Headphone Benchtest
Headphone Benchtest NIGEL JOPSON conducts a group test of eight headphones
/ Audio Precision AECM206 Headphone Test Fixture
T
his is our second headphone group test, and we’ve put into practice some of what we learnt from the first test we staged in Resolution V15.8. We’ve focused on the type of headphone which might be chosen by production pros as a reference when mixing, and this time we’ve also included open back headphones in the test. We took a straw poll of several audio pros, and found that most were willing to commit at least £300 to a ‘benchmark headphone’ purchase. Accordingly we tested a group of cans in the £200-£1,600 range. Headphone measurements are taken at what is known as the Drum Reference Point (DRP), a point representing the human eardrum. In other words, for a headphone to sound like a loudspeaker with a flat frequency response to the human brain, it must produce a frequency 26 / April 2019
/ APx analyser & APx1701 Transducer Interface
response curve like Figure 1b. This frequency response curve is a correction curve, or transfer function, that represents the effects of the torso, head, pinna and ear canal.
For our 2016 test, we used ‘Kemar’ a very expensive Head And Torso Simulator (H.A.T.S.) manufactured by Danish company G.R.A.S. Sound & Vibration. Basically a dummy head and torso with a couple of measurement mics installed where the ear drums should be. The torso is necessary for many statutory tests manufacturers of headsets are required to perform. Anatomically flesh-correct though Kemar was, I found it quite difficult to ensure a tight fit for all headphones on his crash-dummy head. With open-backed headphones, there’s also the issue of picking up low-end rumble or squeaks within the testing room — a H.A.T.S. would probably be in some sort of anechoic environment in a lab. Audio Precision to the rescue! AP very kindly loaned Resolution an AECM206 Headphone Test Fixture, introduced in June 2017 ($11,232), a more compact — but incredibly heavy — fixture mounted on a resilient base to isolate ambient noise. Equally capable in both R&D and production test applications, it is well-suited for testing circum-aural, supra-aural and intraconcha headphones and earbuds. The AECM206’s high level of acoustic isolation also enables the measurement of noise-reduction performance of ANC (Active Noise Cancelling) headphones, as well as the evaluation of hearing protection ear muffs. Importantly, the compact size allowed me to place the AECM206 in an iso-box while performing frequency sweeps and sine wave tests. I also found the design made it easy to ensure a tight