Harman JBL MS-A1004 Guide De L'utilisateur page 5

What is the best procedure for choosing a crossover frequency and slope (see Figures 3a and 3b)?
A crossover is a pair of filters that divide the audio signal into low frequencies (bass) and high frequencies (treble) so that
only the appropriate signals are sent to speakers that are designed to reproduce a limited range. For example, a tweeter
is designed to play only high frequencies, and too much bass can cause damage. A woofer is designed to make only low
frequencies and does a poor job of reproducing high frequencies. A midrange speaker is designed to play frequencies in
between bass and treble (midrange frequencies). Figure 3a shows how these speakers would be divided up across the
20Hz – 20kHz range, using the appropriate filters (crossovers).
Figure 3a.
Low-Pass Band-Pass
Filter Filter
When setting a crossover between a low-frequency speaker and a high-frequency speaker, the high-pass filter (HPF)
frequency should be chosen to keep the high-frequency speaker safe. The low-pass filter (LPF) should be set so that the
hand-off provides smooth response in the region near the crossover frequency. When implementing a crossover between
speakers, use steep (24dB/octave) slopes for both filters to maximize the amount of low frequencies that the high-fre-
quency speaker can handle safely and to minimize the interaction of the sound between the low-frequency speaker and
the high-frequency speaker. Figure 3b shows the differences of 6dB, 12dB and 24dB/octave filter slopes.
If I should use 24dB/octave slopes for crossovers, why do MS Series amplifiers include 6dB and 12dB/octave
slopes too?
If your MS Series amplifier will be used to power a subwoofer in a vented (ported) box, use a 12dB/octave high-pass
filter to protect the subwoofer from damage by limiting the amount of bass that's sent to the subwoofer below the tuned
frequency of the box. A 6dB/octave high-pass filter can be useful in slightly limiting the amount of bass sent to full-range
speakers in systems where no subwoofer will be used, limiting the amount of high frequencies sent to rear speakers.
Why does each pair of channels include a high-pass filter (HPF) and a low-pass filter (LPF)?
In some systems, it can be useful to limit the high frequencies and low frequencies that are sent to a loudspeaker. Use
the HPF and the LPF together to create a band-pass filter for a midrange speaker in systems where the woofer, midrange
and tweeters will be powered by individual amplifier channels. When using the filters to create a band-pass filter, the HPF
can never be set to a higher frequency than the LPF. For example, if the LPF is set to 200Hz, the HPF can be set to any
frequency below 190Hz. This protection prevents errors in setup.
Do MS Series amplifiers include a subsonic or infrasonic
filter for use with vented enclosures?
Yes. If you want to use a subsonic or infrasonic filter with your
subwoofer, configure the channel's crossover as a band-pass filter.
The low-pass filter will limit the high frequencies that are sent to the
subwoofer and the high-pass filter will be the infrasonic filter. Set the
high-pass filter frequency about 10Hz below the frequency at which
the enclosure is tuned and use a 12dB/octave slope (see Figure 4).
About the MS-WBC wireless bass control (sold separately):
The MS-WBC wireless bass control is designed to make installation easy. The circuit is designed for long battery life, and
the amplifier is necessary. The control sends a radio signal to the DSP in the amplifier, so the control may be mounted in a
console or under the dashboard and the amplifier may be mounted in the trunk or hidden behind a panel.
The amount of bass included in recordings varies greatly, and the ability to adjust the amount of bass between songs or
albums is useful. Unlike conventional remote bass controls, the MS-WBC doesn't simply increase the level of the ampli-
fier's channels that are connected to the subwoofer. Conventional bass controls adversely affect the crossover between
the subwoofer and the mid-bass or midrange speakers any time they are adjusted. This causes the bass to sound boomy
or muddy when it's boosted and draws the listener's attention to the location of the subwoofer (see Figure 5a).
Figure 5a.
Crossover Frequency
Changes With Bass Boost
Figure 3b.
High-Pass
Filter
6dB/oct.
12dB/oct.
24dB/oct.
Figure 4.
Figure 5b.
Subsonic Low-Pass
Filter Filter
Crossover Frequency
Constant With Bass Boost
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