Max SPL measures the sound pressure level a loudspeaker is able to produce at particular frequencies. The measuring signal consists of sine bursts, whose level is increased successively while SPL and harmonic distortions are being measured. Stop criteria are a maximum THD value, a predefined input level and limiter detection.

In the Measurement setup the basic configuration for the measurement is set; the frequency points to be measured are specified in the Frequency steps setup.

LS sensitivity proc. is required for the correct normalisation to a distance of 1m.

The distance between microphone and loudspeaker is entered in Mic. dist [m].

Corrected by [dB] is used for shifting the measurement by a constant value, e.g. when measuring with the microphone on a rigid floor by -6dB for regaining free field conditions.

If for Mic. dist [m] a value of 1m is entered and 0dB for Corrected by [dB], no normalisation is carried out and the absolute sound pressure level at microphone position is being measured.

Level steps setup controls the level of the measuring signal.

Rel. start level defines the starting level relative to the maximum output level.

Level increment describes the increment between two particular measurements.

Recovery [s] is a level bound regeneration interval between two individual measurements. The closer the level gets to the upper limit the longer this pause becomes; Recovery [s] defines its maximum.

Pause time [s] on the other hand is inserted as level independent break after each new frequency.

Return to min. makes the measuring level fall back to Rel. start level for the start of each new frequency; otherwise an estimated value for the first Distortion threshold is taken as starting level.

The parameters Burst pause [s], Start offset [dB] and Recovery max@[dB] are newly implemented on 02.09.2016. Using 0 as value for these 3 parameters, MaxSPL behaves as before.

Burst pause [s] defines a third constant pause time between each burst.

Start offset [dB] will be applied only if return to min is deactivated. In this case, Start offset will be added to the relative start level of the next frequency. If, e.g. the next start level is -30dBu and start offset is -5dB, the next frequency would be started at -35dBu.

Recovery max@[dB] clips the recovery time at a level relative to the maximum level to the maximum recovery time. Using this value, the maximum recovery time will be reached earlier, but at low levels the measurement is still fast.

Max voltage rel. frontend defines the maximum output voltage at the line-output of the frontend. Active loudspeakers for example are connected here. dB reference switches the level display between dBV and dBU. Now the maximum measuring level can be specified as Level [dB], in the form of an RMS voltage (Voltage Vrms) or relative to the digital maximum level (Level dBFs).

Max voltage rel. amplifier defines the maximum measuring power when using the internal output stages of the frontend or external power amplifiers.

Amp output allows switching between the use of internal or external power amplifiers. When using external amplifiers, the correct specification of the amplifier gain in the Frontend setup is essential. In Nom. load [Ohm] the nominal impedance of the loudspeaker is entered. Under Nom. power [W] the maximum power for the measurement is to be defined. If this value is chosen too optimistically, the loudspeaker might be destroyed!

Distortion thresholds are the THD limits evaluated during the Max SPL measurement. Every time one of these thresholds is reached while increasing the measuring level, a data point with the currently measured SPL is generated in the corresponding channel (each threshold is monitored by an own channel). If a particular measurement is stopped before reaching the threshold (e.g. by reaching the maximum output level), the corresponding data point is set to the highest SPL measured for this frequency. A maximum of four thresholds can be measured, to be specified as percentage of the fundamental. Threshold values commonly used are 1%, 3%, 10% or 20%. If less than four distortion thresholds are to be monitored, channels can be disabled by entering 0%.

OK starts the measurement; Cancel aborts the procedure.