Sgt. Ear Ache
Major Contributor
Changes over time are what IMAX claim:
US Patent #9648437: Systems and methods for monitoring cinema loudspeakers and compensating for quality problems (Assignee: IMAX Corporation.)
A few quotes (my emphasis):
"[Claim] 5. The method of claim 1, wherein the test signal comprises at least one of: an impulse signal; a chirp signal; a maximum length sequence signal; or a swept sine signal."
"[Claim] 7. The method of claim 1, further comprising: tuning a theatre sound system prior to determining the difference, the theatre sound system including the loudspeaker."
"[Claim] 10. A system comprising: […] an equalizer unit adapted to (i) store the signature response of the loudspeaker, (ii) correlate the signature response to the optimal response, the signature response indicating what the optimal response should be at the suboptimal location of the microphone for the loudspeaker (iii) determine a difference between the signature response and the subsequent response, the difference representing changes in the loudspeaker since capturing the signature response,(iv) compensate for changes to the loudspeaker by modifying an audio signal based on the difference to generate a compensated audio signal and providing the compensated audio signal for output by the loudspeaker such that a response to the compensated audio signal represents the desired response by the loudspeaker in the patron-seating area of the theatre."
As for testing whether the system is functioning, IMAX Digital systems (worldwide) are remotely monitored from IMAX's Network Operations Center in Mississauga, Ontario. In case of driver failure, where possible (e.g. a blown subwoofer driver) the system can be set to compensate for this (e.g. by increasing the output of the remaining subwoofer drivers,) and in all cases a field technician can be dispatched for the installation of replacement parts. Incidentally, the projection system is remotely monitored and automatically recalibrated every day, too.
Yes, none of which necessarily implies the changes in the loudspeaker are a result of burn-in such as it's referred to by audiophiles...
"Cinema loudspeaker systems need to perform reliably for extended periods. This is in conflict with the natural changes in the loudspeaker characteristics due to aging or changing environmental conditions, such as temperature and humidity. These natural changes, among other changing performance characteristics, are a typical problem that occurs over time. Other potential performance issues include (i) one driver in a cluster of drivers within a loudspeaker fails or is experiencing a degradation because of a loose connection or otherwise; (ii) a fuse blows, leaving inoperable the mid-range driver(s) or high range driver(s); and (iii) audio amplifier degradation or failures to degraded sound in the theatre. One approach to recognize one or more of these deficiencies is to repeat a theatre sound system tuning test to determine a performance deficiency.
Additionally, the acoustics of the theatre hall can change depending on the number of viewing patrons present (i.e. acoustics can be different if the theatre is full than if the theatre is nearly empty) and the location within the hall of where the patrons are seated. If the acoustics of the hall has changed, causing a reduction in sound quality, adjustments to the equalization of the sound system may be required to compensate for the change."