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offset bipole enclosure question
offset bipole enclosure question
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Old 9th July 2018, 01:31 PM   #1
ewollowe is offline ewollowe  Australia
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Default offset bipole enclosure question

One of the advantages of a bipole is that with drive units back to back you eliminate of lot of box resonances.

My question is how much would an offset lose this quality?
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Old 10th July 2018, 12:14 PM   #2
jimbro is offline jimbro  United States
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offset bipole enclosure question
I think you would have almost no force cancellation. My understanding is that the most effective method physically couples the two drivers as closely as possible and that this is most desirable in the bass. An offset bipole helps with room modes. I'd vote for the offset in a well braced box.
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Old 10th July 2018, 12:22 PM   #3
ewollowe is offline ewollowe  Australia
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Thanks jimbro,

What about drivers coupled together but well offset from the center of the baffle? Best of both worlds?
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Old 10th July 2018, 02:23 PM   #4
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There are likely other advantages to mounting even monopole drivers off centre, such as more widely distributing/ “randomizing” both panel resonances and edge diffraction artifacts. Whenever possible, I’ve done that, as well as mirror image the driver placements.
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Old 10th July 2018, 02:32 PM   #5
ewollowe is offline ewollowe  Australia
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It seems to be a common theme here. Symmetry is the enemy.
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Old 10th July 2018, 05:31 PM   #6
jimbro is offline jimbro  United States
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offset bipole enclosure question
This is what I think of when I hear offset bipole- http://p10hifi.net/planet10/CSS/EL70...ltl-100909.pdf You could take it further by building one speaker with the back driver below the front and one with the back driver above the front. If you had a wide baffle you could vary where you mount all the drivers and you could use different distances to the side walls. Just ideas to play with. I'm not sure about closely coupled full range drivers. I'd be worried that it would muck up the mids and treble but maybe not. At any rate, you would not get the benefits of that a true offset bipole is designed to give.
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Old 10th July 2018, 10:29 PM   #7
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Quote:
Originally Posted by ewollowe View Post
It seems to be a common theme here. Symmetry is the enemy.
Correctomundo! For high aspect ratio cabs, the subject is acoustical loading in a bounded space, so standing waves/eigenmodes rule and as such, driver[s], vent[s] load best overall at its odd harmonics with max loading when the driver, vent is at the extreme opposite ends [fundamental/1st harmonic] with the trade-off of having the strongest peaks, nulls, smoothing out as the driver is shifted down to a point of diminishing returns based on its length, taper for a given Fb[p].

In a simple sealed or vented alignment OTOH, the air mass 'spring' is considered to have a ~uniform particle density, so no eigenmodes, ergo the driver[s], vent[s] can be anywhere on the box.

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Old 11th July 2018, 01:35 AM   #8
ewollowe is offline ewollowe  Australia
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Thanks guys,

I was quite enamored idea of a coupling the drivers together to make up for my poor carpentry skills but you've pushed me more towards the offset design.
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Old 11th July 2018, 02:02 PM   #9
jimbro is offline jimbro  United States
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offset bipole enclosure question
What drivers will you be using?
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Old 11th July 2018, 10:16 PM   #10
ewollowe is offline ewollowe  Australia
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What drivers will you be using?
I've got a bunch of different drivers lying around from various projects but would most likely use the widerange tangband W3-871 or some of the cheap 8" fullrangers I have. I've already made a very basic 12"sealed sub and also have four 8" polycones for future bass duties.

Like many here I spend far more time thinking about building speaker than actually cutting wood and now my new job is really eating into the time I have to mess around with this hobby :/
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