by Pablo Bellinghausen –
Of all the factors that allow a home or project studio to improve the sound of their final product, acoustic treatment is often the one that is given the least consideration. This is likely because it is by nature unglamorous, and lacks the “cool factor” a shiny new piece of equipment can bring to the table. It is, however, one of the things that will truly help the budding producer or sound engineer get better results out of their equipment.
In our last instalment we saw how to position speakers in a small room; in short, the best position is the middle of the narrowest wall in a rectangular room, quite close to the back wall.
However, this positioning assumes a specific style of acoustic treatment in order to overcome the biggest problems that arise from that room shape.
The Quick-and-Dirty Test
A good way to understand the way your room really sounds like is to use a portable stereo recorder set at the listening position and record some music while it plays through the speakers. Most decent portable recorders in the market will have a relatively flat and uncoloured sound, and the mics will have a wide pattern that will pick up the room sound pretty accurately. In an ideal situation, the resulting recording should sound a bit more reverberant and “roomy”, but almost as clear and balanced as the original. Sadly, in most untreated rooms, this is not at all the sound we get; instead, it will be boomy, unfocussed and unclear. This is exactly what acoustic treatment is meant to fix.
Here is the song “Hey Nineteen” by Steely Dan, one of the most widely renowned recordings in terms of production quality, recorded through a high-end pair of PSI Audio A17-M (worth £2.8k) and through a pair of Studiospares Aktiv6 (worth £199), in two separate environments (an average meeting room with plasterboard walls, and a professional Esmono sound booth).
PSI Audio A17-M (Booth)
Studiospares Aktiv6 (Booth)
PSI Audio A17-M (Meeting Room)
Studiospares Aktiv6 (Meeting Room)
PSI Audio A17-Ms in the booth, recorded through the internal Zoom H5 mics
The PSI monitors have far more transparency, bass punch, and treble clarity than the Studiospares Aktiv6 speakers. However, the acoustics of the meeting room hide most of these nuances; the reverberation overpowers the midrange, the stereo imaging is compromised, and the bass is inconsistently skewed to one side. The example shows that it might actually be better to use budget monitors in a properly treated room than high-end ones in an environment with such poor acoustics.
Choosing Absorption Material
Before looking at the placement of our acoustic panels or tiles, it’s important to choose them correctly; and even though the choice of absorbers can baffle newcomers, in reality all that really matters is the absorption rating at a specific frequency. Higher-quality products will look better and be sturdier, but most importantly, they’ll be more effective at a similar size and depth. Premium models also often come with an absorption graph that allows for a more informed choice at the moment of purchasing, as well as having a fire rating if they are to be placed in commercial installations.
As a rule of thumb, it’s better to have fewer absorbers that are thicker and denser, than to have far more thin, light absorbers.
This is because the latter will only tend to dampen high frequencies; having too many cheap, light, thin foam tiles will completely dampen the treble, yet leave the bass and lower midrange almost untouched; the resulting sound will be dull, boxy, and boomy. This is a very common fixture in budget studios, and it is often makes recordings and mixes instantly sound amateurish.
Most foam will have a density between 30 and 60 kg/m³, whereas more expensive fibreglass bass traps can be as dense as 100 kg/m³. Similarly, the cheaper foam tiles will be as thin as one inch, whereas the better bass traps can have a depth of up to ten inches.
Primacoustic Broadway panels: Absorption ratings of three thicknesses (96 kg/m³ density)
A cheap way to enhance the effectiveness of any absorber is to leave some space between it and the wall. The extra distance allows lower frequencies to be absorbed as well. This works on any surface, but is especially useful when placing bass traps around corners; even a thin panel placed diagonally in a corner will have a huge boost in low-frequency absorption.
Primacoustic FullTrap panels: Absorption ratings at two different positions
Smaller rooms, particularly ones approaching a cubic shape, will have very strong resonances on a small subset of frequencies (usually between 50 and 400 Hz), some of which are hard to fix using standard absorbers. The best thing to use in that case are tuned absorbers that convert the sonic energy into heat, thereby “sucking” the sound out of the room at a specific frequency. These are far more expensive than basic panels, but will ensure absorption of only the problematic frequencies.
The first thing to treat are the reflections from the wall behind the speakers that create comb filtering. Whenever the speakers are in a room, there will be specific frequencies that get cancelled out, sometimes as much as 30 dB!
The closer the speakers are placed close to the back wall, the higher these frequencies get, usually going to almost 300 Hz if the distance between the cone and the wall is less than a foot. This is a good thing, since at that point these reflections can be tamed through standard foam or fibreglass absorbers behind the speakers. This allows for a flatter frequency response throughout the room. In the smallest rooms, it is actually both relatively cheap and a good idea to cover the whole wall with a thick absorbing layer of material (8″ or more) because that pretty much gets rid of any back reflections, which can fix many other problems along the way.
The second most important area to treat are the “first reflections” on the side walls. Their position can be deduced by bearing in mind that that sound travels in a straight line. Some people use mirrors in order to find the exact spot, but if the absorbers are large enough, then an approximate position is enough.
The next step is to treat the back wall, which will to a certain extent depend on the size of the room; in a larger room (distance between the front and back wall being more than about 5 m) the best-sounding alternative is to use a certain amount of broadband diffusion in order to smoothen the sound of the reflections of the back as opposed to just dampening them. This creates a nice shimmery reverberation that is diffuse enough not to interfere with the instruments’ tonality and space, and just adds enough liveliness to the room to make it feel natural. If the room is less than 5 metres deep, then diffusion will not be enough to spread out the back reflections, which need to be treated as first reflections and therefore dampened as well.
A central diffuser and light absorption on the sides controls reflections at the back without deadening the room too much
The next thing to focus on is bass trapping, which is critical in small rooms if one needs to monitor any low frequencies, whether in music or sound for video. This is because low frequencies are far less directional than higher frequencies, which causes them to spread in all directions at the same time. This exaggerates reflection interaction, increases phase cancellation, and causes longer decay times for certain notes, causing the dreaded, ringy “one-note bass” which is the bane of the home studio producer. In most small rooms, it really is fair to say that the more bass trapping, the better. It is the most expensive type of absorption, but it can be bought progressively with few side-effects.
The position of bass traps themselves is not as critical since low frequencies are not very directional, but they are most effective when they are placed in corners due to the way sound bounces in a room, particularly the ones closest to the speakers. If budget is more important than aesthetics, one can leave a few inches of space between bass traps in order to maximise their surface area, which slightly increases their absorption power at no extra cost.
Carpet sounds like a good idea to treat the floor, but the same reasoning applies there: thin materials are almost useless for anything but the highest frequencies. A wooden floor with a thick, plushy rug at the listening position is often the best way to go. That, plus a couple of absorbers on the ceiling (called “clouds” if they are hanging down from it) on top of the area between the speakers and the monitoring position will tame the main vertical reflections.
Basic treatment under £1k and correct placement, like the above, can make a home studio sound truly professional. However, solutions under £200 can already make a noticeable improvement.
It is important to try to make the the room as symmetrical as possible; assymetrical reflections can create severe stereo imaging problems, which can render accurate monitoring impossible. If the room has a lot of gear, it can cause an acoustic imbalance that can only be redressed through treatment.
A professionally-treated control room with fibreglass absorbers, diffusers and bass traps.
Following these simple steps can allow you to improve the sound of your home studio enormously, but it is important to remember that there are many variables at play. As with any studio purchase, if you’re not quite sure of how to set everything up, it is always best to contact your favourite audio equipment retailer and get free personalised advice for the specific room you’d like to use.