Passive Radiator Subs
G'day there Tax-dodgers, MoFo's and Retards, (take your pick and just one, Graham)
Finally I am ready to build 2 of http://www.vikash.info/audio/xls10/
I have the Peerless 10" XLS (XXLS?) 2nd hand from Andrew Aslan, here's hoping that if they were ever in the Bathurst system that they have not been bashed against the stops too hard/often.
I bought 10" PRs 2 years ago from Parts Express IIRC, I don't think the 12" ones were available. Convention says the PR should be larger than the driver. I'm hoping that with only a small/medium room, 2 subs won't need loads of excursion.
I bought 2 plate amps (oamps?) 200w(?) with variable phase, which seems preferable to a 180o switch.
25mm MDF should be simple build and strong enough to eliminate bracing. I presume PRs don't need bracing as much anyhow and I will glue some pieces of timber along the joins.
Then LOTS of measurements, one sub in a corner, the other moved around the place, varying the phase at each location, then moving the mic around for each sub location ..(hmm maybe should just worry about the Listening Position or wetspot.)
Any suggestions on the above will be gladly accepted, digested, filtered to retain the good bits and adopted, if shoeless and found wandering the streets.
I can feel a GTG coming up soon.
Comments
Are the PRs Peerless or PE?
Peerless. Got a part number and some T/S parms 'n all.....
thinking of adding pieces of gold to "tune" the PR, since it won't tarnish.
where is it written the PR should be bigger than the driver?
18mm ply & bracing would be my preference
How many litres?
Hippy ! It is written 3 posts earlier - do I have to go searching ?? can't you google up PRs and have a read ?
Something about the limits of their excursion being easily achieved, so suggestion is to increase the area to avoid Xmax. Perhaps "convention" was a little presumptuous but I have seen it more than twice as a recommendation.
just googled "passive radiators larger" and got hits.
"Now, we need to select an appropriately-sized passive radiator. ALWAYS use a passive radiator that is larger in diameter than the active driver, as the displacement of the passive radiator usually has to be 1.5 to 2 times that of the driver." this was in some knob's article -http://www.mh-audio.nl/PassiveRadiator.asp
You can model it easy enough in Unibox. Probably more important for HT than music, HOWEVER Nigel why don't you go whole hog and put two PRs in each box.
Then you can make sealed boxes for the other woofers and replace the 8s
Assuming you are using the 830452 and 830481, here's the excursion graph with 300W
With two PRs. Needs weight added to the PRs, but if they are on opposite sides of the box the force will tend to cancel.
I has thunk about this a bit more and decided that my idea was crap and John's suggestment is much better. So I will install 2 opposed PRs to reduce the box dancing around the room and this will also address the concern of using PR with a same size driver.
I was going to use the tuning specs (weight added to the PR) in the project I mentioned in Post#1, but that won't be appropriate any more. I'll have to do some research to work to understand how to done did it. or trial and error ? - more to learn.
What number are the PRs?
http://www.d-s-t.com.au/data/outsourced/Dual_PassiveRadaiator/dual10.htm
This is interesting & relevant to me.
Nige/John, as it happens, I have an unlabelled (unknown) 8" sub driver & 2 x matching PRs.
Both the driver & the PRs seem to be of good quality, with a large motor & VC on the sub & well weighted PRs.
The original owner fried the amp & dismantled the box some years ago.
Now I have the driver & PRs.
The original owner thinks the original box "was about 300mm cubed on the outside."
I presume 16mm & unbraced.
How do I determine the correct litre capacity of the box.
I want use this as a hidden tune up sub behind the rear seat of my cinema room.
What say you?
Graham,
it is a great idea. Don't know how many subs you have but some say multiple is better than one. As for calculating the volume of the box, without being too anal, you should unbolt the driver or a PR and have a look inside. Have a look at bracing and the thickness of the cabinet walls. Ultimately you should check its performance which has some scope for modification by varying the weight added to each PR. This adjustment will cater for a variation in box size as well so being super accurate with the box volume is unnecessary. The plate amp might invade the box as well, so you might lose a litre or 2 on bracing and amp, but you won't know, if you don't go.
John,
the PRs are not Peerless. I finally opened one up and surprise, it is a Scanspeak PR 26W-00-00. I trust the other 3 are the same !!
Nige
In the cinema room (for want of a better name) 1 currently run 2 x 18" vented subs in ~250 litre boxes.
http://celestion.com/product/86/ftr184080hdx/ :-b
I don't have the original box fro the 8" driver & PRs, I only have the driver & PRs. %-(
The PR 'discs' are already quite heavy & look to be 'built for business', so I don't think I want/need to modify them.
Rather, I am trying to determine correct box enclosure size for driver & PRs as is.
If original owner is sorta correct, it have orginally been a 25-30 litre enclosure.
I can build a larger enclosure, eg 370 x 370 x 370. ~35 litres. Suck it & see. It's only plywood & time. :->
I can get a sub plate amp from Paul, unless someone here has one not being used...
Graham
Coincidence, my subs will be 370mm external cubes using 25mm MDF, no bracing.
Using 10" driver and PRs. Target is around 30L but accuracy is less important when I can just add/subtract a washer or 2 off the PRs.
John can explain what you will need to do to tune/optimise the sub.
Graham, you really need to measure the parameters of the driver in order to model it and know what the correct (range of) volume is. There is some info on the REW help about how to do that, I will dig it up in a minute. Otherwise, you could simply build it "about 300mm cubed on the outside" and see how it went. You can reduce the volume by putting blocks in it, no way to increase it of course but it's better to be too small than too large because if too large you will get a "hump" at the tuning frequency that you will not be able to get rid of (whereas too small will just result in reduced output). I suppose in either case you could EQ but I would prefer the latter than the former.
http://www.roomeqwizard.com/wizardhelpv5/help_en-GB/html/thielesmall.html#top
(I've never done it - shame on me X_X )
Thanks John
Is there anything REW can't do?
Doesn't make my coffee. Mmmmm cooooffffeeeeeee
Nigel, the spec on the Scanspeak passive has a higher Xmech than the Peerless, so it's possible to use just one I think. However it has higher mass (400g) so the tuning is lower. If you use two of them, you'll never get anywhere near their limits, here's the modeled response with two of them weighted to 512g:
You can see the light blue line, that's the resonance I was talking about on the phone. And the black line is the output from the woofer, you see the notch at the tuning frequency. Adding more weight will reduce the tuning frequency - increase output at 20 Hz and reduce it 30-40 Hz. BTW you do want to make sure they are the same I think.