Capacitor Biasing in Crossovers

[GM]

OK, time to show my ignorance...... Sadly, I have zero formal education on the subject, only some technical references I consider beyond reproach that in my ignorance I could very easily be misinterpreting, so by leakage current, are you referring to the cap's conductance due to the electrical circuit's capacitive reactance WRT frequency or......?

I've always taken for granted that 'conductance' means just that, (current/whatever) flow that can be a considerable percentage of the whole in a tweeter's XO BW if I'm understanding what I'm reading correctly.

GM

[mah]

Conventional electron current does not flow through a capacitor, except for a small current due to leakage impedance. However, charge transfer occurs from plate to plate enabling current to flow in the external circuit.

Also, current does not flow through a transformer with separate windings.

[mah]

Thanks, bfish,

Interesting, especially the bit about capacitor transient response. I would like to see the math or physics behind the claims.

Marshall.

[bfish]

Thanks, bfish,

Interesting, especially the bit about capacitor transient response. I would like to see the math or physics behind the claims.

Marshall.

You're welcome.

Well, zero-crossover distortion is well documented. Various amp topologies address it (or not) in different ways. By biasing the signal with a DC offset, you can elevate it so it never crosses zero. The CC method definitely achieves this, at least as long as the circuit voltages don't exceed the bias level. The only real question...is it audible, or at least enough to warrant doubling the size and cost of the crossover capacative elements.

[GM]

Thanks for the info guys!

GM

[mah]

Link posted on current thread on this topic on the Hi Eff Speaker Asylum:

http://manuals.harman.com/JBL/HOM/Te...800SE%20ts.pdf

[mah]

One on distortion in cables and dialectric biasing in cables:

www.audioholics.com/education/cables/cable-distortion-and-dielectric-biasing-debunked

This site has a lot of good stuff on cables and other things.

[bfish]

Thanks for the info guys!

GM

You're welcome. And it's a rare day when I can say that to you.

...zero-crossover distortion is well documented...

Guess I should qualify that a bit... it's well documented in amps and active devices. I'm having trouble seeing how it would mean squat to a chunk of wire...

It's a bit amusing the number of low-component-count minimalists that forget the nasty effects of all caps and have no problem doubling the cap count to get some ambiguous "low level detail".

One of these days I'll change my signature to;

"Just another reason to biamp".

[wws944]

Roger Russell (former head of McIntosh Labs loudspeaker division) has some interesting things to say about 'high end' loudspeaker cable. See: Speaker Wire

The rest of Rogers site is also a lot of fun to read. He has some amazing info there.

[bfish]

...so by leakage current, are you referring to the cap's conductance due to the electrical circuit's capacitive reactance WRT frequency or......? ...

Consider a caps' construction. Two conductive 'plates' are separated by a very thin, non-conductive dielectric material. No way for current to flow unless the breakdown voltage of the dielectric is exceeded, or the dielectric is damaged in some other way, such as deterioration of the dielectric oxide in electrolytic caps. Leakage current is undesirable, it's the result of the dielectric material being a less-than-perfect insulator and passing a negligable current flow. Leakage is also the reason a charged, out-of-circuit cap will eventually discharge itself.

The mechanical analogy I was taught was that of a thin rubber diaphragm stretched across a water pipe, where the water pressure represents voltage. As the pressure (voltage) on one side of the diaphragm increases, the diaphragm stretches towards the side of lower pressure, forcing water movement in that direction. As the pressure decreases, the stored energy is discharged, and the cycle reverses in direction, following the alternating pressure source. Energy is transferred, but no current actually passes thru the diaphragm, save for a tiny bit of leakage through a pinhole (imperfect insulator). Exceed the pressure the diaphragm can withstand, (breakdown voltage) and it bursts, allowing flow (a short).

Another telltale sign is that caps have no current or dissipation rating as do all conductors or resistive devices that actually carry current. Nor do they produce the heat indicative of power dissipation.

I found this animated gif that shows a similar analogy in a smoothing application, as used in a power supply;