[ADUHF]

I always appreciate the help with the math and science. I'm really not a master or expert on that stuff, so it's always a little awkward for me to poke my nose into these conversations as if I know what I'm talking about. But, like you, I like to help where I can and it seemed like a question was asked that I (more or less) knew the answer to. I used to let people know the limits of my understanding straight off the bat, but that just made people assume the math was just another opinion on the Internet and therefore something to be argued with. Now I let people assume I'm an expert and then be embarrassed by it later.

I'm perfectly willing to admit that 120dB is completely ludicrous. I'd like to actually measure how loud I listen, but I really don't want to buy I measurement mic just so that I can do one measurement once, just so that I can look more like an expert on the Internet.

There are always risks involved in stepping into convos like this. So it is appreciated when people are willing to make the extra effort to do so. You are all top notch in my book!

The empirical validation is much appreciated here, as I'm learning. Great discussion.

While we were all doing our math homework, I had sent a message to Matthias Carstens, who is the head of RME product development, asking him if the ADI-2 can sufficiently drive 300 Ohm headphones (e.g. HD800, ZMF) and his reply: "Of course it can."

I'm going to go ahead and trust the math, the head of product development from RME, and my own ears. That being said, I will continue to test drive separate amps, listen for myself, and see if I can note a preference towards a separate amp or the RME.

I am still trying to better understand the effects of power, voltage, current, impedance (both source and load-related) and damping on a headphone's sound quality. And the best ways of optimizing all the above.

Part of the problem is that I still don't have a really good grasp of all the fundamentals of how headphones and amps work. And need to do more reading to get a better understanding on this. These are a few things (I think) that I've picked up both from the discussion here and looking at other info elsewhere though....

More power = more volume in a headphone. Since power = both current and voltage though (technically multiplied, rather that added), you can potentially get more power or volume from either one. An amp varies the amount of power or volume of a headphone by varying the voltage it can receive though. So an increase in voltage also = more volume.

Amps will deliver different amounts of current to different headphones, based on their impedance. But for a given load impedance, the current should always be more or less constant. So the power/volume is always varied by the amount of voltage that particular pair of headphones receives. (There are some amps which can vary the power and volume by varying the current rather than voltage, but those are special cases.)

Amps and headphones are connected in series. Which means that their impedances combine. And more impedance on either the source or load means there is less current between the two.

What I'm still having some trouble understanding though is why it seems easier to drive both low and high impedance headphones to higher volumes with a higher impedance amp, rather than with a lower impedance amp. Because the lower impedance amp should allow the headphone to receive more current.

The headphone amps that I've used in the past always had somewhat higher impedance, generally more in the 20 to 50 ohm range. But somehow they were able to drive both types of headphones to higher volumes, even though they are (apparently) outputting less current. How is this possible? Is it just because they have alot more voltage?

 

[ADUHF]

Here's some infographic on what average SPL the ears can tolerate for different time windows. According to this, a 120dB SPL transient peak doesn't necessarily cause hearing loss but from what I know about the average level of my music and how much time I spend on listening to music, 120dB would be well over the safe threshold for me.

Fwiw, I don't think anyone here is talking about listening at a sustained volume in that range. Hearing loss can occur with sustained volumes that are much lower than 120 dB. So that would be madness. And would solely be for brief transients.

I was probably exposed to sustained levels approaching that range though at some of the noisier clubs and concerts I attended as a misguided youth. And I am still suffering for it.

 

[bigshot]

The problem is, someone says something like “80dB is as loud as anyone would ever want to listen to music”, which is pretty accurate, and then someone thinks of a reason to up that a little. Then the next guy ups it again. Pretty soon it bears no relation to reality.

If music is at a sustained peak value of 80dB and you’re just barely able to stand it, there is absolutely no way a transient peak would hit 120dB. That’s 16 times as loud! No engineer would let something like that by. It would be like a high caliber gunshot at close range. It would be well beyond the flinch line, into wince territory.

A 90 dB transient would be twice as loud as the sustained peak. Even that is highly unlikely in commercial music, because the CD would have to be normalized down to half volume level to accommodate the transient without digital clipping. Not gonna happen. 10dB headroom, accommodating up to 90dB is already overkill.

This is exactly what I’m talking about. A number with a real world meaning gets thrown out, then the theoretical “what if’s” push it into crazy land with a straight face. 16 times as loud as anyone could possibly stand! Sit back and Amir will say we need 130 and 32 times as loud as you can stand.

 

[VNandor]

Fwiw, I don't think anyone here is talking about listening at a sustained volume in that range. Hearing loss can occur with sustained volumes that are much lower than 120 dB. So that would be madness. And would solely be for brief transients.

I sure hope so. What I was hinting at is what @bigshot said. If the playback hits a 120dB peak (even if it's just really short term) it's practically guaranteed it's also hitting average volumes that are way too loud to listen to, certainly more than 80dB which is already pretty loud for average levels.

 

[bigshot]

Exactly.

 

[ADUHF]

I sure hope so. What I was hinting at is what @bigshot said. If the playback hits a 120dB peak (even if it's just really short term) it's practically guaranteed it's also hitting average volumes that are way too loud to listen to, certainly more than 80dB which is already pretty loud for average levels.

Exactly.

Yes. I think I can see your points on that.

