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Please explain HP impedance in regard to orthodynamics

post #1 of 7
Thread Starter 

I've researched, but I'm still at a bit of a loss.  Here is the riddle.

 

Hifiman he-6 Impedance: 50 Ohm - efficiency 83.5

Grado impedance: 32 Ohm - SPL 98

Sennheiser Impedance: 300 Ohm - SPL 97

Beyer DTxxx Impedance: 250 Ohm version SPL 96

 

The Hifiman cans are the most difficult to drive.

 

Is the impedance measured on a different scale for orthos?  Efficiency plays a part here, but I still remain confused as to how to use these numbers when picking an amp for any of these.

 

I'm sure this is a thread that has been up before, but with the BS search on head-fi, I cant find it.

 

Help

post #2 of 7

This should answer all your questions and clear up some misconceptions that are propagated on this forum.

post #3 of 7
Quote:
Originally Posted by Keithpgdrb View Post

I've researched, but I'm still at a bit of a loss.  Here is the riddle.

 

Hifiman he-6 Impedance: 50 Ohm - efficiency 83.5

Grado impedance: 32 Ohm - SPL 98

Sennheiser Impedance: 300 Ohm - SPL 97

Beyer DTxxx Impedance: 250 Ohm version SPL 96

 

The Hifiman cans are the most difficult to drive.

 

Is the impedance measured on a different scale for orthos?  Efficiency plays a part here, but I still remain confused as to how to use these numbers when picking an amp for any of these.

 

I'm sure this is a thread that has been up before, but with the BS search on head-fi, I cant find it.

 

Help


Impedance is the measure of electrical resistance.

Efficiency is how much of the power consumed actually does work.

Sensitivity, or load, is how much work is done at a given power level.

 

Ohm's are related to how much sound you get at a given mw only because it impacts how many mw your amp can deliver.

 

What you are seeing with the orthodynamics being insensitive is their power requirements. They are doing more work and so require more power.

 

 

 

In terribly simplistic terms think of it like this:

 

You have a 9 volt battery and 2 motors.

 

Motor #1 is very small, like a little PC fan but because it has a low number of windings it has a high impedance and so when you connect it to the battery it spins at 10,000rpm. It is not doing as much work because it is small, there for it doesn't need as much power. If it were more efficient then the battery will last longer but it will spin at the same speed. And sensitivity, in the case of a fan would be the amount of air it moves relative to how much power it consumes.

 

Motor #2 is larger than the first one, like a much larger pc fan and has more windings which makes it have less resistance, but since the motor is much larger it takes more work to make it move so it only spins at 7,000RPM on the same battery. It has less resistance but it is doing more work and so it requires more power. Higher efficiency means the battery will last longer but it will still only spin at 7,000RPM. And sensitivity, in the case of a fan would be the amount of air it moves relative to how much power it consumes.

 

 

Therefor if you want to power it to the same level as motor #1 you need a more powerful power source.

 

 

 

A high impedance dynamic headphone does not require as much power as a low impedance orthodynamic and so you must use a 'bigger battery' more powerful amplifier to drive the orthodynamic to the same sound levels as the dynamic.

 

 

Try not to confuse sensitivity with efficiency. A highly sensitive headphone will produce a lot of sound without a lot of input. A highly efficient headphone will not run your battery down in your phone as much as an inefficient headphone driven to the same level, all other things being equal.


Edited by Kodhifi - 1/21/13 at 12:20pm
post #4 of 7
post #5 of 7
Quote:
Originally Posted by Keithpgdrb View Post

I've researched, but I'm still at a bit of a loss.  Here is the riddle.

 

Hifiman he-6 Impedance: 50 Ohm - efficiency 83.5

Grado impedance: 32 Ohm - SPL 98

Sennheiser Impedance: 300 Ohm - SPL 97

Beyer DTxxx Impedance: 250 Ohm version SPL 96

 

The Hifiman cans are the most difficult to drive.

 

Is the impedance measured on a different scale for orthos?  Efficiency plays a part here, but I still remain confused as to how to use these numbers when picking an amp for any of these.

 

I'm sure this is a thread that has been up before, but with the BS search on head-fi, I cant find it.

 

Help

 

Heya,

 

To make it completely simple and avoid lengthy reading, there's two things to consider. 1) think of orthos how you think of speakers, not headphones and 2) a lot of these numbers should not be looked upon with linear expectation.

 

Ignore impedance. It's a value that really doesn't have a huge effect on what you're looking into. You'll find headphones with 25ohms and 600ohms both needing an amplifier, and examples of both working fine with no to minimal amplification too. How impedance affects things is more important to relate to how the amplifier being used works and how well it generates voltage and where it's peak values are depending on the kind of amplifier it is. The same can be related to low impedance. Orthos happen to be low impedance, but are not sensitive, they require a lot of current from an amplifier, instead of voltage, to move the diaphragm which in turn gives you sound. So that low sensitivity in the 80's on the HE-6 tells you it needs a ton of current from an amplifier. Like a speaker does. A high impedance headphone that is sensitive (like Sennheisers) need some voltage from an amplifier, but do not need much current. This is much more common of a headphone in the headphone world.

 

End of the day, this all revolves around how an amplifier works. If you read up on how an amplifier works with a load with relation of voltage and current, you'll understand the impedance/sensitivity relationship much more and it will all make better sense.

 

Very best,

post #6 of 7
Thread Starter 

this is all extremely helpful.  It seems I have indeed been looking at this incorrectly for a while.  I was always under the assumption that the impedance number defined how powerful an amp you needed, and nothing else.  I will continue to read this.  

post #7 of 7

Impedance:

 

This is the amount of current that will be drained per unit of voltage (Voltage / Current). For orthodynaic (aka planar magnetic) headphones, the impedance is (usually) purely real (resistive) so all frequencies are affected equally by it.

 

Your music player (let's say an ipod) outputs a fixed voltage for a selected volume level regardless of what headphones are plugged in. The lower the impedance of the headphones, the more current the ipod will need to source. Since output devices can only source so much current, you may experience clipping or distorted sound if your source or amplifier doesn't meet this requirement.

 

Feel free to read up on Ohm's Law for more information

 

Power:

 

Electrical power is the product of voltage and current (P = V*I). Obviously, if you have high impedance headphones, you will need to turn the volume knob up higher to achieve the same power output as with a lower impedance load.

 

Efficiency:

 

Not 100% of the power that your headphones dissipate is used to form sound. Some turns to heat, some to mechanical power, etc. Efficiency is the percentage of the power used that does valuable work (creates sound).

 

Sensitivity:

 

Since the efficiency actually changes with regard to power consumption, the efficiency is typically only provided for a single power level. However, instead of giving a percentage @ the specified power level, companies will often provide this data in terms of how much power you will need to provide the headphones to achieve a certain loudness -- this is sensitivity.

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