Speaker damping paint/coating

perkri

Member
2017-12-05 7:59 pm
Hi.

Been looking all over for some answers to what would work as a damping spray/paint/coating for the interior of the enclosure?

Not sure if this is even something that should be done?

Not like it'll be easy to remove once applied.

I've built two sets of speakers from plans off the Frugal-Horn site Double mouth BVR's

(Kongo and Kirishima)

Want to coat the interiors to deaden the "boxes"

Has anyone done this?

If so, what materials have been used and to what effect?

Thank you in advance,

Per
 

Attachments

  • IMG_4756.jpg
    IMG_4756.jpg
    406.1 KB · Views: 357
  • IMG_4814.jpg
    IMG_4814.jpg
    948.7 KB · Views: 355
You are aware that this is more or less the inverse of the design intention?

You cannot erradicate panel resonance. Not in this physical reality. All you can do is move its Fs and harmonic modes to a region where they are less likely to be excited, i.e. preferably outside the main operating BW of the enclosure. Which gives two options, down or up in frequency. The former requires very large quantities of mass (concrete levels) in order to move the panel Fs and its harmonic modes sufficiently below the operating BW of a bass enclosure for them not to be triggered. The alternative is to increase panel rigidity sufficiently to push the panel Fs significantly above the operating BW of the enclosure (which also raises its Q) where there is little energy left to excite it. Adding significant mass to the panels of this enclosure simply lowers their Fs toward the region where it is more likely to become excited.
 
Another way is to use a design that lessen the impact of resonant behaviour, or to make internal surfaces that to various extent helps direct the internal resonances away from the driver.

This is more or less what Scott here is saying.
Pending on the design, some BLH's can be great at that. Intentionally directing the energy to something useful, as opposed to something unwanted.
Sealed TL's is another example, but they work more towards dampening the internal reflections rather than making them more useful.

Otherwise:
If you have a sub, you'd want to brace it to get a higher resnonance than the band of frequencies you're using it for.
If you have a "top" or small FR box/enclosure, you'd ideally also want to get the resonance outside of the intended passband, but it can be more difficult since making a box with lower resonance in some cases make things worse. Internal braces with reflective surfaces can in some cases help direct the energy away from problem areas, but it can be difficult to plan for small details like that.

In a hurry so don't have time to look things over, or elaborate further...
 
What i did in my 2 way WAW setup, is making the top following the bbc principle (mass loaded lossy cabinet) where the front and back are screwed with rubber seal in between on the cabinet and the rest is damped with bitumen to bring the reonance frequency outside the passband (<200Hz). The cabinet has to be made from thinner plywood (i used 12mm).

The sub is reverse, 18mm plywood and heavy braced to bring the resonance up to above the passband (> 300Hz). The crossover between the two seperate boxes is at 250Hz now (after a lot o tinkering to get it right).

This worked out better than i expected. The sound is way more open than the same drivers with more or less the same crossover in the previous version.

But like said before, with the speakers you build, the resonance of the cabinet is inherent to the design, so damping it will mess up the sound.
 
I think we need to be a little careful here to distinguish what is under discussion. The question was about panel damping, not acoustic damping. These are functionally very different matters (and I should add that these enclosures were certainly not designed to have audible panel resonance).

Adding panel damping (mass damping) will not significantly alter the acoustic behaviour of the horn. All it will do is lower the resonant frequency of the panels -likely to a region where they are more, not less, likely to be triggered and cause unwanted audible colouration. Adding acoustic damping (e.g. various felts, fibreglass, jute, stuffing etc.) conversely will damp the acoustic output of the horn, which was not what was being asked.
 
Last edited:
Because he's asking if previously mentioned "silly paint" will make any meaningful difference. That's why it's not about the 'energy distribution, handling or dampening'. A piece of aluminium foil glued to a surface will have more impact, still nothing to write home about and also irrelevant.
If it helps you feel better it's more about what does not help, or make close to insignificant impact on 'energy distribution, handling or dampening'.
 
Really? The OP asked about damping paint. Quote:

Want to coat the interiors to deaden the "boxes"

Has anyone done this?

If so, what materials have been used and to what effect?

Close quote.

That is a question that is specifically about 'energy distribution, handling or dampening', unless we have entered an alternate physical reality where panel damping of any kind is, by some osomosis previously unbeknown to woman-born, unconnected to such matters. The degree of effectiveness is irrelevant to that fundamental starting point. Thus, before you joined the thread, the gentleman received several replies to his question, which had already covered what was required, the essence of which can be distilled into two basic points:

1/ These enclosures do not require panel damping, which will be counter productive, and

2/ Paint of the types commercially available will have no practical impact upon panel resonance (aka 'energy distribution') anyway.
 
As a couple of general notes on that:

-Bracing does not increase damping in the ordinarily understood sense. It just increases the resonant frequency of a panel of a given material & dimensions (and raises the Q of that resonance).

-Bitumen applied to a panel adds mass, and thereby lowers the resonant frequency (and Q of that resonance).

As a result, you have to be careful if you do both, since one counteracts the other. You add bracing to increase the Fs of a panel, and then by coating those panels with bitumen, you lower the panel Fs back down again. ;) A small amount strategically placed may be useful, but it depends on the type of enclosure. With the speakers in question, the object is to shunt panel Fs as high as possible. They don't need additional bracing if a quality grade of void-free ply is used as the internal horn structure already provides that.

Basotect has decent acoustic damping properties; these enclosures were designed for a minimal quantity of acoustic fibreglass board, natural-fibre felt (wool, jute, recycled denim etc.) but it would serve as an alternative.
 
Life's too short -crack open your choice of refreshment and try to forget the lunacy that's going on around us all at present. :drink:
Indeed, but what I meant was: That's what I get for not reading stuff and posting replies when I'm in a hurry.

I favour watching The Grand Tour. ;)
Just barely had the time to note your reply whilst on the airport, was deeply disappointed when it turned out there's nothing new since that 1st episode on 4th season...

The James May going to Japan thing was pretty good though, was sort of funny when he was trying his hand on piano tuning.
 
Last edited: