New portable headphone measuring setup

Discussion in 'Measurement Setups, Systems, and Standards' started by La Cenric, Dec 13, 2018.

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  1. La Cenric

    La Cenric Friend

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    Straight to the point, I'll be attempting to head into the headphone measuring game. A bit of new territory for me so looking for some additional pointers/advice from the measuring heads here (@Hands, @purr1n, @cskippy, @ultrabike etc. feel free to chime in).

    Current setup with HD800:
    01b7c6b94e0e560359fa359d8e64e136a402bef3fc.jpg

    Reusing my IEC microphone to mimic the input/transfer impedance of the inner ear per Bruel & Kjaer's researched recommendations. Can't find a ITU-T P.57 compliant ear (or relevant clone) so I've resorted to using the MiniDSP EARS for now. A bit of a placeholder in that regard, at least until I can find something more accurate.

    Additional purpose is to be portable hence the foldability:
    014322b143fe7926ab9c4045eec52b01e7893f83ec.jpg

    Procedures and settings are similar to that of my IEM measurements (also shameless plug to my subreddit where I'm updating measurements/impressions more frequently) though I will be running the headphones off of a iFi Micro iDSD BL for power and SPL reasons. Due to the equipment (literally a phone) and the environment, I'll only be taking frequency response measurements. Also, probably only right-channel measurements due to ear used.

    FR graphs acquired, processed from raw data gathered by an iPhone 7 Plus on the AudioTools app and subsequently generated with REW:

    HD600.png
    Sennheiser HD600

    HD650.png
    Sennheiser HD650

    Sennheiser HD800 with SDR

    The data should be closer to that of Innerfidelity's raws, Rinchoi's raws, Stereophile's data, Clarity Fidelity's rig or RTing's stuff. Looks pretty good with the HD650, though the HD800 graph has me scratching my head a little.

    I'll be heading out tomorrow to get more measurements of other headphones for testing and calibration (feel free to request any) but once all my hardware and settings are finalised, I'll go out full-force with the data collection.

    Raw data can be provided if needed, just ask.
     
  2. purr1n

    purr1n Finding his inner redneck

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    Are you mounting the microphone flush with the EARS or using some of the canal? Taking a wild guess here that the microphone you are using is mounted flush.

    The HD800 measurement looks like the microphone may have shifted. The EARS when used with the included microphone as-is in the canal has a high Q resonance around 4.5kHz. When the microphone is flush mounted, this resonance goes away (per @Hands' results). I would expect that if the microphone fell back a little creating a canal, but of shorter length, the resonance would come back at a higher frequency, i.e. 6kHz per your HD800 results.
     
  3. La Cenric

    La Cenric Friend

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    I did some extra measurements if anyone needs a reference point for where I'm going with this. Some are unusual/niche models since I just wanted to try them, but again just request for something and I'll get right to it.

    Audio Technica ATH-ADX5000
    ADX5000.png

    Final Audio D8000
    D8000.png

    Focal Utopia
    Utopia.png

    Klipsch HP-3
    HP3.png

    Meze Empyrean
    Empyrean.png

    Sennheiser HD800
    HD800.png

    Sennheiser HD800S
    HD800S.png

    Stax SR-L700
    L700.png

    @purr1n I am using the IEC-provided external canal simulator so the EARS canal is effectively bypassed in this case. The only "component" of the EARS I'm using is its artificial pinna. The 6k spike on the HD800 measurement doesn't seem to be a consistent resonant artifact of the system (as shown in the re-measurement above) and should be part of the transducer. Also seems to be consistent with current reports of the HD800S having a lower 6k spike, per the comparison plot I made below:

    HD800 vs HD800S
    HD800vHD800S.png
     
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  4. Superexchanger

    Superexchanger Friend

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    Thanks for providing these data for our review. If you'll indulge a basic question, can you take a stab at what's responsible for the variance of the response in certain frequency bands only depending on placement (c.f. Empyrean varaince 4k-10k, 800S 10k-20k, & the near absence of variance in D8000 over the whole sweep).

