A comparison of the effectivity of various speaker damping materials

[RickS]

Still waiting on the snow test.

oops, your timing is bad, our temps are going to 45F tomorrow. 

 

[Groove01]

all panels

Thanks!

 

[Scott Lanterman]

oops, your timing is bad, our temps are going to 45F tomorrow. 

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 (zero distance). 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....

View attachment 391678

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.

Hi Rick,

These are interesting measurements. As a never built a speaker before person I think the first step of the journey would be to understand how to replicate these measurements. Is there a more detailed how to on how to replicate this and the set up needed? For me I am more fascinated to learn the engineering then anything else and the process of getting to high performance.

 

[RickS]

Hi Rick,

These are interesting measurements. As a never built a speaker before person I think the first step of the journey would be to understand how to replicate these measurements. Is there a more detailed how to on how to replicate this and the set up needed? For me I am more fascinated to learn the engineering then anything else and the process of getting to high performance.

The equipment and conditions I used are described in the OP. You do have to be very consistent at keeping the mic at the same distance. As for replicating for learning purposes, not sure the value in it. You would need to buy and build C-Notes and obtain the different damping materials. I had to tear down my test rig a few times, so am confident the results can be replicated. This thread is also one fairly narrow aspect of speaker design.

There are a few good books on speaker design and building that would be a better way to start. Measuring your exisiting speakers in room is also a good start. If you have not already done so, get a copy iof REW software and a USB mic and start taking some measurements.

 

[cavedriver]

Acousta-Stuf has pretty informational data sheet…

https://www.parts-express.com/pedocs/manuals/260-317--acousta-stuf-polyfill-1lb-bag-user-manual.pdf

Only lacks an NRC but suspect that may have to do with its form factor. They do supply NRC info for the denim…

View attachment 399527

All those products that are used for sound absorbing panels for studios and walls in homes have curves like that, where the main difference is how far into the bass frequencies the product absorbs, with thicker laying materials generally going lower- so 2" of batting behind a fabric screen goes ~200 Hz lower than 1" of batting for example. Reminds me that I have a hallway in my house that connects a bunch of rooms where I'd like to cover the walls in denim or something to kill sound transmission...

 

[RickS]

With the Ohio tax holiday picked up more Acousta-Blue. Had some Amazon gift money to spare and bought the Frost King equivalent. Frost King was inexpensive (on sale for $10), but you get enough for a couple of bookshelf speakers. It is much thinner (10mm vs 20mm) than Acousta-Blue and so easier to use in smaller spaces. Quality seems about the same.

After I get done with bass module effort, will do a measurement comparison.