Rod Elliot who is running the site don’t want us to link to individual pages. Therefore you have to use the Search function and search for “Current Drive”.

ICurrent drive raises the output impedance of the amplifier and that is sometimes beneficial, read the article.

This is an overview of the destructive effects that voltage drive has on the performance of electrodynamic loudspeakers. A more comprehensive treatment of the subject can be found in the book Current-Driving of Loudspeakers: Eliminating Major Distortion and Interference Effects by the Physically Correct Operation Method by Esa Meriläinen.

Today, practically all available audio amplifier and loudspeaker equipment works on the voltage drive principle without significant exceptions. This means that the power amplifier acts as a voltage source exhibiting low output impedance and thus strives to force the voltage across the load terminals to follow the applied signal without any regard to what the current through the load will be.

However, both technical aspects and listening experiences equally indicate that voltage drive is a poor choice if sound quality is to be given any worth. The fundamental reason is that the vague electromotive forces (EMF) that are generated by both the motion of the voice coil and its inductance seriously impair the critical voltage-to-current conversion, which in the voltage drive principle is left as the job of the loudspeaker.

http://www.current-drive.info/

The First Watt Model F1
Current Drive Power Amplifier
And Introducing A Pair Of Matching DIY Loudspeakers:
The BassZilla Leopard And Panther
http://www.enjoythemusic.com/magazine/equipment/1204/firstwattf1.htm

Also unusual is the amplifier itself, the brainchild of Nelson Pass, and as far as I know, the only current-drive design currently available to the consumer. Before you get the idea the F1 is in fact an ordinary consumer product, take heed of the following excerpts from the F1 owner’s manual, penned by none other than Nelson himself.

While I have a nice business (Pass Labs) to tend in the daytime, sometimes I come home and can’t resist making something. First Watt is a kitchen table operation – the projects that are not appropriate for my day job.

F1 is Nelson’s first “kitchen table” design in the First Watt series – a 10 wpc, stereo transconductance power amplifier; a fancy name for an active current source. The F1, unlike a voltage-controlled amplifier, attempts to sink a constant current into the loudspeaker – irrespective of variations in the load impedance. There is only one gain stage, operating in pure “Class A” mode: 100 watts per channel are dissipated to deliver a precious 10 watts to the speaker. The amplifier runs hot to the touch and requires plenty of ventilation. And, of course, no feedback is used to reduce distortion. Despite the lack of feedback, this is probably the quietest amplifier money can buy, with a typical figure of about 100 pico-watts noise (pico-watt is one trillionth of a watt).

“This is a tinkerer’s amplifier, and experimental tool. If you just want to be a consumer, then buy something else, otherwise be prepared to patiently experiment with your system to get the best performance.”

Mills and Hawksford coined the term current drive in 1989, in two essential papers published in the Journal of the Audio Engineering Society, dealing with Current Drive Technology.

Current drive offers a major alternative to the speaker-amplifier interface. A transconductance amplifier is operated as a current source with a high source impedance relative to that of the speaker. The output impedance must also be linear and frequency independent. An ideal current source would possess an output impedance so large as to be considered infinite relative to that of the speaker. The F1′s 80-ohm impedance is certainly adequate in this regard. As a result, as Nelson puts it: “the amplifier delivers a precise current to the voice coil of the loudspeaker driver, ignoring the series impedance elements in the circuit, including the wire, the inductance of the voice coil, the resistance of the voice coil versus temperature – all that stuff.”

Current drive offers the potential for dramatic reduction in moving-coil speaker distortion due to power compression and other voice-coil non-linearities. However, there are two basic practical problems to overcome. On the amplifier design side, it turns out that it is difficult to design a high-power current source.

Consider that a woofer’s resonance region is no longer current limited and sinks the same current as the frequency band above resonance. That makes for a huge boost in bass response around the resonance region.

The bottom line is that using drivers of differing nominal impedance but identical sensitivity ratings will result in output mismatches. Finally, conventional parallel type crossover networks do not work well with current sources.

Other article on same topic:
http://www.6moons.com/audioreviews/firstwatt/firstwatt.html