A comparison of the effectivity of various speaker damping materials

[Rick Sykora]

Have seen a lot of discussion about speaker damping and many applications seemed to be ad-hoc. Admittedly, even the use of damping for Directiva r1 was more of a guess than I was comfortable suggesting. Having acquired many different types of materials from different DIY projects, I felt it was time to better understand how effective they are. There are many ways a speaker can resonate and potentially affect the sound quality. The driver(s) have resonances, and the cabinet and various parts (panels, vents, terminals, etc.) can resonate at many frequencies (and harmonics of those frequencies).

This study is mainly targeted to see how effective various damping materials are for a target speaker. As is relatively inexpensive and had some extra parts around from the one I built for Amir's testing, the target speaker is the Dayton C-Note. The C-Note has some good sound qualities but also exhibited some issues common to many speakers. That said, it is a small speaker and so panel resonances are not a major focus. Also, most materials used for panel damping require adhesives and would require more resources and testing to ensure each speaker cabinet was acoustically identical.

The test setup uses REW, a UMIK-1 microphone, my MOTU m4 and a Hypex amp to drive the C-Note speaker, Measurements were taken in nearfield at the center of the C-Note port. The measurements are unsmoothed and gated at 200 ms (which yields 5 Hz resolution). Here is the initial measurement for the undamped C-Note as supplied by Parts Express....

Can see the primary output of the port is around 38 Hz using the specified 7 inch port length. While there is another slight resonance just below 300, the real concerns are the ones around 600 to 1600 Hz. Some of this is low enough in frequency and high enough in magnitude to flow around the baffle and shows in Amir's Klippel measures. As we get much above 1000 Hz or so, the speaker more fully transitions to 2pi space and you are less likely to hear those resonances. Still might explain rippling between 1000-2000 Hz in Amir's results. The woofer has some known ringing around 7 kHz but the crossover kicks in and does not make an appearance (and at over 40 dB below is not audible and so did not show it).

Next will look at how adding some Sonic Barrier (per the designer) affects the port output.

 

[Rick Sykora]

Did not have the recommended 1/2 inch Sonic Barrier, but did have the more layered 1.25 inch, so used it and here is comparison to baseline...

Here we see some decent attenuation (black trace) from 280 to 500 Hz. For the more onerous resonance, about a 20 dB drop and ugly peaks get a haircut. Some additional tapering occurs from 1500 to 4000 Hz. As will see in later tests, this is one of the top results.

Next let's look how the other recommended damping (Acousta-stuf) does in comparison...

 

[Rick Sykora]

Here is about 36 g (a nice handful) of Acousta-Stuf compares. This enough to fill about half the cabinet when fluffed...

After seeing Sonic Barrier, this result (blue trace) is underwhelming. Notably if you were expecting more improvement as some suggest. We get some decent attenuation between 300 to 600 Hz, but aside from the notch around 1200 Hz, not much improvement on the critical problem area around 700 Hz. Above 2000 Hz, there is very little improvement.

EDIT: when the above result did not do as well as Dacron sheets, forced me to go back and use a more official quantity of Acoust-stuf: Here is the updated result:

Interestingly, with the larger amount of Acousta-stuf is almost identical to the Dacron sheet performance.

 

[Rick Sykora]

As for major expectations, next I tested (original) NoRez....

The good news is that it performs as well as the 1.25 inch Sonic Barrier (I posted a direct, detailed comparison in the NoRez alternatives thread). The bad news is that it not better than SB despite GR's claims and is slightly more expensive. It also required a custom build as it is not flexible enough to be applied via the woofer hole. So, you can ignore the slightly lower main port output as it is likely due to slight differences in the woofers between the units. Also, if you have done nearfield testing, you know how much even a millimeter of change in the mic distance can impact results. So all these tests have some margin for error as simply changing materials requires repositioning the DUT.

NoRez 2 has an even thicker layer for panel damping and so is likely even less flexible. GR has also changed the open cell foam to be less dense and without the nice top finish. Since it takes another cabinet to test, am less inclined to test it. Would be nice if GR showed some measurements. As Danny contracts the manufacturing, does he not even have the supplier test?

 

[Rick Sykora]

I found an error in some of my earlier testing so need to retest (all posts have been updated), but plan to show other damping materials like cotton blanket, Dacron sheeting, open cell foam and 3/4 inch Sonic Barrier. So more to come!

 

[Dave Zan]

... Measurements were taken in nearfield at the center of the C-Note port. The measurements are unsmoothed and gated at 200 ms (which yields 5 Hz resolution). ...

