[GustavMahler]

I understand that if the sensitivity of headphones are 100dB, It means that from every 1 mW from the source it produces 100dB (Actually i am not sure if it means it is producing 100dB..). Impedance demermines the electrical power required by the headphones. Now of course the PS1000e (32ohm)  need less electrical power than the HD800 (300ohm). But the sensitivity of the HD800 is 102dB compared to the Grado's 99dB. Isn't it supposed to be the contrary? I know i must mix up something here. Thanks

 

[RRod]

  I understand that if the sensitivity of headphones are 100dB, It means that from every 1 mW from the source it produces 100dB (Actually i am not sure if it means it is producing 100dB..). Impedance demermines the electrical power required by the headphones. Now of course the PS1000e (32ohm)  need less electrical power than the HD800 (300ohm). But the sensitivity of the HD800 is 102dB compared to the Grado's 99dB. Isn't it supposed to be the contrary? I know i must mix up something here. Thanks

 
The part you're missing is the power rating of amps at given impedances. Here's the list for the Magni2:
Maximum Power, 16 ohms: 1.8W RMS per channel
Maximum Power, 32 ohms: 1.2W RMS per channel

Maximum Power, 50 ohms: 1.0W RMS per channel

Maximum Power, 300 ohms: 260mW RMS per channel

Maximum Power, 600 ohms: 130mW RMS per channel

 
When you combine:
.the impedance of the heaphone
.the sensitivity of the headphone
.the power of the amp at the headphone's impedance
 
you can answer the question: can this amp drive this headphone loudly enough?

 

[GustavMahler]

Thanks! Now i get it. The sensitivity does determine the dB level you get when the headphones receive a certain amout of electricity, But the impedance decreases the amout of electricity, Thus lower mW=Lower dB level. Thanks!
Another question-What is the impedance of the AMP and what does it have to do with all this?
And also, Why do beyerdynamic make the same model with different impedences? What do they add/make better/change in the higher impedences that actually make them of higher impedence? And i can't seem to find the power ratings for amps at given impedances..

 

[RRod]

  Thanks! Now i get it. The sensitivity does determine the dB level you get when the headphones receive a certain amout of electricity, But the impedance decreases the amout of electricity, Thus lower mW=Lower dB level. Thanks!
Another question-What is the impedance of the AMP and what does it have to do with all this?
And also, Why do beyerdynamic make the same model with different impedences? What do they add/make better/change in the higher impedences that actually make them of higher impedence? And i can't seem to find the power ratings for amps at given impedances..

 
Well the amp has it's own output impedance that can affect the sound of the headphones if it gets too high relative to the headphone's impedance. The "rule-of-thumb" I've seen given as a 1:10 to 1:8 minimum ratio of amp-to-headphone impedance. Using a very low impedance amp is an easy way around this, but you can find headphones to match any amp, including the headphone amp of your favorite DAP.
 
The Beyers have different impedances to allow for different applications (mobile, all-around, stationary). Impedance can be affected by all kinds of things (wiring, etc.); I don't know the specifics for the Beyers.
 
Lots of gear is woefully short on specs. If you can't find it yourself, ask in one of the equipment forums, or stick to equipment that is more transparent with its specs.

 

[GustavMahler]

On the iBasso DX90 specs it says: 
Output Level: 1.7Vrms (1kHz 0dB)
and then: Output Level: 1.3Vrms(Low gain), 2.0Vrms(Mid gain), 2.8Vrms(High Gain
 
I guess that in the amp specs it is measured in Volts and not watts, Right? 
And i know it is a noobish question, But a DAC doesn't  have any impedance/power output, right?

 

[Head Injury]

  On the iBasso DX90 specs it says: 
Output Level: 1.7Vrms (1kHz 0dB)
and then: Output Level: 1.3Vrms(Low gain), 2.0Vrms(Mid gain), 2.8Vrms(High Gain
 
I guess that in the amp specs it is measured in Volts and not watts, Right? 
And i know it is a noobish question, But a DAC doesn't  have any impedance/power output, right?

Voltage is used to determine power at a given impedance. Power = Voltage squared / impedance. Most amps won't be able to drive their max voltage into low impedances though, which is where it gets tricky. I wish more manufacturers would publish more specs.
 
DACs have an output impedance and power. Their output impedance is typically much higher than an amp, and they're designed to feed very high impedance loads (the amp) so they have little current and power. The standard voltage output for DACs is 2 Vrms, but desktop solutions alone can range from 1 to 3 (or more) Vrms. It's actually very important to level match a system for a fair comparison even when just changing DACs, because their voltage can differ so much. My Essence STX, for example, was measured by Stereophile as having 2.16 Vrms at the line out. This is enough to make it 0.66 dB louder than a 2 Vrms DAC like the ODAC when using the same amp and volume level. That's just enough to make it sound subjectively better without being obviously louder. That's probably why ASUS did it.
 
