[stonyboys]

I'm looking at a pair of srh440s that have an impendence of 55ohms. Will these have to depend on an amp or do they work straight outta my iPod? I really don't wanna spend another 50$ to get a decent amp...

 

[Landis]

They'll run absolutely fine out of your iPod.

 

[stang]

Yup, the SRH440 are very good straight from an iPod. The SRH840 is the harder to drive one

 

[stonyboys]

wait, lower impendence = requires more power? SRH840 is 44ohms...

 

[stonyboys]

and RE0 is 64ohms...

erm........ is there some other factor?

 

[driscoz71]

just a guess, but i would bet efficiency comes into play too. Also, my srh440's work fine on my ipod.

 

[mike2079]

Quote:

Originally Posted by stonyboys /img/forum/go_quote.gif wait, lower impendence = requires more power? SRH840 is 44ohms...

you were right before. more impedence(Z or R) requires allows less current (I) to drive given a voltage (V), I = V/R. more current = more drivable.

I just got my SRH440s a few days ago, still burning them in, but the store demo ones worked great with my mp3 player.

 

[stonyboys]

wait, so RE0 is easier to drive? makes sense since it has a smaller driver, but i thought it only sounded good with an amp.

 

[Helmore]

Quote:

Originally Posted by stonyboys /img/forum/go_quote.gif wait, so RE0 is easier to drive? makes sense since it has a smaller driver, but i thought it only sounded good with an amp.

It's about both the impedance and the sensitivity of the headphone. The impedance rating of a headphone will tell you how much power a particular amp/source can run through it if you know the amount voltage and current it can provide. The equation for the amount of power you run through the headphone is simply:
Power = P = I*V = R*(I^2) = (V^2)/R
Where V the voltage is, I the current, P is power and R (mostly called Z in the case of impedance) the resistance/impedance.
When you know that you also have to also have to consider the headphone's efficiency/sensitivity. When 2 headphones are provided the same amount of power, they won't usually both be running at the same volume level (SPL). Its efficiency is usually expressed in the form of the amount of volume per milliWatt and sometimes the volume per Vrms, I.E. dB/mW or dB/V both at 1kHz.
Just an example:
Headphone A has:
- Impedance of 64 Ohm
- Sensitivity of 106 dB/mW

Headphone B has:
- Impedance of 32 Ohm
- Sensitivity of 100 dB/mW

In this case Headphone A and B should both provide the same volume level out of your iPod and are both relatively easy to drive from your iPod.

Headphone C has:
- Impedance of 50 Ohm
- Sensitivity of 110 dB/mW

Headphone C should be louder than both A and B.

Hope that helps somewhat.

 

[Helmore]

Quote:

Originally Posted by stonyboys /img/forum/go_quote.gif wait, so RE0 is easier to drive? makes sense since it has a smaller driver, but i thought it only sounded good with an amp.

The Shure SRH440 has:
- Impedance of 44 Ohm
- Sensitivity of 105 dB/mW

The Head-Direct RE0 has:
- Impedance of 64 Ohm
- Sensitivity of 100 dB/mW

You will be able to get higher volume levels with the Shure SRH440 than with the RE0, but both can easily be driven directly from an iPod. As with every headphone though, you'll be able to improve on what the iPod can provide by using a proper amp and DAC/source. That has less to do with the amount of power the amp can provide, although that does help, but also a lot with the quality of the signal. The impedance rating and sensitivity don't tell you much about the improvements you can get from using a better source and amp, they only tell part of the story.

 

[stonyboys]

oh thanks a lot for that, helmore. i'm guessing that with 32ohms and a sensitivity of 115dB/mW, the K81DJs will go louder than the SRH440?

 

[Helmore]

Quote:

Originally Posted by stonyboys /img/forum/go_quote.gif oh thanks a lot for that, helmore. i'm guessing that with 32ohms and a sensitivity of 115dB/mW, the K81DJs will go louder than the SRH440?

That sensitivity figure of the K81DJ is in dB/V, not in dB/mW.
Because they have an impedance of 32 Ohm at 1 kHz, which is also where they rated its sensitivity, you would be giving them 31,25 mW with a 1 Vrms source. For ease of calculation, lets just say you would be giving them 32 mW if you gave them a 1 Vrms voltage. That's 32 times more power than what's used in the dB/mW rating (duh

), but that rating uses a logarithmic scale to express the Sound Pressure Level (SPL) and every 6 dB is twice the volume (IIRC). 32 = 2^5, and 5 x 6 = 30 which would mean that the sensitivity of the AKG K81DJ is 85 dB/mW. In other words, even the Head-Direct RE0 would be louder.

The Shure SRH440 has:
- Impedance of 44 Ohm
- Sensitivity of 105 dB/mW

The Head-Direct RE0 has:
- Impedance of 64 Ohm
- Sensitivity of 100 dB/mW

The AKG K81DJ has:
- Impedance of 32 Ohm
- Sensitivity of 85 dB/mW

We're not taking any variations in measurement into account though and I might be wrong on some of my calculations. In other words, take these numbers with a grain of salt and just use them as a rough guideline.

 

[stonyboys]

say what??? will the K81DJ sound any good through my ipod?

 

[stonyboys]

bump for needed help

 

[paulb09]

The AKG website says "Sensitivity (dB/mW, dB/V*)" for its headphones these days. What "V*" means I don't know, but the K81DJ gets ample volume from my iPod, so a figure of 115 dB/mW at 32 ohms sounds like a good one to me.