The audio system that never changes. An impossibility?

Although I have made no hardware changes to my audio system in over 18 months, I occasionally make small changes to the DSP configuration: crossover frequencies, slopes etc. I don’t expect to hear any huge transformation in the sound, but I have an idea that by making these changes it has almost the same effect as moving the speakers slightly, or changing the room furnishings, or even fitting new drivers. In other words, keeping the sound fresh to my ears. Maybe placebo, maybe not.

Standard audiophile lore would suggest that somewhere out there is true perfection, or at least a true optimum, that can be found if only the audiophile spends long enough looking, and spends enough money. I think a more realistic view is that apart from an anechoic chamber, any system/room combination has certain characteristics that can at first sound fresh to the listener’s ears, but which eventually become over-familiar. I would hope that by starting with a ‘straight’ system in terms of linearity, damping, phase distortion and crossover accuracy, we automatically get closer to optimum than we otherwise could. But it seems logical that what quirks and idiosyncrasies do remain will be constant and may eventually become wearing on the ears, just as listening to live musicians playing in a particular room for hour after hour, day after day from the same seat would tend to over-emphasise certain aspects of the room’s acoustics (and house PA).

The user of a multi-driver speaker with DSP has an advantage, I think, in that a subtle change to the crossover frequencies and slopes may have very little effect in theory, but in practice will change the speaker’s interaction with the room in subtle time domain-related ways – not simply like adjusting a tone control. We may shift the average vertical position at which a certain frequency range is emitted by the speaker, or affect how two drivers with differing dispersion angles blend together. Other aspects that will be affected include the excitation of any breakup tendencies in the driver cones at certain frequencies, and the contribution of doppler distortion. No single setup will ever be optimal in all areas and with DSP we don’t have to settle on a particular setup forever.

I recently made a small adjustment to the depth of my speakers’ baffle step compensation curves. It seems to me that there is a significant audible difference* between curves that are only 1 dB different. In this case, 5 dB seemed somewhat lacking in top end while 4 dB was too far the opposite way. I settled on 4.5 dB.

With such subtle differences being audible*, I began wondering about the magnitude of effects due to temperature and humidity. There’s an online calculator for absorption of sound by the atmosphere. It may be surprising to learn that at 14 kHz, for example, in typical indoor conditions, the attenuation of sound varies between about 0.2 dB/m and 0.4 dB/m, while at lower frequencies the attenuation is negligible. So if I am interpreting this correctly (and please, do correct me if I am wrong), by listening at 3m from the speakers we could effectively have variations of 0.6 dB of treble attenuation on the direct sound, dependent on the season and use of heating, air conditioning and so on. Furthermore, the reflected sound would vary even more heavily, so I don’t think this effect is negligible by any means. Such variations are presumably more significant than might be encountered by changing cables and other audiophile tweakery.

(Which speaker system will be the first to include sensors for atmospheric temperature and humidity..?!)

All of which brings me to the main point: there are very few things that a conventional audiophile can do to keep the sound of their system ‘fresh’ by deliberately introducing subtle variations, or to compensate for unwanted changes in treble response due to the atmosphere or their ears. The chances of their achieving anything like the optimal setup in the first place are remote. If I am right, and variations in broad EQ of less than 0.5 dB can cause audible problems, then it seems to me that the ability to adjust the system via DSP is vital to avoid frustration, expense and never-ending equipment ‘churn’.

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UPDATE 04/01/15: Here is an account of an apparently-small difference in treble balance being found to be significant audibly:

…The Salon2 has a level switch for the tweeter that operates in 0.5dB steps, and it turned out that the optimal treble balance would have been between two of those steps. With the switch affecting the entire range covered by the tweeter, a level difference of just 0.25dB turned out to be significant.

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* The usual caveats apply to such subjective statements.

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