Studio Acoustics: An Informative Article from our Cleveland Studios
Studio Acoustics Basic Elements
There are several considerations to take into account when building or selecting a recording studio. The room itself is very important, because no matter how good the sound is, the environment affects how we perceive the sound and how the microphones pick up the sound. If the room is in the city, sound leaking in (and sound leaking out) can be an issue.
The dimensions and shape of the recording room
The overall dimensions of the room determine how different sized oscillations (or frequencies) of sound act. Every room has one main frequency that fits best in its dimensions. Rooms with no parallel walls are best (but not a circle for obvious reasons (convex surfaces focus vibrations. ever been inside a big pipe?) . But overall, dimensions outside a square are best. This is why an acoustic guitar is rounded and not a square. A few different dimensions inside the guitar correspond to different notes.
A square or cube shape would resonate one tone louder than the others. The natural resonant frequency of the space. These days, a simple computer algorithm can be used to determine the expected frequency response of a given space.Another handy tool is Bolt’s Graph, which is a visual representation of what room ratios have the best frequency response.
Most acoustic treatments either utilize absorption or diffusion. Absorption is the addition of sound-absorbing material to a room to soak up the sound and create “dead” air. Foam or egg crate cardboard, rugs, fiberglass, or mineral wool all work at varying degrees for different frequencies. Of these materials, mineral wool or rock wool is by far the cheapest and most effective. DIY mineral wool panels can easily be made by simply using a wooden frame, a piece of cloth, and some staples. If desired, different color fabric can be used to brighten the atmosphere of the studio. The chart below outlines the differing absorption rate of Roxul Rigid Rockwool which is what we use in our studio in Cleveland.
Roxul Rigid Rockwool Absorbtion Rates for Several Frequencies
Diffusion in the studio
The most effective way to achieve a well balanced frequency response is diffusion. Diffusion is the use of different shaped recording panels to change the geometry of the room, randomizing the acoustic profile and flattering the frequency response. By reflecting sound waves at different points, different frequencies are now able to resonate, and the sound becomes more balanced. Diffusion-based acoustic improvements can be conveniently made by modifying the layout of a recording space. To break up the overall profile of a wall, furniture, especially pieces that are heavy dense furniture like bookshelves or wood cupboards, can be properly place in the corners of a room to create a better sound chamber. Be wary of perfectly square rooms, as those are the worst for resonating acoustic sound. Try to think about eliminating parallel surfaces wherever possible.
3D Quadratic diffuser
Another great acoustic diffusor is a 3-D quadratic residue diffuser, or a 3-D skyline diffuser. Different sized wooden rectangular prisms can be assembled in a “skyline” configuration and hung on the wall to create resonance of different tones. A 2-D version can be made as well using the QRD Well Depth Calculator to determine a frequency response favorable to the acoustic environment. It helps to take an impulse response of the room to see a detailed frequency response and determine problematic frequencies to target.
The typical main problem
Problems, however, can quickly arise with the parallelism of most floors and ceilings. While it is possible to obtain a studio space with a sloped ceiling, flat ceilings are much more common. This parallelism will most likely be problematic in the higher frequencies due to an effect called flutter echo or comb filtering. Most studio guides recommend doing as much as 100% ceiling absorption to avoid flutter echoes while using only about 50-75% on any parallel wall surface.
Density of materials as an acoustical property
Materials often come in different densities; the higher the density of a material, the lower the frequency it will absorb. Bass frequencies are best absorbed by thick layers of high density material. This is best achieved by corner bass traps. Bass traps are similar to sound-absorption panels, but are shaped as right triangles and placed in the corners of the room.
The floor material is yet another factor added to the sound of a room. Most studios use a “floated” floor, one that is not originally attached to the building. If that method is unavailable, carpets and rugs are a great substitute for absorption.
Every room has one main resonant note, tone, or frequency that is dominant, prevailing over the other less powerful resonances. These resonances correspond with a frequency that’s wavelength is exactly the same as the dimension of the room. Quickly imagine a large bass frequency of 160hZ containing a wavelength of 7 feet as a large jump rope in a room, you can understand how different frequencies can build up stronger than others in a given space.
Our next article is entitled Studio Layout, and deals with how the recording environment is set up. Or contact us