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Old 14th February 2013, 10:12 PM   #11
SY is offline SY  United States
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Quote:
Originally Posted by Harleyjon View Post
I am sorry but "low microphonics" in a crossover, that has no gain?
Yes. Do you want the transfer function of the filter to wiggle around with the acoustic output? We call that effect "distortion." Since crossovers are generally inside of a cabinet, it becomes double-plus-ungood because of the very high SPLs to which the cap is subjected.
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Old 14th February 2013, 10:13 PM   #12
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I wouldn't build speakers with a passive crossover anymore. I'd either build using a quality FR driver or multi-amp with an active crossover.

I won't go into the arguments as to why this is preferable, but it's arguable that it is.

That's not what you asked, but I think it's in context.
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Old 14th February 2013, 10:33 PM   #13
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Originally Posted by counter culture View Post
I wouldn't build speakers with a passive crossover anymore. I'd either build using a quality FR driver or multi-amp with an active crossover.

I won't go into the arguments as to why this is preferable, but it's arguable that it is.

That's not what you asked, but I think it's in context.
Electronic crossovers are the choice of us professionals. I have worked with PA systems and home audio systems and passive crossovers give rise to vibration issues. In that, they tend to fall to bits. Never ever have I in 45years had a microphonic issue, just capacitors shedding their wires because the builder didn't allow for vibration.
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Old 14th February 2013, 10:35 PM   #14
SY is offline SY  United States
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I use a mixture so am likely to cheese off everyone.
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Old 14th February 2013, 11:03 PM   #15
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dre,
Sy is correct about just using a name brand capacitor and forget the audiophile nonsense. I actually know a capacitor manufacturer and I have seen more than one audiophile capacitor that is nothing more than a standard cap with a fancy cover. What I have done with passive crossovers in the past was to use either metalized film or foil/film polypropylene caps. You could use polystyrene but they are not quite a good as the polypro. Don't try and find high value capacitors, use multiple caps of lessor value and add them together to get the values you want. This has the advantage of being able to use lower cost capacitors and hand select the caps that give you the final values you are after. A bunch of 100mfd caps are much cheaper than say one 300mfd cap. Most caps are going to be 10% values and the multicap approach allows you to get values much closer. I usually get within 1% by using multiple caps and I usually also have some very low value caps to help get the numbers this close. Another thing to look for is the voltage rating. I use all 100volt capacitors unless they may be 250volt but that is just because I got some of those cheap, they are a little larger but they are better than many of the 25volt caps in a passive crossover.

As for air-core coils I only use these not any with ferrite cores. But though you will hear about the magic of air core dimensional ratios there is another method that you can use. You can if you wind your own coils use a solenoid winding instead. Take a small wooden dowel and wind the coil on the wooden dowel. You can leave the dowel in place and use it to help mount the coil if you leave a portion of the dowel sticking out. The wood is non inductive and can not saturate. Use a large gauge wire like 16 gauge wire. Because the diameter of the wood dowel can be as small as 1/4 inch the actual length of wire necessary to wind the coil will be less as the inside coils will have a small diameter and this takes much less length. This will also lower the Dcr value of the inductor as the wire length will be much less.

Just my 2cents worth of knowledge.
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Old 15th February 2013, 12:26 AM   #16
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Any opinions on stacked film vs. wound for polypropylene caps?
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Old 15th February 2013, 07:35 AM   #17
benb is offline benb  United States
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Here's an older thread with some ideas for "high quality" caps in crossovers:
Using Batteries to Bias crossovers into Class A, how does it work?
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Old 15th February 2013, 11:34 AM   #18
DF96 is offline DF96  England
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That is an amusing thread. If a capacitor is linear and well-behaved then a DC bias does nothing. If a capacitor is non-linear (all caps are slightly non-linear, but usually far too small to notice) then the main effect of a DC bias is to change a little odd-order distortion into a greater amount of even-order distortion (plus probably some remaining odd-order). If this change is audible then the solution is to use a better dielectric (more linear) or better cap construction (e.g. tighter winding, which is normal for ordinary commercial caps anyway).

If there is a zero-crossing issue with current, as some claim, then DC bias does not change this at all - the AC current still goes through zero as before. It would change a voltage zero-crossing issue, but there is no evidence for this as far as I am aware. Dielectrics don't do anything strange at zero electric field.

Sorry to go a bit OT, but it is surprising what some people believe.
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Old 15th February 2013, 02:55 PM   #19
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DF96,
This is no different than those who truly believe in the boutique capacitors. As I have stated here and in other threads I have actually seen some of the high end brand names wound on the exact same machines with the same films as the standard capacitors. The only differences were as simple as a nice pretty wrapper and at best I saw some that used a braided lead-out wire instead of a solid lead. They looked pretty but the electrical properties were identical. The only thing that some of these manufacturers had to pay for was the different film wrapper cover and a simple pad printer artwork change. It was a fraud to say the least, but it wasn't the actual capacitor manufacturer making the claims just the sellers of the parts.
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Old 15th February 2013, 03:21 PM   #20
DF96 is offline DF96  England
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You could argue that morally the manufacturer is an accessory to the fraud, but I guess most just turn a blind eye to it. Legally the blame rests with whoever makes the silly claims. However, if they are sufficiently extravagant that a normal sensible person would know that they are false then a court might find that they were merely 'advertising puffery' and not fraudulent! If you have to tell a lie, make it a big one.
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