Hello All,
Now that I have a GRAS 45CA on my bench along with an AP analyzer I have been doing some catch up with what type of testing is being done with headphones. We are aware of the research that Harman has been doing and published AES papers. There is also an IEC international standard for headphone testing. I suppose that I will need to pony up and purchase a copy for my bench.
IEC 60268-7, Sound system equipment, Part 7: Headphones and earphones
Audio Precision is an industry leader in audio test equipment. GRAS is also an industry in sound and vibration measurement instruments. AP and GRAS are now under one roof and ownership.
AP has published an application note “Application Note: Headphone Electroacoustic Measurements”. You can download the Application Note at AP.com, you will need to sign up and log in to download.
So what needs to be measured? First off to be put on the list is Frequency Response, “Frequency response is the single most important aspect of the performance of any audio device. If it is wrong, nothing else matters.” (Floyd Toole, 2009)
I am purposely leaving out the “Harman curve” for future discussion. The Harman research speaks of speakers measured and equalized in the free field as being the standard that our ears are used to hearing. Assuming that to be the case, headphones that sound most like a set of those speakers in a “standard” listening room will be preferred by the large majority of listeners. Of course your mileage may vary.
AP says that the IEC standard address most measurements as being “Objective” as in being measured with calibrated instruments and coordinated with measured human hearing,
@overkilly will be pleased that the IEC standard allows some subjective equalization of frequency response curves. Human subjects do a qualitative determination of equal loudness of tones between speakers and headphones. This all ties back to laboratory quantified measurements.
This is a personal impression. The first Headphone thing to be included in the measurement report is Frequency Response. The next thing included should be some sort of equalization to bring the FR back to near the Frequency Response of free field equalized speakers in a “standard” listening room.
More of my musing; personal equalization curves are the last thing to measure and do not belong in a headphone measurement report.
Thanks DT
Comments about what should be measured and reported?