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post #16 of 46
Quote:
Originally Posted by Bill-P View Post

Headphones like the 880 will scale up with better amps. While it's no slouch by any standard, I wouldn't say the E7 is sufficient for driving high impedance headphones. Even the E11 struggles somewhat with 250 Ohm IMO. You need... a lot more power to really see how much better your headphones can be.

I agree. At home i use a firepod (it's for recording but it has a strong headphone amplifier) and a denon receiver which also has a strong headphone amp. The headphones sound better with those but they still sound good on the smaller stuff.
post #17 of 46
Quote:
Originally Posted by planx View Post

 

So... If this is true, I wouldn't be able to hear anything with my 600ohm AKG K141s..? No, not true. I was able to reach a comfortable listening volume with the K141, but the volume was very high on the iPhone4. The main difference is even though it can still technically "power" the AKGs, it doesn't have enough current to power it stable. There is significant bass loss and it sounds like a completely different headphone. Like MalVeauX says, the difference between the 80, 250, and 600 ohm Beyers are insignificant to many users (I'm not quoting him. Just rephrasing what I read a while back. Please correct if incorrect Mal).

 

To OP, you will be able to obtain excellent answers from the user MalVeauX. Just shoot him a PM with your Q's

 

Volume also has to do with sensitivity (SPL) and not just impedance. My answer was extremely contracted. However, impedance still plays a role.

http://www.soundonsound.com/sos/jan03/articles/impedanceworkshop.asp

 

And everyone experiences volume differently from my experience. But also from my experience, I have found more people stating that iPhone 4 driving 250 Ohm headphones is generally not loud enough for them.

 

You may be okay with generally lower volume, but that doesn't mean everyone is okay with that low a volume, and it's always better to have more headroom than to max out an amp or source trying to drive a headphone.

 

That said, though, personally, I find the difference between different ohm ratings of the Beyers (32, 80, 250, 600) pretty apparent. I had a Beyerdynamic DT880 600 Ohm just a short while ago. Without going too much into individual characteristics, I'd say... the higher the ohm rating, the more "refined" the sound becomes on those headphones, but the power requirement also shoots up exponentially. The 600 Ohm Beyers in particular need a lot of power.

 

Quote:
Originally Posted by planx View Post

The E11 "struggles"? I tried the Beyer DT990 250ohm with the Fiio E11 and I thought the two were very good together... Power isn't absolutely everything with these headphones... Power matters a lot with Orthos, but with dynamics with High Impedance, I find that anything that is rated to power 150-300ohms is sufficient for almost everything. Good example is my old Hifiman EF2A. They powered my 600ohm AKGs fine. Actually sounded very nice together

 

Power is actually pretty important for the Beyers. You can get good listening volume out of the E11, I won't deny that, but it's still not driving the DT990 "properly" from my experience. You can get much better sound from a better amp.

 

Otherwise, more expensive amps seem redundant...

 

I think the same thing holds true for your AKG headphone. Though I don't have that particular model, so I have no idea how it works.


Edited by Bill-P - 9/29/12 at 5:53am
post #18 of 46
Quote:

Originally Posted by Bill-P View Post

 

 but the power requirement also shoots up exponentially. The 600 Ohm Beyers in particular need a lot of power.

 

This statement is false. Power requirement is a function of sensitivity (in dB/mW), and it is the same for all three impedance versions. Indeed, here is what Tyll Hertsens measured for the DT880:

 

 32 Ω: Power Needed for 90 dB SPL:    0.47 mW

250 Ω: Power Needed for 90 dB SPL:    0.38 mW

600 Ω: Power Needed for 90 dB SPL:    0.43 mW

These values are within a range of less than 1 dB, and it is basically just random manufacturing variation. Higher impedance needs higher voltage, but it is not an "exponential" function, the voltage required - assuming a constant sensitivity - is proportional to the square root of the impedance. So, a 600 Ω driver needs 4.33 times higher voltage than an equally efficient 32 Ω one, and only 1.55 times as high voltage as a 250 Ω one. Note that the voltage most sources can output decreases when the load impedance is very low.

 

Quote:

Originally Posted by Bill-P View Post

 

Power is actually pretty important for the Beyers. You can get good listening volume out of the E11, I won't deny that, but it's still not driving the DT990 "properly" from my experience. You can get much better sound from a better amp.