 

[VNandor]

Actually, there's one more thing that comes to my mind when deciding on the amount of power needed for headphones which is equalizing. The correct way to equalize is to make sure you only cut by either using a negative global gain or only using negative gain with the filters in the first place. So if someone had an amp and headphone pairing that only barely got them to the volume levels they wanted, the EQ would push the volume level down which would be a bad thing in this case.

 

[bigshot]

Reserving a 10dB headroom would cover EQ too. It's rare to need to EQ that much. The only time I can think when you'd do that is to boost bass in cans that don't have bass to boost, but that is a futile effort anyway.

 

[VNandor]

Reserving a 10dB headroom would cover EQ too. It's rare to need to EQ that much. The only time I can think when you'd do that is to boost bass in cans that don't have bass to boost, but that is a futile effort anyway.

I don't think you fully grasp what I'm saying. Once you apply EQ to the signal, the overall volume level of the signal has to go down if you want to avoid digital clipping. If someone had an amp that could barely supply enough power with an unaltered signal, there's no more power left to compensate for the reduction caused by the EQ.

 

[bigshot]

Right, but I'm saying that you need a 10dB headroom on your amp over maximum normal listening volume. The added 10dB headroom would give you room to double the weaker signal.

Here is the question I've been answering...

I can also see some potential advantages in the rendering of transients, at the extremes of the volume range, with an amp that provides a bit more headroom. But I don't really know what is a reasonable range for this kind of thing with higher quality recordings. And whether 1/3 of a watt is really sufficient for enjoying full dynamic range recordings, for example. Because most of the stuff I listen to is heavily compressed in terms of its dynamic range, in order to boost its loudness. So it requires less amplification.

The question was how much headroom does an amp need properly render transient peaks? I pointed out that 10dB more than covered that. Now we're talking about EQ. 10dB is enough to cover that too.

For playing back commercially recorded music, a 10dB buffer over the amp's maximum volume is plenty enough.

On my AVR, the volume is measured in terms of -dB below zero, which is the theoretical limit of the amp. Generally, I play modern movies (which are more dynamic than most music) at -9 to -15dB, depending on the level of the soundtrack on the disc. I've never run into an instance where my amp was insufficient.

You can go ahead and buy an amp as big as Hoover Dam, but it's not going to make any difference. When it comes to headroom, enough is all you need. That's true of a lot of things in home audio... frequency extension, transparent noise floor and distortion, lossy audio artifacting, etc.

Audiophools are always hedging their bets, arguing that enough is never enough. "If a response that goes to 20kHz is good, then one that goes to 40kHz must sound better, right?" "If I gain ride the fadeouts on songs by a massive amount, I can hear the digital noise floor- therefore a noise floor below -120dB is necessary." "I used to have an amp with .01% distortion. Now I have one with .005% and it sounds much better." You can see bologna like this in a lot of the threads on Head-Fi. One person mentions a threshold of transparency or recommended spec and then all the armchair experts try to think of a rare exception that might mean that figure is a little too low. Then another armchair expert tries to one up the first armchair expert by mentioning an even more unlikely exception. Again and again until we are running down a rabbit hole into La-La Land. It has nothing to do with how an amp or DAC actually performs in the real world. It's all inside of people's heads. It's ego gratification. They aren't actually helping anyone put together a good sounding stereo system. "I'm not a doctor, I just play one on TV."

 

[ADUHF]

I think I am just way confused at this point, and you should pretty much disregard everything that I've said here. Including my comment about using dB/V rather than dB/mW to compare the volume of different headphones.

Nothing is making any sense to me at this point with regard to volume, power, impedance, current, voltage, etc., and how these functions are related in an electrical device. I simply don't get it.

 

[bigshot]

Reader's Digest version: Calculate the numbers to determine how loud a signal you can produce. If the maximum volume output is above 90dB, you should be fine. More isn't better, but too little is definitely worse.

Don't buy transducers with crazy non-standard specs that require crazy non-standard amps to drive them. The benefits aren't anywhere near enough to justify the inconvenience. In fact, there may be no benefit at all.

 

[VNandor]

The question was how much headroom does an amp need properly render transient peaks? I pointed out that 10dB more than covered that. Now we're talking about EQ. 10dB is enough to cover that too.

Using EQ would definitely increase the difference between the peak levels and "sustained peak" levels. Anyways, I hoped that going into the details would be helpful instead of confusing but I'm clearly wrong so I might just stop posting on this topic.

 

[bigshot]

How would EQ increase the dynamics of transient peaks?

 

[ADUHF]

Using EQ would definitely increase the difference between the peak levels and "sustained peak" levels. Anyways, I hoped that going into the details would be helpful instead of confusing but I'm clearly wrong so I might just stop posting on this topic.

Fwiw, I think most of your input has been good here, VNandor. I simply can't put all this stuff together in my head, which is not your fault or anyone else's here.

Fwiw, your comments about EQ make some sense, if you're going by the volume of an amp based on listening. Perhaps less so, if you are using measurements, because the goal of EQ is generally to make the loudness more perceptual balanced across the frequency range at your target dB level.

I think bigshot's point on this is simply that the change in overall levels between an EQ-ed and un-EQ-ed headphone would generally be too small to make a noticeable difference in the sound performance, even if you have to raise the amp a few dB's to compensate for the equalization.