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High Efficiency Speaker Asylum Need speakers that can rock with just one watt? You found da place. |
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High Efficiency Speaker Asylum Need speakers that can rock with just one watt? You found da place. |
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In Reply to: RE: JBL Scoop posted by Hornlover on September 28, 2007 at 08:33:11:
The optimum Qts for minimum box size and maximum bass extension is 0.312
Qts in the range of 0.25~0.40 is OK.
If much higher than 0.40 a sealed box is indicated, if much lower than 0.25 a horn is indicated.
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A little known fact is you can 'burn' Qts if it is lower than what you need(no more than 20%).Another tactic would be to use the low Qts to reduce the box size and raise the Fb to keep it flat.
The optimum Qts for an equalized 6th order Butterworth design(not to be confused with a bandpass design)is .312 .The formula for box size is Qts*Qts*4.1*Vas=Vb.The formula for Fb is (Fs/Qts)*.312 .For a Qts of .312 the Faux(eq frequency)=Fb with a Q of 2 .
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Box size is roughly proportional to the square of the Qts, so the lower the Q the smaller the box. Also the lower the Q, the higher the efficiency. Bass rolls off though if the Q is too low, the magnet can be too big for its own good.
For a vented box, the optimum Qts is 0.312
0.312 gives the best bass extension, minimum box size, and highest efficiency.
Posted by djk ( M ) on July 25, 2005 at 00:55:59
A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB).
A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB).
A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB).
The correct box size for a Qts=0.312 woofer for the 6th order vented design is Vas*4.1, Fb=Fs=Faux, Q=2 for Faux.
Without the Q=2 filter the box is an SBB4, with the best transient response of all the standard vented alignments, with the filter it is a B6(maximally flat).
The link describes a couple of DIY 6th order sub designs from JBL.
http://www.lansingheritage.org/html/jbl/reference/technical/1983-subs.htm
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The Qts of the old JBL drivers is way to low to be optimum for bass reflex.
Will they work?
Sure.
But they will sound more balanced in a BLH.
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Follow Ups
- Low Qts - djk 03:03:05 09/29/07 (0)
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