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Bob350L
11-12-2017, 12:59 PM
Howdy all,

1st post from a long-time reader.

I have acquired a pair of 119HS-1 woofers. These woofers were used in the Control 10's .
Looking at C4 of the crossover schematic,
http://www.jblproservice.com/pdf/control%20series/control%2010lr.pdf
a value of 66mfd is clearly shown.

Can this value be correct?

Is it supposed to be 6.6mfd?

I understand that the woofer has a rising response and I believe that part of the low-pass
is response correction.

Any help would be appreciated.

Thanks,

Bob

Earl K
11-13-2017, 07:15 AM
Hi Bob,

You'll need to run a frequency sweep or two to determine if C4 needs to be either 66uF or 6.6uF ( a response curve will give a solid hint )
- ( btw, mfd was replaced by uF, more than a few decades back now ;) ).

L2, C4 + R1 taken together create a ( parallel ) notch filter ( wired in series ) into the woofers circuit.

If C4 is as the cut-sheet states ( 66uF ) then the notch is centered at 462hz .
- ( btw, a small increase in the value to 68uF moves the notch center a bit lower to 455hz )

If C4 is valued as 6.6uF, then the notch moves up to a center frequency of 1460hz ( just past the stated crossover point of 1100hz ).
- ( 6uF centers the notch at 1531hz while the notch moves downwards to 1438hz with a 6.8uF cap ).

There's no real way to just guess which notch is most appropriate for any semi-pro woofer ( having a rising response ) since these notches can be useful when trying to either flatten a mid-band response bump or to perhaps better fit 2 curves together within the crossover area ( perhaps due to a 1500hz peak on the woofers FR that can adversely effects the combined response at crossover ).

I'd simply buy a non-polar 60uF electrolytic cap ( if convenient +/or available ) and then either a 6uf to 6.8uF polypropylene capacitor to explore all the options.
- in case you're un-awares, paralleling two caps together creates a new value from their summed values ( IOW ; 6uF + 10uF combine to 16uF when the two are wired in parallel ) .
- this 68uF cap available from Parts Express (https://www.parts-express.com/68uf-100v-electrolytic-non-polarized-crossover-capacitor--027-356) slightly moves the notch center slightly downwards to 455hz ( as previously stated ) .

Notch Frequency =
1 / ( 2 x Pi x ( sq root of Capacitance x Inductance ) )

Capacitance is expressed in Farads
Inductance is expressed in Henry's

:)

Bob350L
11-13-2017, 07:43 AM
Earl K,

The info in your response is exactly what I had hoped for.

Thank you so much. This place rocks!

By the way, between my use of mfd (thanks for the correction) and all of the grey in my beard,
one might assume I'm an old codger.

You would be unequivocally........... correct.

Thanks again,

Bob

Ruediger
11-13-2017, 08:16 AM
Together with L2 and R1 it forms a lossy parallel resonance circuit.

Ruediger