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Subwoofers can be a very important part of making a business music system outstanding. The Control
19CS and 19CST in-ceiling subwoofers provide good bass from an extremely compact enclosure that can
be installed into a ceiling.
The number of subwoofers to use, where to position them, how to set the taps (on 70V/100V units) and
how loud to run them can vary depending on the characteristics of the individual situation, such as
placement, boundary loading, size of the room, coupling of multiple speakers/subwoofers, type of music,
type of activity, and the expectations of the listeners. The following guidelines are therefore in very
general terms.
Crossovers
The Control 19CS exhibits a gentle, natural low-pass roll-off. It can be connected in parallel with Control
24’s or Control 26’s in most applications. This results in a balanced sound. However, the overall
performance of a system can be further improved by actively crossing the system over between the full-
range speakers and the subwoofers, instead of overlapping them.
Using an Active Crossover – A better overall sound can be attained by using an active crossover and a
separate amplifier channel for the subwoofers. When subwoofers and full-range speakers are
operated in parallel (from the same full-range signal), a frequency response bump in the band where
both speakers produce sound (between 80 Hz and 160 Hz) can result. This gives the impression of
strong mid-bass or high-bass, which is often acceptable or desirable, but it may lessen the
impression of low-bass (subwoofer). Using an active crossover, set between 80 Hz and 120 Hz --
4
th
Order (24 dB per octave) is recommended -- results in very flat frequency response down to
45 Hz, giving strong low-bass and a higher fidelity sound.
Stand-alone outboard electronic crossovers are available, but can be expensive. Inexpensive
crossover modules are available for the JBL MPC power amplifiers, providing active crossing-over
at an affordable price. MTC-X100 is a preset at 100 Hz (24 dB/oct) and the MTC-XU is a
universal crossover module with a wide selection of crossover frequencies. These modules solder
onto the existing input cards of the JBL MPC power amplifiers.
Target SPL for the Subwoofers – Typically, the goal for subwoofers is for them to be somewhere
between the same loudness and 10 dB louder than the mid-high/full-range speakers in the system. Low
level music tends to require subs to be louder compared to the mid-high/full-range speakers, because at low
sound levels the human ear needs more bass for a perception of well balanced sound. Given the same
music, higher levels of music can sound well balanced with less RELATIVE bass. There is also some
music types and applications, like dance music in upscale fashion retailers, that require more subwoofers.
Setting the ratio of subs to mid-high/full-range speakers somewhere between 0 dB and +10 dB is usually a
good starting point.
Positioning of the Subwoofers – Placing a C19CS subwoofer within 3 feet of a wall increases its output
by 3 dB. Placement within 3 feet of a corner increases its output yet another 3 dB (or 6 dB total, as
compared with being located away from a wall or ceiling). In these cases, there is both an increase in
sensitivity (output per watt of input) and in maximum total SPL capability.
How Many C19CS Subwoofers to Use – Light background or foreground music usually does not require
subwoofers. The Control 24C and Control 26C produce adequate bass levels to be able to turn the bass up
(via tone control or EQ) and get good full-range sound for low-level music reproduction.
The following ratios are no more than rough guidelines intended as starting points. The system designer
needs to compute the SPL capability and determine that it will meet the user-expectations for the
application. (Note: The following assumes that the speakers are all installed in the ceiling away from
wall and corner boundary surfaces (not getting the bass reinforcement from these boundary surfaces) and
that 70V/100V models are tapped at their highest tap settings.)