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tjrad
04-26-2009, 04:25 PM
Anybody know the displacement of a 128h?

Thanks,
Tom
duaneage
05-01-2009, 12:23 AM
Anybody know the displacement of a 128h?

Thanks,
Tom
Vas is around 7.9cu feet on a good day. Specs are published for all JBL woofers on this forum search around a bit and you'll fnd a large chart with all drivers listed.
Allanvh5150
05-01-2009, 01:13 AM
Vas is around 7.9cu feet on a good day. Specs are published for all JBL woofers on this forum search around a bit and you'll fnd a large chart with all drivers listed.

I think he was meaning the physical displacement of the driver not the cabinet.

Allan.
duaneage
05-03-2009, 07:36 AM
And that is what 7.9 cu ft is. Qts is around .23 and the FS is 23 or so. YMMV and these numbers are approximate. Only testing will show for sure what a given pair are doing these days. SD is determined by measuring the cone. All specs are published for free on this driver at jblpro.com or this forum.

If he is looking for an answer to his isobaric problem that has already been covered.
Earl K
05-03-2009, 08:46 AM
I think he was meaning the physical displacement of the driver not the cabinet.

- JBLs' Pro twelves having 4" voice-coils are typically stated as displacing .15 cu ft ( within an enclosure ) .
- Their 3" voice-coiled model # 2020H is stated as displacing .11 cu ft according to a product sheet ) .

- The 3" voice-coiled 128H ( with a slightly smaller magnetic assembly ) should be a bit less than the 2020H / I'd guess .1 cu ft .

- FWIW, the addition of standard amounts of fiberglass damping materials reclaims these driver displacements / as well as the typical bracing displacements ( so it's all a bit of a moot question for a standard BR design ).

>< cheers :)
duaneage
05-03-2009, 10:54 AM
Difference in terminology. As to how much air is lost by having the driver in the box too, a usual recommendation is to bump the box volume 10-15% above calculated to accommodate bracing, ports, crossover and driver parts.


One way to determine it more precisely is to close the ports and measure FS in an enclosure. Then the volume of air inside can be extrapolated. deduct bracing and the port and you are left with a pretty close figure for driver volume. There are always leaks around the surrounds and through the dust cap, though minor, so in the end it comes down to an approximation at best.
tjrad
05-03-2009, 02:14 PM
Hi Guys,

Thanks for the numbers... I estimated about 100 cu in, so I'm pretty close.

Tom