Here are the specifications of the AKG Q701 as set out on the AKG PDF.

Key Specifications

➔ System: Dynamic

➔ Design: Semiopen-back headphones

➔ Colours: Black with lime accents, white with lime

accents, lime with black accents

**➔ Frequency range: 10Hz to 39.8kHz**

➔ Sensitivity: 105dB SPL/V

➔ Input impedance: 62 ohms

➔ Maximum input power: 200mW
➔ Net weight (without cable): 235g

➔ Cable: 99.99% oxygen-free cables, 3m

➔ Main connection: Hard gold-plated jack cables plug and

contacts

These are the main factors. Using this website:

http://www.apexhifi.com/specs.html to better understand the logarithm.

Or basically decibel sensitivity over volts = decibel times 1 milliwatt + 10 times log base 10 to the power of P. P=Power required.

So what does all this mean? We know that the Q701 output a 105dB SPL at 1mW. The impedance or resistance of the cans is 62 ohms. Right in the gray area of headphones as we know them. The unset standard being 32 ohm or < is low impedance and 100 ohms or > is high impedance headphones. The base rule of thumb is that on low impedance headphones, a higher current is required to drive a headphone correctly, or more efficiently. On the other hand, at a higher impedance the demand requires more volts. So now let's bring it all together and really confuse the **** out of people.

32 ohm or less = higher demand on current. I.E. An amplifier that has a higher current output would be more ideal for those rates headphones.

100 ohm or more = a higher demand on voltage. I.E. An amplifier that can output a higher voltage.

So as we can see the problem with the Q701 are that they fit in the gray area. We require an amplifier that excels in both current and voltage and strikes a good balance.

(The pictures of the graphs would go here but I am not sure if I am allowed to use you know who's graphs.)

**(Can't post the pictures due to a watermark with a link to his site on them)

From the picture we can see that 33 Ohms runs at 4.2V and 80 Ohms runs at 5.2V. A whole voltage in between. There is a 47 Ohm difference in this chart at the given rates. The Q701 being 62 Ohms fits 29 Ohms higher than the 4.2V mark and 18 Ohms less than the 5.2V. We can guess that the O2 amp roughly drives the Q701 at 4.58V. Though this math is good theory, it is probably not correct in practice. Using

http://www.onlineconversion.com/ohms_law.htm Ohm's law calculator and factoring in a rough guess of 4.58V at 62 Ohm resistance we can deduce a current of 7.38 MA or 73.87 mA. (Mega amps and milli amps.) and a 338.32 mW. (milla watts)

Let's say you now want to listen to music at 60 dB. (About a conversation at 1 meter.)

mW = 4.58^2/62. 338mW = 4.58^2/62 or Power required is 338 milliwatts = 4.58V to the power of 2 divided by 62 Ohms.

The Q701 requires 1mW to produce 105 dB sound pressure level with an impedance of 62 Ohms.

Now we would have to factor in the algorithm from above.

http://www.1728.org/logrithm.htm
dBSPL = dB(1mW) + 10 * log_{10} ^(P)
dbSPL = 105(1mW) + 10*log 10^(338mW)
or

dbSPL = 105dB(mW) + 10*2.53mW rounded up. We would get a sound level 130.2 dB or 130 dB. 130 dB is the threshold of pain. It would litterally hurt your ears. So how do we determine how much power is required to drive the Q701 comfortably at 60 dB? Well now that we know the max level of sound we can work the from the dB P2P backwards.

1mW = 10^([60 - 130.2{1mW}]/10) ... 1mW = 10^([60-130.2]/10) ... 1mW = 10^(-70.2/10) ... 1mW = 10^(-7.2) or 1mW = 6.3e -8 or 1mW = 9.12 : -9.12mW

Using their forumla we can:

E=sqrt(P*R), or sqrt (-0.00912*62) = sqrt(-0.56544) or -0.75V. So at 4.58-0.75 we get 3.83V to drive the headphones at a comfortable level (60dB) at a resistance of 62 Ohms or impedance.

So if my calculations are correct. Any amplifier able to produce 4.58V at 62 Ohms resistance should drive the Q701 without a problem. Using 0.073W.

So saying that the Q701 running at a peak voltage of 7 volts when using AC power would require 112mA. The O2 far exceeds the required amount to power it.

(7V/62Ohm yields 112mA).

The O2 amp far exceeds the requirements set out by the K701 series headphones and the Q701 headphones are of the same caliber.