Response Of Modified 3152A Network; Notes On Preventive Maintenance - JBL 4671 Instruction Manual

FIGURE 18. RESPONSE OF MODIFIED 3152A NETWORK
H. Notes on Preventive Maintenance:
Nothing lasts forever; however, a properly specified,
installed, and operated motion picture sound system
comes as close to beating the odds as anything we know
of. There are a few points of preventive maintenance
which will make the theater operator's life a little more
bearable, and we present them below:
1. Establish fixed gain and equalization settings and
operating levels in each audio chain, and make abso-
lutely sure that all operating personnel adhere to those
settings. Most high-frequency component failures re-
ported to us from the field can be traced directly to
overdriving those components. Locking type controls on
amplifiers will discourage tampering. The JBL models
6230, 6260, and 6290 amplifiers are available with such
controls.
22
LF (8ft)
13 dB
FREQUENCY
2. An experienced technician should regularly check
out each audio chain to ensure that no changes have
been made.
3. Make sure that any changes in third-octave sys-
tem equalization are carried out by an experienced engi-
neer using the correct measuring instrumentation.
4. The audience is the first to hear a problem, so
monitor carefully any complaints from patrons. Until you
find out differently, assume that the patron's complaint is
legitimate.
5. Routine replacement of drivers is not generally
recommended; however, over years of operation, a
compression driver diaphragm may simply give in to
metal fatigue. Our current titanium diaphragms are much
less susceptible to this than were older aluminum ones.
HF (16ft)
10 dB