Cornwall B3 70uF cap crossover question

[funkwrench]

Hello,

Just a quick question: What is the purpose of the big, 70uF cap across the woofer in my Y vintage Cornwalls? I have heard of this cap casually referred to as the garbage cap, or some such thing. Is this a high-pass component, meaning is it passing garbage low freqs, e.g. <20hz; or is it part of a low-pass filter, sending higher freqs to ground? Thinking about this thing keeps me awake at night.

Thanks!

Joe

[funkwrench]

Sorry, the robot cut-off my original question. Nothing important but here it is:

Hello,

Just a quick question: What is the purpose of the big, 70uF cap across the woofer in my Y vintage Cornwalls? I have heard of this cap casually referred to as the garbage cap, or some such thing. Is this a high-pass component, meaning is it passing garbage low freqs, e.g. less than20hz; or is it part of a low-pass filter, sending higher freqs to ground? Thinking about this thing keeps me awake at night.

Thanks!

Joe

[WMcD]

It is part of the low pass filter. The other component is an inductor. These make sure that only low freqs go to the woofer. A good thing.

It is a relatively big value at 70 uF. Therefore it is most likely a non-polarized eletrolytic. I have heared people criticize the use of electolytics, particularly when there is an alternative. But in this case there is no reasonable alternative. You could spend a lot of money on paralleled film caps. [Whoops, see below, djk points out some good deals. Prices have come down since I was buying caps some years ago.]

There is a theory out there that components in series with the driver must be high quality because the signal goes though them; and that components which are across the driver, i.e. connected to ground need not be. The theory is that the path to ground does not affect the signal; it is just shunting to ground. This is contrary to common-sense engineering.

There really is no "garbage" issue. Klipsch is widely known as an excellent manufacturer. It is odd that people think they are doing something cut-rate.

Wm McD

[djk]

For a while Klipsch used one of the big 70µF film caps like they used in the Klipschorn, then they decided to save money and go for the inexpensive electrolytic.

Madisound has some surplus polypropylenes that would cost $11.34 to make a pair of 70µF, Solen will cost $38.20 a pair, Parts Express has a couple of brands in the $35 a pair region.

[funkwrench]

Thanks for those responses. Parts express sells good replacements - I think a 68mF Jensen is what I used - that may have cost about 30 for the pair. No matter, it was only the question of the high or low pass that troubled me.

Cheers.

Joe