Head-Fi.org › Forums › Equipment Forums › Headphones (full-size) › Headphones and Amps (how I understand it)
New Posts  All Forums:Forum Nav:

Headphones and Amps (how I understand it)

post #1 of 142
12/26/10 at 2:35am
Thread Starter 

Hi Everyone,

 

This is post is not to spur arguments but more for me to understand something.  I recently got HD650 headphones and read many posts on whether they need amps or not.  To start with a small background I have a Masters in Electrical Engineering but it is not in circuits.  However, I still took all the core circuit classes so I understand voltage power and impedance.

 

Here are is a basic assumption I am making which is necessary to understand things: HD650's (and most dynamic headphones) use a combination of electromagnets (probably coil), permanent magnets, and some type of cone or for lack of a better way of putting it "air pump."  I'm going to additionally assume that the coil takes up 100% of the impedance (probably wrong but just to make this simple because thats what makes the difference).  So anyone that knows the impedance model would know that V = Z*I. or I = V/Z 

 

 

Switching to the Time domain it becomes the following:

 

Vl = Vi*cos(wt).  Or, in otherwords I = Vi*cos(wt)/jwL or I = Vi/L sin(wt) Where L is the inductance of the electromagnetic coil, w is the frequency Vi is the voltage from the amp or wherever the jack is.  All this is to say that, CURRENT and VOLTAGE has a LINEAR relationship.  

 

Magnetic power of a coil = N*I where N is # of coils and I is current through the coils. 

 

The cones are moved by the electromagnet, the power of the magnet is directly proportional to the # of coils and the Current.  Since the # of coils are constant, the only thing that changes with the voltage is the current.  as explained above coils*current translates to magnetic power.  more voltage is linearly more current.  so +2 volt would be +2 current which would be increase the power of the magnet by the # coils * 2 (if there were 10 coils it would increase the magnetic power from x to x+20).    All this is to say is that all increased voltage will do is increase current which increases the electromagnetic power of the coil which will push more air in the cone (without changing the frequency that the cone pushes the air) which makes the music sound louder AND THAT IS ALL.  Nothing about the voltage should change the frequency at which the cones move!!!!!  Additionally, the more coils the more powerful the electromagnet will be and the less voltage you would need for a loud sound.  The only probably I would have is if L was so big that V/L was really small such that the magnetic power could not move the cone, but this would cause NO SOUND or very little sound.  So if voltage has no effect on frequency how is it that an amp (which only increases the voltage output) will make the sound of the headphones be better?  I would understand if one enjoys the color an amp makes, i.e., if an amp puts out more voltages at certain frequencies, but the sound should not then be "better," just different equalization.  

 

So why is it that people believe that an amp (100% neutral amp) would make headphones sound better?

 

Now, I could be wrong, and if I am, please explain what I am missing. I believe all the equations I put up are correct.  

 

I did not post this to piss anyone off. I'm simply explaining how I understand speakers and amps.  I would like to understand why a high quality amp is required from an engineer's standpoint in case there is an actual reason.  Anyone with an EE degree could verify what I have said, though it's been a while so something might possibly be wrong.  

 

I completely understand that a great source might be required, because it is where the signal is coming from, and a bad signal will always produce a bad sound.  It is this requirement on an amp for quality sound idea that I do not understand.

 

I watched this lecture to brush up on my circuits (if you haven't taken a circuits class you'll probably be lost but if you have this is a really good brush up on the impedance model of circuits): http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-002-circuits-and-electronics-spring-2007/video-lectures/lecture-17/

 

sorry for any grammar or spelling errors, I am too lazy to proof this.

 

Thanks!

 

Reply

Gear mentioned in this thread:

Sennheiser HD 650 Headphones
post #2 of 142
12/26/10 at 3:01am

A little science certainly wouldn't go astray on this forum, however rusty. I'm technically ignorant so don't understand your figures, but neither do I understand the call for a powerful amp to drive the 650, which I've always found one of the easiest cans to drive. I'm prepared to accept that a reasonable amount of power is a Good Thing; where I draw the line is in the fervent insistence of some here that only a dedicated amp will do. From long experience, specifically with the 650, I've found any good brand integrated will sound just fine with the 650, with no gain whatsoever to be found in dedicated amps (I exclude the very expensive examples, which I've not heard and consider vast overkill anyway).

