Pretty much every home studio I’ve been in has suffered from a null at the listening position, slap bang in the middle of the most crucial area of the bass. It’s so ubiquitous I take it for granted. It’s not in every studio but it’s in an awful lot. Why is this and what, if anything, can you do about it?

Why Do Nulls Occur?

A null, an area in a room where a frequency dramatically reduces in level, happens because of acoustics. No big surprise there. More specifically, if the null is really big it’s very likely it’s because of axial room modes. Acoustics can get bewilderingly complicated if you really get into it but the good news is that axial modes are the most significant kind of room mode and are the simplest to understand.

Sound waves of different frequencies all have a specific wavelength and rooms all have specific dimensions. In a typical room there will be three room dimensions - height, width and length. Each of these dimensions will result in three frequencies at which standing waves occur. These are the axial room modes. There are other modes but the axial modes have the most pronounced effect.

Depending on the size of your room the frequencies at which these axial modes affect reproduction will vary but to taking an example of 80Hz. The wavelength of an 80Hz sound wave is approximately 14 feet. While the size of the kind of domestic space which is likely to be repurposed into a studio will vary depending on where in the the world you happen to live, in the UK in a typical domestic setting 14 feet is right in the zone when it comes to room dimensions you might encounter. If you live in suburban Australia you might well have a larger typical room size, if you’re in New York possibly rather less but the principle stands.

Something which varies rather less is the space required for typical equipment. With a suitable desk, equipment and monitors you’re likely to need a few feet to accommodate them. Unless you’re really compact and right up against a wall you’re probably listening from at least 5 or 6 feet out into the room. In my studio I’m going to be around a null in that important bass area, and I’m far from alone in that.

Why Does The Bass Disappear?

A quick explainer of what is happening here, without getting too deep. If a frequency is being reproduced in a space which matches the dimensions of the room, a standing wave can develop at the frequency whose wavelength coincides with the dimensions of the room. This results in areas in the room where the level of this frequency is very loud (an ‘antinode’) and areas where the frequency almost disappears (a ‘node’). Anyone who has ever observed a guitar string playing a 12th fret harmonic will have seen this pattern of maximum movement at 25% and 75% of the string’s length, and a minimum at 50%. There are other frequencies, multiples of this lowest frequency, which match the room’s dimensions in the same way as there are other harmonics which can be brought out on a guitar string but the lowest is the most significant.

The video below is an excellent illustration of the problems modes create. The video does go on to focus on the presenter’s particular product but the use of props at the beginning is great!

If you’re lucky enough to have a larger room you will find that the frequencies affected by axial room modes become correspondingly deeper, though to get below 20 Hz you would need a really large space. So room modes are a fact of life for anyone other than people who mix in free space, at the tops of flagpoles or in the basket of hot air balloons!

What Can You Do?

So what can you do about them? Well one of the things which can help is orientation. The modes exists in the room but you do have a choice over where you place yourself and your equipment in your room. Room dimensions do affect how significant the contribution of room modes are and certain ratios of room dimensions relative to each other can give the most evenly spaced modes, meaning that the damage is minimised. The worst case scenario is a cube, as all three modes are at the same frequency, Meaning the issues will be up to three times worse. Actually the worst case scenario is a sphere but if you are trying to mix in a sphere you deserve all the problems you will encounter!

The conventional wisdom is to set up your studio firing down the longest axis of the room. This is fine in principle but practical issues often come to the fore here. In my studio I work across the room. Both of my ‘end’ walls have doors in them. Russ has the same arrangement and did change from firing across his studio to down the studio but then changed back. And in his new studio build James Ivey chose to fire across the room. There is more to using a space than just how it aligns itself with the room’s acoustic character, it needs to be a space in which you can live and work.

Placing yourself and your equipment so you are approximately a third of the way along the longest axis is a commonly suggested option. This seeks to minimise the effect of the mode by placing the listener halfway between the two ‘worst’ places to be - the node, where the standing wave is loudest, and the antinode where it is quietest. If you can do this then great, however practicalities often conspire to make this impossible, particularly in smaller rooms.

