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stevem
11-30-2004, 09:01 AM
Is there any reason why you shouldn't put two woofers (operating from 300 Hz down) in one large vented enclosure, instead of an enclosure with two separate vented compartments inside? Will they interact with each other, or just behave as a single larger driver? Thanks!

GordonW
11-30-2004, 10:26 AM
As long as the woofers are IDENTICAL (ie, same model) wired in PARALLEL, they should work fine. If they're in SERIES, they should optimally be in seperate compartments. Parallel woofers can "self-balance" themselves pretty well...

At less-than-300 Hz, a pair of woofers should pretty much act as one big woofer. Wavelengths at 300 Hz are about 3 feet... so, pretty much any woofer 15" or smaller should work paired up at that crossover point.

Regards,
Gordon.

Tom Loizeaux
11-30-2004, 05:29 PM
As long as the woofers are IDENTICAL (ie, same model) wired in PARALLEL, they should work fine. If they're in SERIES, they should optimally be in seperate compartments. Parallel woofers can "self-balance" themselves pretty well...
Regards,
Gordon.

Gordon, please explain why woofers wired in series should be in seperate compartments.

Thanks,

Tom

Lawrence HF
11-30-2004, 06:18 PM
Hello Steve, from the reading I've done, the power handling of two LF units mounted close together will be 3 DB higher, and mutual coupling may give 2dB more at low freq. Also the polar radiation patern will not be as wide as one unit if mounted side by side. The recommendation is one above the other, close.Read more in, From sound recording by John Eargle.

GordonW
11-30-2004, 07:57 PM
Gordon, please explain why woofers wired in series should be in seperate compartments.

Thanks,

Tom

Basically, because the back EMF from one driver can modulate the signal to the other. In some (albeit rare) situations, this can lead to an 'oscillation' between the drivers... where one will move "in" while the other is moving "out", to a small relative degree. This condition is exacerbated in situations where the driver parameters are not exactly the same (ie, one has a stiffer spider/surround than the other, not uncommon)... two drivers with slightly different resonant frequencies can act different near/between the resonance points.

OTOH, drivers in parallel, the back EMF effects will be swamped by the damping of the amp. Unless you're using an amp with a high output impedence (ie, tube amp or any other amp with output transformers), the amp should "control" the drivers pretty much completely, especially in the case of JBLs where more driver damping comes from the motor (instead of the suspension), relative to other brands of speakers.

To be fair, this is usually a VERY small effect... but if the ideal is "perfect sound", it's something that's simple enough to avoid...

Regards,
Gordon.

stevem
12-01-2004, 07:27 PM
If you had a choice, though, would you use one enclosure or two? Assuming identical woofers and parallel connection.

Alex Lancaster
12-01-2004, 08:30 PM
:) I would use one enclosure, separated by a board, for rigidity; though it makes them more difficult to move.

Tom Loizeaux
12-02-2004, 05:48 AM
The question was ...why is working them in series any more problematic then working them in parallel?

Tom

4313B
12-02-2004, 06:19 AM
"Best Practice" is a single volume for each transducer. Reference systems such as the 4435 as opposed to the 4350. ;)

This question came up awhile back so I bothered to ask a few guys at JBL how they felt knowing full well what their answers would be.

For Project May, "worst case" was going to be a large single volume for the dual 1500AL's. Note that large single volumes can be "good enough" for some applications.

stevem
12-02-2004, 08:37 PM
Thanks, everyone. I really appreciate the help.