Passive radiator phase question

jimbo1421

Hello,

This question has bugged me for awhile. If one does the press test on a midwoofer the passive radiator is pushed out by the air pressure. So when the MW is pulled inward in response to an audio signal the passive radiator is pushed out, right? Does this mean that it is out of phase with the MW? If so, does it matter at all that it is not in phase? Inquiring minds want to know.

Regards,

Jim

MillerLiteScott

This has also bugged me. But after noodling it through a little knowing that a PR is an expensive port. If I understand it correctly with my little brain, what the PR is doing is reflecting the back side excursion of the active woofer similar to the port is venting the back side excursion of the active woofer in a ported design.

Am I correct?

Scott

FTGV

jimbo1421 wrote: »

Does this mean that it is out of phase with the MW? If so, does it matter at all that it is not in phase?

As with a port it will be in phase with the driver over a small range of frequencies above their tuning point,then progressively going out of phase with the midbass below that.

skrol

A related thought ...
I have wondered about time / phase delays between the MW's vs the PR in arrangements like the RTA11TL. For example, the top MW is farther away from the PRs than the bottom MW. Configurations like the Monitor 10 would not have an issue as both PRs are equal distances from the PR.
Stan

FTGV

skrol wrote: »

A related thought ...
I have wondered about time / phase delays between the MW's vs the PR in arrangements like the RTA11TL. For example, the top MW is farther away from the PRs than the bottom MW. Configurations like the Monitor 10 would not have an issue as both PRs are equal distances from the PR.
Stan

Relative location of the midbass's wouldn't matter as the PR is excited by their combined back wave or pressure.

FTGV

Here is some good info regarding PR's.http://www.aespeakers.com/PRFAQ.php

yepimonfire

there was a really good illustration on how this works, but i forget where to find it. no it is not out of phase whatsoever. above the tuning frequency, the port does not pick up the energy, the woofer does, at the tuning frequency, the woofer barely moves as the energy is directed to the port, below the tuning frequency, the driver behaves as if it is out of the box, which causes ported and passive radiator cabinets to have an extremely steep roll-off below the tuning. a sealed box with LF extension of 40hz will drop at about 3-6dB an octave where-as a ported one drops 12-24 dB an octave and eventually has no useful output below a certain octave. for example my PSW10 is tuned at about 35hz, at 30hz the driver produce only a slightly audible sound and it vibrates erratically, below 30hz there is absolutely no audible output and the driver unloads. i had a sealed KEF sub once that had a -3dB response to 35hz but it would play audibly at 15hz (i am still young enough to hear 15hz) ports are a trade off but they gain an extra octave at least. if my PSW10's driver was loaded in a sealed box it would probably roll off at 45hz.

heiney9

FTGV wrote: »

Here is some good info regarding PR's.http://www.aespeakers.com/PRFAQ.php

Great link; adding it to my favorites.

H9