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How do "details open up" with amping a headphone?

Discussion in 'Sound Science' started by wiljen, Apr 4, 2017.
  1. Wiljen
    I keep hear about "Details opening up" with amping and I am at a complete loss as to why this would be true unless it is on the human side of the equation and is based on more detail being available to our ears at higher volume levels. Somebody please take a look at my understanding as written below and tell me what I am missing.

    A given iem/headphone has an impedance or ability to resist the flow of current that changes at different frequencies but is generally summarized by a single value such as 32 ohm, 50 ohm etc. This characteristic is specific to the drivers used and does not change regardless of what kind of circuit you put in front of the driver.

    Sensitivity in dB is the ability to produce sound given a specific amount of current to work with and is measured at a specific frequency in order to provide an apples to apples comparison as some frequencies will be more than the listed sensitivity and others less due to the fact that some sounds require more energy to reproduce than others.

    Based on the above if one amp is capable of providing 300mW into a 50Ohm set of headphones with a sensitivity of 92dB (1kHz,1mW), If we back away from the maximum to allow for the previously mentioned impedance variation and use an output power of 200mW, how would it not produce the same exact sound at the ear as any other amp that was set to push 200mW output?

    I don't understand how more detail can be present in the same signal and mathematically the numbers are the same unless you increase the current outflow of the system which is exactly what an amp is designed to do. I can only surmise that what is perceived as "details opening up" is actually the ability to boost volume to a level where those details that were always present in the signal are now audible to the listener.

    So if I own the headphone I referenced above (Fostex Trp series) as most of us do and can happily listen to them with an amp that puts out up to 1Watt (Magni2) there really would be no benefit in chasing an amp that can push the headphones to their maximum input power of 3 Watts as all this would accomplish is the rapid destruction of my hearing.

    What am I missing in this equation?
  2. VNandor
    I think you are missing two points here.
    1. Those specs doesn't give you the full picture. If we assume that amplifiers don't have various distortions then this
    would be true.
    To give you an example, some amp manufacturers give these characteristics, typically harmonic  distortion and noise. Let's say amp "A" has <1% THD +N @ 300mW  while amp "B" has <0,1% THD +N @ 300mW. In this case, amp "B" could be considered to be better than amp "A".
    As far as I know, this figure varies over the frequencies so a THD+N (y) vs. frequency (x) plot wouldn't be a flat line. I don't know if an amp's spec sheet provides a worst case scenario or some sort of averaged number. So theoretically, two amps might be differerent despite the fact they had the same specs given, depending on how the measurements were done/calculated.
    An even easier to understand example would be the amp's frequency response. So if amp "A" had a frequency response of 20Hz-20kHz +-0,1dB but amp "B" had a frequency response of 20Hz-20kHz +-1dB then amp "A" could be considered better than "B".
    So all in all, providing enough power is not everything, the amp has to tick other boxes as well to be transparent.
    2.The other thing you miss is that the "details opening up" were most likely observed by humans, and not tools. Maybe the guy who said that might have looked at an oscilloscope but I somehow doubt that. Our perception has its limitations and obviously we might not hear a difference when there is some but the less obvious thing is that we might hear some difference when there wasn't any.
    What I'm trying to say here is that what we perceive is not always the actual sound due to the physical limitations of our ear/brain and due to various perception biases. So how one perceives sound might change despite changing two audibly transparent amps.
  3. Wiljen
    Thanks, that 2nd part of your comment (We don't necessarily hear exactly what is present in the signal) is exactly what I was attributing this phenomenon to. I had not considered the distortions in the equation as I had thought anything with a high enough distortion to be audible was probably a poor enough choice for that particular application that it should be avoided. Perhaps that was an oversight on my part and does account for some of what is being heard. Hard for me to call it 'details' when it is more likely distortions introduced by the equipment though.
  4. Roseval
    Perception [​IMG]
  5. castleofargh Contributor
    different amps will have different levels of fidelity and the distortions or noise they'll bring may occur differently at different places. they will also not all have a dead flat signature(even less so once loaded). and the impedance could sometimes impact the sound coming out of the headphone. we follow impedance bridging for headphones precisely to limit such possibility, but many audiophiles decide they know better, so who knows what result they get with some exotic designs.
    now most people will talk about the sound opening up thanks to the 4gigawatts of their new amp, without a hint of proper testing and close to no understanding at all about electricity. they think of power specs as money, the more you have the better it is. you can save a lot of time dismissing inconclusive rambling right away instead of trying to objectively look for the conditions that may or may not explain it.