 

That said, I'd be happy to see a scientific debate here on why all that power--or rather current--is necessary.  Other phones I've had, like the Denon D2000, have been very hard to drive, but the 650 seems to me a piece of cake    

 

Reply
post #3 of 142
12/26/10 at 11:46am
Thread Starter 

Ill try to explain what I said as simply as possible with videos and stuff.

 

http://www.youtube.com/watch?v=VN0tmyyC0ak&feature=related

 

This is how a basic speaker is made.  if you go to around the 2 minute mark it shows that they use a "voice coil" which is just a coil of wires that when u run a current through it creates electromagnetic power which would then attract or repel a permanent magnet depending on the poles of the permanent magnet and the poles of the electromagnet.  the electromagnet's poles change by switching the current from 1 direction to the other direction.  when the current on the electromagnet is switched at a certain frequency that frequency will be translated to the cone by moving the cone at that frequency, causing that cone to make that frequency sound. (sound is made by vibrating the air and hence our ear drums at certain frequencies). 

 

OK

 

now electro magnets.  Wikipedia: http://en.wikipedia.org/wiki/Electromagnet

 

if u look at that page down at magnetic field created by current.  U see an equation for magnetic field by a coil on a iron core and an air gap.  in our case we have no air gap.  therefore, the magnetic power = N*I.

 

So we know how much magnetic power is generated to move the speaker depends on the number of coils times then current.  There is no way to know the number of coils, but the more the better generally.  However, more coils usually increases impedance which is represented by Z.  Z is a complex number that represents the impedance of the coil which has a component L.  L of an inductor increases by the the squared number of coils:  Wikipedia, http://en.wikipedia.org/wiki/Inductor (go to cylindrical air coil inductance formula on the chart).

 

Now you'll just have to trust me on this one because I can't find much on wikipdea on this.  but V = IZ  assuming the coil takes up 100% of the impedance.  Where Z = Ls and where s = jw where j is an imaginary number and w is the frequency.   So I = V/Z and when transfered to the time domain = V/jwL.  Actually I found it on wikipedia omg lol.  http://en.wikipedia.org/wiki/RL_circuit go down to parallel circuit where they have a resistor and a inductor and they determine the current through the inductor. 

 

It also shows that I will lag the voltage by 90 degrees.  just so  you know what that means, take a sin graph and shift it over the pi/2.  or in other words when the voltage is at the very peak the current will be at half it's peak.  but that doesn't matter, all that matter is that the magnitude of the current is capped by V/L.  However we know the value of L is 600 =P.  so what happens?  well lets say u have 6 volts going in.  then ur current will (AT MAX) be 6/600 = 1/100.  Ok, thats going to translate to magnetic power of N (number of coils in the HD650's coil magnet) * 1/100 = N/100.  The FREQUENCY never changes by the voltage max, or it shouldn't.  

 

now, if someone told me that a source could not do a certain frequency at certain voltages, I would understand that.  For example, if your soundcard had trouble doing 5khz frequencies at 6 volts such that it didn't do actually 5khz, then it would screw with the sound because it wouldn't be the correct frequency.  You would then have to keep the volume low from ur output so that it could still do the correct frequency and then have your amp, amplify that frequency to your headphones to get the correct level of volume you wish to have. 

 

Now people might say, well u need more "POWER" to move that magnet right? well yes and no.  More power , which = I^2R or V^2/R, is just more voltage or current which is just going to stretch the speaker more so that it moves more air which is making it louder.  If you didn't have enough power to move the speaker, the speaker would just not move and you would not hear the sound!.  Speakers do more than 1 frequency, so it is possible that it has power to drive some frequencies and not others making it sound bad.  OK that might be true, but then you would just turn up ur volume which would increase the voltage going to the speaker until it CAN produce those frequencies. 

