Subwoofer Design............

[speakeroligist_38]

Good morning people hope all is well with everyone. I just purchased (2) Acoustic Research powered subs that has an 8" driver AND a Passive Radiator. Have been told that because of this design the 8" sub can extend a little deeper than it would otherwise w/o the passive radiator. Is this true? A former co-worker has this sub and it does seem to play quite low for only being an 8" sub. It is also kinda punchy sounding which I prefer as opposed to being too boomy. Anyways, just wanted to see if any of you guys knew so I could understand sub woofer design a little better. Feel free to chime in people. Have a great day.

[kexodusc]

Yeah, your passive radiator is resonating, despite not being electrically connected to the amp or woofer, so it's emitting sound for free...not all that different from how a ported sub works...at the fundamental frequency, the 8" woofer is barely moving, and the passive radiator is doing all the work. The punchiness isn't surprising. PR's are sort of a cross between ported and sealed subs, and share a bit of the strengths of both.

[speakeroligist_38]

I understand a little better. Thanks Kex--will be sure to let you know how it all sounds when I get it set-up and run the YPAO.

[Geoffcin]

Yeah, your passive radiator is resonating, despite not being electrically connected to the amp or woofer, so it's emitting sound for free...not all that different from how a ported sub works...at the fundamental frequency, the 8" woofer is barely moving, and the passive radiator is doing all the work. The punchiness isn't surprising. PR's are sort of a cross between ported and sealed subs, and share a bit of the strengths of both.

It's unusual in that the radiator is 12" while the woofer is 10". I think they did that to break up any possible resonants betweent them. Like you said, it's a bit of both worlds in that the bass is nearly as tight as a sealed (acoustic suspension) cabinet, but with better extension & output.

[kexodusc]

The difference in size is between PR and woofer probably has more to do with desired mass/tuning than breaking up resonants...you use to see companies put little discs to mass load the passive radiators, but if the box is big enough, a larger, heavier woofer works better.
Cheap measurement setups and software are making PR's really popular in the DIY world again...their use to be too much trial and error, but now it's not so bad.
Wish there were more PR's in speakers, period. The 2.5 way seemed to have replaced them though.