How do headphones actually work?

[qpwoeiruty]

I find it very interesting to see how different kinds of headphones work. I am also researching this topic to see if i can present a research paper on it.....so far however i havent found much useful information...... I myself own ATH M50's.....So what is the physics behind these amazing speakers?...... I am sure a lot of people would find this interesting, myself included...... 

 

[scompton]

There's a coil of wires wrapped around a stationary magnet.  As electricity flows though the wire, the wire moves.  It's attached to the diaphragm, moving it and producing sound.
 
http://en.wikipedia.org/wiki/Headphones#Technology

 

[qpwoeiruty]

Could you be a little more specific? How do the wires actually move the diaphragm? And also, how exactly does the diaphragm produce sound? I think that its due to its vibrations, but that still doesnt explain why is the diaphragm cone-shaped? And how exactly is the electricity transmitted? 

 

[dan1son]

Then there's electrostatics, orthodynamics, and armature drivers that work differently. 
 
electrostatics use two plates, one positively charged and one negatively charged, and a diaphragm in between them that is extremely low mass.  The charges on the plates are changed quickly causing the diaphragm to move.  They usually have MUCH higher voltage charges than a standard magnetic driver.
 
Orthodynamics are similar to electrostatics except the plates are magnets arranged in a sort of matrix and the diaphragm is given the signal to move itself back and forth.  Still has the sandwich idea which has the advantage of the entire diaphragm moving together instead of from one point like a standard driver.
 
Balanced armature drivers are kind of like a dynamic driver in a sealed in box except instead of the diaphragm being directly connected to the voice coil it's external and attached to an arm which moves in between two stationary magnets.  The arm is magnetically charged with tiny voice coils on one end and moved between magnets on the other.  Then a small rod is attached to it and then to the diaphragm.  That's all inside of a tiny sealed box with one hole.  That allows for completely sealed IEMs.
 
 
With the exception of electrostatics, speakers are extremely simple devices.  Put a suspended diaphragm attached to an electromagnet near some kind of solid magnet (or just magnetic metal) send it an A/C signal and poof you have sound.  The hard part is finding the right amount of winding, perfect suspension material (usually the surround of a speaker), rigid enough yet light enough diaphragm, heat dissipation to support high currents and friction, etc. 

 

[dan1son]

Quote:

Could you be a little more specific? How do the wires actually move the diaphragm? And also, how exactly does the diaphragm produce sound? I think that its due to its vibrations, but that still doesnt explain why is the diaphragm cone-shaped? And how exactly is the electricity transmitted? 

 
The wires are connected to the voice coil which is just an electromagnet.  It's sent an A/C voltage signal which changes the magnets polarity causing it to move back and forth at the same frequency as the A/C signal.  The back and forth movement of the diaphragm causes compression in the air at the same frequencies the signal has which produces sound, just like the movement of a drum head.  The diaphragm is cone shaped because cones are far stronger than flat surfaces, especially when the voice coil can only be attached at one point (the tip of the cone in this case). 
 
Electricity is just transmitted as an alternating current voltage signal that matches the waves of the music.  Higher voltage and/or higher current = more magnet movement thus more air compression and volume. 
 
 
Records are the simplest way to understand reproduction end to end since they physically contain a groove that matches the wave of the music.  The needle does exactly the opposite of a speaker, taking physical movement, turning it into a magnetic signal, turning that into a voltage signal, which is then amplified and driven into a speaker. 

 

[scompton]

Quote:

Could you be a little more specific? How do the wires actually move the diaphragm? And also, how exactly does the diaphragm produce sound? I think that its due to its vibrations, but that still doesnt explain why is the diaphragm cone-shaped? And how exactly is the electricity transmitted? 

 
One end of the coil is attached to the diaphragm so when the coil moves, the diaphragm moves.
 
All sound is produced by pressure waves in a media so, yes, the movement/vibration of the diaphragm causes the sound.
 
I'm not sure what you mean by how is the electricity transmitted.  It's transmitted thought the wires.
 
Headphone diaphragms aren't really cone shaped.  I'm sure the shape of various diaphragms were derived though lots of research. 
 
 

 

[qpwoeiruty]

Thats a great explanation!

 

[eujaee]

Cool thread.  What I always wondered was how a single vibrating diaphragm can produce multiple frequencies at the same time.  I'm not scientifically minded, so if you could keep the explanations on the Barney level, that would be great.

