Posted March 7, 2006, 10:41 a.m.
By Gary Bromham
When preparing a space for recording and mixing we enter a potential minefield, as no two areas will sound the same, and therefore no one-solution-fits-all instant fix is available. There are, however, a few systematic processes we can run through to facilitate vastly improving our listening environment.
When putting together a home studio, it is very easy to spend sometimes large sums of money buying equipment, and then to neglect the most important aspect of the sound; namely the environment set up and used for recording. No matter how much we spend on computers, speakers, guitars, keyboards or amps etc., we have to give priority to the space in which they are recorded.
Whether it be a house, apartment, or just a room, the method is still based on our ability to soundproof and apply sound treatment to the area. It is extremely difficult to predict what will happen to sound waves when they leave the speakers. Every room is different and it’s not just the dimensions that dictate how a room will sound. Assorted materials which make up walls, floors, ceilings, windows and doors - not to mention furniture - all have an effect on what we hear emanating from our monitors.
Fig 1. A vocal booth with off the shelf acoustic treatment fitted.
Whether we have a large or a small budget to sort out our space, there are a number of off-the-shelf or DIY solutions we can employ to help remedy our problem. It should be pointed out at this stage that a high-end studio and a home project studio are worlds apart. Professional studio design demands far higher specification and uses far narrower criteria as its benchmark, and therefore costs can easily run in to hundreds of thousands!
Why do we use acoustic treatment?
An untreated room - particularly if it is empty - will have inherent defects in its frequency response; this means any decisions we make will be based on the sound being ‘coloured’. If you can’t hear what is being recorded accurately then how can you hope to make informed decisions when it comes to mixing? Any recordings we make will inherit the qualities of the space in which they are recorded. Fine if it’s Abbey Road or Ocean Way, but maybe not so good if it’s your bedroom.
No matter how good the gear is, if you want your recordings or mixes to sound good elsewhere when you play them, then you need to pay attention to the acoustic properties of your studio space.
Begin with an empty room
When our shiny new equipment arrives in boxes, our instinct is always to set it up depending on whether it ‘looks right’, as if we are furnishing our new apartment.
Beware. Your main concern is not to place gear and furniture where they look most aesthetically pleasing, but where they sound best. The most important consideration is to position the one thing that takes up zero space but ironically consumes all the space. It is called the sound-field, or the position in the room where things sound best.
One of the things I have learned is that the most effective and reliable piece of test equipment is - surprise surprise - our ears! Of course we need more advanced test equipment to fine-tune the room but we need to learn to trust our ears first. They are, after all, the medium we use to communicate this dark art of recording.
Before you shift any furniture, try this game.
Ask a friend to hold a loudspeaker, and whilst playing some music you are familiar with, use a piece of string or something which ensures he or she maintains a constant distance from you of say 2-3 metres. Get them to circle around you whilst you stand in the centre of the room listening for the place where the room best supports the ‘sound-field’. The bass is usually the area where you will hear the greatest difference. As a guide listen for where the bass sounds most solid or hits you most firmly. Why am I focusing on bass? Because, if you get the bass right, the rest will usually fall into place.
Also, avoid areas where the sound is more stereo (we are after all holding up just one speaker, a mono source); this is usually an indication of phase cancellation. Beware of areas where the sound seems to disappear.
Finally, having marked a few potential positions for speaker placement, listen for where the speaker seems to sound closest at the furthest distance. We are looking for a thick, close, bassy and mono signal. When we add the second speaker this will present us with a different dilemma but we’ll talk about speakers later.
Remember: Though you may not have any control over the dimensions of your room, you do have a choice as to where you set up your equipment, and where you place your acoustic treatment. As well as the above techniques there are other things to consider.
- It is generally a good idea to set up your speakers across the narrowest wall.
- As a rule, acoustic treatment should be as symmetrical as possible in relation to your walls.
- Ideally your speakers should be set up so that the tweeters are at head height
- The consistency of the walls has a huge bearing on the sound. If they are thin partition walls then the bass will disperse far easier and be far less of a problem than if they are solid and and prevent the bottom end from getting out. (This is a Catch-22 as thin walls will almost certainly not improve relations with neighbours!)
