JBL MS-A1004 User Manual

Also see for MS-A1004: User guide User guide

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5www.jbl.comWhat 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 thatonly the appropriate signals are sent to speakers that are designed to reproduce a limited range. For example, a tweeteris designed to play only high frequencies, and too much bass can cause damage. A woofer is designed to make only lowfrequencies and does a poor job of reproducing high frequencies. A midrange speaker is designed to play frequencies inbetween bass and treble (midrange frequencies). Figure 3a shows how these speakers would be divided up across the20Hz – 20kHz range, using the appropriate filters (crossovers).Figure 3a. Figure 3b.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 thehand-off provides smooth response in the region near the crossover frequency. When implementing a crossover betweenspeakers, 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 andthe 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/octaveslopes too?If your MS Series amplifier will be used to power a subwoofer in a vented (ported) box, use a 12dB/octave high-passfilter to protect the subwoofer from damage by limiting the amount of bass that’s sent to the subwoofer below the tunedfrequency of the box. A 6dB/octave high-pass filter can be useful in slightly limiting the amount of bass sent to full-rangespeakers 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. Usethe HPF and the LPF together to create a band-pass filter for a midrange speaker in systems where the woofer, midrangeand tweeters will be powered by individual amplifier channels. When using the filters to create a band-pass filter, the HPFcan 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 anyfrequency below 190Hz. This protection prevents errors in setup.Do MS Series amplifiers include a subsonic or infrasonic Figure 4.filter for use with vented enclosures?Yes. If you want to use a subsonic or infrasonic filter with yoursubwoofer, configure the channel’s crossover as a band-pass filter.The low-pass filter will limit the high frequencies that are sent to thesubwoofer and the high-pass filter will be the infrasonic filter. Set thehigh-pass filter frequency about 10Hz below the frequency at whichthe 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, anda separate, wired connection to +12V is included for those who never want to replace the battery. No wired connection tothe amplifier is necessary. The control sends a radio signal to the DSP in the amplifier, so the control may be mounted in aconsole 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 oralbums 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 betweenthe subwoofer and the mid-bass or midrange speakers any time they are adjusted. This causes the bass to sound boomyor muddy when it’s boosted and draws the listener’s attention to the location of the subwoofer (see Figure 5a).Figure 5a. Figure 5b.EnglishLow-PassFilterBand-PassFilterHigh-PassFilter6dB/oct.12dB/oct.24dB/oct.SubsonicFilterLow-PassFilterCrossover FrequencyConstant With Bass BoostCrossover FrequencyChanges With Bass Boost