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I am considering going active at the moment and read that it was essential to use series protection caps to avoid damaging diaphrams.Is this the case? and if so , what value would be typically used on a compression driver crossing around 650hz? Would a series cap affect any values for a passive low pass applied to the same drive unit?
Also would it not affect the drive unit damping as well?
Follow Ups:
It isnt always needed. I ran my Altec 802's without one for 30 years, and never had a problem. Most people will never have a problem. If you are using a tube amp, then its not needed, since a tube amp's transformer cannot pass DC. It is a rare case where a solid state amp will fail, and apply the full rail voltage to the output, but it can happen. If this possible failure mode makes you feel uneasy, then a series cap can help to protect your voice coil. In all of my years in audio, I have bi-amped many systems. I have seen this failure mode only once, and that was with a rock bands PA system.
Depends on the dc resistance of the voice coil....
Thanks for that. So the value should be the same as for a first order passive high pass? I had heard that, but some people have claimed you should actually do without it.If it's neccessary with compression drivers to fit this, why bother to go active at all? I'm confused. Everyone talks of the advantages of hardwiring the drive unit to the amplifier, but then it's suggested that you cannot do that safely.
The usual practice is to use a value equivalent to a 1st order filter 1 octave below the crossover frequency. With a low crossover use two caps, parallel values with a 10:1 ratio. The main reason for doing so is to protect the driver from DC (in case of amp failure) and turn on/turn off transients.The advantage of bi-amping has little to do with direct wiring to the amp. It's to get the advantages of high crossover slopes, elimination of passive crossover insertion loss, noise and distortion, reduction of IM distortion and being able to use two smaller amps rather than one larger one.
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