Audio 1.'Incredible' Front Room:
Audio 2.'Incredible' Center Room:
Audio 3.'Incredible' Back Room:
Three audio examples demonstrating the different levels of room ambience present on a vocal sample played 0.5 m/2.5m/5m from the speakers in a wooden floored room.
The Live Room
If you are lucky enough to have plenty of space and are able to use a distinct live area the rules we need to observe when treating a listening area don’t necessarily apply here. Drums, for example, often benefit from lots of room ambience, particularly if bare wood or stone make up the raw materials of the room. I’ve also had great results recording guitars in my toilet, so natural space can often be used to create a very individual sound. Indeed, I’ve often heard incredible drum sounds from rooms you wouldn’t think fit to record in.
Fig 2. Reflexion Filter made by SE Electronics.
It is often a good idea to designate a small area for recording vocals or instruments which require relative dead space. It would be unnatural (not to mention almost impossible) to make this an anechoic chamber, devoid of any reflections, but at the same time the area needs to be controllable when we record. Most of us don’t have the luxury of having a separate room for this and have to resort to other means of isolating the sound source like the excellent Reflexion Filter made by SE Electronics. This uses a slightly novel concept in that it seeks to prevent the sound getting out into the room and subsequently cause a problem with reflections in the first place. Failing this, a duvet fixed to a wall is often a good stopgap and the favourite of many a musician on a tight budget.
Time for Reflection
Every room has a natural ambience or reverb, and it should be pointed out at this stage that it is not our aim to destroy or take away all of this. If the control room is made too dry then there is a good chance that your mixes will have too much reverb, the opposite being true if the room is too reverberant.
The purpose of acoustic treatment is to create an even reflection time across all - or as many as possible - frequencies. It obviously helps if the natural decay time of this so called reverb isn’t too excessive in the first place.
Higher frequency reflections, particularly from hard surfaces, need to be addressed as they tend to distort the stereo image, while lower frequency echoes, usually caused by standing waves, often accent certain bass notes or make others seem to disappear. High frequency "flutter echoes", as they are known, can often be lessened by damping the areas between parallel walls. A square room is the hardest to treat for this reason, which is why you generally see lots of angles, panels and edges in control room designs. Parallel walls accentuate any problems due to the sound waves bouncing backwards and forwards in a uniform pattern.
Fig 3. A graph showing different standing waves in a room
Standing, or stationery, waves occur when sound-waves remain in a constant position. They arise when the length of this wave is a multiple of your room dimension. You will hear an increase in volume of sounds where wavelengths match room dimensions and a decrease where they are half, quarter or eighth etc. They tend to affect low end or bass (because of the magnitude of the wavelength). For this reason they are the hardest problem to sort out, and because of the amount of absorption and diffusion needed generally the costliest to sort out. Further explanation is required.
Suppose that the distance between two parallel walls is 4 m. Half the wavelength (2m) of a note of 42.5 Hz (coincidentally around the pitch of the lowest note of a standard bass guitar-an open ’E’) will fit exactly between these surfaces. As it reflects back and forth, the high and low pressure between the surfaces will stay constant – high pressure near the surfaces, low pressure halfway between. The room will therefore resonate at this frequency and any note of this frequency will be emphasized.
Smaller rooms sound worse because the frequencies where standing waves are strong are well into the sensitive range of our hearing. Standing waves don't just happen between pairs of parallel surfaces. If you imagine a ball bouncing off all four sides of a pool table and coming back to where it started; a standing wave can easily follow this pattern in a room, or even bounce of all four walls, ceiling and floor too. Wherever there is a standing wave, there might also be a 'flutter echo'.
Next time you find yourself standing between two hard parallel surfaces, clap your hands and listen to the amazing flutter echo where all frequencies bounce repeatedly back and forth. It's not helpful either for speech or music.
