4. What about loudspeaker abuse in normal operation? Should there be any de-rating of systems to allow for this?
Yes. JBL defines the following three categories of loudspeaker application, each requiring an
adjustment of the system's IEC rating:
A. For carefully monitored applications where peak transient capability must be maintained, a system should be powered with an amplifier capable of delivering twice its IEC rating. For example, a studio monitor system rated at 300 watts can be safely driven by an amplifier capable of 600 watts output.
Discussion: Careful monitoring is the key here. High quality music production today demands high peak factors in the recorded signal. Such peak signals are normally of such short duration that they hardly stress the system's components. Thus, the extra 3-dB margin (times two) of power will result in cleaner overall operation of the system, with less listening fatigue.
B. For routine application where high continuous, but non-distorted, output is likely to be
encountered, a system should be powered with an amplifier capable of delivering the IEC rating of the system.
Discussion: This case describes the bulk of sound reinforcement activities. Such systems can often be inadvertently overdriven, or can go into feedback. When powered with an amplifier equal to their IEC rating, the user is guaranteed of safe operation.
C. For musical instrument application, where distorted (overdriven) output may be a musical
requirement, the system should be powered with an amplifier capable of delivering only one-half of the IEC rating for the system.
Discussion: Much rock music is produced at full output with the amplifier well into clipping, and this is a matter of musical choice. When an amplifier capable of, say, 300 watts of undistorted sinewave output is driven well into clipping, its output power can approach 600
watts! So, Berating the system to one-half its IEC power will result in safe operation of the loudspeaker.
For a more detailed discussion of these topics, see JBL Technical Notes, Volume 1, Number 16.