[Rhydon]

Perhaps someone can help me with a problem i've been exploring. How likely is it for current headphone amps to successfully drive an 8 ohm headphone, 95-100db sensitivity?

 

[NA Blur]

It depends upon the sensitivity of the headphone / speaker.  If you are really asking can a modern headphone amp drive an 8 Ohm speaker ( not headphone ) then the answer is not likely.  If you have an 8 Ohm headphone like an IEM the answer is probably.
 
Please list in more detail what headphone you are talking about and the listed sensitivity for said headphone.
 
The general formula for calculating these things is:
 
P = 10^((dBspl - dBsens)/10)
Then using P = V^2/R one can determine the voltage.
 
dBspl = loudness in dB ( typically around 90-105 dB )
dBsens = sensitivity of headphone / speaker ( watch the units here as a headphone is in mW while a speaker is in W )
P = power in watts
V = voltage
R = Resistance typically non reactive
 
As you can see without knowing the sensitivity there is no way we can simply answer your question.  It would be as if I asked you how fast your car can go if your car weighs 2000 lbs.  The answer depends on a few more pieces of information.

 

[Rhydon]

Thanks NA Blur, that equation helped.
 
Sensitivity would be around 95-100db. Full size.

 

[NA Blur]

If the sensitivity is 100 dB you need the per mW, per mV, or per W.
 
If you use 110 dBspl for the desired loudness then:
 
P = 10^((110 dBspl - 100 dBspl/mW )/10)
P =  10 mW
 
P = V^2/R  and R = 8 Ohms
 
10 mW = V^2/8 Ohms
.01 W *8 Ohms = V^2
V = squareroot of .08 W Ohms
V = approximately .282 Volts or 282 mV
 
Current Calc:
I = (10 mW / 8 Ohms )^.5
I = .035 A or 35 mA
This is from P = I^2 * R
 
I think just about any headphone amp with decent reviews here can output that much current at the .282 volts level.  Just be sure the output impedance of the amp is lower than say 5 Ohms.
 
You will need an amp that can deliver at least 35 mA into an 8 Ohm load.
 
Anyone else see an issue with my calcs?

 

[Armaegis]

I like to use this site for quick calculations: http://www.headphone-amplifier.com/calculator.htm
 
The numbers look good to me.