Let me preface this that I am not looking for product recommendations, just clearing up some science and nomenclature of the listed specifications for amplifiers for headphones and for the headphones themselves.
I am working on a project that involves making a custom PCB to house a DSP chip and an amplifier and I thought I needed up to 2 watts for the power amplifier, but other forums said I needed only a fraction of that.
Now here's my confusion:
This is a link to the headphones I own. They are 50 ohms impedance planar magnetic. Under the specifications, the sensitivity is listed as 92dB/mW, and max input power is 3W. T60RP : RP Stereo Heaphones
If this is true, then I should be able to use a pretty low power amplifier. However, I am using a $100 monoprice liquid spark which can output 1.3 watts at 50 Ohms. I use it with the volume more than halfway up. My friend said it could because it could be that my amp has a logarithmic potentiometer knob. He also said that the sensitivity should be in dB/mV, and that dB/mW is efficiency so I'm confused about that too.
I also notice that more expensive headphone amps for much more expensive headphones have a lot more power. Why would this even be necessary?
I am working on a project that involves making a custom PCB to house a DSP chip and an amplifier and I thought I needed up to 2 watts for the power amplifier, but other forums said I needed only a fraction of that.
Now here's my confusion:
This is a link to the headphones I own. They are 50 ohms impedance planar magnetic. Under the specifications, the sensitivity is listed as 92dB/mW, and max input power is 3W. T60RP : RP Stereo Heaphones
If this is true, then I should be able to use a pretty low power amplifier. However, I am using a $100 monoprice liquid spark which can output 1.3 watts at 50 Ohms. I use it with the volume more than halfway up. My friend said it could because it could be that my amp has a logarithmic potentiometer knob. He also said that the sensitivity should be in dB/mV, and that dB/mW is efficiency so I'm confused about that too.
I also notice that more expensive headphone amps for much more expensive headphones have a lot more power. Why would this even be necessary?
I've never come across a commercial amp which uses a linear volume control. Wouldn't be very user-friendly as all the usable volume range would be compressed at one end. Bottom line - its going to be a logarithmic volume control.
As regards sensitivity and efficiency, I think your friend isn't quite correct. Efficiency is measured in % (acoustic power out divided by electrical power in) and isn't really relevant. dB/W is power sensitivity and dB/V is voltage sensitivity.
Planars are amongst the least efficient headphones going so I doubt if a lot more power than 3W is needed for any headphone. I seem to recall the HE-6 is the most insensitive planar at 83.5dB/mW.
As regards sensitivity and efficiency, I think your friend isn't quite correct. Efficiency is measured in % (acoustic power out divided by electrical power in) and isn't really relevant. dB/W is power sensitivity and dB/V is voltage sensitivity.
Planars are amongst the least efficient headphones going so I doubt if a lot more power than 3W is needed for any headphone. I seem to recall the HE-6 is the most insensitive planar at 83.5dB/mW.
92 dB / mW @ 50 ohms translates to 105 dB SPL @ 1 V.
Measured: 104.4 dB.
About 12.6 mW into 50 ohms for 103 dB and 63 mW (1.77 Vrms into 50 ohms) for 110 dB SPL. About as much voltage as for a HD600/650/DT880 or similar but with more current capability.
Yes. More than halfway up could still be 16 dB down from maximum output.
Besides, in the linear range below maximum output,
output level =
input level (!)
+ amplifier voltage gain
- volume pot attenuation.
Gain settings on the Liquid Spark are +3 dB and +6 dB nominal, a bit of a strange choice also considering what seems to be about a 6 dB difference in noise level between the two (measurements). That would mean that you may well be at below overall unity gain still. Sounds about right if you're not having any major digital attenuation (no ReplayGain or similar in use?) and a DAC with a 2 Vrms @ 0 dBFS output level.
Strictly speaking he is in fact correct, and the good folks at Fostex were a bit sloppy. The distinction between the terms is not always very clear.
Some planars are down in the 80s of dB SPL @ 1 V. Close to 10 times the power required for those.
Also, bragging rights.
I don't think there is one headphone that needs >1 W for 110 dB. Running out of gain before this point is a very real possibility though, depending on your source levels. Few amplifiers cover a truly wide range of gain settings (as in >20 dB).
BTW - you may want to alert moderation to have this moved to Headphone Systems.
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