Wild Burro Field Coils!

[dave slagle]

Have you determined whether the output impedance of the power supply affects the sound? After all the voicecoil and field coil work like a transformer and the field coil may behave differently if it has a high source impedance or low source impedance. One easy way is to use a LM337 CCS to power it instead of a voltage supply.

Hey,

Using a voltage source vs. a current source does make a difference in sound but thus fat I haven't put a finger on what it actually does since different field coils seem to respond differently. What differences I hear seem to be in the lower frequencies) The differences in sound can be quickly compared by using a CCS and then simply decoupling it with a cap.

Another fun thing to do is to share the supplies and this gives another variation on the sound (again I hear it mostly in the bass)

If the field coil is large enough to self-resonate, I wonder if it could cause oscillation for the amplifier?

not the amplifier, but field coil is an inductor and placing a current source in series with an inductor can lead to instability of the CCS.

Also, I keep wondering why manufacturers use resistive voicecoils when they could just use copper and an external resistor.

simply put the amp turns of the voice coil determine the efficiency of the speaker. The resistance is a byproduct of the turns and is a liability. Take a Lowther which has 62 turns. In order to get 8W out you need 1A of current which translates to 62 amp turns. a single copper foil turn would require 62 amps of current and the net result would be the same dissipation and the same heating.

dave

 

[keantoken]

Thanks for your response Dave. I will try to make some worthwhile points with my limited knowledge.

You are right, I didn't realize the field coil could oscillate with the CCS. If only the bass is affected, then bypassing the coil with a small capacitor might remove the possibility of oscillation. I'm thinking 1n-100n.

I would imagine the voicecoil and field coil are coupled close enough to work like an impedance transformer. Therefore a field coil fed with low impedance would act like a shorting ring for the voicecoil. IIRC the new drivers use a shorting ring already, so this may be mitigating the effect of field coil drive impedance. I may be totally wrong here because I have not studied speakers, but if the shorting ring only affects high frequencies, then it would explain why it does not mitigate the effect of field coil impedance drive on the bass; if there were no shorting ring maybe the effect would be larger.

Then perhaps if the shorting ring is omitted, the field coil can be used to shape the electrical characteristics of the voicecoil. Perhaps a field coil with low enough internal resistance to perform the same function as a shorting ring would not have enough turns to produce the strong field needed. Perhaps a tapped field coil with different gauge wires would work.

- keantoken

 

[StevenZ]

Shame these never became available. I would have loved to own some.

 

[ejfud]

Wonder if Paul still has these or if they found there way to FNG Doug.

 

[pjanda1]

Sadly for me, they found a home. I really enjoyed my time with them, but honestly, law school isn't super conducive to listening time. And, they weren't really mine to begin with.

It isn't as if making these is impossible. But, the parts are very expensive and they require a ton of labor. We're talking $2k per pair neighborhood retail.

But, for folks who are interested, I think Dave Slagle has the parts to build another pair. For the right price, he might even explain how to put them together

Paul

 

[d to the g]

FNG

Sadly, I had to look that up.