A comparison of the effectivity of different speaker panel damping products

[Rick Sykora]

After testing a number of speaker cabinet damping products, as some of them also claim panel damping properties, wanted to test them (and more) for effectiveness. These include:

1. Sonic Barrier lightweight vinyl damping
2. Sonic Barrier Acousta-Stuf (3/4 or 1.25 inch)
3. GR Research NoRez
4. Amazon butyl rubber sheets
5. simple bracing/reinforcement

Have had some feedback to test a more liquid approach as well but am still researching. Green Glue compound has been suggested but is more of a Constrained Layer Damping (CLD) approach and does not readily compare well to the others. Hy-Tech makes a product called Acousti-Coat but is $55/gallon and really do not need that much. Seems as though some automotive undercoating products seem a better fit. Am looking for more proven, economical solutions for purchase (no homemade concoctions). Suggestions?

The other major task is to create a consistent test fixture for each sample. I have some 2x4 sheets of 1/2 inch MDF that I plan to cut into strips and use as the test medium. Also have a bolt-on Exciter that can consistently torque on the board as a sound source. Measuring may be a bit trickier. Being consistent with a microphone may be difficult if the panels are hanging but not sure an accelerometer is more consistent and seems more intrusive. Open to proven advice/ideas here. Maybe @Frank Dernie or experienced mechanical engineer members?

 

[DonH56]

I would use either an accelerometer or a PZM mounted directly to the panel under test. Note that how you mount and support the panel will also influence the results. That said, an ME or speaker designer will be (much) more competent than I to comment!

 

[Frank Dernie]

After testing a number of speaker cabinet damping products, as some of them also claim panel damping properties, wanted to test them (and more) for effectiveness. These include:

1. Sonic Barrier lightweight vinyl damping
2. Sonic Barrier Acousta-Stuf (3/4 or 1.25 inch)
3. GR Research NoRez
4. Amazon butyl rubber sheets
5. simple bracing/reinforcement

Have had some feedback to test a more liquid approach as well but am still researching. Green Glue compound has been suggested but is more of a Constrained Layer Damping (CLD) approach and does not readily compare well to the others. Hy-Tech makes a product called Acousti-Coat but is $55/gallon and really do not need that much. Seems as though some automotive undercoating products seem a better fit. Am looking for more proven, economical solutions for purchase (no homemade concoctions). Suggestions?

The other major task is to create a consistent test fixture for each sample. I have some 2x4 sheets of 1/2 inch MDF that I plan to cut into strips and use as the test medium. Also have a bolt-on Exciter that can consistently torque on the board as a sound source. Measuring may be a bit trickier. Being consistent with a microphone may be difficult if the panels are hanging but not sure an accelerometer is more consistent and seems more intrusive. Open to proven advice/ideas here. Maybe @Frank Dernie or experienced mechanical engineer members?

It is decades since I was doing noise and vibration work but did use a product called coustilam FS, they have updated products now. It was a triple layer product.

There is a thin layer of foam which is bonded to the panel and damps it then a dense layer as a transmission barrier (it used to be lead iirc dense and air tight are the key things for a sound barrier) then a thicker layer of foam to reduce reflections from the panel surface.

I built cabinets for KEFkit 3 baffles (basically a Kef Concerto baffle complete with T27, B110, B139 drivers and DN12 iirc crossover) and lined them with coustilam FS. Around 50 years ago now

 

[MCH]

Not sure if it fits more here or your other thread, but covestro makes noise absorption foam, mostly for automotive I reckon, under the brand Baynat. Maybe not available to the general public but I don't know.

Noise-cancelling innovation creating personalized passenger experiences | Covestro AG

Today, traveling by car is just a way to get from A to B, but that is all changing. In the future, vehicles will be designed to give a new user experience. The adoption of autonomous and smart technologies will transform car interiors into a mobile office, an entertainment center or a place for...

solutions.covestro.com

 

[Tinker]

@Rick Sykora the difference in your testing will be limited to the thickness/mass of the products supplied to you in their stock form.

The silicon solution can vary and be applied thicker and more irregular. More/less sand. I can put blobs into corners. Apples to apples seems problematic. Comparing Green glue to silicon at equal thickness would certainly be interesting!

 

[Rick Sykora]

Not sure if it fits more here or your other thread, but covestro makes noise absorption foam, mostly for automotive I reckon, under the brand Baynat. Maybe not available to the general public but I don't know.

