Inductor ratings and tolerances for crossovers

[bustedguild]

Finally gearing up to build a set of Markwart crossovers for my Altec 604 8g's, and could use some guidance on inductors.

Jeff spec's copper foil inductors, which is fine and dandy, but I am having a really hard time finding a 16awg 0.40mH option for the tweeter section. Parts Express has no problem delivering a 0.39 +/-3% option (both Dayton and Jantzen) which lands me between 0.402 to 0.378mH. My question, how sensitive is a crossover of this design to inductor tolerance? Can I get away with a 0.39mH inductor for the tweeter, or should I be hunting around some more?

Thanks in advance!

 

[homebrew]

If you're replacing the original inductors (which usually isn't advised) in addition to the correct inductance, the original resistance also needs to be matched with the originals. Assuming the PE inductors are rated at .39mH, a tolerance of +/-3% should be fine.

 

[bustedguild]

If you're replacing the original inductors (which usually isn't advised) in addition to the correct inductance, the original resistance also needs to be matched with the originals. Assuming the PE inductors are rated at .39mH, a tolerance of +/-3% should be fine.

It will be a fresh build from scratch actually. Jeff just specs copper foil inductors that area minimum of 16awg. No mention of resistance.

 

[homebrew]

Resistance of the inductors is as important as inductance. A properly designed crossover will account for both.

 

[bustedguild]

I don't doubt you, homebrew. Maybe it'll be easier if I just post the schematic? Note the text at the bottom of the linked pdf that indicates changes for the 8g.

http://home.earthlink.net/~jmarkwart/id11.html

 

[homebrew]

A crossover schematic won't give one the response curves of the drivers and crossover combination. The effects of the inductor resistances need to be modeled in a design program to get some idea of their influence on the finished product. I am assuming that your crossover designer did not use cookbook formulas which are essentially useless.

By the way, I don't see the .40mH inductor on the schematic.

Look, maybe I'm being too anal about this. Try the crossover and see if you like it. After all, that's what really matters, isn't it?

 

[elnaldo]

I think if you have a spec with the wire AWG, that implies a resistance. I'd choose one inductor close to that AWG value.

 

[homebrew]

Just FYI, foil inductors have a lower resistance than wire inductors of the same gauge and inductance.

 

[bustedguild]

I think if you have a spec with the wire AWG, that implies a resistance. I'd choose one inductor close to that AWG value.

That was kind of my assumption given the language on Jeff's website...spec was for at least 16awg when using copper foils. I'm still trying to determine if a 0.39mH will suffice in place of a 0.40mH

 

[elnaldo]

That was kind of my assumption given the language on Jeff's website...spec was for at least 16awg when using copper foils. I'm still trying to determine if a 0.39mH will suffice in place of a 0.40mH

0.39 is perfectly fine. I'm sure that 0.01 is less than the accuracy of a measuring device. I think you won't notice a difference even with 5% to 10% differences.