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Why do we have amps and headphones with large resistance levels?

post #1 of 46
Thread Starter 

So I have a pair of Beyerdynamic dt 880 600 ohms. Some of my friend were listening an they asked me why I needed to drive them with an amp and wouldn't it be more efficent if the headphone company simply made the exact headphone with a lower resistance level. I thought about this and had no idea why this was. Anyone know the answer?

post #2 of 46

My best guess.

I believe it's preferred to use high impedance headphones for certain recording studios functions.

And home receivers headphone jacks work best with high impedance headphones.

So there is a current market for high impedance headphones.

Also I believe it's only been with the release of iPod and better portable audio players, that has caused a growing demand for quality low impedance headphones.

 

Plus, I've found stuff sounds really good at 600-Ohms.

post #3 of 46
Thread Starter 
Quote:
Originally Posted by PurpleAngel View Post

My best guess.

I believe it's preferred to use high impedance headphones for certain recording studios functions.

And home receivers headphone jacks work best with high impedance headphones.

So there is a current market for high impedance headphones.

Also I believe it's only been with the release of iPod and better portable audio players, that has caused a growing demand for quality low impedance headphones.

 

Plus, I've found stuff sounds really good at 600-Ohms.

But what is the point? Wouldn't it be convinent just to make the headphones have a low resistance so it works for any setup?

post #4 of 46

you don't get something for nothing... higher impedance means more wire, more wraps... which means more magnetic flux... which means more dynamic response given the same mass of movement... means better tighter sound with more headroom.

 

think about it this way, why do sports cars have more powerful engines? it is all about no compromise performance.

post #5 of 46

the Z thing again:

Quote:
Originally Posted by jcx View Post

Beyer's comments are suspect - probably marketing not understanding the tech

 

for the same motor structure - same mag field, same voice coil dimensions - you are "free" to design to "any" impedance you want by using the same weight of copper - trading of turns count against wire size - within the limits of practical wire size, some "2nd order" limitations of fill factor/insulation thickness tradeoffs

 

the effect is like having a "ideal transformer" built in - the electro-mechanical driver properties are identical except for the terminal impedance scaling factor - the the electro-acoustic response should be the same as well

 

for Beyer to claim that the same model # with different impedance has different "speed" means they didn't follow this well known motor design principle and deliberately designed in different responses

 

or the marketing guys just couldn't refrain from making something up

 

some pro monitor headphones have high enough Z, low enough sensitrivity to directly connect to some audio power amp output at levels suitable for drivng loudspeakers

post #6 of 46
Quote:
Originally Posted by Saleri View Post

But what is the point? Wouldn't it be convinent just to make the headphones have a low resistance so it works for any setup?

Most headphones sold in the world are somewhere between 32-Ohm and 60-Ohm

Headphones for portables would be in the 16-Ohm to 40-Ohm range (?)

 

Low impedance headphone may not work with every headphone jack on the planet.

Receivers (at least most) can not work as well with low impedance headphones.

post #7 of 46

Well the DT880's are available in 32, 250 and 600 ohms.  So you have your choice for your needs to some extent. 

 

Some sources like say a computer sound card have limited voltage to use.  A lower resistance with a given voltage gives more milliwatts output.  Higher resistance requires more voltage for a given milliwatt level of output. So you might need an amp.  This is much simplified.  I realize this doesn't really answer your question much.  

post #8 of 46
Thread Starter 

But why do some companies still make headphones with large resistance levels? What's the point?

post #9 of 46
Quote:
Originally Posted by Saleri View Post

But why do some companies still make headphones with large resistance levels? What's the point?

Because there are headphone jacks in the world that can not effectively work with low impedance headphones, only high impedance headphones.

post #10 of 46

http://www.head-fi.org/a/headphone-impedance

 

These covers the basics of it reasonably well.  

 

Lots of it is historical, and for different situations different values work out the best.  LowZ phones are needed by modern low voltage chip sources.  Studios that use possibly several phones driven at once prefer them to be HiZ to not load down the source if more than one phone is used.  Old tube equipment had higher voltages and low z phones would have not worked well with the higher voltage.  Some old transistor receivers actually tapped the speaker outputs with a voltage divider.  Left you with plenty of voltage though a bit higher output impedance.  Worked fine with the HiZ phones without needing an actual separate circuit for the headphone.  And prevented phones from loading the speaker output in any manner that could matter. 

