The all-important control room
It’s essential to get your control room right first, then sort out your recording rooms. If your monitoring environment is rubbish, how can you expect to make good judgements on the sounds you’re recording in other rooms, let alone try to mix and master it all when it’s recorded? Our quest for good monitoring and great-sounding rooms is thwarted by the unholy trinity of anti-bass, honk and reflection. Fortunately there are sonic equivalents of garlic, holy water and silver bullets to help stave off these evil forces, which we’ll show you in the following walkthroughs – and these techniques apply equally to both control rooms and recording spaces.
Bass nodes and modes
Rectangular rooms inevitably suffer from standing waves or ‘modes’. These are a bigger, badder version of what happens when you blow over a bottle and make it resonate, or sing in the shower and find a particularly loud note that seems to fill the space. A normal-sized room will have X and Y dimensions that are long enough to correspond to long-wavelength bass and subbass frequencies (300Hz and below), and being
“The bass response is invariably at its weakest at the halfway point of a rectangular room”
amongst the resonance of these low frequencies results in an inaccurate listening environment and, ultimately, a mix with a bottom end that sounds totally different when played anywhere else.
Imagine you can see two big, luminous sine waves hovering in your room when you play a low bass note on your synth; one lengthways, one widthways. If you move around the room these frequencies will appear to be louder at points where the sine waves are peaking, and quieter where they trough. There will also be points where the two different frequencies will meet and interfere with each other, causing exaggerated peaks and troughs, and if your listening position happens to be in one of these places, you’re going to end up with a highly compromised sound – either too much or too little of the modal frequencies. As well as that, loud, high-pressure anti-nodes occur near hard walls, and are often the reason why you might hear more bass on the sofa at the back of the control room than in between the speakers. This all creates a very uneven bass response that in turn causes an unbalanced listening environment.
The 38% rule
Most domestic rooms are rectangular and suffer from these bass issues, but on the other hand, it’s easier to target problems in a predictable room, so you’re actually probably starting from a fairly positive position. The bass response is invariably at its weakest at the halfway point of a rectangular room, so listening at the centre of a square will be disastrous.
Fortunately, we can use the ‘38% rule’ to find a position in the room where we’re least likely to encounter bass nodes or interference. This rule says that a point 38% into the length of the room is most likely to offer an interference-free listening position. If you measure 38% in from both ends of your room, then, you’ll get two options. Some engineers also do the 38% calculation on the width of the room, which gives four starting positions at which to place the chair. See the walkthrough over the page for more on this.
Tune your room
Finding a good listening position can solve your bass problems, but it may be that the modal frequencies of your room are just too boomy. This typically happens at around 65Hz and 125Hz. Unfortunately, no amount of foam, egg boxes or mattresses will solve this problem – you will need bass absorbers. A perusal of the websites of manufacturers like Real Traps and RPG will reveal some great and effective products, but they can be prohibitively expensive. A single 50-500Hz low-frequency absorber can cost £300 or more – and you might need six of them to deal with your issues!
It’s not difficult to make your own versions of all this stuff, though. Low-frequency absorbers work by vibrating in sympathy with the low frequencies and are mostly constructed from metal and high-density foam or rubber. From old BBC documents to public patent information from the Fraunhofer Institute, it’s all there if you look. We already have, and here we’ll show you how to make your own dual-function treatment panels using sheet steel, rubber and the amazing MelaTech melamine foam (quite expensive but worth every penny). These will handle both low- and mid-range absorption. You can’t make your own microphones or speakers, but with a couple of hundred quid you can make your own acoustic treatments. Admittedly, you may need the assistance of someone who understands basic DIY, but all of this is doable – we know, because we’ve done it.
COMPUTER MUSIC