Damping materials

[MT_bassbone]

I am working on a speaker build and the plans call for a combination of two 2mm thick sheets of alubutyl and 3mm hardboard (inner most layer) to be applied to inner walls of the boxes followed by 20mm of foam all over the inside. There is also a blanket of damping behind the tweeter in the upper part of the box. Would there be any measurable difference using the 3-layer foam product available at Parts Express?

https://www.parts-express.com/Sonic...ing-Material-w-PSA-18-x-24-260-535?quantity=1

I am guessing the answer is likely not much. Similar to the Baltic Birch vs MDF argument for cabinet materials. I am using BB for this build.

If there is a huge difference, educate me.

 

[CptKaos]

" If there is a huge difference, educate me."
dampening = making something wet
damping = vibration reduction

 

[MT_bassbone]

" If there is a huge difference, educate me."
dampening = making something wet
damping = vibration reduction

Good point CptKaos. Pardon my Montana public school education. LOL. I updated the post.

 

[a4eaudio]

Or not...

 

[NTK]

We do have a thread on this topic.

A comparison of the effectivity of various speaker damping materials

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...

www.audiosciencereview.com

 

[a4eaudio]

I am working on a speaker build and the plans call for a combination of two 2mm thick sheets of alubutyl and 3mm hardboard (inner most layer) to be applied to inner walls of the boxes followed by 20mm of foam all over the inside. There is also a blanket of damping behind the tweeter in the upper part of the box. Would there be any measurable difference using the 3-layer foam product available at Parts Express?...
...I am guessing the answer is likely not much. Similar to the Baltic Birch vs MDF argument for cabinet materials. I am using BB for this build.

There is probably very little difference. If it were me, I would use cheap butyl rubber sound deadening material by Amazonbasics and the 30mm Acousta Blue denim damping material from parts express.

Note that the butyl rubber and the hardboard called for in the plans reduce the volume of air in the cabinet, whereas open cell foam and the denim material doesn't. So not having the 3mm hardboard will give you a little more air volume in the cabinet, You can calculate the approximate difference and it is likely only a small % of the cabinet volume, unless it is a very small speaker.

 

[Fledermaus]

But, but, if you omit the [outer shell/butyl/thin hardboard] sandwich, you'll miss the constrained layer damping likely intended in the design - is it a great loss, I don't know.

 

[Wolf11Man]

While the hardboard layer doesn't help that much, the aluminum-butyl stuff has a huge effect in keeping the outer panel silent. It works because the viscous butyl is covered by the tensile-resisting aluminum. I would use it. Ideal is a 3mm thick version, if you only get thin stuff, you may double up. It is a good idea to put some primer on the inside panels before applying the self adheasive alubutyl. Just use some left over paint you sure have and let dry over night. The effect strongly depends on the bond of the viscous layer on the panel. Raw BB doesn't bond well.
Don't use any bitumen based stuff, it doesn't work the way alubutyl does.
The 20mm foam can be replaced by the sonic barrier material. The effect is is mainly for higher frequency, reducing reflections inside. You can also use some denim stuff. Just be sure to fix it with some kind of elastic glue. SIKA products like Sikaflex are perfect for the job, working on aluminum and fibers as well. It stays elastic, cures fast and is impossile to remove.
The blanket behind the tweeter will be polyester fiber I guess. It forms a kind of acoustic sump which reduces the resonance of the cavity. Can be replaced by Rockwool or similar.
Using baltic birch or MDF is more a question of price. In my part of Europe BB is completely overpriced, just like any wood material.
I use both, depending on what I get and how the finish is planed.

 

[MT_bassbone]

Are the Amazon brand aluminum butyl sheets any good? They are certainly cheaper. I have the PE foam discussed above and also the shredded denim for the upper part of the cabinet behind the tweeter.

 

[a4eaudio]

The Amazon Basics isn't very clear on how thick it is, but the main complaint in negative reviews is that it is not as thick as Amazon claims. I believe it is supposed to be 1.5 to 2mm and it is questionable whether it is that thick.

You can get Siless branded product in 80 mil (2mm) 120 mil (3mm) and 157 mil (4mm) thickness. The branded product is quite a bit more expensive, but probably a case of "you get what you pay for". The question of how much those thicknesses matter is unanswered. The tests I have seen using either an accelerometer or a measurement mic have not reported measurable differences with/without butyl mat. However, I know several people who say they can tell an audible difference - and these are not the people who believe in Snake Oil products.

 

[alex-z]

The question of how much those thicknesses matter is unanswered. The tests I have seen using either an accelerometer or a measurement mic have not reported measurable differences with/without butyl mat.

I modded some Celestion 5 MKII bookshelf speakers last year, including 2mm butyl sheets. Specifically the Amazon Basics 14.5x10", 2mm thick when checked with calipers.

For context, these are speakers with 12mm particle board cabinets. Expect less dramatic differences with better materials like 19mm MDF.

That is the cabinet side with a piezo pickup. Woofer being driven with no crossover. Most improvement in the 1000-4000Hz region can be attributed to the butyl sheets. 3 small braces help the 200-1000Hz region and 12mm felt helps above 5000Hz.

The on-axis SPL is perhaps more telling. There is 3-4dB of smoothing in the mid-range, indicating that any remaining resonances are low Q value.

Anecdotally this made female vocals, woodwind instruments, and piano sound significantly more defined.

For modifying existing speakers I think it works great. For new builds I prefer a thicker CLD design, something like 3mm neoprene sandwiched between 12mm MDF walls provides significantly more damping.

 

[JohnnyNG]

Just use some left over paint you sure have and let dry over night. The effect strongly depends on the bond of the viscous layer on the panel. Raw BB doesn't bond well.

Thanks for this as I'll be applying some 4mm alubutyl to a couple of my DIY BB cabs. Stuff worked really well on my Ikea salad bowl spheres.

 

[Wolf11Man]

For modifying existing speakers I think it works great. For new builds I prefer a thicker CLD design, something like 3mm neoprene sandwiched between 12mm MDF walls provides significantly more damping.

Neoprene is no viscous material. It will not have the damping effect of butyl. Neoprene is more of a spring type of material, flexing back when pushed in. It could make sense for the 4th layer in a speaker
The way the alubutyl works is the combination of a very viscous liquid and the tensile strength of the aluminum layer. Solidly glued to the 3rd layer, in this case the outside made from wood, it takes up its movements/ resonances in the viscous butyl and converts them into heat.
You do not get that from Neoprene, so you only have a sandwich, but no CLD. Just like bitumen or rubber, which is not viscous like butyl.
The great advantage of alubutyl is its relative low weight and very little volume. You sure can get compareable results from other constructions, but usually with more volume and weight.
This has nothing to do with speaker voodoo, but is a very common problem solver for weight critical noise problems, for example on passenger ships. Also, (alu-) butyl is no expensive material. Of course that changes when it is sold for DIYS...

 

[Chrispy]

Might like this article https://data-bass.com/articles/5cace1c48c663e0004cd9ce2