Blog: Upgrade Inductors with Care

Our little group of tweekers has had excellent results with these and DC resistance has matched well, 

https://www.parts-express.com/Jantzen-8375-1.2mH-14-AWG-Copper-Foil-Wax-Coil-255-565?quantity=1&utm_source=google&utm_medium=cpc&utm_campaign=18127373971&gclid=Cj0KCQjwnf-kBhCnARIsAFlg491XJqYfXUsKKkOsZODZzCZjc1ea9QX66fklmemooPpmCyRKtNONE3YaAhI4EALw_wcB

@carlsbad2  Glad to hear it, but I just can't get my hear around using wax in a coil. :D

@erik_squires That i something I don't have an explanation for--just following the suggestions of those that came before me on this project.

A word of caution about the blog linked to in the first post. I don't know who the author is, Squires claims he wrote it but I see Nigel Tufnel's name at the bottom of page. 

There is a lot of misinformation here that could lead someone astray, or after reading this even avoid starting the modifications. 

"You CAN change inductor gauges but you must monitor changes  to the system impedance, frequency response AND power handling to do so correctly."

This is followed with: "Always compensate for lower DCR with additional series resistance"

When calculating the value of a coil for a certain XO frequency we need a value for XL.

To calculate the XL (inductive reactance) necessary for a chosen XO point the formula is:  XL =2PiFL

Note there is no 'R' in the equation, yet the blog states: "Always compensate for lower DCR with additional series resistance"

The point of using a coil with thicker wire is to avoid heating of the coil leading to thermal compression and to improve damping factor which has a noticeable effect on the bass performance. Adding resistance is to negate $$$ spent on an amp with desirable high damping factor. It's the high DF that controls the voice-coil/cone for clean detailed bass. The only time a low DF will work is when the speaker designer is specifically designing for tube amps. 

I could go on but suffice to say the article linked to appears to be by someone not fully conversant with the workings of the all important crossover.

@carlsbad2,

Hi, the waxed coil you linked to I have found great on tweeters, also the baked varnish coils are pretty good. Not yet tried the foils on the bass section, mainly because of price. When I made my own I used to dip them in warmed up epoxy which sets like a rock and then mount them on a flexible mastic.

Thanks @lemonhaze .  I'll be putting a 12 awg foil into service on my bass section very soon.

So we just started talking about what we had found to work without thanking @erik_squires for the work on his blog, discussing the perils and what could go wrong.

jerry

Hi @lemonhaze - The whole point of the post was that in real life inductors are not ideal and you should take DCR into account before making modifications because any good speaker designer will use it to their advantage, and design the entire circuit with that DCR in mind.  If you are just replacing coils with bigger and bigger conductors without compensating for lost DCR you are basically ignore an aspect of the crossover you should not.

This is something you can do and should do when using modern crossover simulators. I’m sorry this went completely over your head.

I don’t say not to upgrade the coils. I say to measure what you are doing carefully and take into account possible unexpected effects.

Watt for watt, coils are more thermally stable and often handle power much better than resistors. I wrote a whole section on why this is and you totally read past it. <sigh>

Thermal compression is something we worry about much more in a driver, but again, run the math. That’s what simulators are for. You’ll find that for the most part the power dissipated before the driver is far less than the power dissipated in the driver so it’s not the issue you think it is.

Need to make a correction for clarity. I should have said:

You’ll find that for the most part the power dissipated in crossover components before the driver is far less than the power dissipated in a driver so it’s not the issue you think it is.

Thank you, @carlsbad2 

I find it interesting that Rockport, which don’t skimp on price when building their speakers, don’t use foil inductors. They claim they do not sound as good as perfect lay coil inductors.

Anytime I every upgraded my speakers or built a kit pair, I always used foil thinking it was the best. But I never thought to compare them.

@agisthos over in the DIYaudio forum you'll find builders who have, and many prefer iron core for woofers due to bass slam.