Wow...
Do inductors have a sound? Yes they do affect the sound, for example if they are used in a crossover filter in a loudspeaker (I presume that that is what the question is all about). And they are supposed to, that is the whole point with them.
Then there are a few side effects of when using them that potentially can make the speaker sound differently if different types of inductors are used. I'll try to list them in order of importance:
Series resistance: The copper wire has a resistance, and this will have to be considered when designing the filter.
Inductance tolerance: This is typically not a problem. The tolerance of the inductance is mostly well within what is needed in filters. However, there might be problems finding inductors of exactly the desired value, and if so, that might be problematic.
Non-linearity of an iron core coil: Some high-inductance coils have an iron core in order to increase the inductance without increasing the number of windings and thereby the resistance. However, the core can become saturated if the current is high, and this wil produce distortion. It is very important not to run currents larger than the recommended current of such inductors.
Nothing
Nothing
Mechanic sound: Running a current trough the coil might cause vibrations in the coil. This will actually produce sound directly from the coil. If the coil is mounted outside the box, the sound may be audible if the speaker drivers are replaced by artificial loads. If they are mounted inside the box I can hardly imagine that there would be a problem.
Capacitance: There will be small capacitances between the windings of a coil. These can be included in the crossover simulation and very rarely produces any problems.
Other even smaller effects that I won't even bother putting here...
Passive filters are more difficult to design* than active filters, if they are perform well they have to be custom made for the drivers in question. On the other hand there are some unique advantages with passive filters; first is the simplicity, they do not require multiple amlifiers, and most commercialy available amplifiers assume that passive filters are used. Second there is a possibility for the advanced designer to play with the driving impedance in order to reduce the distortion.
If one hears differences between inductors, one must first look for the three first groups. IMO it is very unlikely that the latter groups will ever be the cause for audible differences.
To state that inductors are bad and that they should be avoided is IMO not very well substantiated. It must be based on a few unsuccessful designs of passive filters, or possibly even "off the shelf" filters, that were not adapted to the specific design.
*...depending on how one look at it. Active filters typically require some OPamp circuitry, power supply etc it is clear that this might require skills that are not required for passive filters. However, what I mean here s that finding hte values of the coils and caps of a passive filter requires some simulation, whereas the component values in an active filter might be taken from tables without major problems.
Do inductors have a sound? Yes they do affect the sound, for example if they are used in a crossover filter in a loudspeaker (I presume that that is what the question is all about). And they are supposed to, that is the whole point with them.
Then there are a few side effects of when using them that potentially can make the speaker sound differently if different types of inductors are used. I'll try to list them in order of importance:
Series resistance: The copper wire has a resistance, and this will have to be considered when designing the filter.
Inductance tolerance: This is typically not a problem. The tolerance of the inductance is mostly well within what is needed in filters. However, there might be problems finding inductors of exactly the desired value, and if so, that might be problematic.
Non-linearity of an iron core coil: Some high-inductance coils have an iron core in order to increase the inductance without increasing the number of windings and thereby the resistance. However, the core can become saturated if the current is high, and this wil produce distortion. It is very important not to run currents larger than the recommended current of such inductors.
Nothing
Nothing
Mechanic sound: Running a current trough the coil might cause vibrations in the coil. This will actually produce sound directly from the coil. If the coil is mounted outside the box, the sound may be audible if the speaker drivers are replaced by artificial loads. If they are mounted inside the box I can hardly imagine that there would be a problem.
Capacitance: There will be small capacitances between the windings of a coil. These can be included in the crossover simulation and very rarely produces any problems.
Other even smaller effects that I won't even bother putting here...
Passive filters are more difficult to design* than active filters, if they are perform well they have to be custom made for the drivers in question. On the other hand there are some unique advantages with passive filters; first is the simplicity, they do not require multiple amlifiers, and most commercialy available amplifiers assume that passive filters are used. Second there is a possibility for the advanced designer to play with the driving impedance in order to reduce the distortion.
If one hears differences between inductors, one must first look for the three first groups. IMO it is very unlikely that the latter groups will ever be the cause for audible differences.
To state that inductors are bad and that they should be avoided is IMO not very well substantiated. It must be based on a few unsuccessful designs of passive filters, or possibly even "off the shelf" filters, that were not adapted to the specific design.
*...depending on how one look at it. Active filters typically require some OPamp circuitry, power supply etc it is clear that this might require skills that are not required for passive filters. However, what I mean here s that finding hte values of the coils and caps of a passive filter requires some simulation, whereas the component values in an active filter might be taken from tables without major problems.
To original poster:
IMO, you will not hear the difference, but the money you spend won't be a waste as long as you learn something from it. 😉 Beware of i-did-it-itis, the very act of changing something based on a decision you made will influence you to think it is better afterward.
Notes to others:
The formula for inductance is an approximation. Inductors do vary in inductance with frequency, some more than others. This is why measuring an inductor at 400Hz with an inductance meter is a potential source of error unless your crossover is at 400Hz. This doesn't mean that your crossover will sound bad, it just means that your inductance value won't be as accurate as you think...
Inductance meters with a fixed measurement frequency are for parts sorting or matching, not for precision measurement.
I found a hand rolled inductor in a box of free electronics stuff (I got a whole box of 1/4W resistors, 10ea 1ohm-10meg) at a rummage sale, I played around with it and found that it made noise due to loose windings. I started unwinding it and found that the person who made it was very meticulous and put a layer of electrical tape between each layer. IT had a core which could be removed and the core definitely increased the vibration. That's the only "sound" I have ever heard from an inductor. 😉
Some Cerwin Vega speakers I bought in college (I know...they aren't hooked to anything now) have ferrite cores not much bigger than pencil lead. They add a "happy" distortion to everything when played loudly. They actually have mylar caps, though. sorta puzzling. These have 97dB sensitivity, so normal listening was much less than a watt.