 

OK, all this is to say that all the AMP does is amplify the voltage of the signal (hopefully equally to all parts) going to the headphones (it will likely introduce some noise because all amps do)  and should not make any difference in how the headphones sounds.  I have a assumption here being that increased volume knob or button on your computer just increases the voltage output of the sound signal (I do not see why it would not be this).  

 

Therefore, I cannot see why amps are needed for headphones where the volume you get is sufficient from your source. SOURCE is important and I would never debate that.  AMPs only introduce noise as a trade for increased signal strength.  If an amp has made something sound different, it is the AMP introducing noise to your signal (even if that noise is making the signal sound nicer). any additive to the original signal is considered noise.  

 

I'll gladly be proven wrong.  If I'm missing something please tell me.  But I don't currently see why an amp is needed for any DAC that goes to sufficient volumes without an amp.  It seems that money would be better spend on quality lossless music files and good sources. 

 

It is also true that low impedance does not mean louder music at all.  impedance only changes how much current is going through the coils depending on the voltage.  the # of coils is also important to determine the loudness of the music.  

 

This link to the wiki page has a person trying to describe some of the ideas.  do a search for atothex.

http://www.head-fi.org/wiki/a-hopefully-helpful-headphone-buying-guide-for-newbies-by-boomana

 

However he makes the mistake of saying that current intensity is measured in watts.  that is not true or at least no one speaks of current intensity as power.  I do not know what he is talking about.  though P does = V*I.  additionally he is wrong about how low impedance changes how freely electrons move (but a lot of people make the mistake of thinking that current movement is done by electron movement).  Technically yes electrons move, but very slowly, and in an AC circuit they basically don't migrate at all, there was a famous court case with a state that tried to tax electricity as a imported good because they said they were importing electrons and lost because they proved this was not true HAHA.  ANYWAYS, the guys statement about shorting and sensitivity could be correct, however, shorting is not an issue with changing voltages which is happening here.  Even IF a short was created nothing bad happens with a short unless something starts over heating.  Sennheiser is also not very stupid, they probably have a resistor to take the rest of the load if a short is created (assuming a short is even a danger).

 

Now the sensitivity, hmm, I have no idea about this but I would expect higher sensitivity would produce quicker and faster sound.  I'm guessing sensitivity has to do with how much power is needed to move the speaker membrane a certain distance? what ever I feel like i have gone off track.

 

In conclusion, please let me know why an AMP is needed for high impedance headphones and what mistake I am making in determining that AMPs do nothing but increase signal strength.

 

Thanks!!!

 

Reply
post #4 of 142
12/26/10 at 2:46pm

Yikes, there are a lot of assumptions being made here. I can see the point that you're trying to make, but a lot of your conclusions are built upon oversimplifications.

 

Rather than try to pick apart your massive wall of text, let me try to draw some comparisons:

- The power in a car engine is essentially derived from combustion driving the pistons. If I want more power, can I simply pump more fuel and increase the size of the pistons? There's so much that goes into the support of engine, I can't even begin.

- Can a track runner undergo surgery to lengthen his legs so he can run faster? What about balance, what about speed, are longer strides offset by slower pace, etc.

- Will a rowing team go faster if you simply tell them to take bigger strokes? Your body is weaker at extended position so you lose power, or rather your power transfer is less efficient

 

An audio signal is more much complex than just a sine wave.

 

There is more to sound than just volume.

 

You can't just feed a signal into a voice coil and assume that your output actually matches what you put in.

 

An amplifier (whether discrete, tube, opamps, etc) doesn't magically make a signal bigger. There is a lot happening in the background there to try to create that amplification accurately. Heck, in most applications there's a voltage gain stage which handles just the voltage amping, then a separate current stage that provides all the juice. Now you have to get those two parts to cooperate in a nice manner. After that, how do you ensure that the whole shebang actually transfers accurately to the headphones? Just tapping the + and - terminals to the corresponding output doesn't necessarily produce the best results. There are buffers, impedance matching concerns, etc.

 

Do you want to talk about power supply? Getting a clean source of power, whether AC or DC is an endless hassle. How do you prevent AC ripple or DC offset? AC contamination has been plaguing audio ever since its inception. Even the simplest of opamps or discrete amping topology will create DC offsets which feedback into your input.

