XTA DPA SERIES Operator's Manual

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XTA DPA SERIES Operator's Manual Manual pdf 73 page image

DPA Series — DPA80/DPA100 Operating Instructions Page 73taxSetting Accurate Limiter Thresholds — Peak LimiterAssuming the RMS limiter has been set correctly and, just as importantly, attack and releasetimes have been chosen as appropriate to the driver to be protected, the peak limiter istypically set to limit overshoot to 3dB above the RMS limiter threshold.This would allow peaks of twice the RMS power level to reach the outputs. If the driver has apeak power capability of more than double the rated RSM power, then this value can beincreased.To calculate the setting for the peak limiter it’s:10 x (Log10(Peak Power / RMS Power))So for example, a 15” driver has a quoted RMS power handling of 800W, and a peak powerhandling of 1600W, the calculation is(1600/800) = 2Then Log 10(2) = 0.3010Then 10 x 0.3010 = 3.010 or 3dBSpeaker manufacturers may quote AES power in place of RMS power and “Program” insteadof “Peak”. These terms, whilst not strictly interchangeable, are similar as a “pair” ofmeasurements. AES tends to be a slightly more conservative rating given the definition ofhow it is measured. If AES power is quoted, then it normally is paired with the “Program”rating and so the calculation of the threshold for the peak limiter is still valid.Setting Appropriate Attack and Release TimesAs stated earlier in this appendix, having control over the attack and release times of theprogram limiters allows the user to balance the required subjective quality of the limiteragainst the driver protection requirements. It does also mean that an incorrectly set limitermay sound awful!In particular (as with all limiters) using too fast an attack or release time will result inexcessive low frequency distortion. When setting limiter attack and release times during thecrossover configuration there is an option for automatic limiter time constants. Use thisoption if you are unsure how to set the time constants manually. See page 41 for details onhow to turn this option on.We recommend the use of the automatic setting.In this mode the time constants will be automatically set from the high pass crossover filterfrequency according to the table below:High Pass Filter Auto Attack Time Auto Release Time<10Hz — 31Hz 45mS x16 (720mS)31Hz — 63Hz 16mS x16 (256mS)63Hz — 125Hz 8mS x16 (128mS)125Hz — 250Hz 4mS x16 (64mS)250Hz — 500Hz 2mS x16 (32mS)500Hz - 1kHz 1mS x16 (16mS)1kHz — 2kHz 0.5mS x16 (8mS)2kHz — 32kHz 0.3mS x16 (4mS)