Matching low frequency response on both channels

[castleofargh]

Don't want to base everything on old news, but over the years I got the idea that Hifiman was among the worst in term on driver consistency. So maybe they needed to get rid of that issue so much that they have started to pay extra attention? In any case, 0.1dB is a pipe dream. If they actually said it, it's probably a lie.

But on average they are pretty well matched, I would say below 1 dB for most of the frequency range shown. It is extremely hard to impossible to have perfectly matched drivers just because of the physics involved. Also, remember that measurements have resolution limits (this rig had a limitation with THD, It cannot measure below 0.02%).

THD is irrelevant for a FR sweep. The main difficulty for me is to place the 2 drivers exactly the same way on the dummy head. And in most cases, we'll measure headphones with one mic on each side, so the apparatus also needs impeccable matching it rarely has.
But with IEMs like in OP's case, it usually comes down to keeping the insertion identical, and trying to minimize the variations from how the tips get in the "canal". 2 issues that a listener will also encounter, like headphone positioning.

 

[bigshot]

THD is irrelevant for a FR sweep. The main difficulty for me is to place the 2 drivers exactly the same way on the dummy head. And in most cases, we'll measure headphones with one mic on each side, so the apparatus also needs impeccable matching it rarely has.

I'm thinking that the deviation the OP is talking about might just be due to the things you mention there. OP, did you do multiple tests switching sides each time and averaging the results? I think multiple measurements might reveal a deviation in testing that accounts for your difference in response.

 

[carmatic]

I'm thinking that the deviation the OP is talking about might just be due to the things you mention there. OP, did you do multiple tests switching sides each time and averaging the results? I think multiple measurements might reveal a deviation in testing that accounts for your difference in response.

The tests I did were of 3 alternating insertions of each driver

The eartip was first inserted into the mic tube, it is a very tight fit so it stays in the tube for the duration of the test

then the driver is inserted into the eartip, and connected to the cable, and the sweep is recorded
followed by detaching the driver from both the eartip and cable, and replacing it with the other driver, and a sweep is recorded
then that other driver is detached
and the whole thing is repeated 3 times

 

[carmatic]

And part of the motivation of doing it was to document it for other people to follow, I only used a cheap desktop microphone glued to some tubing, and the software was also free, so cost shouldn't be a barrier for others to try it with their own IEM's

 

[bigshot]

How did you determine that you could hear the imbalance?

 

[carmatic]

As I said, they try and they do a good job at it. This is a graph of the Susvara, and they seem to do a good job:

that graph looks very attractive to me, especially since I seem to be more sensitive to low frequency mismatch
although the rest of the frequency response looks quite compromised, I will have to try them out myself to see if the experience of such a mismatch at the higher frequencies will be a bad one

::edit:: the only problem being that this is a full size headphone, not an IEM , and it costs 15x as much as the ATH E-70 which I currently own

 

[carmatic]

How did you determine that you could hear the imbalance?

I listen to bass-heavy music (example: https://www.hardcorepower.nl/) and play video games with explosions etc
at low frequencies, its equal parts hearing it and 'feeling' more of the intensity from one side
I spent many hours detaching the Etymotic drivers from the cable and blindly reattaching them without looking at their serial numbers, I really wanted to believe that maybe it's just my own hearing or something, but I could no longer deny that there was a mismatch, and so I set up this frequency sweep experiment to put some concrete data into what I was hearing

 

[KeithPhantom]

quite compromised

With over-ear headphones, FR is interpreted in a different way since they deal with Concha gain and other physiological amplifications in the process of the pressure waves reaching your inner ear. It isn't the best FR I've ever seen, but it is an example of how matched you can have your drivers if you really cared about this aspect in headphones/IEM engineering.

 

[carmatic]

With over-ear headphones, FR is interpreted in a different way since they deal with Concha gain and other physiological amplifications in the process of the pressure waves reaching your inner ear.

this is why I am a believer in IEM's , the less there is between the driver and my eardrum, the purer the sound

 

[bigshot]

I spent many hours detaching the Etymotic drivers from the cable and blindly reattaching them without looking at their serial numbers

How many trials do you think you did, and what percentage of time were you correct? Did you keep track?

this is why I am a believer in IEM's , the less there is between the driver and my eardrum, the purer the sound

Do you sit in the front row at concerts?

 

[carmatic]

How many trials do you think you did, and what percentage of time were you correct? Did you keep track?

like I said, countless times, in fact I have resorted to routinely switching the drivers so that the imbalance is on the other side so that it doesn't 'get boring'
The moment I can find an IEM with a guaranteed low-end match, I will ditch my current pair immediately

 

[carmatic]

Do you sit in the front row at concerts?

why would I wear IEM's when I go a concert? much less when I'm at the front row?

 

[bigshot]

You'll also want to be in the center, or the left/right balance will be off!

The reason the company won't cover it under warranty is that the problem you are describing in great detail should be well below the threshold of audibility. I'm thinking either bias crept in there somewhere or the imbalance between channels is much more than you think it is. I'd suggest double checking by testing multiple times blind without looking every time (get someone else to administer it to you) and to remeasure it several times to make sure it isn't just the way you have inserted the drivers in the holder.

 

[carmatic]

I want to look for new IEM's with matching low frequency responses, I don't want to mess around with my current IEM's anymore

 

[bigshot]

I'd suggest buying somewhere with a two week no questions asked return policy then.