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In the confusing and highly subjective world of professional audio, there are few absolutes. Just as a musical performance affects each of us in different ways, the accuracy of a particular monitoring system is a potential minefield of subjective impressions. No single studio monitoring design stands head-and-shoulders above any other, and in many cases, we lack sufficient understanding of the basic laws of acoustics to even make a meaningful comparison of monitoring systems.
Our industry has demonstrated that it can develop the innovative technology required to digitize a signal, store it on a variety of media, perform sophisticated processing and then deliver it to the consumer as a compact disc or digitally encoded soundtrack. Why is it so difficult to produce a full-bandwidth signal in the engineer's listening environment?
The dilemma can be attributed directly to the very way in which our hearing apparatus work. A great deal of our auditory perception is based upon psychoacoustic cues and ear-brain computations. For example, there are certain primal frequencies to which we respond autonomically; such a response relates to the body's autonomic or automatic biological response mechanism. We don't really understand much about what triggers the terror response, for example, or the comforting reality initiated by subsonic, neonatal sound signatures.
But beyond the psychological interplay that certain sounds engender, there are more important parameters that influence the way we perceive sound. They affect the quality and linearity of a monitor system, with its sometimes non-complementary, time-dependent and time-independent characteristics. Having produced a pressure waveform from two ideal point-source radiators, we can accurately model the paths of these signals as they interact and reflect from the walls, ceiling and floors, then combine at the listening position. With sufficient computational power, we could easily predict the impulse response of the modeled environment and come to some useful conclusions about the linearity of the resultant waveforms.
What would be harder to predict, however, is the time-dependent effect that the room and its contents have on these single-frequency test tones-being produced, let's assume for the moment, at fixed levels. Add in continuously changing levels and frequencies, and it becomes clear that the dynamic interplay of program material strongly influences the way the time-averaged signals are perceived at the listening position.
Now consider the time-dependent effects on replay level and frequency content of absorption by the materials making up the room's boundaries, and a room model comprising a multidimensional array of simultaneous equations that would be virtually impossible to compute in real time. It's no wonder that many sound system designers and acousticians rely upon intuition and prior experience when developing control room layouts.
This can be good news and bad news for the owner of a recording or production facility. If the designer is worth the fee, then his or her ideas can be heard in a number of environments where the results are evident. We need to acknowledge, however, that acoustics, like every other scientific endeavor, is constantly being updated as new information comes to light. Unfortunately, our industry is too small to maintain a large pool of researchers who can extend the boundaries of our knowledge on control room acoustics.
Of course, there are many talented individuals employed by loudspeaker manufacturers, acoustic design firms and other organizations actively involved in the development of accurate-sounding playback environments. By and large, however, their activities are relatively uncoordinated-not too surprisingly, given the competitive nature of the studio design industry. The result is that our understanding of acoustics and sound propagation within closed environments remains pretty much open for interpretation.
How can I be so adamant that this body of fundamental information is still unrefined and constantly evolving? Simply by looking and listening to a number of the newer rooms that have been completed within the past 12 to 18 months. Almost without exception, each of them looks and performs differently. A project recorded and mixed in one room will sound slightly different in another (notice that I pass on offering good/bad value judgments?). Cosmetics aside, the actual look and feel of each room is also very different, even if the same designer or design firm was involved. This suggests that our theories of the way sound should be projected and contained within the listening environment-let alone what constitutes the “ideal” SPL/response balance we are after-are far from mature.
In particular, I am still surprised that few of these contemporary designs take into account the fact that day-to-day changes in the environment can affect the way sound behaves within the room. We would expect the physical material from which the monitoring system was constructed to deteriorate over time due to moisture, atmospheric pollutants and natural aging. We also need to consider the myriad ways in which the room's internal volume and reflective surfaces influence the sound characteristics. A well-behaved room with a single engineer located at the sweet spot, and monitoring at modest levels, will produce very different results when filled with a dozen people who need to have the boxes turned up by several decibels. And if the ambient temperature and/or humidity is allowed to rise beyond the values for which the room was optimized, the spectral balance of the material being monitored may very well tilt toward some less-acceptable portion of the audio bandwidth.
All of this suggests that no acoustic theory is yet to be trusted as a solution to the vexing problem of making sound behave within a closed environment. Furthermore, a great deal of investigative work needs to be done on the time-dependent nature of sound propagation-particularly at medium-to-high monitoring levels. A holistic approach to the problem will deliver a more meaningful insight than theories of cabinetry or travel-path analysis.
Acoustics is a complex science. I expect that within the next year or so, its leading proponents will unveil a fundamental breakthrough in our understanding of the optimum techniques for fabricating accurate, pleasant-sounding control rooms.
Given the complexity and high number of variables involved in the monitor/room interface, what is the best and most efficient way to evaluate studio monitoring systems?
My best advice would be to consider the following:
1. Choice of Venue: Always evaluate the monitor system you plan to install in the room itself in the exact position it will be used. Simply setting up a half-dozen pairs of near-fields on stands in the studio and expecting to be able to evaluate one against the other is foolhardy, to say the least. Locate the cabinets exactly where they will be used every day; in that way, you will be saved from eye- and ear-opening surprises! Orient the monitors in the familiar equilateral triangle layout, with 60-degree subtended angles and (if possible) at ear level; experiment later with variations.
2. Auditioning Materials: Choose audio examples with which you are very familiar, preferably a first-generation track that you recorded yourself. Use simple, acoustic-based material to start with and listen at moderate levels. (Save your ears and critical-listening functions for as long as you can.) Gradually work you way to more complex material as you determine the degree of accuracy in faithfully reproducing the sounds on your tapes or favorite CDs.
3. What to Listen For: Assuming that you are familiar with the material being auditioned, listen for both linearity-smooth response at all frequencies of interest-and accuracy. In the monitoring system, the stereo/surround sound image should appear to be floating in space, with neither the speaker locations nor the walls detectable when you close your eyes. In other words, the sound should not appear to be coming from the speaker locations. To ensure that the response is smooth from low to high frequencies, try one of the better-sounding sample CDs that contains glissandos or piano runs, and at equal playback levels.
4.What Might Be Wrong? Space precludes me from listing every factor that might upset the creation of a viable, accurate and realistic stereo/multichannel sound image. But consider the following:
Are the amplifiers matched to the speaker system? (Try auditioning a set of the new generation of high-definition, self-powered monitors if you are still unconvinced that amplifier/speaker matching is of critical importance.)
Do the speakers and amplifiers have sufficient power-handling capacity to cope with high-level transients? If they sound good at modest levels but rather odd at high SPLs-stereo that wanders off-center, notes that fall away too suddenly or the presence of clipping artifacts-then you might need more powerful amplifiers or cabinets with more SPL efficiency and/or capacity.
Is the rough sound you might be hearing attributable to other non-acoustic factors such as console splash or standing waves/resonance within the control room? The former can be eliminated by re-aiming the monitors, while the latter can be minimized by moving the cabinets and/or altering the playback level.
5. Electromechanical Factors: Ensure that you are comparing apples with apples and not confusing the issue by evaluating systems that are unequal to the job at hand. For example:
Keep amp-to-speaker cables as short as possible and use high-quality materials with adequate power handling.
Ensure that both ends of the amp-to-speaker cable are terminated properly with hardware that is up to the job of reliably passing the power you are running through the system.
Look within the cabinets for high-quality components and circuit boards, linked together with reliable, robust connectors, terminators and cable.
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