In Reply to: RE: 21" subwoofer posted by Pro Sound Guy on July 13, 2010 at 13:27:09:
That spec makes me a little skeptical. It wouldn't be the first time a typo has appeared in a catalog listing. Or a sketchy brand has printed incorrect information due to ignorance or deception. If they're as wrong as that about efficiency, I'd hesitate to trust anything they say about it.
It may be good value for a home infinite baffle or open baffle design. Possibly a vented box if you're willing to measure the actual T-S parameters.
The manual here: [url]http://www.pyleaudio.com/manuals/PDW21250.pdf[/url]
has T-S parameters, and says efficiency is 100 dB +/- 3 dB
Fs 22.4
Re 6.3
Qms 2.5961
Qes 0.3801
Qts 0.3315
Vas 703.8 liters
Sd 0.1706 m^2
EBP 58.8
Xmax 9 mm
The original post by Magnetar with the T-S specs was moved to Texas (baby, bathwater...) and I can't find a link to it. In a previous post he says every driver was slightly different, like different baskets and terminals and dust caps, although cone, magnet and surrounds appeared to be identical.
Quoted from another forum...
"From Magnetar over on DIYaudio.
Using 250 grams "mass loading" method and LIMP this is pretty much where they all average-
FS - 31.61
RE - 5.59
RES- 59.81
QMS- 4.03
QES- 0.38
QTS- 0.34
L1- 1.88
VAS - 274.29 liters
SPL - 95.4
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Follow Ups
- 107 dB/1w/1m? - bassbinotoko 12:18:51 07/16/10 (0)