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But How Does It Sound?

Inside loudspeaker specifications -- what's useful and (especially) what's not, explained in detail.

Editor’s Note: This article originally appeared in the November/December 2001 issue of Live Sound International magazine.


At the announcement of my children’s birth, the first thing everyone asked was “what did they weigh?”

It always struck me as somewhat peculiar. Of all the personal qualities you could discuss, such as the color of the hair, or how healthy they are, weight seems a strange specification.

Fancy telling somebody that you have just purchased a new car: “Oh really, what does it weigh?”

Weird & Wonderful
Talking of weird and wonderful specifications brings one to the subject of loudspeaker specs and how meaningful they are—or not—as the case may be. From a design point of view, the manufacturers’ specs of a drive unit are obviously important when you have to select a suitable driver from a whole load of available units.

They don’t give you the slightest clue to how they will sound, but the printed spec is a starting point. Having narrowed down to a handful of units whose sensitivity, frequency band and power handling matches your requirements, the only way of assessing their performance is to load them in your box and listen to them.

This is a highly subjective process, and quite often a driver with an inferior spec, such as a lower efficiency, just happens to sound better. One is reminded of the story when a supplier to one of the world’s biggest guitar amp manufacturers had just acquired a new all singing and dancing computer analysis program in its R&D department. The supplier’s biggest sales volume was to that guitar amp maker.

Accordingly, they put their driver through the analysis. For the first time, they discovered multiple anomalies in its performance which, until then, had proved impossible to measure. The cone was breaking up at high sound levels, causing loads of distortion.

With the aid of the new computer analysis, they produced a near perfect driver, and with great pride, presented it to the guitar amp manufacturer. Following a long silence, they pursued their engineers for some response. “Totally useless!” came back the reply.

As you might expect, that particular driver displayed a distinctive cone break-up which emphasized the best characteristics of the electric guitar. The new driver, although technically faultless, lacked that musical character. More to the point, it had exactly the same printed specifications.

Root Problems
The principal problem in all of this is that the accepted specifications for drive units have simply been applied to complete loudspeakers. Despite the numerous scientific principals common to drive units, the final and singular purpose for them is to convert electrical energy to acoustic energy, a process which can be definitively measured.

However, a complete loudspeaker has a much more ethereal purpose, to convert electrical information into music. This is a highly subjective assessment, and the standard specifications, which may be useful in the selection of drive units, are virtually meaningless in the selection of a loudspeaker system. In other words, the manufacturers specifications as they stand have little or no bearing on the sound of their loudspeakers.

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