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Old 22nd July 2019, 05:30 AM   #11
jerryo is offline jerryo  Isle of Man
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I have two pairs of these drivers in storage and have considered a clamshell isobaric build but I know that the t/s parameters vary quite a bit from the original values through storage.
These drivers offer the possibility of bonding the two driver faces together giving zero volume between them which is perfect for isobaric. How would you treat the t/s parameters though for vas and box volume calculation. Take the actual driver measurements and run those through an isobaric setting on say winisd Or measure the two bonded drivers t/s parameters considering them as one driver? Difficult to do added mass method for vas
As it is winisd has given me a nice flat, low response in a 43 litre box to a -3db of sun 30hz as a clamshell isobaric. (No extra internal volume for second driver)
If two of these drivers having differing t/s parameters are bonded together face to face their individual parameters will be averaged between them, no/yes?
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Old 25th July 2019, 06:49 PM   #12
badman is offline badman  United States
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The best choice is to use a push-pull manifold, with the drivers spaced as closely as you can (while respecting that they need at least 2cm of clearance between cone/magnet for safety). From there, you can take the driver specs and plug them into a box designer with 2 drivers. Fc and will likely be a touch lower due to the airload, but it may not be measurable in impact (on a downfiring manifold, you get effectively a much more bandpass-like behavior, beneficial for a sub).

But in any case, push-pull is like a better isobaric for distortion and output reasons (but with 2x the box size).
"The dawn of Bose created the "Man Cave" and reduced testoterone levels worldwide by 18.5 per cent" Peteleoni
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Old 25th July 2019, 07:11 PM   #13
jerryo is offline jerryo  Isle of Man
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I was under the impression that a clamshell isobaric set up was probably best. The B139 drivers are perfect for this because of their flat faced cones allowing, as mentioned, the possibility of bonding the two cone faces together therefore giving zero enclosed air mass, which also helps with overall box size. I’ll probably give it a go and then measure the resultant combined double driver and see what the t/s specs turn out to be.
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Old 25th July 2019, 08:22 PM   #14
tsmith1315 is offline tsmith1315  United States
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jerryo, read again and you'll see that badman is not suggesting an isobarik system, but a manifold.

It's two drivers loaded into a slot with an open end, with one driver mounted backwards, thus wired out of phase. "Push-pull" is relative to the baskets, not relative to the manifold/listener. The output of both cones radiates through the slot. Isobarik pairs only have one radiating surface.

Clamshell mounting gives the same, if not better, properties of cancelling basket resonance/distortion because the baskets are usually mounted on opposite sides of the same baffle, thus more closely coupled. Sensitivity is 6dB better in the manifold, at a cost of 4x the required internal box volume.
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Old 26th July 2019, 04:58 AM   #15
jerryo is offline jerryo  Isle of Man
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I realise that, but as you point out there is a considerable increase in box size. I don’t need high spl’s but rather a compact box volume and depth of bass.
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