Independent Acoustics and Noise Control Expertise
Part E | Sound Insulation Regulation | Robust Details | Building Regulations
SOFFIT MOUNTING CONTROL ROOM MONITORS
Speakers have two theoretically ideal
working conditions. The first is if its radiation space is into a full space
(spherical radiation) or into a half space (hemi-spherical radiation).
To achieve ideal full space conditions the speaker needs to be small compared to the
radiated wavelength. Because the speaker front baffle is small the higher the frequency the
smaller the radiation angle will be.
The frequency response dip caused by a reflection.
Generally, in most rooms, free
standing speakers are surrounded by walls/ceiling/floor that will generate
reflections. These surfaces act as acoustical mirrors to the
speaker's radiation, enhancing or cancelling
the direct sound, depending on the phase difference between
the reflection and the direct sound where you are sitting.
The frequency of the first dip can be calculated by measuring the distance of the speaker to the wall. Divide 340 (the speed of sound in metres) by four times the speaker distance and you will have the dip frequency. Obviously further cancellations will occur at increasing harmonic frequencies.
The frequency response dips caused by a wall reflection.
Moving the dip frequency
There are basically two ways to do this.
Flush Mounting Benefits
Flush mounting speakers into walls also has the advantage of eliminating
unwanted secondary reflections from the speakers edges because of the reduced
diffraction effect so the frequency response and imaging is much more stable.
The speakers need to be mounted exactly flush with the front wall. There must not
be any gaps or edges between the loudspeaker cabinet and the room wall.
A speaker mounted flush in the wall will tend to excite ALL the standing wave modes in a room. The only effective way to overcome this problem is to heavily damp the rear wall of the control room at low frequencies with low frequency absorption material.
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