Loudspeakers: Objective evaluations - Part 5: Professional monitor loudspeakers

[Part 1 begins with a look at the two basic radiation patterns of sound sources. Part 2 answers the question "If we want to measure a loudspeaker, and from those measurements try to anticipate how it might sound in a room, what should we measure?" Part 3 reviews results of the author's elaborate subjective-objective investigation into loudspeaker evaluation. Part 4 reviews the measured performance of some real-world consumer loudspeakers - some good and some not so good.]

18.5 EXAMPLES OF PROFESSIONAL MONITOR LOUDSPEAKERS
Monitor loudspeakers (the real thing, the ones used in recording studios, not the consumer loudspeakers that are sometimes called "monitors" or "reference monitors" for image building) are important to our industry. It is through these loudspeakers that musicians, recording and mastering engineers, and producers get to judge what they are doing. This was first discussed back in Chapter 2. There it was explained that the idea of monitoring through bad loudspeakers to get an idea of what the product might sound like to the average consumer is not a particularly useful idea because there are no standards for failing to be good.

There are an infinite number of ways to sound bad. But as we have seen in this chapter, there seems to be a rather limited number of options to get high subjective ratings - that is, to sound good. A long-term look at the audio industry at all of its levels leads to the conclusion that the vast majority of loudspeaker designs aim to be flat on axis. Many fail, and they fail in many different ways.

The one thing that poor-sounding, usually inexpensive, loudspeakers have in common is a lack of low bass. Thus, the suggestion is that audio professionals use the very best, most linear, most neutral loudspeaker they can find for all of their monitoring tasks. If they wish to hear how their artistic creation will sound through average inferior loudspeakers, use a high-pass filter to progressively eliminate the low bass; higher cutoff frequencies would then represent lower sound quality categories.

However, many years ago, the Auratone 5C came upon the monitoring scene. It was represented as a means of evaluating what "average" sound systems might be like. A few samples showed that it was not a very consistent "standard" for the absence of excellence. Nevertheless, it became one of the loudspeakers that recording engineers liked to find in studios as they traveled around (familiarity is a good thing). It may also have been a factor in the popularity of near-field or close-field listening, where small loudspeakers are perched on top of the meter bridge of a recording console.

In any event, with the passage of time, other small loudspeakers found their ways to the meter bridge, and one of the products that really took hold was the Yamaha NS-10M. This was part of a series of high-quality loudspeakers, aimed at the professional but also at the high-end consumer market. The top of the line NS-1000M was distinguished by having beryllium dome midrange and tweeter diaphragms, something very adventurous in the mid-1980s. In some ways, they set new standards of performance, especially, as I recall, in terms of low distortion and the absence of resonances in the transducers.

In a discussion with one of the design engineers, the author was told that the bookshelf loudspeaker, the NS-10M, was intended to be listened to at a distance in a normally reflective room. The bass contour allowed for some bass boost from a nearby wall, and the overall frequency response was tailored for a listener in what then would be called the reverberant sound field, which, it was thought in those days, was best characterized by sound power. So the NS-10M was designed to have flat sound power. Figure 18.22a shows that they succeeded very well.

About the same time, JBL Professional made a monitor loudspeaker using drivers of much the same size, but being interested in delivering accurately balanced sound to listeners not far away, they designed their product to have a flat on-axis frequency response. Figure 18.22b shows that they succeeded very well. Also shown in Figure 18.22 is the directivity index, and it can be seen, especially in the overlaid curves in (b), that they are almost identical.

FIGURE 18.22 Two small 7- to 8-in. two-way loudspeakers with similar directivity indexes, each one optimized to a different target. (a) The Yamaha NS-10M was designed to have constant sound power. (b) The JBL 4301 was designed to have constant on-axis frequency response.

Interesting, two very similar loudspeaker systems engineered for different purposes: one of them to deliver accurate sound at short listening distances and the other at long listening distances. So which one ends up being the informal international standard near-field monitor? The one designed to be listened to at the far end of the room, the NS-10M! How could this happen? How could audio professionals be so wrong? Unfortunately, the whole truth may never be known, and one suspects that there are some good stories among industry insiders, but from this perspective, there is a possible reason: familiarity.