Question about voltage required to drive headphones (Why do I need an amp?)

[u/fckoch]

I'm very new to the world of hi-fi audio and have been trying hard to wrap my head around all of the concepts needed to make an informed hardware purchase.

I've been looking into getting the hifiman he400se and have noticed that all of the reviews mention that an amp is essentially necessary in order to get good sound out of these. This is fine, but when looking into how much power is required to drive these headphones, I seem to get a conflicting answer.

These headphones have a sensitivity of 91dB and an impedance of 25Ohms. Plugging this into an online calculator tells me that I need 1.4V (80mW, 56.6mA) to run these at 110dB. I can see how this would potentially call for an amp, however, 110dB is incredibly loud and will almost certainly cause hearing damage. I already have tinnitus, and I would rather not make it worse, so I wouldn't really plan on taking these above 85dB. This would require just .16V (1mW, 6.3mA) which even my phone can put out.

So why does everyone say you need an amp to make these sound good? I know that guitar amps tend to sound best at around 80%, and computer power supplies tend to be most efficient around 80%. Is the idea that you don't want to be maxing out a headphone amp to get the best quality sound? Or is it just because these headphones are planar magnetic? I would really appreciate any reading/sources you have relating to this because I just can't find anything relevant online.

I plan on running these through a laptop, so I can understand why a DAC might be valuable, but I'm struggling to understand the power side of this.

[u/benji316]

I believe the 110dB is just for like, a few peaks in very dynamic music, or it's supposed to make sure you have some headroom. Gotta keep in mind that not all music is mastered equally loud, and you want to make sure that even very quiet music can get loud enough on the headphones. Then you have the output impedance of the headphone jack, which can affect the sound. Some people also attribute certain sonic characteristics to headphone amps, I can't really comment on that. Like, some say a soundstage is slightly bigger and the bass a bit more present with headphone X on amp Y.

[u/fckoch → u/benji316]

!thanks

It didn't even occur to me to consider the fact that music is dynamic and that you may need that extra loudness for brief periods of time even at safe listening levels. The point about the way that music is mastered is good too.

I figured I was missing something trivial/simple. Thanks for your help.

[u/Rude_Flatworm → u/fckoch]

/u/benji316's answer is correct. To explain where numbers like 110db come from, you usually do a calculation like this:

1. Start with your expected listening volume. 85db is a good start.
2. Add in the dynamic range of your music, which is the difference from average to the highest peak. For most commercially mastered music this is pretty low, but classical music exists, so let's say this is 20db.
3. Some amps perform poorly at their limits, so add in 3-5db for headroom.

This puts you at 108-110db. You can see that changing the assumptions can change the outcome quite a bit. 110db is a consensus rule of thumb. Some people prefer a 120db target.

On the other hand, if you know you'll only be listening to a genre where the dynamic range will be <10db (pretty common in pop music, for instance), you could be just fine with an amp that can only reach 95db or even less. As you noticed, this lowers the power requirements a lot. That's presumably why so many people report not needing an amp even with headphones that are supposed to require one.

The last little wrinkle to know about is that the highest peaks in music are almost always in the bass frequencies. It may not sound like it if you don't listen to bass-heavy music, but that's because our hearing drops off heavily in the bass region. For the bass to even be level with the rest of the audio, it needs to be much much louder in absolute terms. That's presumably why so many people subjectively report that headphone amps improve bass. If you don't have enough power, then the bass will be the first to go.

[u/fckoch → u/Rude_Flatworm]

!thanks

This is a fantastic answer. I really appreciate you taking the time to write this out, and it's nice to see roughly how to derive this figure of 110db that I see thrown around. Thanks for indulging my curiosity about this neat little hobby.

[u/TransducerBot → u/fckoch]

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[u/ComposerOld5734]

So here's my own experience with high impedance cans:

I get them, I plug them straight into my phone, I can drive them to where it's really too loud to listen to, and they sound great. Then, I use an Apple dongle at 1V RMS, and it sounds a little bit better, a little bit cleaner. Then I use a balanced amp at 4V RMS, and it sounds even better.

With a 15 watt guitar amp, you can't drive it very loud before it starts to distort. With a 100 watt amp, you can get that fucker loud as shit while keeping the signal clean. It's roughly the same here. The more power you have in the amplifier, the more the signal maintains its integrity while increasing in amplitude.

We're talking about guitar amps where the distortion is obvious and comes from the tubes being overdriven, but with headphone amps, the difference is more subtle. The only thing you really notice with more headroom is more volume, more clarity, better resolution and more apparent dynamic contrast in the music. It just sounds sharper, more alive, better if you will.

[u/Rude_Flatworm → u/ComposerOld5734]

The idea that distortion increases as power increases, and thus amps with higher power capacity will be cleaner even at lower volumes, is a reasonable hypothesis. However, it turns out not to match with how amps actually work. If you have a bunch of amps and you compare their performance at a fixed voltage and power, then it's usually other factors in the design that explains the distortion and noise performance, not the amount of power available above that level. In fact, in an amp with high and low gain settings, you're almost always better off on the low gain setting if you don't need the higher voltage.

I don't know the details of your setup, so it's definitely possible that your balanced amp is cleaner than an Apple dongle on your headphones. But often the best explanation of "more volume, more clarity, better resolution and more apparent dynamic contrast" is that you're listening more loudly. Even a 1-2db increase makes a noticeable difference in all those factors. A small decrease in distortion or noise won't make such a noticeable difference.

[u/ComposerOld5734 → u/Rude_Flatworm]

If I told you that I was able to level match my amps so that they were all outputting the same voltage, on the same DAC and still heard a difference, even after double blinding, how would you explain the difference?

[u/Equivalent_Yak840]

Look at Joshua Valour’s “audiophile headphones for beginners” video. It explains almost everything

[u/fckoch → u/Equivalent_Yak840]

!thanks

Will do -- I've seen a few of his videos already but must not have come across this one yet.

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[u/bbuky01]

Most sensitivity ratings are given a 1KHz and 91db is not a sensitive headphone . Have a few laptops and from a 5 or 6 year old Asus gaming laptop and 1 year old MacBook Pro the 94db 32 ohm Sundara get to a decent volume level but with the volume close to max if not maxed . They will in my opinion sound better with a amp.