 

etc etc etc

Reply
post #5 of 142
12/26/10 at 3:17pm

Silly guy. 

 

Nobody wants to listen to all that technical talk about science and equations based on facts. 

We all know that amps run on magic. 

And magic, my friend, can only be explained through colorful adjectives used by liberal arts degree holders.

There may be one or two other people on this board that cares about "science." 

But be warned.  Science will only bring you trouble. 

 

Because you're new, let me show you the ropes.

Here are the facts that you should know before discussing anything: 

 

1. Upgrading cables can make music sound different:  bright or dark, veiled or crisp.  Paying more for the cable will not always, but almost always make your headphones sound better.

2. Sources need to have a neutral sound signature, but it is good when the amp changes the sound signature.  It is preferable for the amp to add warmth when it is lacking, or add detail to already warm sounding headphones.  Clearly, amps are not only about power, low noise and low distortion.

3.  Double blind A/B testing is completely pointless and proves nothing.

4.  Science is its own bias.  Therefore, opinions based in science, are usually less valid than another's conjecture. 

5.  Music can sound "fast" or "slow" depending on what your combination of equipment is. 

6.  Burning in aka playing your headphones for about 100 hours or so will make them sound even better than new.  This is not because your ears adjust to the sound of the headphones, or somehow get used to the equipment. 

 

Welcome to head-fi:  where the creationists of electronics enthusiasts gather. 


Edited by sugarkang - 12/26/10 at 3:19pm
Reply
post #6 of 142
12/26/10 at 5:54pm
Thread Starter 
Lol sugar.

@arm, sorry I'm replying on my phone so I can't address everything.
But, nothing u said makes anything I said wrong. The amp may do things to try to reduce noise when it amps a signal but that does not mean it makes the signal any better. Ur comparison if increased voltage to longer arms makes sense. As for rowing, if everything else stayed. The same and they just increased stroke size or speed then yes they would go faster. Hhahaha
Reply
post #7 of 142
12/26/10 at 6:07pm

amping does make a difference. i'm not a trained electrical engineer, so i won't try to describe why, but it's definitely true, even if it is just that last 10% sometimes.

 

all i know is that my HD650's suck out of a PA2V2(2.4 volt power supply) and kick major ass out of my HeadRoom amp(15 volt power supply). the PA2V2 couldn't drive them to acceptable levels, and the HeadRoom drives them to insane levels with plenty of headroom to spare. (pun intended)

 

my pair of IEM's also sounded better out of the PA2V2 than they did plugged straight into my smartphone. even if it was only 10% better, it was still better.


Edited by jasonb - 12/26/10 at 6:15pm
Reply
post #8 of 142
12/26/10 at 6:57pm

Surely someone with a master's in EE knows that amplifying a signal and transferring power is not a trivial thing, correct? (especially when this power is translated into mechanical movement) There are always irregularities to the amplification. Heck, the type of amplification even have classifications (ie: class A, B, A/B, T, etc) which all accomplish the same thing different ways and have their pros and cons each, nevermind the bajillion methods to accomplish each type.

 

I'm not even sure what kind of point you're trying to make anymore...

 

Speakers will clip if you underpower them. The voltage peaks get clipped out and/or current clips out because the amplifier can't push out enough Now you wind up feeding clipped square waves through the amp and blow the circuit. That's sort of an extreme case though, but it's an example of insufficient power.

 

Orthodynamic and electrostatic headphones are also notoriously hard to drive. Sure you could plug them into the headphone jack of your ipod, but you'll barely get any sound out of it. Heck, I tried driving some stats through a tube amp which has a huge voltage gain but low current, and the headphones sounded awful. You could literally hear the low end clipping. I'm not talking audiophile geekery of "depth" and "fullness", but actual clipping and degredation of the audio signal because the amp couldn't handle it.

 

 

Quote:
As for rowing, if everything else stayed. The same and they just increased stroke size or speed then yes they would go faster. Hhahaha

 

And that assumption of "if everything else stayed [[the same]]" is very very wrong. You can't just make things bigger and assume everything else falls into place.

