Bi-Polar Capacitors (Sound)
The following list of capacitors that are used by sound decoders where a Bi-Polar (Non polar) capacitor is wired in series with the speaker. The terms "Bi-Polar" and "Non Polar" refer to the fact the capacitor has no DC polarity. There is no "+" or "-" terminals or markings as such on the capacitor. You cannot hook it up backwards!
If you look at the picture on the left, the top one is marked "N P" for Non Polarized.
In the Next picture we have some other capacitors with the markings of "B P" for Bi-Polarized.
If you want to learn more about why these capacitors are needed or used, see at the bottom.
The following parts are available at MOUSER: http://www.mouser.com
Parts in bold are the best parts to use in terms of physical size.
Why a Bi-polar or Non Polarized capacitor?
Normally capacitors do NOT have any polarization of any kind. See: Capacitance However, the common Aluminum Electrolytic (AL) type offers a lot more capacitance per volume at the lowest price than any other capacitor technology. The consequence of AL capacitor is that it is polarized capacitor due to the physics/chemical properties involved inside the capacitor. Fortunately most electrical circuit designs use DC power, in which case the polarized nature of a AL capacitor is NOT a disadvantage.
So what happens if the circuit involves AC power such as found in Audio Circuits. More specifically when working with speakers?
It turns out that using those other types of capacitors, (Not AL), will result in a physically large and expensive capacitor.
Enter the Bi-Polar AL capacitor. This can be done with the use of a "circuit trick" of placing two polarized AL capacitors in a "BACK to BACK" series configuration. The negative terminals of both capacitors are tied to each other and insulated leaving only the two positive terminals free for circuit connection. Both capacitors must be EXACTLY the same make and model capacitor. This is how these Bi-polar AL capacitors are built. The manufacture simply puts these two capacitors inside one package giving it the appearance of a single capacitor.