In our recent podcast with Marcel Schecter of Genelec we discussed the importance and influence of the room a monitoring system is placed in on the sound of that monitor. All good quality monitors are commendably flat when tested on axis in an anechoic chamber. All of that goes out of the window when that monitor is placed in an actual studio.

We all know this but actually solving the acoustic challenges a room introduces can seem overwhelming, so much so that many people do nothing. Marcel is experienced in helping people with this and as a response to the podcast we felt there are three related stages to how a monitoring system ends up ruined by the studio it’s being used in.

So to address the title of this article, how do so many of us ruin good studio monitors?

• Firstly we (unavoidably) put them in a room - What happens to spoil things when we do this?

• Secondly, we don’t measure the response of those monitors in that position, in that room. If we don’t understand the problems, how can we fix them?

• Thirdly we don’t treat the room. Either we do nothing, we don’t do enough, or we do the wrong things.

In this article we collate some of Marcel’s points from the podcast. These are edited quotations, with some language changed to make it more readable.

Put It In A Room

What are some of the common acoustic problems in recording studios that you find, and how can they be solved?

The room acoustics are the problem. It all starts with being in a room. Genelec’s R& D director Aki Mäkivirta sums it up with a nice quote, he tells everyone “Physics stays on version 1.0”. In an ideal world it would be possible for us to listen to the material we mix coming from our speakers to our ears without any difference. It would be linear from the speaker to our ears - This is what I mix, this is what I hear. The moment you are in a room, all of these things change. The main problem is the room itself. And of course the main issue all of us are struggling with is usually the bass range. You have really long wavelengths in the bass range. Two, three, four, five meters. For example, 100Hz has a 3.4 meter wavelength. This energy is within your room and gets reflected all the time.

A problem with speakers is that speakers are usually completely omnidirectional in the bass range. So the energy gets everywhere and is then reflected. And the first thing you usually are aware of if you walk around your room that you can find spots where there is a lot of bass and other spots where there is almost no bass. This is defined by so called room modes or standing waves. Above the bass range, in the mids and in the highs, it's more about early reflections which are easier to address using acoustic treatment.

Should speakers be placed close to, or far away from walls?

Really far away is OK. Because what we are talking about is “speaker boundary interference response”. You always get an interaction between the direct sound from the speaker and the sound that is reflected by the back wall.

At one meter away from the wall this would mean we have direct sound, and then we have a reflection from the rear of one meter (speaker to rear wall) plus one meter more (sound reflected from the wall back past the speaker) travelling towards our ears and these two sound waves combine and the problem is then they cancel out at a certain frequency. So for example with one meter distance to the wall, you will get a cancellation at approximately 90 Hz. To get deeper into that, this is the so called Quarter Wavelength Rule and if you know that then you can easily calculate which frequency has a notch in relation to what distance your speakers are from the back wall. At more than two or three meters away this cancelled frequency gets low enough not to matter as much because the further away you are from the wall the lower the frequency that is cancelled out will be. For example, at three meters it's below 40 or 45 Hertz, which is usually fine but otherwise, you will always get a significant cancellation.

We usually recommend to go really, really close to the wall. One thing that you should be aware of is that with a speaker close to a wall you will always get more bass. This is called ‘Wall Load’. The good thing is, if the speaker is close to the wall, it sums up in phase. So it just gets louder and there's no cancellation and you should be able to just reduce the amount of bass the speaker is emitting using trim controls.

Don’t Measure It

It’s clearly important to tailor the response of the room but to understand how to fix the issues we have to know what those issues are. How can we do that why can’t we just use speaker calibration to measure and fix in one step by adapting the monitors to the room?

From the beginning, Genelec speakers had dip switches, so they already had been able to adapt to the room. In 1978 when we brought out our first speaker for the Finnish broadcasting Company YLE, they asked for a speaker that was adaptive so that you can make sure that in spite of the room, you can still reach a neutral or linear frequency response, and to do this you will have to have filters built in. Later on, we realised that a lot of people never made use of these dip switches because they always thought, “It's fine. It's a studio monitor. It's linear. So why should I do anything about it?”

We had to make sure that people realised how big the impact of their room acoustics are. So we tried to make it possible that people could easily measure their speakers. It was always possible for engineers to set up a third party measuring system and to measure the frequency response, but we wanted to make it really easy.

This is why we invented SAM - Smart Active Monitoring. These monitors are smart because they can adapt to what's going on in your room. They automatically calibrate using the GLM kit, which comprises a network adapter and a measuring microphone. Every speaker plays back a sweep. This sweep is recorded by the microphone and then our GLM loudspeaker manager software gets the results. You can see the influence of your room at your listening spot. Then the software calculates filters to compensate in a really intelligent way, focusing on the bass range. We don't use too many filters, we don't touch the high midrange and the highs at all because it's highly dependent on the position and we always want to make sure that you have a wide sweet spot.

But the crucial bass range is really well compensated. For example, if there is a cancellation you will always have to look for better placement or for better acoustic treatment. If something is canceled out, for example, due to a back wall reflection, if you tried to boost this frequency you would also boost the reflection from the wall which is causing the issue and the cancellation would still happen. Filters can easily correct over-prominent frequencies by cutting that frequency using a filter. But we can't do much about dips using filters. We have some amount of positive gain implemented in GLM, but we only use it for overall tonal balance. So it's usually with wide Q’s. But a narrow dip can never be fixed with a filter boost.