 

Reply
post #9 of 142
12/26/10 at 7:31pm



 

Quote:
Originally Posted by Armaegis View Post

Yikes, there are a lot of assumptions being made here. I can see the point that you're trying to make, but a lot of your conclusions are built upon oversimplifications.

 

Rather than try to pick apart your massive wall of text, let me try to draw some comparisons:

- The power in a car engine is essentially derived from combustion driving the pistons. If I want more power, can I simply pump more fuel and increase the size of the pistons? There's so much that goes into the support of engine...



 I'm curious about this stuff myself. I think EE's analogy was similar to yours. If the amp source is supplying the horsepower and the headphone is providing the torque what differentiates some of these amps from others. I know from personal experience I experienced a dramatic difference going from the uDAC to my Sparrow. One has a dedicated power source and one is USB. Big difference. But what is going on behind the scences in an expensive amp versus something less expensive? If both amps have a dedicated power source (fuel) and both are creating sufficient horsepower why would the voice coil (the torque converter) if you will in the analogy perform differently?

Reply
post #10 of 142
12/26/10 at 9:00pm


However, any signal, no matter how complex it is, can always be broken down into a sum of sinusoidal functions. I agree that there are some oversimplifications in OP's arguments:

 

1. Impedance of a headphone does not vary as jwL. Impedance vs. w plots of different headphones are different. I don't know why this is so.

2. You are also assuming that output voltage will not vary with load impedance of the circuit. Basically, the Vout/Vin should be linear throughout, which is easiest in Class A biasing. 

 

Circuits is not my area of specialization as well, I'd love to see some inputs from more experienced people, probably someone with DIY experience.

Quote:

 

An audio signal is more much complex than just a sine wave.

 

 

Reply
post #11 of 142
12/26/10 at 9:44pm

Electrically, the headphone load is a little more complicated than what you're describing, even for the typical moving coil (dynamic) drivers that are in most headphones.  In the very least, this is evidenced in the impedance vs. frequency graphs of many different headphones.  Also, movement of the transducers and the production of sound waves--the mechanical aspect--is out of my specialty as well.

 

Anyhow, the difference in amplifiers on audio fidelity has to do with the nonlinearity of the amplifiers and various nonideal effects.  Different amplifiers will have different total harmonic distortion (THD), intermodulation distortion (IMD), signal-to-noise ratio (SNR), crosstalk, power supply rejection ratio (PSRR), etc.  A bad amplifier may be as loud as a 100% neutral amplifier, but it might have noticeable harmonic distortion that the other does not when given the same input.  In a simple test case, you can send a 1kHz sine wave to amp A and the same signal to amp B and measure what comes out on the output.  You might see significant power on 2kHz, 3kHz, 4kHz, etc. harmonics on the output of a poorer amp, as just one example.

 

Short answer:  you should consider the amp as part of the source in your below assessment.  A poorer amp will distort the signal coming out of the DAC by more, thus giving a "bad" signal to the headphones or speakers even if the signal out of the DAC was "good."  A theoretically perfect amp would reproduce exactly the same shape of the input it was given no matter what it was being loaded with, and no matter how the input changed.  i.e. you can put in any kind of waveform in, and the output would be exactly the same as the input but twice (or 1/54, or whatever) the amplitude of the original.  In reality, you can't do that perfectly. 

 

"I completely understand that a great source might be required, because it is where the signal is coming from, and a bad signal will always produce a bad sound.  It is this requirement on an amp for quality sound idea that I do not understand."

 

How accurate an amp needs to be for no humans to be able to tell them apart...is a topic for another day.  Also, some people like amps with intentional distortions, and that's well and good too.

