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Old 11th January 2013, 06:53 PM   #1
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Default Headphone maximum power

Hi there,

I'm trying to design my first complete headphone DAC/amplifier and I would like to know where I can find, in the general case, the maximum power for an headphone, according to his nominal impedance.

I've seen some amplifiers providing more than 500mW @ 600ohm, while some headphones cannot support more than 100 or 200mW at the same impedance... I really don't know what information I can trust and I'll be pleased if it exists a document which talk about maximum power of some headphones.

Thanks,
BT
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Old 11th January 2013, 07:09 PM   #2
Mooly is offline Mooly  United Kingdom
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I think the question is really what voltage do the headphones need, rather than "power".

I did some tests when designing a headphone amp and found that it was under 1 volt peak/peak for low impedance phones. 500mw into 600 ohm is 17 volts RMS so that means an amp running on over 50 volts dc in total... which has to be way over top.
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Old 11th January 2013, 07:12 PM   #3
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5 volts rms will kill your ears so ±12-15 V supply voltage is more than enough. 1-2 volts for a low ohmish headphone is enough.
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Old 11th January 2013, 07:28 PM   #4
paulb is offline paulb  Canada
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You could calculate power/voltage/current requirements using the headphone sensitivity, impedance, and some upper value of loudness (say, the threshold of pain).
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Old 11th January 2013, 07:30 PM   #5
jcx is offline jcx  United States
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Default 1st headphone amp design Q: for which headphone?

sensitivity, Z and target SPL are good things to know how to relate

I don't think there is any standard for max power ratings - most headphone coils will mechanically bottom at low frequency at still "safe" electrical drive levels - long before heating softens glues, damages insulation, melts wires

given the wide range of sensitivity, Z among headphones a particular amp's I,V capability will likely be inappropriate in the sense of being potentially dangerous to some while not even being able to drive to reasonable SPL some other headphones

Last edited by jcx; 11th January 2013 at 07:40 PM.
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Old 11th January 2013, 08:55 PM   #6
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Thanks a lot for your answers.

Quote:
Originally Posted by Mooly View Post
I think the question is really what voltage do the headphones need, rather than "power".
Yes, indeed. The main aim of my question is to know if there is a lot of differences in volt to have the same audio level for two headphones with the same impedance.

If not, it's easy to calculate the maximum voltage of my signal and the output impedance of my amp.
For eg, if I need 3V to reach 120dB with a 32ohm headphone and 11V for a 600ohm headphone, i can calculate that I need a 13V signal with a 106ohm output impedance. So the audio level will be the same for this two headphones, and i'll not have to change volume if i change headphone


I've just done some mesurements with my 32ohm HD448. 500mVpp if more than enougth (i usually listen music around 100mVpp with this one).
But I have no idea of the voltage value nedded for a high impedance headphone.
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Old 11th January 2013, 09:15 PM   #7
balerit is offline balerit  South Africa
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Just don't blow your hearing, headphones are very dangerous to your health.
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Old 11th January 2013, 09:27 PM   #8
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Quote:
Originally Posted by balerit View Post
Just don't blow your hearing, headphones are very dangerous to your health.
Don't worry... my ears are too precious for me :/
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Old 11th January 2013, 10:08 PM   #9
Blues is offline Blues  United States
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Default Beyerdynamic T1

These are 102dB/1mW at 600ohms beyerdynamic T 1

sqrt(1mW*600) =0.775V; So we need 0.775V to get us to 102dB -very, very loud directly into our ears; On these headphones, this gives us an idea we should be listening at <<0.775V which is not even half of what typical digital sources' line level outputs provide

Extended levels of 87dB is deemed to cause hearing loss by OSHA. 120dB is at the threshold of pain for humans.
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Old 11th January 2013, 10:59 PM   #10
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I've built a couple of headphone amps,with around 1W of output per channel. I can tell you-that's a stupid amount of power for headphones. WAY more than is even safe/sane. (ESL 'phones,etc. might be a different matter.)

As a ballpark guesstimate,a couple of volts (assuming low-ish Z 'phones) is probably plenty. It will depend on your particular set of cans.


Whatever you do,be extra careful with headphones/headphone amps. Test the amp with a small speaker or something first. NOT with headphones on your head! If something were to go wrong,a loose connection,oscillation,etc. it could easily damage your hearing.
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