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But How Does It Sound?

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

Maximum Output Level
This is possibly the daftest spec of all. How manufacturers measure this totally escapes all of us. How do they test it? What with? Do they play a sine wave at a single frequency that gives the most output, then with a sound level meter measure the result when they turn the wick up?

To get a maximum figure, do they keep on turning it up until the loudspeaker blows up, then measure the level just before it exploded? Do they play it in a small absorbent room that sucks up the sound, or in a large reverberant hall which may offer 20 dB of room gain?

Do they use pink noise, which most fairly covers the 20 Hz to 20 kHz spectrum? Do they play music? Which is more real. If so, do they read the average level or the peak level? And then, over which period of time? So it goes, on and on.

Still, the most popular output measurement, because it’s the easiest and definitely most inaccurate way, is to calculate the maximum output level. For example, the bass is 2 x 15-inch and the manufacturer spec is 100 dB at l watt, and we use two of them si that’s 103 dB at 1 watt (not correct). We horn-load them, so that adds 5 dB. Then add the low-mid drivers, the mid and the high drivers, and somehow they arrive at a total of 108 dB at l watt.

Now we rate this system at 800 watts RMS. Because doubled wattage gives a 3 dB increase, then as 1 watt is 108 dB, 2 watts is 111 dB, 4 watts is 114 dB, and so on. Therefore, 512 watts gives 135 dBm. With total power handing of 800 watts, this system therefore has a maximum sound output level of 138 dB. Nonsense! Believe it or not, I have heard all these versions from different manufacturers, and it is the one spec that seems to be under control of those spurious marketing departments.

There is not a lot to say with this spec. Any loudspeaker will vary from a few ohms at just one minimum point, then rise to all sorts of values everywhere else in the spectrum. The spec should really say nominal or minimum impedance, but don’t forget if you drive a loudspeaker hard, it gets hot and the impedance goes up anyway.

This wonderful spec that is now all the rage. Polar diagrams of individual drivers and complete systems is a useful specification if measured properly and left alone by the sales department’s graphic designers, but I suppose that is really too much to ask.

We are now told that “Our bass bin had more throw than his.” Wonderful how these salesmen have gotten around the fundamental laws of physics. We used to talk about dispersion, but now it’s all throw. The fact is, a conventional loudspeaker system has reasonably wide dispersion. If you reduce it’s horizontal (or vertical) dispersion, it will be louder in front—it throws more. End of story.

If a salesperson tells you his loudspeaker has longer throw than anybody else’s, and still has wide dispersion, he may think he is full of knowledge, but you know what he is really full of.

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The Bottom Line
Read the specs by all means, but don’t take them too seriously. You cannot blame the marketing department for modifying the specs because they are paid to sell as many loudspeakers as they can.

It’s a lot of money to spend at the whim of a sales brochure or what somebody else has told you. There’s only one way to audition a loudspeaker, and that is put it beside another loudspeaker in the same room, using the same power amps and cables, and do an A-B test. Also, have it installed by the same technician because I’ve seen some wicked tricks with salesperson demos. Any reputable manufacturer would welcome such an opportunity to demonstrate the prowess of its products.

If he doesn’t have time for that or tells you he doesn’t need to do that because his products are so popular, you’ve probably saved yourself a lot of money. No amount of technical specifications and trendy advertisements will tell you what the loudspeaker actually sounds like.

The real qualities of a loudspeaker, like definition and clarity, the bite of a snare and the kick of a bass drum, are impossible to describe with words and figures, so go for a demo and have confidence in your own ears. They were, and always will be, the best judge.

Stephen Court of Court Acoustics in England pioneered work on high-power touring systems in the 1960s and 70s, and produced the first music line array—Black Box—in 1975. His work on evaluating loudspeakers led to his development of the test CD SoundCheck, which he co-produced with Alan Parsons at Abbey Road Studios in London and which became the best-selling test CD used worldwide as a reference for the subjective evaluation of loudspeaker systems.

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