Field Coils for Audio Systems

[K3RMIT]

Heard these twice at shows

also OMA as well horns done well have a sound very close to real I must say

 

[AMR / iFi audio]

Heard these twice at shows

This is very interesting, thank you for sharing! Any particular element in these that you enjoyed the most?

 

[dcathro]

Apparently, Audio Note are in the process of making a field coil based speaker. Details here.

 

[Audiophile Bill]

Apparently, Audio Note are in the process of making a field coil based speaker. Details here.

A field coil version of the AN-E. They seem to suggest that it beats all their permanent magnet versions - that is very interesting. I would imagine AN will build a very good power supply for these motors too tbh.

 

[cal3713]

This is very interesting, thank you for sharing! Any particular element in these that you enjoyed the most?

Agreed, they look great. But boy, the five channels of independent amplification would be a bear...

 

[dcathro]

A field coil version of the AN-E. They seem to suggest that it beats all their permanent magnet versions - that is very interesting. I would imagine AN will build a very good power supply for these motors too tbh.

I would also imagine that they will be exquisitely priced .

 

[Audiophile Bill]

I would also imagine that they will be exquisitely priced .

Yeah I was thinking that lol

 

[the sound of Tao]

I would also imagine that they will be exquisitely priced .

You bet your Faberge eggs they will be… they’ll be positively bejewelled.

 

[DaveC]

My position is similar.

I have heard and enjoyed Lowthers on many occasions, but did not feel that I could live with them. I have been curious about the Voxativ and AER, and also the Feastrex.

I chose to go with Supravox widebander because there is no wizzer and therefore I felt that I could integrate a tweeter and have a smooth
response.

Will be watching with anticipation on how Bill's experiment goes.

IME there are no wideband drivers that work well above 12-15 kHz. You get output, but compared to a high quality tweeter it's uneven and has artifacts from breakup and the limits of the mechanical crossover... i.e. transition to the whizzer or small diameter VC. This includes all of the AER, Voxativ and Feastrex drivers. It's like expecting a full range driver to do the same thing as a 15" woofer. No way that's ever going to happen!

However, many can't hear clearly in that frequency range anyways... in my testing there are only a minority of folks who are very sensitive to this. So, despite the fact the HF quality isn't great you can still get output and get that sparkle and air, and some may prefer that to a tweeter for various reasons.

My midrange driver has no whizzer but it does have a smaller diameter VC that allows for 20 kHz output, however I prefer to roll it off and use a tweeter. I think it's possible to use a 1st or 2nd order xo with good results, but in my speaker that'll be optional and I have decided to allow the user to adjust the system. You'll be able to run the mid full range at the top end or use the xo, as well as having the option to not use the tweeter at all.

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As far as FCs, bonzo got it right imo, it just depends on implementation... like everything else.

Also, you may be able to get a FC to not sag as much but if people PREFER SAG then who cares? People often prefer FC power supplies that use unregulated tube outputs just so they DO sag. People roll rectifier tubes in amps so they get the sag characteristics they prefer. Certain cheap power cables touted on here are what they are because they sag... they are basically a resistive power conditioner. Resistors can be used for AC power conditioning just like you use in a PS after rectification.

IMO the only plus to a FC power supply is it's adjustability, it gives the user something else to tweak to their liking, or to adapt TS parameters to various enclosures. The proof of this is the existence of excellent drivers using ALL types of motors. Comparisons are usually not valid because they are seldom both optimized, like trying to compare a tube vs SS amp on a speaker with a high phase angle. Tells you absolutely nothing but gives people things to speculate on, and most likely derive incorrect conclusions from.

 

[DaveC]

I would love to know what is in the upper AER and Voxativ drivers that makes them so expensive.

I know we live in a world where the price is often based on what the buyers are prepared to pay, and the more expensive something is the more desirable it is.

You got it. It's absolutely nothing except for the exclusivity that comes with high prices.

You generally get a more expensive motor but that's a relatively small actual expense vs charging 5-figures for a driver.

IME these drivers are arts and crafts. You can do the same with the right paper and cutting machine, and many, many hours of time. It's not very complicated... AER got started by modding and copying Lowther. And Voxativ got started by copying AER and even trying to take over AER's name, lol.

 

[Carlos269]

IME there are no wideband drivers that work well above 12-15 kHz. You get output, but compared to a high quality tweeter it's uneven and has artifacts from breakup and the limits of the mechanical crossover... i.e. transition to the whizzer or small diameter VC. This includes all of the AER, Voxativ and Feastrex drivers. It's like expecting a full range driver to do the same thing as a 15" woofer. No way that's ever going to happen!

