CanJam at RMAF 2012 Show-Stopper: The Sublimely Transparent Freqphase JH13 and JH16 from JH Audio
Jerry Harvey Audio Freqphase JH13 and JH16
A little more than a year ago I started noticing that multi-driver IEMs had a lot of problems with phase shifting. It's very similar to the phase coherence issues that multi-driver speakers have; there's a section of John Atkinson's "Measuring Loudspeakers" that explains it quite well. Anyway, I measured a bunch of the JH Audio custom demo units borrowed from HeadRoom, and I noticed it there as well. I had a talk with Jerry about it a year ago, and he said it's sort of the nature of the beast.
Evidently, Jerry has had a brainstorm on the subject, and with the introduction of his new Freqphase products he's found a way to create multi-driver IEMs with a time-coherence of around 10uSec. The problem is that in the speaker world there is evidence that time coherence is of secondary importance. Here's a quote from JA's article mentioned above:
Floyd Toole, now with Harman International but then with Canada's National Research Council, in his summary of research at the NRC into loudspeaker performance that is described in two classic 1986 papers [32, 33], concluded thusly: "The advocates of accurate waveform reproduction, implying both accurate amplitude and phase responses, are in a particularly awkward situation. In spite of the considerable engineering appeal of this concept, practical tests have yielded little evidence of listener sensitivity to this factor...the limited results lend support for the popular view that the effects of phase are clearly subordinate to amplitude response."
This is also my view. Of the 350 or so loudspeakers I have measured, there is no correlation between whether or not they are time-coherent and whether or not they are recommended by a Stereophile reviewer. However, I feel that if other factors have been optimized—on-axis response, off-axis dispersion, absence of resonance-related problems, and good linearity—like a little bit of chicken soup, time coherence (hence minimal acoustic phase error) cannot hurt. In my admittedly anecdotal experience, a speaker that is time-coherent (on the listening axis) does have a small edge when it comes to presenting a stereo soundstage, in terms of image focus and image depth. But time coherence does not compensate for coloration, poor presentation of instrumental timbres, a perverse frequency balance, or high levels of nonlinear distortion.
Personally, I'm going to guess it may be more important in headphones than speakers as we hear so much of the direct sound without all the room reflections. Why do I make this guess? BECAUSE THE FREQPHASE JH13 I HEARD AT THE SHOW WAS JAWDROPPINGLY CLEAN!!! Every once in a while a headphone comes along that sounds better to me than anything I've ever heard before, and it's always a stunning experience. So it was with the new JH13 and JH16. My current JH13s are my favorite custom IEM; juicy and lush, they never fail to please me. With the new Freqphased JH13 some of the lushness was gone, but it was replaced with a sublime clarity I've simply never experience with headphone before. It was the show-stopper for me.