    My uneducated guess is standing wave behavior modulated by the pinna/pad volume, giving each model some characteristic range of position-impacted frequencies, but fails to explain why the D8000 would be so immune.

    Not really an issue since averages are given, but the physical reason for this type of thing is interesting to me.
     
    Last edited: Aug 21, 2019
  5. cskippy

    cskippy Creamy warmpoo

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    That notch at ~2.5kHz looks like concha gain to me. Try removing it with a calibration curve and updating your measurements. I feel a lot if your measurements have excess energy in this area.
     
  6. La Cenric

    La Cenric Friend

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    Update: just received the full GRAS 43AG-7 set, so now I'm all set to start building my headphones measurement database. This is the setup:

    [​IMG]
    GRAS KB500X artificial pinna > GRAS RA0402 pre-polarised "high resolution" IEC60318-4 coupler > B&K 1704-C-102 CCP signal conditioner (powered by separate USB bus) > Motu M2 audio interface > PC (REW)

    The foldable mounting system in the first post has been repurposed to accomodate the RA0314 cheek plate to keep everything as portable as possible. That said, the whole setup doesn't look too portable as it is right now, but after a bit of velcro and tetris-ing each of the components into a half-decent singular block, I should be ready for heavy-duty data collection.

    I'll be replacing the laptop with a smaller 8" one as well, one with more than one USB hub (curse you Microsoft) so that I can power the signal conditioner off the laptop itself rather than requiring a separate power source. Yes, the Micro Black Label in the pic above is being used as a glorified powerbank. Don't judge.

    Measurements obtained from this setup will be compatible with most academic target curves, most notably the Harman Target and KEMAR-based diffuse field measurements. That said, I'll be using my own "proprietary" neutral target curve when publishing these graphs (basically flat in the bass till 1kHz, then Harman OE for the rest), though compensations to other targets will be made available in the future on my website's graph comparison tool.

    Measurement procedure:
    1. CCP conditioner at x1 gain, interface at 50% gain
    2. Levels normalised to -20 dBFS
    3. 1M sequence length @ 192kHz sample rate, 2 sweep average
    4. Each channel is measured 3 times, each time taking the headphone off the rig and putting it back on. Positions are not forced to be "intentionally different" so as to simulate natural placements.
    5. All .mdat data is saved, though due to the noisy measurement environments the other non-FR metrics may not be very useful and so will not be published.
    Here are 6 preliminary graphs of the Sennheiser HD600, HD650, HD800S, Focal Clear, Audio Technica ATH-M50X and Hifiman HE1000 V1 after 6 hours of testing and trial-and-error. The first few months with a new rig are always the toughest...

    HD600.jpg
    HD650.jpg
    HD800S.jpg
    Clear.jpg
    M50X.jpg
    HE1000 V1.jpg

    Will gather more data soon, so stay tuned.
     
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  7. La Cenric

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  8. nishan99

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    Any idea why the Verite measurements are this inaccurate in the treble region?

    • 5k peak should be 6.2k
    • 11k peak should be 8k instead of the big dip
    • 18k peak should be 14k

    Am I missing something here? because that's what I am hearing with my pair.

    Is it the positioning of the headphones that can cause those shifts or is it something else?

    [​IMG]
     
  9. La Cenric

    La Cenric Friend

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    Perceived peaks and dips in a headphone are dependent on your pinna structure (also canal structure).

    I don't claim to have accurate measurements even on this industry-standard rig (no rig, not even the new B&K 5128, will ever get 100% accurate measurements for the reason that they typically approximate a human head), but rather I focus on precision, repeatability and comparability between each measured headphone. Hence, the creation of the graph comparison tool.

    So while you may not agree that the Verite graph I generated has the exact peaks and dips that you hear (for instance, the KB5000/KB5001 artificial pinna has a known null at 8-9kHz, something that may not be the case for your specific ear structure), you can at least infer that the Verite would be relatively recessed in the 1-4kHz regions in comparison to a HD600, and also have a greater 5-6kHz response in the same comparison.
     
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