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Old 21st July 2013, 11:36 AM   #1
Westy37 is offline Westy37  Australia
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Default 2-way passive open baffle

Just looking for feedback on an idea I have for a passive two-way open baffle speaker.

I've got four of these Peerless SLS 12" 830669 woofers (see attachment for specs) that I'd like to make something with. I'm thinking of using them on a baffle not too much wider than the woofers themselves, so about 350mm wide. However this is somewhat flexible, I could stretch it out to maybe a ma of 450mm

I'm thinking of crossing over somewhere between 150-300hz or so to some widerange 4" Mark Audio CHR-70 (see attachment for specs).

For aesthetics I want to keep with a simple U-frame baffle, with all drivers firing forwards. I'm looking to do a regular height floorstander (approximately 1m)

What do people think in terms of feasibility? Any anticipated major difficulties or things I need to rethink before proceeding and ordering parts/wood etc? Will things work out with matching sensitivities of these drivers? As there will be two woofers per side, will it work wiring them up in parallel for a 4ohm nominal load. Good idea? Bad idea?

Any ideas or feedback is welcome
Attached Files
File Type: pdf SLS12 830669.PDF (538.0 KB, 49 views)
File Type: pdf CHR-70.PDF (758.1 KB, 30 views)

Last edited by Westy37; 21st July 2013 at 11:56 AM.
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Old 21st July 2013, 05:30 PM   #2
Rudolf is online now Rudolf  Germany
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With regard to sensitivity a single SLS12 would be a much better partner for the CHR-70. Two SLS12 in parallel are way too loud. Two SLS 12 in series have comparable sensitivity to a single one, but need inductors in the range of 20 mH to work.
But of course the CHR-70 can hold up to a pair of SLS12 regarding maximal volume. It is a good example why active dipole woofers are preferred by many.

When undamped U frames reach their resonance frequency, they have turned from a dipole pattern to an omni pattern. You need to damp U frames to avoid that. A U frame with 30 cm depth has its resonance at just below 200 Hz. Perhaps you would be better off with less depth - maybe 20 cm. But this might already give stability problems with stacked SLS12 drivers. Thats one of the reasons why I prefer H-frames with 15 cm depth to either side .

undamped U frame 30 cm.gif

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Old 21st July 2013, 11:27 PM   #3
Westy37 is offline Westy37  Australia
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Rudolf thanks for the informative reply. So if I were to use a single SLS12 would I still be looking at an inductor value of around 20mH? Would there be any advantage of using the pair of SLS12 and wiring them up in series?
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Old 23rd July 2013, 02:07 AM   #4
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Westy,

I assume you've seen the Manzanita OB which uses the same Peerless woofer:
Fast, fun, Inexpensive OB project John Busch uses a 20mH inductor on a single 830669 woofer.

I've built a pair of Manzanitas using the Peerless 830669 and Vifa TC9FD-18-08 full range. I like the bass from these OBs even though it doesn't extend particularly low. However the little Vifas don't have a very clean top end and I'm thinking of substituting them with something else, so I'm very interested to see how your project goes.

Graham.
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Old 23rd July 2013, 05:33 AM   #5
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Quote:
Originally Posted by Westy37 View Post
Rudolf thanks for the informative reply. So if I were to use a single SLS12 would I still be looking at an inductor value of around 20mH? Would there be any advantage of using the pair of SLS12 and wiring them up in series?
A pair of SLS315 sounds better than one, less distortion in the midrange and far better bass.
See my project : Big passive OB project
See the last posts.

A 4" alone cannot handle two SLS315, you needs two them or a 5" and cut them above 500Hz... If you want go to 300Hz, use a 7".

If you wire them in series, the inductor goes to 40mH... I like the sound in series but no real advantages.

Last edited by jerome69; 23rd July 2013 at 05:36 AM.
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Old 23rd July 2013, 04:58 PM   #6
Rudolf is online now Rudolf  Germany
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Quote:
Originally Posted by Westy37 View Post
Rudolf thanks for the informative reply. So if I were to use a single SLS12 would I still be looking at an inductor value of around 20mH? Would there be any advantage of using the pair of SLS12 and wiring them up in series?
I see two reasonable approaches if you already own the CHR-70:
1.
You can give up a bit of the power of two SLS12 by putting them on a very slim open baffle. This allows to move the crossover up to 500 Hz to meet the CHR-70. When the CHR-70 has no duty below 500 Hz, you can have a smaller baffle for that driver with less pronounced dipole peek and dip.
Below are simulations for free air and for floor mounting. Note how the high crossover perfectly avoids any deep floor bounce cancellation (Allison approach). Crossover values would be 8.2 mH and 100 F for the low pass and 3.9 mH plus 22 F for the high pass.
Simulations are for 3 m distance to get a valid floor bounce situation.

OB CHR70 2xSLS12_1.gif
OB CHR70 2xSLS12_2.gif

2.
You can use a single SLS 12 in a H frame. I will come along with a simulation of that later today. Don't expect any coil >12mH.
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Old 23rd July 2013, 06:59 PM   #7
Rudolf is online now Rudolf  Germany
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This is the single SLS 12 in a H frame.
Again simulations are presented for free air and floor based situations. The crossover point is lower, but still no deep floor bounce cancellation. Crossover values are 12 mH and 150 F for the low pass and 5.6 mH plus 47 F for the high pass.
Simulations are again for 3 m distance to get a valid floor bounce situation.

H frame CHR70 1xSLS12_1.gif

H frame CHR70 1xSLS12_2.gif

In the low pass we had 8.2 mH for the parallel drivers and now have 12 mH for the single driver. The drivers in series would need ~20 mH. The values are somewhat inversely proportional to the Re values of the combined drivers.
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Old 25th July 2013, 07:32 AM   #8
Westy37 is offline Westy37  Australia
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Thank you so much for putting forward some really good solutions. Having read a little bit more I'm starting to understand that active crossovers seem to be the easiest way to implement what I want to do here. I've ordered a miniDSP 2*4. I have some experience using these so should be able to work something out eventually!
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