Nexo Alpha System - Manual (Page 19)

α α α
P 19
USER MANUAL
VERSION :1.01
DATE : 06/10/10
The speed of sound C varies with temperature according to the formula below :
273 t 20 C
+ ° =
where t° is the temperature in °C
The delay time between two sources spaced at a distance d is then :
∆t = C/d
3.4. D IRECTIVITY - C OVERAGE
The two main qualities one might expect from a cabinet for array constructions are :
• a good directivity control in the mid an high frequency region, which guarantees the steadiness of the
interference region where dips and lobes occur ;
• a strong roll-off of the directivity function at the -6dB cut-off angle, which minimises the size of the
interference region.
The Alpha series cabinets were designed to respect these two criteria. Particularly, the Alpha M3
features a constant coverage angle +/- 5° from as low as 800 Hz up to 12 kHz, with high values of dB
loss / degrees at cut-off angle.
3.4.1. D IRECTIVITY OF M ULTIPLE S OURCES - W HAT H APPENS ?
In order to understand the coverage behaviour of combined sources, wavelength must be related to the
space between sources.
The wavelength
λ (in meters) of o sine wave is determined by :
λ = C/f
where f is the frequency of the sine wave
This gives :
λ(20Hz) = 17 m, λ(100Hz) = 3.4 m, λ(1kHz) = 34 cm and λ(20kHz) = 1.7 cm
• interference
The distance between sources generates a pathlength difference between the two signals that is nil on
axis and increases with the listening angle. If this pathlength difference increases to half the wavelength
in a specific direction, the two signals will cancel in that direction. This phenomenon is often described
as « interference ».
pathlength difference between two sound waves
Pathlength
difference