## 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.