Monitoring On Loudspeakers (Part 1)
When you come to choose an amplifier, mixing console, or a tape machine, the task of focusing on a few models is relatively easy, because the main parameters — like power output, or the number of tracks/channels — are obvious. With speakers, the parameters you're looking for are more diffuse in that there isn't necessarily one overriding and key aspect to help narrow down the choice. Also, loudspeaker specifications, whilst useful, will only describe the reality of the sound that you'll perceive in your home environment from one small angle.
To make this business even more perplexing, monitor speakers often are not monitor speakers, for today, quite a few domestic hi-fi models can outperform their professional cousins.
In order to play or produce good music, everyone has to develop an instinctive awareness of the medium — of sound — and part of this involves the development of a set of aural 'images', which are, if you like, reference points or beacons by which your music and musicianship is navigated. If music could be transferred telepathically, all would be well, but in practice, music is delivered through speakers in the end. The most crucial aspect of any studio monitoring system is for its intrinsic qualities to mirror your own perception of sound. No part of the monitoring system influences the basic and immediate qualities of sound more than the speakers you use.
Rule number one for assessing speaker systems is to first of all assess the people you're with. People with strong personalities can affect your perception and though this needn't necessarily be for the worse, capital expenditure on a pair of monitors should perhaps rest upon your own judgement. It's interesting that accusations of 'brainwashing' at speaker demonstrations have been voiced in the realm of esoteric hi-fi!
Rule number two; choose the music you need to test the speakers with care. Avoid music which invokes too much emotion, or, equally, too little. Listen to a broad range of musical styles, and pick on any pieces containing sounds you have found to be lacking in the past on other systems.
Thirdly, and fairly obviously, your idea as to what constitutes a 'good' speaker depends on how developed your aural imagery and overall reference is. Hands up those of you who've laughed at hi-fi enthusiasts spending hundreds of pounds on speakers despite having never experienced live music, or taken time out to hear acoustic instruments 'in the flesh'? As a consequence, their aural image is not only artificial, but also faulty, being constructed around the 'average' of lots of imperfect speaker systems.
We all perceive sound in different ways, and yet, there's a remarkable consensus between people who listen to lots of music — be they musicians or simply music lovers — as to what's basically truthful. Anyway, it might help before deciding on an expensive pair of speakers to refresh your ears by listening to the instruments you don't actually play yourself, in as many circumstances as possible, from concerts to solo performances. Perhaps this should include listening to the music you intend to use for auditioning, on any quality hi-fi speakers that you can lay your hands upon. All this will give your ears 'more to go on', but for the ultimate clarity of perception, put cotton wool in your ears for 24 hours before auditioning; resting the ears in this manner enables the initial impression to be almost purely spontaneous and therefore accurate.
The above test procedure will sensitise your ears, and you'll have to be careful to go easy on the level for the first few minutes. In this particular instance, the necessary low level listening will reveal lots of detail, but normally it doesn't. For this reason, studio monitoring needs to be loud — it's an alternative to sensitising your ears, allowing them to focus in on the details of the sound.
One region where domestic hi-fi speakers, which would otherwise make good monitors fail, is in regard to their sensitivity and the maximum SPL (sound pressure level = loudness) they can attain. In theory, you should monitor music at its 'live' level. This demands short term SPLs in the 130 to 140dB region, and mean SPLs of 105 to 130dB. As we shall see, apart from disturbing other people, if your studio isn't adorned with lots of acoustic isolation, attaining these levels in a small room may prove expensive, awkward, or even impossible.
At this point, you have to decide on a compromise in any case, because only a few fanatics (like myself for instance) will ever attempt to reproduce music at live levels. Most of the people who will eventually listen to your music will do so at considerably lower levels. This seems helpful, until you ask yourself 'At what level will people listen?' The trouble is, you don't know — and yet this aspect will have a profound effect on what they hear, essentially because the sensitivity of the ear to different parts of the spectrum varies according to SPL. In short, high levels mean more (audible) low bass, for instance, plus the ability to pick out individual sounds, particularly harmonics, in much greater detail.
The pragmatic way around this problem is to have monitors capable of shaking the building, and then to use them at levels commensurate with expedience. In other words, aim for the ultimate capability, even if you don't always need (or use) it. This has important ramifications vis-a-vis dynamic colouration, as we shall see in another instalment.
To clarify the physics of the situation, we'll finish with a look at the meaning behind sensitivity and power ratings.
A typical, up-market hi-fi loudspeaker will give an SPL of 83dB(A) at one metre, with an input power of 1 watt. Let's assume, for simplicity, that the SPL at your listening position (perhaps six feet away) is 6dB less ie. 77dB at 1 watt at 2 metres. This speaker will probably handle 100 watts, so let's assume that it's hooked up to a 100 watt amplifier — all genuine mean (or RMS) watts! So what's the maximum SPL? Well, 100 watts is 100 times greater than the reference power (1 watt), ie. a 20dB power ratio. In terms of SPL (which is strictly analogous to energy rather than power, but is, in this instance, dimensionally equivalent), this is also a 20dB increase. So for our 100 watts, we'll achieve a maximum SPL of 97dB.
A more efficient professional studio monitor might have a sensitivity of some 103dB at 1 watt at 1 metre; say 97dB at the listening position. So assuming it can handle 100 watts, it'll give 117dB for the same input power! For our first speaker to achieve this SPL, it would need to be driven with a (hypothetical) 10kW amplifier!
So high sensitivity isn't simply a means of getting by with smaller amplifiers but also making high monitoring levels a reality in the first place (note that the second speaker would attain the same loudness with 1 watt as the first can achieve with 100 watts).
In short, speaker efficiency (or sensitivity) is more important than sheer power capacity, just as a 150 horse power agricultural tractor isn't a lot of good for fast motorway driving!