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high impedance headphones need a dedicated amp to sound good... please can we kill this myth?

post #1 of 59
9/16/12 at 11:16pm
Thread Starter 

I keep hearing this over and over again. It is usually advice given to a neophyte who just bought some sort of full sized headphone, and is less than pleased with their sound quality.

Of course, the issue is with voltage swing not being large enough to make headphones play sufficiently loud. It is actually low impedance headphones that drain all of your source's current, causing bad response.

 

So then why do people always give this advice when people don't like the way their headphones sound?

It would be extremely obvious to them if they weren't loud enough. They'd say something like "These headphones aren't loud enough". But I've rarely heard anyone say that. 


Edited by Eisenhower - 9/17/12 at 6:44pm
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post #2 of 59
9/17/12 at 5:28am
I've heard explanations that amplification is needed to overcome peaks in the impedance vs frequency and subjective testing tends to confirm. Interested to hear the science behind this question.
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post #3 of 59
9/17/12 at 7:01am
Quote:
Originally Posted by Loquah View Post

I've heard explanations that amplification is needed to overcome peaks in the impedance vs frequency and subjective testing tends to confirm. Interested to hear the science behind this question.

 

It is another common myth, you do not need "more power" to handle impedance peaks. That assumption would imply that the ideal way to drive headphones is to use a current source ("infinite" output impedance), while in reality amplifiers are designed to behave as voltage sources with near zero output impedance. Therefore, at the impedance peaks, actually less power is needed for a flat response. What makes such peaks somewhat challenging is that they make a low output impedance more important, and the amplifier needs to be able to handle the high reactance without stability issues. Neither of these are directly related to "power", however, and peaky low impedance (such as that of a balanced armature IEM) is more difficult to handle than peaky high impedance.

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post #4 of 59
9/17/12 at 7:24am
Quote:
Originally Posted by Eisenhower View Post

I keep hearing this over and over again. It is usually advice given to a neophyte who just bought some sort of full sized headphone, and is less than pleased with their sound quality.

Of course, the issue is with voltage swing not being large enough to make headphones play sufficiently loud. It is actually low impedance headphones that drain all of your source's current, causing bad response.

 

It is unfortunately very hard to kill such myths, as many people keep repeating them without actually knowing what they are talking about, but the fact that it is so widely spread makes the myth look like generally accepted "science" that is backed by authority. In my opinion, these are the main sources of this belief:

- many devices have excess gain and clip at high volume, therefore the headphones could indeed end up being "loud enough" but sounding bad

- the allegedly loud enough volume might not be loud enough after all; humans are not very good at judging absolute loudness, especially when relying on long term auditory memory, and level matching issues are a major source of alleged differences between the sound of amplifiers

- it is not uncommon for devices with high maximum output voltage, such as tube amplifiers and the headphone jacks of speaker amplifiers, to have very high output impedance as well; this will typically boost the bass on full size dynamic headphones to some extent, giving the subjective impression that a (technically better) source with low output impedance is "underpowered"

- as usual, expectation bias plays an important role; after reading comments from many people that headphone X will sound bad from amplifier Y, it is hard not to expect that to be the case

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post #5 of 59
9/17/12 at 10:18am

Strange myth indeed. I believe the only benefit of a high headphone impedance is to get a high damping factor, so the amplifier has better control over the transducers. The effect is probably negligible with any well-designed amplifier with a low enough output impedance, even the one in an iPod.

