Sound projectors are suitable for situations requiring high sound pressure and high quality for music distribution. They feature a broadband speaker housed in a cabinet designed to achieve a high, well-defined sound pressure beam and good frequency response.
They include an anchor for wall or ceiling installation. Many models are designed for outdoor installation.
Their sensitivity is high, and therefore their acoustic performance; high sound pressure levels are achieved with only a few watts of power and lower amplification costs (>105 dB SPL at 20 W).
The quality of music reproduction is good thanks to the wide bandwidth, exceeding 15 kHz in many models.
The most efficient models can reach 20 to 30 m with a good sound pressure level.
Special two-way models are available for hallways, and suspended models to bring the speaker closer to the listener.
A compromise between high sound pressure and good quality for music distribution.
They are installed in sports venues, parking lots, train stations, bus stations, subways, and more.
Distribution recommendations
Under conditions such as those mentioned above, the installation recommendation would be:
- In narrow areas with low ceilings (subway platforms, parking lots) every 5 to 10 m
- In narrow areas with high ceilings (shopping mall aisles) every 10 to 20 m
- In open-plan areas, each projector covers between 200 and 400 m2
Exercise
Public address system for a railway station with three platforms, each 70 m long, two of which are double (with tracks on both sides). The mounting height is 3.5 m, and the ambient noise level is 70 dB SPL.
NUMBER OF SPEAKERS
- The spacing is determined by the platform characteristics. A typical value is every 6 m.
- On a 70 m platform: 70/6 = 11.67 (~12 projectors).
- On double platforms, 12 projectors face one track and 12 face the other.
- A total of 60 loudspeakers will be required.
ACOUSTIC CALCULATIONS
- Distance from loudspeaker to furthest listener: d2 = 62 + (3.5-1.5)2 : d = 6.32 m
- Attenuation at listener height (1.5 m): 20·log 6.32 = 16.02 dB SPL
- Required SPL 1 W, 1 m (SNR = 15 dB): 70 + 16.02 + 15 = 101.02 dB SPL
- Therefore, a loudspeaker with a maximum SPL > 101.02 dB SPL can be used