  6. ProtegeManiac Contributor
    THD and Noise. Using a better amp will allow you to listen louder, yes, but you get less distortion and noise, so there's less modification to the sound getting in the way of what you're listening to. Some amps don't actually "boost" the bass but people hear more of a "bass slam" for example, and they attribute that to greater current delivery, which is somewhat true for some headphones but then they do that with headphones that don't need that much current. Rather, such amps more likely are just adding less noise that gets in the way of some bits of the music, and when it comes to bass, we inherently hear it less well than midrange (evolutionary reality on the brain's side; that doesn't mean the bass is ignored, it just tends to get...weird). An amp that can pour more power (not necessarily a hell of a lot more than you need) while keeping noise and distortion even lower, helps a lot.
    Also note that "inaudible" isn't exactly the same as indistinct - a lot of people just base the idea on "1% and below I'm sure you won't hear it" but then you have a Violectric or Meier go up against a motherboard or smartphone and as long as you do a blind test at a loud enough level, I wouldn't be surprised if anybody but the tone deaf can pick out the amps as their favorites.
    Just note that this doesn't mean you need some kind of balanced amp with earth shaking output and some magical feedback circuit to have a good amp with low noise and distortion. Basically, you can stick with the Magni2, because as much as there might be audible benefits from the blacker background of a Classic FF or V281, it won't necessarily be worth another $500 to $800 bucks to you. Just sit and enjoy your headphones with that amp.
  7. limpidglitch
    I think it is as simple as people tending to turn things up a notch or two when they plug their headphones into a new amplifier. Especially if it has a big, shiny, heavy volume knob.
    And everything, including details, improves when you turn it up a bit.
  8. castleofargh Contributor
    sure the magic of not level matching anything can't be underestimated.
  9. pinnahertz
    It's always tricky trying to use generalities to describe specifics.
    The audibility of something like THD is not simple, and the real problem is we refer to THD as a single number, or perhaps a set of numbers and frequencies.  Actually, the audibility has a lot to do with the spectra, the specific distortion products created and where they land relative to the fundamental.  I single THD figure, even of 1%, pretty much tells us nothing.  For example, a series of ABX tests involving distortion done in the early 1980s showed that some rather startlingly high THD figures were not differentiated from the sub .1% ones.  Even-order harmonic products are less objectionable than odd-order, etc., etc.  Another factor is how rapidly THD increases with level within the normal operating range.  A very slow onset would be less audible than repeatedly crossing a sudden hard clipping point, for example. So the short story is, I can't fully agree that "Details" are related to THD.
    Noise, on the other hand, is easily quantifiable, basically by looking at two parameters: level and spectrum.  Again, a single unweighted noise figure isn't of much use in audio, but weighted figures give us a decent idea of how it will sound.  But for noise to affect details it has to be at least audible amid the music.  That means the test music will have to be recorded in a really quiet studio, and not be an analog recording.  Then, with no signal, the amps residual noise should not be audible in normal listening conditions (a very quiet room for open phones, etc.) Once you've hit that point, it no longer matters.  So I can't agree that noise hides or reveals details either, unless it's the result of such a poor design that it's audible with no signal.
    "Slam"...that's tricky.  It gets down to careful measuring of the specific devices, but generally it is a form of relative bass boost, perhaps dynamically, perhaps load related, but is easily measured.  The loaded high level response test or tone burst would show what it is.  The one amp I tested that I felt had a bit of extra slam showed a gently shelved bass boost. 
    However "Slam" and the idea of "Details opening up" are both subjective descriptions based in an emotional response.  With the tremendous non-audio biases and influences involved in audio gear, it's really very possible, even likely, that neither actually exists, but rather are the result of powerful expectation bias.  Frankly, a properly designed headphone amp, that's one designed with the right gain, operating range, and intended to drive real headphone loads, will sound identical to another properly designed headphone amp outside of any special processing.  
    You have to be really careful about generalizing the relative performance of a high-ish end headphone amp vs a smart phone's headphone jack.  Check out some of the measurements that have been done on iPhones, for example.  The internal headphone amps are indeed, and are easily, audiophile grade.  My personal anecdote on this is that I recently tested a well respected headphone amp, and my test source was an iPhone 6.  The most astonishing part of the test was the level matched ABX/DBT, which confirmed the difference between the amp and the iPhone output jack was undetectable (unmeasurable too). The amp was so quiet that I couldn't tell if it was on or not without checking the front panel. I literally had to check my connections several times to make sure it was in the circuit at all.  It was, and it's contribution to the SQ was zero, neither negative nor positive, using 3 radically different kinds of headphones and earphones (open, closed, and IEM).  And yet, before the test I had the sense of enjoyment of my new headphone amp!  So, bias proven.  The amp improves nothing, but adds cables, a box, and complexity.  But before a real ABX/DBT, I thought it sounded vaguely "better".  
    Intensecure likes this.
  10. FiGuY1017
    Sorry not sure where to post this ?. Is there such a thing as a 6.3mm to 6.3mm jack? Google didn't pull up anything definite or where id purchase such a thing. I'd like to lessen the wear and tear of my 6.3mm jack on my heron 5 amp. *guess i could daisy chain a 3.5 adaptor to a 6.3mm adaptor.
  11. pinnahertz
    What is the purpose of the headphone jack?  To provide reliable contact to the headphone plug.  Given the price of the Heron 5, one would expect them to have used a premium jack with adequate contact surface plating thickness, adequate contact area and pressure to ensure many years of reliable low resistance connection.  But what you want to do is add at one or more sets of contacts in series with that jack, probably inexpensive, thinly plated, weak contact pressure jacks that will no doubt wear out long before the original Heron jack.  Although, I admit to never having seen a 1/4"/6.3mm jack actually just wear out in my 5 decades in audio, I would suggest that fewer mechanical connections is always better.
    Leave it alone, this is a futile pursuit. 
  12. OddE

    -What @pinnahertz said.

    Also, adding an adapter is more likely to increase wear than anything else - do keep in mind that what you are effectively doing is increasing the length (and mass!) of the plug, so that the socket will have to cope with larger (mechanical) stress.

    Out of curiosity, I just looked up the specs on the (locking) jack sockets I use in my projects - they are good for >10,000 cycles, according to the manufacturer. Knowing Neutrik, I strongly suspect they might as well have written >>10,000 cycles - they are not prone to overstating the capabilities of the kit they make. (To put 10,000 cycles in perspective, that's three times a day for ten years - and that is the absolute minimum.)
  13. FiGuY1017
    Good point,if I get 10 years out of anything made these days I feel like I did pretty good. I'll just leave it be. Thanks for the help!
  14. pinnahertz
    And if it fails then, IF it fails, you replace it with a new one that costs $5.  I've never changed a jack because it wore out.  The really cheap ones break, but that's not the same thing.  Radio station use - that's more like 10x a day - I never changed a headphone jack because it wore out. 

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