Limiter Settings for PA Systems: Protecting Your Sound

Limiters serve as the last line of defense in PA systems, preventing signal peaks from damaging speakers or causing distortion. Proper limiter configuration balances protection with sound quality, allowing dynamic performance while establishing absolute output ceilings.

Understanding Limiters

Limiters are specialized compressors with very high ratios—typically 10:1 or higher, often infinity:1. When signal exceeds the threshold, the limiter clamps output to prevent further increase.

The threshold setting determines when limiting begins. Signals below threshold pass unchanged; signals above threshold get reduced to stay at or near the threshold level.

Attack and release times affect how the limiter responds to transients. Fast attack catches peaks but may alter punch; slower attack allows some overshoot but preserves transient character.

Speaker Protection Settings

Protection limiters prevent speakers from exceeding their power handling capacity. Setting the threshold requires knowing the speaker’s continuous power rating and the amplifier’s output capability.

If amplifiers can deliver more power than speakers can handle, limiters must prevent the excess power from reaching drivers. Calculate the voltage that corresponds to the speaker’s rated power and set the limiter threshold accordingly.

QSC, JBL, and other manufacturers provide recommended limiter settings for their speakers. Following these recommendations ensures proper protection without unnecessary sound quality compromise.

System Processor Limiters

Digital system processors like Lake, BSS, and dbx DriveRack include output limiters on each channel. These processors sit between mixer and amplifiers, providing system-wide protection.

Setting processor limiters requires understanding the entire signal chain. The limiter threshold should prevent the amplifier from clipping and prevent the speaker from exceeding its thermal or mechanical limits.

Multiple limiter stages may operate throughout the system. Output limiters on the processor, clip limiters on amplifiers, and protection circuits within powered speakers all contribute to system safety.

Attack Time Settings

Fast attack times (0.1-1 ms) catch transients quickly but may reduce punch on percussive material. The limiter engages before the transient fully develops, softening the initial impact.

Slower attack times (5-20 ms) allow transient peaks through before engaging. This preserves punch but allows brief excursions above the threshold. For speaker protection, this may be acceptable if the overshoot duration is short.

Most protection limiters use fast attack settings. The brief compromise in transient response is preferable to speaker damage.

Release Time Settings

Release time determines how quickly the limiter returns to unity gain after the signal drops below threshold. Fast release (50-100 ms) recovers quickly but may cause pumping on sustained signals.

Slower release times (200-500 ms) provide smoother operation but may keep the signal compressed longer than necessary. Auto-release functions adjust release time based on program material.

For speaker protection, release time matters less than attack time. Once the dangerous peak has passed, recovery speed affects sound quality but not protection.

Peak vs RMS Limiting

Peak limiters respond to instantaneous signal level. They catch brief transients that might escape RMS detection but may react to harmless peaks.

RMS limiters respond to average signal level over a time window. They better reflect actual power delivery to speakers but may miss brief high-energy transients.

Many protection systems use both—a peak limiter for transient protection and an RMS limiter for thermal protection. The combination provides comprehensive coverage.

Setting Thresholds Correctly

Conservative threshold settings ensure protection but may engage limiting too frequently, audibly affecting dynamics. Aggressive settings preserve dynamics but provide less protection margin.

Start with manufacturer recommendations where available. Adjust based on the specific situation—louder venues may benefit from slightly lower thresholds; dynamic acoustic shows may need more headroom.

Monitor limiter activity during performance. Occasional peak limiting is normal; constant limiting indicates the threshold is too low or the system is being pushed too hard.

Powered Speaker Limiters

Powered speakers from QSC, JBL, Yamaha, and EV include built-in limiters optimized for the specific driver and amplifier combination. These limiters are pre-configured and typically not user-adjustable.

Some powered speakers offer DSP presets with different limiter behaviors. “DJ” modes may allow more output with less protection; “speech” modes may prioritize clarity with more conservative limiting.

Trusting built-in limiting while avoiding input clipping keeps powered speakers operating safely. Red input LEDs indicate the need for level reduction at the source.

Amplifier Clip Limiters

Many professional amplifiers include clip limiters that engage just before the amplifier clips. Crown, QSC, and Powersoft amplifiers offer this feature.

Clip limiters prevent the harsh distortion that occurs when amplifiers run out of headroom. They also protect speakers from the high harmonic content present in clipped signals.

Enabling amplifier clip limiters provides an additional protection layer beyond system processor limiting.

Listening for Limiter Artifacts

Over-aggressive limiting sounds compressed and lifeless. Transients lose their impact; the overall sound becomes flat and fatiguing.

Pumping occurs when the limiter rapidly engages and releases, causing audible volume fluctuations. Adjusting release time or threshold typically resolves pumping.

Well-configured limiting should be nearly inaudible during normal operation, engaging only on unexpected peaks while preserving the natural dynamics of the performance.