Quiz: WFS – Holophonix Learning Platform

1. Principle of WFS

9

Select the correct statements

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

2. Inter-acoustic spacing

7

The inter-acoustic spacing

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

3. The loudspeakers used for WFS

2

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

true
false

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 useful radiation angle increases.
is the distance between the acoustic centres of the loudspeakers in a WFS line.
depends solely on the inter-acoustic spacing.
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.

6. Front-fills vs FOH

2

A WFS line used as front-fills

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

7. Source positions relative to the WFS line

3

Select the correct statements

Sources behind the line cannot be too close to it, as only a few loudspeakers will be driven.
It is preferable to position sources in front of the WFS line as close as possible to the listeners.
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

false
true

9. Spatial aliasing

3

Spatial aliasing beyond a certain frequency

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

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

11. Minimum delay

3

Using “minimum delay” mode

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.
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).

12. Source movement and transposition

3

The movement speed of a source behind a WFS line

must be slow to avoid a transposition effect.
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.

13. Advantages and disadvantages

6

Select the correct statements.

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

WFS (Wave Field Synthesis)

Quiz: WFS Quiz