The use of mass damping in enclosures

[jim85iroc]

Dynamat and similar products have been used for years to damp resonances in steel body panels in cars. I also use it to stiffen & damp my fiberglass kick panel enclosures, and it seems to deaden them very well. Has anybody lined the inside of a speaker box with it? I recall reading an article a number of years ago, maybe in Voice Coil, that stated something along the lines that lining your enclosure with this stuff can increase resonance compared to raw MDF, but that doesn't really make sense to me.

I've got a couple enclosures that I'm building for a set of Recession-Buster-Reference speakers (Woo!, I'm finally building them) that I'd like to dampen, but before I do I want to make sure I'm not doing more harm than good. Likewise, I'm going to be building a small center channel speaker for my parents with 1/2" MDF, and due to the thinner walls, I'd like to use some mass damping.

[Pete Schumacher]

Re: The use of mass damping in enclosures

Dynamat and similar products have been used for years to damp resonances in steel body panels in cars. I also use it to stiffen & damp my fiberglass kick panel enclosures, and it seems to deaden them very well. Has anybody lined the inside of a speaker box with it? I recall reading an article a number of years ago, maybe in Voice Coil, that stated something along the lines that lining your enclosure with this stuff can increase resonance compared to raw MDF, but that doesn't really make sense to me.

I've got a couple enclosures that I'm building for a set of Recession-Buster-Reference speakers (Woo!, I'm finally building them) that I'd like to dampen, but before I do I want to make sure I'm not doing more harm than good. Likewise, I'm going to be building a small center channel speaker for my parents with 1/2" MDF, and due to the thinner walls, I'd like to use some mass damping.

It can only help damp resonance. There are cheaper alternatives to Dynamat that will do the same thing, add constraining to control panel resonances.

You still need stuffing to control interior standing waves.

[jim85iroc]

Re: The use of mass damping in enclosures

It can only help damp resonance. There are cheaper alternatives to Dynamat that will do the same thing, add constraining to control panel resonances.

You still need stuffing to control interior standing waves.

Sure there are cheaper alternatives... like the roll of Peel & Seal that I intend to use.

I just want to make sure that I'm not doing more harm than good before I stick this crap on, because once I do, it's a done deal. I can't imagine that it would have any negative effects, especially on the 1/2" enclosure.

[billfitzmaurice]

Re: The use of mass damping in enclosures

I just want to make sure that I'm not doing more harm than good before I stick this crap on, because once I do, it's a done deal.

You're not doing more harm than good, but wasting money? Probably. The best resonance control comes from panel to panel bracing. Using products like you mention are alternatives to employ when you can't use bracing, as inside a car door.

[jim85iroc]

Re: The use of mass damping in enclosures

You're not doing more harm than good, but wasting money? Probably. The best resonance control comes from panel to panel bracing. Using products like you mention are alternatives to employ when you can't use bracing, as inside a car door.

Bracing will be employed too, but because I make my front baffles removable, I really can't brace them. I want to be able to damp the front & rear baffles.

Likewise, I'm throwing together a cheap center for my parents, and I'm using 1/2" MDF to keep the size down. I figured that a little bit of mass damping in that enclosure can help. I have plenty of peel & seal around, so it's really not going to cost me anything.

[jbruner]

Re: The use of mass damping in enclosures

Do yourself a big favor and bond some aluminum sheet to the damping layer. I used 1lb vinyl barrier and some 0.025" thick aluminum on 1/2" mdf. The results are impressive. It is much, much more effective than the damping layer alone.

[Bob Brines]

Re: The use of mass damping in enclosures

Before I got hammered to death for using MDF (amongst the single-driver crowd, nothing but Baltic birch is acceptable), I built a lot of cabinets with 1/4" HardiBacker (a cement board) Liquid Nailed to 3/4" MDF. Very dead cabinets.

Bob

[charlielaub]

Re: The use of mass damping in enclosures

Before I got hammered to death for using MDF (amongst the single-driver crowd, nothing but Baltic birch is acceptable), I built a lot of cabinets with 1/4" HardiBacker (a cement board) Liquid Nailed to 3/4" MDF. Very dead cabinets.

Bob

It is important not to confuse panel bracing with panel dampening. Bracing mostly adds stiffness, which just shifts the panel resonance frequencies upwards and doesn't dissipate any energy so resonances remain.

