Quiz: WFS – Holophonix Learning Platform

1. Principle of WFS

9

Select the correct statements

For a source reproduced in WFS, the loudspeakers must emit the source signal at different levels.
Holophony is the perfect reproduction of an acoustic wave regardless of frequency.
For a source reproduced in WFS, the loudspeakers must emit the source signal with different delays and levels.
Each loudspeaker is managed individually by the algorithm.
For a source reproduced in WFS, the loudspeakers emit the same signal.
There is no sweet-spot.
For a source reproduced in WFS, the loudspeakers must emit the source signal with different delays.
The loudspeakers of a WFS line are called secondary sources.
WFS reproduces the primary spherical wavefront emitted by a source using a linear array of secondary sources.

2. Inter-acoustic spacing

7

The inter-acoustic spacing

is the distance between the acoustic centres of the loudspeakers in the WFS array.
defines a maximum frequency called the aliasing frequency, beyond which holophony is not achieved.
must be as small as possible.
must be the same between listeners.
must be the same between loudspeakers.
more faithfully reproduces secondary wavefronts as it decreases.
is the distance between a listener and the nearest loudspeaker in a WFS array.

3. The loudspeakers used for WFS

2

The loudspeakers used for WFS can be of different brands, types and sizes

false
true

4. Listening zone of a WFS system

3

The usable zone for experiencing WFS reproduction

is located on the central axis perpendicular to the loudspeaker line.
is limited in width by the length of the line.
allows listeners to perceive and localize reproduced sources in the same way.

5. Critical distance

6

The critical distance

decreases as the inter-acoustic spacing decreases.
depends on the inter-acoustic spacing and the useful radiation angle of the loudspeakers used.
is the minimum distance required between a listener and the WFS line for them to perceive sound from at least 3 loudspeakers.
is the distance between the acoustic centres of the loudspeakers in a WFS line.
depends solely on the inter-acoustic spacing.
decreases as the useful radiation angle increases.

6. Front-fills vs FOH

2

A WFS line used as front-fills

is denser than the main system (FOH) because the audience members are closer.
can have a larger inter-acoustic spacing than the main system (FOH).

7. Source positions relative to the WFS line

3

Select the correct statements

It is preferable to position sources in front of the WFS line as close as possible to the listeners.
Sources behind the line cannot be too close to it, as only a few loudspeakers will be driven.
Sources cannot be positioned in front of the line unless the density is very high or the inter-acoustic spacing is extremely small.

8. Delay Lines and Under-Balcony Delays

2

WFS can be used for WFS lines located far from the sources

true
false

9. Spatial aliasing

3

Spatial aliasing beyond a certain frequency

will not allow homogeneous reproduction of all frequencies within the listening zone.
can be reduced by decreasing the inter-acoustic spacing.
does not allow localization of reproduced sound sources.

10. Edge effects at line boundaries

3

A WFS loudspeaker line is not infinite. The secondary wave is truncated. Therefore, at the boundaries

diffraction can be eliminated by windowing the loudspeaker levels (progressive attenuation).
the reproduced secondary wave is diffracted.
the reproduced secondary wave is a plane wave.

11. Minimum delay

3

Using “minimum delay” mode

can be used if the acoustic level of a diffused source is significant and mixes with the amplification.
Is recommended because the distance between sources and each loudspeaker is taken into account and can generate significant delays when sources are virtual (physically absent sources).
should be avoided if the acoustic level of a diffused source is significant and mixes with the amplification. It could cause comb filtering (“comb filtering”) due to acoustic summation near the line.

12. Source movement and transposition

3

The movement speed of a source behind a WFS line

must be fast to avoid a transposition effect.
causes a variation in the delays (“vdelay” or “variable delay”) calculated for each loudspeaker and produces a transposition (pitch shift in the musical sense) of the signal, analogous to the Doppler effect.
must be slow to avoid a transposition effect.

13. Advantages and disadvantages

6

Select the correct statements.

WFS does not require a large number of loudspeakers.
Source localization depends on the listener’s position.
The source is perceived and localized at the level of the loudspeakers.
Source localization is independent of the listener’s position.
WFS can produce comb filtering at high frequencies.
Localization is precise across a large area of the audience.

WFS (Wave Field Synthesis)

Quiz: WFS Quiz