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Could somebody please confirm if the sensitivity is in dB SPL/mW or dB SPL/V? On the box it says that the EFFICIENCY is 93 dB, but here it says that the SENSITIVITY is 93 dB.
I asked this question some time ago and never got an answer.
I can tell you that the math only makes sense on these things if it's efficiency (dB/mW). That's the assumption I've been working from.
If it's sensitivity (dB/V) you need an amp that can drive 35V at 1A to kinda drive them properly. 35V*1A=35W, or is a loudspeaker amp to those who don't speak audio math.
If it's efficiency, you only need to be able to drive around 6V-8V @ ~200mA. Practice tells me this is closer to the truth as well. O2 drives them wonderfully and it lands right in that range.
Thanks for the reply, what you said totally makes sense and I was thinking along the same lines. Massdrop should take this seriously as this makes a big difference in whether an amp that someone has can drive it or not.
How does one determine the efficiency from listed amp specs (posted mine below)? If my amp is loud enough, is it possible that I am missing out on some of the spectrum or detail? Why do they make this so hard to understand? Ahhh.
Schiit Magni 1 Specs:
Frequency Response: 20Hz-20Khz, -0.1db, 2Hz-200KHz, -3dB
Maximum Power, 32 ohms: 1.2W
Maximum Power, 50 ohms: 1.0W
Maximum Power, 300 ohms: 260mW
Maximum Power, 600 ohms: 130mW
THD: Less than 0.005%, 20Hz-20KHz, at 1V RMS
IMD: Less than 0.007%, CCIF
SNR: Greater than 100db, unweighted, referenced to 1V RMS
Crosstalk: -70dB, 20 Hz-20KHz
Output Impedance: Less than 0.1 ohms
Gain: 5 (14db)
Topology: Fully discrete FET/bipolar, Class AB, DC coupled throughout
Protection: standard failsafe DC power input and muting relay
Power Supply: “wall wart” style 16VAC transformer, regulated +/- 15V rails
Power Consumption: 4W
The efficiency is a headphone spec not an amp spec. What you have to do is use the impedance and efficiency/sensitivity, output power of the amp, and some logarithms to determine if you're reaching a sufficient peak volume to fully reproduce the signal. From there the only guess work is in whether or not your amp can supply the necessary output current to drive the load since the output power is typically limited by the V rails rather than the Iout capacity. I'd need to know which headphones you're talking about to crunch the numbers, or you could go look up the reddit/r/headphones calculator spreadsheet and fill it out yourself keeping in mind that different people have different ideas on what "fully driven" means.
Having your amp be "loud enough" is not a good indicator that you're getting everything in the signal. I can make my HD6XX "loud enough" using my phone, but I must say that it sounds terrible.
Why is it so complicated? Because engineers don't often consider trying to make things as simple as this easy for those without the same mathematical backgrounds. There's been an interesting set of articles ongoing on innerfidelity by Bob Katz discussing this very topic. Look got thr "How Insensitive" series.
If headphone manufacturers were to use units of X dBSPL for Y dBu to indicate sensitivity/efficiency rather that dB/mW or dB/V and amp manufacturers were to follow suit and use dBu to indicate their output power, the math becomes simple addition which most folks can manage. That's the short version, but I'd encourage you to read the articles.
I currently have a Fiio E10K, which can drive HE4XX to 115dB. Do you think getting an O2 amp will make a big enough difference? I am currently [after a burn in of 25 hours] quite disappointed by how narrow the soundstage of HE4XX is (though, I am coming from HD598), and I am wondering if Fiio E10K is the problem.
Really appreciate your describing this topic in a little more detail and pointing me to resources.
By the way, the headphones I'm discussing are these, the HE4XX.
Here's my take that others are free to argue, and I know there are those in the audience who will.
You need to be able to get higher than 120dB due to sporadic high level transients that show up in tracks fairly often. O2 will definitely get you there for HE4xx. You do not want to listen at that level for any sustained period of time though. Its sound stage on O2 is fairly flat as well but compared to HD6xx, for example, HE4xx's sound stage is enormous and O2 is all I'm driving them with. O2 sounds quite good, but it doesn't have the sound stage that some amps do. I don't know of anything that beats it for the money though, unless you build it yourself.
Well rather than running the numbers through my calculator, I can tell you it certainly has sufficient voltage levels to drive the HE4xx, but I can't say anything about current. These need at least 200mA of output current output to fully drive them to my standards. I'm not sure what kind of components they use as the output stage for your Magni1 or I could give a better guess.
Try it out and see if you like it ;-)
Thanks for your reply, even though NwAvGuy did say (here: http://nwavguy.blogspot.in/2011/09/more-power.html) that 110-115 dB was enough with 120dB being preference of the purists, I do feel that the superior quality of O2 over E10K should make a difference, and I also read people being disappointed with the performance of E10K with HE 400i, the flaw of recessed mids being my experience too.
I joined the Massdrop O2 drop, thanks again.
You can try cranking up the volume. I find that the mids are much less recessed when you're listening quite loudly. They really do clean up a lot with some volume.
NwAvGuy also indicates that peaks of 30dB above your RMS listening levels are quite common. I don't consider it fully driven until you can cover 90dBSPL rms which puts the peaks at 120dB with some overhead. Running too near to the rails causes distortion in the signal so I prefer to have some overhead. I know, 90dB is pretty damn loud, but sometimes I just really get into a track.
If you go deaf, at least you can keep educating us on amp power requirements! 😂
Based on the [genius] power requirement spreadsheet, Magni 1 with HE4XX is in the green. Thanks again.
@Heefty from time to time the volume returns to the right earcup but its still crackling as hell. Its impossible to listen anything with that much distortion and noise from the cracklings. Its like you have blown your subwoofeer and trying to get some sounds out of it. Ive contacted both Massdrop sup team and Hifiman supports. For now noone have answer me and im starting to panic :(
Take a deep breath. It will take some time for them to see your contact. I'm fairly confident, you either have a broken wire, or a bad solder joint, but let the responsible parties fix it.