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.

For more info see the Freqphase blog post on the JH Audio website.

Share | |
COMMENTS
donunus's picture

Oh my F^&% GAwd! Now I will need to spend money on these. It seems that IEMS have finally been perfected. Or is there still something wrong with them...

noahtheviking's picture

I bet it was suprising to hear some that were clean go jh

mward's picture

So is Freqphase built into every new JH13/JH16, or is it an optional feature? Is it shipping now? 

I couldn't tell from JH's web site. 

habu-joji's picture

Having a jh13 pro in production since a week or two, I asked jh's consumer service about it. 

They told me that every JH13 and JH16 Will now ship with the freqphase tweak. 

So for now, it's by default.

HammerSandwich's picture

"...time-coherence of around 100uSec..."

Where did this number come from?  I didn't see it in JH's blog post.

I realize that 100uSec represents a typical figure & that the phase shift varies with frequency.  However, JH's graph shows much better performance at higher frequencies & significantly more than 100uSec of delay at 20Hz.

100uSec also indicates an arrival-time difference equivalent to roughly 1-3/8".  That distance seems unreasonably large inside an IEM.

(I greatly hope that I haven't goofed up my arithmetic...)

Any clarification would be welcome, Tyll.

Tyll Hertsens's picture

Good question. I can only repeat what Jerry said. We'll have to wait and see what further info LH Audio puts out. What ever he did, it was audible clearer than the previous JH13 incarnation.

thune's picture

If I'm hearing it correctly from the video, Jerry says (at 42 seconds):

Basically what we figured out is; you have to have all the arrival times within a hundredth of a millisecond to have a coherent phase response in the ear-piece.

Assuming he didn't misspeak, this would be <10uSec.

HammerSandwich's picture

Yep.  Wish I'd watched the video before posting earlier...

Tyll Hertsens's picture

Yer right.  I'll change the copy.

zobel's picture

No doubt he uses an artificial ear of some sort, a dummy head? Is he really able to get good data above 2kHz? He also must use MLSSA to find excess phase so that positioning of drivers can be graphed without regard to frequency response.

Multi-driver systems in headphones, especially in big circumaural designs, have not been successful, likely due in large part to phase linearity problems. I wonder how the acoustic phase of single driver phones measure at the eardrum?

I've noticed when building loudspeakers, a good crossover will force the woofer and tweeter to be in phase throughout the overlapping stop bands of the two drivers, and when connected in reversed polarity, a deep null will occur in the frequency response at the crossover frequency.

On most of my projects, I found that reversing the tweeter's electrical phase and using a modified third order crossover, the woofer and tweeter are closer in acoustic phase than non-reversed electrical connections, due to driver offset, with the tweeter mounted further out on the baffle and closer to the listener or measuring mike.

There are other aspects to consider, such as lobing angles over the stopband, but like Tyll noted, phase non-linearity in loudspeakers is normal and not usually much of an issue in reverberant fields. Imaging may be slightly improved with linear phase,, but that is often washed out by recordings that are multi-tracked and multi-miked and anything but phase correct to begin with. Nearfield moniters are more like headphones, and having more linear phase is important for imaging and spatial information.

Tyll Hertsens's picture

When I visited him he was using a simple ear canal coupler. He's since improved the electronics from what I can gather. The unusual aspect of his measurement system is that it gives continuous readings so he can adjust the driver and bore geometries real time as he makes the physical adjustments. 

Don't know much more than that, but I do know he's got a pretty good grip on the technical aspects of his work.

dumbo's picture

 

Hi Tyll,

 I'm about to pull the trigger on the JH-13s but am also interested in the Ety HF-3's with custom ear molds. Would custom HF3's  have any positives over the JH-13s or would they be trounced by the big boys in every respect? 

P.s. Just to put things in perspective I'm  HUGE fan of the K701's and prize acurate no nonsense "analytic" sound.

Peterson245's picture

Wow, Its wonderful. He did a fantastic job. I am really impressed while looking Multi-driver systems in headphones, especially in big circumaural designs.

X
Enter your InnerFidelity username.
Enter the password that accompanies your username.
Loading