This is a new version of the now deprecated “DFHRTFs Used at Headphones.com” post from Blaine, updated to reflect the newest information (and allow me to update it further in the future). For things that are unchanged I’m just going to leave what he wrote, but obviously some things have changed which I’ll touch on below.
I’m posting the HRTFs we’re presently using for compensation of headphone measurements, and their provenance.
Their data can be found at the Google Sheet here, or at the header links below.
4128 DF HRTF
This one is based on the kludgiest data we have currently. This DF HRTF was derived from the free field data that Brüel & Kjær make available for the 4128C with the straight canal pinnae, but it is limited in spatial breadth/resolution—it would ideally have more underlying data at a finer spatial resolution at the sides and rear, but B&K does not provide this data with the 4128. As you can probably see, it’s been smoothed a fair bit - variably by frequency - because the “free field” that B&K used for the 4128 wasn’t all that free, and there were meaningful modal resonances in the response. In the long term, this is going to be the most likely next target for replacement as a result, so watch this space.
5128 DF HRTF
This one also comes from the official data from B&K, which thankfully is a lot more actually free field this time. Both the 5128 and 4128 averaging math was done by the eternally lovely Oratory1990 in correspondence with Blaine LaCross, so big shout out to them both here! We’ve done a little bit of additional windowing manual smoothing to get rid of rockiness in the upper midrange and lower treble, because we think the compensation baseline for judging transducer-based devices should be reasonably smooth, as no one intentionally tunes a ‘rough’ response in their headphones, and leaving small wiggles in the response might make people assign undue importance to these features.
KEMAR DF HRTF using the KB500x pinnae
This was part of a group effort between Oratory1990, Blaine LaCross, and myself. Oratory1990 took the KEMAR with the KB500x pinnae attached to an HRTF measurement lab where we were able to get a full host of individual HRTFs for the head, and then he supplied Blaine and I with the resulting data. I calculated the Diffuse Field HRTF from the data, and then Blaine initially did some post-processing to get a result that made sense because, as you can see from the video here, WARNING: LOUD, the lab isn’t perfectly anechoic, so windowing was necessary to remove the influence of reflections below 2 kHz or so. However, I ended up rewindowing the results at a later date to get a cleaner/more accurate result. After all was said and done, we got a DF HRTF we are very happy with—much happier than when we were using the DF HRTF for the wrong pinna(!) for our data using this ear.
KEMAR DF HRTF using the KB0065/66 pinnae
This is probably the least often used HRTF since only I use this set of ears. It comes from the SONICOM HRTF dataset and was again calculated from constituent Free Field HRTFs by me. The measurement methodology can be found in part here, though there were a few things that had to be confirmed in private communications with the people responsible for measuring (many thanks to Isaac Engel, Lorenzo Picinali, and Ollie Turvey for assistance). In the SONICOM dataset, DF HRTFs for the KB0065 and KB0066 + GRAS RA0045 occluded ear simulator are measured, but we only use the DF HRTF of the former KB0065 pinnae because the KB0065 and KB0066 pinnae are actually asymmetrical, the clone rigs used by most people (eg. me, @MRS, and GadgetryTech) are actually solely based on the KB0065 right ear and an identical (but mirrored) copy for the left ear. This is another one we’re quite happy with.
Headphones.com IEM Diffuse Field HRTF (for use with IEMs measured on 5128)
A while back our pal Joel Merrifield did a mathematical estimation based on the human DF HRTF from ISO 11904 of what a DF HRTF using the 5128’s ear canal but human outer ears would look like, and this became known as JM-1 DF. However, we’ve recently taken the measurements necessary of the 5128’s ear canal—as well as accrued a much larger dataset of human blocked canal HRTFs—that’s allowed us to follow this theory to its logical conclusion. We’ve combined the 5128’s ear canal with the average human pinna effects (blocked canal DF HRTF) and the result we have is a DF HRTF that we think is ideal for IEMs—which are measured using the 5128’s ear canal, but judged via the pinna effects that human listeners expect. I go a little more into the specifics here, but realistically all you need to know is this is the most theoretically sound Diffuse Field HRTF baseline for compensating measurements of IEMs on the 5128.
∆ Headphones.com IEM Diffuse Field HRTF (for use with IEMs measured on 711)
I’ve mocked up a “delta target” based on an average of the differences of the type 4.3 (5128) and 60318-4 (711) couplers - this methodology in inherently and always inaccurate for any specific case due to the variation in output Z, but if you would like to see it anyway, it is included in the above spreadsheet.
This is easily the HRTF we are least happy with, but it has unfortunately become a bit of a methodological necessity. This is based on the Headphones.com IEM DF HRTF above, but altered with a delta calculation based on data from Oratory1990, csglinux, and Sean Olive measuring the difference between IEMs measured on IEC 60318-4 couplers vs. the 5128. We encourage people to be skeptical of results published with this baseline, or really any measurements of IEMs taken on IEC 60318-4 couplers.
If anyone has questions, feel free to ask here!