[mindbomb]

Idk if this was brought up in this thread, but Tyll measured the q701, and it took 300mV to reach 90db. The specs say it does 105db at 1V. How can this be? Was he using a tube amp (high output impedance)? Are the specs wrong?

 

[Head Injury]

  Idk if this was brought up in this thread, but Tyll measured the q701, and it took 300mV to reach 90db. The specs say it does 105db at 1V. How can this be? Was he using a tube amp? Are the specs wrong?

A lot of the measurements Tyll has done on power requirements don't match manufacturer specs. There's a lot of variation between the same models, too. Whether this is a fault with his measurements or the manufacturers', I don't know.
 
His K701/Q701 ones are consistently higher that 105 dB/V though, between 0.283 and 0.320 at 90 dB. So I'd trust them over the manufacturer specs in this case.
 
(note for those who don't math: Tyll's measurements come out to about 100 dB/V, so you lose 5 dB and need about 70% more voltage than advertised to get it back)
 
It's possible AKG measured the volume at a different frequency. The K701 is about 5 dB louder at 2 or 3 kHz than the 1 kHz Tyll uses, for example.

 

[XERO1]

  Idk if this was brought up in this thread, but Tyll measured the q701, and it took 300mV to reach 90db. The specs say it does 105db at 1V. How can this be? Was he using a tube amp (high output impedance)? Are the specs wrong?

Tyll's measurements state that it took 0.318Vrms (Volts-Root-Mean-Square) and only 1.68mW (Milliwatts) or 0.00168 Watts of power to generate 90db of output from the Q701. And if one does some simple approximations, the Q701 should require only about 25.2mW of power into 60 Ohms to reach 105db of output.
 
A voltage measurement alone is not a very good indicator of a headphones real-world sensitivity. A mW-to-dB measurement is much more accurate.
 
So technically, the Q701 should be a pretty easy load to drive.  But owning a pair myself, I can confirm that the Q701 needs a pretty powerful &/or smooth sounding amp in order to prevent their upper-mids and treble from sounding really bright and harsh at high SPLs.

 

[Head Injury]

 
Tyll's measurements state that it took 0.318Vrms (Volts-Root-Mean-Square) and only 1.68mW (Milliwatts) or 0.00168 Watts of power to generate 90db of output from the Q701. And if one does some simple approximations, the Q701 should require only about 25.2mW of power into 60 Ohms to reach 105db of output.
 
A voltage measurement alone is not a very good indicator of a headphones real-world sensitivity. A mW-to-dB measurement is much more accurate.
 
So technically, the Q701 should be a pretty easy load to drive.  But owning a pair myself, I can confirm that the Q701 needs a pretty powerful &/or smooth sounding amp in order to prevent their upper-mids and treble from sounding really bright and harsh at high SPLs.

Voltage measurements are just as good an indicator if you know the impedance, which we do. It's easy to derive voltage from power and vice versa with the impedance. Voltage is actually a better indicator because a good amp will put out about the same voltage into any realistic load, whereas power will change with impedance.
 
It takes 31.6x as much power to increase volume by 15 dB, not 15x. It's exponential, not linear. You need about 53 mW for 105 dB, or 1.78 Vrms.
 
And yes, this is a lot for that volume at 60 ohms, especially for a dynamic headphone. This is the same voltage a HE-500/560 needs. The only headphones that come to mind that need more are the HE-6 and the 600 ohm DT880/990, excluding special cases like the K1000 and electrostats.
 
Kinda makes you think, doesn't it? 1.78 Vrms is pretty easy for an amp to do, yet it's one of the toughest loads a headphone will present. And yet people think they need to hook their headphones up to speaker amps

 
 
EDIT: Looks like the regular DT880 250 and T1 need about the same voltage, but to their credit it's easier for some amps to generate it at these high impedances, if they have high output impedance or limited current.

 

[mindbomb]

So, going by the innerfidelity measurments, this headphone is harder to drive than 300 ohm sennheisers and 250 ohm beyerdynamics, and the sensitivity values given by AKG are misleading.

 

[Shazb0t]

I have used the O2 for a few years to power my Q701, seems to do a fine job.  I am one of those crazies that uses a 50 watts/channel speaker amp to power my HE-6's though.

 

[XERO1]

 
Voltage measurements are just as good an indicator if you know the impedance, which we do. It's easy to derive voltage from power and vice versa with the impedance. Voltage is actually a better indicator because a good amp will put out about the same voltage into any realistic load, whereas power will change with impedance.
 
It takes 31.6x as much power to increase volume by 15 dB, not 15x. It's exponential, not linear. You need about 53 mW for 105 dB, or 1.78 Vrms.
 

 
Thanks for the info.
 
