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Old 1st December 2006, 09:06 AM   #1
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Default Commercial isobaric sub inspiration

Hi,

I'm fairly new to the concept of isobaric subs. Yesterday I was in a hifi store listening to the B & W PV1 sub, and it performs very well indeed, the bass is tight and well defined, probably the best commercial music sub I have heard so far. Would it be possible and worth the effort to try to do something similar diy-style?

PV1 white paper

Can someone help me by elaborating on the pros and cons of the B & W PV1 sub design? If I interpret the white paper (link above) correctly, the drivers are mounted back-to-back and connected in phase. As I understand it this doesn't help to reduce distorsion originating from the drivers, but reduce vibrations in the enclosure and makes for a very stable sub ...


Regards,
M.A.
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Old 1st December 2006, 12:09 PM   #2
BAM is offline BAM
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I don't think the PV1 is an isobaric sub, just your typical sealed enclosure with a driver on each side.
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Old 1st December 2006, 03:01 PM   #3
theNoid is offline theNoid  United States
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Quote:
Originally posted by BAM
I don't think the PV1 is an isobaric sub, just your typical sealed enclosure with a driver on each side.
Yuppers BAM.

The PV1 is a great sounding subwoofer but as far as I am concerned, you can build just as good sounding of a sub for a lot less money. Just my thoughts.

If you are truly interested in isobarik designs, here is quickie info page to check out... http://www.the12volt.com/caraudio/boxes2.asp

Noidster
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Old 4th December 2006, 07:25 AM   #4
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Thanks for the info. It's no isobaric design, my bad. However, I think it is a great sounding sub, and I am curious about the driver configuration:

- Does to driver arrangement of the PV1 create a better radiation pattern than a single driver sealed sub, or is it a monopole source anyways? The PV1 is claimed to excite less room modes than a traditional sub ...

- How important is it to reduce vibrations in the cabinet by having the drivers cancel each other out like in the PV1? You don't see subs like that very often ...


M.A.
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Old 4th December 2006, 12:06 PM   #5
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Hmm, did some more searching and found one answer to my second question regarding cancellation of vibrations:

dual driver vibration cancellation really does work!

According to this, there really is a point in employing push-push, or even better, push-pull mounting.

Still, wonder why it isn't used more often then ... I can understand why push-pull probably isn't a viable commercial option, with one driver at the back with the magnet sticking out ...

M.A.
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Old 4th December 2006, 12:21 PM   #6
AMV8 is offline AMV8  United Kingdom
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Hi

I have just finished building 4 bass/sunwoofer units. My main speaker is a 5" direct connected midrange and I added a bass/subwoofer with a single pole filter at 100hz. 2 base units used 12" units and the other two used 15" base units. All base units with very large magnets.

I found that a sealed box design gave me the best results - that is smoothest delivery and tightest base. I found that I prefered the tighter base from a sealed box to the higher volume at lower levels from a vented enclosure. ( I was able to design a vent using calculation and experimentation.) However I prefered the sealed box.

I also tried isobaric and other dual combinations of speakers. I had difficulty in obtaining a clean sound. Using two speakers seemed to blur the notes. I spoke to Max Townshend about this as he lives near me. He confirmed that it is very difficult and nearly im[possible to design a dual speaker unit without considerable computor access and chamber testing. He said that his Glastonbury speakers, which I think use dual 8" base units, had the same problems untill he spent money on chamber testing and computer design.

What I also found was that the one item that made the biggest difference in giving me a tight base was the rigidity of the mid enclosure. Yes not the base enclosure but the mid enclosure. That does not mean that you do not need a reasonably rigid base cabinet but it does mean that I found the regidity of the mid range cabinet to tbe more important. Wilson and B&W also use very rigid mid range units. At one time I think that wilson used a stone mixture for the mid unit box. My experience leads me to believe that unless you can find a ready made diy isobaric design that it may be better to stick to a simpler design.

I hope this helps and good luck either way.

Don
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Old 5th December 2006, 03:39 PM   #7
lne937s is offline lne937s  United States
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Im using a Mirage BPS 150i sub with drivers on opposing sides, push-push.

I live in an apartment and the force cancellation lets me play it louder without transmitting vibrations to the floor. You have to figure for every action there is an equal and opposite reaction. An amount of force equal to that being used to move the air is being transmitted to the floor, then walls, windows, etc. Not only do these vibrations create their own sound waves and rattles, but they bother the neighbors. I know some people who use isolation platforms to dampen the subwoofer. I think this works better, you can leave your cd's on top of the sub and never hear any rattling.
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Old 5th December 2006, 06:54 PM   #8
theNoid is offline theNoid  United States
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Quote:
Originally posted by mac-attack
Hmm, did some more searching and found one answer to my second question regarding cancellation of vibrations:

dual driver vibration cancellation really does work!

According to this, there really is a point in employing push-push, or even better, push-pull mounting.

Still, wonder why it isn't used more often then ... I can understand why push-pull probably isn't a viable commercial option, with one driver at the back with the magnet sticking out ...

M.A.
I have used such an arrangement many times in the past. Usually on the opposing ends of a length of PVC pipe.

Noidster
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Old 6th December 2006, 04:00 AM   #9
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Here is isobaric subwoofer (12" car drivers are prepared to put into the folded horn box) on the attached picture.

After finishing it I started thinking it was may be waste of materials: if I used separate 12" drivers total square of them would be bigger so less power will be needed for the same acoustical pressure. It means less distortions. In case of isobaric arrangement symmetricity compensates even harmonics, while I believe resulting odd harmonics will be higher than in the 1'st case, with more square and less power.
Am I right or wrong?

Click the image to open in full size.
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