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post #6 of 59
9/17/12 at 10:34am
I did a comparison using Sennheiser HD590s and an iPod Classic. There was a definite improvement in both volume and dynamics using a cmoy amp. It wasn't massive, but it was enough of an improvement to clearly hear.
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post #7 of 59
9/17/12 at 10:41am
Thread Starter 
Quote:
Originally Posted by stv014 View Post

 

It is unfortunately very hard to kill such myths, as many people keep repeating them without actually knowing what they are talking about, but the fact that it is so widely spread makes the myth look like generally accepted "science" that is backed by authority. In my opinion, these are the main sources of this belief:

- many devices have excess gain and clip at high volume, therefore the headphones could indeed end up being "loud enough" but sounding bad

- the allegedly loud enough volume might not be loud enough after all; humans are not very good at judging absolute loudness, especially when relying on long term auditory memory, and level matching issues are a major source of alleged differences between the sound of amplifiers

- it is not uncommon for devices with high maximum output voltage, such as tube amplifiers and the headphone jacks of speaker amplifiers, to have very high output impedance as well; this will typically boost the bass on full size dynamic headphones to some extent, giving the subjective impression that a (technically better) source with low output impedance is "underpowered"

- as usual, expectation bias plays an important role; after reading comments from many people that headphone X will sound bad from amplifier Y, it is hard not to expect that to be the case

 

Those are valid points, but an amp distorting/clipping within it's designed volume range is definitely not the norm for most reputable companies (Apple etc...), since that is a flaw (in my opinion, I guess). Ironically some people suggest using a tube amp as a solution.

 

I've used high impedance headphones with an ipod, and even when I think it is "loud enough" (although I might be deluded), I am still a ways from maxing out the volume. But I've never anyone suggest "Have you tried turning up the volume?" when someone else is not getting the sound they want. Rather it is always "Buy a headphone amp! Don't you know anything?"

 

Quote:
Originally Posted by RazorJack View Post

Strange myth indeed. I believe the only benefit of a high headphone impedance is to get a high damping factor, so the amplifier has better control over the transducers. The effect is probably negligible with any well-designed amplifier with a low enough output impedance, even the one in an iPod.

 

Unlike the cable myths, nobody ever calls anyone out on this one. Granted, there is more truth to having a good amp, but it certainly doesn't warrant the incessant demand that everyone remotely concerned about sound quality must use a headphone amp always for any headphone impedance > 50 ohms or whatever, when the opposite is more likely true.


Edited by Eisenhower - 9/17/12 at 11:07am
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post #8 of 59
9/17/12 at 11:17am
Quote:
Originally Posted by Eisenhower View Post

I keep hearing this over and over again. It is usually advice given to a neophyte who just bought some sort of full sized headphone, and is less than pleased with their sound quality.

Of course, the issue is with voltage swing not being large enough to make headphones play sufficiently loud. It is actually low impedance headphones that drain all of your source's current, causing bad response.

 

So then why do people always give this advice when people don't like the way their headphones sound?

It would be extremely obvious to them if they weren't loud enough. They'd say something like "These headphones aren't loud enough". But I've rarely heard anyone say that. 

I'd ask those people if their source is loud enough with the new headphones.

 

If it is: tell them to return the headphones and maybe give suggestions that the OP will be more pleased with.

If not: suggesting an amp doesn't seem to be wrong.

 

My guess on why people always give this advice instead of telling them to return the headphones is that it's often the people owning the headphone in question that will reply in such threads. They probably love the headphone and its sound signature, so it must be something else. What's left? The amp and further up the chain the dac.

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post #9 of 59
9/17/12 at 12:08pm

I think part of the issue is a lack of volume matching when comparing.  The sequence might go something like this:

 

  1. Get headphones with high impedance
  2. Listen — and perhaps not at a satisfyingly loud volume (after all, going close to 100% can't be good, can it?)
  3. Get more powerful amp
  4. Listen again — but at an unintentionally louder volume (after all, there's so much of the volume rotation left on this shiny and powerful amp!)
  5. Things sound different and better because of the louder volume, even any differences in performance and expectation biases aside

 

Put more food on the plate, and people will eat more...

 

There's often no sense of a loudness reference, just 10% / 50% / 100% in software, and 9 o' clock / 12 o' clock on a potentiometer or other volume slider, which don't map to meaningful units when comparing different headphones.

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post #10 of 59
9/17/12 at 2:11pm
Thread Starter 
Quote:
Originally Posted by bigshot View Post

I did a comparison using Sennheiser HD590s and an iPod Classic. There was a definite improvement in both volume and dynamics using a cmoy amp. It wasn't massive, but it was enough of an improvement to clearly hear.


