Remaining_problems Wave_field_synthesis

1 remaining problems

1.1 sensitivity room acoustics
1.2 high cost
1.3 aliasing
1.4 truncation effect

remaining problems

the perceptible difference concerning original sound field reduction of sound field 2 dimensions along horizontal of loudspeaker lines. particularly noticeable reproduction of ambience acoustic damping required in rendition area accurate synthesis. damping, however, not complement natural acoustic sources.

sensitivity room acoustics

since wfs attempts simulate acoustic characteristics of recording space, acoustics of rendition area must suppressed. 1 possible solution arrange walls in absorbing , non-reflective way. second possibility playback within near field. work loudspeakers must couple closely @ hearing zone or diaphragm surface must large.

high cost

a further problem high cost. large number of individual transducers must close together. otherwise spatial aliasing effects become audible. result of having finite number of transducers (and hence elementary waves).

aliasing

there undesirable spatial distortions caused position-dependent narrow-band break-downs in frequency response within rendition range – in word, aliasing. frequency depends on angle of virtual acoustic source , on angle of listener loudspeaker arrangement:

f

alias


=


c

Δ
x

|
sin
⁡

Θ

sec


−
sin
⁡

Θ

v


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{\displaystyle f_{\text{alias}}={\frac {c}{\delta x\left|\sin \theta ^{\text{sec}}-\sin \theta ^{\text{v}}\right|}}}

for aliasing free rendition in entire audio range thereafter distance of single emitters below 2 cm necessary. fortunately our ear not particularly sensitive spatial aliasing. 10–15 cm emitter distance sufficient. on other hand, size of emitter field limit representation range; outside of borders no virtual acoustic sources can produced.

truncation effect

another cause disturbance of spherical wavefront truncation effect . because resulting wavefront composite of elementary waves, sudden change of pressure can occur if no further speakers deliver elementary waves speaker row ends. causes shadow-wave effect. virtual acoustic sources placed in front of loudspeaker arrangement pressure change hurries ahead of actual wave front whereby becomes audible.

in signal processing terms, spectral leakage in spatial domain , caused application of rectangular function window function on otherwise infinite array of speakers.

the shadow wave can reduced if volume of outer loudspeakers reduced; corresponds using different window function tapers off instead of being truncated – see discussion in spectral leakage , window function articles how choice of window function affects signal response.