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Old 26th July 2003, 04:18 PM   #1
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Default Subwoofer Alignments - Please Explain

Can someone explain to me the significance of the different subwoofer alignments? Specifically the different Q alignments...sometimes they are named, sometimes not. (sealed examples of Bessell, butterworth, chebychev or the vented alignments of EBS, SBB4 etc.)

Are these recommended Q values for driver/enclosures or purely guidelines etc?

Someone please explain the theory and reasoning behind these different alignments.

Thanks!
Jim
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Old 27th July 2003, 12:23 AM   #2
Ron E is offline Ron E  United States
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They are mathematical abstractions, which were more useful in the age before personal computers when it was difficult to run a simulation and plot the results.

They still make excellent starting points.

QB3/SQB3 - Quaasi third order butterworth
B4 - butterworth 4th order - maximally flat amplitude
BE4 - Bessel 4th order - maximally flat delay
SC4/C4 - chebyshev equiripple

SQB3 and C4 are nonflat alignments. SQB3 has a peak and C4 has ripples near cutoff.

B4 and BE4 are only valid at one Qts value for a given amount of losses. for Ql=infinity, B4 is at Qts=0.3827, alpha=1.414, h=1
for Ql=7: Qts=0.4048, alpha= ~1 and h=1.

Calculation is not trivial, but is explained in JAES by Small in the early 70's.

Don't get tied to alignments, they are not required for good sound.
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Old 27th July 2003, 12:30 AM   #3
SY is offline SY  United States
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Dickason explains this and the tradeoffs in the Loudspeaker Design Cookbook, with lots of useful charts, graphs, and tables. If you know the stuff in there, it will dramatically narrow down your sim work and actual measuring and cutting.
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