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Topic: Regarding headphone ohms and sensitivity in regards to amplification.  (Read 571 times) previous topic - next topic
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Regarding headphone ohms and sensitivity in regards to amplification.

I’m wondering if anyone could answer a question that I can’t seem to find a solid answer for. I own a pair of Sennheiser HD600 headphones that I sometimes like to use with my iPhone and lightning dongle. The headphones are 300 Ohms, but they’re also pretty efficient. I can achieve a loud enough listening volume with this setup, though my MacBook has a louder output. I’m under the impression that if a loudspeaker or headphones are loud enough, than the amplification is doing its job and no more thought needs to be given to it. What I’m not clear about is the fact that, while these headphones are rated at 300 ohms, there are parts of the frequency range that are actually up to 600 ohms. Does this mean that having insufficient power could adequately power parts of the frequency range but not other parts and change the frequency response?

Re: Regarding headphone ohms and sensitivity in regards to amplification.

Reply #1
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What I’m not clear about is the fact that, while these headphones are rated at 300 ohms, there are parts of the frequency range that are actually up to 600 ohms. Does this mean that having insufficient power could adequately power parts of the frequency range but not other parts and change the frequency response?
No.  Headphones and speakers are tested/specified with a "constant voltage" source (independent of impedance).

If the output impedance (of your phone or computer)  is low relative to the load (the headphones), then the output voltage remains constant as the load impedance changes.  

Where the impedance is higher you'll get less current (Amps/milliamps) and less power (Watts/milliwatts), but if the frequency response is flat that's what's important.

...With regular low impedance headphones, depending on the headphone amplifier circuit  there can be "interaction" between the source impedance and load impedance (so you're not getting constant voltage) and the varying impedance can affect frequency response.   That's not even a question with higher-impedance headphones (when driving by a headphone amp capable of driving "normal" headphones).

Of course real world audio is not constant voltage, but the voltage-output should be independent of the load.
 

Re: Regarding headphone ohms and sensitivity in regards to amplification.

Reply #2
Quote
What I’m not clear about is the fact that, while these headphones are rated at 300 ohms, there are parts of the frequency range that are actually up to 600 ohms. Does this mean that having insufficient power could adequately power parts of the frequency range but not other parts and change the frequency response?
No.  Headphones and speakers are tested/specified with a "constant voltage" source (independent of impedance).

If the output impedance (of your phone or computer)  is low relative to the load (the headphones), then the output voltage remains constant as the load impedance changes.  

Where the impedance is higher you'll get less current (Amps/milliamps) and less power (Watts/milliwatts), but if the frequency response is flat that's what's important.

...With regular low impedance headphones, depending on the headphone amplifier circuit  there can be "interaction" between the source impedance and load impedance (so you're not getting constant voltage) and the varying impedance can affect frequency response.   That's not even a question with higher-impedance headphones (when driving by a headphone amp capable of driving "normal" headphones).

Of course real world audio is not constant voltage, but the voltage-output should be independent of the load.
 

Thanks so much for the reply as I should be able to figure this out on my own, but I guess it’s over my head and I need to go a few layers deeper with my audio knowledge. So consequently a higher impedance driver is actually even less likely to experience frequency response changes, but would be less efficient as well? I’ve pretty much narrowed down needing a DAC and amp as audiophile misinformation from my own subjective experiences and from what I can understand on a technical level, but the argument I’ve received back  that seemed even somewhat credible to me was that headphones can experience audible frequency response changes due to being underpowered.

Re: Regarding headphone ohms and sensitivity in regards to amplification.

Reply #3
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So consequently a higher impedance driver is actually even less likely to experience frequency response changes, but would be less efficient as well?
Right.  

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would be less efficient as well?
;) Technically...  We should say "less "sensitive" (not as loud with the same voltage).  They aren't necessarily less "efficient" because that's a measure of how efficiently electrical power is converted to acoustic power.   And at higher impedance you are consuming less electrical power (mW).   Impedance or resistance is the resistance to the flow of current,  so higher impedance means lower current and lower power.   (i.e. You can often get more power from an amplifier by using 4-Ohm speakers instead of 8-Ohm speakers, until you go too low and fry the amp.)

