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Old 19th November 2011, 05:52 AM   #11
Francec is offline Francec  Australia
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Perhaps the OP should say what he/she means before any further conjecture?
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Old 19th November 2011, 07:47 AM   #12
eccdbb is offline eccdbb  United States
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planet10 you got the right picture- almost. I'm planning on putting the woffers in OB, so that the side walls are open. Midrange and tweeter section will be above, and obviously a plank of wood at the bottom for the base. I want to use this on a desk, so no vibrations and minimal cabinet volume. I tried a sealed cabinet, but the dimensions were too big, so therefore OB. Frequencies will be from bass to around 500hz, so baffle effects are negligible. There will be a high pass to prevent over-excursion.

Last edited by eccdbb; 19th November 2011 at 07:50 AM.
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Old 19th November 2011, 10:26 AM   #13
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Teledyne AR9 is built that way with the woofers in phase near the floor and the back wall. With the speakers carefully positioned and equalized they can produce extremely powerful low distortion bass, as good as I will likely ever want or need. Parts express now offeres a similar design.

Dayton Audio RS1202K 1000 Watt Dual 12" Subwoofer Kit 300-766

If I were building a high end system at the moment, I'd start with two of these.
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Old 19th November 2011, 01:57 PM   #14
eccdbb is offline eccdbb  United States
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12" is too wide on the desk. I was thinking 2 Dayton RS150T-8's on the bottom facing forward and back, and 2 Neo8's on the top. Any suggestions?
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Old 19th November 2011, 04:33 PM   #15
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Quote:
Originally Posted by eccdbb View Post
planet10 you got the right picture- almost. I'm planning on putting the woffers in OB, so that the side walls are open. Midrange and tweeter section will be above, and obviously a plank of wood at the bottom for the base. I want to use this on a desk, so no vibrations and minimal cabinet volume. I tried a sealed cabinet, but the dimensions were too big, so therefore OB. Frequencies will be from bass to around 500hz, so baffle effects are negligible. There will be a high pass to prevent over-excursion.
Take the sides away from what i'll drawn and all bets are off... you will get better performance from a single driver.

Do note, that if you want any bass, an OB will be "bigger" than a box.

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Old 19th November 2011, 08:26 PM   #16
eccdbb is offline eccdbb  United States
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Why better from a single driver?

What does your second statement mean?

2 Dayton RS150T-8's can fit in a ~7" open cube, although they give up on bass pretty early.
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Old 19th November 2011, 08:45 PM   #17
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Originally Posted by Soundminded View Post
Teledyne AR9 is built that way with the woofers in phase near the floor and the back wall. With the speakers carefully positioned and equalized they can produce extremely powerful low distortion bass, as good as I will likely ever want or need. Parts express now offeres a similar design.

Dayton Audio RS1202K 1000 Watt Dual 12" Subwoofer Kit 300-766

If I were building a high end system at the moment, I'd start with two of these.
Nice, almost exactly my future sub build.

I would like to use those same subs for a front/back "bipole" style sealed box design with LT equalization. Oh yeah, and make that a stereo pair.
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Old 5th December 2011, 05:54 PM   #18
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there was a classic KEF speaker that used this method with a port, which produced a cardioid pattern. The 104/2. Good sound.

Click the image to open in full size.

You can see the speakers through that hole. The advantage is that it removes overall vibration, since the speaker cones' moments of force cancel out. To get optimum results, the speakers' chassis must be coupled, KEF achieved this with a metal pole, which you can also see through the hole.

Used without an enclosure and a port, I'm not sure what a donut shaped dispersion would be called, probably toroidal. I suspect that's what you would get with speakers facing each other.
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Old 5th December 2011, 06:21 PM   #19
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Originally Posted by bishopdante View Post
there was a classic KEF speaker that used this method with a port, which produced a cardioid pattern. The 104/2. Good sound.
Yes, good sound but not a cardiod pattern. This gave normal omni LF response.

Drivers where acoustically in phase, meaning positive volts moved both units into the center cavity. This had the cones moving in opposite directions (realative to "up") so the force canceling rod and compliant mounting greatly reduced cabinet vibration. Finally, since one woofer is moving into the magnet structure while the other is moving out, a great deal of even harmonic distortion is cancelled.

David S.
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Old 6th December 2011, 07:17 AM   #20
eccdbb is offline eccdbb  United States
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I tried modeling these two cases:
1. cones moving in opposite directions 7" apart
2. cones moving in same direction, 7" apart

and I'm getting a high pass at ~200hz for the first case. Does that really happen? For the second case, it's a flat response.

If I make them closer, the high pass point moves up; farther, and it moves down.

For both cases, polar response is the same at all angles.

Can someone verify what actually happens in real life?
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