I will try them stand-alone at first. If I have to augment them on top, then I have some pretty special custom built Lohmann AMT drivers, hand built in Germany, that I will try with them.
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Field Coils for Audio Systems
- Thread starter Audiophile Bill
- Start date
I will try them stand-alone at first. If I have to augment them on top, then I have some pretty special custom built Lohmann AMT drivers, hand built in Germany, that I will try with them.
I have read that also. Running them off of batteries again would make things more involved and complicated.
Are you going to market this class D amp?I'm not aware that sag in the magnetic field results in lower ordered harmonics! I would expect greater IMD and slower risetimes.
While the lower orders are useful for masking the higher orders, if you can reduce the overall distortion signature, the result is greater focus, greater resolution, but otherwise the same organic (musical) presentation. Encouraging distortion, even if its lower orders, IME while euphonic, results in less resolution- it might be fun but it does not bring you closer to the musical event. In high end audio, the assignment is to get as close to the musical event as the recordings will allow. One has to be pragmatic that distortion can't be eliminated. Reducing it, as long as the resulting distortion signature is benign, is paramount to getting things to sound real.
The class D project for us was really affirming of this idea; it measures considerably lower in overall distortion compared to our OTLs but otherwise has a very similar distortion signature. If compared side by side on a speaker that both amps are happy with its really obvious from the neutrality of the class D that with our OTLs we were on the right course all along; they sound so similar they are hard to tell apart (what you hear as different is the bass presentation, since the class D acts as a near perfect voltage source, and its also a bit more focused). Its nice to have a 'solid state' amp that sounds as smooth, liquid and detailed as a good tube amp and that both are simply sounding true to the recording.
In a nutshell if the power supply is regulated but otherwise the same voltage and current (so driver parameters are unchanged for the most part...) then you hear a greater sense of speed and realism from the regulated supply, where an unregulated supply is not that different from Alnico in its sound- IMO making one wonder why go through the additional expense??
Field coils cost a lot more $$$ to produce according to every manufacturer I've talked to that works with them. The industry moved away from field coils in the 1950s for precisely this reason!
Agreed.
I confronted him once on audiogon about his outlandish claims; he had a 'circuit' that could correct for 'Doppler Effect in amplifiers' and worked at a 'microscopic' level... Assuming it worked, somehow it produced a correction output but he was unable to produce a metric to show how it was affecting distortion or bandwidth or anything?? Seriously? I asked him why he didn't use the circuit itself as the measurement tool to know when it was 'doing its thing' and he didn't respond. Occam's Razor has a way of sorting out things like this pretty quickly- there's a very good reason its the oldest principle in science
The eagle has landed, the Supravox 215-2000 EXC field-coil drivers arrived today:
The Open Baffles are painted and ready:
The HP & Harrison adjustable DC power-supplies are also in:
The two power-supplies will give me the flexibility to experiment with one power supply per driver or to have the one larger 10A power supply power both drivers’ field-coils.
I have some interesting plans for powering the voice-coils but need to work on the concept and implementation before divulging too much.
Fun times ahead.
The Open Baffles are painted and ready:
The HP & Harrison adjustable DC power-supplies are also in:
The two power-supplies will give me the flexibility to experiment with one power supply per driver or to have the one larger 10A power supply power both drivers’ field-coils.
I have some interesting plans for powering the voice-coils but need to work on the concept and implementation before divulging too much.
Fun times ahead.
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Very cool, looking forward to hearing more about them...BTW. be prepared for a not so extended high frequency range. I have the Alnico version and they sound great but highs are attenuated...even on-axis. Ultimately I could not listen to them all alone and that is why I have coupled them with a compression driver/horn for the upper frequencies. Not sure what kind of bass you will get with an open baffle because mine are in a TQWT type back horn. In that configuration I get flat to 30Hz in-room.
Very nice Carlos!
Looking forward to see how you get on with them.
I am also curious to see how different yours are to mine. I understand Supravox has revised the 215 recently - would love to see some detailed pics of the drivers.
Interesting, also that you have the same power supply as me. I use big Agilents to drive my bass field coils.
Cheers David
I also found that I needed to augment the response with a tweeter. At what frequency do you bring the tweeter in, and how do you manage the crossover?
Well, I tried to run them up quite high and cross around 8-12khz but now I cross them at a pretty low 1Khz to a fairly large horn (18 Sound XT1464) and 1.4 inch CD (Beyma CP755Ti) or a Iwata 600 and 1 inch CD around 1200Hz (Beyma CP350Ti). This was determined purely empirically where I simply found that the horn sounded better in the lower-upper treble. Attempts to move that up to 2Khz or 5Khz etc. always bring me back to 1Khz. I also tried down to 650hz and 800hz sounded good also but the blend is better at 1Khz.