Quote
but the argument I’ve received back  that seemed even somewhat credible to me was that headphones can experience audible frequency response changes due to being underpowered.
It should be linear until it's overdriven to the point where can't mechanically move freely.    


Re: Regarding headphone ohms and sensitivity in regards to amplification.

Reply #4
Quote
So consequently a higher impedance driver is actually even less likely to experience frequency response changes, but would be less efficient as well?
Right.  

Quote
would be less efficient as well?
;) Technically...  We should say "less "sensitive" (not as loud with the same voltage).  They aren't necessarily less "efficient" because that's a measure of how efficiently electrical power is converted to acoustic power.   And at higher impedance you are consuming less electrical power (mW).   Impedance or resistance is the resistance to the flow of current,  so higher impedance means lower current and lower power.   (i.e. You can often get more power from an amplifier by using 4-Ohm speakers instead of 8-Ohm speakers, until you go too low and fry the amp.)

Quote
but the argument I’ve received back  that seemed even somewhat credible to me was that headphones can experience audible frequency response changes due to being underpowered.
It should be linear until it's overdriven to the point where can't mechanically move freely.    



I guess “sensitive” makes a lot more sense in that respect and thanks so much, that’s a question that had been on my mind for a long time and I didn’t want to spend money and perform an ABX if it isn’t neccesary as I don’t have access to a dedicated headphone amp. I’m unsure as to why higher ohm headphones are always said to require amplification in certain circles, but I guess it could be placebo or that some enjoy colouring more neutral amps with tube amps, as a guess anyways.

One last question, hopefully it isn’t rude to go off topic rather than make a separate post but an issue I’ve struggled with for years with headphones is that I have a rather large head and consequently have never found any over ear headphones to be comfortable, including the ones I own that most would say are fine. For extended listening sessions, I only ever really find earbuds to be comfortable. Is it theoretically possible to eq earbuds to sound like neutral over ear headphones?

Re: Regarding headphone ohms and sensitivity in regards to amplification.

Reply #5
I’m unsure as to why higher ohm headphones are always said to require amplification in certain circles,

Most of the time if you ask people who think that to explain themselves, it is because they mistakenly assume that a higher impedance is a larger, rather than smaller, load.

Re: Regarding headphone ohms and sensitivity in regards to amplification.

Reply #6
From voltage to power is Voltage*Voltage/Impedance. The power difference between 600 ohm and 8 ohm will be 8/600 or -18 dB. With the same sensitive (dB/watt) you need SQRT(600/8) = 8 times more voltage from the amplifier. I think that’s the problem. For small devices (phones), the voltage is limited by the power source, and that can result in distortion.

Re: Regarding headphone ohms and sensitivity in regards to amplification.

Reply #7
  For small devices (phones), the voltage is limited by the power source, and that can result in distortion.

This is actually the misconception I alluded to above. If you plug a higher impedance load into a lower voltage source like a phone, it presents a smaller load, which draws less power. Distortion will actually go down since the maximum power draw has been reduced. You may be limited to a maximum volume lower than you want (although probably not), but you will get lower distortion.

Re: Regarding headphone ohms and sensitivity in regards to amplification.

Reply #8
  For small devices (phones), the voltage is limited by the power source, and that can result in distortion.

This is actually the misconception I alluded to above. If you plug a higher impedance load into a lower voltage source like a phone, it presents a smaller load, which draws less power. Distortion will actually go down since the maximum power draw has been reduced. You may be limited to a maximum volume lower than you want (although probably not), but you will get lower distortion.

That’s the impression I was under years ago before I began reading headphone reviews , although I had no idea why. Isn’t this the idea behind using higher resistance in headphones to begin with? Otherwise, why make headphones in the first place with higher impedance?


 
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