Noise-Cancelling Headphones Test Sequence

Introduction

The purpose of this sequence is to test both the passive and active attenuation from noise cancelling headphones. The left earphone is measured using pink noise played for 10 seconds at 90dB SPL from 100 to 10 kHz on an external loudspeaker.
The analysis is performed in parallel with 1/3rd Octaves using our Real Time Analyzer virtual instrument. Three measurements are performed, first with no headphones (unocluded ear on the Head and Torso Simulator – HATS), second with the headphones on but the noise cancelling circuit turned off (passive attenuation of the headphone ear cup), and then third with the noise cancelling circuit turned on (active noise cancelling). Most noise cancelling circuits are more effective at lower frequencies and the passive attenuation is more effective at high frequencies as seen in the example in the display below. Further post-processing of the data calculates the passive and active attenuation curves and overall averages in dB. Of course, more attenuation is better because there is less noise heard by the person wearing the headphones.

Final display of 1) Unocluded ear, Passive attenuation, Active Noise cancelling 2) Passive and Active attenuation curves 3) Average attenution

Required Equipment
Hardware

• Head and Torso Simulator (B&K Type 4128 or equivalent)
• SoundConnect Microphone power supply Listen p/n 4020
• Small loudspeaker
• Amplifier (Crown D45 Listen p/n 5600)

Software

• SoundCheck 7.0 or later
• Signal Generator Listen p/n 2014
• RTA option Listen p/n 2005
• Post-Processing Listen p/n 2004

System diagram

Hardware Setup & Calibration

1. The Head and Torso Simulator (HATS) left ear simulator needs to be calibrated before measuring the headphones. Refer to the HATS manual for further instructions on mounting a microphone calibrator over its artificial ears. In the SoundCheck Microphone calibration editor, select B&K 4231 & UA 1546 ear adaptor for calibrating the B&K 4128 HATS artificial ears (similar in sensitivity to the B&K 4134 pressure mic).
2. Connect the left artificial ear into SoundConnect microphone power supply and the microphone power supply into the left input of the sound card.
3. Connect left output of the sound card to the left input of the amplifier.
4. Connect the left output of the amplifier to a good loudspeaker that will be used as the noise source. The loudspeaker needs to have a fairly flat frequency response from 100 to 10 kHz so that SoundCheck can equalize it to within +/-1 dB. It also needs to be fairly omni-directional so that the attenuation results are not position sensitive.
5. Run the Anechoic Room output calibration from the Calibration Editor to equalize the loudspeaker at 90 dB SPL.

You are ready to start the sequence. If you just want to look at stored measurement data, select Recall Data at the beginning of the sequence.

Further sequence development

This sequence has been designed for simplicity and has been written for one channel only. Ways in which you could modify or further develop the sequence include:

1. Measure both left and right earphones
2. Change the test level
3. Add multiple noise sources to create more of a reverberant field (e.g. sound coming from all angles). You may need to use a multichannel sound card for more than 2 noise sources. Make sure the noise sources are uncorrelated.
4. Measure attack & release time of the noise cancelling circuit using the Attack & Release optional module

• Level demo sequence to see how this is done)

Download Sequence Documentation (PDF)

Download Sequence (Zip file)

To run the sequence in SoundCheck, please save the zip file to your hard drive, then follow the instructions in "Sequence Editor: Exporting/Importing a Sequence' section of the manual. Download Manual.