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.
In order to run the 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.
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.
This sequence satisfies the requirements of Section 8.3 Input Voltage. The sequence uses a Simulated Program Source (SPS) stimulus (pink noise, 20 Hz-20 kHz, shaped according to IEC 60268-1) and a 500 Hz sine to determine the DUT’s voltage sensitivity. The sequence calculates the SPCV (Simulated Program Characteristic Voltage, e.g. voltage required to produce 94 dBSPL) for the unfiltered SPS response and the A weighted/free-field corrected response as well as the 500 Hz 94 dB voltage sensitivity.
The sequence first recalls the SPS WAV file, free field correction and A weighting curves into the memory list. It then enters a loop which will run 5 times. First, two signal generators and two multimeters open and the user is prompted to adjust the DUT position on the HATS to produce maximum level on the L & R HATS Ears. The sequence then plays and records the DUT’s response to a 500 Hz 50 mV stimulus. Next, two Signal Generators and two RTA virtual instruments will open. The signal generators play the SPS and the RTA spectrum of the response is saved to the Memory List. A series of post-processing steps follow to apply the weighting and correction curves, calculate the LAEQ and then the Simulated Program Characteristic Voltage is calculated along with the 500 Hz voltage sensitivity. Finally, a Statistics step calculates the running mean of the SPCV and 500 Hz values. The data from each loop iteration is displayed as it is acquired. After 5 loop iterations, the mean values for SPCV, SPCV weighted/corrected and 500 Hz sensitivity are displayed in a table.
This sequence satisfies the requirements of Section 8.2 Electrical Impedance, Section 8.6 Frequency Response and Section 8.7 Amplitude Non-linearity. The sequence uses a stepped sine stimulus to measure frequency response, THD and impedance, a composite signal of 70 Hz and 600 Hz with an amplitude ratio of 4:1 to measure intermodulation (IM) distortion and two sinusoidal signals, separated in frequency by 80 Hz to measure difference frequency distortion.
The user is first prompted to enter the rated voltage. This value is converted to dBV and used to calculate the IM and difference frequency stimulus levels. The sequence then runs through a series of Play and Record and Analysis steps to calculate the Frequency Response, Impedance, IM distortion and Difference Frequency Distortion of the DUT which are then shown on the final display.
Section 8.11 Sound Attenuation references the ISO 4869-1 standard which uses human listeners and subjective “threshold of hearing” metrics to determine attenuation values. We encourage interested users to obtain a copy of ISO 4869 but in its place we offer an updated version of Listen’s ANC Headphone Test Sequence. This sequence uses a pink noise stimulus to characterize the passive, active and total attenuation of noise cancelling headphones. It can also be used to characterize the passive attenuation only of a standard (non-ANC) headphone.
Noise speakers are set up adjacent to the HATS left and right ears. First, a pink noise stimulus is played from the noise speakers and recorded by the unoccluded ears. An RTA spectrum of the response is calculated and named Unoccluded Spectrum. Next, the user is prompted to place the DUT on the HATS. If it is an ANC headphone, the ANC circuit should be turned off. A pink noise stimulus is played from the noise speakers and recorded by the occluded ears. An RTA spectrum of the response is calculated and named Occluded Spectrum. The play and record acquisition takes place 3 times and the user is prompted to reposition the DUT on the HATS in between acquisitions. A statistics step calculates the mean of the 3 unoccluded measurements. The user is then asked if the DUT has an ANC circuit. If the answer is No, the sequence jumps to post-processing steps which calculate passive attenuation and the final display step. If the answer is Yes, the user is prompted to turn the ANC on and the sequence repeats the passive measurements. A series of post processing steps calculates the attenuation curves, their average values and shows them on the final display.
This sequence satisfies the requirements of Section 8.10 Unwanted Sound Radiation. The sequence uses a stepped sine stimulus to measure the sound radiation from the DUT as well as the DUT’s crosstalk (e.g. signal level at the HATS R ear of a stimulus played from the DUT’s L output.
The sequence first plays a stepped sine through both channels of the DUT and captures the sound radiation from the DUT using 2 reference mics. Heterodyne analysis is used to calculate the fundamental of the L & R radiation. The sequence then goes through a series of acquisition steps to generate four fundamental curves which are then post-processed to calculate crosstalk. Crosstalk and radiation curves are then shown on the final display.