One question: If you take measurements near field, why restrict to 200 ms, why not, say 1 sec and have 1 Hz resolution?
200 ms will capture reflections out to ~110 ft/34 m, so it's practically useless to exclude room reflections.
If you have measured outdoors then you have captured the ground reflections anyway, and distant walls should be irrelevant compared to the near field.
Is it some aspect of REW that requires such a measurement technique?

Thanks for the data, would love to see rockwool or fibreglass comparison!

Best wishes
David

 

[Rick Sykora]

One question: If you take measurements near field, why restrict to 200 ms, why not, say 1 sec and have 1 Hz resolution?
200 ms will capture reflections out to ~110 ft/34 m, so it's practically useless to exclude room reflections.
If you have measured outdoors then you have captured the ground reflections anyway, and distant walls should be irrelevant compared to the near field.
Is it some aspect of REW that requires such a measurement technique?

150 ms is what have been directed to use from REW and tried 200 and it made no difference. So used 200 just as a point of diminishing return and yielded a nice, round 5 Hz resolution so stuck with it.

Thanks for the data, would love to see rockwool or fibreglass comparison!

I do not have rockwool but fiberglass is doable. I do not like working with it but will do for comparison since it has been a mainstay.

 

[Blumlein 88]

I know cabinet resonance is not your main concern, but I wonder if any of this transfers a bit more to the cabinet? Could you do some sort of simple test for that. Maybe laying the box on different sides till you find a spot or two with some resonance you can feel. Then maybe something simple minded like laying a cell phone on it using the built in accelerometer to get some quantified measures. Maybe just doing this once with the empty box and once with the good stuff like the Sonic Barrier and the stiff NoRez.

Easy to dream up testing for someone else to do. So whether you do this or not, know I like your testing this and it is good info you are providing everyone here. Thanks.

 

[terryforsythe]

Did not have the recommended 1/2 inch Sonic Barrier, but did have the more layered 1 inch, so used and here is comparison to baseline...

View attachment 391739

Here we see some decent attenuation (black trace) from 280 to 500 Hz. For the more onerous resonance, about a 20 dB drop and ugly peaks get a haircut. Some additional tapering occurs from 1500 to 4000 Hz. As will see in later tests, this is one of the top results.

Next let's look how the other recommended damping (Acousta-stuf) does in comparison...

Is this the sonic barrier you used?

Sonic Barrier 1-1/4" 3-Layer Acoustic Sound Damping Material with PSA 18 x 24"

Sonic Barrier 1-1/4" 3-Layer Acoustic Sound Damping Material with PSA 18 x 24"The Sonic Barrier 1-1/4" 3-layer composite damping material is a premium acoustic absorption and barrier material. It uses the three layers to achieve excellent reduction of sound energy from the inside of the...

www.parts-express.com

 

[Dave Zan]

150 ms is what have been directed to use from REW and tried 200 and it made no difference. 200 just a point of diminishing return and yielded a nice, round 5 Hz resolution so stuck with it.

Sorry, I don't use REW yet and I don't understand your comment.
Where does the "150 ms is what have been directed to use from REW" direction come from? I couldn't find it in the REW help when I did a quick check.
If you use a swept sine, which I believe is the REW default, then the time is a function of the sweep parameters.
Can you explain your set up?

I do not have rockwool but fiberglass is doable. I do not like working with it but will do for comparison since it has been a mainstay.

Thanks on the fibreglass, I don't like to work with it myself either but, as you say, it is a mainstay so a useful point of comparison.

Best wishes
David

 

[Chrispy]

For subs but thought I'd add a link to this thread along the same subject line https://data-bass.com/#/articles/5cace1c48c663e0004cd9ce2?_k=utreqa

 

[kyuu]

Thanks for this. Wish you could test rockwool but the fiberglass will be very illuminating also. I'm assuming that the same principles that apply here for speaker enclosures would also apply for wall cavities into which in-wall speakers are installed. I've been thinking of filling the wall cavities with either fiberglass or rockwool, and perhaps applying sonic barrier to the wall directly behind the speaker.

 

[teamrob]

Here is about 36 g (a nice handful) of Acousta-Stuf compares. This enough to fill about half the cabinet when fluffed...

View attachment 391747

After seeing Sonic Barrier, this result (blue trace) is underwhelming. Notably if you were expecting more improvement as some suggest. We get some decent attenuation between 300 to 600 Hz, but aside from the notch around 1200 Hz, not much improvement on the critical problem area around 700 Hz. Above 2000 Hz, there is very little improvement.

