The acoustics of a room have a great influence on the quality of the sound in home recording studios, home cinemas, hi-fi or control rooms. Even the excellent sound of professional studio monitors or hi-fi speakers can be severely impaired by missing or incorrect room acoustic treatments. Especially the bass range often sounds unbalanced and muddy in rooms without acoustic modules. A big problem in acoustically untreated rooms are the so-called room modes. This article explains what room modes are and how you can prevent them using bass traps.
What are Room Modes?
While high frequencies are emitted directionally, lower frequencies disperse spherically. When the sound waves of the low frequencies hit the solid boundary surfaces of a room (walls or ceilings), they are reflected. When reflected waves hit each other, they superimpose and interferences occur, i.e. cancellations or amplifications of individual frequencies. Standing waves, also called room modes, are particularly noticeable and bothersome.
Room modes occur whenever the room length is a multiple of the wavelength of a frequency. If this is the case, the cancellations and amplifications of certain frequencies invariably occur at the same spots in a room. Especially small, square rooms with parallel walls are prone to room modes and require suitable room acoustic solutions.
How Do Room Modes Sound?
A room mode consists of oscillation nodes and antinodes. These cause the cancellation or overemphasis of individual frequency bands at various fixed positions in the room. This means that you do not hear certain frequencies at all or hear them at up to twice the volume. In particular, the resonance of a room mode at your listening position can make listening to and editing sound much more difficult and annoying. But not only the frequency response suffers from room modes. Since the sound waves are reflected back and forth between parallel walls, the affected frequencies stay longer in the room. This additionally causes a lack of definition in the bass range and often contributes to a “muddy” and “boomy” sound.
If you want to hear room modes, simply play test tones with low frequencies (between 80 and 200 Hz) through a speaker or subwoofer in your room. Then, as you move around the room, the volume of certain test tones will vary greatly at different positions – this is how you can detect room modes.
What Can Be Done About Room Modes?
Individual room modes are excited to different degrees depending on the speaker placement, and perceived to different degrees depending on the listening position. By changing the speaker and the listening position, the composition of the frequency bands in which over-emphasis and cancellations occur can be changed. However, since the possibilities here are limited and the results often are not satisfying, room acoustic treatments become indispensable in order to effectively fight room modes.
Especially effective against room modes are bass traps (also called bass absorbers) with sufficient depth, which are placed in the corners. In the corners, the dispersion of room modes from all three room dimensions is most even, so bass traps can develop maximum effect here. It can be helpful to place several bass traps next to and on top of each other, so that room modes in lower frequencies are effectively dampened. This way, the bass range gets more focused and can develop more punch.
When buying bass traps, however, make sure that the higher frequencies (above 1 kHz) are not absorbed too much in order to obtain a natural, vivid room sound.
We will gladly support you in optimising the acoustics of your room. With a diameter of 43 cm, the HOFA Basstraps are designed to effectively fight room modes: they absorb over 90% of sound energy in the range from 80 Hz to 200 Hz – without excessively damping higher frequencies.
Find more information about the HOFA Basstrap here.
If you have problems with room modes or need help optimising your room acoustics, just get in touch with us.
