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In Reply to: RE: How do I demagnitize my speakers, would that not make them useless... posted by ABliss on March 06, 2015 at 19:18:17
A speaker well worth investing in and not compromising on with the crossover.
I an not into caps, especially names, series, etc. I have found in the past oil caps tend to be less harsh with cone drivers. Also, whenever possible, I try to build a bank of caps rather than use a single for a couple of reasons. First, with a cap checker you can build a matched set of caps. You mention a 15 mfd cap. If you buy a pair lf caps the a +/- 10% spec, you could end up with 1 reading 135mfd and the other being 165mfd. Each are in spec but, look at the difference between them. That is a 20% difference. Using multiple caps allows mixing to bring that difference down significantly. I did this recently and using 2 caps to make a single matched the pair to be the exact schematic specification and within .1mfd difference between the pair. If I used a single 10% I would be in spec if the difference was .8mfd.
The other spec of concern is the esr. This is the effective resistance in circuit of the cap. Ideally, there should be none so, only the driver's impedance is seen. Resistance is lowered when caps are put in parellel. Say 2 caps have an esr of 2 each. The result is 1.
Another cap consideration, though not related to this discussion is the working voltage. There are formulas on the web to calculate it but if considered it can act as a speaker protection device. A rough estimate for an 8-ohm driver is about 1 volt for the maximum output voltage of the amp. This is why with many speakers you will find caps with voltages close to the maximum recommended amp power. The value chosen in a well engineered crossover was not dictated by price, cap quality, etc as many diy and nonpros propose. Better a relatively cheap cap than an expensive driver. Recently, I was reminded of this when I screwed something up and sent a massive pulse into a Klipsch Heresy II. The tweeter cap let go saving a far more expensive tweeter.
You have a great speaker system. Spend some time to get them up and running. Then spend some time mating them with a system. Thankfully the company and Richard are still in business.
Don Brian Levy, J.D.
Toronto ON Canada
Follow Ups:
"The other spec of concern is the esr. This is the effective resistance in circuit of the cap. Ideally, there should be none so, only the driver's impedance is seen. Resistance is lowered when caps are put in parellel. Say 2 caps have an esr of 2 each. The result is 1."
You are assuming that all these caps have the same ESR, which is unlikely.
ESR isn't typically mentioned in speaker crossover capacitors, that may be a bit of a hint (that's it's universally quite low).
"A rough estimate for an 8-ohm driver is about 1 volt for the maximum output voltage of the amp."
Huh? For an amp that puts out 2.83 volts at 8 Ohms (1W), you want a 4V rated cap? I would want a rating 1.4 times the incoming voltage... When a cap "goes", it often fails shorted, which is not good for your tweeters.
Check the formulas. My # for 8 ohms is just an estimaate, not per the formula. The formula does yield something higher than what I stated, though it varies. I only know of one speaker stating a max voltage and plugging the perameters into a formuala years ago it came close to what I estimated. At the time McIntosh advertised its output voltage. The speaker was rated at 50 volts and the MC250 was listed at 49.5 volts. I used that pairing for some 40 years with no issue and nothing ever went wrong.
Don Brian Levy, J.D.
Toronto ON Canada
Uh, Ohm's law anybody?
50V into 8 Ohms is just over 300 Watts.
50V of AC signal into a 50V DC rated cap will have unfortunate consequences.
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