Loudspeaker Sound Reproduction Philosophy
For the loudspeaker designer, there is a philosophical problem. What are the ultimate criteria? There are a number of common standards:
- Greatest truth to fidelity – accuracy;
- Best stereo imaging;
- Lowest cost; most economical;
- Subjective taste, personal, friends, corporate;
- Best compensation for particular sound source, recording company, media;
- Best copy of another’s design.
When I was learning the trade at Acoustic Research (1961), the discussion was between objective accuracy and someone’s taste. Ed Villchur was the eloquent champion of objective accuracy. He made sure that the company had all the latest testing equipment, plied the consumer magazines with his theories, and invented mind-catching demonstrations. One of these was the “Live Versus Recorded” techniques. He would put on a performance of a string quartet during which the musicians would occasionally “lip-synch” with a recording through the AR speakers, and Villchur would ask the audience if they could detect when that was happening.
For years, I was under the spell of Villchur’s thinking. I was very slow to realize that he did not always practice what he preached. I should have realized when he used his “live versus recorded” technique in fine tuning the AR-4 by playing recorded sound through his favorite AR-3 and then comparing that with the original tape-recorded sound through various configurations of the AR-4. Of course as the company’s speaker technician I had done all of the testing of all of the models and knew intimately that there were problems with the AR-3, which, by virtue of Villchur’s personal preference, were then copied into the AR-4.
I had designed a version of the AR-4 which I both thought was more accurate and which I preferred, thereby avoiding the philosophical question, at least in that instance.
There is much more to be said about these criteria and those listed above, but I will get back to that later.
Some of the elements of speaker accuracy:
- frequency response (flatness);
- distortion (absence of);
- dispersion (uniformity in three dimensions);
- minimum phase (In control theory (http://en.wikipedia.org/wiki/Control_theory) and signal processing (http://en.wikipedia.org/wiki/Signal_processing), a linear, time-invariant (http://en.wikipedia.org/wiki/LTI_system_theory) system is said to be minimum-phase if the system and its inverse are causal (http://en.wikipedia.org/wiki/Causal_system) and stable (http://en.wikipedia.org/wiki/BIBO_stability).-Wikipedia)