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Topic: Why do Recording Devices Have Such High Output Impedance? (Read 452 times) previous topic - next topic

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Why do Recording Devices Have Such High Output Impedance?
I have a budding musician friend and I'm putting together a basic recording hardware kit for her for Christmas. I have a BR-80 coming and am planning to pair it with an SM-57 and my slightly used AKG K240s. The thing is, the BR-80 has a listed output impedance of 22 ohms. Following the 1/8th rule you would need 176 ohm headphones to guarantee performance, which is somewhat uncommon and nowhere near the K240s 55 ohm rating. Other recording gear seems to follow the same pattern and I can't find any reason for that. Does anybody have an explanation, and should I really be worried about this? I have a spare headphone amp with low impedance I can include but that's not exactly convenient.

Thanks!
  • Last Edit: 22 November, 2017, 09:43:50 AM by nintendoeats

  • saratoga
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Re: Why do Recording Devices Have Such High Output Impedance?
Reply #1
Cost savings. I don't think you have to worry that much.

Re: Why do Recording Devices Have Such High Output Impedance?
Reply #2
Hmm, ok. I have no context for how much it costs to make a low-impedance output circuit. I do know that the 700 dollar Scarlett 18i8 has a 10 ohm impedance, but I suppose they aren't expecting the headphone-out to be used for mixing or other serious duty.

  • bennetng
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Re: Why do Recording Devices Have Such High Output Impedance?
Reply #3
More I/O in the same series just means increased cost if leaving unused, with ADAT you get additional 8... digital channels.

  • Destroid
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Re: Why do Recording Devices Have Such High Output Impedance?
Reply #4
Not sure if I understand the OP's question. What is known is that studio headphones have high impedance so that multiple sets of headphones can be connected for multiple listeners.
"Something bothering you, Mister Spock?"

  • DVDdoug
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Re: Why do Recording Devices Have Such High Output Impedance?
Reply #5
Quote
The thing is, the BR-80 has a listed output impedance of 22 ohms. Following the 1/8th rule you would need 176 ohm headphones to guarantee performance, which is somewhat uncommon and nowhere near the K240s 55 ohm rating.
22 Ohms might be the minimum recommended load.      Most users don't understand the implications of source impedance and if the spec says 8 Ohms, they might think you can connect an 8-Ohm speaker.    ...When you look at amplifier specs they don't give you the source impedance, they give you the recommended (or minimum) load impedance, and if you are lucky they give you a damping factor so you could calculate the source impedance.

Also, that 1/8th rule is for "critical listening".  Monitoring isn't that critical, and you shouldn't be using headphones for mixing/mastering anyway.

Re: Why do Recording Devices Have Such High Output Impedance?
Reply #6
[22 Ohms might be the minimum recommended load.      Most users don't understand the implications of source impedance and if the spec says 8 Ohms, they might think you can connect an 8-Ohm speaker.    ...When you look at amplifier specs they don't give you the source impedance, they give you the recommended (or minimum) load impedance, and if you are lucky they give you a damping factor so you could calculate the source impedance.
That's a good thought. The BR-800 only lists a "recommended headphone impedance" range, so it's possible that the BR-80 spec was just badly labelled.

Also, that 1/8th rule is for "critical listening".  Monitoring isn't that critical, and you shouldn't be using headphones for mixing/mastering anyway.
Ideally yes, but in her case it's either headphones or laptop speakers. I want her to get the best she can out of what I'm giving her, but that doesn't extend to buying studio monitors.

  • eric.w
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Re: Why do Recording Devices Have Such High Output Impedance?
Reply #7
Check out reference-audio-analyzer which has predicted frequency response change for a given headphone / source impedance:
http://reference-audio-analyzer.pro/en/report/hp/akg-k-240-studio.php#rw6

So in this case for 20 ohms source impedance, you're looking at +1.5dB at 100Hz, and +1dB at 10kHz and above.

Re: Why do Recording Devices Have Such High Output Impedance?
Reply #8
Check out reference-audio-analyzer which has predicted frequency response change for a given headphone / source impedance:
http://reference-audio-analyzer.pro/en/report/hp/akg-k-240-studio.php#rw6

So in this case for 20 ohms source impedance, you're looking at +1.5dB at 100Hz, and +1dB at 10kHz and above.

Cooooooool, that is a handy tool. Thanks.

  • dneern
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Re: Why do Recording Devices Have Such High Output Impedance?
Reply #9
This link explains where the 1:8 rule comes from it's a good read:
http://nwavguy.blogspot.com/2011/02/headphone-amp-impedance.html

It says that the smallest audible difference that a normal person can hear is 1dB, so if you're under that number you should be good.

Re: Why do Recording Devices Have Such High Output Impedance?
Reply #10
This link explains where the 1:8 rule comes from it's a good read:
http://nwavguy.blogspot.com/2011/02/headphone-amp-impedance.html

It says that the smallest audible difference that a normal person can hear is 1dB, so if you're under that number you should be good.

I am well familiar with that article. NwAvGuy is, of course, the second coming of Jesus Watt.