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Old 11th December 2011, 03:20 PM   #1
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Default What if Fs=Fb in ported box???

Well we know that in free air at Fs= impedance =max.

I have 15 inch paradimg drivers with Fs=18Hz , can i tune it to 18 Hz. currently using them in 2.5 Cuft sealed enclosure, they need good boot at LF to give 20ish output.

So the plan to go ported around 6-7 cuft .

Would it then have max or min impedance or current draw ?

Any draw back of doing it or should it tune it lower 13-15 Hz???


thanks
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Old 11th December 2011, 04:09 PM   #2
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Quote:
Originally Posted by muddasirwaheedmalik View Post
So the plan to go ported around 6-7 cuft .
A good starting point is that given by small-margolis in 1981:
Vb=Vas*20*Qts^3.3
Fb=0.42*Fs*Qts^-0.96
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Old 11th December 2011, 04:17 PM   #3
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Quote:
Originally Posted by muddasirwaheedmalik View Post
Well we know that in free air at Fs= impedance =max.

I have 15 inch paradimg drivers with Fs=18Hz , can i tune it to 18 Hz. currently using them in 2.5 Cuft sealed enclosure, they need good boot at LF to give 20ish output.

So the plan to go ported around 6-7 cuft .

Would it then have max or min impedance or current draw ?

Any draw back of doing it or should it tune it lower 13-15 Hz???


thanks
If you tune Fb to Fs, the impedance peaks (approx 1/3 oct each side IIRC) will be of equal magnitude. Tune lower, and the peak above Fb will be greater in magnitude than the one below Fb. Note that at Fb, impedance is at a minimum.

All of this is pretty much irrelevant if you're using a decent solid state amplifier - they'll drive any weird impedance curve you like.

Chris
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