 

As far as power is concerned, "properly driven" is when even the highest peaks of the audio signal are not clipped or significantly distorted at the preferred listening volume. There are other factors that affect sound quality, but they generally do not improve (and often even get worse) with a lower load impedance. The E11 is enough for many people who do not listen to music with a huge dynamic range, and do not like (or have already) hearing damage. When driving high impedance headphones, its performance also does not significantly deteriorate with increasing output voltage until the clipping level is reached. There is no evidence that headroom that is never used inherently improves sound quality. Otherwise, it would be best to connect headphones directly to high power speaker amplifiers, and get better sound that way. In subjective comparisons, more powerful amplifiers often sound "better" simply because of not matching the volume properly (matching the volume by ear typically errs on the side of making the device that is louder at the same position of the volume control louder; this is also why higher gain - even digital gain - is often perceived as sounding better).


Edited by stv014 - 9/29/12 at 6:49am
post #19 of 46
Nice post.

Tube amplifiers I think behave differently though I don't know about how that works in headphone amps. I know with many tube guitar amps to get the best sound quality, you have to turn the gain all the way up. They even make limiters so you can do this at lower volumes. Of course you can also just select less powerful amplifiers. My brother has a beautiful sounding 17 watt Fulton Webb guitar amp. My take with home audio is that tubes are a bad thing. They color the sound. So I want to have neutral headphones and digital amps because I want to hear what the artist intended. In loudspeakers, power does seem to affect sound quality at low volumes. I am not an engineer so, to the previous poster, why is that and why wouldn't it apply to headphones. As an example, bass frequencies generally need more power. So it seems that with inferior amplification you'd be likely to experience a thinner sound. Treble, of course is very easy to drive so I agree with you there.
post #20 of 46
Quote:
Originally Posted by stv014 View Post

This statement is false. Power requirement is a function of sensitivity (in dB/mW), and it is the same for all three impedance versions. Indeed, here is what Tyll Hertsens measured for the DT880:

 

 32 Ω: Power Needed for 90 dB SPL:    0.47 mW

250 Ω: Power Needed for 90 dB SPL:    0.38 mW

600 Ω: Power Needed for 90 dB SPL:    0.43 mW

These values are within a range of less than 1 dB, and it is basically just random manufacturing variation. Higher impedance needs higher voltage, but it is not an "exponential" function, the voltage required - assuming a constant sensitivity - is proportional to the square root of the impedance. So, a 600 Ω driver needs 4.33 times higher voltage than an equally efficient 32 Ω one, and only 1.55 times as high voltage as a 250 Ω one. Note that the voltage most sources can output decreases when the load impedance is very low.

 

 

As far as power is concerned, "properly driven" is when even the highest peaks of the audio signal are not clipped or significantly distorted at the preferred listening volume. There are other factors that affect sound quality, but they generally do not improve (and often even get worse) with a lower load impedance. The E11 is enough for many people who do not listen to music with a huge dynamic range, and do not like (or have already) hearing damage. When driving high impedance headphones, its performance also does not significantly deteriorate with increasing output voltage until the clipping level is reached. There is no evidence that headroom that is never used inherently improves sound quality. Otherwise, it would be best to connect headphones directly to high power speaker amplifiers, and get better sound that way. In subjective comparisons, more powerful amplifiers often sound "better" simply because of not matching the volume properly (matching the volume by ear typically errs on the side of making the device that is louder at the same position of the volume control louder; this is also why higher gain - even digital gain - is often perceived as sounding better).

 

Sorry, you are right. I should have written "voltage" instead of "power".

 

However, to be more clear, the voltage required is actually:

 

Voltage^2 = Power * Impedance

 

therefore...

 

Voltage = Square Root of (Power * Impedance)

 

Since Impedance is not constant depending on the frequency, the voltage requirement may still shoot up. You are assuming both constant sensitivity and constant impedance, which is not the case all the time.

 

For instance, take a look at the impedance over frequency chart of the DT880 250 Ohm.

 

 

Around 100Hz (mid-bass), the impedance shoots up to well above 300 Ohm. At which point, the headphone will need to draw more voltage in order to output the same power.

