Studio acoustics is a large and rather complicated subject but you don’t need to be an expert to do a good job of your mixing or mastering. I’m going to go through the main points and show how to easily and quickly achieve a professional listening environment.
When mastering, it is vital that we are able to accurately monitor the sounds that we are working on. A major part of this is the build quality of the speakers and how flat – and therefore accurate – their frequency response is.
However, an occasionally overlooked yet vital element is the design of the room within which we’re working. A fantastic monitor speaker response would be practically wasted in a room which unduly colored the sound they produced. As an extreme example, imagine setting up your speakers at one end of a tunnel, then trying to produce an accurate mix from the other. As you can imagine, the physical manipulations of the tunnel will warp the direct speaker sound, completely changing the way we perceive it.
Although less obvious, an unsuitable mastering environment can also be quite harmful to the end result.
Depending on its size, shape and reflective characteristics, certain frequencies – or bands of frequencies – can be perceived at different levels from others. If the room happens to reflect more higher frequencies than others, then the sound you are hearing may appear brighter than it really is. If the room exaggerates the low end, then the speaker sound will appear to have more bass than is actually in the mix. Similar to how the speakers have a ‘frequency response’, the room’s response to different frequencies will vary also. The more ‘neutral’ our room’s response, the more accurate the sound reaching our ears will be.
So before we discuss factors like monitor placement and acoustic treatment, let’s first look at one of the most fundamental aspects which influence the way we perceive sound within the room – the size, shape and raw surface materials of the room.
Size & Shape
The worst-case scenario for a room would be a perfect cube with flat walls, floor and ceiling.
Apart from the walls, floor and ceiling allowing the sound waves to reflect around the room, changing the way we perceive the sound (which will be discussed shortly), the major problem is the cube shape itself as it causes a specific set of frequencies to appear to be louder compared to the speaker sound, particularly in the lower frequencies. This is due to a phenomenon known as “standing waves” – sound waves that literally become trapped between parallel surfaces such as walls, bouncing back and forth, overlapping with each other perfectly, reinforcing themselves every time.
Rooms with parallel walls will “resonate” at certain frequencies. The frequency at which resonance occurs is referred to as the room’s “mode” and is directly related to the distance between the walls (a sound wave’s frequency is directly related to its physical length in meters).
No matter what distance the parallel walls are apart, a sound wave of some frequency will be able to fit exactly into that space, then flip over when it hits a wall and go back the other way, perfectly in time with its immediate following sound wave (at that same frequency). Theory states that when you allow two identical sound waves to add together, they double in size.
Interestingly, half that frequency can do the same thing – it hits the wall, flips, then goes back, meaning it fits itself in between the walls after two trips. This adding also occurs when the frequency is doubled, quadrupled, octupled and so on, as they all still fit perfectly into that space.
When this reinforcement happens, a doubling of sound pressure will occur for that particular frequency, which can work out to a 3 dB rise in audible level in the main area of the room. Quite a dramatic difference where audio accuracy is concerned.
What you will also find is that depending on where you are sat, you will experience differences in the way the room resonates. Two identical waves overlapping will increase the audible level of that frequency. However when two waves overlap whose wave cycles are opposite (anti-phase), a cancelation will occur giving the perception of a reduction in that particular frequency. The overlapping of identical waves is known as “constructive interference,” whereas the overlapping of anti-phase waves is known as “destructive interference.” Some areas of the room may cause constructive interference, while other areas may cause destructive interference.
Where possible, choose a room that deviates from a cube, ideally one that is fairly symmetrical, with slopes, uneven features and details that help to redirect and diffuse reflections and lessen the impact of resonances. If this is not possible, don’t worry as I’ll be showing you how to lessen the impact of resonances using other methods.
Some of you may have heard of the term “golden ratio” when referring to studio design. This is the ratio between the height, width and length of a room. If you are lucky enough to be in a position to “choose” the dimensions of your room, then you may consider using the golden ratios to do so.
Originating from ancient Greece, these ratios have been applied in many subjects and practices; from architecture to classical music, and even to book design. They also occur frequently in nature which is how they were first discovered.
In regards to studio design, the golden ratios are a proven way to obtain a more accurate listening space as they allow for a uniform distribution of resonant frequencies around the room (yes, resonance still occurs).
As for how they are calculated, the level of mathematics is probably too advanced for this mastering tutorial. In any case, the purpose of this mastering tutorial is to show you how to achieve a professional finish by utilizing what you already have. So rather than have you build an extension on the side of your house, let’s move on to how you can transform an existing room into a reliable listening environment.
A surface material will have different reflective characteristics depending on the frequency of the sound wave hitting it.
A soft surface material such as carpet will absorb much of the higher frequencies preventing them from being reflected back into the room. However, a low frequency will pass straight through the carpet to the reflective solid surface beneath. A heavy drape may provide control of midrange and higher frequencies but again, the lower frequencies find their way through.
Controlling the lower frequencies requires more elaborate efforts than the use of things like drapes, or carpet; their long wavelengths require the use of much larger objects.
Just before we reach the discussion on how to control these troublesome reflections, I’d like to point out one more issue you will face – the “hanging around” effect of the lower frequencies caused by the solid surfaces beneath the soft furnishings reflecting the sound waves back into the room, and the resonating “trapped” lower frequencies which subsequently take longer to disperse their energy.
The result is a lack of definition in the low end as the sonic information literally starts to smear.
So we know that the room’s reflections alter the perceived speaker sound. Should we attempt to ‘remove’ the reflections from the room? Fortunately, it’s okay to have some reflections in the room, we just need to ‘neutralize’ them the best we can so we can trust the speaker’s sound.
Before you begin budgeting for acoustic treatment, there’s a lot that can be done using the everyday things around you.
As well as audio gear, the room will most likely contain some furnishings which will aid the absorption of reflections, as well as irregular surfaces that serve to break up and scatter incoming sound waves, preventing them from building up and appearing louder in certain areas of the room.
As mentioned, lower frequencies are more of a problem as they can travel straight through thin coverings like curtains and carpets which are effective against high frequencies. Large furniture with soft surfaces such as beds, sofas and padded chairs all soak up a certain amount of the lower frequencies because their material is porous but quite dense, so although the powerful low-frequency energy is able to enter the material as vibration, a lot of the energy is dispersed as friction and heat. This is similar to how professional “bass traps” work – the vibrations cause the fibers inside the dense mineral wool filling to rub together converting kinetic energy into heat.
Half-full bookshelves, angled sofas, a laden coat stand, an open wardrobe, anything that is either absorptive or uneven – and may help to divert and fragment the direct speaker sound – is a worthwhile consideration.