Electrolytic caps for low frequency

[Ccdave]

What would be the reason to use low cost electrolytic caps for the woofer on a 3 way crossover design. Seems like the poly caps are used more for mids and tweeters

[mikee3333]

Because the lows are base and brutal, they require only an age-old fat cap.

The middle class and the upper class are more delecate.

[kevinkr]

Generally larger values are required at low cross-over frequencies, cost and size are usually a primary consideration - performance in a budget/compact design may be of secondary or even lower importance.

[Cal Weldon]

Because the caps on a woofer are shunting? If they're not they're used as protection from infrasonic or close to it and are the only ones the manufacturer could use and still make a profit.

[MCPete]

Caps in-series with a woofer can lower f3 of the woofer. Recently I put 800uF in-series with a woofer to lower f3 from 80 Hz to 60 Hz. For some DIY-types, such as myself, for that much capacitance, I had to do it with NP electrolytic.

To further reduce the cost, I used 4 polarized electrolytic, two 330uF back to back in parallel with two 470uF back to back.

Not that anybody really cares, and this is wandering away from the original query, but I'll put this out there anyway.

Have there been any scientific studies showing that (new) electrolytic capacitors are severely detrimental in some way?

[woody]

Walter Jung did a large study " Picking Audio Capacitors " where he showed the distortion caused by diferent capacitor types. In paticular electrolitic caps used in coupling have a great deal of distortion. But perhaps when just used for your woffer
you may not notice the distortion. But in a case like yours you may want to try aplying a DC bias to the junction of your polarized electrolitics and in your case a
9V battery and resistor any where between 10K and 200K would work and the battery should last for a long time.

[Wavebourn]

Couple of electrolytics back to back, and simple diode rectifier across them does the job (2 diodes and 2 resistors). No need of any battery, and absolutely no audible distortions, if resistors are say 1 K, at least 500 times more than impedance of a voice coil.

[MCPete]

The following is from an application guide for Al electrolytic caps, by Cornell Dubilier:

"If two, same-value, aluminum electrolytic capacitors are connected in series, back-to-back with the positive terminals or the negative terminals connected, the resulting single capacitor is a non-polar capacitor with half the capacitance. The two capacitors rectify the applied voltage and act as if they had been bypassed by diodes. When voltage is applied, the correct-polarity capacitor gets the full voltage."

According to the above, you can make a non-polar from two polarized caps by connecting them back to back, and that's it, no other components are required.