the beveridge difference

In this essay, Rick Beveridge gives his views on how (and why) his products differ from others...

First, just what is a Beveridge speaker? It is not just a single design variation, trick, or gimmick. It is, instead, an integrated design concept; a unique and complete set of ideas and choices, working harmoniously together to produce unique results.

As far as I am concerned, the acoustic lens is the first thing that differentiates a Beveridge speaker from all others. The lens, which my father first conceived in 1965, converts the transducers' planar wavefront into a cylindrical pattern, while maintaining phase coherency and uniform amplitude.

When used in a "line source" (floor-to-ceiling) configuration, this allows the full range of frequencies to be heard throughout the room. In addition, the design provides exceptional stereo imaging.

A lesser known attribute of the acoustic lens is its ability to reinforce the bass notes. The lens, working in conjunction with the cabinet, significantly lowers the bass "floor" of the speaker. The Model 2 can go all the way down into the 50 cycle range. The Model 1 can reach well down into the lower 30 cycle range. Note that we are talking about full-range electrostatic reproduction here, without crossovers or supplementary dynamic drivers.

In order to maintain the system's phase coherency, my father decided to discard (absorb, really) the back wave. This decision reduces the total sound pressure that the speakers can produce, but there seems to be no way to keep the back wave "in phase" with the front wave at all frequencies and points in the listening area.

The Beveridge transducers are unusual in several respects. Unlike the membrane in a "constant charge" system, the Beveridge membrane is fully conductive, with a resistance of less than one ohm. This allows our membrane to be actively driven, producing the same output levels as a "constant charge" system running at twice the drive voltage. In addition, our system does not suffer from the common ailments of constant-charge systems: long start-up and recovery times, charge migration, and dust build-up.

The ability to use a fully conductive membrane is provided by a truly unique stator design. This stator has been a Beveridge hallmark since we made the first ones in 1958. Its electrical properties are unique, employing distributed resistance and capacitance to produce an even electrostatic field without arcing, corona, and related problems.

The physical properties of the Beveridge stator are also noteworthy. It is quite rigid and has an effective "openness" to airflow of 50%, yet it drives essentially the entire surface of the mylar membrane.

The Beveridge speaker is driven by its own integral amplifier. By using a direct-drive (OTL), vacuum-tube amplifier, we are able to supply the large voltage swings and current requirements required by the transducers. In addidion, the fact that the amp is built into the speaker virtually eliminates the usual problems associated with speaker cables.

The Model 2 and its predecessor, the Model 1, are the purest expressions of my father's designs. They embody a truly unique set of design choices and compromises, with correspondingly unique performance characteristics.

The Beveridge speakers are neither easy nor inexpensive to produce. The drive electronics, lens assemblies, and transducers are complex and time-consuming to fabricate. Consequently, these speakers are unlikely to be available at anything approaching mass-market prices.

On the other hand, by producing the systems to order, we can offer almost any desired finish, including a wide variety of veneers. We can also build speakers of specified heights, units that are specifically designed to be installed in a wall, etc.

These advantages, plus the greatly increased quality control gained through custom building them myself, are my reasons for only building new speakers to order, on a semi-custom basis.