Yamaha NEXO Alpha & Alpha E Series Owner's Manual download pdf (Page 11)

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ALPHA ARRAYS - SOME BASIC RULES

ALPHA SERIES USER MANUAL V1.0

DATE: 14/01/00 18:27

Alpha Arrays - Some Basic Rules

The concept of arraying speakers derives from two requirements:

• Increased sound pressure level;

• Extended coverage area.

Array behaviour is very complex, and a bad design can lead to very poor results. The Alpha

system was designed to be flexible, allowing the user to optimise the design for a dedicated

situation; its development included a long measurement program on a very large variety of arrays.

Below are some simple rules that the user should respect.

Alpha S2 Placement

The nominal efficiency data for Alpha S2 is given for when positioned on the floor (half-space).

When flown the acoustic output on axis will be 3 dB lower and if positioned in a corner the acoustic

output on axis will increase by 3 dB.

SPL Versus Frequency

Array frequency response is strongly related to wavelength and array architecture.

• At low frequencies, wavelength being very large in relation to the size of the cabinets,

speakers set close to each other will always radiate in phase. The gain in sound pressure

level LGSPL will be of 6 dB per doubling, i.e. if n Alpha S2 or B1 are installed:

LGSPL(20Hz-100Hz) = 20 log10(n)

• In the mid frequency range, the gain depends on the configuration of the array, and will

range from 3 to 6 dB per doubling, i.e. for n Alpha M3, M8, EM or EF:

10 log10(n)

≤ LGSPL(100Hz-1kHz) ≤ 20 log10(n)

• At high frequencies, wavelength being short in relation to the size of the cabinet, the gain

level is smaller: no gain will be obtained for cabinets angled at their nominal coverage,

maximum gain will be obtained for n cabinets pointing in the same direction. Therefore,

the gain will range from 0 to 3 dB per doubling; for n Alpha M3, M8, EM or EF:

≤ LGSPL(1kHz-10kHz) ≤ 10 log10(n)

SPL Versus Distance

In open-air conditions, the level of sound at a given distance is related to the following parameters:

• The size and the geometry of the source, which determines the shape of the sound wave

(spherical, cylindrical, plane);

• Hygrometry and temperature: viscosity of the air and thermal conduction cause an energy

loss increasing with frequency. This phenomenon is referred to as excess attenuation.

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Yamaha NEXO Alpha & Alpha E Series Owner's Manual Page 11