Current drive, or more general, driven with a source impedance profile other that zero has proven beneficial for almost all loudspeaker drivers. Complete speaker with passive crossovers or other filter circuits less so.Anyone compared the distortion affect on speakers with voltage drive amplifiers vs current drive amplifiers?
Thanks for this teaching.Current drive, or more general, driven with a source impedance profile other that zero has proven beneficial for almost all loudspeaker drivers. Complete speaker with passive crossovers or other filter circuits less so.
Most voice-coil driven drivers like to see low to moderate impedance around system resonance, to provide some reasonable amount of damping. Elsewhere, as high impedance as possible impedance is better and the benefit is largest with less than stellar drivers (a Purifi driver gains very little from being current-driven, for example).
- Power compression is bascially absent
- Effect of modulation of voice-coil inductance vs excursion is bascially absent
That catches two major sources of distortion and/or non-stable behavior.
Other driver types like air motion transformers do respond well to pure current drive.
To sum up, current drive is no one-size-fits-all approach. When driver behavior is closely examined it turns out that for every driver in a given situation there is a optimum source impdance profile vs. frequency that achieves the best results overall (with regard top distortion but as well other aspects, like recovery from excursion overdrive etc). It almost never is zero. Sometimes it might even be negative (at and below resonance)!
Zero source impdance for amps was introduced not because it is technically better than everhing else, rather it was a way to standardize things so different speakers can be paired with different amps and not worry about frequency response changes.
@sergeauckland: EQ is the least of your problems here, even with pure current drive. Measure the impulse response of the current under voltage drive and voila, you directly obtain the required EQ to make it behave and sound the same wrt frequency response.
While this is true, nobody would use current drive like that. So your bold-faced objection does not hold in practice.Speakers are designed, tested, and specified with a constant* voltage source. A true constant current source would give you terrible frequency response because it will track the impedance curve.
Exactly. You have to find the best source impedance (in a frequency range) by measurement and critical listening.In some cases, a low driving impedance can sound better also in mid or treble area. One has to test this with each driveunit.
There are examples of current drive in commercial speakers. Kii Three's midrange driver is current-driven. Tweeters in ADAM F-series were current drive (and woofers were mixed-impedance drive) -- I designed those, incidentially ;-) Some German servo-controlled speakers use current drive on the tweeter section as well.With that said, most high end manufacturers of studiomonitor with very low distortion and very good sound such as Genelec or Neumann or Linn products with their exakt technology - they all use direct coupling between amplifiers and drivers, even for tweeters.
Did some research, nothing unexpectedAnyone compared the distortion affect on speakers with voltage drive amplifiers vs current drive amplifiers?
In which case, what's the difference between current drive and voltage drive?A paramount, even though actually trivial thing to consider is the follwing:
When the voltage on the driver terminals is the same, the frequency response and overall behavior is the same, too, regardless of what the drive impdance is. It cannot be any other way.
That's the way you actually must compare different drive impedance, dialing in always the same voltage at the driver for same SPL response (as otherwise the frequency response difference will dominate).
The true difference is in the fine-print: Distortion and large-signal behavior (error recovery).
I think I have just explained it here (and other places): The difference is in the "fine-print" once the frequency response is dialed in to be the same with whatever source impedance one is using.In which case, what's the difference between current drive and voltage drive?
We must have very different definitions of voltage drive (i.e. zero source impedance) and current drive (infinite source impedance).
I have tried feeding a jbl compression driver with a high impedance compensating the frequency response with a dsp and the sound didnt get any better. So best try and listen/measure in specific cases If its worth it . I tested this also in the HYBRID project, with a dometweeter in a waveguide and didnt get any soundquality gain, and the sound was by some listeners perceived as worse.You can find much more on it here.
For fulrange speakers in an active system it seems to be a good idea as it reduces distortions, especially 3. and 5. degree. I plan to do some measurements on my own with my fulrange horns this year. But as I don’t have a current drive amp I will introduce a resistor before the driver.
I run these drivers in horns and all I read regarding those high efficiency full range drivers they like current drive. I will report back if I found time to test.My conclusion so far is that the sound gets better in most cases with directly coupled low impedance power amps in an active system, even at higher frequencies.