Sound of inductors?

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Thomas

Thomas

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Joined 2001
#1
During the calibration process in justmls, I played arround with diferent components verifying the calibration.

Sudenly! What's that? Do I hear a sound from somewhere? Every time I press 'meassure' I hear the noise. I realized it came from the inductor placed on top of my old denon amp I use for these meassurements. The amp chassis somehow amplified the noise. Hmm...

I tried diferent inductors and the noisiest was the 'traditional' 1.2mm2 air-core inductors. The most quiet I could find was a copper foil inductor.

No sound from capacitors though.:smash:
 
#5
yes I have experienced this with a cheap stock crossover in the past. you could actually here the instruments and make out the lyrics (admittedly it sounded very tinny) even without it sitting on anything but the carpet!

If i hoolked it up to the amp and didn't connect any speakers to it, it was most apparent! required a reasonable amount of power to start it off, but it was an interesting observation to say the least!!

Tony.
Tony.
 
#9
wintermute said:


I am absolutely dead serious!!!! I suspect I was saturating the coils, they were air cored on plastic bobins. I think the crossover was only rated at 60W and I may have been feeding in a bit more power than that 😉

Tony.
Click to expand...


Air core on plasic bobins can ssturate? Is the conductor size the limiting factor?
 
#11
I think if you pass enough power through them any coil will saturate, could be wrong though 🙂 I was probably feeding a 60W coil close to 100W..... the other possibility is that the coils were not as tightly wound as they should be.

I'm wondering if I still have those crossovers, I think I threw them out when I cleaned out my garage (for obvious reasons 😉 )

Tony.
 
#13
No this is not a joke but a very real problem. Yes filter coils do make sound and with the bad ones lots of it. It's really not that hard to imagine, the coil itself is a magnetic forcefield wich acts on the difference in force field between the windings. Test it for yourself, unhook your speakers frome the crossover, replace them with 8 ohm resistors and play some music, you are defenitly going to hear the music from the coils in the crossover. And yes, foil coils and coils where the wires are glued/baked togheter are making much less noise than standard coils.
 
#15
Sjef said:
No this is not a joke but a very real problem. Yes filter coils do make sound and with the bad ones lots of it.
Click to expand...

! ! !

Thank you very much for this useful information. Even though I'm using an active crossover, I'll still be using coils for the baffle step driver rolloff, so this comes right at the nick of time.


Francois.
 
#16
First thing - an air core coil won't saturate at all in the normal sense (air is linear up past megagauss flux densities, as its permeability is scarcely different from that of a vacuum), and if a coil is designed right it should have low enough resistive drop so that you won't run afoul of its L/R time constant with any current your amp can deliver. At high excitation levels, the wires in an inductor can rattle together and make noise. This can be fixed by dipping the coil in some varnish. Ordinary polyurethane varnish will work in a pinch. If a coil is parked next to a piece of sheet steel, it could possibly turn that piece of steel into an impromptu diaphragm.

Core materials like ferrite and steel can make noise due to magnetostriction. I've heard singing output transforers in an old Sansui tube amp...
 
#17
Re: Re: Sound of inductors?

soongsc said:


Are these inductors in the speaker or are they amp output inductors?
Click to expand...

It was crossover components for speakers I was meassureing.

I tried my assembled croosover with 6ohms resistors insted of the drivers. Well, who need drivers? The crossover plays just fine by itself. :xeye:
 
#18
I tried diferent inductors and the noisiest was the 'traditional' 1.2mm2 air-core inductors. The most quiet I could find was a copper foil inductor.
Click to expand...

A major reason I prefer to use foil inductors. Just think of the effect on the signal going to the speaker this has. It can't be good. Of course, if you pot an air core inductor, you can gain much of the same advantage of a foil inductor.
 
#19
wrenchone said:
... At high excitation levels, the wires in an inductor can rattle together and make noise. This can be fixed by dipping the coil in some varnish. Ordinary polyurethane varnish will work in a pinch. If a coil is parked next to a piece of sheet steel, it could possibly turn that piece of steel into an impromptu diaphragm.

Core materials like ferrite and steel can make noise due to magnetostriction. I've heard singing output transforers in an old Sansui tube amp...
Click to expand...


Has anyone tried using something like "crazy glue" to let the glue seep between inductors and glue them together? I seems a lot simpler than dipping them if you are using air cores on bobins.
 
#20
What's so hard about dipping a coil in a can of varnish? You solder a wire to one of the leads to act as a handle,, let it hang in the can for about 15min, then hang it up for a bit to drip the excess back into the can. From there, you can let the coil air dry or stick it in a toaster oven at around 100C for an hour. This is the way we do limited run production magnetics at work. The only difference is that we use a professional transformer varnish. Plain polyurethange varnish is still pretty good, though, and a lot easier for an amateur to score..
 
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