SOME NEW DEVELOPMENTS that at first glance seem "far out" are about to become realities. One is a double voice-coil speaker. A speaker normally needs only one voice-coil, but the added coil will permit direct mixing of input signals. This will result in a common bass output for use in a subwoofer that can be added to both channels of a stereo system, but without external accessories. Developed by Royal Sound for use in mobile sound systems, the new speaker is reportedly being modified for the home audio market as well (which itself is a novel twist, since as a rule mobile equipment has evolved from fixed-installation designs).

Equally innovative is Royal's new "d.c. to d.c." pulsed power supply which changes one value of d.c. voltage to another without the need for a mechanical vibrator (the familiar, "converter"). The power transfer is accomplished quietly and electronically, and with less bulk than conventional systems require. While future applications seem fairly wide, the present use of the new power system is for vehicular sound rigs.

The world's first commercial version of a "ribbon" phono-disc cartridge has been announced by the new firm of Nagatronics. The ribbon element, a delicate sliver of proprietary material, replaces the coils of a conventional pickup. Since it has no internal inductive reactance, this cartridge is said to be inherently phase coherent and, to that extent at least, capable of rendering "purer" or more accurate disc playback. First models, in an integral shell that will fit many (though not all) tone arms, is priced at $220; a "head amp" to boost the signal costs another $250.

Something approaching science fiction is an "induction power transfer" system still under wraps abroad. It is basically a technique for supplying a.c. voltages without the use of power cords plugged into sockets. A counter-top, for instance, could be "energized" from underneath so that an appliance -- fitted with a suitable "receiving" element -- placed on the counter-top would become electrically powered. The counter-top itself would be safe to the touch.

While the above developments represent new, or even exotic, technology, there also is a radically new approach under way to the producing of more familiar types of products, embodied in a group known as "NAD" (New Acoustic Dimension). NAD is a worldwide association of audio dealers who, according to director Martin Borish (former head of AR, Inc.), "directly assume responsibility for the product and marketing decisions customarily made by the audio manufacturer." With members in more than 20 countries in Europe, the Middle East, and the Orient, NAD has just formed a U.S. branch based in Lincoln, Mass. NAD claims that its product decisions result in better value for the consumer dollar. Moreover, says NAD, their membership's close contact with the public makes for better-informed choices of what products to offer and how to promote them. So far NAD has developed four receivers, five amplifiers, and two tuners. More products will follow.