 

[mikeaj]

It's vibrating in a way that contains multiple frequencies.  All sounds except pure sine waves contain multiple frequencies, just some louder than others.  Each driver is following an input like one of these (top is L and bottom is R; the voltage across the driver looks like this over time), and that input contains multiple frequencies.  You can think of the positions of the drivers following the waveforms below.
 

 
Quote:

Cool thread.  What I always wondered was how a single vibrating diaphragm can produce multiple frequencies at the same time.  I'm not scientifically minded, so if you could keep the explanations on the Barney level, that would be great.

 

 

[scompton]

Quote:

Cool thread.  What I always wondered was how a single vibrating diaphragm can produce multiple frequencies at the same time.  I'm not scientifically minded, so if you could keep the explanations on the Barney level, that would be great.

Think of it this way, headphones are essentially a reversed microphone.  A dynamic mike is essentially the same as a dynamic headphone except that the diaphragm is moved by the pressure waves from external sound.  As the diaphragm moves, it moves the coil which generates an electric current which is either recorded on analog media or converted to digital and recorded on digital media.  When the music is played back, the reverse happens, the same electrical signal is created from either an analog or digital source and is sent to a voice coil that moves the diaphragm in the exact same way as the original mike's diaphragm was moved.
 
Someone in the ortho thread experimented with using an ortho headphone as a mike and it worked.  Condenser mikes and electret headphones use the same technology.
 
http://en.wikipedia.org/wiki/Microphone#Speakers_as_microphones
 
Edit:  In the above link, they talk about the Yamaha Subkick mike which is a 6.5 inch woofer mounted in a 10 inch drum shell.
 

 
 

 

[Curly21029]

Buncha scientists up in this thread.  To answer the OPs question... miracles.
 
Just being silly of course.  Great information here.  Thanks all for the read.

 

[obzilla]

Quote:

 To answer the OPs question... miracles.
 

I was totally going to say "magic,.. duh!".
 

 

[eujaee]

 
Quote:

It's vibrating in a way that contains multiple frequencies.  All sounds except pure sine waves contain multiple frequencies, just some louder than others.  Each driver is following an input like one of these (top is L and bottom is R; the voltage across the driver looks like this over time), and that input contains multiple frequencies.  You can think of the positions of the drivers following the waveforms below.
 

 
 

Thanks for this, I mostly understand this explanation.  It's hard to picture what the driver is doing, though.  I hope this next question makes sense, but here goes.  I'm picturing 30Hz over a 1s interval, one wavelength, and I can see how the driver would vibrate.  Then I'm adding a 90Hz signal over 1s and at the same amplitude so I got three wavelengths inside the 30Hz wavelength.  This I cannot picture, because it seems one signal would be trying to make the driver vibrate at 30Hz, the other one trying to make it do 90 at the same time, er wait a second.  If I added the two together, would the picture be more like the graph you posted?  And then add a bunch more to get something as jaggy as your graph?  If so, I still can't picture how the driver would move to make the two frequencies at the same time.  Maybe Barney's too advanced, I need it broken down Teletubby style.

 <edit 05/11/11 12:58>
I've thought about it over lunch and I think maybe you've already answered my question in your post.  Tell me if this is correct.  Say I can look at the driver from the side and my eyeballs are super fast.  I pick a point on the driver and watch it in slow-mo as the signal from your graph comes through.  The dot's motion would exactly trace the ups and downs of the graph and this motion would make many frequencies at the same time because if you added up all the waveforms for the different frequencies in the music, it would look like that graph?  And I should of used 1Hz and 3 Hz instead of 30 and 90.  If this is not right, it may be hopeless.
 

 

[LizardKing1]

It envolves magnets, so only a mormon member could tell you how they work.
 
PS: Insane Clown Posse just announced they're planning to use the thread's title as their new hit single.

 

[Wildstar]

 <edit 05/11/11 12:58>
I've thought about it over lunch and I think maybe you've already answered my question in your post.  Tell me if this is correct.  Say I can look at the driver from the side and my eyeballs are super fast.  I pick a point on the driver and watch it in slow-mo as the signal from your graph comes through.  The dot's motion would exactly trace the ups and downs of the graph and this motion would make many frequencies at the same time because if you added up all the waveforms for the different frequencies in the music, it would look like that graph?  
 

That's it.