Why Doesn’t Everyone Use Bass Traps?

So with speaker placement and listener placement adjusted to be as practical as possible, both from an acoustic and an ergonomic viewpoint what else can you do? The most obvious solution is bass trapping. Bass trapping works by absorbing bass energy. The problem is that you need a lot of it to make a significant difference. There are tuned absorbers which can be used to address specific issues but the most common, and most useful type is the broadband absorber. The construction of these varies but effective bass trapping takes up space, up to a quarter of the wavelength of the lowest frequency to be trapped. In small studios space is at a premium so regardless of how necessary trapping is to address bass problems, many people don’t do it.

Standing Waves Affect The Reverb Too

Something which is important to bear in mind when talking about bass problems is that as well as affecting the amplitude of bass in the room, this kind of room resonance also affects the relative decay times of different frequencies. The problematic bass frequency will ring on longer in the room. This is why while EQ and speaker calibration can help, it can never completely solve room mode issues.

While bass issues will always be present in an inadequately treated room, poor placement of speakers and equipment can further exacerbate the problem. One technique which is often cited by users of subwoofers is to place the subwoofer at the listening position and to audition the response from various positions around the room where the sub might potentially be sited. This is done by crawling around your studio as you need to place you ear in the potential position the subwoofer might occupy.

However silly this might feel, it illustrates a relevant point, that the response of a room is different at the bass end that it is for the rest of the audio spectrum, it behaves in a different way. Without going too deep, the response of a room is based on pressure at the low end and velocity from the midrange up. The best choice for where to put your speakers in your room depends on what frequency they are reproducing.

The Best Place For Stereo Might Not Be The Best Place For Bass Reproduction

There are practical issues which dictate where equipment is placed in a space relative to the listener. Stereo imaging relies on the appropriate placement of speakers relative to the listener, the position of these speakers may or may not be the ideal position for bass reproduction but the often marginal gains of where to put your bass drivers shouldn’t be at the expense of the rest of the audio spectrum.

Taking this into account does suggest that using a subwoofer might be beneficial. However when I’ve tried subs I’ve found that one single position tends to move the problem around more than make it go away. One possible strategy is to introduce a second sub, as having all of your bass energy coming from a single point does leave it vulnerable to destructive interference, however having two subs does open up the possibility that the subs can interfere destructively with each other. It’s worth considering the distance between them when installing.

Turning It Up Won’t Fix A Room Mode Null

Just putting more energy into the room won’t ever cure a null. Brute force doesn’t work. A very clever solution, which takes the idea that the best location for a sub woofer changes depending on the frequency it is reproducing in a given room is found in the Genelec W371A Woofer system, which uses multiple drivers at different points in space to create a flat frequency response, in this Complementary Mode the woofers operate independently of each other and because the dual drivers in each woofer are a significant distance apart they can work together to use their spatial relationship to avoid room issues as much as possible. Very clever and something I hope will work its way downmarket, the W371A isn’t an inexpensive product…

Bass issues are a fact of life and how far you are prepared to go to address them is very much your choice. Of course the most reliable way to address the influence of your room is to check mixes in other spaces, hence the popularity of checking mixes in the car or a fiend’s studio. This also is a big reason why using a mastering engineer is such a good idea. The simplest step you can take is to be aware of the specific issues in your room. Get a measurement mic, they aren’t expensive, and use some calibration/measurement software to get some accurate data on the issues you face in your specific space. You’ll probably have a good idea but once you see those big peaks and troughs at the bottom end you’ll better understand those mix translation issues you have. I know that in my studio I don’t hear 80Hz properly. When I eventually finish my studio (famous last words) it might be somewhat better but in the meantime I know what I can and can’t trust and that keeps me out of trouble most of the time. What about your studio?