Passive radiator. Good or bad?

[colinB]

Looking at a BK xls200 sub and a more expensive REL T1 at the moment and the main difference i between the two is the REL has a passive radiator.
Dont know much about passive radiators apart from they are meant to extend the bass. Do they work or are they a flawed compromise?

[Reid Malenfant]

Hi colin, a passive radiator (PR) is basically taking the place of a reflex port, though it is a little bit more complicated than that due to it having it's own suspension compliance. I think it's fair to say though that if you regard it as a bass reflex port you'll understand how this damps the driver at the PRs resonance frequency with the enclosure, just like a reflex.

There are a few good things about them ;) They are often used in an enclosure where it'd be impossible to fit the required diameter port to prevent turbulence because it'd simply be too long & add significantly to the enclosure volume. As well as that because you actually have a diaphram of a good size acting as a port there is zero turbulence & as a consequence no chance of port chuffing :)

If Rel are using a PR you can be sure they know what they are doing. Effectively an enclosure using a PR will be slightly smaller (no port) that a reflex enclosure of the same volume & reproduce as deep as the reflex but with no port noise. It will however roll off below the PR resonant frequency faster than the equivalent reflex, as it's out of phase anyway it really does matter a hoot :eyebrows:

Hope that helps :)

[colinB]

Yeah thanks, i understood that, which makes a change. Bass theory normally baffles me by the time i get to the second paragraph.
The strange thing about REL is they recommend putting the sub in the middle of the room?!

[colinB]

Sorry, they recommend the corner of the room is what i meant.

[Reid Malenfant]

It's not too difficult to design a speaker to take advantage of corner loading ;) All you need to do is make the thing roll off gradually as the bass goes deeper & the gradual increasing gain from corner loading will flatten the response :)

It also means that the thing would likely go much louder in the deep bass than the enclosure & driver dimensions would at first appear :eyebrows:

[colinB]

It sounds like the REL is a better design than the BK . Im just looking for a bit more punch and a bit more lower end which i think the BKs 10" peerless driver might give me.
Might have to come down to what deals are around.

[DSJR]

ABR's (auxiliary bass radiators) got themselves a bad name in the olden vinyl days because the "control" in the bass wasn't always there, especially when playing warped records when both driven and passive drivers would wobble all over the place. especially notable on KEF R104's I remember, as many of these were used with the LP12 in its fruitiest form - NOT a good idea...

Now, before Marco has another coronary because I'm sort of referring to his Ditton 15XR's (one of the best known ABR equipped speakers of its time), may I say that with MODERN sources, analogue or digital, this just doesn't occur, as the bass of even a budget priced vinyl spinner seems better than ever and of course, digital doesn't have the possibly huge sub 20Hz arm/cartridge rises either...

In my opinion, nowt wrong with a passive radiator, if it's done sympathetically and with skill.

[Reid Malenfant]

Best thing to do is get a listen to them both :) Whatever you do for your own sake make sure that whatever you go for has not only got a switch to change the phase 180 degrees, but also a control that allows you to shift the phase (like a volume control) from 0 - 180 degrees to any amount! This is vital to get the thing to integrate with your normal speakers... Also make sure that you cann shift the crossover to the sub low enough, i have no idea what your main speakers are but 30 - 35Hz is probably going to be ok.

As Dave pointed out the Kefs with PR or as Dave mentioned ABR (same thing) got a tad wobbly with subsonics, i know as i had Cadenzas :lol: You need not worry about that with an active sub, there will be a steep cutoff filter to prevent overload on subsonics.

[colinB]

I get woofer wobble on my AVI neutrons when there is surface noise on a LP:eek:

[colinB]

One thing ive noticed, you rarely get REL T series on e bay. Lots of stratas but Ts are hens teeth.

[Reid Malenfant]

I get woofer wobble on my AVI neutrons when there is surface noise on a LP:eek:
Aye, that because there isn't a steep filter to stop the amp reproducing subsonics which there would be in the sub ;)

[Welder]

I’ve got one; two in fact, made by Volt ;)
If the radiators are well designed and the bass drivers get close in frequency response to the tuning of the ABR then imo they are far better than a port in a conventional speaker.
You do of course have to pay some attention to the enclosures because at low frequencies everything wants to get in on the act.
I think REL know what they’re doing. They make top class subs.

[Reid Malenfant]

I’ve got one; two in fact, made by Volt ;)
Name dropper :eyebrows:

I have 4 x 15" PR made by Exodus Audio PR-15 (80mm pk/pk) & they'll need that travel to, or most of it :ner:

Also 8 x Kef BD139 :cool:

[Welder]

Well Mark, if you’re going to like that………………:lolsign:
The Exodus PR is a nice ABR as well; a clever design with regard to tuning.
Don’t know anything about the Kef’s; never owned a pair and never heard them either.

Anyway, what I wanted to make clear before Mark started sticking his tongue out at me was, Rel make the best subs out there, no ifs, no buts, and if they’ve stuck an ABR (probably a Volt ;)) in their design its there to do a job and if you can afford to buy that model then I wouldn’t hesitate.

Setting them up is another matter :eyebrows::doh:

(OMG, Mark is boss mod in this section…………..
sry Guv)
:eek:

[Reid Malenfant]

:lolsign:

Quit worrying John :)

Rel are good & well designed subs, i don't think they have ever made a bad one & they are all musical, which is less than could be said for some cinema subs :lol:

[Techno Commander]

REL are good. Especially the Volt loaded ones.