I’m thinking about measuring unit variation, checking channel balance, experimenting with physical mods, or EQing to various targets. Some of that wouldn’t need a measurement compensated to a standard rig, but just the same model measured on the kit rig.
In fact now that I’m thinking about it, the compensation wouldn’t even need to be published by Headphones.com if the standard rigs and kit rig measurements are. The kit rig users could do the required calculations easily if they wanted.
Oh, I see what you’re saying. Yeah no, it would make way more sense to supply a DFHRTF with any customized measurement rig than to try and calibrate a specific headphone measurement for that rig.
Before Harman, headphones like the HD600 and H650 were often used as benchmarks for comparing measurements. And they still are now. One potential problem with this is the effect of pad wear on the response of the higher frequencies (illustrated here). That could be mitigated though by using fresh pads for the calibration measurements.
There could be better options for this though.
I am basically just translating what Resolve and Cam said above. But for good calibration, what you probably need is a sound source that’s readily accessible, affordable, highly standardized, exhibits minimal unit and positional variation in its sound, that’s close to both the FR and acoustic impedance of the sound stimulus you intend to measure. For most people, this would probably eliminate free and diffuse field, since those require special gear and spaces for measurement.
If you’re using open headphones, then an open headphone that measures very consistently would probably be a good solution. If you’re measuring closed backs, then a closed back with good consistent sealing would probably be best.
Another option would be a pair of speakers with good directivity indices, EQ-ed to a specific in-room response, such as an approximately -0.85 dB/octave slope. This would require a dummy or real head and shoulders to interact with the sound field for the in-ear speaker measurements. And if you’re mostly measuring headphones, the acoustic Z might be a bit different.
I don’t know much about mics. But I believe @Resolve uses a blocked ear mic for some of his tests. Dunno what model though.
Renting (or borrowing?) a rig might be another option. Though there will probably be a learning curve at first to using one. I haven’t tried it, but miniDSP EARS might be another option with some possible uses for over-ears, according to Brent B.
This is also just my personal opinion, but I think it would also be to Headphones.com’s benefit to encourage and facilitate calibration to their raw measurements, where possible and applicable. Other graphers compare notes like this all the time when doing measurements. Especially when they’re first starting out, and getting up to speed with a new measurement system.
I’ll throw out a couple other lower-cost suggestions for possible calibration references, and maybe some others here can either agree, or disagree and offer some better alternatives.
For open-backs, I was thinkin of the Drop/Senn HD6XX, which is less expensive than the HD600/650. And for the closed backs, the new Fiio FT1 looks like it could have potential. Both are under $200, have good extension in the treble, and the cups look large enough to fit most ears. They also appear to have close to neutral tuning, though the Fiio looks a bit warm in the bass.
Still lookin for some other good (and maybe better soundin?) low-cost options. A couple headphones like these might get the ball rollin though.
In addition to the 6XX, the planar magnetic Fiio FT1 Pro is another relatively affordable open-back headphone that looks like it could have some potential for this purpose. Tuning also looks pretty good (though the “BBC dip” is pretty apparent in the upper mids).
After looking at some reviews of the Fiio FT1 and FT1 Pro, I’m somewhat less convinced that they might meet all the criteria for a good calibration reference. This would be due mainly to the design or size of the pads. But Resolve also found a noticeable left/right imbalance in the FT1 Pro he reviewed.
The 6 series Sennheisers still look like they could be one of the better options for open-backs, provided the effects of pad wear can be accounted for. Sennheiser’s mfring and QC usually seems to be pretty good. So maybe the newer HD 490 Pro would also be another good option. It’s hard for me to see where to find enough consistency though without spending a little more for better designed headphones along these lines. Or without making a few more compromises or concessions on the FR or “technicalities”. Most of the lower end headphones I’ve used have some potential issues of one kind or another with things like fit, cup size/shape, ergonomics, QC, L/R driver consistency, etc. that would probably make them a bit more questionable for use as a calibration reference.
The miniDSP EARS would also not be ideal for my measurement uses because it has no head and shoulders, and does not have as realistic ear canals or pinnae as some of the industry standard rigs. I wonder though if the default ears on this rig could be removed and possibly replaced with something that’s more effective along these lines.
Most here are probably familiar with the new HBK 5128 simulator that Headphones.com currently uses, and probably some of what makes it different than previous “711” rigs. Fwiw, this video explains some of the changes to the new Head Acoustics HMS II.3 LN HEC along a similar lines, including the new Type 4.4 pinna and more human ear canal (HEC)…