 

Same story with DT990 250 Ohm here. In fact, much worse:

 

 

DT990 250 Ohm suffers from an impedance swing up to 350 Ohm in the mid bass region.

 

Lack of voltage will obviously drop bass volume significantly for the DT990. But looking at the charts, it's also obvious that both the DT880 and DT990 will lose "clarity" (high frequency) as well since impedance ramps up for higher frequencies.

 

Disregarding the voodoo around subjective and objective "listening", physics says you need more "volt" in general to drive the DT880 and DT990... and from my experience, the Fiio E11 is not adequate. Simple as that.

 

You may get away with the Fiio E11 at lower volume with less dynamic music, but when you ram into something with high dynamic range, or when you need to ramp up volume because the source is too quiet, then there's a problem.

 

Also, not all speaker amplifiers output high voltage out of their headphone jacks. It depends on how stuffs are connected inside as well.


Edited by Bill-P - 9/29/12 at 9:12am
post #21 of 46
Quote:

Originally Posted by Bill-P View Post

 

Since Impedance is not constant depending on the frequency, the voltage requirement may still shoot up. You are assuming both constant sensitivity and constant impedance, which is not the case all the time.

 

This is also incorrect, although you are not quite the only one spreading this myth. Amplifiers are normally designed to behave as close to an ideal voltage source as possible. That means that their output voltage does not depend on the load impedance (within reasonable limits, i.e. as long as the amplifier can supply enough current). If the voltage does increase at impedance peaks, that means the amplifier has a significantly greater than zero output impedance. Making the voltage a linear function of the load impedance implies an (ideally) infinite output impedance, or, in other words, the amplifier then becomes a current source. Anything in between translates to some finite non-zero output impedance. A near-zero output impedance, or, in other words, a nearly ideal voltage source, is generally considered to be the best for driving dynamic transducers, as it maximizes electrical damping, and the amplifier has the best control over the drivers, reducing resonance and distortion. Check this article for some experiments regarding the effect of the output impedance of an amplifier driving dynamic headphones.

 

The DT990 does not require more voltage, let alone power at the frequencies where you see a peak on the impedance graph. The reason why that peak is there is that it is the primary resonance frequency of the driver, where it actually becomes more efficient (imagine trying to swing a mass suspended on a spring, it takes the least effort to achieve a high amplitude at the frequency where it resonates). It is also where the DT990 already has a large hump in its frequency response. An amplifier that increases its voltage at the resonance frequency, i.e. one with a high output impedance, would just make the bass even "boomier" than it already is.

 

It is important to note that the above issues are separate from "power". If you connect the DT990's to a 1000 W speaker amplifier that likely has an output impedance of less than 0.1 Ω, then it will not output any significantly higher voltage at the resonant frequency than it does at 1 kHz. On the other hand, a PC motherboard audio output with 75+ Ω output impedance would behave more like what you suggest.

 

Quote:

Originally Posted by Bill-P View Post

 

Also, not all speaker amplifiers output high voltage out of their headphone jacks. It depends on how stuffs are connected inside as well.

 

I meant the speaker outputs, if it was not obvious enough.

post #22 of 46
Quote:

Originally Posted by Bill-P View Post

 

Disregarding the voodoo around subjective and objective "listening", physics says you need more "volt" in general to drive the DT880 and DT990... and from my experience, the Fiio E11 is not adequate. Simple as that.

 

It is not enough for you, but enough for others. There is no single standard "required voltage" that applies universally to everyone. Depending on the dynamic range of the music, and personal (volume) preferences, it can vary by a factor of as high as 10 (or 100 for power). It is fine to suggest to someone who neither has the E11, nor knows the peak SPL that would be needed, that it might not be enough. However, for those who can already tell that it is fine for their usage with headroom to spare, there is no point upgrading for the sole purpose for getting even more power in the hope that that will somehow magically improve the sound quality.

post #23 of 46

Wait... what!? You want to connect a headphone to... a speaker output of a speaker amp!?

 

And no. That's not a 'myth'. I'm not sure what you are trying to say up there regarding damping factor... However, it is not necessarily applicable to headphones because headphone drivers are negligibly light in mass... and is therefore much easier to "control" than speaker drivers. A damping factor of a sufficiently high amount (higher than 1) is usually enough to control headphones.

