>
> Cross posting from another list I lurk as the subject is of interest to m=
e
> as well (but the original list isn't as likely to get as good of a reply
> as here):
>
>> This circuit is alleged to be a bandpass audio filter:
>>
>>  Vin ---------||--------()()()()----------------- spkr, 8 Ohm
>>      --|                                     |---
>>        ///                                 ///
>>
>>  Value for C: 33uF, 66uF   (Cut: 600Hz, 300Hz)
>>  Value for L: 0.68mH, 1.5mH, 2.18mH  (Cut: 2.4Khz, 1KHz, 700Hz)
>>  Rolloff -6Db/octave.
>>
>> This is a common circuit in Yaesu's external speaker enclosures
>> such as SP-5, SP-6, SP-767.
>>
>> This is pretty goofy looking. I presume that the input in 8 Ohm.
>>
>> The caps are intended to implement a highpass, obviously,
>> the inductors a low pass.
>>
>> How to analyze this to reproduce the mfg's assertions about the
>> band limits and rolloff?
>>
>> Digital filters are a lot simpler (I have nice books about them!).
>
>
> Thanks in advance...
>

Well, you can use LTSPICE (from http://www.linear.com ) to do an analysis
of it. But, it just looks like a series resonant circuit. The resonant
frequency would be 1/(2*pi*sqrt(L*C)). The Q is X/R where X is the
inductive or capacitive reactance at resonance. So, get the frequency from
above, then use XL=3D2*pi*F*L. If you assume the driving amplifier is a zer=
o
ohm source, and the speaker is 8 ohms resistive (simple analysis), the R
is 8 ohms. BW between the two -3dB frequencies (Fl and Fh) is Fc/Q where
Fc is the resonant frequency. The center frequency Fc =3D sqrt(Fh*Fl) (it's
the geometric mean, not the arithmetic mean).

The roll-off will be 6dB/octave or 20dB/decade on each side.

Harold



--=20
FCC Rules Updated Daily at http://www.hallikainen.com - Advertising
opportunities available!
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.