Acoustic columns incorporate several identical speakers mounted in a row. This speaker arrangement reduces the vertical coverage angle and expands the horizontal coverage angle. In highly reverberant venues, such as churches, speaker columns direct the acoustic beam directly onto the audience, avoiding reflections and echoes that reduce intelligibility.
Acoustic columns diffuse the sound layer at the listener's height and do not project it toward the ceiling.
The sound pressure of these speakers is quite high (over 100 dB) and the frequency response is adequate for music and speech.
The mounting height, tilt angle, and orientation must be calculated so that the axis of the acoustic beam passes at the listening height (between 1.5 and 1.6 m) of the furthest listeners.
The reach of a speaker depends on its physical height, due to the amplitude of the sound beam mentioned above. A distance between 10 and 20 times their height is considered (for example, the span of a 0.7 m tall column will be between 7 and 14 meters).
The usual arrangement is to distribute the columns along the two side walls of the auditorium. This is often the case in religious venues, assembly halls, conference rooms, etc. They are also suitable for railway or bus platforms, indoors or outdoors.
Distribution recommendations
Under conditions such as those mentioned above, the recommended installation would be:
- In reverberant enclosed spaces (churches) on both sides of the auditorium, every 5 to 10 m, depending on the dimensions of the chosen column.
- In noisy spaces such as platforms, every 5 m.
- In other low-reverberant and/or quiet spaces, every 10 to 15 m.
Exercise
Audio reinforcement in a church with three naves, the main one measuring 12 x 20 m and the side naves measuring 6 x 6 m (only the audience area). Ambient noise level of 50 dB SPL.
NUMBER OF SPEAKERS
- Mounted on columns or walls, at audience height; approximately 1.5 to 2 m high.
- Main nave, columns on both sides of the nave, every 5 m: 20·2/5 = 8 (4 columns on each side)
- Side aisles, columns on one side of the nave, every 5 m: 6·2/5 = 2.4 (1 column in each nave)
- A total of 10 acoustic columns are required.
ACOUSTIC CALCULATIONS
- Attenuation at the furthest point (6 m, in the center of the building): 20·log 6 = 15.56 dB SPL
- Required SPL 1 W, 1 m (SNR = 15 dB): 50 + 15.56 + 15 = 80.56 dB SPL
- Therefore, a loudspeaker with a maximum SPL > 80.56 dB SPL can be used.
- For distance (6 m at the furthest point), it should have a height of about 60 cm, which allows for overlap with the acoustic beam from the columns on the other side and improves acoustic coverage.
