Passive Radiators

[Guenter]

I had come to know about Passive Radiadors through JBL in the
60's. I know they have meanwhile fallen out of favour when
compared to the performance of vented boxes - except for very
special applications such as when the duct dimension won't fit
the speaker box. I would be very interested to read JBL's take
on things while they used them. Although I've tried, I can't find
any literature about these on the 'Lansing Heritage' site. Is it
there by chance and I'm simply not finding it?

Thanks for any help

[4313B]

I couldn't find anything in the Library. I'll try to find my old passive radiator instruction manual, scan it, and send it to Don. I really liked the PR8 and PR10 based systems back then. The PR300 in the L150/L150A wasn't half bad either In general, I wasn't real enamored with the PR15x, although the L220 was pretty decent.

I think GordonW has experience with modern passive radiators.

[GordonW]

Well, as was said, the vast majority of PR applications in modern times, have been to deal with an otherwise impossible port. Though, given this, I'd hedge to say, that the speakers using these PR's, probably sound BETTER than they could, even IF a port COULD have been used. My favorite example of this breed, at the moment, is the Boston Acoustics PV1000 subwoofer... a 10" woofer, a 10" PR, both EXTREMELY long-throw designs, in a box literally one foot cube, with a 1000 watt (and yeah, it REALLY does 1000 watts, seen tests!) amp. Flat down to 22 Hz, REAL PITCH DEFINITION (a real rarity!), formidable output, VERY low distortion or any other noise components.

One other "semi-modern" application (ie, newer than the JBLs mentioned), was the Electrovoice Interface A... an 8" 2-way, with a 12" passive radiator, in a VERY small box (3/4 cubic foot, IIRC)! This speaker impressed the hell out of me, for such a small cabinet... it's probably the smallest space, I've ever heard AUTHORITATIVE 30 Hz bass output out of, that did it even remotely well. And the Interface A did it with aplomb.

I think, really, the reason we don't see PRs much anymore in full-range cabinets, is a) the tendency for smaller and smaller baffles (a large-area PR is less usable, from a fitment standpoint), and b) the cost factor (which is magnified, in cases where multiple small PRs have to replace a single large PR, such as the "mini tower" smal-baffle case alluded to above).

There's absolutely nothing wrong with PRs from a technical performance standpoint- in fact, the ability of them to BLOCK midrange output from escaping from the inside of the cabinet ("port talk", where midrange travels through the port tube, and radiates out into the room, can "smear" the sound of many speakers, that don't have sufficient midrange absorbtion and sensible port placement) can give speakers using them significanly more midrange resolution, at least in theory...

Also, one other minor factor- if you take the time to model speakers with ports and PRs in many box-modelling programs, you will find that SOMETIMES, a PR will result in a LOWER usable bass cutoff point, than a port can, by a small margin. I've had it go both ways, depending on parameters... with some woofers a PR is better, with some, a port works better... but with some woofers (I've not really codified the case well enough to this point, to give a general predictive regimen, sorry), it can result in a better low-end curve, especially in cases where near-wall or near-corner integration is important (ie, boundary-sensitive response "shaping").

Regards,
Gordon.

[DavidF]

It seems that JBL used the PR in its larger boxes (note the L150 that uses the 128H in about 3 cu. Ft. vs L112 in about 1.75 Cu Ft.) and in its designs for the consumer market. As mentioned, the PR would be preferable to huge ports needed to compensate for larger-than-optimum volumes. Also, the closed aspect of the PR would help protect unloading of the woofer at very low frequencies before effective infrasonic filters became more common in the consumer electronics.

There have been many PRs used in all price ranges in the not too distant past, but they seem to be most popular in the subwoofer category recently.

David F

[Guenter]

[QUOTE]Originally posted by Giskard
[B] I'll try to find my old passive radiator instruction manual, scan it, and send it to Don. I really liked the PR8 and PR10 based systems back then.

That would surely be a wonderful literature addition. Although
I think I do understand the idea behind them, and nicely elucidated on by GordonW, thank you, it will be interesting to
now read - with the old proverbial 20/20 hind sight - what JBL's thinking was when they used them in the 50's amd 60's.

thanks

[bldozier]

I'm looking into building a dual 12" 2203/124 cabinet, i wanted input if i would just be better off using a custom pr12...
would a pr15 work in a 4350b style cabinet has anyone tried.