 

Read this:

http://gilmore2.chem.northwestern.edu/faqs.htm

 

Quote:
  • With loudspeakers, the lower the amplifier's output impedance, the higher the damping factor into the rated load. Damping factor is given as the ratio of loudspeaker impedance to the amplifier's output impedance. As the theory goes, the higher the damping factor, the better the amplifier's ability to control a loudspeaker's low frequency response (when the motional reactance of the system is at maximum), because the low output impedance of the amplifier allows any back-emf generated by the loudspeaker to be absorbed by the amplifier. That theory has been discharged by members of the audio community as unsubstantiated.

    However, even if the theory were correct for loudspeakers, its applicability to headphones is suspect. John Woodgate, a contributor to The Loudspeaker and Headphone Handbook (1988), had the following to say about the effect of damping factor on headphone performance:

     

    • Headphone transducers are resistance-controlled, not mass-controlled like loudspeaker drivers above the main resonance. In any case 'damping factor' is largely nonsense - most of the resistance in the circuit is the voice-coil resistance and reducing the amplifier source impedance to infinitesimal proportions has an exactly corresponding effect on damping - infinitesimal.

      However, the source impedance affects the *frequency response* of a loudspeaker because the motional impedance varies with frequency, and thus so does the voltage drop across the source impedance. This means that the source impedance (including the cable) should be less than about one-twentieth (not one two-hundredth or less!) of the rated impedance of the loudspeaker, to give a *worst-possible change* in frequency response from true voltage-drive of 0.5 dB.

      The motional impedance of headphone transducers varies very little (or should vary very little - someone can always do it wrong!) with frequency, so the source impedance can be high with no ill effect.

    The IEC 61938 international standard specifies that headphones should be driven by a 120 ohm source - regardless of the impedance of the headphones themselves. If the headphones were designed to this standard, then an amplifier's high output impedance should have little effect on the sound of the headphones. In general, headphones with a flat impedance curve over the audio range will not be affected by high output impedance. For example, in May 1995, Stereo Review published a review of the Grado SR125 headphones. The impedance curve of the SR125s, which have a nominal impedance of 32 ohms, varied from 31 to 36 ohms over the entire 20Hz to 20kHz spectrum. Not all headphones may be as well behaved as the Grados, but neither do they usually have the roller-coaster impedance runs of a loudspeaker. Tube amplifiers (with their high output impedances), it should be noted, have very low damping factors.

 

And I think I'll leave the rest at that. It looks to me like we're not on the same page, and a drawn-out discussion won't change anything since you are "resistant" to the idea that a more powerful amp would bring better sound quality... regardless of the fact that there are many who claim that much.
 

But I'll say this much: not all of the stuffs happening in the audio world are myths. Whether you believe them or not... is up to your own choice and knowledge.


Edited by Bill-P - 9/29/12 at 10:40am
post #24 of 46
Quote:

Originally Posted by Bill-P View Post

 

Lack of voltage will obviously drop bass volume significantly for the DT990. But looking at the charts, it's also obvious that both the DT880 and DT990 will lose "clarity" (high frequency) as well since impedance ramps up for higher frequencies.

 

See the output impedance explanation above for why this is wrong. But for the "low power = lack of bass" myth specifically, note that humans are more sensitive to bass at higher loudness (see here). So, a more powerful amplifier listened to at a higher actual volume will be perceived as having "more bass", independently of any impedance issues. On the other hand, the headphone outputs of many speaker amplifiers and receivers, and OTL tube amplifiers, have huge (often several hundred Ω) output impedance. These coincidentally also tend to have fairly high maximum output voltage, therefore, it is not surprising to see people thinking that the bass boost actually resulting from the high output impedance is because of "more power".

post #25 of 46
Quote:
Originally Posted by stv014 View Post

 

See the output impedance explanation above for why this is wrong. But for the "low power = lack of bass" myth specifically, note that humans are more sensitive to bass at higher loudness (see here). So, a more powerful amplifier listened to at a higher actual volume will be perceived as having "more bass", independently of any impedance issues. On the other hand, the headphone outputs of many speaker amplifiers and receivers, and OTL tube amplifiers, have huge (often several hundred Ω) output impedance. These coincidentally also tend to have fairly high maximum output voltage, therefore, it is not surprising to see people thinking that the bass boost actually resulting from the high output impedance is because of "more power".

