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Old 8th January 2003, 11:47 AM   #1
Danne is offline Danne  Sweden
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Default XLS-Subwoofer question: Two passive radiators instead of one

Hello everybody.
I’m about to modify my Peerless XLS 10” sub. Today, my box is 27 litres and I use the driver together with one 385 gram passive radiator (265 gram plus 120 gram added). I’ve not simulated this box myself and don’t know the tuning frequency. Now I’m going to build a new box with the same tuning frequency but two passive radiators (265 gram plus something). The new box will be slightly larger to compensate for the new radiator volume but how much mass should I add to the two radiators? Is there someone with simulation software that wants to help me with a simulation?

Thanks
/Daniel
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Old 8th January 2003, 04:06 PM   #2
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The formula for a cone volume that is 11 inches around and 4 inches high is 126 cu inches-about two liters. throw in the volume of the basket rungs and you have 2.5 liters.

So you only have to increase your box volume 2.5 liters-less than 10% of a 1 cu ft box.

Do me a favor-what are the outside dimensions of your box and what thickness of materials did you build it with? Also, if you have the dimensions of your sub amp that have attached, please give them also. If you don't have the sub amp dimensions, just tell me the approximate power-they are likely to be equal to other sub amps in size.

I would like to simulate the box as it is now, so I can simulate a box that gives the same response.

PS: If you just want to cut an additional hole in the box you have now to mount the second passive radiator, that additional passive rasiator will not throw things off by much. A less than 10% difference in box volume will raise your -3 dB down point by maybe 1 or 2 Hz-essentially unhearable.
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Old 8th January 2003, 09:15 PM   #3
Keld is offline Keld  Sweden
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Hi

Quote:
The new box will be slightly larger to compensate for the new radiator volume
If you use your old box I think you can forget about adding volume. there will be almost no difference if your box is well build (thick material). See pic below.

I have tried running a sim with 27 liter net volume, with one and two PR's, and I dont really see a big advantage running with two PR's, but theory is theory. I would say that having two PR's on opposite sides will stopp your sub from "rocking". and thats good!

when running with one PR I would try adding 80-100gr in your current sub and get some 2-4 hz lower almost for free.

in the sim with two PR's I get quite high weight for the same tuning (21,5 Hz) 730 grams! I dont know if thats to much for the slave.

The numbers above are calculated with Unibox and asuming 27 liters NET volume. And be sure to get a second oppinion! and why not your own, download Unibox.XLS , and play around with it. Get it here: http://www.danbbs.dk/~ko/ubmodel.htm
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Old 9th January 2003, 09:59 AM   #4
Danne is offline Danne  Sweden
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Thank you for your replies.

A little more detailed description of my problem seems to be necessary: When running the sub at high SPL’s I get very large excursion in my PR, that’s why I would like to use two of them.

Kelticwizard:
The net volume of my present box is 27 litres. And it will still be in my new one. My problem is how to tune the two radiators. I imagine they should be heavier then today’s 385 gram. What I’m thinking about is the analogy to a ported box, if you have a box with a specified port and you want to use two, to lower the speed, you have to make them longer. Shouldn’t my radiators be heavier?

You asked about my box and amp. The box has outer dimensions of 366x366x366 mm, the material is 5 mm steel and 18 mm pinewood, internally the box is braced with ø8 mm steel rods. The amp is a Hypex HS 200, which is placed outside the box.

Keld:
I have downloaded the software (Thanks) and simulating my driver and one 385 gram PR in net volume of 27 litres makes very large excursion under 30 Hz. Mechanical Xmax is +/- 22 mm for the PR so problems do occur approaching 25 Hz, so my apprehension seemed to be correct, maybe. Simulating with “Minimal leaks” and “Minimal fill” (I guess the rods will slower down the air in the box a little bit) I get an Fb of 23.68 Hz. When trying 2 PR’s and aiming for this 23.68 Hz the weight of the PR’s is exactly doubled 770 gram each. Can’t really be a coincidence, doubled “piston area” doubled mass? Or?

In the plot one can compare the excursions for the single PR and the double PR designs. The SPL and the excursion for the driver remains the same.

/Daniel
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Old 12th January 2003, 11:55 AM   #5
Nisbeth is offline Nisbeth  Denmark
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Danne, not sure if this is any help, but I remember that the Danish magazine "High Fidelity" had an article last year (issue 3/2002 p. 51) about designing a Dual-PR subwoofer. The designer used the 12" XLS drivers but the article might be some help anyway. Maybe the local library can get the magazine for you.

/U.
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Old 12th January 2003, 01:36 PM   #6
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Hi danne,

A few people in France have worked on building the ultimate subwoofer with SWR269 10'' XLS Peerless Driver.

We started first by building a 1+1 subwoofer, then (and few did) a 2+1 subwoofer.

I made a lot of simulations and published curve on our DIY french forum (www.homecinema-fr.com), as others did.

I never listened to a 1+2 version but simulations show that :
- power handling is (of course) incresead
- excursion is reduced
- 400 gr mass on each passive unit is needed
- F-3 is higher than 1+1 version
- volume needeed to achieve F-3 around 30 Hz (let's say 29/31 Hz) is around 35 useful liters.
- a real strong amplifier is needed (your hypex should fit)

Now, if you experience dangerous excursion (peek to peek is 25 mm with the SWR269, so it really shakes), it might be dued to :
- a bad location of your subwoofer
- an innapropriated bassboost (it SHOULD be defeated with this kind of sub)

Considering your volume and additionnal mass to the passive unit, the Fc shoud be around 20 Hz. I personnaly use 25 liters with 1 active and a 400 gr passive unit and - in simulation - I get F-3 at 22 Hz.

Note that there is no way to get such a low Fc with 2 passive units in a reasonnable volume...
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