 

 

Some RMAA results might be relevant for illustration.  Yes, RMAA isn't a perfect test suite, but it's sufficient for our purposes here.  You can see how an amp even performs significantly differently even compared with itself when given different loads.  The first link is of the Cowon D2 player (and its internal amp).  The second is of the Cowon D2 through a Headsix amp.


http://rmaa.elektrokrishna.com/Comparisons/Comparison%20-%20Cowon%20D2%20-%2016%2C%2080%2C%20300%2C%20600%20Loads.htm

http://rmaa.elektrokrishna.com/index.php?dir=Comparisons/&file=Comparison%20-%20Cowon%20D2%20-%2016%2C%2080%2C%20300%2C%20600%20Loads%20-%20Headsix.htm

 

http://rmaa.elektrokrishna.com

 

 

last edit for today:  upon rereading, I think maybe you or some people in general sometimes forget that you have what amounts to an amp section in every single source.  There's no way a DAC chip is outputting 10mW power or whatever with the kind of characteristics you want, so you need some kind of buffer (read: amp), current driver (read: amp), external amp (read: amp), op-amp (read: amp), or amplifier section (read: amp) in between that and the output to your headphones.  The question is never about whether or not you need an amp.  It's about whether or not you need a better amp.

 

Some people throw around the term "unamped" or talk about using headphones/IEMs straight out of a sound card, portable player, motherboard audio chip, etc.  All those have amps of some sort inside.


Edited by mikeaj - 12/26/10 at 10:09pm
Reply
post #12 of 142
12/27/10 at 12:01am
Quote:
Originally Posted by mikeaj View Post

Some people throw around the term "unamped" or talk about using headphones/IEMs straight out of a sound card, portable player, motherboard audio chip, etc.  All those have amps of some sort inside.



 Yes, and that's a point that warrants a whole other thread. I often wonder what people mean by that when it's impossible not to have an amp of some sort. Often they'll even be using an integrated amp or receiver and ask if they need an amp, meaning a dedicated HP amp. That kind of irritates me. 

Reply
post #13 of 142
12/27/10 at 12:05am
Quote:
Originally Posted by Armaegis View Post

 

I'm not even sure what kind of point you're trying to make anymore...

 

 



 

EEtrunks: "Therefore, I cannot see why amps are needed for headphones where the volume you get is sufficient from your source. SOURCE is important and I would never debate that.  AMPs only introduce noise as a trade for increased signal strength.  If an amp has made something sound different, it is the AMP introducing noise to your signal (even if that noise is making the signal sound nicer). any additive to the original signal is considered noise."   

 

 I believe these two pieces of the jigsaw belong together.


Edited by pp312 - 12/27/10 at 5:27am
Reply
post #14 of 142
12/27/10 at 12:31am

I bought a cheap amp to play around with and discovered what all the fuss is about.  In short, raising volume causes distortion.  The better the equipment used to raise the volume, the less distortion is added.

 

I run my sound card -> a cheapo computer speaker amp -> a cheapo headphone amp

 

If I set all 3 devices to about 10% volume, very little sound comes out.  If I crank up the volume to a desired listening level on any one part of the chain, differences can be observed.  The DAC in my sound card produces a nasty scratching sound when pumped up to 250% in software.  The speaker amp produces an aweful low hum when cranked all the way up.  The headphone amp on the other hand, can take the 10%->10%-> signal and boost it up to my desired volume without introducing any noticeable distortion.

Reply
post #15 of 142
12/27/10 at 3:10am

guess the question is not 'does it sound better with AN amp ?', but rather 'could it sound better with A DEDICATED amp ?'.

 

I completely subscribe the mikeaj post.

 

all devices -even the hp socket of a CDP, or an mp3p, or whatever- have some sort of amplification behind; and it is true that an amp always intoduces noise on the signal.

so, there's a matter of better and worse amps (due to economical reasons, hp-outs of CDPs and mp3ps are often -not always- 'poor'); and, maybe what's more, there's a matter of better and worse matching between amps and headphones.

I appreciate the ironic post by sugarkang about science and magic normal_smile%20.gif, but be careful not to reach the opposite extreme, according to which: "science is true; don't let facts deceive you". wink_face.gif

now, it is a common experience that some headphones sound truly bad with some amps and truly good with some others (mainly in terms of dynamic), and that some headphones are less demanding than others about that.

 

Reply
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Headphones (full-size)

Gear mentioned in this thread:

Sennheiser HD 650 Headphones
Head-Fi.org › Forums › Equipment Forums › Headphones (full-size) › Headphones and Amps (how I understand it)