Do measurements always tell the whole story?

In audio forums there is usually a clear dividing line between ‘subjectivists’ and ‘objectivists’, with the objectivists maintaining that measurements can tell us all we need to know. In audio magazines, subjective opinions in reviews are sometimes supplemented with objective measurement results. But are measurements always meaningful? It seems to me that there is at least one area where this may not be true, and only a rational approach can explain what’s going on.

We all know that most speakers are necessarily made from several drive units, each of which covers a narrow part of the audio spectrum. The crossover filter is designed to split the high power signal on the basis of frequency, and divert the appropriate components to the appropriate drivers. This can be done in several ways. What may seem surprising is that even though the overall system can be designed to have an apparently-flat frequency response with low distortion, this may only be valid for steady-state sine waves, and it does not automatically translate into perfect performance for real music.

The areas that I find particularly fascinating (because no one in the audio business seems to question them) are:

  • bass reflex
  • arbitrary manipulation of the phase response

These are tricks that enable speaker designers to achieve the perfect overall frequency response using nothing more than nature’s own pure, organic components like coils of wire, waxed paper and glue, but which have the potential to do very strange things to the sound.

I have listed some of the strange things that bass reflex speakers do, before. Now I am straying into more areas of ‘the craft’ that I have avoided serving an apprenticeship in, and would appreciate any comments that could provide authoritative information. But my suggestion is that there are sonic peculiarities in speakers that most audiophiles – and even some designers I would bet – are not aware of. The mantra “phase doesn’t matter” allows a designer to pull any trick he likes in order to get a flat frequency response, as measured with sine waves. For a dissenting view, though, I can do no better than refer you to a possibly-unique speaker review. The writer goes into incredible detail about the audible effects of a particular crossover. Just one of several sonic peculiarities is described thus:

“… our human hearing could perceive and assess the Tamino as having a very severe hole or dropout in its tonal balance, in this critical band of the midrange. Note that a conventional sine wave or FFT measurement of the Tamino’s frequency response would not show this cancellation…”

– and this is a speaker he likes!

As far as I can work out, most multi-driver speakers must be subject to these kinds of sonic peculiarities regardless of the apparent perfection of their measurements. Different types of sound will be affected in different ways, transients being affected differently to steady tones. So while one musical phrase or sound may highlight complex anomalies that are reminiscent of a recessed mid range (for example), the next sound may not – and attempting to fix the problem with basic EQ either internal or external to the speaker cannot work. Needless to say, the errors are fundamental, and cannot be corrected by upgrading to a better quality of waxed paper and wire coils. Nor drivers. Nor $10,000 speaker cables.

The DSP active speaker with phase correction, on the other hand, simply tries to avoid all this stuff, and I think you can hear it; the sound is solid and coherent from top to bottom.

If what I am suggesting is true, I think it explains an awful lot!


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