Logitech Squeezebox Instructions Manual page 10

Figure 12: Family of low-frequency equalization curves (blue) and simulated low-frequency system response
(green). The curves show cutoff frequencies ranging from 20Hz to 137Hz in 1/3-octave steps. For clarity, the
blue curves are offset by +20 dB. The green curves correspond to the final overall frequency response of the
system (simulated in this figure). They are 4
The method we chose for bass extension with Squeezebox Boom is to make the overall low
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frequency roll-off a 4
the subwoofer section of this paper. By applying the compensation of Figure 12 in series with a
th
variable frequency 4
frequency we desire as seen in Figure 12, which shows an entire family of filters with cutoff
frequencies ranging from 20Hz to 137 Hz in 1/3 octave increments. The choice of cutoff
frequency is based primarily on the final signal strength going to the speakers, and whether or
not there is a subwoofer plugged in. The true beauty of the Squeezebox Boom architecture is
that we can dynamically and silently switch among any of the filters as volume settings and/or
signal strength changes. Currently, we implement a sliding cutoff frequency based on volume
setting.
Figure 11: Actual in-box frequency response measurements of the family bass extension filters used in
Squeezebox Boom.
©2008 Logitech
-order Linkwitz-Riley filter. The reason for that choice will become clear in
-order Linkwitz-Riley filter, we can choose any low frequency cutoff
Squeezebox Boom Audio Design
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-order Linkwitz-Riley high pass filters.
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