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Old 11th October 2004, 04:48 PM   #1
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Default Loudspeaker Alignment questions..

Would want to know how does the below alignments actually sound?
1)B4
2)B3 AND QB3
3)C4 AND QC4
4)BB4 AND SBB4

why are these alignments kinda prefered compared to the standard B4 .Are speaker box manufacturers utilizing them in their products faithfully..?
Anyone has a link where i could utilize the above alignments in a software or spreadsheet?
thanks in advance!
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Old 11th October 2004, 07:54 PM   #2
pxr5 is offline pxr5  United Kingdom
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sound impression depends upon fc as well as q
a q value of 0.5 or less is good from a clarity point of view
but with a highish fc, say 75 hz you'll not hear it.
i've aimed for a speaker q of 0.25 and had to stick with box resonance of 45hz and used a linktwitz transform circuit to end up with qtc of 0.49, fc 18 hz and sounds fairly well balanced and tight with baffle step of 4db in 45 cubic meter room.
of course ya need to consider xmax for all the differing alignments as q 0.8 with fc 30hz just aint gonna work
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Old 11th October 2004, 10:30 PM   #3
Ron E is offline Ron E  United States
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The alignments you mention (Except for BB4 & SBB4 for which I am unsure of the origin) are those with interesting properties that communication engineers working in the telephone/radio industry decided had advantages for some reason or other. Their main advantage was that they were easy to calculate in the age before computers. They still make good starting points or sanity checks for your designs, but there is nothing magical about them.

B4 is butterworth 4th order - the denominator polynomial has the well known butterworth coefficients.

BE4 is Bessel 4th order, with Bessel coefficients

C4 is Chebyschev 4th order - with Chebychev coefficients. SC4 is an extension of C4 for lower Q drivers.

QB3 is Quasi-butterworth 3rd order. SQB3 is an extension of QB3 for drivers with higher Q's than QB3 applies to.

I know how to calculate all of these, and I was once as keen to find out about them as you may be. After I figured it out, I noted that there was little need. These alignments do not even apply to more complicated models.

The two sets of curve fit equations below (from memory) will get you a good starting point :
(Attributed to Samll-Margolis, 1981)
Vb=20*Vas*Qts^3.3
Fb=0.42*Fs*Qts^-0.96
F3=0.26*Fs*Qts^-1.4

(Attributed to DB Keele, Jr.,?)
Vb=15*Vas*Qts^2.87
Fb=0.42*Fs*Qts^-0.9
F3=0.26*Fs*Qts^-1.4

Having graphed all of this stuff together, I will say that both of these appear to be curve fits of QB3 for Qts<0.4 and C4 for Qts>0.4, but they have different Qts ranges, hence the different values. Trying to use these curve fits outside of 0.5>Qts>0.2 is probably a mistake.

Don't get hung up on alignments. It is a waste of time. Just make sure your speaker has a monotonically increasing SPL curve (no peaking) and you are almost assured of good response.
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