Cabinet resonance - when and why NOT to fight it? - diyAudio
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Old 8th March 2011, 07:28 PM   #1
hebrer is offline hebrer  Slovakia
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Default Cabinet resonance - when and why NOT to fight it?

Hi, the usual wisdom for speaker cabinet building holds that the more one can eliminate cabinet resonance, the better. The theory is that the only thing than should resonate is the driver diaphragm/cone and everything else should be damped and as made rigid as possible.

Having recently done some reading on Bud Purvine's approach to cone treatment and some more reading on resonances at Mother Of Tone presents: The Altmann BYOB Site, I wonder if there are people in DIYAudio community who tried not to eliminate/reduce cabinet resonances but rather accepted them and tried to make the best use of this acoustic phenomenon.

Clearly, a speaker cabinet is different from a musical instrument which relies on resonances to achieve its characteristic sound, but there are still people who believe that using wood (e.g. birch plywood) makes speaker cabinet sound more "musical" than MDF or concrete or other artificial material...

In addition, there is the issue of lacquer/finish of wood which has impact on the sound.

Has anyone here done some off-the-mainstream experiements in this direction? What were your results?

Thank you for sharing...

Peter

P.S. I should mention that personally I prefer to listen with my ears than with measuring instruments. Therefore, I am not against "colored" sound if it is pleasing. Also, having wonderfully linear response curve in anechoic chamber (or other not real-life scenarios) is less relevant for me.
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Old 8th March 2011, 07:50 PM   #2
chrisb is offline chrisb  Canada
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oh boy, here we go again
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Old 8th March 2011, 07:55 PM   #3
hebrer is offline hebrer  Slovakia
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Hi Chris,
the automatic suggestions of diyaudio when I started this topic were all related to *eliminating* resonances - I could not find anything similar to the topic of working with resonances. Your reaction would indicate you are able to direct me to some (perhaps controversial) threads on this topic... If so, that will be appreciated.
Peter
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Old 8th March 2011, 08:17 PM   #4
hebrer is offline hebrer  Slovakia
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Chris,

perhaps a sub-question closer to home to your views: some time ago I built a pair of Metronomes with enabled Fostex FE127eN drivers. I used 3/4" birch plywood.

All panels of plywood had a synthetic lacquer finish both inside and outside. What differences (if any) might be expected if a finish using natural resins would be applied (e.g. dammar lacquer or similar)? How about selective placement of enabl patterns on speaker panels?
Peter
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Old 8th March 2011, 08:19 PM   #5
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Run a search & you'll find dozens of the damn things all over the place, either in threads on other topics, or with dedicated threads.

Best discussion is here: Wood & Varnish

Eliminating cabinet resonance is a bit of a misnomer TBH, because you can't. Therefore, assuming that you wish your loudspeaker to reproduce what is on the recording and not add colourations of its own devising, it becomes a matter of controlling the panel resonance, i.e. pushing it to a region where there is less energy available to excite it, and it is thus more easily rendered inaudible. Effectively that means above or below the functional BW of the cabinet. Below is impractical for a bass enclosure since the lower the panel Fs the greater is its BW and amplitude. Typically it's easier to go for panels with a high stiffness to weight ratio which will lift their natural resonant BW above the box's operating zone, where there is very little energy available to excite them, and thus it is very easy to render it ~inaudible with a minimal amount of damping.

If we're talking about a box that is deliberately designed to resonante / designed like a musical instrument, we're into deep subjective territory. Since properly controlling such resonances is beyond the facilities of the average DIYer (and most speaker companies), the blunt fact is that any such resonances are thus a distortion / colouration of the original content. It might be euphonic distortion / colouration, but it's still distortion / colouration.

Last edited by Scottmoose; 8th March 2011 at 08:25 PM.
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Old 8th March 2011, 08:28 PM   #6
hebrer is offline hebrer  Slovakia
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Thank you Scottmoose for your response. The discussion at the link you gave is very informative and very much what I was looking for.
Peter
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Old 9th March 2011, 11:15 AM   #7
DrBoar is offline DrBoar  Sweden
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If you buy into the laquer religion there are many faith healers around to pick from. From an engineering perspective there are several solutions/compromises. If the bassdriver is also the midrange driver you can have thin walls 9mm plywood and thick damping material like the Spendor BC1. The resonances are taken down from the very important midrange into the bass range were it does less harm. The price to pay is less definition in the bass range. In a 3 way system the bass can cabinet can be made very stiff to keep it above the used range. The german magazines Klang & Ton and Hobby &HiFi have done extensive measurements to measure the effect of different cabinet material, differerent braces and different laminations. There is also some on the net on this subject.
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Old 9th March 2011, 05:03 PM   #8
hebrer is offline hebrer  Slovakia
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Apparently some people must hold some pretty strong opinions on this issue if it warrants the label of "laquer religion" I never guessed simple curiousity could put someone at risk of being associated with this "religion"

Thank you for the reference to Klang & Ton and Hobby & Hifi.

It seems people are very particular where they direct their beliefs in the audio hobby - in measurements, crossover voodoo, cabinet varnish etc. etc. etc.

I love the sheer number of topics to be discovered as upgraditis develops
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Old 9th March 2011, 05:13 PM   #9
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by hebrer View Post
Chris,

perhaps a sub-question closer to home to your views: some time ago I built a pair of Metronomes with enabled Fostex FE127eN drivers. I used 3/4" birch plywood.

All panels of plywood had a synthetic lacquer finish both inside and outside. What differences (if any) might be expected if a finish using natural resins would be applied (e.g. dammar lacquer or similar)? How about selective placement of enabl patterns on speaker panels?
Peter

My earlier eye-rolling was in anticipation of the thoughtful discussions and cheerful consensus that generally follow such an innocent query as in your OP . In other words, "no, actually"

There are lots of folks with different reasons for sealing/finishing all exposed interior panel surfaces, whether overlaid with absorbent damping materials, mass loaded or constrained layers. As I've not experimented or auditioned any such, I can't comment other than "that'd be a lot of extra work".

Dammar varnish is part of Dave's treatment regime for certain Fostex drivers, but I've not personally experienced it for any other purpose. My use of lacquers is restricted to top coat on finishing of veneered speaker cabinets and furniture, and after trying a couple of water based and polyurethanes, have settled on sprayed catalyzed nitro-cellulose lacquer for ease of application and quality of finish.


Yes, I have heard what selective EnABL patterns can do on the front/side panels of speaker enclosure. At least when applied by Bud, they further assisted a Fostex FE127E/Fonken enclosure's "disappearing act". Quite a few others have reported the same experience with other designs.
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Old 9th March 2011, 06:37 PM   #10
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Lacquer, varnish, or paint does not have nearly enough mass, stiffness, or damping effect to make any audible difference on something as heavy and stiff as a typical loudspeaker box. The only way I can think or that it might make a difference is by sealing out moisture. But that is a stretch.

I play saxophone. Many players believe the lacquer on a sax affects its sound. It does not. However, re-lacquered horns are suspect for good reason. The process requires buffing. Buffing enough to remove normal scratches can affect the sound. I know from experience. I told the @#$%^& guy not to buff the scratches out. A perfectly good vintage Selmer SBA tenor came back from the shop thin as an eggshell and ringing like a bell. I sort of got off track, didn't I?
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