Measuring SPL of Portable Devices to EN 50332-2
Test sequence for separately measuring the maximum sound pressure level for portable music players and the earphones/headphones
These two sequences follow the test standard detailed in EN50332-2 for measuring the maximum levels of portable music players and earphones/headphones. This section of the standard covers the individual testing of the devices rather than the combined testing that is detailed in -1. Note that the physical setup and connections will be different between the two sequences. Please read the hardware and calibration sections of this instruction carefully.
The sequence for testing the music player involves loading a weighted pink noise stimulus file (as specified by IEC 268) onto the portable device and playing it through the headphone jack (connected to a 32 ohm load) at the player’s maximum volume. The RMS voltage is averaged over 30 seconds, and the result must be less than 150 mV.
The sequence for testing the headphones requires the device under test to be connected to an amplifier whose output impedance is less than 2 ohms. The amplifier’s outputs are split, connecting one side to the headphone and the other directly to the input of the soundcard. This is done to measure the voltage at the headphone while the amplifier is under load. This also requires an audio interface with 4 inputs, as two will be connected to the amplifier outputs and two will be connected to the HATS ears (via the microphone preamps).
The first part of the sequence uses the electrical loopback from the amplifier to measure the amp’s gain using the IEC weighted pink noise file. This result is stored and applied as calibration data to the subsequent measurements.
The headphones are positioned on a head and torso simulator (HATS). First, two signal generators play the noise file while the signal is monitored through the ears on two multimeters. This allows the user to position the headphones to produce maximum output.
Next, two signal generators play the IEC weighted pink noise file at a level of 50 mV while the signal from each ear is recorded, and a 1/3rd octave curve is analyzed. An A weighting is applied to the curves, as well as a free field correction for the HATS. The values between 20 Hz and 20 kHz are summed to indicate the overall weighted sound pressure level. The ratio between stimulus level and sound pressure level is used to calculate the stimulus level required to produce 94 dBSPL at the ears. The standard refers to this value as the wide band characteristic voltage or WBCV. The WBCV for each headphone must be greater than 75 mV.
- Audio interface with minimum of 4 inputs (i.e. Lynx Two or RME Multiface/Fireface)
- Head and Torso Simulator (with Free Field correction curves)
- Microphone Power Supplies (SoundConnect or equivalent)
- 4231 calibrator
- Amplifier (Output Impedance < 2 Ohms)
- SoundCheck 13.0 or later
- 2004 – Post Processing
- 2005 – RTA
- 2009 – Statistics
Note: Run the sequences directly from their exported folder rather than importing them into SoundCheck.
- Load the file IEC 268_1 pink.mp3 or IEC 268_1 pink.wav onto your portable music player and set the device to maximum volume.
- Connect the outputs of the left and right side of the music player to inputs 1 and 2 on the soundcard.
- The first time you open the Headphones sequence you will see the channel relinking dialog. Click the dropdown next to all four channels and choose Add to System Calibration. Then click OK.
- Next you will be prompted whether to import calibrated devices associated with the new channels. Click Yes.
- Likely you will then be asked whether to overwrite the device ‘unity cal (Read-only) in.dat’. Click No to All.
- Last, the calibration editor will open so that you can assign hardware channels to the newly added signal channels. Assign the Loopback channels to Inputs 3 and 4. Assign the EN50332 Amp channels to Outputs 1 and 2.
- Connect the HATS microphone outputs to the preamplifiers, and connect the preamplifier outputs to inputs 1 and 2 on the soundcard.
- Calibrate the HATS ears as per the instruction in the SoundCheck manual (using the Ear Sim L and R signal channels).
- Open the free field correction curves for your HATS into the memory list. Save the two curves into the single file HATS FF Correction Curves.dat located in the sequence folder. Overwrite the existing file.
- Connect outputs 1 and 2 of the soundcard to the inputs of the amplifier.
- The outputs of the amplifier will be split, with one part going to the headphones and the other to inputs 3 and 4 on the soundcard.
You are ready to start the sequence.
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