32 Ohm- actual impedance at diff. frequencies? - diyAudio
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Old 27th February 2014, 12:34 AM   #1
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Default 32 Ohm- actual impedance at diff. frequencies?

My questions-

Would you say that any commercial headphones or earphones rated as 32 Ohm almost without exception stay within say + or - 20% of rated impedance at any frequency within the frequency handling range, or is the opposite the case?

Having developed a passive cross-feed network (read a collection of resistors and capacitors connected between an amp and pair of headphones), the impedance of the headphones remaining fairly constant at all frequencies is necessary in order for the correct crossing over to occur. I'd like to be able to say that at least almost all headphones rated 32 Ohm will work properly with the network, but I haven't been able to get any really solid information about this issue. NWAVGuy sort of gives an answer.

Any help is appreciated,
cT
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Old 27th February 2014, 02:52 AM   #2
TMM is offline TMM  Australia
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It's probably safer to assume they are within +/-50% or worse. Here is the impedance vs freq of my Audio Technica ATH-AD900:
Click the image to open in full size.

If the filter needs to be accurate with a wide range of headphones, it is better to implement it actively.

Last edited by TMM; 27th February 2014 at 02:54 AM.
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Old 27th February 2014, 03:13 AM   #3
jcx is offline jcx  United States
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Tyll Herstens could be your friend

look up the company he started Headfi.com, tech section - "build a graph" Learning Center - Build a Headphone Graph | HeadRoom Audio

and his current InnerFidelity posts, measurements
Headphone Buyers Guide | InnerFidelity
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Old 27th February 2014, 07:24 AM   #4
jcx is offline jcx  United States
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headroom.com was Tyll's company

head-fi.org is a headphone enthusiast site with some useful info and lots of fanboyism, echo chamber, audiophoolish noise diluting the useful stuff
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Old 27th February 2014, 01:36 PM   #5
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Quote:
Originally Posted by TMM View Post
It's probably safer to assume they are within +/-50% or worse. Here is the impedance vs freq of my Audio Technica ATH-AD900:
Click the image to open in full size.

If the filter needs to be accurate with a wide range of headphones, it is better to implement it actively.
Thanks for the input,

Except for the (resonant?) peak at 100 Hz, that graph doesn't look too bad, considering that relative audio intensity in frequencies > 10 kHz is much less.

A survey of the impedance Vs. frequency characteristics of current 32 Ohm headphones is I suppose what I'm after; I certainly would hope that that isn't something I would have to do myself!

Regards,
cT
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Old 27th February 2014, 01:46 PM   #6
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Quote:
Originally Posted by jcx View Post
Tyll Herstens could be your friend

look up the company he started Headfi.com, tech section - "build a graph" Learning Center - Build a Headphone Graph | HeadRoom Audio

and his current InnerFidelity posts, measurements
Headphone Buyers Guide | InnerFidelity
jcx,

Thanks for those links; I'll take a look.

For anyone else interested, I did find the blog at the below URL fairly informative:

http://nwavguy.com.blogspot/2011/02/...explained.html
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Old 27th February 2014, 02:58 PM   #7
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For anyone interested, I did a quick survey of four headphones specified as 32 Ohm: Beyerdynamic DT232, AKG K 271, AKG K81 DJ, and Grado SR 60. Attached is a Headroom graph of Impedance W.R.T. frequency. Thanks again to jcx for the link to Headroom's "Build a Graph".

Regards,
cT
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File Type: png graphCompare.php.png (59.5 KB, 132 views)
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Old 27th February 2014, 03:18 PM   #8
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Speaker impedances vary massively over the audio frequency range.

Look up a datasheet on any speaker and you will see it is far from flat especially around the resonant frequency.
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Old 27th February 2014, 04:15 PM   #9
jcx is offline jcx  United States
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most headphones are single driver so will just have a bass mass/spring reasonance peak, possibly some visible Z rise from inductance at high freqeuncy

and many may simply have so much R and such low electromechanical coupling that they are nearly flat with frequency - Orthodynamics are commonly very flat Z

but there are multidriver headphones - some pricey iem in particular - they can have several peaks/dips spread over the audio spectrum

Last edited by jcx; 27th February 2014 at 04:18 PM.
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Old 28th February 2014, 03:42 PM   #10
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Here are some more critical examples.
Click the image to open in full size.

Crossfeed is something best implemented somewhere in an amplifier or in software. Jan Meier put his in between two gain stages but basically you can do this at line level as well (with higher impedances).
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