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In Reply to: RE: PPSL hit box posted by moray james on July 27, 2014 at 15:20:49
"I am sure that there is some form of damping which could be included into the cavity and on the driver basket which would go a long way to help it's just a matter of experimenting. I am sure some significant improvement could be found. "
I have done extensive testing with a wide variety of materials in varying thickness: acoustical felt, cotton, fiberglass, polyfill, lamb's wool.
None of them provide a "significant improvement", all of them are capable of reducing a peak around 170 Hz, but also reduce the output level below that by a similar amount, net result is just less output, with a similar peak.
And a day's measurement work, and a lot of cleanup after...
Follow Ups:
Thanks Art: It's hard to imagine that the there is much ability to resonate within the plenum with a cone basket and a motor stuffed into the middle of it but it obviously has to resonate at some frequency and as you measured it does. Your observation that the damping you experimented with also caused a drop in output below 170 Hz is to me very interesting indeed. Perhaps that suggests that the resistive drag on the air flow is one possible issue within the plenum? Maybe attempts to breakup the resonances with reflectors or diffraction devices would be a more effective approach to stop the resonances while at the same time allowing free air flow within the cavity to. so the goal would be to have minimum air turbulence inside of the plenum. Tough to do but the first thing that comes to mind is to eliminate and minimize corners inside the plenum.
Thanks again Art for posting this info as it is so very interesting. Best regards Moray James.
moray james
Last night I lowered the crossover point of the low-pass section to my current ppsl's to 125Hz. It was 250hz before. This has minimized the cavity resonances quite a bit, so, I can only estimate they are somewhere in the area of around 200hz + -
This supports my earlier theory that these things (ppsl) are best served up as woofer duty only.
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