Current-Driving of Loudspeakers: Eliminating Major Distortion and Interference Effects by the Physically Correct Operation Method

Why have the basic laws of electrodynamics been disregarded in the design of loudspeaker operations? A frank exposure of the flaws of voltage drive and a thorough, groundbreaking guide to the physically reasonable way of operating electrodynamic loudspeakers - current-drive. The author argues that the sound quality of virtually all existing speaker systems has been severely impaired by the manifoldly indefinite electromotive forces induced in the voice coil (arising from both motion and inductance), that corrupt the flow of current; and what's dramatic - the measurable evidence is plain and overwhelming. These inherent EMFs in themselves can never be suppressed by any kind of amplifier, but their detrimental effect on current and hence on sonic performance can be eliminated by adequate source impedance. Thus, the secret of valve amplifiers also becomes apparent. Written for all from the academic community to lay hobbyists. Besides new concepts for amplifier and speaker design and demonstrative projects, the book also features novel ideas for modelling, filter design, measurements, and protection; and an enlightening tutorial on analogue linear systems. For more details and sample pages, visit www.current-drive.info

"The most valuable contribution of the book is that it unveils various noise mechanisms related to voltage control, and explains how they spoil the performance of a loudspeaker (not just in terms of increased harmonic distortion . . . ). That is, the central contribution of the book is to spread awareness of the phenomena. . . . The book does also tell us how these noise mechanisms can be removed with correctly executed current control. The author claims that a radical betterment in sonic performance can be achieved with rather simple means and principles. For example, according to Meriläinen, current driving demands active loudspeakers no more than voltage driving does.

The second valuable feature of the book is that it straightens many misconceptions in audio. For example, the traditional marriage of the amplifier impedance and the loudspeaker load assumes that the tiny output impedance of the amplifier nicely controls the woofer's cone displacement. But Meriläinen shows that the electrical damping related to voltage driving is in fact totally irrelevant outside the area of the fundamental (bass) resonance frequency. Also, many believe that it's beneficial e.g. for the speed of the sound that the mass of the cone is minimized. According to Meriläinen, there is no need to be concerned about where exactly the cone is at a certain point of time but only that the cone all the time has the signal related acceleration. And so on.

The third major contribution of the book relates to the control of the loudspeaker's behavior at bass frequencies. A single most important reason why markets have produced so few . . . equipment working on the current driving principle is that the control of the woofers' resonance under current driving conditions is considered to be hard to realize. The book addresses the problem and presents new practical methods and circuits to cope with the technical obstacles to a wider use of current driving."

Mauri Pännäri, Inner-Audio web magazine