IMO, you will not hear the difference, but the money you spend won't be a waste as long as you learn something from it. 😉 Beware of i-did-it-itis, the very act of changing something based on a decision you made will influence you to think it is better afterward.
Notes to others:
The formula for inductance is an approximation. Inductors do vary in inductance with frequency, some more than others. This is why measuring an inductor at 400Hz with an inductance meter is a potential source of error unless your crossover is at 400Hz. This doesn't mean that your crossover will sound bad, it just means that your inductance value won't be as accurate as you think...
Inductance meters with a fixed measurement frequency are for parts sorting or matching, not for precision measurement.
I found a hand rolled inductor in a box of free electronics stuff (I got a whole box of 1/4W resistors, 10ea 1ohm-10meg) at a rummage sale, I played around with it and found that it made noise due to loose windings. I started unwinding it and found that the person who made it was very meticulous and put a layer of electrical tape between each layer. IT had a core which could be removed and the core definitely increased the vibration. That's the only "sound" I have ever heard from an inductor. 😉
Some Cerwin Vega speakers I bought in college (I know...they aren't hooked to anything now) have ferrite cores not much bigger than pencil lead. They add a "happy" distortion to everything when played loudly. They actually have mylar caps, though. sorta puzzling. These have 97dB sensitivity, so normal listening was much less than a watt.
Ron E said:
Is that so...? I had always imagined that a normal air core coil mainly has a frequency independent inductance and a likewise frequency independent resistance. That is about it.
Or do you mean iron core inductors? Or possibly the inductance of a voice coil. If so, I agree.
No, I don't mean voice coils, nor just iron or laminated cores. In a Speaker Builder test ~15 years ago, actually an iron core tested lowest for inductance variation, better than an air core and a laminate core....
Svante said:
No, I was not talking about those "off the shelf" passive xovers. I have never touched those things in my life. And every speaker with xover I've built has one thing in common: their xovers always takes very long time to develop. I am always very picky on them. Maybe, eventually some of them were inevitably "unsuccessful". I did my best after all. I've tried different slopes, different Q, differet frequencies, but they just can't keep up with the active ones. So I gave up the passive xovers, especially inductors in the low pass filters.
IMO (maybe somewhat extreme), multi-way loudspeakers with passive xovers are only for conveniences of use & marketing. Of course some of the products in the market are successful (in some ways at least). But if they can go active, there must be significant improvements.
Speaker systems with active xovers look more complex at the first sight. In fact they avoid very many difficulties & uncertainties between amps & drivers. As said above, they are indeed simpler in the filter designing.
Doing it right, active filters can be very simple & elegant. If you don't like OP amps, just take other devices you like. It's not that hard, please feel free to give it a try if you haven't. (so much useful information lying around here somewhere or elsewhere in the internet... )
Conveniences of use & marketing are not our business. Because we are DIYers. IMO, except wires, nothing should be there between amps & drivers. (OK, a single small caps in series with super tweeter is acceptable.)
If you don't like multi-amp systems, please try single driver (fullrangers). Try them, and you'll see (hear).
Ron E said:
This is interesting. How was this inductance variation measured? And how large was the inductance variation?
CLS said:
Ok, I think we should agree on that we disagree, then... 🙂
Test results
Hello soongsc,
you can find the results in the product catalogue from Mundorf, on page 10 they show a graph from the test I was referring to: http://www.mundorf.com/downloads/info-news/MUNDORF_News_&_Product_Range_hi_res_EUR.pdf . Both the baked varnish coils and the vacuum impregnated coils still show significant resonances! I believe these resonances are related to the physical dimensions of the coil and only indirectly to the actual inductance (which off course has an influence on the coil’s size).
I remember the 2 kHz because my speakers have a noted sound pressure peak at 2 kHz, exactly at crossover frequency between the direct coupled midrange Horn and the Tweeter, which has a 12dB highpass filter with a pretty standard inductor, and I was toying with the idea of replacing this inductor with a foil inductor. My reasoning was that the resonances of the standard coil and ensuing higher inductance could have a negative impact. Incidentially, the manufacturer is now offering a speaker upgrade with new drivers and a new crossover with a foil inductor.
Hello soongsc,
you can find the results in the product catalogue from Mundorf, on page 10 they show a graph from the test I was referring to: http://www.mundorf.com/downloads/info-news/MUNDORF_News_&_Product_Range_hi_res_EUR.pdf . Both the baked varnish coils and the vacuum impregnated coils still show significant resonances! I believe these resonances are related to the physical dimensions of the coil and only indirectly to the actual inductance (which off course has an influence on the coil’s size).
I remember the 2 kHz because my speakers have a noted sound pressure peak at 2 kHz, exactly at crossover frequency between the direct coupled midrange Horn and the Tweeter, which has a 12dB highpass filter with a pretty standard inductor, and I was toying with the idea of replacing this inductor with a foil inductor. My reasoning was that the resonances of the standard coil and ensuing higher inductance could have a negative impact. Incidentially, the manufacturer is now offering a speaker upgrade with new drivers and a new crossover with a foil inductor.
Re: Test results
I would agree that the foil type would vibrate the least, but the wire types are of different guages, and it seems natural that the larger size would vibrate less. I wonder why they did a comparison like that?MRupp said:
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