Limiter Calculator

How to Set Speaker Limiter Parameters

Why Limiters Matter

Loudspeaker drivers have two fundamental failure modes: thermal (voice coil overheating) and mechanical (cone over-excursion). The RMS limiter protects against the first; the peak limiter protects against the second. A properly configured limiter keeps the system operating within its safe range without shutting down the show.

Understanding the Three Tiers

• RMS / Continuous (AES): Thermal protection. Limits continuous RMS power to the driver's rated thermal capacity. AES standard (AES2-2012): pink noise with a 12 dB crest factor, 2-hour test. (The older AES2-1984 edition used a 6 dB crest factor.)
• Program: The 2× RMS (+3 dB) default is a conservative convention. Actual musical crest factors are higher (~6–10 dB), which is why program ratings are not a substitute for a proper peak limit. Less commonly used in the 2020s; many manufacturers only publish RMS and peak ratings now.
• Peak: Mechanical protection. Prevents cone over-excursion. If your speaker doesn't list peak power, the calculator assumes RMS × 2 (+3 dB) as a conservative default.

"RMS power" is industry shorthand; strictly it is the continuous (average) power corresponding to the rated RMS voltage into the load.

Finding Your Speaker's Real Specs

Manufacturer spec sheets are the authoritative source. Look for:

• AES power rating (continuous pink noise, 2-hour test)
• Minimum impedance (Z_min), not the nominal impedance. Z_min is often around 80% of nominal for passive cabinets, but varies by driver and enclosure; always read the actual Z_min from the impedance curve on the data sheet.
• Peak or program power: some manufacturers publish only one or the other.

Amp Gain vs Sensitivity

When the limiter lives in the console or DSP before the amplifier (the most common configuration), you must account for amp gain:

Threshold_in (console/DSP) = Threshold_out (speaker) − Amp_Gain

Example: 500 W RMS into 8 Ω (using the nominal rating here for a round number, use your driver's actual Z_min in the calculator) → 63.25 V → 38.2 dBu at the speaker. With a 32 dB amp gain, the console threshold is 38.2 − 32 = 6.2 dBu (1.58 V).

If your amplifier is spec'd by sensitivity (e.g. "1.4 V for full power") rather than gain in dB, use the Amp Sensitivity mode; enter the amp's rated power and the load it was rated into (from the amp spec sheet, e.g. 8 Ω, not the speaker's Z_min) and the calculator derives the gain for you.

Setting the RMS Limiter

The RMS/thermal limiter attack should be slow enough to ignore musical peaks and respond only to sustained overpower that heats the voice coil. Typical values are in the ~50–500 ms range: larger LF drivers (greater thermal mass) toward the slower end, small HF drivers toward the faster end. Release is longer than attack (typically ~0.5–3 s), so gain reduction does not pump and the coil can cool.

The calculator's per-type attack values (HF ≈ 20 ms, MF ≈ 50 ms, LF ≈ 150 ms, Sub ≈ 200 ms) are a heuristic synthesized from common system-engineering practice, not a manufacturer specification, and they key on driver type only: they do not scale with the entered power. Real implementations vary widely: some DSP platforms use multi-second RMS attack times or model voice-coil temperature directly (Powersoft TruePower, Linea Tmax/Vx, d&b), so the manufacturer's own limiter preset always takes precedence over these heuristic values. Values are clamped to a sane range (attack ~10 ms–1 s, release ~0.3–3 s); treat them as starting points and defer to the manufacturer's recommended settings.

Worked example: an LF driver → attack ≈ 150 ms, release ≈ 450 ms.

Setting the Peak Limiter

The peak limiter guards against mechanical over-excursion. Its attack should be long enough to span roughly one full cycle of the driver's lowest reproduced frequency, so the limiter shapes the level envelope without clamping within a single cycle and distorting the bass waveform:

• Attack ≈ 1000 / HPF ms (about one cycle at the crossover frequency), with a 0.1 ms floor. Leave HPF blank for a full-range cabinet and the calculator assumes a 50 Hz low-frequency cutoff → attack ≈ 20 ms. This is an assumption, not a spec: full-range low-frequency cutoffs vary, so if your cabinet's actual −3 dB cutoff differs, enter it as the HPF for exact timing.
• Release multiplier: HF = 4×, Mid = 8×, LF/Sub = 16×, with a sensible minimum release of 20 ms (clamped to [20, 500] ms). Very low HPFs hit the cap: at 20 Hz the formula gives 800 ms, which is clamped to 500 ms.

For a subwoofer with a 40 Hz high-pass filter: attack = 25 ms, release = 400 ms.

Safety Margins

Many system engineers set limiters 2–3 dB below the calculated RMS rating for insurance. This is common practice, especially for systems in less controlled environments. The safety margin input lets you do this; enter 2 or 3 and all three thresholds are reduced by that amount.

Multi-Way Systems

Each driver in a multi-way system needs its own limiter calculation because power handling and impedance differ by driver type. The calculator's "Add Section" feature lets you set up HF, MF, and LF sections independently, each with its own thresholds and its own crossover HPF (so the HF section gets a fast peak attack, the LF section a slower one).

Testing Your Settings

• Set the limiter at the calculated threshold
• Drive the system hard; the limiter should engage on peaks without audible pumping
• If the limiter engages too early, reduce the safety margin or check your impedance value
• If the limiter never engages, double-check your amp gain value
• Use your ears and a measurement rig; no calculator replaces real-world validation