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The Objective vs The Subjective

Analyzing the performance of a microphone preamplifier or an A/D converter is relatively straightforward, measuring and analyzing the performance of loudspeakers is a whole different game

Starting with the second-ever issue of Pro Audio Review, I contributed reviews and bench tests to the magazine before taking a different path for over a decade; now I’ve come full circle. I’ve maintained access to sophisticated test equipment from Audio Precision and Prism Sound over those years, digging into the performance of gear through the capabilities of these diagnostic tools, charting the performance of ever more neutral gear as well as learning to quantify the traits of “gear of character” to develop some sense of the aspects of sonic performance that engineers describe in terms of tone and color. Analyzing the performance of, say, a microphone preamplifier or an A/D converter is relatively straightforward; a battery of standard tests quantify distortion, linearity, frequency response, and other behavior to yield a objective picture of performance.

Measuring and analyzing the performance of loudspeakers is a whole different game. In general, loudspeaker behavior can’t be considered in isolation, as transducers interact with their environment, that environment affecting the results yielded when applying the same tests to loudspeakers as used for devices that have electrical inputs and outputs. After Rob Tavaglione performed his one-engineer’s-application evaluations of the speaker systems in this month’s Session Trial, I received one each of the monitors in the trial while their mates went off for photography.

The measurements done for the bench test accompanying Rob’s evaluation included a range of tests (conventional distortion, tone sweeps, multi-tone, and noise analysis) that can all be affected by the monitoring environment. The test microphone and preamplifier become a part of the test results. Without the benefit of one of the most expensive tools in loudspeaker testing — an anechoic chamber — these tests do not remove the environment from the testing, but can still provide a measure for relative analysis, letting us discuss how the loudspeakers perform compared to one another in a similar environment.

Technological advancement has helped in one significant way that does minimize the effect of the loudspeaker’s environment when testing transducers. By using FFT analysis, and windowing the results of a fast stimulus/measurement procedure in time, the test can look at just the primary stimulus/response and ignore the portions of the response that come from the listening environment (room reflections). Proven mathematical algorithms built into the test software — in this case, Prism’s dScope III — are then used to derive the frequency response yielding, in effect, an impulse response derived measurement without the difficulty of performing classic impulse response testing.

While, if I were a loudspeaker manufacturer, I’d still want lab conditions and an anechoic chamber to develop the data for published specifications, this exercise in relative measurement did provide a basis for comparison that is complementary to the purely subjective listening tests. We at PAR will be interested in hearing your subjective responses to our efforts in objective as well as subjective gear evaluation.