## Continuous vs Peak SPL
The maximum SPL figure on a loudspeaker specification sheet is almost always a peak figure, not a continuous figure. Peak SPL is measured using short burst tones at the point of incipient distortion or protection engagement — too short for the voice coil to accumulate significant heat. The cabinet operates at a level it cannot sustain for more than a fraction of a second.
Continuous (RMS) SPL is the level the system can maintain over a defined window — typically two hours with a band-limited pink noise signal — without thermal damage. The continuous figure is invariably lower than the peak, often by 6 to 12 dB. When a manufacturer reports only a peak figure without specifying the measurement window, continuous performance is unknown.
## Why Cross-Manufacturer Comparisons Are Unreliable
There is no mandatory industry standard for how SPL measurements are reported. One manufacturer measures peak at 10% total harmonic distortion (THD). Another at 3% THD. A third reports calculated SPL from sensitivity and rated power without acoustic measurement. A fourth reports from a semi-reverberant room that adds several dB of acoustic gain to the result.
A cabinet claiming 140 dB peak SPL and another claiming 136 dB may perform identically — or the 136 dB cabinet may be the better performer if its measurement was made under more rigorous conditions.
## What 10% THD at Max SPL Means
When maximum SPL is specified "at 10% THD," the cabinet is producing a level of distortion where 10% of total acoustic output is harmonic distortion rather than the original signal. It is audibly, obviously distorted — not a usable operating point for professional work. It is the physical limit before mechanical failure, used as a standardised measurement reference.
A cabinet's usable professional operating maximum is better understood as the level at which distortion remains below 1 to 3% THD — typically 6 to 10 dB below the stated peak figure. SSOUNDS publishes both peak and continuous SPL with stated measurement conditions, and provides THD-versus-level data so engineers can identify the true operating envelope rather than the emergency ceiling.