Click here to download an MP3 file demonstrating a sequence of the four types of speaker performance described on page 7-2 following the picture sequence 7-2A, B, C, D and after a tone blip, 7-2A again.

By measurement, the peak level in each example is the same but note how the perceived loudness varies in the examples. In the case of B, the sucked-out midband, the overall sound is gutless and weak, although not particularly unpleasant, unlike C and D which are unpleasant. Carefully note that when D fades to A via the tone burst, correct-sound A usually sounds coloured in comparison with D. The ear is capable of retraining itself so that wrong-sound can become acceptable, but the biological process of adaptation consumes mental energy and comes at a price - listener fatigue.

Great care that has to be applied when evaluating loudspeakers to guard against drawing the wrong conclusion - hence the use of known (but not necessarily perfect) reference speakers and an instantaneous change over-box.

If a loudspeaker evaluation through a blind curtain does not include a known reference loudspeaker (or better still, real live musicians or vocalists) then it is almost certain that under those quasi-scientific test conditions and with no visual cues and a short exposure period, the casual listener would usually select type C with a 'projected' balance or even type D. Types A (and B) with a more accurate but softer, less incisive sound would make less of an impact through the curtain. However, if a known reference is introduced, the situation completely reverses, and C and D would be exposed as coloured.

The moral of this story is to anticipate the psychoacoustics of how the ear works and to insist on scientific methods and procedures. To select loudspeakers for serious use without such checks and balances is very unwise and inevitably leads to user's listening fatigue as a longer exposure to the loudspeakers reveals their true nature.