# Question about impedance and soundcards



## SergeD (Jan 16, 2018)

I agreed to buy (irresistible price) a second hand studio headphone Koss Pro 4AA. I also bought a used Steinberg UR12 soundcard. Reviews about both devices are quite good. 

About the heavy Koss, it appears that they have a high impedance of 250 ohms. I wonder if the UR12, connected to a powered USB hub, will perform correctly when coupled with the Koss.

Thanks for any advice.


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## Joe Maron (Jan 16, 2018)

Just try them... if they sound loud enough for you, then all's good. I regularly plug in my DT-770 Pro's (also 250 Ohms but 96 dB spl) straight to my notebook's headphone jack, and they sound perfect. Heck, I'll even plug them into my iPhone and they sound just fine.


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## wst3 (Jan 16, 2018)

Designing a proper headphone amplifier is tricky business, largely because headphone impedance can range from 8 ohms to over 300 ohms.

A higher impedance set of headphones poses one set of challenges, a low impedance set another. I don't know what the UR12 uses for an output stage, but if it is USB powered it may struggle a little to drive any headphones. As mentioned above, try it. If it doesn't work then you'll need to add a dedicated headphone amplifier.


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## SergeD (Jan 16, 2018)

So it could only result on a lack of volume, nothing to damage electronics parts. I will buy that Koss, it seems that higher impedance headphones are more suited for critical listening and this is what I want. 
Thanks both for your comments and suggestions. 
The USB hub has a power adapter by the way.


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## rrichard63 (Jan 16, 2018)

SergeD said:


> So it could only result on a lack of volume, nothing to damage electronics parts.


No physical damage, but the effect of impedance mismatches can sometimes include altered frequency response as well as lower volume.


SergeD said:


> The USB hub has a power adapter by the way.


I believe that doesn't matter. The Steinberg unit is still bus powered. An audio interface with its own power supply is likely (no guarantee) to be more powerful.


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## SergeD (Jan 17, 2018)

I guess you're right, and the altered frequency response may result in less flat frequency response?

Found here http://nwavguy.blogspot.ca/2011/02/headphone-amp-impedance.html
"most headphones work best when the output impedance is less than 1/8th the headphone impedance"

So, 250/8=31.25 should well fit for the Scarlett 2i2 having a 10Ω headphone output impedance.
The 40Ω headphone output impedance of the UR should not fit correctly, hum...


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## yhomas (Jan 17, 2018)

SergeD said:


> I wonder if the UR12, connected to a powered USB hub, will perform correctly when coupled with the Koss.



Very close to all headphone amplifiers will correctly drive 250 ohms, but the max output may not be quite as loud as some may want.

In general, higher impedance headphones require more voltage/power to produce the same volume levels, but most amps will correctly drive higher impedances.


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## SergeD (Jan 18, 2018)

Finally, I got the headphone, plugged into the soundcard and have plenty of volume.Headphone amplifier is maybe not necessary.


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## Jeremy Spencer (Jan 18, 2018)

It's always best practice to connect your interface directly to a USB port, not a hub.


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