What is a monitor? A loudspeaker cabinet designed for monitoring in recording studios, radio or television stations, by sound operators in general, and by musicians on stage. Near-field monitor: a studio monitor designed for listening very close to the cabinet. Stage monitor: a low-profile, wedge-shaped cabinet that can be aimed at the performer on a stage. Studio monitor: a loudspeaker cabinet designed for monitoring in recording studios and radio or television stations.
Monitors
However proud we may be of our sound system, whether home or professional, the result depends to a highly significant degree on the response the listening system we have installed is capable of delivering.
When deciding which monitor will best suit our needs, we will have to consider a large number of parameters, headed by frequency response, coloration, transient response, harmonic and intermodulation distortion, sensitivity, phase distortion, output power, dispersion, cabinet type and placement.
By way of a quick introduction, the following lines aim to present in summary form some of their most important characteristics, as well as operating conditions, above all those that in one way or another affect the sound they produce, whether in sound reinforcement applications or for monitoring in production or broadcasting. These are comments born of 30 years in the profession, but unquestionably the personal opinion of those who will use the equipment every day must always prevail over them.
Speaking of loudspeakers
We know that a single loudspeaker cannot cover the entire audible range, since it is very wide (spanning 20 Hz to 20 kHz); moreover, radiating very low frequencies (below 100 Hz) requires large elements or some reinforcement of the weak radiation of a small loudspeaker. At the same time, high frequencies radiated by a large source become very directional, concentrating their energy in very small areas.
For all these reasons, loudspeakers are grouped in acoustically designed cabinets to produce broadband sound sources capable of reproducing audio as naturally as possible. This is the concept of the cabinet or monitor: a unit made up of two or more loudspeakers and electrical filters, known as crossover networks, that separate frequencies into the operating bands for each loudspeaker, so that, in addition to widening the source’s bandwidth, a larger area is covered with acceptable quality, the efficiency of the loudspeakers is increased and they are protected.
The cabinet has an importance that is often ignored, since a series of movements, reflections, air compressions, etc. are generated inside it, which will change the sound of our system, causing very distinct coloration depending on its construction, its interior, the absorbent materials used, whether it is sealed or has air vents.
Placement, directivity…
The working philosophy in the audio world is based on exhaustive control of the system’s overall sound in different acoustic spaces. There are critical decisions, such as placing the sound image, equalization, balance and timbre, that must necessarily be made within a narrow range (approximately +/- 30º horizontally and +/- 15º vertically), since it is in this working area that engineers, producers and musicians make their critical mix decisions, and it is where the monitors optimize the control room’s response.
Doing this properly requires a transparent, flat monitoring system, so that the monitors seem to disappear, which would let our attention focus fully on the sound. We should also let ourselves be won over by monitors that offer a wide “sweet spot,” making the area of the control room where the information coming from the speakers is heard best as large as possible. Granted, there will always be an ideal spot, but the point is to find monitors in which the mix doesn’t “fall apart” alarmingly as soon as we move a little. It’s the search for minimal off-axis coloration and a gradual, not unpleasant transition when moving your head in any direction.
Directivity is extremely important; it is the characteristic that defines how the loudspeaker distributes its radiation in space. Practically all manufacturers include polar diagrams in which we can check the directivity of the product we are buying. Despite what some of them say, however much they insist, there are no omnidirectional loudspeakers or cabinets capable of emitting sound with a uniform radiation angle at all frequencies. It’s true that in circular loudspeakers horizontal and vertical directivity are the same, but it varies outrageously with frequency, the radiation angle narrowing as frequency increases.
What is desirable is a cabinet with reasonably uniform directivity across frequencies toward the front and with minimal side and rear radiation to avoid unwanted reverberation.
We could say that a woofer would have the widest directivity, while a tweeter, on the contrary, would have the narrowest; for this reason we should aim the highs toward the listening position so that the sound engineer doesn’t lose these frequencies.
Technical aspects
To make it easy to connect a variety of sound sources, and bearing in mind the dual or triple use we might make of them if necessary, each monitor should be equipped with a balanced XLR input for direct compatibility with professional equipment, a balanced jack input and an unbalanced RCA input. And while we’re asking, binding posts for bare wire wouldn’t go amiss either…
We have to clearly distinguish between electrical power on the one hand and acoustic power on the other. The first tells us how much power the loudspeaker can absorb before being damaged. As for acoustic power, to give a summary that can serve as a reference, we could measure sensitivity by checking the sound pressure a loudspeaker emits at a distance of one meter with one watt of input.
Let’s be clear that a monitor with more ways is not always better than another for that reason alone. The goal is to achieve a highly linear frequency response from the system, but with too many ways, in addition to phase shifts, the sound of a given instrument emerges from several loudspeakers at the same time, while the harmonics of the same sound emerge from another loudspeaker or others, which can end up confusing the listener.
Some of the models we will find have crossovers with a selectable operating mode. There are 3-way models that can run in bi- or tri-amplified mode, and 2-way models that are bi-amplified or passive. The latter (two-way) are probably the favorites for near-field monitoring, especially for audio editing work and control rooms in recording studios.
And speaking of preferences, passive enclosures are sought after by professionals for whom clarity matters more than any other important parameter in sound reproduction.
Bass reflex systems have the advantage of being faster (and not needing powerful magnets), but larger designs often have bass that is not easily controllable. Fortunately, there are now many two-way bass reflex designs with a very fast bass roll-off that are at the same time very dynamic.
In any case, I never tire of repeating that you have to test a lot before making a decision, since one of the worst things that can happen is hearing details and harmonics in the studio environment that then disappear when the work is played back in the homes of buyers or listeners.
To be continued
It’s reassuring to know that changes in manufacturing techniques mean the systems we can buy on the market today have extremely low failure rates, statistically below 0.5 per thousand, which makes the loudspeaker and monitor industry one of the most reliable in the world of entertainment and communication.
As a curiosity and proof of the veneration some of these manufacturers feel for their star products, we must mention Yamaha’s legendary NS10M Studio monitor, which from its introduction in the eighties until recently was a mainstay in many studios. The decision to stop making it was taken when the pure virgin pulp that gives the woofer its distinctive white cone was no longer available.
Manufacturers can overwhelm us and try to convince us with numbers, diagrams and all kinds of results from exhaustive tests, but if the sound doesn’t win us over, those definitely aren’t the monitors we’re looking for. And on that point we’re not willing to give an inch, are we?
