Arcline 8/212 User Guide V1.0
Page 49
Line sources
If we use an imaginary sound source, e.g. an “ideal” line source that produces a theoretical
cylindrical wavefront, we could restrict the radial expansion to width only.
Figure A.2: Theoretical “ideal” line source
The height of our theoretical wavefront would remain constant with distance – see illustration
above.
Reducing the radial expansion from two dimensions to one would reduce the sound pressure
attenuation from 20 x Log
10
2 = 6 dB per doubling of distance to 10 x Log
10
2 = 3 dB per
doubling of distance. The technique effectively extends the system’s nearfield.
The only snag with this imaginary “cylindrical” radiation pattern is that it rarely exists in practice
unless you believe some manufacturers’ sales hype or install an infinitely long array (or a floor-
to-ceiling array where the floor and ceiling are perfectly hard boundaries).
Polar response vs array length and signal wavelength
A real-world (i.e. finite-length) vertical array’s vertical directivity will increase with frequency and
array length and the wavefront certainly won’t be cylindrical over a wide frequency range.
A straight vertical array will exhibit the directivity function for a uniform line source (assuming
it’s driven with constant amplitude and phase over its length).
Its directivity function will vary with the array length ÷ wavelength (L/
λ
):
11 Appendix A - Line array basics
Summary of Contents for Arcline 212
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