High Efficiency Speaker Asylum: Re: Define High Efficiency by Steve Schell

You have posed some good questions. I'll take a shot at answering them.

Loudspeakers are, as a class, some of the least efficient devices created by mankind. Efficiency expresses the percentage of acoustical power output for electrical power input, and the typical figures are shockingly poor. For the usual, inexpensive consumer speaker system produced today, the efficiency is typically less than one percent i.e. 1% sound output, 99% heat output. Besides requiring more input power, there all sorts of horrible side effects from this: high distortion levels, compressed dynamic range, decreased lifetime being among them.

Speaker efficiency can be measured in several ways. Often it is specified as "sensitivity", measured as sound pressure level on axis, at a one meter distance, with a one watt input. These measurements are not directly comparable from speaker to speaker, as their radiation patterns vary dramatically. More relevent is the total power output, although this is rarely specified.

The tried and true methods of achieving high speaker efficiency were pioneered in the 1920s and 1930s, when the efforts of the finest engineers of the day were brought to bear on the challenge of providing sound to the motion picture theatres. They had no choice in the matter, as amplifier power was very limited. They employed light moving mass, maximum voice coil conductor length, high gap flux density, compression and horn loading to increase efficiency as much as possible- up to 50% over a limited frequency range in some cases.

To return to your questions, high efficiency does not necessarily imply high quality- there are plenty of small, nasty sounding reentrant paging horns. Speakers have to be designed for relatively broad, flat frequency response in addition to high efficiency to sound good in a hi fi context. High efficiency speakers useful for hi fi also tend to be expensive, as their construction is elaborate, using costly materials and close tolerances. I think it is a real shame that the world has "gone cheap" with so many products today, including loudspeakers. Most speakers available to consumers today are not built nearly as well and do not sound as good as the speakers in the console radios of the 1930s- what a deal!

So it seems that assembling a high efficiency speaker system, the kind that will make visitors sit down and say "Wow, this is unbelievable!", takes time, patience, some education, and the assembly of some unlikely looking components. Sounds like it could be the start of a nice hobby!

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