Cool, really love seeing practical experiments like this!

When using Polyfil I normally use around 8.5g a litre as a starting point, so 77g assuming the 9L internal volume for the C-note I found online is correct. It would be interesting to see if using that amount improved things at all for the C-note.

I've also been using carded lambswool recently so would be interested to see how that performs as it seems preferential for the environment to using a plastic.

You may have inspired me to do some testing myself, if I do I'll post the results in this thread.

 

[Rick Sykora]

Is this the sonic barrier you used?

Sonic Barrier 1-1/4" 3-Layer Acoustic Sound Damping Material with PSA 18 x 24"

Sonic Barrier 1-1/4" 3-Layer Acoustic Sound Damping Material with PSA 18 x 24"The Sonic Barrier 1-1/4" 3-layer composite damping material is a premium acoustic absorption and barrier material. It uses the three layers to achieve excellent reduction of sound energy from the inside of the...

www.parts-express.com

Yes, and looks as though I should call it 1.25 inch to avoid confusion with the single layer variant.

 

[Rick Sykora]

Sorry, I don't use REW yet and I don't understand your comment.
Where does the "150 ms is what have been directed to use from REW" direction come from? I couldn't find it in the REW help when I did a quick check.
If you use a swept sine, which I believe is the REW default, then the time is a function of the sweep parameters.
Can you explain your set up?

Will detail more in the OP when I am done with posting results. As REW has changed over time, the 150 ms “default” may have been deprecated, but yes it is swept sine.

 

[Rick Sykora]

I know cabinet resonance is not your main concern, but I wonder if any of this transfers a bit more to the cabinet? Could you do some sort of simple test for that. Maybe laying the box on different sides till you find a spot or two with some resonance you can feel. Then maybe something simple minded like laying a cell phone on it using the built in accelerometer to get some quantified measures. Maybe just doing this once with the empty box and once with the good stuff like the Sonic Barrier and the stiff NoRez.

Yes, but as I mentioned, would need to use the adhesive backing and then is difficult to swap. I also have a Sonic Barrier lightweight vinyl and some other materials marketed for reducing panel vibration. My plan is to do them as another test set on a longer panel as that is the target application and should apply to lower frequencies than the little C-Note. Due to "defects", I do have some extra C-Note cabinets and may be able to do some limited testing with one of them.

I am also planning to do some variations and combinations as my time allows. As @teamrob mentions, there have been rules of thumb for polyfil quantities and know it will be useful to show how little or so much material is used and whether it is more effective or not. For example, is it sufficient to cover just one each parallel side with Sonic Barrier? There are also different polyfil materials that could be compared.

Easy to dream up testing for someone else to do. So whether you do this or not, know I like your testing this and it is good info you are providing everyone here. Thanks.

Thanks and would expect nothing less from ASR members! And yes, the permutations may get overwhelming but am open to member proposals.

Plan to do my best to accommodate reasonable requests. Some of the damping materials are only available in larger quantities and/or are costly as well. So intend to accept donated damping material alternatives for testing eventually.

 

[sigbergaudio]

Interesting thread. I've found this type of material to be very effective (in several layers where necessary), do you have something like that and plan to include it in your testing?

Jantzen Audio Felt for speaker damping, 8 mm - Fidelity Components Shop

Jantzen Audio Sound absorbent Felt for speaker damping, 8 mm, by 1m2,

www.audiohobby.eu

 

[Thomas_A]

Good thread. Would be interesting to look at distortion at 1 meter as well. At least between worst and best, if time permits.

 

[Rick Sykora]

Interesting thread. I've found this type of material to be very effective (in several layers where necessary), do you have something like that and plan to include it in your testing?

View attachment 391811

Jantzen Audio Felt for speaker damping, 8 mm - Fidelity Components Shop

Jantzen Audio Sound absorbent Felt for speaker damping, 8 mm, by 1m2,

www.audiohobby.eu

I bought some acoustical felt to use for front panel diffraction years ago. It was not that effective and so applied it around the house for ventilation and other sound treatment. I should have enough to try on the C-Note.

Thanks for the reminder as felt is another mainstay and like more eco-friendly alternatives as well. 

P.S. may have just enough but if you want it tacked in place, will take some time to do.

 

[Rick Sykora]

Good thread. Would be interesting to look at distortion at 1 meter as well. At least between worst and best, if time permits.

Will consider but likely have to do under more controlled conditions. Have already found that my current room is less than optimal and will take some time and effort to do meaningful distortion testing (notably at longer distances).