Isobaric driver orientation: which is best? - diyAudio
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Old 20th November 2001, 10:02 PM   #1
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I am designing an isobaric (isobarik?) vented sub and would really like some input on the driver configuration. The typical gasket to gasket 'clam shell' driver mounting would certainly be easier to build but wouldn't orienting them front to back and in-phase yield better sound? It just seems that having the sound radiate from the front of the cone directly into the room would be more effective.

Also, when designing the enclosure, if the drivers are mounted in-phase will I have to make any allowances for the small front chamber?

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Old 21st November 2001, 12:41 AM   #2
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Clamshell style is certainly easier to build and also much less likely to have problems. They're also usually smaller, because you only need a single enclosure. Polar alignments frequenly have standing wave problems, while clamshell alignments are no different from normal enclosures. However, clamshell designs are unlistenable for a number of reasons outside of the low frequencies. The design still works well for a subwoofer. Just not for anything else.

What drivers do you want to use for this? Efficiency is always a problem with isobaric designs, and not all drivers are suited to the job.
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Old 21st November 2001, 12:56 AM   #3
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clamshell is best ..... the others sound worse and will kill your drivers quicker.

in the clamshell config, you will get nothing but bass from the speaker all the rest gets cancelled.

also, in the clamshell config, you dont get a higher spl because there is 2 drivers, infact you get less. The output will be -6dB when compared to a single driver so you will need more power.

dont use a ported box ...... it's just not worth the trouble for an isobarik speaker.

[Edited by AudioFreak on 11-20-2001 at 10:45 PM]
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Old 21st November 2001, 01:09 AM   #4
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Default WARNING!

How many watts will you be driving your Isobaric-coupled woofers with? You should either change the design to a sealed box or use fewer watts. My Sledgehammer subwoofer used a ported box with clamshell woofers, back before I knew better. It sounds okay, but I found that it's easy to overdrive the woofers to the point where the voice coil former strikes the backplate, possibly damaging my woofers. Also, please make sure your box is the right size. My Sledgehammer subwoofer (soon to be replaced by the new American Thunder subwoofer) has a box that is 1.5 times the size it should be, and I think I may be sacrificing output and flat frequency response. This is my other reason for building my new subwoofer.

Either sealed box or fewer watts.
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Old 21st November 2001, 01:34 AM   #5
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Linn used two speakers facing the same direction (in both the Sara and the Isobarik), but with an certain amount of space for the front chamber. Both Loudspeakers were very well sealed. They can sound very good and tuneful in the bass, but are hell of a load to amps.
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Old 30th November 2001, 11:50 PM   #6
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Question Linn iso

Are the woofers in phase or out?
David
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Old 1st December 2001, 01:08 AM   #7
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When both the drivers are facing the same way, they are wired 'in phase'.
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Old 1st December 2001, 01:13 AM   #8
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Make sure in your clamshell config the driver completely hidden by the other driver and cabinet is wired in phase with the rest of your speakers, or else your isobaric setup will be out of phase with the rest of your speakers.
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Old 1st December 2001, 06:12 AM   #9
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Default Phasing

Thanks,
I have some old Jenson 15" alnico woofers that were made for less than 200 Hz. I want to do something with them and thought this might be just the thing for a high efficiancy sub.
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Old 1st December 2001, 06:22 AM   #10
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Isobaric Subs are not Efficient.

They let you use an enclosure with 1/2 the volume but are significantly less efficient (clamshell is the most inefficient an is 6dB less efficient than a single driver).
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