Crossover for current drive

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Since a current amp is also a high output impedance amplifier, the frequency response at the speaker will track the magnitude of the impedance. This is a concern normally with tube amps.

So, whichever design you go for, you want to have the smallest impedance changes. For first order crossovers, they seem equivalent.

Also, you can use a couple of techniques to flatten impedance rises. Some do this excessively, but for a current amp this may be mandatory.

I strongly suggest you grab XSim and use it to simulate some of your ideas. Even if you can't measure the drivers, at least having an idea of the shape of the impedance curve can be really helpful to you.

Best,

E

At first order, they are very similar.
 
Series and parallel crossovers can work for flat impedance.

http://www.diyaudio.com/forums/multi-way/302001-flat-impedance-flat-power-response-design.html

If you use Zobel impedance correction and standard filter values, you will end up in the right place with either type.
Impedance Equalization (L-Pad) Circuit Designer / Calculator

Troublesome issue is the bass response, which has an impedance peak that is hard to equalise in practise. Needing big values in the LCR. Bafflestep correction is the other reason impedance goes to pieces, but can be corrected with an LCR around 1kHz.

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I can't imagine 6dB/octave electrical slopes will work well with many tweeters, but might be OK with some woofers.
 
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Are you thinking of a finite output impedance or an infinite one?
would series or parallel crossover be preferred?
I don't think this is the question to ask. If current is constant, think of bleeding it off. Where a parallel crossover for a voltage source begins with a series element then a shunt one, begin instead with a shunt one to gain control of the impedance at that point.
 
You probably saw this book in your travels. It talks about current driven crossovers in depth, I didn't understand any of it. :p
Current-Drive - The Natural Way of Loudspeaker Operation

I wouldn't spend too much time on theories of voltage or current drive. They end up in the same place if you get impedance flat. Which is the whole point.

There are people who say that voltage feedback amplifiers are indifferent to impedance. Well, that's rubbish. They don't like low impedance and high phase angle. And will blow up if you mess up completely! :D

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I take impedance seriously, AND energy/power response. Even at supersonic frequencies. But a gentle bell-shaped curve is OK too. Nothing difficult there. But the fact is that amplifiers work best into a resistive load.
 
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pentode output with current sense feedback so high impedance but obviously not infinite.
Steve makes a good point (They end up in the same place if you get impedance flat.). I have a few ohms at the output of my amps and do this. Since the outcome of a non flat speaker impedance (the reason for there being a peak around a crossover) is disconnected from the amp (and isn't a problem) using a conjugate circuit is the reasonable way to prevent the response following the impedance.
 
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I read the pass paper and could relate fig 5A to what I was saying before. I think it remains to define what is a current source driving the speaker. IMO a source resistance greater than 8 ohms would be leaning that way, but add an order of magnitude or so for the real thing.
 
I was just remembering two years of my life that I spent building a current amplifier with current feedback. I probably knew just enough to be dangerous in those days. :eek:

It was a sort of Class AB transistor design, where I took the current off the transistor collectors, rather than the usual emitter follower style of regular HiFi amps.

It was fast and detailed, but the impedance and heat and stability issues were horrible. See, this sort of design is out of kilter with 99% of loudspeakers. Most of them go inductive at high frequency, for instance.

It'll never be commercial, and I actually doubt if there is any real benefit, these days, since I now fully understand Norton-Thevenin equivalents.

There may be benefits to valves and MosFETs, because they are inherently fast wide-bandwidth devices. Impedance flattening might help too. But all this current-voltage topology stuff is Fool's Gold, IMO. Your little £300 Rotel HiFi amp actually works very well.
 
There was a postscript to this. I took the amp up to a PA company, who were working on an active speaker for commercial venues.

We did an A/B comparison with a simple sort of John-Linsley Hood design. It's embarrassing to admit, this little power amp was just sheer quality. It's always been an odd design to look at, because the output is assymettric, and that isn't fashionable these days. But it works. :D
 

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Are there any drivers specifically made for being current driven? Has anyone ever heard a system that was specifically designed as such? Would field coil drivers benefit from current drive?

One advantage of current drive is that it should not care about cable resistance or changes in voice coil resistance as the driver warms up.

In theory, converting voltage to a current to drive the voice coil seems more elegant, but all systems end up converting voltages to changes in air pressure. If you can't hear the difference between voltage drive and current drive then it shouldn't really matter until technology advances and changes that ;)
 
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There was a postscript to this. I took the amp up to a PA company, who were working on an active speaker for commercial venues.

We did an A/B comparison with a simple sort of John-Linsley Hood design. It's embarrassing to admit, this little power amp was just sheer quality. It's always been an odd design to look at, because the output is assymettric, and that isn't fashionable these days. But it works. :D

I am flattered you used my artwork.
 
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