However, many can't hear clearly in that frequency range anyways... in my testing there are only a minority of folks who are very sensitive to this. So, despite the fact the HF quality isn't great you can still get output and get that sparkle and air, and some may prefer that to a tweeter for various reasons.

My midrange driver has no whizzer but it does have a smaller diameter VC that allows for 20 kHz output, however I prefer to roll it off and use a tweeter. I think it's possible to use a 1st or 2nd order xo with good results, but in my speaker that'll be optional and I have decided to allow the user to adjust the system. You'll be able to run the mid full range at the top end or use the xo, as well as having the option to not use the tweeter at all.

-------------

As far as FCs, bonzo got it right imo, it just depends on implementation... like everything else.

Also, you may be able to get a FC to not sag as much but if people PREFER SAG then who cares? People often prefer FC power supplies that use unregulated tube outputs just so they DO sag. People roll rectifier tubes in amps so they get the sag characteristics they prefer. Certain cheap power cables touted on here are what they are because they sag... they are basically a resistive power conditioner. Resistors can be used for AC power conditioning just like you use in a PS after rectification.

IMO the only plus to a FC power supply is it's adjustability, it gives the user something else to tweak to their liking, or to adapt TS parameters to various enclosures. The proof of this is the existence of excellent drivers using ALL types of motors. Comparisons are usually not valid because they are seldom both optimized, like trying to compare a tube vs SS amp on a speaker with a high phase angle. Tells you absolutely nothing but gives people things to speculate on, and most likely derive incorrect conclusions from.

Agree, the adjustability is really the net benefit of Field Coil motors/drivers. And agree with the analogy, with the preference in degree of sag and how it relates to swapping/rolling rectifier tubes in power-supplies.

 

[Atmasphere]

IMO the only plus to a FC power supply is it's adjustability,

I've been running regulated supplies for quite a while. No sag- the supply has a display that shows current draw and the voltage which never change. When you compare a driver with sag in the magnetic field (any driver with a permanent magnet) to one with a field coil of otherwise the same construction you can hear the difference immediately- its not subtle. The same is true if you use a power supply for a field coil that has tubes (Tungars) and isn't regulated, as opposed to a regulated supply. You hear the difference right away.

Some people do like colorations. That's why SETs exist (the colorations of them related directly to their distortion). But I've found that when you get rid of the distortions (without otherwsie screwing things up) the same people that liked it before like it even better. I will concede one thing- set up plays an enormous role. Its easy for me to see how you put an inferior amp on a FC that has a saggy power supply and you might like that better for some reasons than if you put that same amp on a FC that had a good supply; the latter would expose the failings of the amp with great ease rather than covering them up.

 

[Carlos269]

Ralph, this becomes a circular argument: you got rid of the output transformers with the OTL topology, now go on and get rid of the tubes, then implement feedback in the solid-state amplification stage and if you carry this further you will end up with a Halcro style design with 0.0000001% THD. Now do you think that a scientific instrumentation amplifier sounds as good and organic, as natural as your OTL’s? Or even as good as a colored SET DHT design? Distortions is not all bad, this is readily empirically demonstrated.

 

[Atmasphere]

Ralph, this becomes a circular argument: you got rid of the output transformers with the OTL topology, now go on and get rid of the tubes, then implement feedback in the solid-state amplification stage and if you carry this further you will end up with a Halcro style design with 0.0000001 THD. Now do you think that a scientific instrumentation amplifier sounds as good an organic as your OTL’s? Or even as good as a colored SET DHT design? Distortions is not all bad, empirically demonstrated.

This sounds a bit Off topic to me since this sounds like a question about why we're working with class D.

But its an easy answer. First, we can't get distortion that low just for the record, but our class D Beta units are lower distortion than our OTLs. They do use feedback; the trick there is that in most amps that use feedback the simple fact is they don't use enough. This results in the feedback adding distortion of its own in the form of higher ordered harmonics which are highly audible- contributing to harshness and brightness. We've been hearing this in solid state amps for the last 60 years.

If you run enough feedback you can get around that problem! But most amps lack the phase margin and the gain bandwidth product to allow for that much feedback. But in a class D amp you exceed the phase margin on purpose- which causes it to oscillate- and the oscillation is used as the switching frequency. In this way you can have enough feedback to do the job properly; the feedback will clean up the mess it creates and even correct for phase shift.

