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Old 21st February 2013, 01:25 AM   #1
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Default 2 Drivers in one enclosure

Hi All,

I know this question has been answered already but I'm having trouble finding a thread. Sorry for asking again. 3 questions:

1. 2 drivers in a passive radiator design, both in a single enclosure. Desired location for the 2 drivers is not symmetrical in the enclosure. Does this pose a problem? Or does driver location not matter. Bracing for enclosure will not be symmetrical either.

2. Same question for passive radiator location.

3. If there is an existing thread, can you point me in the right direction?

Thanks for putting up with this question again.
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Old 21st February 2013, 06:33 PM   #2
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Quote:
Originally Posted by mikealanlee View Post
Hi All,

I know this question has been answered already but I'm having trouble finding a thread. Sorry for asking again. 3 questions:

1. 2 drivers in a passive radiator design, both in a single enclosure. Desired location for the 2 drivers is not symmetrical in the enclosure. Does this pose a problem? Or does driver location not matter. Bracing for enclosure will not be symmetrical either.

2. Same question for passive radiator location.
As long as the drivers and passive radiator are located within 1/4 wavelength of each other at the highest frequency of operation, location won't make a difference.

At 100 Hz, 1/4 wavelength is 2.8 feet, just under a meter.
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Old 21st February 2013, 06:44 PM   #3
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Default Great Information

Weltersys,

That is great information! Thanks for sharing the knowledge.

Best Regards,
Mike
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Old 7th March 2013, 10:27 PM   #4
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Yeah, in theory it doesn't make a difference. In reality, there are probably differences, but very small.

One note, though: if the drivers are opposed i.e. mounted directly opposite and moving in-phase (that is, the the cones move away or towards each other at the same time), vibration can be reduced a lot.
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Old 7th March 2013, 10:47 PM   #5
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Head Unit,
I think that the reduction of vibration only holds if the two devices are physically linked, tied together from the magnetic structure or such. Two speakers on opposing sides that are not linked could in fact multiply the effect as the baffles would see double the loading from the two drivers.
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Old 9th March 2013, 07:19 PM   #6
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Originally Posted by Kindhornman View Post
Head Unit,
I think that the reduction of vibration only holds if the two devices are physically linked, tied together from the magnetic structure or such. Two speakers on opposing sides that are not linked could in fact multiply the effect as the baffles would see double the loading from the two drivers.
You are correct.
What Head Unit perhaps meant is that rocking motion of a large panel (or cabinet) can be reduced by opposed drivers.

As an example, large drivers with heavy cones will cause "wall flop" when mounted as an infinite baffle in a wall, while when mounted in a plenum, the plenum mounted to the wall, the wall will move little.

Same thing on a cabinet, the whole cabinet will tend to walk around with front mounted cones, but when the cabinet uses a plenum (which can be parallel walls or a "V" shape) the cabinet will remain stationary.
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Old 9th March 2013, 08:04 PM   #7
badman is offline badman  United States
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Quote:
Originally Posted by Kindhornman View Post
Head Unit,
I think that the reduction of vibration only holds if the two devices are physically linked, tied together from the magnetic structure or such. Two speakers on opposing sides that are not linked could in fact multiply the effect as the baffles would see double the loading from the two drivers.
The coupling from the box is enough for some force cancellation, IME- better still is to couple the drivers directly, but much of the force still cancels in a "normal" box, where the baffles are narrow relative to the driver diameter (1.5x or so). Wider baffles reduce this effect, but one can cross-couple the panels, and not the drivers, and achieve some of the same benefit.
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Old 9th March 2013, 08:25 PM   #8
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Welterssy and Badman,
I agree that there are multiple mechanisms at work here. Yes you can tie the structure together rather that the two devices and achieve basically the same effect. I have a friend who built some rather large PA enclosures and what he did in that application was to use a tension compression method of rods to tie the opposite sides together. What happens when you sometimes use just bracing to tie the two sides together is that the initial compression of the two sides is lost as the wood relaxes over time and hence his solution of tension/compression to keep the panels tied together. It was an interesting solution to a long term problem in a fixed installation.
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