Measuring Headphones Using a Head Microphone
The most important thing in a good headphone measurement is to use a proper head microphone. We use a Head Acoustics Artificial Head Measurement System to perform headphone measurements in compliance with industry standards. Wolfgang, as we call him, has soft outer ears just like you and I. The material is designed to have the same acoustic absorption characteristics as human skin and bone. Wolfie has ear canals, too. At the bottom of each is a calibrated instrumentation microphone. When we place a pair of headphones on this head, the overall acoustic coupling to the microphones is just like it would be on the "average" human. The acoustic response of each head is measured before leaving the factory and calibration curves are sent along with each head. We use these curves to subtract from our measurements to get our reference for "flat".
We also have to make sure everything is very quiet around the head. We have a small anechoic chamber in which we mount the head and other required equipment. The anechoic chamber prevents sound from the headphones from getting out into the room, bouncing off a wall, and then coming back into the headphone and disturbing the measurement.
Analyzing the Microphone Measurements
The test signals are generated, and the microphone return signal is analyzed by an Audio Precision System Two Cascade audio analyzer. The headphones are driven by a HeadRoom Max headphone amplifier. All measurements are done with the volume at the headphones at 90dB SPL@1kHz. A Sound Pressure Level of 90dB is a little louder than normal listening volume; headphones should be able to reproduce well at this level.
When we perform a headphone measurement we carefully place the headphone on Wolfgang; close the door on the chamber; punch the "go" button on the computer that controls the Audio Precision; the AP executes the measurement script, sequentially performing the tests. When it’s all done, the data is saved to a folder and then uploaded to the website for display. Pretty simple really, once you’ve figured out how to do it---which wasn’t quite so easy; but it was fun.
Headphone Single-Point Specifications
On the specifications tab of all product pages, you will see single point specifications, such as impedance, isolation, total harmonic distortion and other data points. Single Point specifications are provided by headphone manufacturers. See our Glossary to learn more information about headphone data.