I agree about your comment about distortion; in any amplifier that sounds organic and musical, it will be found that the lower ordered harmonics (in particular the 2nd and 3rd) will be the primary distortion product. In fact there will be enough of it that it masks the higher ordered harmonic content (which is what happens in a good tube amp). It works out in our class D amp that the non-linearities that exist in the encoding scheme and dead time circuit result in lower ordered harmonic generation. So it sounds very much like our tube amps- smooth, detailed, relaxed- no brightness or harshness.

So its not a circular argument- its simply applying engineering with an understanding of what distortions the ear does not care about and those that it does.

 

[DaveC]

This sounds a bit Off topic to me since this sounds like a question about why we're working with class D.

But its an easy answer. First, we can't get distortion that low just for the record, but our class D Beta units are lower distortion than our OTLs. They do use feedback; the trick there is that in most amps that use feedback the simple fact is they don't use enough. This results in the feedback adding distortion of its own in the form of higher ordered harmonics which are highly audible- contributing to harshness and brightness. We've been hearing this in solid state amps for the last 60 years.

If you run enough feedback you can get around that problem! But most amps lack the phase margin and the gain bandwidth product to allow for that much feedback. But in a class D amp you exceed the phase margin on purpose- which causes it to oscillate- and the oscillation is used as the switching frequency. In this way you can have enough feedback to do the job properly; the feedback will clean up the mess it creates and even correct for phase shift.

I agree about your comment about distortion; in any amplifier that sounds organic and musical, it will be found that the lower ordered harmonics (in particular the 2nd and 3rd) will be the primary distortion product. In fact there will be enough of it that it masks the higher ordered harmonic content (which is what happens in a good tube amp). It works out in our class D amp that the non-linearities that exist in the encoding scheme and dead time circuit result in lower ordered harmonic generation. So it sounds very much like our tube amps- smooth, detailed, relaxed- no brightness or harshness.

So its not a circular argument- its simply applying engineering with an understanding of what distortions the ear does not care about and those that it does.

IME the better class D amps... ones that are not that expensive either... have figured this out while some more prominent and expensive applications have not.

A while ago I suggested a D amp would pair much better with SET amp than they might think to drive woofers, but someone shouted that down and/or PM'ed the person and they canceled their order. IMO that was a mistake and the closed-minded person could have learned something rather than just assumed they knew how an amp they never even listened to would sound.

I would be interested to hear a non-sag FC application, it sounds like something I'd like.

However, there's mountains of evidence on this site that many would not prefer it... I'm not sure it would sound natural.

 

[Atmasphere]

I'm not sure it would sound natural.

My sarcasm meter is going off...

 

[Solypsa]

You got it. It's absolutely nothing except for the exclusivity that comes with high prices.

You generally get a more expensive motor but that's a relatively small actual expense vs charging 5-figures for a driver.

IME these drivers are arts and crafts. You can do the same with the right paper and cutting machine, and many, many hours of time. It's not very complicated... AER got started by modding and copying Lowther. And Voxativ got started by copying AER and even trying to take over AER's name, lol.

Isn't most audio manufacturing like this? Pretty basic mechanical assembly etc.

Not trying to excuse 5 digit drivers as obviously there is some huge margin...

The idea of making my own driver as a diy project is pretty appealing. Just buy off the shelf baskets, model the field coil magnet parts, get them made and wind it up, pick a spider and surround from someones catalog or get really crafty and make them. Wind up a voice coil on a former material you like and make, pulp some cones over a cone shape you make,

Err still sounds fun but gonna have to think a little harder before diving in

 

[Carlos269]

This sounds a bit Off topic to me since this sounds like a question about why we're working with class D.

Ralph, the point that I was making and the takeaway is that it doesn’t really matter where on the playback chain the non-linearities occur, whether in the DAC’s DSP design or reconstruction filter, in the amplification stage’s unregulated power-supplies, or in the speaker’s driver motor with its magnetic field flux sag; what matters is the resultant sound; and most prefer the organic nature of the SET DHT’s lower ordered harmonics (in particular the 2nd and 3rd), magnetic tape low frequencies non-linearities or transformer saturation and find that it’s what sounds most like live music.

I was not aware of your Class D amps development. This reminds me of when the late Paul Weitzel of Tube Research Labs fame went from all tube designs to solid-state designs and ultimately Class D amp designs. Love to hear more about your Class D amps, they appear to be special or a novel approach. Please share a link or product information on a new thread.

 

[Lagonda]

I would also imagine that they will be exquisitely priced .

And dipped in silver !

 

[the sound of Tao]

And dipped in silver !

Sure I have a little bit of a thing for upocc silver… some may even call it a bit of an addiction perhaps