Earfun Free Pro 2 - "smooth" tuning (Patreon)

Update: this tuning has been replaced with the “neutral” tuning to be found here: https://www.patreon.com/posts/60665035

Only difference is the name and the extended range of available resonance frequencies. At the same time I tweaked bass a bit for an even flatter response.

I have finished my personal tuning for the Earfun Free Pro 2 which is optimised for a 6100Hz ear-canal resonance. All other tunings for other resonances will follow bit by bit and will be added within the attached txt-file.

To let you know how critical it is to select a tuning as close as possible to one's resonance, I prepared some measurements demonstrating the responses with 100Hz offsets up to 6300Hz in green and down to 5900Hz in red. 

I can actually reproduce these values by pushing it either deeper or try wearing it more shallow than I usually do. The effect for wearing it "wrong" are easily hearable for me, if I wear it more shallow or deeper the first effect is upper treble starts to lack then, the definition gets lost, and I start hearing some slight harshness, similar effects you also get by repositioning an over-ear to find the sweet spot. 

Here a measurment of my reference unit for left and right overlaid with the Harman target: 

compensated for the Harman target:

Some words about the tuning: I called it "smooth" because when playing pink noise it should basically sound like a constant flow with no frequency really sticking out. There is a slight bias towards 8-10K this is the coloration of pink noise you would get when listening to speakers in front of you more or less as some kind of perceived average, I didn't want to reproduce this perfectly as it is very tough but rather opted for an overall coherent and smooth image. Try playing pink noise and if it's not smooth, but you hear some scruffines or harshness you know that it's not the desired response you are getting. I could have tuned it strictly towards the Harman target and had a version like this before, here both versions overlaid with green being the "Harman-tuning":

To my surprise I really enjoyed that Harman tuning in the beginning and somehow approached it on my own at least with upper mids and treble, but the more I listened the more I heard some harshness, as I also had the bass manually readjusted towards that target the overall sound lacked body, appeared too bright and it was simply not smooth overall neither did it capture the character of a fronal standing speaker, the perceived spectrum was scruffy, although not totally bad, it was not a continuous spectrum. I had to depart from the target mainly in the region of 6-9khz and tune by ear in this area, to compensate for the reduction I needed to boost the area around 10khz to make the sound coherent and similar to before again. The upper bass hump compared to Harman is actually necessary to give the sound some body and the overall balance sounds way more similar to what I get from a flattened HD600. The bass would maybe need further work but it already reached the maximum limit of -12.99dB reduction. The overall color of both headphones appears similar to me they differ within some slight details and in overall smoothness. I actually prepared a tuning for my HD600 which sounds pretty simialr to this here bit it needs like 20 filters to get rid of all small resonances. If you switch from a HD600 to the Earfun (assumed you use the correct tuning) it should still sound alike, just better, way more transparent and detailed, the effect is actually quite stunning, every other headphone will start sounding off. 

Here a measurement of my second (brighter sounding) unit:

There is some slight imbalance on both, but not something one would notice without a direct comparison. Thanks to this imbalance they have a different imaging, but both sound "realistic" to me, sound stage is amazing with both of them.

Here both units overlaid with both channels averaged together with the Harman target:

The biggest difference between both units is this "hump at 10k, it makes one of them a tad brighter, a bit more than this and it would be too bright, you would start hearing it as a peak, which fits into the tuning though, it doesn't stand out and sound out of place, but from some certain point the response will start losing its smoothness if the peak became even higher on other units. This could be the only bigger "issue" between different units, and some deviation in upper treble, some units may need a bit more uppter treble boost others less maybe, you need to adjust this to your taste and unit, I tried finding values which would fully satisfy me, not being too bright not being too muddy. The same settings work actually for both my current units although one will still appear brighter, it's not to such a degree it would be annoying, the other unit compensates with more upper treble instead. The settings are still easily adjustable for some further tweaking and I will make a separate post on explaining them again when everything is done.

