Monitors and monitoring

Your monitors want to tell the truth – are you listening? Howard Turner hacks through the monitoring myths to help you hear what’s really happening.

Monitors and Monitoring

Your monitor speakers are the most important investment you will make in your studio, bar none. They enable you to accurately judge your material. You can be using Pro Tools or an Edison wax cylinder, Pro24 or Logic, but if you can’t hear what’s going on, then you might as well give up before you start.

Studio monitor or hi-fi speaker?
First of all, let’s get one thing straight – studio monitors and hi-fi speakers have very little in common other than being made mostly of wood and having wobbly plastic bits on the front. Hi-fi speakers are designed to flatter the programme material (ie. hide any shortcomings), and to sound rich and full by using harmonic tricks to extend the apparent bass response. And they must be cheap to produce. They’re also never expected to have to play back anything other than nice, mixed, compressed finished material – no solo’ed kick drums here. As a result, your average 100W RMS hi-fi speaker has a tweeter rated at 3 or 4 watts, if you’re lucky, and this will burn out the first time a decent lump of feedback or high square-wavy synth is chucked at it. And that speaker was never designed to run at anything like its rated power for more than a few minutes at a time.
Studio monitors are different beasts altogether. They are designed to tell the truth at all times (however painful that may be); they must show up every bit of programme distortion; they must deliver accurate bass within the constraints of the cabinet size; they must be able to survive feedback and high transient impulse noise; and they must be capable of running at rated full power for extended periods. It’s also likely that a speaker rated at 100 watts will contain a tweeter rated at a minimum of 50 watts.

Get active
By making everything sound ‘nice’, those hi-fi speakers make mixing almost impossible – and they’re probably going to blow up, to boot. So now that the hi-fi wonders are safely in the dustbin, what sort of studio monitors are going to be best for you? Nowadays, there are almost as many new manufacturers making monitors as there are producing microphones, and inevitably some are great, some are not so great, and a few are little more than hi-fi speakers in disguise. So beware – and do buy with your ears…
Monitor speakers can be divided up in two different ways. Firstly, there are two-driver and three-driver (and more) systems; secondly, and possibly even more importantly, there are either active or passive speaker systems. It’s simply not possible to manufacture a single speaker capable of producing both the raw energy required for bass reproduction (the cone needs to move a long way) and the fast changes of direction required for treble (transient) reproduction. Consequently, speakers come with separate drivers, each coping with a small part of the frequency range – a great idea until we try to cope with managing how only the right part of the frequency spectrum goes to each driver.
Passive systems take a speaker-level feed from a separate power amplifier. A passive (or unpowered) crossover then splits the signal and feeds the right bits to each driver. Because the whole splitting operation in a passive speaker is carried out on speaker signals that are at high(ish) levels of voltage and current, the technology is, by necessity, crude – all coils, fat capacitors and big wire resistors – and none too subtle when it comes to fine-tuning the speaker to the room.
A ‘proper’ active system splits the signal at line (or mixer) level with a great deal of finesse. The split signal is then sent to several dedicated amps, each working with, designed for, and damping its own driver. Accurate crossover control is therefore possible because small, line-level signals are more easily manipulated, and a good match to the room is achievable. Beware though, a lot of passive speaker manufacturers have jumped on the active bandwagon by bolting an amp on the back of a speaker with a passive crossover and calling it ‘active’. If it hasn’t got an amp for each driver, it’s merely a passive design in drag!

All those drivers
The driver issue is one that also has great influence over what ends up leaving our studios. Domestic two-driver speakers split the sound between the woofer and tweeter at around 2kHz. The consequence of this is a blip in the frequency response curve right at the point where the bite of the snare, the rasp of the vocal, and the snarl of the guitar all lie. As a result, it’s easy to over-cook these elements when mixing with a two-driver monitor system, resulting in mixes that are painful to listen to on a car hi-fi, PA system and the like.
A three-driver system with a mid-range driver dedicated to these critical frequencies creates two crossover points, one above and one below the critical 1-2kHz region, resulting in a more faithful reproduction of the important speech frequencies. This may well sound ‘over-middley’ to our ‘two-driver’ ears at first. We need to ‘unlearn’ the conditioning of listening to two drivers and start to listen to these three-driver systems as though we are in the room with the musicians. Once you have acquired this ability, the difference in perception can be astounding.

