User Manual

2
Figure 1: Typical calculation results for directionality of line-array speakers
2. Three key features of VXL audio performance
Key feature
1
Small speaker units
More than anything else in developing the line-array speakers of the VXL series, we were resolute in our selection of
smaller speaker units in order to optimize the distinguishing acoustic performance of the line array—namely, narrower
vertical dispersion combined with wider horizontal dispersion—for the typical frequency range of speech.
Based on an inventive redesign of the 1.5-inch subminiature full-range driver originally developed for the VXS1ML
ultra-compact surface mount speaker, the VXL speaker units combine a large voice coil with a neodymium magnet.
Thanks to this, they can deliver distortion-free sound over a broad band of playback frequencies, with wide 170°
horizontal and vertical dispersion.
Line-array speakers actively utilize phase cancellation of the output of speaker units that are arranged close to one
another in a linear pattern, in order to project the combined sound in a cylindrical pattern. This characteristic feature
allows dispersion in the vertical plane to be controlled, but the degree to which this is possible depends on the distance
between the speaker units and the overall length of the array.
The three arrays of the VXL series—namely, the VXL1-8, the VXL1-16, and the VXL1-24—have respectively 8, 16, and
24 closely vertically packed speaker units, and the distance between the units is roughly 43 mm.
We can better understand the relationship between unit separation distances and directionality in line-array speakers by
looking at some simple math.
Figure 1 compares the directionality of a pair of line-array speakers that have the same overall length but a different
unit separation—(a) shows the frequency-specic directionality for a separation distance of 43 mm, as in the VXL
series; (b) shows the same for 86 mm, double this distance. The strong propagations of sound seen at directions other
than directly in front of the array are known as grating lobes, and in practical terms, they represent certain frequencies
being projected strongly from the array in a direction other than the one being targeted. The result of this phenomenon
is impaired clarity due to undesirable reections and an inconsistent distribution of sound pressure. Unit separation
distance determines the frequencies at which grating lobes occur and their corresponding distances. For example,
where D is the separation distance and
λ
is the wavelength, the effect of the grating lobes diminishes in the range of
frequencies for which D/
λ
< 1, in other words, where the wavelength is larger than the unit separation distance.
In contrast to grating lobes occurring at 4 kHz and higher in case (b), which has a large unit separation distance, there
is a shift toward the high end of the spectrum in case (b), with these lobes occurring only at 8 kHz and higher. We can
conrm, therefore, that the use of smaller units, which in turn allows for smaller unit separation, reduces the effect of
grating lobes on the principal speech frequencies.
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Case (a): 43-mm spacing between speaker units Case (b): 86-mm spacing between speaker units