly placed.

I stuffed fiberglass insulation into my speakers (ports are plugged). It certainly is effective. Next time I open my speakers, though, I probably will replace it. I was leaning toward picking up some Rockwool from Home Depot. I'll review your data before I do so. I might choose something else.

I have a little bit of NoRez in the speakers, but I ended up pulling out most of it so that I could add wood glue fillets to my cabinet joints when I realized that they were not glued together all that well. (The sticky backing on NoRez is very strong. It was difficult to get out.)

 

[Rick Sykora]

Recovered the NoRez from that test speaker by slicing off the cabinet back. It is rabbeted so plan to repurpose with a removable back for later testing. Will be easier to test more damping products if I can get a good seal. Will also be less wear on the woofer screws.

 

[Rick Sykora]

@Rick Sykora could you do a test with snow inside the enclosure?

Give me a few months!

More seriously a big thanks for a very interesting thread. The shifts in port output due to some amount of "making the box appear bigger" stuffing effect? Or what do y'all think is up with that? C-Note is not physically big, could the internal linings be rerouting airflow internally and changing the apparent tuning? And the somewhat steeper cutoff at the lowest frequencies seen in post 57 and others, what's up with that?

Damping affecting box volume has been overblown and is not as much of a factor for a vented box. For the overstuffed C-Note, it could be increasing the apparent volume around the main output as this would account for the lower f3. Would need to deeper dive into that use case.

Another parallel topic would be the usefulness of various stuffings on sealed boxes for purpose of increasing the apparent acoustic volume. (And also damping internal waves re-radiating back out the cone). If you or someone does a thread like that it would be really cool; the only such I know of is the chapter in Vance Dickason's Loudspeaker Cookbook which while great is long in the tooth by now (I haven't read the much more expensive 8th edition yet).

The sealed use case is simpler and not sure much could be done beyond what Dickason and others have. For sealed designs, I think the most interesting recent aspect is applying the Linkwitz transform. Not sure how bounded it is, but seems much easier than constantly changing out internal damping materials. That said, their application is not mutually exclusive either.

 

[Rick Sykora]

Here is a look at progressively greater amounts of Acousta-Stuf...

Once we get to the recommended amount (around 85 g) we reach a point of diminishing returns between 300-600 Hz. The port resonance damping keeps improving all the way up to 190g (black trace). At this point, it is not quite as effective as some of the better solutions and is at the point where adding much more would be difficult to keep from interfering with the woofer and the port.

My takeaway is that Acousta-Stuf looks to be useful between 300-600 Hz but any more than the recommended amount becomes wasteful, To better address the port resonance, would employ one of the more effective damping materials (or shorten the port).

 

[TunaBug]

Any insight into how the different materials hold up over time? Will they settle or compress? In other words, how will they sound in 20 years?

 

[Rick Sykora]

Any insight into how the different materials hold up over time? Will they settle or compress? In other words, how will they sound in 20 years?

Mainly what the manufacturers claim (if anything). Some of the open cell foams seem risky to me but may be less so than cotton or felt. Anything natural is at risk of attack unless it is treated. If my target was to ensure decades of useful life, would be using Dacron or other synthetic stuffing (like Acousta-Stuf).

Having had some 20+ year old speakers, the only parts I have seen fail are foam surrounds and sorbethane.

P.S. should add have seen surround failures to but not sure whether a material issue or adhesive related.

 

[cavedriver]

Mainly what the manufacturers claim (if anything). Some of the open cell foams seem risky to me but may be less so than cotton or felt. Anything natural is at risk of attack unless it is treated. If my target was to ensure decades of useful life, would be using Dacron or other synthetic stuffing (like Acousta-Stuf).

Having had 20 year old speakers, the only part I have seen fail are foam surrounds and sorbethane.

I have a big Heathkit "Legato" speaker from the 60's. It has scrap cotton batts in it. They seem to be holding up ok but of course I haven't done any testing so this seems like a great question.

 

[Rick Sykora]

I have a big Heathkit "Legato" speaker from the 60's. It has scrap cotton batts in it. They seem to be holding up ok but of course I haven't done any testing so this seems like a great question.

Notably, how any material holds up in humidity extremes?

Cotton in particular seems as though it might change if exposed to high humidity over time.

 

[hex168]

Any thoughts on damping that has a mass-loaded layer (such as one of the Sonic Barrier 3-layer materials) applied to the outside of a cabinet? Might it reduce transmission of sound from the cabinet walls?

I admit I am unclear on the propagation mechanisms of sound from cabinet wall vibration to the air, or I would try to figure this out.

 

[Rick Sykora]

Any thoughts on damping that has a mass-loaded layer (such as one of the Sonic Barrier 3-layer materials) applied to the outside of a cabinet? Might it reduce transmission of sound from the cabinet walls?

If the goal is to reduce the panel vibrating, pretty sure inside vs outside mounting is unlikely to make much difference. What is the use case for outside? A padded speaker?

I admit I am unclear on the propagation mechanisms of sound from cabinet wall vibration to the air, or I would try to figure this out.

Ofc, the vibration source is the woofer, but propagation will depend on cabinet material(s), shape, dimensions, port tuning (if used) and how the driver is mounted.