QSC Audio CX168 user manual Clip Limiter, Low Frequency Filter

SETUP: MODE SWITCHES: CLIP LIMITER AND LOW FREQUENCY FILTERS

Clip Limiter

The CX168 amplifier has separate clip limiters for each of the 8 channels. These clip limiters respond only to actual amplifier clipping. Amplifier clipping generates internal error signals which cause the clip limiter to quickly reduce gain and minimize the overdrive. To preserve as much of the program dynamics as possible, limiting occurs only during actual clipping. Each channel’s clip limiter can be switched on or off individually.

The clip limiter is internally set to respond as fast as possible after clipping is detected. For program material that is primarily “full-range”, the effect on the overall audio quality should be imperceptible. We recommend using the clip limiters for almost all applications, especially full-range audio applications. Clipping can cause high-frequency artifacts to be output to the speakers, potentially damaging fragile high-frequency drivers.

For program material that is primarily low-frequency in nature (low-frequency or subwoofer drive) this may be perceived as a “rubbery” effect on the audio. If this is the case, it may be preferable to turn the clip limiters off and let the amplifier clip occasionally. With robust, low-frequency drivers, the occasional clipping should cause no problems.

Low Frequency Filter

When driving speakers with limited low frequency response, it is important to limit the low frequency response of the amplifier. Doing so can result in more usable bass response since the speaker is not being overloaded by very low frequencies it can’t handle.

Explanation- Low frequency sound waves require much more speaker cone motion to produce the same apparent loudness as higher frequencies. Properly designed speaker enclosures help the speaker to move more air with less motion using techniques like porting. Such enclosures only benefit from porting down to a certain frequency. Below this frequency, the speaker is “unloaded” and is basically free to move around uncontrollably without producing much bass. Limiting the frequency range of the low frequency content enables the speaker to behave the way it was designed to. If frequencies lower than designed are supplied to the speaker, performance will degrade.

All low frequency filters will change the character of low frequency transients. For best results, the cabinet design, speaker capabilities, and program material must be taken into account when configuring low frequency filtering.

CAUTION! Clip limiting reduces extreme overdrive peaks, allowing a higher average signal level without distortion. Increasing the gain with the clip limiter engaged until clipping is again audible, can double the average output power. Be careful not to exceed the power rating of the speakers!

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