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Headphones sensitivity, impedance, required V/I/P, amplifier gain

Discussion in 'Sound Science' started by xnor, Jun 15, 2013.
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  1. ab initio
    I find myself digging for it a lot, too lol
  2. brunk
    Subbed, thanks for all the work Xnor.
  3. Dano91
    Those measurements for LCD-2 and LCD-3 seems strange to me. lcd-3 should definitely be more sensitive.. Maybe I'm wrong, but didn't you swap it?
  4. stv014
    It is probably mostly a result of random manufacturing variations. At InnerFidelity, there are several LCD-2 and LCD-3 measurements, and both typically vary in the range of 0.15-0.25 Vrms at 90 dB SPL, with the exception of one LCD-2 (older revision) sample that needs only about 0.1 Vrms.
  5. miceblue
    Yeah, Tyll has like 4 different measurements for the LCD-2 and all 4 are different. -_-
  6. xnor
    Yeah, if you compare the most sensitive LCD2 he measured with the one rev2 he measured you get about 6.5 dB difference.
    Difference between the LCD3's is about 4 dB. So all numbers are average, and as stated in #1, can be off by +/- 3 dB.
  7. sgrossklass
    Are you sure about K271/272 sensitivity? Going by Tyll's results, they ought to be at 107-110-ish dB/V. Spec is 104.
    Data for more / older headphones (usually spec, some measured) is available in ye olde sensitivity table in my spreadsheet department, along with a simple sound output level calculator btw. Maybe I'll port some of these to JS so they can be used online.
  8. stv014
    It could be 97 dB/mW (translates to about 109 dB/V) instead of 97 dB/V.
  9. xnor
    Fixed based on IF's measurements. Either seems to be something wrong with other measurements I've found on the interwebs or the drivers compress/distort extremely at "higher" SPL.
  10. Joe Bloggs Contributor
  11. imackler
    Thanks for the thread! Quick question: W/ the T50RP (and its many mods)... is there any science behind the idea that these headphones crave lots of power, like 2 MW per channel? Or do you think this is bunk? 
  12. xnor
    Careful, M means mega and m means milli. [​IMG]
    From the table in #1, Fostex T50RP need roughly 37 mW (milliwatts) or 1.4 V for 110 dB SPL.
    iPods output around 1 V (=> 107 dB SPL), Sansa Clip 0.5 V (=> 101 dB SPL).
    Those are peak levels with sine tones. The average SPL with real music is lower (see first post, subtract about 6 dB for highly compressed music, up to about 20 dB for uncompressed classical.)
  13. Bassman999
    Can you add Beyer 880 and 990 at 600 ohms?
  14. An00bis
    I've googled this for hours. What's the formula for the maximum SPL output of headphones?
    "Target SPL is 110 dB SPL."
    okay, but isn't that a bit high? the internet tells me that after 75-80dB permanent hearing damage can occur, isn't 110dB a very dangerous sound level?
    "The source is assumed to output 2 V. The amp is assumed to be a voltage source (0 ohm output impedance)."
    Fortunately my DAC has the same voltage.
    "Voltage, current, power are RMS figures."
    RMS? I have absolutely no idea what that means. I presume someone who knew what RMS meant would already know that voltage,current and power were "rms figures".
    "S@1V is the sensitivity with 1 V, 500 Hz sine wave input in dB SPL."
    Why 1V? Why 500Hz? If it's "@1v" does that mean that my DAC would have to be turned at 50% so the 2v output becomes 1v?
    "Z is the impedance at 500 Hz in Ω."
    if the source has "0 ohm output  impedance" then why is impedance even important here, or is this the impedance of the headphones? again, why 500Hz? What's so special about this frequency?
    "Voltage is the required voltage to reach the target SPL."
    what kind of voltage? the 2v from the source or the 1V from the "s@1V"?  if I turn the sound to 25% will the voltage become 500mv?
    "110 - (X + 20*log10(2 / voltage_required_to_reach_X_dB))."
    Wait... wasn't 110db the target db level? I see that the formula starts with 110-something, I presume the initial value comes from the 110db target, but then what does X stand for? am I supposed to replace 110 there as well?
    In another thread,where THIS WRONG FORMULA was posted: SPL (dB) = 20 log(Sensitivity * (Voltage (volts) * 2 / Impedance (ohms)) * (Max Output Voltage (volts) * (volume level fraction)^2) / (2*10^-5))  xnor (OP) wrote this: "Add to the sensitivity specified as x dB SPL/1 Vrms the following: 20*log10(V)"
    isn't that already in the formula? where should i put it? and what does V stand for? voltage? what kind of voltage? 
    how can we properly measure the sound level of headphones with a spl meter? should I just put a mike in the air and touch it with one headphone or wouldn't it be better to create a full-scale model of a human head made from tissue of similar acoustic properties to real flesh and bone, dig a tube that has the shape of the ear canal and put a microphone at the end of it? 
    everything is so god damn confusing! do I have brain damage or is this stuff simply confusing as hell? is this thread for the average headfi user or is it aimed at EE graduates? If so then why did you bother explaining the simple things like "The amp is assumed to be a voltage source (0 ohm output impedance)."? Those are things you learn in High School. On the other hand, everything else is very confusing. I wasted an entire day trying to figure this out.
  15. miceblue
    First of all, it says right under the chart on the first post:

    Source = DAC, so the DAC outputs 2 V into the amplifier, which is pretty common for DACs marketed for headphones

    Root Mean Square? It takes a 2-second Google search to look that up.

    How loud the headphones get with a 1 V input (usually it's measured with a 1 mW input) is the sensitivity of a headphone
    A quick 2-second Google search can demonstrate that too:

    Z usually implies the load impedance, which is the headphone

    It's how many volts (RMS?) it takes to reach 110 dB SPL (the target SPL as defined above)

    You're missing the context for that formula
    Gain ≠ target SPL; that formula is to determine how much gain your amplifier needs to reach X dB SPL (110 dB SPL is the maximum, so you can calculate the gain to reach 105 dB SPL for example)

    You're missing the context for that formula again
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