I would think increasing volume (gain) increases dynamics,

Let's say with gain=1 the peak sound is at 4 and the minimum is 1 (arbitrary units). That means that the "dynamics" is 4 - 1 = 3

If you increase the volume such that gain=5, the peak will be now at 5*4=20 and the minimum at 5*1=5, so dynamics = 20 - 5 = 15

 

So unless you are maxing out your ipod's volume, I don't understand your point. You have to the normalize output decibels to compare dynamics accurately.


Edited by Eisenhower - 9/17/12 at 2:12pm
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post #11 of 59
9/17/12 at 2:38pm

So, is it more about sensitivity or something?

 

I ask because when I was looking to buy some closed cans once, I distinctly remember testing the Shure SRH840s and the Ultrasone HFI-680s. The thing I remember is that the HFI680s sounded completely uninspiring out of my iPod while the SRH840s sounded great, but when I connected to an amplifier, the sound of the 680s took off. I had previously put this down to impedance as the 680s are higher, but I understand what you're all saying above.

 

So, what's the key if it's not volume? I can recreate this over and over as a blind test to prove that it's more than just a volume normalising issue.

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post #12 of 59
9/17/12 at 3:35pm
Thread Starter 
Quote:
Originally Posted by Loquah View Post

So, is it more about sensitivity or something?

 

I ask because when I was looking to buy some closed cans once, I distinctly remember testing the Shure SRH840s and the Ultrasone HFI-680s. The thing I remember is that the HFI680s sounded completely uninspiring out of my iPod while the SRH840s sounded great, but when I connected to an amplifier, the sound of the 680s took off. I had previously put this down to impedance as the 680s are higher, but I understand what you're all saying above.

 

So, what's the key if it's not volume? I can recreate this over and over as a blind test to prove that it's more than just a volume normalising issue.

 

If there is an answer to this, I'd like to know as well!

I still retain that it is a myth. It might be the case that ipods distort at high volume levels, but that is only one type of source (and typically an uncommon one for high impedance cans).

 

I can't tell you that you are mistaken in your listening tests, but I would note that it's not easy to normalize volume levels by ear (as stv014 pointed out above, it is hard to quantify absolute volume by ear). A measurement mic is the best way. You could probably calculate it as well given the headphone's sensitivity and the amplifier's power output for a given volume level.

 

It could be that your amp is coloring the signal in a way that pairs nicely with the Ultrasones (aka they have synergy). Your "uninspiring" might be my "accurate", as they are often synonymous. Also you'll find plenty of people who would tell you that the Ultrasones don't need an amplifier because they are only 75 ohms.


Edited by Eisenhower - 9/17/12 at 3:55pm
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post #13 of 59
9/17/12 at 3:42pm

Sensitivity (dB SPL @ 1 Vrms, 1 kHz) of the 680s is lower. Volume definitely plays an important role in what we prefer. mikeaj explained it pretty well.

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post #14 of 59
9/17/12 at 4:56pm
Quote:
Originally Posted by Eisenhower View Post

So unless you are maxing out your ipod's volume, I don't understand your point. You have to the normalize output decibels to compare dynamics accurately.

The volume is pretty much maxed out with those cans. I think it was an issue of headroom.
Edited by bigshot - 9/17/12 at 4:57pm
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post #15 of 59
9/17/12 at 6:44pm
Quote:
Originally Posted by xnor View Post

Sensitivity (dB SPL @ 1 Vrms, 1 kHz) of the 680s is lower. Volume definitely plays an important role in what we prefer. mikeaj explained it pretty well.

 

So does this mean that they need more power because of being less sensitive than other cans (e.g. SRH840s) and therefore don't have the headroom to create the same dynamics as a more sensitive headphone?

 

Quote:
Originally Posted by bigshot View Post


The volume is pretty much maxed out with those cans. I think it was an issue of headroom.
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