[passerby999]

same as title...anybody helps?

 

[PFKMan23]

Not really. Sensitivity (and other factors) play just as large a role if not more than just the impedennce. For example, I feel that my k701s improve quitea good bit with an amp, just as much as my 650s, if not moreso in certain cases.

 

[Asr]

Also one vendor's Ohm does not necessarily equal another vendor's Ohm. Case in point: my KSC 75 and MDR-V6 are both rated at 60 Ohms. However, given one volume setting, while the KSC 75 might sound ok, the MDR-V6 sounds positively underpowered.

 

[drarthurwells]

In general, lower impedance is less resistance to the incoming signal which allows for greater headphone volume, if the impedance matches the amp. Portable sources work best (give higher headphone volume) with lower impedance headphones (say 32 ohms).

External amps usually match better with headphones higher than 32 ohm impedance, however.

In general, higher sensitivity means higher volume. Higher sensitivity is higher efficiency of the ehadphone - more volume with less amplification.

The SA5000 has higher sensitivity than the K701, and plays louder than the K701, even though both have similar impedance. If both also had similar sensitivity they would have roughly equal volume at the same signal amplitude.

 

[kramer5150]

nope... its the sensitivity that determines whether or not you need amplification. I have yet to hear a headphone that didn't improve with adding a robust amp circuit, versus an under powered source.

 

[creyc]

Any particular headphones "impedance", given as an average resistance value, determines the resistance the amp sees. Be it the internal amp in your iPod or in your Hornet headamp. Now the more the resistance, the higher the voltage will need to be from the amp to get the same amount of power. We can thank Ohms law for defining that for us.

Say you have a headphone like a Sony V700, with a very low impedance. (we'll say 16 ohms) It doesn't require you turn the volume knob up very high to be loud. Does this mean this headphone is more efficient or maybe it produces sound out of thin air? Obviously not. That volume knob doesn't adjust how much power your amp puts out, nope not at all, because there are two attributes used to describe electrical energy.

To keep things simple we'll just say you're merely raising and lowering the voltage when you turn the volume knob. Going back to the example, lets say the amps volume is set to put out .4 volts. The headphone load is 16 ohms. Ohms law says current = volts / ohms.
current = .4v/16ohm
current = .025A
current = 25mA
Thats 10 mWatt of power moving the diaphragm. (power = amperes x voltage)

Now lets take a 600 ohm AKG. Putting out that same .4 volts (same place on the volume knob) we get:
current = .4v/600ohm
current = .00067A
current = .667mA
Thats .267 mWatt of power moving the diaphragm.

Thats about 37.5 times more power output to the Sonys. Go ahead and divide 600ohms by 16ohms and you guessed it, 37.5 times more resistance on the AKGs.

The important thing to notice through all of this is the current values for both. 0.667mA of current is easy for any built in crappy amp to put out. 25mA is quite a bit more. At higher volume levels that goes up even further, and those headphones are rated at up to 1W of power, meaning they would pull 250mA from your poor little built in amplifier chip.

At high levels of current these power conscientious op-amps in iPods and laptops simply can't keep up. What you hear as a result is distortion, clipping, and all kinds of other nastyness to the sound quality. A headphone amplifier has plenty of current to keep up with your headphones demand. Which is why one is preferred even on low-impedance cans.

Part two might be a quick breakdown of high high impedance headphones need amps. Though I'm sure you know at least one good reason.

Notice how loud those 600ohm cans are on your iPod? No? ahh...but of course.

 

[passerby999]

anybody attended the national meeting and listened to the new e500 can say anything about them? do they need an amp also? if they do, which one will be the best fit then?

ps.my source is the ipod V

 

[sayrum]

Quote:

Originally Posted by creyc Any particular headphones "impedance", given as an average resistance value, determines the resistance the amp sees. Be it the internal amp in your iPod or in your Hornet headamp. Now the more the resistance, the higher the voltage will need to be from the amp to get the same amount of power. We can thank Ohms law for defining that for us. Say you have a headphone like a Sony V700, with a very low impedance. (we'll say 16 ohms) It doesn't require you turn the volume knob up very high to be loud. Does this mean this headphone is more efficient or maybe it produces sound out of thin air? Obviously not. That volume knob doesn't adjust how much power your amp puts out, nope not at all, because there are two attributes used to describe electrical energy. To keep things simple we'll just say you're merely raising and lowering the voltage when you turn the volume knob. Going back to the example, lets say the amps volume is set to put out .4 volts. The headphone load is 16 ohms. Ohms law says current = volts / ohms. current = .4v/16ohm current = .025A current = 25mA Thats 10 mWatt of power moving the diaphragm. (power = amperes x voltage) Now lets take a 600 ohm AKG. Putting out that same .4 volts (same place on the volume knob) we get: current = .4v/600ohm current = .00067A current = .667mA Thats .267 mWatt of power moving the diaphragm. Thats about 37.5 times more power output to the Sonys. Go ahead and divide 600ohms by 16ohms and you guessed it, 37.5 times more resistance on the AKGs. ...

so, does this mean on my iaudio u3 i wouldn't necessarily need an amp ( do to the sound output of 60mw (based on 30mw + 30mw 16ohm))?

 

[fewtch]

If you consider the only "need" re: headphone amps to be loud volume levels, then yes -- the lower impedance, the less you need an amp.

If you consider SQ to be the primary factor, then the lower the impedance the more you need an amp, because you'll get distortion with a circuit that provides inadequate current. This is presuming you have a headphone good enough to register subtler differences in amps (KSC75/35 may not qualify), and that the musical genre(s) you listen to need low distortion to sound good. Some metal and hard rock has so much built-in distortion (not to mention poor recordings) that ultimately it may not matter that much.

 

[passerby999]

thanks for the reply, now i have a clearer view.

it seems i have to say sorry to my wallet again?

 

[creyc]

Oh and I forgot to make any mention of peak current!

This a a brief instant in time where current can go through the roof before returning to normal levels. When a hard bass note hits you want enough power on reserve to accurately and effortlessly produce the sound. It's in these peaks where you will hear the first degradation in audio quality on a poor amp.

 

[recephasan]

Yea, the technical stuff is all there, but the main reason for the amp is not matching impedances so it sounds louder or anything.

It is because the headphone, at any given volume, sounds better when driven with a supply that can deliver the required current. The portables cannot deliver throughout the full frequency spectrum. As the amp gets better, it can "source" the current better. That is the same reason power supplies are mucho important, too.

The source (lineout) gives the voltage commands, and the amp translates them to current.
The amp is still outputing voltage. But since V=IR, and R (actually Z) is constant at a given frequency, the capacity of the amp to follow the input is determined by whether it can deliver the current, I.

Most portables fall short of this because at any given slice of time, there are many frequencies that are output and the weak amplifier cannot supply the required current. So the output of some frequencies suffers. Hence the "opening up" of the sound with a good amp.

Did I just make it all sound more confusing?

 

[F107plus5]

More confusing?

Nope,....well said!