Noise-cancelling innovation creating personalized passenger experiences | Covestro AG

Today, traveling by car is just a way to get from A to B, but that is all changing. In the future, vehicles will be designed to give a new user experience. The adoption of autonomous and smart technologies will transform car interiors into a mobile office, an entertainment center or a place for...

solutions.covestro.com

Thanks, but not clear from their website either.

 

[Frank Dernie]

Open to proven advice/ideas here. Maybe @Frank Dernie or experienced mechanical engineer members?

FWIW We made a rig to test various products. It was effectively a 24" wide by 12" high by 12" deep box with a removable wall in the middle, on one side of the wall was a bell and there was a microphone on each side. We tested products by using them on the removable wall, ringing the bell and comparing microphone signals.
Damping the panel made a bit of a difference, a layer of foam made a negligible difference unless it was on the bell side where it slightly reduced the sound but only on the bell side. What made a big difference was a dense airtight wall, ⅛" lead sheet was good, which made no difference on the bell side but reduced the level a lot on the other side.
Damping is fine for panel resonance but heavy and airtight for transmission.

My current speakers have cabinets made from 10mm and 12mm ally plate bolted through battens using machine screws and "O" rings in grooves. Very heavy, completely airtight. Very expensive to machine...

I am sure they are good sound barriers but don't know how much difference it makes but think it can't be worse.

 

[Rick Sykora]

If my testing shows that a product is not very effective, is a useful data point anyway...

Once am able to confirm my test fixture is operating consistently, will state the test conditions and note the test results. Plan to review the test protocol here before I start comparison testing. So as with some of what Frank and Don mentioned, the locations of the exciter and measurement sensor (mic or accelerometer) need to be defined and potential ramifications understood.

As I alluded in my OP, not planning to to CLD testing here, but if time and materials allow, maybe in a next round.

 

[cavedriver]

Found this paper a while ago (or someone else shared the link) on panel damping that I wanted to read but they want $33. maybe someone with a journal subscription service can pull it down and share the results:

E-library page - AES

AES E-Library ← Back to search

aes2.org

 

[cavedriver]

This youtube video has made the rounds of course, but for those that haven't seen it just skip to ~32 minutes in where he does about 10 minutes of testing on panel vibration and CLD damping solutions. It's where I got the decidamp reference, and also note he mentions an accelerometer for ~$20 from Digikey:

 

[cavedriver]

Another thread on ASR that is specifically on CSD that could take some pressure off this thread for the people that want to read specifically about constrained layer damping since that's not the focus of this thread at this time:

Constrained layer damping

Hi all, For a while I've been busy trying to design a speaker for the first time. So I have learned a lot these last few months and I know it is only the surface of knowledge. Now, my focus has shifted towards the enclosure itself and in this proces I came across this video which involved...

www.audiosciencereview.com

 

[Rick Sykora]

Another thread on ASR that is specifically on CSD that could take some pressure off this thread for the people that want to read specifically about constrained layer damping since that's not the focus of this thread at this time:

Constrained layer damping

Hi all, For a while I've been busy trying to design a speaker for the first time. So I have learned a lot these last few months and I know it is only the surface of knowledge. Now, my focus has shifted towards the enclosure itself and in this proces I came across this video which involved...

www.audiosciencereview.com

Thanks for the reminder and here is another comparable set of tests including different cabinet materials and CLD:

Box Construction Methods | somasonus

www.somasonus.net

The internal stuffing materials are more limited but includes discontinued Ultratouch denim. His test fixture uses a woofer as a passive radiator and so seems comparable to what I did with the C-Note port. I am hoping my charts are easier to compare as had some difficulty with his presentation.

 

[Tinker]

This youtube video has made the rounds of course, but for those that haven't seen it just skip to ~32 minutes in where he does about 10 minutes of testing on panel vibration and CLD damping solutions. It's where I got the decidamp reference, and also note he mentions an accelerometer for ~$20 from Digikey:

Excellent! Thanks for posting this. I wanted to mention the knuckle test but it's not very scientific unless of course, a scientist is the one who does it.

 

[hex168]

A caution regarding undercoating materials I have heard but cannot vouch for is that they can outgas solvents which can affect the drivers.

 

[Rick Sykora]

A caution regarding undercoating materials I have heard but cannot vouch for is that they can outgas solvents which can affect the drivers.

