User Manual

Multichannel Monitoring Tutorial Booklet (M2TB) rev. 3.5.2
Masataka Nakahara : SONA Corporation
©2005 YAMAHA Corporation, ©2005 SONA Corporation
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If bass management is to be applied in a professional playback environment, the filter response must be
meticulously matched between the bass management controller and speakers, and a sub-woofer of
equivalent grade to the main channel woofer units must be considered, taking careful thought for its
placement. Bass management that simply imitates [Fig. 35] is likely to cause various monitoring problems,
such as separation of sounds and unnatural localization of sound sources.
In the sections that follow, we discuss filter response for bass management controllers.
■ Low pass filter
[Cutoff frequency]
This must be set to a frequency low enough that the low-frequency signal reproduced by the sub-woofer
will not have a sense of direction.
However if the cutoff frequency is set excessively low, this will narrow the bandwidth that is handled by
the sub-woofer, and the improvement in low-frequency response will be less.
A frequency lower than 60 Hz is ideal if we give priority to spatialization, but in view of how this affects
the improvement of low-frequency response, a cutoff frequency of 80 Hz is usually specified.
[Slope]
If the slope is gradual, sounds higher than the above-specified cutoff frequency may be heard, and this
will produce a sense of directionality from the sub-woofer.
Conversely if the slope is too steep, the sense of unity between the main speakers and sub-woofer will be
diminished, and sounds will tend to split between the low range and the mid/high range.
In most cases, a slope of –24 dB/octave is used.
■ High pass filter
[Cutoff frequency]
The identical cutoff frequency used by the low-pass filter is also used by the high pass filter.
[Slope]
The slope must be such that it will cross optimally with the low-pass filter.
Here it is important to consider not only the response of the respective filters, but also the response of the
speakers that are used.
In other words, “filter response” + “speaker response” = “crossover response.”
Here we will discuss the slope of the high-pass filter with the assumption that the following specifications
have already been determined.
• LPF fc = 80 Hz, –24 dB/oct.
• HPF fc = 80 Hz
The playback bandwidth of the sub-woofer usually extends above the cutoff frequency of the low-pass
filter that is applied. This means that the low-frequency response played back from the sub-woofer will be
identical (fc=80 Hz, -24 dB/oct.) to the specifications of the low-pass filter.
Therefore, this same “fc = 80 Hz, –24 dB/oct.” will apply to the low-range response of the sub-woofer
playback.
The cutoff response of the main speakers played via the high-pass filter must be targeted to this “fc =
80 Hz, –24 dB/oct.”
Example 1) If the main speakers are a small type whose response falls off at 12 dB/octave below 80 Hz,
the “high-pass filter response” = 12 dB/octave.
Thus, “filter: 12 dB/oct.” + “speakers: 12 dB/oct.” = “crossover: 24 dB/oct.”
Example 2) If the main speakers are large speakers that are able to reproduce below 80 Hz, then “high-
pass filter response” = 24 dB/oct.
Thus, “filter: 24 dB/oct.” + “speakers: 0 dB/oct.” = “crossover: 24 dB/oct.”