Originally Posted by kryptonitewhite
Oh yeah, huh... it's not the driver creating the port resonance with the driver making it at that frrequency... helmhertz? Got it
PRs have resonance don't they? Or is that just at the tuning?
The helmholtz resonance of either ports or PRs is not a problem.
The problem is the quarter wave resonance of ports and transmission lines.
Now with TLs you actually use the first QW resonance to augment the slope in driver response, and stuff the whole line with polyfill adequately to cut higher harmonics until they're down to +/- 1db at which point we can effectively call them inaudible. The tradeoff is a loss in line efficiency but the sloping response tends to work decently enough in rooms. For main speakers that means any line harmonic are NOT audible!
Not many people stuff their ports like that, especially not a for a sub optimized to only operate with a low pass filter at 80hz or 100hz for max output. The port is only there to be a pressure loaded mass of air, and any QW behaviour is just a side effect. In that sense, using a mass of something else that won't have such a side effect does make sense. I'm sure there's other small resonances higher up in frequency (IE 400hz?) but i'm not sure they'll be excited because Passive Radiators barely move so high up in frequency.
Now one might say a 140hz vent QW resonance (of a 48" long tube) is a problem. But an 80hz 4th order low pass is pretty significant imo. Here's an example of a speaker with a 110hz vent resonance:http://forums.audioholics.com/forums...4&postcount=58
And that guy claims he doesn't hear any vent resonance.