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Old 10th October 2005, 11:27 AM   #1
klitgt is offline klitgt  Denmark
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Default Copper foil versus wire in inductors

Do any of you have any experience with replacing standard coils in speaker crossovers with this type of coil (copper foil).
What is the expected audible improvement?
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Old 10th October 2005, 12:47 PM   #2
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Personally I think you'd hear zero improvement but it may sound a little different.

Good XO component vs. good expensive XO components is a daft argument.
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Old 10th October 2005, 01:41 PM   #3
AuroraB is offline AuroraB  Norway
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Generally, foil inductors have lower DC series resistance , and this might affect the bass tuning, or the low pass response. For parallell coils, the effect is smaller, ....
but-- the human mind is a very powerful tool.......
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Old 10th October 2005, 01:54 PM   #4
kevinkr is offline kevinkr  United States
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Copper foil inductors generally have lower resistance than standard wire inductors which will result in higher Q - this isn't necessarily always a good thing as it results in changes in x-over behavior in the transition region of the filter. (Typically excessive peaking just below the x-over frequency)

I learned the hard way that the components chosen by the speaker designer often have characteristics such as ESR in the case of capacitors and DCR in the case of inductors which may deliberately be used to control the Q of the filter being implemented.

I rebuilt the xo in a pair of AR 58's years ago and got more resolution and badly overdamped bass response - overall I did not like the result, much less musical and I didn't realize at the time what the problem was.

If you are designing from scratch none of this is really an issue if you use a good design tool and have the specs for the parts you are planning to use.

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Old 10th October 2005, 04:24 PM   #5
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Apart from measureable properties such as lower DCR (typically) there are things that are different to "normal" wire inductors, which probably can't be measured, but may be audible nevertheless. Such as the di-electric. Polyprop versus a varnish type of coating? And the thickness which is said to influence things like skin-effect (which many dismiss as irrelevant in AF) Also the taughtness with which the respective coils are wound might influence sound...for instance the foil might "ring" more...

O yes..and I suppose the capacitance will also be very different between the types. ( Which I notice is not mentioned in the datasheet)..I suppose it is the same as with psu chokes where you want as little hf to pass as possible...i.e. you want as low as possible capacitance as that will pass the hf ..in this case a musical signal ..but still) It seems to me ..purely from a theoretical point of view that the foils are almost how you would build a capacitor (only it is one big foil not 2)

Feel free to disregard my pseudo scientific garble..either because it is not an answer to your question or because you think it is claptrap.
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Old 10th October 2005, 10:41 PM   #6
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Hi Bas,

I have found copper foil/teflon-tape DIY inductors superior to wire wound in high current applications. I built 1' wide foil inductors for my Apogee Full Range speakers where the Krell amps push 70 amps into a 0.1 ohm load. Under high currents the foil inductors do not create audible vibration noise like wire wound. It is easier to uniformly wind 12 guage copper foil than 12 guage wires.

The best digital amps use foil inductors for their high current output filters.
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Old 10th October 2005, 10:52 PM   #7
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I agree with you Bas about the capacitance.

The distributed capacitance is huge in those and I've measured 1/2 uF from a 5mH coil of tape/poly.
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Old 10th October 2005, 11:01 PM   #8
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Quote:
Apogee Full Range speakers where the Krell amps push 70 amps into a 0.1 ohm load
Wow..that a lot of current!

Quote:
Under high currents the foil inductors do not create audible vibration noise like wire wound.
I believe you..that sounds very plausible now that I think it over carefully....


Quote:
I've measured 1/2 uF from a 5mH coil of tape/poly.
Pheww...
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Old 11th October 2005, 12:08 AM   #9
soongsc is offline soongsc  Taiwan
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In my experience, the sound stage is more correctly presented, there is slighly more detail, and the bass is a little better. "I think the bass was better because the foil inductor had a larger cross section than the wire I used (#14 versus #16) though.
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Old 11th October 2005, 05:30 AM   #10
Jay is offline Jay  Indonesia
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I think the foil tends to be preferable mainly because of the low DCR (in series with woofer). In 'character' of the sound, I think I like Solen Heptalitz better. I think this in line with general phenomenon: stray (probably silver) is soft or suitable for bass, solid (probably copper) is suitable for tweeter (detailed). I'm not sure if Solen Heptalitz is exactly better but I don't bother to use more expensive than a heptalitz.
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