Max SPL vs Frequency Sequence
A sequence to characterize the performance of transducers by measuring how much voltage is required at each frequency to drive the transducer to specified limits of THD, Rub & Buzz, Perceptual Rub & Buzz or Compression
This sequence characterizes the performance of transducers such as speakers, microspeakers and headphones by measuring how much voltage is required at each frequency to drive the transducer to specified limits of THD, Rub & Buzz, Perceptual Rub & Buzz or Compression. This is useful for detailed transducer analysis and determination of optimal power rating.
The sequence begins by asking the user to input a limit value for the metric of interest (it is suggested that only one metric at a time be tested) and a stimulus start frequency. The sequence then plays the stimulus start frequency in a loop, increasing the level +3dB with each loop iteration until the limit is exceeded. The stimulus level is then adjusted -3dB and the sequence continues to a second loop which increases the stimulus level +0.5 dB with each loop iteration until the limit is exceeded. At this point, the limit results are saved to an Excel file, the stimulus frequency is incremented by a constant multiplication step and the process is repeated until the loop repetition value is satisfied. Every time the main loop is completed, the individual SPL and Stimulus Level x-y pairs are concatenated to master curves. At the end of the sequence, the Max SPL and Stimulus Level curves are autosaved in .dat format
- Listen SCM 3 reference microphone or equivalent Part # 4002
- Listen AudioConnect Audio Interface/microphone power supply or equivalent Part # 4050
- Power amplifier – Listen SCAmp Part # 4060
- SoundCheck Basic version 16.0 or later
Setup & Calibration
Caution: Take care when setting the limits for the various metrics. You may damage your DUT if the limits are set too high. It is good practice to make a trial run with an artificially low limit and then increase the limit to a more practical value for subsequent testing
- Connect your audio interface output 1 to the input of your amplifier
- Connect the output of your reference microphone’s power supply to input 1 of your audio interface
- Calibrate your amplifier and reference microphone per the instructions in the SoundCheck user manual
- Connect your DUT to the output of the amplifier
You are ready to start the sequence.
Additional Sequence Notes
- The sequence default settings will measure the DUT at 1/3 octave frequency resolution starting at 50 Hz and ending at 20 kHz (27 frequency points).
- Stimulus resolution is controlled by Step 7 Stimulus Resolution Multiplier. You can use different constant values in this step to produce different stimulus resolutions:
|Stimulus Resolution||Constant value|
|1/3 octave (default)||1.259|
- If the frequency resolution is increased (or the frequency range is otherwise edited), the number of times the main loop in the sequence is applied needs to be adjusted accordingly. This value can be adjusted by right clicking on step #81 Max SPL End in the Sequence Editor and selecting the Configure Step The Step Configuration editor will open and you must edit the After xx repetitions value to reflect the new requirements.
Further sequence development
This sequence has been designed to be accessible to 100% of SoundCheck customers. Ways in which you could modify or further develop the sequence include:
- Headphone/earphone testing