Loudspeakers: Objective evaluations - Part 5: Professional monitor loudspeakers

Figure 18.23a shows measurements of an NS-10M manufactured about 12 years after the one shown in Figure 18.22. It has changed and in a very interesting way. The original loudspeaker had a strong suggestion of the Auratone 5C shape in its on-axis frequency response, but this vintage is even more similar. Figure 18.23b shows that the 1997 version of the NS-10M behaves like a slightly smoother Auratone 5C with better bass extension. (Don't forget: familiarity.)

FIGURE 18.23 (a) and (b) show that the Yamaha NS-10M performance drifted from that of the original version shown in Figure 18.22a. It is now even closer to the performance of the Auratone 5C, shown in (b), but it is slightly smoother and has more extended bass. The loudspeaker in (c) has a basic similarity, but the midfrequency emphasis is moderated. It is lower in amplitude and slightly lower in frequency. The loudspeaker in (d) also has an underlying midfrequency emphasis but adds some high-Q resonances around 600 Hz and 2.5 kHz that add an annoying "personality" to the playback. Why? (e) shows a loudspeaker that seems to be trying to be flat but fails at both frequency extremes: "punchy" bass due to the 80–100 Hz, underdamped woofer bump, and rolled-off high frequencies. The fact that all of these monitors, some more than others, exhibit high-frequency roll-off is puzzling in an age when arguments are being made that bandwidth beyond 20 kHz is a necessity for monitoring.

The other measurements depict monitor loudspeakers that seem to suffer from the "wandering standard" syndrome. If you like it, buy it. But isn't that what consumers do, not professional audio engineers?

These are but a sample of the wide range of loudspeakers offered to audio professionals as monitors. Nowhere in the informational literature for these products is there any technical data to suggest what the loudspeaker might possibly sound like. Listen to it, and if you like it, buy it. The problem is that the performance of a monitor loudspeaker can be reflected in the recordings made while using it. The art can be corrupted in a way that may not have been intended, and, once done, it can never be restored to what it might have been. Recordings are forever.

Meanwhile, other manufacturers have pursued another goal, spectral neutrality, to give listeners in the control room an unbiased perspective on what they are doing. Figure 18.24 shows a little historical perspective on some monitor loudspeakers that were intended to hit the same performance target. Obviously, as time passed, technology and engineering methods improved, and the deviations from the target are now very small indeed.

FIGURE 18.24 Examples of loudspeakers designed to be as spectrally neutral as possible. (a) A classic of the industry, the JBL 4310, from 1968. The performance objectives for this loudspeaker are no different from those for excellent loudspeakers today: flat on-axis frequency response and constant directivity. It was limited by the technology of the period. (b) Evidence of 26 years of progress in transducer and system design. (c) and (d) Recent models from two manufacturers an ocean apart who clearly agree on what the performance target is. Both of these manufacturers reveal enough anechoic data on their loudspeakers for consumers to anticipate the excellent performances depicted here.

This entire chapter full of data on loudspeakers is both reassuring and disappointing. The reassuring part is that there are monitor loudspeakers in circulation that can allow recording personnel to anticipate, very accurately, what might be heard by many consumers.

The performance objectives for the professional monitor loudspeakers shown in Figure 18.24 are the same as can be seen in the consumer products in Figure 18.14 (R and I), 18.16, and 18.17. Those products were a sample of many readily available products from several major manufacturers, covering a wide price range. All, especially the lower-priced ones, are very popular, so one can be assured that increasing numbers of consumers are equipped to hear the art very much as it was created. This is good news.

The sad news is that there are loudspeakers at all price levels that perform badly. There is no excuse for this inadequate behavior; the "bill of materials" would have permitted loudspeakers of much higher performance to have been built. Was it deliberate, a misguided notion of what sounds good? Was it incompetence, knowing what is wanted but not being able to get there? In a few cases, it seems to be simple carelessness.