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Headphone CSD waterfall plots

Discussion in 'Headphones (full-size)' started by purrin, Aug 13, 2011.
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  1. purrin
     
    Quote:

    Tyll's already got that covered. His square wave measurements look good.
     
    A nice square wave at 30Hz or 50Hz really doesn't say much. They are unique though to each headphone. I'm under the impression that some people think that a good looking square wave correlates with maintaining a low frequency or bass response. This is not necessary true! A square wave consists of the specified frequency and the summation of odd integer harmonics at successively lower levels, going on to infinity. Square waves do not happen in nature. You pull a third or fifth harmonic out of phase slightly, the square wave collapses. Other than determining how damped or over-damped a driver is, they are not that useful (at least from a speaker builder's point of view.)
     
    I remember when the LCD2s first came out, and one of my first impressions was that they sounded slightly over-damped (meaning the signal had little ringing but probably didn't reach its theoretical high and low levels.) Of course someone would slap the perfect looking LCD2r1 square wave measurement in my face and tell me I was wrong. The funny thing is that square wave measurement definitely showed the LCD2r1 was over damped! IMO, a little bit of extra ringing in the square wave to allow the high and low level peaks to reach closer to their potential is preferable to nice almost perfect squares with little ringing.
     
  2. Reticuli2
    Fascinating.  The LCD-2 doesn't look overdamped on any of Tyll's measurements, but that might explain some of the DT1350's very nice square waves but slightly overly damped, restrained impulse response. And the Shure 535 amazing waveforms and very overdamped impulse.  In the case of the Fostex, stock there appears to be a very near-term reflection on the impulse that crushes the initial wavefront.  So it comes off as "overdamped" (???) on its impulse then very slow and oddly smooth & rounded on its 300hz waveform.  The Smeggy Thunderpants seems to have moved that first bounce further into time and suppressed it a little, letting the initial impulse go full length without overdoing it.  That's pretty amazing that the LCD-2 and the Smeggy mod both have such low distortion, fairly neutral balances, un-supressed impulses, and still have square square waves.  They seem to be in a class all their own.  The next tier looks to be the HD800 (maybe in a class all its own amongst dynamics?), ER4, Q701, the T1, and followed by a bunch of other IEMs with less balanced responses but otherwise nice measurements.
     
    Maybe you just heard the LCD-2 as dark.
     
    "Tyll's already got that covered. His square wave measurements look good."
     
    Right, hence the need to get him an ESP to test.  Hopefully that's one of the stats he's getting ahold of.
     
  3. arnaud Contributor
    I agree that I don't see the value of a step response be it repeated at 30, 50, or what not Hz to see the low frequency behavior of a driver. A step is fundamentally the same as an impulse, it is a broadband excitation and the higher the bandwidth of the headphone response, the closer it will be to the original step. I don't see how this relates to low frequency response. But I am no expert in headphone measurements so could be missing something.
     
    Quote:


     
     
  4. arnaud Contributor
     
    Quote:

    This is still being worked out. One possibility is that Purrin's test does not actually pull the resonances from the earcup as "naturally" as Tyll's dummy head test. I don't reveal his trick, you'll have to pull his nose. Second possibility is we're seeing the first modes of the (small) test cell in which Tyll is doing the measurements (it's probably not truly anechoic until 500Hz or 1kHz).
     
     
  5. arnaud Contributor


    Quote:
     
    Absolutely correlated. Resonant frequency is the octave band where it occurs (e.g. 2kHz). Ringing relates to the damping of the resonance (e.g. 2ms of so called "reverberation time" or "time day"). Typically, you should see a correlation between how sharp the resonance is (in the freq. domain) and how long it takes to settle (in the time domain).
     
    BTW, as mentioned by Purrin, these resonances can come from the transducer, or enclosure, or a coupled driver-enclosure resonance. It gets messy with headphones as there are front and back chambers, partially opened design, all kinds of latitude for the designer to tune the resonances. As for tuning the damping, it boils down to material properties for the driver and acoustic lining (ear pads and others) / grill mesh / leakage from the open headphone. 
     
  6. purrin
    I'm creating a special mount right now to take the Grado cups out of the equation. If you see posts soon, that means I'm at least partially successful.
     
  7. Reticuli2
    Is there such a thing as too tall/big of a simple impulse response, or are you just looking to make sure it's not way over damped and that it settles quickly?
     
  8. purrin
     
    Quote:
     
    Personal preferences come into play. Trying to max out a step response with insufficient dampening will cause oscillations and ringing. It's kind of like setting up a car suspension. Worn shocks and you bottom out and bounce all around.  
     
     
     
  9. purrin
    IMPORTANT NOTICE: I corrected a bug in my program that made headphones with closed or semi-closed characteristics look worse than they really were. Sony XB700 and Koss DJ100 owners can now rejoice! I've gone back and made all the appropriate corrections to the graphs.
     
  10. purrin

    SR80i Cups

     

    Stock Plastic

    SR80.txt.jpg
     

    Martin Custom Audio Wood Mushroom Cup

    That 2k ridge can probably be tamed with some felt lined inside the cup. The second ridge past 5k stops at 2ms where the energy gets distributed. On the stock cup, the ridge extends for another 2-3ms. Is the Grado wood cup magic is a result of the resonant chamber created by the cups? Also note some of the 9k ringing is gone (compared to stock plastic cup or liberated driver.)
    SR80iMartinCustomShroom.txt.jpg
     

    Stock plastic cup, grill removed, inside lined with 2mm foam flush with inner cup

    SR80iGrilledremovedinsidelinedwithfoam.txt.jpg
     

    "Liberated" SR80i driver

    SR80iLiberatedDriver.txt.jpg
     

    SR80iCompare.gif

    Black - Martin Custom Cup w/ comfy pads
    Red - Stock Grado Cup w/ comfy pads
    Purple - Liberated SR80i Driver.
     
  11. 200poundsofamp
    Could you post the full graph of LFFs mod, or is the <1k stuff not very different from stock?
     
  12. JamesMcProgger
    Purrin, i like what you did with the SR80.
     
    is the "Martin Custom Audio Mushroom Cup" a full shell or only the outer cup?
     
  13. Anaxilus
    Hmm, still something looks off about the DJ100.  I wonder if it's not sealing w/ those angled pads because they should have more present and impactful bass than the HD558.  Unless I had some odd gear synergy w/ them.  Honestly they should sound better than the low end Grados.  I'll need to have a listen to them again and see whats up.
     
  14. purrin
     
    Quote:


    I didn't apply compensation for the DJ100 graphs so the low end FR at t=0 on the CSD shows lower than it should be.
     
  15. purrin
     
    Quote:

    It's a full cup. I had to "liberate" the drivers from the plastic cup to install.
     
     
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