Audio 4. Subtractor in Reason:
Here’s an ascending sequence created in Reason using Subtractor set to a basic sinewave. Whilst in the listening position play back at normal listening level. In a good room the levels will be even but if some notes are more pronounced or seem to dissapear this usually indicates a problem at certain frequencies in your room.
Fig 4. A chromatic sequence using Subtractor created in Reason.
Download this as a Reason file and convert the notes in the file to frequency and wave length.
Absorption or Diffusion...that is the question?
The two main approaches when sorting out sound problems are finding the correct balance between absorption and diffusion. While absorbers, as their name suggests, absorb part of the sound; diffusers scatter the sound and prevent uniform reflections bouncing back into the room.
Absorbers tend to be made of materials such as foam or rockwool. Their purpose is to soak up sound energy. Foam panels placed either side of the listening position help with mid or high frequencies or traps positioned in corners help to contain the unwanted dispersion of bass.
Diffusers are more commonly made of wood, plastic or polystyrene. By definition they are any structure which has an irregular surface capable of scattering reflections. Diffusers also tend to work better in larger spaces and are less effective than absorbers in small rooms.
Companies such as Real Traps, Auralex and Primacoustic offer one-stop solutions to sorting out acoustic problems. Some even provide the means for you to type in your room dimensions and then they come back with a suggested treatment package including the best places to put it. These days I think these offer excellent solutions and are comparatively cheap when you look at the solutions they offer. What they won’t give you is the sound of a high end studio where huge amounts of measurement and precise room tuning is required but leaving science outside the door they are perfect for most project studios.
The DIY approach can be viewed from two levels. The first, a stopgap, where we might just improvise and see what happens. The second, a more methodical, ‘let’s build our own acoustic treatment because we can’t afford to buy bespoke off the shelf tiles and panels’ approach.
- This could simply be a case of positioning a sofa at the back of the room to act as a bass trap. Putting up shelves full of books which function admirably as diffusers. Hanging duvets from walls or placing them in corners for use as damping. I even know of one producer who used a parachute above the mixing desk to temporarily contain the sound!
- Build your own acoustic treatment. I personally wouldn’t favour this as it is very time consuming and also presumes a certain level of abilty in the amateur builder department. The relative cheapness of ‘one solution’ kits where all the hard work is done for you also makes me question this approach. However, there are numerous online guides for building your own acoustic panels and bass traps which can save you money.
Though speakers aren’t directly responsible for acoustic treatment their placement within an acoustic environment is essential. I’ve already suggested how we might find the optimum location in a room for the speakers; the next critical thing is to determine the distance between them. If they are placed too close together the sounds panned to the centre will appear far louder than they actually are. If they are spaced too far apart then you will instinctively turn things panned in the middle up too loud. The sound is often thin and without real definition.
Finally, speaker stands or at least a means of isolating the speaker from the surface on which it rests is always a good idea. The object is to prevent the speaker from excessive movement and solidify the bass end. MoPads or China Cones also produce great results
The role of headphones in any home studio becomes an important one if you are unsure of whether to trust the room sound and the monitors. This, in essence, removes acoustics from the equation. Though I would never dream of using them as a replacement for loudspeakers, they are useful for giving us a second opinion. Pan placement can often more easily be heard along with reverb and delay effects
With only a small amount of cash and a little knowledge it is relatively easy to make vast improvements to the acoustics of a project studio. A science-free DIY approach can work surprisingly well, particularly if you use some of the practical advice available on the websites of the companies offering treatment solutions. Unfortunately, most musicians tend to neglect acoustic treatment and instead spend their money on new instruments or recording gear. When we don’t get the results we expect it is easy to blame the gear rather than look at the space in which they were recorded or mixed. Do yourself a favour - don’t be frightened, give it a go. Before you know it you’ll be hearing what’s actually there!
Gary Bromham is a writer/producer/engineer from the London area. He has worked with many well-known artists such as Sheryl Crowe, Editors and Graham Coxon. His favorite Reason feature? “The emulation of the SSL 9000 K console in 'Reason' is simply amazing, the new benchmark against which all others will be judged!”