In some cases you can drive a headphone directly with a DAC, but the headphone needs the right impedance and power requirements to not color the sound. A high, flat impedance and enough sensitivity to reach adequate volumes with a DAC's limited voltage, for example. Audeze's new 1200 ohm planar headphone might be the perfect candidate when it comes out.
 
I should start this rumor, it might take off like the speaker tap one. The less wire the better, right?

 

 

[GustavMahler]

If the DAC's output is higher, It will sound better than it would sound with the same volume with a lower output DAC and AMP because the DAC output shows less distorsions, Right? So it's better to have a higher output DAC than a higher output AMP? And is the pre-amp built in the DAC or the AMP? And how is the amp different from the pre-amp?
"A high, flat impedance and enough sensitivity to reach adequate volumes with a DAC's limited voltage"
Why is it better to have a higher impedance with only a dac? I can understand why high sensitivity is important, By i thought a lower impedance would be better with the limited output of the DAC (For higher volume). I think you talk about sound quality rather than volume-So how does the high impedance affect sound with the low output of the dac? 
Also if i try to calculate the dB of the DX90 with the 600ohm DT990 it doesn't really make any sense:
1.44v/600ohm=0.0024. Sensitivity is 94dB, So:
2.4mW*94dB=225dB
There is no way it gets to 225dB..

 

[MindsMirror]

 
Also if i try to calculate the dB of the DX90 with the 600ohm DT990 it doesn't really make any sense:
1.44v/600ohm=0.0024. Sensitivity is 94dB, So:
2.4mW*94dB=225dB
There is no way it gets to 225dB..

The equation for power is P = V^2/R, so the power at 1.44VRMS into 600Ohms is 3.456mW.
 
dB is a logarithmic scale. 225dB is not 2.4 times as much power as 94dB. An increase of 3dB means double the power. 3.456 is almost 4 times larger than 1, so the volume is just less than 6dB above 94dB. Using a formula for calculating dB or a dB calculator, the exact value is 5.4dB, so the volume of the headphone at 1.44VRMS would be 99.4dB.

 

[GustavMahler]

Great explanation, Thanks! I found this site http://www.sengpielaudio.com/calculator-db.htm-I enter the ratio (in mW) and choose energy size- And i got 5.385, Just like the 5.4dB you said. As long as you go up in the dB scale, The numbers that change a certain amount of loudness get smaller, Right?
How can i know what is a sufficient max dB level for specific cans? The optimal spl varies with different cans (Some 250ohm cans sound good on dx90, and some 250ohm don't), Is that correct? Where can i find the optimal spl?
Ive seen a 600ohm headphones and after calculating i got over 100dB with my portable DX90. Where is the trick? It cannot really power them, So how can i know?
And please give more details about the dac power output and how it affects the amp/headphones
Thank you very much! I've learned a lot from you!

 

[MindsMirror]

A DAC does not need to deliver any power to the input of the amp. The amp input has a very high impedance in the order of 1MOhm. If 1VRMS is delivered to 1MOhms, power delivered is very small at only 1uW. The reason that the output impedance of the DAC is not important is because of the large input impedance on the amp. Similar to the 1:8 or 1:10 guide that people mention regarding amp output and headphone impedances, the output impedance of the DAC should just be small compared to the 1MOhm impedance that it is driving.
 
If you calculated that the amp can produce 100dB with some headphone, that means that it should be able to produce a 1KHz sine wave at that loudness. You probably don't listen to just a 1KHz sine wave though. Music has peaks and dynamics that extend above the average or RMS level. The amp needs to be able to handle those too.
 
My album with the highest peaks is Dire Straits' Brothers In Arms, which reaches full scale and has an average loudness level roughly 25dB below. So, I need 25dB of headroom. If you wanted to listen to that album loudly at 90dB for example, you might need an amp that could produce at least 115dB with your headphones, so that it can handle the peaks without distortion.

 

[GustavMahler]

 Impedance is not that important in measuring a speaker's power-Is that correct?
So i only need to look how many watts the amplifier produces? I found this calculator and there isn't an impedance input, So that's why i got this conclusion:http://www.crownaudio.com/elect-pwr-req.htm
What is an Amplifier Headroom?
Also in this calculator from the distance of 3M, Sensitivity of 89dB and desired listening level at my distance of 90dB and headroom of 3dB (What is a headroom..?)
i get 23watts. Is it possible? I thought it would require much more power..
For measuring headphone spl, I need tp select factor and energy, to enter the mW in the factor field and then to add the number in the dB field to the headphone's sensitivity, Right? Please approve if it's correct.. 
Last thing-I've heard the ps1000e (32ohm) With the naim DAC-V1 with its <10Ω headphone amp and it sounded great, And the ratio is less the 8:1 of course.. So..?
Thank you for the help! You really help me obtain a lot of interesting and important knowledge!