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But How Does It Sound?

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

More to the point is that without some form of discipline in their issue, they are at the whim of whoever prints the brochures, making them even more meaningless.

We’re all aware of loudspeaker reviews in the hi-fi press, with a proliferation of ludicrous terms like “boxiness” and “cardboardiness,” but how do you express clarity and definition with language? It’s a bit like explaining the difference between red and blue to a blind person.

What makes this so unfortunate is that many customers rely on specifications to assist them in the choice and purchase of a loudspeaker system.

Consider the recent trade show when a customer visited the one manufacturer’s stand and commented that he intended to purchase a competitive manufacturer’s loudspeaker because it had twice the output.

The fact is that both those products used the identical ATC drive units did not change the fact that their specifications appeared in manufacturer’s printed brochures with two totally different output levels.

Accepted Specs & What They “Mean”
Frequency Response: 40-18,000 Hz is the typical first line. Without any indication of amplitude deviations such as ± 3 dB, it is as meaningless as 0-60 mph (miles per hour) without the time coordinate.

The problem is, most loudspeakers deviate from a straight line across the spectrum. Engineers generally understand this because while the drive unit should have an even response, the final loudspeaker may be “tweeked” to sound better at the expense of this linearity. With the possible exception of a studio monitor, how a loudspeaker sounds musically is what the finished product is about.

Because the loudspeaker may have been modified to sound better or because many of the finer response deviations are a function of the measuring system having no relation to the final sound, these deviations are conveniently omitted, or modified by the marketing department to look more attractive, turning a useful parameter into a meaningless one.

If one particular manufacturer of stage monitors is to be believed, this may even be accompanied by a frequency response graph, which displays an incredibly even response (think Bonneville Salt Flats) before dropping off, not at the standard 12 dB per octave dictated by the laws of physics, but at an incredible 47 dB per octave.

Our sales director once asked me for more response curves to assist his marketing efforts against our competitors. I explained that I didn’t object to showing fellow designers our curves, but if they were to be published as a sales aid, I assured him that would be the end of his sales.

I also explained that the pen recorder an engineer uses is quite different from the marketing department’s pen recorder, which has an infinitely high paper speed and an infinitely low pen speed in order to reproduce the nice flat line shown in sales brochures. Again, a useful specification is turned into an absolutely meaningless squiggle.

Another Lesson Learned
Long ago, I was auditioning monitors for a major studio in London. We all turned up with our measuring equipment, test tapes and recordings of drum solos, orchestral spectaculars, organ pedal notes and so on. Our common belief was that, specifications aside, if any loudspeaker could faithfully reproduce a full drum kit or orchestra, nothing more could be reasonably expected.

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Along came a little man from BBC Research with a scruffy old tape on a plastic spool. He had us all running round the studio trying to find a machine which could play at 7 ips (inches per second, a measure of tape speed). To our amazement, his tape was a rather noisy recording of somebody talking. That BBC boffin shrugged his head and went home.

I queried him later and he said, “Specifications don’t mean a thing to me. I’ve known the man on that tape for 30 years. If the speaker can’t even reproduce his voice, what’s the point in playing music?” He was Spencer Hughes, who later formed the Spendor Speaker Corporation.

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