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/vbulletin/showthread.php?p=58784#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.:applaud:

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. :p

[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? :p

[GordonW]

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

See my comment about "badly designed" above... :p

Regards,
Gordon.

[4313B]

D'oh!

They were cute at the time though! :rotfl:

[Regis]

Maybe it's the room loading, maybe it's the tile floors in front of the L-150X's or a number of things including the 2214H's (JBL never did put a pair of these in a PR application...), but the pair that's in the smaller family room, goes way deeper than my L-300's in a larger room. The L-300's are corner loaded and close to the wall, yet the L-150's still outbass the big beasts (they won't get as absolutely loud) but at 10 watts, some of the source material will actually make the air in the room vibrate. The patio doors and cabinets in the kitchen rattle, it's that low, yet it still sounds tight.

It was nice to demonstrate the pair to Steve Gonzales and watch his jaw drop (remember, he has two pairs of L-220's and L-222's that will give you a pretty good thumping, just standing there). You might remember he wrote this "The addition of the 2214H's proved to be a HUGE improvement!. Those L150's ROCK!!. The bass is SLAMMING!. Not a bit muddy or boomy, just tight punchy DEEP LF PRESSURE WAVES."

If there is an advantage to the 15"rs in the big beasts, is that the bass is exceptionally tight and it does go body-vibration on the couch low. But they just don't get as low as the L-150's in the other room, I don't know why as my experience is limited. Thinking a big cab with a woofer like the 2214H might just be the reason.

[Ian Mackenzie]

Has any one here ever made PR?

I did a speaker workshop course some years ago and its quite simple.

You just need a raw frame and an appropriate surround.

We used a thin sheet of ply cut into a circle the diameter of a nominal cone and carefully glued it to the surround and made a rear lateral stabaliser using rubber bands.

They worked perfectly and were kind of fun. Kind of reminds me of the Contrabass motors.

So if anyone wanted to play around with a PR its fairly easy to arrange.

Ian

[DavidF]

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.
Ian

I know what you mean, Ian. I used to think that EV re-introduced the PR in their marketing first. They used to promote the scientific approach in their marketing. I was later surprised to find out the Polk 10 was around a while and gained steady popularity without the high marketing budget available to EV. The Polk obviously had better staying power as it turned out.

The design in the EV A model seemed the most appropriate application for the PR. The box was very shallow and overall compact. A vent would not work in that application. The PR was provided substantial mass and size relative to the driven 8 inch speaker. The active equalizer spread the response out at both ends and all together an nice compact package with respectable bass, so-so highs I recall. I don't think it ever sold all to well though (or the B, C, or D for that matter).

David F

[DavidF]

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

And, it would have to be the mother of all PRs.

[duaneage]

I have owned a pair of Polk Monitor 10B speakers for 19 years. I really like the bass and midrange performance. They used 2 Audax 6.5 inch drivers and a 10 inch PR. F3 is definately close to 28 Hz as advertised, a feat almost impossible to believe, but they will do it although power handling at that frequency is not as great.

The tweeters are peerless 310665 and while a decent tweeter they are easy to throttle. I replaced mine twice, and IMHO were not a great choice.

I am planning to remake these speakers into a new design. I want tall narrow tower speakers that flank my TV. I plan to mount the drivers in a D'Apollito MTM with the PR on the side. The original box volume is around 2.75 cu ft so that gives me some air to work with.

PR systems have three impedance peaks and tuning them can be a little tricky. I plan to compare an original 10B to my creation so I can make adjustments. The original crossover network should work since the 10B arranged the drivers in a horizantal MTM with close driver spacing. How it will sound vertical will be determined.

I saw a pair of these 10Bs go for over 350 dollars last year on eBay. They don't come up too often. They were not Polks top of the line but they seem to have quite a large following today. The SDA series were supposed to be more advanced but tended to color the sound too much.

[GordonW]

If you're looking for a "higher-performance" tweeter to replace the Peerless 810665, I'd try the Vifa D27TG05. Or, if you want to do a custom crossover (which would actually be better, given the new driver arrangement), I'd seriously look at the SEAS 27TFFC (available from Madisound). You'll blow the woofer to smithereens before you'll damage a 27TFFC, and it sounds AWESOME too. Crossover is really simple, IME... do a 2100 Hz second-order Bessel high-pass on the tweeter (Q=.577), and a third-order acoustic (total slope) lowpass on the woofers, at about 2KHz... with a little tweaking, you can usually get fantastic results...

As for my own experience- I just recently aquired a pair of Polk Monitor 5 and Monitor 7s. While I don't like the Monitor 7 as well as the similarly-sized JBL L19, it's definitely got prodigious botton end extension...

Regards,
Gordon.

[duaneage]

I'll probably dance with the girl I brought on these for now, I have two NOS SL2000 tweeters still in their boxes as spares. I like Vifa tweeters, and they are easy and cheap to repair, and reasonably priced. I have a limited budget for wood only on this so I am going to try and use as much as i can from the 10Bs

Pol Audio made great speakers back then, bass performace was really their forte'

[jandregg]

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.
.................................................. ..................................................

Is there a non-destructive method of measuring the moving mass of a PR?

I always thought the PR15's mass was matched to the LE15a.

John

[duaneage]

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.
.................................................. ..................................................

Is there a non-destructive method of measuring the moving mass of a PR?

I always thought the PR15's mass was matched to the LE15a.

John

PR moving mass can be measured in a test box through derivative calculations but not easily. You can at least get into the ballpark with it and generally if your within 10% in an enclosure your pretty close. Most tuning frequencies shift as the driver heats up anyway.

[slxrti]

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

That maybe the case on paper, it should perform the same or worst.

I tried a passive with a 2235. The bass was much deeper and would rattle the room. The tone quality was more natural, like enhance d130/2205 with much deeper bass.

I plan using 2 passive with my 1500AL, the passive should have 2X the xmax of the driver. That's the reason for 2. it will then crossover to a 2227.

The SR8 passives are limited in this repect
slxrti

[4313B]

I tried a passive with a 2235.Yeah, I used PR15C's with 124A/2203A's, 124H/2203H's, LE14A's, LE14H's, 136A/2231A's, 136H/2231H's and 2235H's.
The bass was much deeper and would rattle the room.That isn't a function of having a PR. ;)



In any case. They make PR's because some people like them.