Specifications

Control limiting system.This system comprises three separate layers of pro-

tection triggered by an infinite variation of possible program conditions. Data

is received on four independent sensor circuits, including Apogee’s exclusive

VIProtect

™ current sensors, and is processed by an analog computer to pro-

hibit the drivers from over-excursion, excessive RMS levels, and excessive

instantaneous peak levels. By sensing voltage and current, the limiter circuits

can compensate for changes in voice coil temperature, ensuring that accurate

protection levels are always maintained.

All of this occurs without compromising dynamic range or otherwise unnat-

urally compressing the program material. The protection circuits only act

when the drivers would otherwise be damaged and, therefore, are excep-

tionally transparent. They are effectively “out of circuit” when below the

threshold of engagement.The result is an extremely clean sound quality, with

effective control of potential damage to the drivers from abusive conditions.

A limiter LED is located on the rear panel of the APL-10, -12, and -SB, intend-

ed to indicate the deployment of the limiters. It is not uncommon to see this

LED illuminate regularly, such as on downbeats and crescendos.

If the LED appears to be "on" more than "off" (i.e., if it is continuously flash-

ing or glowing at a steady state), the loudspeaker system is being pushed too

hard for its size and power output capability.To correct this, reduce the drive

level to the speaker system, or install additional speakers to achieve the SPL

(Sound Pressure Level) required for the application.

(3) A Word About Limiters

Properly designed protective limiters can do wonders to help prevent driv-

er damage and extend normal driver life, but are by no means a panacea.

Apogee limiters do not exhibit “brick-wall” characteristics, as these type of

limiters seriously degrade sound quality. Apogee’s intelligently engineered

limiter circuits provide an excellent measure of protection, while maintaining

sonic purity.

These limiter circuits are capable of effectively reducing program levels that

would otherwise damage the system’s drivers.This takes place with little or

no loss of sonic quality or dynamic range, because the circuits are designed

so that they only engage when driver non-linearity or driver damage would

otherwise occur. However, when a limiter is pushed well past its threshold of

engagement to the point where it is continually “in circuit”, by nature, it

increases the duty-cycle of the program material. This happens because, as

the limiter decreases peak amplitudes, RMS values increase, causing the driv-

ers to heat beyond normal.Additional circuits could be employed to reduce

levels and “clamp” the output of the system, but such circuits would repre-

sent a high level of intervention and be very audible in their action.The prop-

er solution is for the operator to recognize that the system is being pushed

past its capabilities and either reduce operating levels or add additional

speaker systems to provide the desired Sound Pressure Level (SPL).