The recording of the sweep is all you need to get all of this information. Then some really clever guys at our R& D department made it possible to extract all the needed information for a full room acoustic report out of these recordings This is called GRADE - Genelec Room Acoustic Data Evaluation. It helps you to evaluate your situation and helps with planning room acoustics. You can send these reports to an acoustician, and they will give them all the information they need. For example it shows the waterfall plot of how frequencies decay over time and the ratio between direct sound and reflected sound.

Don’t Treat It

It’s all very well to understand the issue, but what sound you do about those issues? it depends on exactly what they are and where in the frequency range they are.

Do you have any opinions on the best kind of material for building acoustic panels?

First of all, you always should know what frequency range are you talking about. For example, if it's about bass trapping, then just forget about a few centimetres of foam because they are irrelevant, absolutely irrelevant for all kinds of bass wavelengths because a wave with three meters wavelength will laugh at the two centimetres of foam that you have on your wall.

As for the frequencies you want to treat. If it's about bass you will need a lot of material. And when we talk about material, it’s usually mineral wool, these materials are better and more effective than foam.

There are also some really good foam absorbers out there. But in general, I would always take a look at the measurements of these modules. Every manufacturer should publish a measurement which clearly shows what absorption they reach in which frequency range. In the end it depends on the thickness of the material, and it's all about taking away the energy in the air due to sound waves. All porous absorbers work like that. The more density, the more effective it is.

When it comes to acoustic treatment, just buying some absorbers and putting them up and hoping it helps probably isn’t going to work out too well. What advice do you have?

I think what's really important to understand that we would never tell anyone that it's just about the calibration. You can change the frequency response, of your monitoring system but of course, you cannot change early reflections. You cannot change the reverberance of your room with calibration. So it's always a combination of the room itself, good acoustic treatment, the room itself, and then calibration can help you a lot with things that otherwise would be almost impossible to do if you don't have enough budget. For example, a room mode at 40 hertz or 50Hz, that gives you a boost of, let's say, 15 dBs would be almost impossible to solve with treatment only because you'd be filling the so much space with treatment.

What About Subwoofers? Can they help solve low frequency Issues?

There are advantages of using a subwoofer compared to using full range speakers because the problems with cancellations due to distances to walls, to the floor and to the ceiling can be helped because you can place it on the floor, directly in front of the back wall. This means that two critical reflection points are already not critical anymore, the floor and the back wall.

And so it's possible if you have a speaker system for, let's say for some reason is not at the wall, it's placed one meter away from the wall because it's closer to you and gives you more direct sound, which can be cool. And let's say because of this we have a notch caused by cancellation at 80 or 90Hz. We could then use a subwoofer with a crossover at 100Hz to address this. That sounds high, I know, but you could use this to ensure that the subwoofer, that does not have this cancellation problem because it isn’t at that distance from the wall, covers everything up to 100 hertz and then the speakers do their job from that frequency up. You would never be able to optimise the placement for such a setup without a subwoofer.

Some people are wary of using subwoofers because they associate them with inaccurate, boomy, over-pronounced bass, but that is usually user error. The problem usually is that the sub’s phase in relation to the speakers is not calibrated. This is something GLM does as well. If you have the level and phase matched between sub and speakers, then when you turn on the subwoofer it sounds like one, larger, system. It should never sound like a speaker plus a subwoofer.

The higher end of the audio spectrum is very location-specific because of stereo imaging and our directional cues work extremely well up there. But as we go down, directionality gets more and more vague until we're at the bottom end where it's kind of everywhere. Because of this it’s possible to place a subwoofer where the room needs it to be and the speakers where the ears need them to be.

How would you go about getting the perfect environment at home for mixing?

If you have the option of several rooms, always choose the largest one. These modal structures just get more critical if a room is small. But usually you don't have this choice, It's just one room that you can use. Then in most cases, if it's a rectangular room I would alway sit on the shorter side. This is because of the patterns of typical room modes. There is a rule most of us have heard about - The 38% Rule,. This refers to sitting 38% of way down the room length. That can be a good starting point for where to place your listening position. And then I would always say, bring the speakers close to the wall. And of course, make sure you compensate for the bass boost this introduces.

And then it's about the room treatment. I would always start with as much broadband absorption as possible. For example, place bass traps in all corners and make sure that you get enough of them. It's not that the manufacturers want to sell you more, it’s simply the way it is. The more you have the better because the more energy you can absorb, and of course forget about all of these two or three centimeter thick panels. These are not absorbers and these won't do anything. Then I would go for regular absorption with panels 10 to 20 cm thick. Treat your early reflection points, but also place them throughout the room and on the ceiling as well. It’s really important because it's also a first reflection point. Then you will realise if you do the measurements that the complete reverberation time of your room will just go down. And this is essential because this will mean you will get a higher precision, more direct sound.

Then I would take a look at symmetry, especially the symmetry around your listening position. For example, if there's a window, just forget about the nice sunshine outside and place a curtain there, but it should be a heavy one!

Conclusion

It’s not easy to get a great sounding mix space, but the law of diminshing returns is at play here. The last 10 percent of improvement is really hard but huge improvements to an untreated space can be made relatively easily if you follow the basic guidelines and understand what can and can’t be achieved using the various methods available to us.