Hello all,
Thoght you might like to read this.
Using Capacitors
Hybrids, Parallels--Voltage and Precision ratings for crossover circuits
Capacitors do two things when used with circuits having alternating current (music signals)
1. They filter the signal—Cross-over according to the size (“value”) of the capacitor in micro-farads and the impedance of the circuit (expressed in Ohms).
2. They also stabilize a circuit in terms of the speed of delivery and recovery associated with an impulse (note of music).
In terms of filtering a musical signal to protect drivers from signal overload from too much volume or too much bas, electrolytic type capacitors and film type capacitors work equally well.
In terms of stabilizing a circuit, film capacitors sound much better (see About Capacitors)
Do Not Use Polarized Capacitors in Crossovers!
Electrolytic types must always be special Non-Polar types (sometimes called Bi-Polar). By definition all film types are non-polar types.
Hybrids/Bypassing
NP Electrolytic capacitors, which are less expensive, can be mixed with film types (which are more expensive) to form a hybrid capacitors that delivers a cleaner signal than a simple NPE type. The practice is called bypassing.
The higher the percentage of film in the bypass/hybrid arrangement, the better the impulse characteristics (i.e. the DF—the measurable Dissipation Factor.) One percent of film will not do much to improve a NPE capacitor’s performance, whereas a 50/50 mix can do a lot.
Paralleling
Capacitors can be mixed, without regard to the type (film or NPE) to build a larger cap that is the sum of the two (or more) individual values. This can be very useful to get special values or to use capacitors on hand rather than paying costly shipping and handling charges to buy individual value capacitors.
Voltage Ratings for Crossovers:
Rating should be about 30 percent above the voltage of the amplifier’s power supply.
For automobile installations any capacitor rated for 50volt use or above is abundant
For home speakers, any capacitor rated for 100volt use or above is abundant.
Higher voltage ratings give only marginal improvements at best, compared to better dielectric material (a basic 100 volt Mylar capacitor will sound vastly superior to a 200 volt NP electrolytic)
A voltage rating expressed in VAC is actually about 50 % greater than the same in DC.
How much precision is necessary?
Capacitors can—and do!--vary in precision (even in the same lot) but always within the tolerance specified as +/-on the cap. NPE caps tend to measure on the high side, film on the low side.
Generally one need only be within 10 percent of the crossover value called for in the design (i.e., for practical purposes, a 4.7uf cap and a 5.0 cap are interchangeable in almost all crossovers).
And This
About Capacitors
What you DON’T hear can matter most
For speaker crossovers and automobile sound installations, capacitors break down into only two types: film and electrolytic. Film caps cost much more than electrolytics to manufacture but they deliver a much better pulse, which gives a “cleaner” sound.
The measure of capacitance is microfarads, written on the capacitor as either “uF” or “mfd.” This tells you what is called the value of the capacitor in uF’s, but it does not tell you about the quality.
Capacitors are essentially batteries that charge and discharge extremely quickly. The better the material used, the better they perform. If you could see sound, electrolytic capacitors would deliver a yellower light and film capacitors would deliver a brighter, whiter light. In midbass and woofer crossover circuits, this is generally not a difference one can hear. In midrange crossovers it makes a difference--and for tweeter circuits, where the ear is especially sensitive, the choice of capacitor can makes a big difference. Here not only film but the kind of film capacitor used can make an audible difference. It is worth noting also, that electrolytic types can dry out, leak, or downright fail over time, while film types never go bad and are even self-healing if overloaded.
Electrolytics employ alum. oxide on a tiny roll of paper with a dab of electrolyte in a can stoppered against leakage. Film caps use a thin strip of flexible plastic with metal particles vapor deposited on the surface and rolled into a cylinder. Whether they are wrapped in tape (usually yellow) or dipped in epoxy (often brown) makes no difference. Also, radial (two legs pointing down) or axial (leads at either end) makes no difference either. Only the material inside matters.
If you want to see the graphics let me know and I can forward it to you.
Dale