Agree, would not endorse that either. Meant any coating that might be used to dampen sound and something that is acceptable in the car’s interior where considerations for human health should cover any impact on drivers.

 

[alex-z]

DAMPING PAD

Solen Damping Pad, Black Alsphat Saturated Felt, Self Adhesive, 39"x39"x1/8"(3.0mm +/- 25%).

www.solen.ca

Bitumen pad is specifically advertised for this purpose, would be good to test both as a surface treatment and a CLD option.

1" wooden dowel vs MDF brace vs cheap lumber is another comparison I would like to see. All 3 are super common bracing techniques, perhaps grain structure of the wood has some downsides vs the uniformity of MDF?

My own measurement rig for panel testing is just a guitar pickup into an audio interface. Rather than use adhesive I just put a fixed amount of weight on top. Doing a bolt-on mount would be trivial with a 3D printer if you want to measure upright.

 

[Rick Sykora]

DAMPING PAD

Solen Damping Pad, Black Alsphat Saturated Felt, Self Adhesive, 39"x39"x1/8"(3.0mm +/- 25%).

www.solen.ca

Bitumen pad is specifically advertised for this purpose, would be good to test both as a surface treatment and a CLD option.

Interesting but does not seem like friendliest option. Know how it smells?

1" wooden dowel vs MDF brace vs cheap lumber is another comparison I would like to see. All 3 are super common bracing techniques, perhaps grain structure of the wood has some downsides vs the uniformity of MDF?

This seems best done via simulation as would be easier to see how changes compare. Maybe @fluid or another more experienced member than I might know.

My own measurement rig for panel testing is just a guitar pickup into an audio interface. Rather than use adhesive I just put a fixed amount of weight on top. Doing a bolt-on mount would be trivial with a 3D printer if you want to measure upright.

Thought a guitar pickup was more based on inductive sensing? My brother is musician and might have something but a decent accelerometer is inexpensive too.

 

[fluid]

This seems best done via simulation as would be easier to see how changes compare. Maybe @fluid or another more experienced member than I might know.

There is a good Audioholics article with some FEA analysis of bracing.

https://www.audioholics.com/loudspeaker-design/detailed-look-proper-loudspeaker-cabinet-bracing

The stiffer the brace the better it works to increase the stiffness of a panel or cabinet
MDF is not ideal for use as a brace for this reason (not very stiff) but if enough of it is used in the right places it still works.

Decent plywood, hardwood like oak or aluminium profiles can all be much stiffer than MDF and brace better with less material than MDF.

Different frequency ranges need different strategies for an ideal cabinet, increased stiffness for low frequencies, increased damping for higher frequencies.
A single cabinet that covers all frequencies has an inherent compromise from the start.

It is easier to measure or simulate what will happen than to assess how audible the effects are though.

 

[Rick Sykora]

There is a good Audioholics article with some FEA analysis of bracing.

https://www.audioholics.com/loudspeaker-design/detailed-look-proper-loudspeaker-cabinet-bracing

The stiffer the brace the better it works to increase the stiffness of a panel or cabinet
MDF is not ideal for use as a brace for this reason (not very stiff) but if enough of it is used in the right places it still works.

Decent plywood, hardwood like oak or aluminium profiles can all be much stiffer than MDF and brace better with less material than MDF.

Different frequency ranges need different strategies for an ideal cabinet, increased stiffness for low frequencies, increased damping for higher frequencies.
A single cabinet that covers all frequencies has an inherent compromise from the start.

It is easier to measure or simulate what will happen than to assess how audible the effects are though.

Thanks, had seen the AH article previously. It is a big gulp but can skip forward to the conclusion if not looking for a science lesson. It does mention part of the issue with building and measuring in that stiffness is critical. However, really need to measure to know when stiff is stiff enough. CLD techniques have a comparable challenge but with added complexity.

 

[mcdn]

@Rick Sykora you may be interested in this post I made a few days ago about some _very_ simple mods I made to a pair of JBL LSR305p speakers, which are notoriously resonant, especially through the bass and mid bass, as they are only made of 15mm MDF and plastic.

I filled the plastic front panels somewhat at random with 300g per panel of polyester filler ("builder's bog"), which sets like stone. I also glued lengths of 10mmx30mm hardwood to the side panels.

More details and pictures in the original post, but for USD30 in materials I got a roughly 10dB broadband reduction in panel vibrations.