 

Some sources mention LoZ phones have fewer turns of wire and therefore are less accurate and more likely to distort which is why higher end phones favor HiZ.  Don't know if that is really a limiting factor or not as some good LoZ phones are certainly available.  

post #11 of 46

Here is the explanation from the Beyer webpage:

 

The higher the impedance, the more power is needed to get a proper output volume from the headphone:

32 or 80 ohms = mobile use with laptop, MP3 Player, portable recorder etc..

250 ohms and higher = for permanent installations, headphone amplifiers etc.

 

Background:

Impedance ist the AC resistance of the headphones' voice coil, which is connected to the headphone amplifier. A impedance of 0 ohms would be a short-circuit of the headphone amplifier output; the headphone amplifier supplies an extreme current and after getting very hot, it either turns off automatically - or dies. The other side of the story is infinite resistance (broken cable); no current flows, but also no audio signals arrives - so, we have to be in between these two: 0 and infinite.

 

In general, headphones with low impedance are designed for use with mobile devices; mobile devices use low power from batteries and therefore also the output power is limited. A low impedance headphone can play (slightly) louder at a low power output. But why high impedance headphones?

 

The impedance is determined by the voice coil (dynamic headphones), which is a wound copper wire (coated to avoid a short-circuit). This copper wire is available in nearly every length, but not in every gauge (thickness) and a thicker wire has less resistance than a thin wire ("less fits through"). The magnetic field of the voice coil depends on the number of windings of the coil, causing a low impedance system to use a thicker (also heavier) wire and since the membrane foil can't be infinitely light-weight, the moving mass (voice coil and diaphragm) is relatively high. It's pretty clear that a higher mass can't move as easily (following an audio signal) as a lower mass. This low mass can easily be accomplished with thinner (lower weight) wire, but the thinner wire has a higher impedance. This means that the DT 770 PRO with 250 ohms sound more natural, but plays (depending on the used headphone amplifier) not as loud as the 80 ohms version.

 

The transducers of the 80 ohms versions are stronger and more powerful, a bit more low-mid accentuated and therefore this version is ideal for powerful reproducing of low-frequency material f.e. coming from a bass guitar. The 250 ohms version sounds more smooth and voluminous and can be used for mixing situations within the studio to analyse the whole mix.

post #12 of 46
Quote:
Originally Posted by esldude View Post

Here is the explanation from the Beyer webpage:
The higher the impedance, the more power is needed to get a proper output volume from the headphone:
Quote:


That first sentence doesn't look right.
A higher impedance headphone will use more voltage, but less current.
Not necessarily more power.

Edited by Chris J - 7/2/13 at 9:36am
post #13 of 46

I can think of a different reason why people buy them: Since many headphone amps have imo too high gain you get more usable volume control range with high impedance cans (assuming similar sensitivity).

 

But yeah, for studio use you can connect many high impedance headphones in parallel without stressing the amp.


Edited by xnor - 6/30/13 at 9:47am
post #14 of 46
Quote:
Originally Posted by esldude View Post

Some sources like say a computer sound card have limited voltage to use.

 

That is not universally true, there are sound cards that can output 7 Vrms voltage into a high impedance load without clipping. That is normally enough even for 600 Ω headphones. Also, it is common for the output impedance to be in the range 10 to 100 Ω. If it is really high, the maximum power output into a 32 Ω and a 250 Ω load may actually be comparable.

post #15 of 46

Low voltage sensitivity can also be an advantage with noisy outputs. For example, my low impedance headphones sometimes have audible interference noises from my laptop, while the less sensitive 250 Ω ones are less affected by this issue while generally still being loud enough.

 

Generally, high headphone impedance can be an advantage if there is enough voltage output, but there are issues with:

- too high output impedance (this is fairly common with certain types of devices)

- too low maximum current output (e.g. from a cMoy amplifier), or high distortion when outputting high current

- capacitor coupled outputs (lower load impedance = more bass roll-off)

- too high gain (as noted above by xnor)

- high output noise voltage even at low volume

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