For me personally this is the best result so far I have managed sound wise. I listened to some of my older tunings for the Free Pro and my first OE tuning, and although they sound a bit strange to me now, they are not bad in such a way that they would contain errors. They have a color which one may like or not, but I was not annoyed by any of them. All of them were far worse than this one here, which sounds simpy "correct" for me. 

It may sound weird, but this is the closest I can imagine in "transparency", the sound immediately reveals if a recording is decent or bad and I simply cannot listen to modern badly recorded pop music anymore as you hear every clipping and distortion issue, besides most recent recordings are just way too boomy. Because of this I started to create my audiophile collection playlists every 2 weeks to have some music collected which is really recorded on a high level and this tuning should in fact reveal all differences, given that you get more or less the same result as me. The only limit right now is the hardware (I don't know if a high-end 8-driver IEM with exactly the same response would sound any different, there is no proof for this) and the other limit of what could be maybe possible is the Bluetooth codec. I personally haven't noticed any issues yet streaming from an iPhone, but for Android it may be advised to disable AAC and choose SBC instead as the SBC codec implementation for the Free Pro 2 is really good, it was also the reason why I let SBC disable completely for the Free Pro OE version, because it was full of artefacts. The Free Pro 2 on the other hand plays clean with AAC and iOS now thank godness.

I will start creating all other tunings when I received my 3rd sample, will average the responses of all and use this as target for tuning. I cannot promise that the results for other resonance frequencies will be as good as my own as I cannot verify them by ear and need to rely solely on meaurements without knowing exactly if I may surpass that line or not and by much to make it still appear similar, I cannot guarantee I will manage as I simply cannot hear if a slight hump here or there isn't already too much. Give me some time please as I want these results to be as good as possible.

Those who had the chance to try the tuning out and have a similar resonance frequency to mine, please give me your thoughts. I wouldn't advise the others to listen to it yet if my resonance doesn't match your own as the results will disappoint you. I am not even sure if you will like the final ones and if my theory so far will really work out, let's hope so!

Also worth mentioning: I created this to be listened at levels around half or slightly below but it is not a tuning for high levels. You would need to adjust the spectrum for high levels and reduce treble. Just try playing pink noise and start increasing volume until you won't get any additoinal detail more within treble, above that level it should only become louder overall all further steps can start appearing too harsh. A real dynamic loudness compensation would be of course the crown.

If there is enough interest I could also try optimising a strict Harman tuning, as I could imagine that my own target won't suit everyone especially depending on how far our HRTFs differ, you may want more 5k boost, while I perfer rather a reduction here otherwise I perceive it as resonance. I could also offer other "flavors", so that you would basically get a completely new headphone every month... 

Update: I was fighting with trying to optimise the sound during the the last days and updated the current tuning  (all previous versions can be find in the archive).

Meanwhile I also got my 4th unit, but didn't even have the time to unbox and test it yet, as I  was fighting with getting the final response as perfect as possible. Here you can see a older measurement of all 3 units (both channels averaged for each unit), these measurements are not up to date anymore, but should demonstrate the sample variation well:

I managed to smoothen the response even more in the meantime and had to reduce 6K and 9k way more than before. I will post a more detailed desciption about the issues I am having with the final tuning. You can notice that most variation is above 13khz. I tried to find a setting which would sound decent with all 3 units, but some units may need additional adjustment from your side. I tried filling up the dip at 13khz to get closer to the Harman target, but this didn't sound good, you may still want to play around with the 12775, 13250 and 16000 filters depending on how much your unit differs. I had to boost 16000Hz to +5dB on one unit, while reducing it to +4dB for the other 2 units. For those who still hear above 20khz, you can fine tune that area on your own to your taste. I I wanted to finish the entire tuning process by the end of this week, but I probably won't manage, Please be patient, it's a tough project which I underestimated a bit.