Isobaric driver orientation: which is best? - Page 3 - diyAudio
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Old 31st December 2001, 05:05 AM   #21
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Hey all, new to this forum. I vote for the clamshell.

For what it is worth I just built a clamshell-oriented ported isobaric sub box. My original intent was to go with sealed isobaric for low tight bass in a small enclosure (for my car). However after testing the unit in the sealed configuration I was unhappy with the SPL for the amount of power applied to it. Knew it would be low (as mentioned in previous posts) but not that low!

Fortunately the existng enclosure was perfect for a ported design. I added a port (tuned out for speaker specs, box volume, port dia, length) and wow what a difference. It is much louder. I cannot wait to get it in my car, so far I have just tested it in the house and it is fantastic.

The response is still low even with the port setup. The response at 45 Hz or so is 5dB louder with the vented box (over sealed) according to the design software. I believe it based on what I have heard so far.

Oh yeah and I used a 3/4" spacer ring between the subs to keep the suspensions from colliding.

FYI - subwoofer specs
Cerwin-Vega HED 10" subs x 2 (on sale at Best Buy cheap)
0.8 cu ft. box built from 3/4" MDF
outer box dimensions 34"x12"x6" (required by car configuration)
12 ozs. of Polyfill added to box
3" dia PVC port, 21" long
estimated Qts = 1.05
estimated Fs = 30 Hz
estimated 112 dB SPL@ 300W RMS
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Old 31st December 2001, 11:58 AM   #22
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great to hear you had success...

just watch the excursion on those drivers....

if they exceed Xmax by too much odds are you'll kill them both @ once.
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Old 31st December 2001, 04:16 PM   #23
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Thanks for the warning. I have already noticed that it is sensitive to subsonic sounds, as is expected from the design, correct? Maybe I need a subsonic high pass filter for it? Do the line input filters work at all? Anyone? Anyone? Bueller? Bueller?...
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Old 31st December 2001, 07:13 PM   #24
JBL is offline JBL  Canada
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Generally isobarik give a lot better quality. It can make miracle with cheap driver.(like those cheap but powerful car sub at consumer electronic shop)

It's definitly less efficient but not that bad.

just use some driver with at least 90 spl/w/m.
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Old 31st December 2001, 09:32 PM   #25
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Yeah, you got it JBL, cheap Cerwin-Vegas from Best Buy :-).

Just got it in the car, finally got the amp straightened out. The demo amp unit I bought was bad, checked the wiring three times before I finally returned it for a new unit....

Anyway, it works very well. It shakes the crap out of the rear view mirror, always a good sign. Not quite a bounce-the-quarter-on-the-roof system, but plenty loud still. The bass response is tight, not muddy, and deep. Punchy, not boomy, perfect.
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Old 1st January 2002, 12:20 AM   #26
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i'd use an electronic 1st order high pass filter @ 7Hz with a Q <0.8 directly before the amp this will be fine so long as the amp doesnt add too much subsonically to the signal ... if it does you'll then need a passive filter.
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