Panel dampening aims to dissipate the resonant energy and reduce transmission of sound through the enclosure walls to the outside. Bob's suggestion of MDF outside walls with HardiBacker board bonded to the inside using a rubbery adhesive is a very good approach to dampening. You need a "stiff-compliant-stiff" type sandwich to maximize loss/damping and these materials provide that.

-Charlie

[davepellegrene]

Re: The use of mass damping in enclosures

On the lines of using harid backer for damping. I am using this product for tile backer on the floor of the job I am doing know. You still put it down like hardi backer with a troweled layer of thin set then a layer over top to set the tile. Nice thing with this product is it cuts real easy with a razor blade knife. Doesn't get nailed down and I think the plastic may work as a constraining layer. I have been using the torch down roofing in my cabinets. I was thinking about putting the Shluter-Ditra over the torch down but not really sure how well it would stick. Maybe heat the torch down up then stick the Ditra into it. Then a layer of thin set. The idea is to try to keep the weight down.

Dave

[billfitzmaurice]

Re: The use of mass damping in enclosures

It is important not to confuse panel bracing with panel dampening. Bracing mostly adds stiffness, which just shifts the panel resonance frequencies upwards and doesn't dissipate any energy so resonances remains.

A sufficiently stiff enclosure doesn't need to dissipate energy, since the panel simply can't flex enough to result in coloration. IMO if you can't brace the cab adequately to eliminate panel flex coloration then by all means damp it out, but bracing should be the primary means of coloration control. That's because energy that must be dissipated within the enclosure is energy that's not realized as sound outside the enclosure.

[davepellegrene]

Re: The use of mass damping in enclosures

This is what caught my eye and gave me the idea.

a) Uncoupling
Tile has been successfully installed for thousands of years by incorporating an uncoupling layer, or forgiving shear interface, within the tile assembly. Schluter-DITRA provides uncoupling through its open rib structure, which allows for in-plane movement that effectively neutralizes the differential movement stresses between the substrate and the tile, thus eliminating the major cause of cracking and delaminating of the tiled surface.

[charlielaub]

Re: The use of mass damping in enclosures

A sufficiently stiff enclosure doesn't need to dissipate energy, since the panel simply can't flex enough to result in coloration. IMO if you can't brace the cab adequately to eliminate panel flex coloration then by all means damp it out, but bracing should be the primary means of coloration control. That's because energy that must be dissipated within the enclosure is energy that's not realized as sound outside the enclosure.

Even with a well braced, stiff walled enclosure, if you play a 300+ Hz tone and put your ear up to the walls they will be singing. For low frequencies, e.g. under 100 Hz, yes bracing alone is fine. But higher frequencies are not removed by even lots of bracing unless there is some damping because the resonances are still there.

Art Ludwig has some interesting observations and comments on panel damping here:
http://www.silcom.com/~aludwig/Loudspeaker_construction.html#Panel_vibration_damp ing

He ends with a reference to some info on constrained-layer damping, which is a good read:

http://www.earsc.com/pdfs/engineering/CLD.pdf

-Charlie

[critofur]

Re: The use of mass damping in enclosures

Sure there are cheaper alternatives... like the roll of Peel & Seal that I intend to use.

I just want to make sure that I'm not doing more harm than good before I stick this crap on, because once I do, it's a done deal. I can't imagine that it would have any negative effects, especially on the 1/2" enclosure.

In fact, based on limited testing I have done peel-n-seal benefits 1/2" panels more than it does 3/4" panels.

Even with a well braced, stiff walled enclosure, if you play a 300+ Hz tone and put your ear up to the walls they will be singing. For low frequencies, e.g. under 100 Hz, yes bracing alone is fine. But higher frequencies are not removed by even lots of bracing unless there is some damping because the resonances are still there...

Calculate the resonant frequency based on the speed of sound in the material and the length.

If you want to make a great enclosure then here's one good idea: space braces sufficiently close so that no panels resonance is within the passband. Also, vary the sizes of panel sections between braces so that they will resonate at different frequencies.

Bracing will be employed too, but because I make my front baffles removable, I really can't brace them. I want to be able to damp the front & rear baffles...

I would still not neglect bracing the front panel, as it is both facing you, and, the closest. Just because it's removable doesn't mean you can't brace it.