 

Uh... no. The high output impedance has almost nothing to do with that bass boost. Bass boosting is actually more of a result of oscillations caused by the opamp... or by other choices done to the design of the amp.

 

But I'm not talking about boosting bass there. I'm talking about actually "getting the right bass that the headphone was designed to output".

 

As for the high output impedance, the headphone output of vintage amplifiers and receivers were specifically to drive high impedance vintage headphones. There were headphones with impedance rating of up to 3KOhm. It's only now that we make an effort to reduce the output impedance because now we are creating voice coils and transducers that are very very small in size (thus they have lower impedance rating), and if the damping factor drops below 1, then it'll actually cause troubles as the amp struggles to "properly" contain oscillations in the drivers.

 

If you want to know, try plugging a low-impedance IEM into a high-impedance tube amp. See if you get any "boosted bass".

post #26 of 46

Hmm.  So, why at the same volume level does a lower power amp sound less "full" with the same speakers. A few examples come to mind.  I can turn up my car stereo to nearly painful levels (in the treble frequencies) but the overall sound is pretty thin.  I add an amplifier to that and at lower volume output levels, the sound is substantially improved.  You are saying this only because of output impedance differences? 

post #27 of 46
Quote:
Originally Posted by Bill-P View Post

Wait... what!? You want to connect a headphone to... a speaker output of a speaker amp!?

 

Well, it is your idea that more power, even when not actually used, improves sound quality, not mine.

 

Quote:

Originally Posted by Bill-P View Post

 

And no. That's not a 'myth'. I'm not sure what you are trying to say up there regarding damping factor... However, it is not necessarily applicable to headphones because headphone drivers are negligibly light in mass... and is therefore much easier to "control" than speaker drivers. A damping factor of a sufficiently high amount (higher than 1) is usually enough to control headphones.

 

Read this:

http://gilmore2.chem.northwestern.edu/faqs.htm

 

It is a fairly old article, and there definitely are many newer headphones that are sensitive to output impedance; the "120 Ω" IEC standard is mostly considered to be obsolete these days. In any case, the following statements should stand for a system with insignificant non-linear distortion; if you think otherwise, then that is indeed a myth, and shows the lack of understanding physics:

- constant voltage source = zero output impedance: voltage does not change with load impedance

- constant current source = infinite output impedance: voltage is proportional to load impedance

- finite output impedance: Vload = Vout * Zload / (Zload + Zout)

You are free to have the opinion that the first case is not the best, and that a good headphone amplifier should have a fairly high output impedance. But that would, in addition to ignoring the advantages of having electrical damping, imply that many highly regarded and expensive amplifiers cannot drive headphones properly.


Edited by stv014 - 9/29/12 at 11:21am
post #28 of 46
Quote:
Originally Posted by Bill-P View Post

Uh... no. The high output impedance has almost nothing to do with that bass boost.

 

Yes, it does. Do you even understand at all what I wrote, or know the basics of how an amplifier works ?

 

Quote:

Originally Posted by Bill-P View Post

 

But I'm not talking about boosting bass there. I'm talking about actually "getting the right bass that the headphone was designed to output".

 

How do you know that the right bass is not what you get when you drive the headphones with a near-zero impedance voltage source ? It is not like a DT990 is in the need of more V-shaped frequency boosting from the amplifier.

post #29 of 46
Quote:
Originally Posted by Bill-P View Post

If you want to know, try plugging a low-impedance IEM into a high-impedance tube amp. See if you get any "boosted bass".

 

I do not recall mentioning IEMs at all. Those have quite different impedance vs. frequency characteristics, and typically do not resonate in the bass range.

post #30 of 46
Quote:

Originally Posted by Bill-P View Post

 

And I think I'll leave the rest at that. It looks to me like we're not on the same page, and a drawn-out discussion won't change anything since you are "resistant" to the idea that a more powerful amp would bring better sound quality... regardless of the fact that there are many who claim that much.

 

Alleged facts that are incorrect but claimed by many are exactly what one would call "myths". I am indeed resistant to the idea that something that cannot be proven credibly (or worse yet, is clearly false to anyone who has the education to understand it), brings better sound quality.

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