yuriv
100+ Head-Fier
- Joined
- Apr 30, 2008
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Hey Yuriv, it's Lachlan! Nice work on the measurements, I'm looking forward to seeing more results. We're discussing the EMI noise and your measurements in this thread, so it's nice to get some actual numbers.
Hi Lachlan and everyone else. I tried to measure the iPhone 6S noise on an analyzer with a lower noise floor than the Focusrite, but I didn't get anything conclusive yet. The noise is definitely there, but the voltages involved are very low. I'm currently evaluating a QA400 analyzer, and here's what it gets:
If I hadn't read about the the iPhone 6S's noise problem, I probably wouldn't have noticed it with my usual headphones and IEMs, and I wouldn't have dug up my UE600vi. In fact, I had to look up which IEMs on Inner Fidelity had the highest measured sensitivity to figure out which one to use. Their headphone measurement data sheets list how much voltage it took to produce 90 dB SPL. As far as I can tell, none of their headphones got a measurement lower than 11 mV rms, which is what Tyll got for the UE600 and a few others models. I suspect it takes even less than that because 11 mV could be getting close to the limits of their measuring system, the way it is set up. My scope can see a fuzzy waveform for a clearly audible 1 kHz tone that is in the hundreds of microvolts range. When I increase the volume, it's still well under 11 mV before it gets pretty loud on the UE600vi.
When I measured the noise on the Focusrite Saffire 6 USB last week, I boosted the instrument input gain to amplify the iPhone 6s's noise as much as possible to make it easier to measure. The 6S is very quiet when it's almost idle and the screen is off. If you short the inputs on the Focusrite, it gets the same measured noise as the iPhone. So the Saffire 6's noise covers up the true noise level of the iPhone 6S. Not so when it's on the app switcher.
Uncalibrated measurements on the Focusrite Saffire 6 + level meter readout
I included the Sandisk Sansa Clip Zip for comparison. On the UE600vi, I can hear noise from the Clip Zip, but it's a soft, constant background hiss, which is not as objectionable. Also, notice on the graph that the higher noise on the Clip Zip happens at lower frequencies, where human hearing is less sensitive. On the iPhone 6S's app switcher, the noise increase is where our hearing is much more sensitive.
Maybe I'll try a better preamp next time. Or I'll leave it to folks with more sensitive equipment to show how big the noise increase really is.
Band aids for those pesky IEMs
The humble voltage divider
I built the voltage divider I wrote about in a previous post and put it between the iPhone and the UE600vi. As expected, the frequency response going to the UE600vi is now much flatter, and the voltage going to it is down by at least 23 dB. The noise at the app switcher screen is all but gone. The down side is that you have to crank up the volume on the iPhone. But the UE600vi is so sensitive that I can get a satisfying level even without going to maximum volume. Maybe for another IEM, a 22+2 split works better than 15+1: less attenuation, but higher (2 instead of 1 ohm) effective output impedance. The humble voltage divider is a useful tool. It can even make a Pono or an AK100 sound good, but that's a subject for another thread.
About five years ago, when we had the iPhone 4 and Antennagate, Apple gave us free bumper cases so that we could get away with "you're holding it wrong." This time, I don't think they're going to give free voltage dividers to a tiny percentage of their customers. Such an adapter can be small, like the P-to-S adapter for the ER4PT. It would be nice if some outfit like Monoprice or Fiio would build one with four conductors so that the headset still works.
Another band aid is to use a headphone amp like a FiiO E5 or E6 for the attenuator instead of a voltage divider. Increase the headphone output volume to maximum on the iPhone 6S to maximize the signal-to-noise ratio (essentially using it as a line output) then cut the level on the amp. Here, the amp really isn't amplifying the signal voltage, but rather attenuating it. In the case of the FiiO E6, the UE600vi picks up a little hiss but it's not nearly as bad as the one on the app switcher. It's quieter if you use the not-so-portable O2. This will sound strange to some, but an HD600 makes the iPhone behave at its best, while you need an amp to make an SE535 sing.
6S, E6, UE600