Speaker placement
Old-fashioned speakers with horn-loaded tweeters were designed to focus all the HF information into a ‘sweet spot’ where you HAD to sit to make any sense of the sound, and to get a stereo image. Engineers and producers used to have to fight to occupy that precious football-sized spot during a mix or a cut. Modern dome-tweeter speakers are designed to produce a wider and more even dispersal of sound, enabling everyone in the room to hear something (tonally) close to what’s happening at the sweet spot (which is also much larger), even if they don’t get the stereo.
For stereo, there are some simple rules regarding placement that will ensure you make the most of your speakers. Firstly, the speakers and listener should be at the three corners of an equilateral triangle. If the speakers are too far apart, you’ll have a ‘hole’ in the centre of the stereo image. In fact, modern dome tweeters enable you to stretch this rule a bit. Today’s domes produce a decent-sized elliptical sweet spot, so by careful placement you can put the engineer at the front of the spot and make room for others to squeeze in behind for critical listening.
The second rule to remember is that the ‘virtual source’ of the sound (see the diagram on the opposite page) should be at ear height, do consider whether you’re likely to be standing or sitting. If you only ever sit to mix, then around 1,300mm is a reasonable height (measure from the floor to your ears, if you’re not sure). If you mix a lot standing up, then raise them to a compromise height of around 1,600mm, for instance. The third rule is that you’ll need to keep the drivers vertically oriented to get the best stereo image. I know you like the look of them when they’re on their sides, but you’ll get much better stereo if they’re upright.
And finally, consider the sub (should you have one). It’s often said that, because we have a hard time telling where bass noise is coming from, the sub can be situated anywhere in the room. But realistically the sub still produces frequencies that yield some positional information, so you’ll need to place it centrally and at the front.
The advent of 5.1 surround monitoring systems has added an extra level of complexity to some setups. For more information on 5.1 speaker positioning, take a look at Ten Minute Master No15 on Surround Sound in Issue 6.

Amps and cabling
If your speaker system is passive, or a big enough active system, then the amps (and, in the case of the active system, the crossovers, too) will probably be mounted remotely in a rack somewhere. This helps get rid of fan noise from big amps, but it also raises two more issues: amp power and speaker cabling. If you buy amps separately from a speaker system, make sure they are big enough. Contrary to the strange hi-fi rule where the speakers should have twice the power rating of the amp, in studios we accept that the amp should have double the rating of the speakers. This is because if the amp goes into distortion, the majority of the distorted signal will route to the tweeter, probably frying it in the process. My old Phase Linear 400 pro amp from the early 70s is 200 watts RMS per channel, but when the meters read 0vu, it’s pumping out just 45 watts – the rest is headroom…
When the signal from an amp forces a bass driver forward, it doesn’t want to stop when it gets to the other end of its travel. The cone overrun generates a small electrical signal that gets back to the amp, which in turn generates feedback to suppress this overrun. If flimsy wires are used between the amp and speaker, the resistance of the wires will hinder this damping, and the consequent cone overrun will make the bass sound muddy, so speaker cabling needs to be massive and of low resistance. A good alternative to pukka audiophile cabling is 2.5mm2 twin & earth solid-core mains cable; it’s cheap and it works brilliantly.

Mounting and stands
When amps were weak and speakers couldn’t handle the power, the only way to get high volume at low frequencies was to mount the speakers in the monitor wall, which has the effect of lifting the bass end by some 6-9dB. Individual monitor walls tended to colour the speaker, making consistency a problem. Today this practice is only required in the largest and loudest pro studio installations. Elsewhere, speakers and amps are more than capable of producing the bass we need without help.
What we do need, however, is to support the speaker rigidly. If the room is well designed, the speaker can be coupled to the room by a simple, rigid and heavy stand: hollow timber filled with sand, a brick column, or similar. If the room is resonant or leaky, then spikes must be employed to cut down structurally-born transmission of bass.

SEE ALSO
Choosing & Using Monitors (Feature)
Monitor Design (10MM)

This feature first appeared in Music Tech Magazine issue 10
Filed under Ten Minute Masters

/mtm/features/monitors-and-monitoring-1

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