Soundstream Technologies 705s - Manual (Page 17)

17
INSTALLATION STEP 9
LSE.Q
THEORY AND USE
LSE.Q is a proprietary subwoofer control circuit included with the Reference705s
amplifier. It is capable of both removing subsonic energy in program material and
providing a variable boost at low frequencies. The circuit consists of two controls.
One adjusts the frequency of operation, and the other adjusts the range of boost.
With both controls adjusted fully counter-clockwise, no boost is applied and the
amplifier is flat in response down to 20 Hz.
The frequency control (Hz) adjusts the starting point of the subsonic filter. This high
pass filter can be adjusted from 20 Hz up to a maximum of 60 Hz. This control is
useful for setting the lowest frequency that your subwoofer will see. (See figure 1)
The Q control adjusts the amount of boost applied at the set frequency.
This is adjustable from .707 (flat) to 2.8 (+9 dB). (See figure 2)
When the Q is set to .707 (Butterworth), LSE.Q acts as a sub-sonic filter
only. (See figure 3)
The simple act of removing the signal below the vented tuning frequency
can improve system output by as much as 3 dB. With Q values greater
than .707, boost is added in addition to the sub-sonic filter. (see figure 4)
Application
Woofers in vented enclosures have good power handling characteristics
above the tuning frequency, but below the tuning frequency, power
handling drops off considerably. This is due to the loss of any
appreciable resistive air mass. At frequencies below resonance, the
woofer starts to behave as if it were
mounted in “free-air”. If we wish to
improve the performance of a
vented system, we should remove
these unwanted signals from our
system. These can be removed by adding the subsonic filter. Figure 5
shows the effectiveness of LSE.Q on woofer excursion. Woofer travel is
7.5 mm at 10 Hz, with LSE.Q properly adjusted, this excursion can be
reduced to less than 1 mm. This is of great benefit to lowering woofer
distortion and increasing output.
Adjustment
An easy method of optimizing your existing subwoofer enclosure with
LSE.Q's “Hz” control is as follows.
1. Adjust frequency and boost control to full CCW position.
2. While listening to music with strong bass content at a moderate level,
slowly adjust frequency control clockwise. Listen for a reduction of
bass response. Now, rotate frequency control slightly backwards.
This serves the purpose of removing the “subsonic” bass energy.
Soundstream’s LSE.Q contains the same type of circuit with the added benefit of infinite adjustability. Our “Q”
and “Hz” control can provide virtually any combination of boost and cut to suit your designs. So, LSE.Q can
dB
Frequency (Hz)
-20
-30
10
-25
-15
-10
5
0
-5
10
50 100 200
FIG. 2 Variable “Q”
Q=2.8
Q=0.707
dB
Frequency (Hz)
-20
-30
10
-25
-15
-10
5
0
-5
10
50 100 200
FIG. 4 Variable “Q”
FIG. 1 LSE.Q
-10
Frequency (Hz) 10
-30
-25
-15
-20
-5
dB
0
5
10
50 100 200
FIG. 3 Variable High Pass
FIG. 5 Limited Excursion
10 Frequency (Hz) 50 100 200
Xd
(mM)
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0