David, I will post some pictures of my drivers later today. I can tell you that mine are not the latest/current version. They are from the early 2000’s and were either hot-rotted, hand-selected, or screened for use in Open Baffles at the factory.
Brad thanks for the advice and guidance. I also noticed that the current version of the driver drops off sharply after 7 kHz.
If I need to augment the high-frequencies, like you and David, I have a pair of RAAL 70-20XR that I can use but will most likely first try a pair of gigantic massive AMT drivers that were custom hand built by Bernd Lohmann in Germany that extend all the way up to 23 KHz, and down to 350 Hz. If either of those two drivers fail to blend well then I also have a pair of Tonian Labs TL-R1 super-tweeters that I think will also be a good match.
It appears to me that these earlier vintage of the driver deliver more extension in the high frequencies than the current version but we will find out if they actually due deliver on that promise or if they will need the additional tweeter/super-tweeter. This is not a trivial resolution as it will impact the amplifier use to drive them because the amplifier could see a lower impedance than I have been planning for. Will need to experiment in a variety of ways.
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Yes. We've already sold a few of the Beta production.
One solution that can work quite well is to install rear firing tweeters, to help with correcting the tonal balance, especially off-axis.
Good luck, I look forward to see what you come up with!
I do have a pair of Fostex T500A MkII tweeters I can let go for a reasonable price... let me know if interested!
I tried ribbons and I think the T500 is better. However, I have found the most important thing is a seamless blend with the midrange, and this isn't that easy to achieve. It depends a lot on the tweeter it's self, so it's a good idea to try as many as possible as well as different positions for the tweeter. The right position also depends on crossover frequency. Also the xo slope is important but also subjective. 2nd order sounds much more modern, 1st order has more overlap which has it's pros and cons.
My mid will also cover up to 20 kHz, but it's not as flat or as accurate as a dedicated tweeter... but some may prefer this to a tweeter as not everyone can hear up that high or is as sensitive to high frequency quality as others.
This is very personal and subjective, I've struggled with it for a long time but finally have decided to offer a choice of no tweeter, 1st order or 2nd order crossover in my speaker using an external crossover with a couple of switches. I prefer 2nd order but it's a bit more difficult to get just right.
subscribed....
Having heard a few FC driver their open, 'forward' and fast sound made me want some too...it's just that the minor issue of needing 6 is a bit daunting.
the Rullit's I heard sounded nice, yet I think they were let down by the implementation with not enough baffle to support wave form propagation.
Rear facing tweeters can do miracles, so can only using one forward facing tweeter. I'm currently quite happy with my JBL 2402 alnico (sine cap filtered)
Having heard a few FC driver their open, 'forward' and fast sound made me want some too...it's just that the minor issue of needing 6 is a bit daunting.
the Rullit's I heard sounded nice, yet I think they were let down by the implementation with not enough baffle to support wave form propagation.
Rear facing tweeters can do miracles, so can only using one forward facing tweeter. I'm currently quite happy with my JBL 2402 alnico (sine cap filtered)
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The driver was originally intended for use in a back loaded horn. Thorsten Loach commissioned Supravox to make an open baffle version, which the company then offered as an option. Not sure if they are still doing this.
I initially tried to run the Supravox full range with no crossover, but found no matter what frequency I brought the tweeter in at, it interfered with the full range. I settled with a quasi first order interchange at 5Khz.
The printed performance graphs for the original driver do not match what I have measured in reality. They are way down once you get above 5 Khz.
The new MK2 version of the driver looks the same from the front - same exponential cone, pleated surround and phase plug, but the motor looks different. Also the specifications are different - 20 watts / 4 ohms vs 35 watts / 6 ohms. These drivers are fragile, and I suspect they had a lot of issues with them being over driven, so came up with a beefier voice coil, which would also reduce the higher frequency output.
I tried that approach, but it just sounded weird to me - they still sounded rolled off, but with this reflected treble.
David,
Good information. My are the Open Baffle version. Here are some pictures of my drivers for your review:
I found a 2nd order LR worked the best. I tried 1st order at various frequencies and 2nd Butterworth but 2nd LR sounded the best in terms of clarity and dynamic punch.
I don't think we are too far apart, I have an inductor followed by an resistor and capacitor to ground tailoring the response into the tweet.
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