Application of Passive Radiators

[Audiokarma]

At Ian's suggestion, it seems useful to start a new thread dedicated to the discussion of Passive Radiators, building on the discussion already started in:

http://www.audioheritage.org/vbullet...8784#post58784

Various manufacturers have utilized Passive Radiators as the basis for their design philosophy. For example, the Klipsch KG series of speakers, and as Ian mentioned, Celestion. Perhaps the most commercially successful application was reflected in nearly the entire line of Polk Audio speakers from late 70's to early 90's, especially the Monitor and SDA series. Through the use of Passives, they were able to achieve LF and VLF from enclosures that used only 6.5" active drivers.

For reference purposes, I'll start with a copy of a brochure I have on hand for the Celestion 662

[Mr. Widget]

Mr. Karma,

I see from your Avatar you have an interest in S7R or S8R systems... are those yours? Have you tried messing around with the weight on your PR15s?

Widget

[Audiokarma]

Hi Mr Widget,

Alas, those are my former S8R's. I included them in my Avatar as a tribute to these beautiful speakers. I never did get around to doing any tweaks with them. I wonder if any other current owners have. I know a couple of other members with some Sovereign S8R's who may possibly be interested in the idea. What were your thoughts on the weighting?

[Mr. Widget]

What were your thoughts on the weighting?

Nothing specific, but as Mr. Edge mentioned ten folks will have ten ideas and I thought it would be interesting to get opinions on these systems with different weights.

Zilch has about ten pairs of Olympuses... maybe we could set up each pair for a different listener.

OK, I am prone to exaggeration a bit... maybe he only has 4 pairs? Quite a few at any rate.

Widget

[Ian Mackenzie]

Actually I always thought the EV interface A (pre Polk) was the most inspiring attempt at least in the U.S.A on using small woofers and a larger (rear) passive radiator. I will try and dig up the paper on it over the weekend.

I have an old speaker building book around somewhere with the LE8T using a passive radiatator.

Ian

[Alex Lancaster]

As I see it, everything costs money and time; Aren´t You better off with a more expensive woofer in a ported box?

[4313B]

get opinions on these systems with different weights.

No different than screwing around with ducted ports. At some point you get the proper mass in the ducted port, or mass on the passive radiator, and viola! It sounds right. It's easier to add or remove mass discs on the PR than it is to cut or add length to a ducted port so maybe that's the fascination some people still have with the PR.

As I see it, everything costs money and time; Aren´t You better off with a more expensive woofer in a ported box?

I can't imagine anyone wanting to degrade the performance of a 1500AL with the addition of a PR.

[Alex Lancaster]

Zackly!

[rloggie]

Weren't the PR's set at the factory as to weighting? What external factors would cause one to need to adjust the weights? Room size? Does someone have a sugguested amount of weight to try on S8R's or S7R's.

[4313B]

A PR will simply wear out from use (legacy JBL PR's especially). This will affect the system tuning. I can't help you with the S7 or S8 as they used the older PR15 and I no longer have a record of that moving mass. I only have the PR15C moving mass and have posted all that PR information somewhere on this forum. If you can't find it, hopefully someone will dig it up for you.

It would be very cool if someone could go to the trouble of getting the moving mass data for all the old JBL PR's. I've asked on this forum before but so far... JBL evidently no longer has records of such things.

[rloggie]

So as they age, would they like more or less weight?

[Audiokarma]

perhaps giskard refers to the surrounds. this is a major issue for the older ESS AMT line

[rloggie]

So as the surrounds "age" would one tune the woofer by adding more weight or removing weight?

[GordonW]

Actually, if you model it, a PR will perform BETTER as the suspension "wears"... as in, gets softer and softer. It becomes closer to a true 4th order alignment, while still having the advantage of KEEPING THE MIDRANGE BOUNCE INSIDE THE CABINET, unlike a port, which is a "direct window" to reflected sound bouncing around inside a cabinet...

Like I've said before... and I actually HAVE used a PR with a 2245... make the suspension soft enough, and the PR will generally result in performance that is, at least subjectively (including the absence of "organ pipe" resonance effects which plague ports) BETTER than a simple ported system...

And no, you should NOT have to change the weight whatsoever, as a PR ages. The PRIMARY function of a PR is the MASS it represents... the compliance effects (ie, the suspension) are a SECONDARY effect, which really don't affect the system resonance significantly. If the PR is stiff enough to change the overall box resonance, then the PR is wrong for the box (and probably is just a plain badly designed PR) anyway...

Regards,
Gordon.

[4313B]

Actually, if you model it, a PR will perform BETTER as the suspension "wears"... as in, gets softer and softer.

But what about all those Lans-a-Loy surrounds?