Treating your Home studio or Recording Studio with Acoustic Treatment
In simple terms acoustic treatment can mean the difference between a good mix and a bad mix. Acoustic treatment is often confused with sound isolation, the 2 have different aims. Sound isolation is about reducing the sound escaping from one environment into another and also stopping sound ingress into an unwanted space (i.e. a studio recording space). Acoustic treatment is installed to help produce a linear in room frequency response.
There are 2 practical ways to improve the acoustic within a room.
1) Absorbing the sound waves.
This greatly reduces the energy of reflected waves and at high frequencies where there is lower energy can produce total absorption. The reason is that the energy entering the material creates friction and meets resistance going in and coming back out.
2) Diffusing the sound waves.
Diffusers reflect sound at different frequencies in different directions than the naturally inclined incident and reflected angles. Diffusion has the effect of reducing parallel surfaces (which can cause severe resonant acoustic issues) and reducing the energy of the waves before they meet the ear.
Absorption can be affective across the spectrum and diffusion practically works at mainly mid and high frequencies.
The major cause of inaccurate room response is reflection from room surfaces and sometimes equipment and mixing consoles. These reflections mix together with the direct energy that emanates from loudspeaker. Because the waves mingle with different phase relationships and multiple frequencies the resulting response is complex and very skewed. It makes effective mix balance and equalization decision making extremely difficult and unreliable.
The good news is that acoustic treatment can resolve many of the problems with very obvious effect. Ideally you would employ this remidial treatment with a software system and microphone which can take room measurements so you can see the statistical improvement. However great gains can be made by employing very well known basic methods without the need for measuring.
1) Side walls are very obvious offenders for what are known as first reflections. The best method is to use 10cm thick RW3 Rockwool slabs (Owens Corning in the USA). One or 2 per side of the room depending on the size. These cut down the mid and high reflections which skew the frequency response and reduce the accuracy of your stereo imaging. If you cannot practically build a wooden frame for these you can use foam tiles though they tend not to be as effective at absorbing lower mid range frequencies. As a general guideline the thicker a material is the lower down the spectrum sound will be absorbed.
2) Ceiling cloud, a cloud is just a fancy name for an absorptive or diffusive acoustic panel suspended from the ceiling. A cloud is normally positioned mid way between the loudspeakers and the monitoring position. The cloud can be spaced away from the ceiling for more effective absorption at a lower frequency. A ceiling cloud can have a very noticeable effect on the stereo imaging as well, more so than one might imagine. Some people prefer a diffusive cloud which keeps a sense of life in the room.
3) Bass trapping is a means of absorbing low frequencies. This is the most awkward acoustic treatment to install due to the bulky nature of the materials required. The simplest of bass trap designs involve straddling an acoustic panel (of approx 10cms depth) across the room corners, ideally from floor to ceiling. A more effective method is fully infilling a corner with an air gap spacing at the rear. This type of bass trap is known as “broadband bass trapping” because it is capable of absorbing a wide range of frequencies to greater or less extent. (The lower the frequency the less effective at a given depth of material) Bass traps are also best made from RockWool or Owens Corning, they need to be of large size as the relative length of a single cycle at low frequencies is very long. To have an impact the bass traps need to be fairly deep.
Foam bass traps at common commercial sizes are at best lower mid range and high frequency traps. This is because the size and depth of the traps is not deep enough to generate sufficient friction to reduce the incident and reflected energy sub 300Hz. Foam traps also tend to have what is known as a lower absorption coefficient than Rockwool or Owens Corning. They do however have their place in improving acoustics.
When planning acoustic treatment consider the practicalities of what you can install in your room and balance it against the size of the panels and traps and work involved.
Note: When handling RockWool and Owens Corning ensure you adhere to handling guidelines and at the least wear a pair of goggles, face mask, suitable gloves and a long sleeve shirt.