[ProjectDenz]

Let me start off by saying that I am quite concerned by the amount of fellow headphone hobbyists around here looking for more higher impedance and lower sensitivity headphones without knowing whether they are powering them properly. Now while it is fantastic that they are expanding their horizons and are whetting their curiosity by moving deeper into the realm of this hobby there really needs to be some clarification about what can and cannot power a higher impedance, lower sensitivity headphone. I feel that this issue has become more prevalent lately.
 
My arguments here will be based of the Beyerdynamic DT440, a 32Ohm, sensitive headphone that does not require any dedicated amplification and it's bigger brother, the Beyerdynamic DT880, a 250Ohm, low sensitivity headphone that really needs some dedicated amplification to shine. Both are neutral headphones and both have the same sound signature (to my ears anyways) except that the DT880 is higher up the chain.
 
 
Ok, down to business. Now I cannot stress enough how important it is to properly power hungry headphones like the DT880. I have seen many threads around here where people are looking to buy the DT770, DT880, or DT990 (talking about 250Ohm and 600Ohm versions) while trying to power them with amplifiers such as Cmoys and little Fiio amplifiers. Let me tell you something folks, if you are not willing to power them properly then you are literally throwing your money down the drain. My DT880 sounds quite harsh in the high end and lacks bass when it is not being powered properly, in fact, my DT440s sound much better than them in this scenario. This is me trying the DT880s with a Cmoy that uses two 9V batteries in parallel to a few Fiio amplifiers such as the E7 and E9 which I have tried in the past even to my Asus ST, which even cannot power the DT880 to its full potential (although it gets it quite close I admit).
 
If budget really is an issue and you can't afford a decent amplifier to go with your higher impedance cans then I really do suggest getting a lower impedance alternative. It's not like top tier headphones that requires no dedicated amplification to shine don't exist. The Alessandro MS-Pro is a prime example, although some amplification does improve stuff a tinsy bit from experience.
 
However, if you must have amplification on a budget then two great low cost amplifiers are the Objective2 amp and the Matrix M-Stage, although more do exist. These can power some of the more power hungry headphones well (I wouldn't hold my breath on top tiered cans like the HD800 or T1).
 
 
The key word here is RESEARCH. Do plenty of research when you are trying to look for higher impedance headphones and research which amplifiers are powerful enough and are great value for money.
 
 
Thank you for your time and I hope I have cleared things up a little bit. This hobby really is fun but does require some good research so you don't end up falling into the wrong places.
 
Please don't be afraid to discuss or share your opinions.
 
 
 
 
 

 
The classic Cmoy, will these power your power hungry headphones?
 
 
 

 
 
The DT880, beautiful, but hungry like the wolf.
 
 

 
The functional DT440, will only beat an underpowered DT880.
 
 

 
The Fiio E7, sadly, won't power your HD600 properly.

 

[cobrasneverdie]

great thread, how does someone that does not know much about amps and headphone determine if their headphones need an amp or not? Also, how does someone determine if their amps are powerful enough to drive headphones to their full potential?
 
What numbers do we look for

 

[ProjectDenz]

Quote:

great thread, how does someone that does not know much about amps and headphone determine if their headphones need an amp or not? Also, how does someone determine if their amps are powerful enough to drive headphones to their full potential?
 
What numbers do we look for

It really is quite hard, especially when you have nothing to compare it to. I remember a few years ago when I was just getting into this hobby I bought myself a HD600. I underpowered it and my source was my motherboard headphone out (yikes!). I thought it was the best sounding thing ever back then, but really looking back, I could had got something for much cheaper that would sound even better due to me not powering them properly or giving them a proper source.
 
It's just something that requires research. Of course asking for help on these forums always helps! But always do your research too.

 

[skamp]

What numbers do we look for

Headphone sensitivity in dB/mW (or converted from dB/V) and impedance, amplifier output impedance and power into a given load. You can also calculate how much power will be required from the amp in order to reach a given sound pressure level.

As a rule of thumb, you also want an amp that has an output impedance that's at least 8 times lower than the impedance of your headphones.

The FiiO E7, for instance, is rated as being able to output 150 mW into a 16 ohm load, and 16 mW into a 300 ohm load. It's said by FiiO to be adequate for headphones in the range of 16 to 300 ohms.

The FiiO E9 is rated at 80 mW into a 600 ohm load (i.e. much more beefy than the E7), and adequate for headphones of up to 600 ohms.

How to convert sensitivity in dB/V into dB/mW:
Sensitivity in dB/mW = dBV - (10 * log(1000 / Z))
Where dBV is the headphone sensitivity in dB/V and Z is the headphone impedance in ohms.

How to calculate required power from an amp in mW for a given SPL:
10^((SPL - sensitivity) / 10))
Where ^ is power(), SPL is the sound pressure level you want to reach in dB, and sensitivity is in dB/mW.

See Headphone & Amp Impedance and More Power?

Example: my Denon AH-D2000s have low impedance (25 ohms) and high sensitivity (106 dB/mW). They require only 2.5 mW to reach a SPL of 110 dB. The AKG K 701, on the other hand, have an impedance of 62 ohms and a sensitivity of 105 dB/V, which translates into 93 dB/mW, which is very low. That means they'll require much more power than my Denons, i.e. 50 mW to reach a SPL of 110 dB (20 times more!).

 

[stv014]

Quote:

Originally Posted by ProjectDenz /img/forum/go_quote.gif
 
My DT880 sounds quite harsh in the high end and lacks bass when it is not being powered properly, in fact, my DT440s sound much better than them in this scenario.

 
Power does not affect frequency response (although other factors do, like output impedance, but these affect low impedance headphones more). I have the 250 Ohm version of both the DT770 and DT880, and the sound does not change much from different sources, as long as the comparison is level matched, and clipping is avoided. The DT440 probably sounds better to you because it gets loud much easier (louder sound is perceived as better quality), therefore what your experiment shows mainly is that non-level matched sighted subjective tests are not reliable.
 
The E9 and Xonar ST are not lacking in power compared to the O2, by the way, all three have about the same maximum output into high impedance loads.
 

 

[stv014]

Quote:

Example: my Denon AH-D2000s have low impedance (25 ohms) and high sensitivity (106 dB/mW).

The AH-D2000 may not be that sensitive actually, it has been measured under 100 dB/mW by Inner Fidelity and doctorhead.ru.
 

 

[stv014]

Quote:

Example: my Denon AH-D2000s have low impedance (25 ohms) and high sensitivity (106 dB/mW). They require only 2.5 mW to reach a SPL of 110 dB. The AKG K 701, on the other hand, have an impedance of 62 ohms and a sensitivity of 105 dB/V, which translates into 93 dB/mW, which is very low. That means they'll require much more power than my Denons, i.e. 50 mW to reach a SPL of 110 dB (20 times more!).

The 110 dB requirement of course depends both on personal preferences, and on the type of material being listened to (wider dynamic range, such as classical music = more peak SPL needed). I normally stay below 100 dB peaks, for example. Every 10 dB of additional SPL requires 10 times as much power, so the potential for variation is quite large. I have seen people claiming that the Xonar ST/STX is "too quiet" with the HD650 at maximum volume and gain (more than 120 dB)