Also, remember that the impedance will often vary quite a bit across the headphone's frequency bandwidth, so this also must be taken into account when trying to calculate how much actual power the headphone will require to reach the desired SPL level.
 
What formula did you use to reach the 53mW/1.78Vrms result?
 
And it looks like I was incorrect, the Q701 looks like it is actually quite difficult to drive, which was exactly what my ears were telling me when I started using them!

 

[Head Injury]

   
Thanks for the info.
 
Also, remember that the impedance will often vary quite a bit across the headphone's frequency bandwidth, so this also must be taken into account when trying to calculate how much actual power the headphone will require to reach the desired SPL level.
 
What formula did you use to reach the 53mW/1.78Vrms result?

Change in power = 10^(change in dB/10), so for 15 dB it comes out to 31.62 times as much power. It's easier to just use the calculator on this site. Then do 31.62 * 1.68 mW = 53.12 mW
 
Then to get voltage take the square root of power in Watts times impedance, or sqrt(0.053 * 60) which is 1.78. This is because P = V^2 / R, the formula to change voltage to power and vice versa.
 
The change in impedance by frequency will already be taken into account by sensitivity, otherwise headphones with very wild impedance curves would have equally wild frequency response curves. Usually volume is measured at 1 kHz only, and the rest can be inferred from the frequency response graph. This is another reason why voltage is a good measure of how a headphone is driven, because it usually won't change with the impedance curve. The impedance curve does play a major part in coloration caused by amps with high output impedance, though, and also might explain the different manufacturer specs.

 

[Andhra]

Hi Everyone,
 
I am very new to this high end audio scene so if anyone could assist me it would be greatly appreciated.
 
I recently received a Akg Q701 as a gift( I'm yet to know how the choice was made but nevertheless).
 
I basically know nothing about amplifiers or anything regarding giving these headphones more juice. Currently I only use my ipod to listen to music and do foresee to use the headphones whilst listening to music on the laptop.
 
If anybody could guide me it would be much appreciated.
 
Thanks

 

[YT-MrEleven1181]

I use the astros mixamp pro and schiit vali with my q701s works nice on the ps4

 

[fauxfreshness]

  Absolutely not true.  It sounds awful on my X3 (which has the same amp section as E11 and E17).  The E12 was able to drive it without altering its sound signature and I've heard that the E9 works well too.

 
Yeah, they sound OK with my X5 in high gain, but went ahead and ran the line out to my FiiO E18 and I was like "oohhh..."  It made quite a bit of difference in the low end without enabling the bass boost, and then turning that on pretty much made the Q701 useful outside of studio work (I use them for testing reverb and instrument position, along with binaural fine tuning).  Granted the person that commented and stated it was fine may be great for him, but in my case I needed the extra power stage of the E18 along with the bass boost.  On FLACs, WAV, and AIFF (or I imagine any other lossless format I'd try) I don't normally use an EQ but find the bass boost useful on the Q701.

 

[buson160man]

Why not both?

The akg 701 is very neutral in most ways. You do need a fairly powerful headphone amp to really get the best of them. The sabre dac chip in the benchmark has a reputation for sounding somewhat analytical . The akg is just being neutral and honest in passing whatever is fed it. That is why a lot of people do not like the 701s because they are very picky about what amp is powering them . Not to mention the quality of the source and the recording as well. Feed them a good source with a amp of sufficient power and they deliver the goods without adding anything to the sound.

 

[cdma2k]

 

Why not both?

The akg 701 is very neutral in most ways. You do need a fairly powerful headphone amp to really get the best of them. The sabre dac chip in the benchmark has a reputation for sounding somewhat analytical . The akg is just being neutral and honest in passing whatever is fed it. That is why a lot of people do not like the 701s because they are very picky about what amp is powering them . Not to mention the quality of the source and the recording as well. Feed them a good source with a amp of sufficient power and they deliver the goods without adding anything to the sound.

the analog output stage of Benchmark including the headphone amp is TI NE5532. It is analytical but artificial and sterile.  opa627 sounds much better and more natural.

 

[i luvmusic 2]

WOW! these Bottlehead SEX and Q701 is really good the bass is deep the treble is nice and smooth.

 

[jodgey4]

The akg 701 is very neutral in most ways. You do need a fairly powerful headphone amp to really get the best of them. The sabre dac chip in the benchmark has a reputation for sounding somewhat analytical . The akg is just being neutral and honest in passing whatever is fed it. That is why a lot of people do not like the 701s because they are very picky about what amp is powering them . Not to mention the quality of the source and the recording as well. Feed them a good source with a amp of sufficient power and they deliver the goods without adding anything to the sound.

We ain't disagreein', sir . The headphones are dry and so is the amp. I like heading the music as it's intended... Not from overly warm or cold setups. I gave a rather neutral and detailed DAC/amp for this reason, with an ES9018 implementation.