IEC-60268-7 Headphone Test Sequences
SoundCheck sequences for the electro-acoustic tests detailed in Section 8 “Characteristics to be specified and their method of measurement” of IEC-60268-7: Sound System Equipment – Part 7: Headphones and Earphones
IEC-60268-7: Sound System Equipment – Part 7: Headphones and Earphones is an international standard intended to characterize the performance of headphones and earphones. The standard itself is a lengthy document, 9 Sections and 3 Annexes covering 46 printed pages. These SoundCheck sequences focus on the electro-acoustic tests which are detailed in Section 8 “Characteristics to be specified and their method of measurement”.
Five separate sequences are provided, each designed to measure specific characteristics. This approach provides the user with the flexibility to measure all or some of the characteristics of their headphone.
To run these sequences, the following hardware is required.
- Audio Interface, 2 outputs x 4 inputs (minimum 2 out x 2 in if input switching is available*)
- Head and torso simulator (B&K HATS or similar)
- Microphone power supply (Listen SoundConnect 2 or similar)
- Microphone calibrator (B&K 4231 or similar)
- Stereo headphone amplifier (the standard specifies a source impedance of 120Ω. If a different source impedance is used, it should be noted in the test results)
- Reference microphones (pair – Listen SCM-3 or similar)
- Noise playback speakers (pair)
- Stereo power amplifier (if noise speakers are not self-powered)
- Impedance Box (pair)
* The Listen SoundConnect 2 microphone power supply can be used as an input switching device, switching between Line and microphone inputs.
- SoundCheck 18.0 or higher
- 2004 – Post processing
- 2005 – RTA
- 2009 – Statistics
Running the Sequences
It is recommended that the sequences be run directly from the IEC-60268-7 folder. The folder contains dependent files required to run the sequences.
Setup System, Hardware and Calibration
Before attempting to run any of the sequences, read the following setup instructions.
System Calibration – Add or Relink Signal Paths
There are several unique Signal Paths used in the sequences which are not a part of the default SoundCheck installation. In order to add these Signal Paths to your System Calibration or relink to existing Signal Paths, you should open each of the sequences individually and, if prompted, add or relink Paths to your System Calibration.
Here is a list of sequences and their default signal paths (unique paths are in bold):
|SPL||Ear Sim L, Ear Sim R, Headphone Amp L, Headphone Amp R|
|Sensitivity||Ear Sim L, Ear Sim R, Headphone Amp L, Headphone Amp R|
|Response, Distortion, Impedance||Ear Sim L, Ear Sim R, Headphone Amp L, Headphone Amp R, Impedance Box L, Impedance Box R|
|Radiation and Crosstalk||Ear Sim L, Ear Sim R, Headphone Amp L, Headphone Amp R, Reference Mic L, Reference Mic R|
|Passive & Active Attenuation||Ear sim L, Ear Sim R, Noise Speaker L, Noise Speaker R|
- In some cases, identically named signal paths may prompt a relink.
- After relinking, you will be prompted to import the calibrated devices associated with the new signal paths. Click Yes to import.
- You will then likely be asked if you want to overwrite the device “unity cal (Read-only) in.dat”. Click “No to all”.
- Next, the System Calibration Editor will open, asking you to assign hardware channels to the newly created signal paths. We suggest the following channel assignments:
|Signal Path||Hardware Channel||Signal Path||Hardware Channel|
|Ear Sim L||Input 1||Headphone Amp L||Output 1|
|Ear Sim R||Input 2||Headphone Amp R||Output 2|
|Reference Mic L||Input 3||Noise Speaker L||Output 3|
|Reference Mic R||Input 4||Noise Speaker R||Output 4|
|Impedance Box L||Input 3*|
|Impedance Box R||Input 4*|
* Reference Mic and Impedance Box can share the same hardware inputs as they are not used together in the same sequence. If more than 4 input channels are available, all input signal paths may be assigned to separate hardware channels.
Setup and Calibration
Detailed setup and calibration instructions are included in the following Sequence Notes.
This sequence satisfies the requirements of Section 8.5 Sound Pressure (Level). Using the DUT’s rated voltage and impedance values, the sequence measures the left/right 500 Hz SPL at the rated voltage level and at 1 mW. It also uses a Simulated Program Source (SPS) stimulus (pink noise, 20 Hz-20 kHz, shaped according to IEC 60268-1) to measure the 1 mW SPL of the DUT’s unfiltered output spectrum and the weighted (A weighting) and corrected (free field correction) output spectrum.
The sequence prompts the operator to enter the rated voltage and rated impedance of the DUT. It then calculates the voltage required to produce 1 mW into the rated impedance. Play and Record Acquisition steps then capture the L/R response of a 500 Hz tone played at the rated voltage and at 1 mW. A subsequent Play and Record step captures the L/R response of the 1 mW Simulated Program Source.
The 500 Hz recorded time waveforms are processed using heterodyne analysis to derive their fundamental values. The recorded time waveforms of the SPS response are then processed using RTA Spectrum Analysis (1/3 octave resolution) and the resulting spectra are A weighted and free field corrected. The spectra are then power summed to derive a single SPL value and the 500 Hz fundamentals are post processed to derive their SPL values.
- SoundCheck 18.0 or later
- 2004 – Post-Processing
- 2005 – RTA
- Audio Interface (2 inputs/2 outputs minimum)
- Head and torso simulator
- Stereo headphone amplifier
- Microphone power supply (2 channels)
- B&K 4231 microphone calibrator
Hardware Setup and Calibration
- Connect the HATS Ear left and right outputs to the microphone power supply and connect the outputs of the power supply to Hardware Inputs 1 & 2 on the audio interface.
- Calibrate the HATS Ears per the instructions in the SoundCheck manual. Use the Ear Sim L and Ear Sim R Signal Paths.
- Connect the left and right inputs of the headphone amplifier to Hardware Outputs 1 & 2 on the audio interface.
- Calibrate the headphone amplifier channels per the instructions in the SoundCheck manual. When calibrating, use the Headphone Amp L and Headphone Amp R signal paths.