I was talking with a friend today and he suggested that capacitors in speaker cross overs go bad with time. Any truth to this?
New Guy Mike – Like many things in audio, the story with crossover capacitors has a small bit of truth to it, and that has been the source of a lot of myth & misinformation.
There are different types of capacitors. The two most common types you'll see in speaker crossovers made today are called non-polar electrolytic (NPE) and metalized polypropylene (MPP).
The NPE caps are usually the least expensive, and the MPP caps (and similar caps made with other metalized plastic films like polyester or mylar) are moderately priced and upwards. Some people refer to these as film caps, without naming the type of plastic film.
Some of the NPE caps (not all) have a solvent inside them which can dry out over time (more than 30 years). If that happens, the caps can loose their capacitance, and go out of spec. The MPP caps have no solvent to dry out, and stay in spec.
The other thing to remember is that some cheap NPE caps may have never been in spec from the time they were new. I know that is true for some (but not all) cheap NPE caps made now. If their label says 6.8 µF ±10%, some will be within the ±10% range of 6.1 to 7.5 µF, and others will be outside of that range. Of course, with 30 year old NPE caps, it isn't possible to know what they were like when new.
All the MPP caps I've had my hands on have always measured exactly as the label says. So if I am building a DIY speaker, I nearly always use moderately priced MPP caps. On rare occasion, to hold costs down, it's worth it to use NPE caps if larger capacitance values are needed.
However, that doesn't mean all NPE caps on older speakers should be replaced. They may not be dried out and out of spec. You can know for sure only if you remove them from the crossover and measure them. And more often than not, any speaker that old, may have a crossover that is poorly designed by today's standards. It will need more than "recapping" to sound good.
A major myth has grown out of all this cap business. People claim – falsely – that different types of caps in crossovers have different characteristic sounds. I am confident that there is no truth to this. As long as a cap delivers the intended capacitance value in a crossover, no one has been able to identify the different types by their sound.
