[yawg3d]

Hi there,

simple question:

I often read about 'easy to drive'/'hard to drive', while it seems that phones with low impedance are called 'easy to drive', those with high impedance are called 'hard to drive'.

Does this mean that for example, if I set up the output volume at my portable MP3-CD-Player to maximum volume, and then plug a HD500 (32 Ohm) and after that, a V6 (sth. like 64 Ohm) to the headphone out, the V6 will only be half as loud as the HD500?

Thanks for answering this newbie question

.

 

[zoot2boot]

I don't think it will be a linear relationship as you describe. amps produce more power into lower impedances which might theoretically double the power with a halved impedance but the componentry of the amp, its power supply and its stability into lower impedances will limit this.

doubling the power into any speaker wont double its volume, other factors such as the surface area of the diaphram will play a larger role i think.

 

[JaZZ]

Basically double impedance means half volume. But beside impedance there's also sensitivity that counts. A 64-ohm headphone with 3 dB higher sensitivity soounds equally loud as a 32-ohm headphone. But that's still not the whole story, because there's also the amp's output impedance in play. If it's clearly higher than say 1 ohm, low-impedance phones won't be as much louder than high-impedance phones as theory dictates.

As to the «hard to drive»... often it's not impedance or sensitivity which causes problems, but the sonic synergy between headphone and amp. And as long as the amp supplies enough voltage, high impedances are the easier load, because they draw less current (= less harmonic distortion) and are less critical in terms of output impedance.

 

[yawg3d]

My HD 500 has 64 Ohm/102 dB, the Ultrasone HFI-650 I am planning to buy has 75 Ohm/94 dB, if I didn't misread anything. Let's say my amp uses a 150 Ohm resistor between Speakers Out and Headphone out, will I be able to use the Ultrasone with it?
Shouldn't be a problem, considering my amp has a volume scale from 0 to 33, and with my HD-500, I am at Volume 11 most of the time, or is it possible that the HFI-650 doesn't fit together with my amp then?

Thanks, yawg3d

 

[JaZZ]

Quote:

Originally posted by yawg3d My HD 500 has 64 Ohm/102 dB, the Ultrasone HFI-650 I am planning to buy has 75 Ohm/94 dB, if I didn't misread anything. Let's say my amp uses a 150 Ohm resistor between Speakers Out and Headphone out, will I be able to use the Ultrasone with it?

Are you sure with the 150 ohm? That's not a good precondition for neutral sound (considering the Ultrasone's expectable ondulated impedance response and the therefore non-uniform attenuation), although not necessarily worse than with your current HD 500. Let's hope there's at least some parallel resistor to compensate for the serial resistor (hence a voltage divider).

Quote:

Shouldn't be a problem, considering my amp has a volume scale from 0 to 33, and with my HD-500, I am at Volume 11 most of the time, or is it possible that the HFI-650 doesn't fit together with my amp then?

From your description a volume problem isn't too likely, but can't be excluded, because the volume scale doesn't represent a measure for the achievable undistorted volume. I think in your situation (if the plain 150-ohm serial resistor is reality) you'd be better served with a higher-impedance headphone. And/or of course with a dedicated heqadphone amp. But I'm sure you already know that...

 

[yawg3d]

I don't know if it's really 150 Ohm. It's a Denon UD-M30 CD-Receiver, there's nothing about the Phone Out Impedance in the Manual. Before the HD-500, I had a pair of Philips SBC HP820 (32 Ohm!) which worked quite well with the amp.

I'm not really happy with the HD500 I have at the moment. It's somewhat strange, while some songs sound really really nice on the HD500, others sound really bad, the lower mids seem to sound 'supressed'.

So I finally decided to get me some new phones, and it looks like I'll have a good opportunity to get some Ultrasone HFI-650 soon.

I DO know that a dedicated headphone amp would be great, but I don't think I can afford one at the moment.

JaZZ, you were wondering about the 150 ohm resistor. Is this quite low, or quite high?

 

[JaZZ]

150 ohm is a high value... there are not much headphone amps around with such a high impedance. If your 32-ohm Philips has worked «quite well», I doubt there is such a high serial resistance. And at the same time it's very likely that the HFI-650 will work even better.

But it's not predictable with certainty -- you have to risk it.

 

[wallijonn]

yawg3d,

I wouldn't worry about impedance, sensitivity or efficency at the moment. for the most part they can't really be correlated. (for example if you read the specs for the Aiwa AK100, they are rated at 16 ohms, blah, blah, blah. they sounded like crap).

you'll just have to buy it and try it out. chances are that the great sound of the HFI-650 will shine through and give you much more than acceptable sound.

 

[hero zero]

just thought I'd post a quick question: does the output impedence of the source or amp have any effect on the sound?

I was using a pair of AKG K141S's [55 ohm] on my equipment, which has low output impedence and it sounded pretty good, but when I used it with the mixers and sources in the studios at the radio station of which I was a member, I noticed that the the bass became really thick and overpresent....any ideas? or whas it just me?

 

[JaZZ]

Quote:

Originally posted by hero zero ...the bass became really thick and overpresent...

That's a typical sign of a high output impedance with the HP amp. The bass-resonance hump in the headphone's impedance curve is less attenuated than the rest of the frequency response, hence you get a bass hump.

 

[hero zero]

Quote:

Originally posted by JaZZ That's a typical sign of a high output impedance with the HP amp. The bass-resonance hump in the headphone's impedance curve is less attenuated than the rest of the frequency response, hence you get a bass hump.

hmm...so the only way to solve this problem is to use lower output impedence or get a pair of cans with higher impedence?

 

[JaZZ]

Quote:

Originally posted by hero zero ...so the only way to solve this problem is to use lower output impedence or get a pair of cans with higher impedence?

Yes... or switch a pair of 40-60-ohm resistors in parallel to your K 141S's voice coils.

 

[bandit1200]

Impedance just implies the ratio of current and voltage needed to drive the headphones.

For a given amount of power driving the headphones,
High impedance phones will require bigger voltages
Low impedance phones will draw bigger currents.

A headphone can be "hard to drive" for 3 possible reasons:

(1) Low Sensitivity
(2) High Impedance
(3) Low Impedance

Sensitivity is a measure of how much power has to be pumped into the earphone for you to hear the music. Low sensitivity phones require more power from your amp to get to a certain volume. Phones with low sensitivity can be "hard to drive" because they require more power.

High Impedance means that the earphones will need bigger voltages to get the same power into them. These headphones can be hard to drive using amplifiers that have limited voltage available, as is the case in many consumer portables. Amplifiers that cannot drive with enough voltage may suffer from low gain, low source voltage (batteries), or excessive voltage drop in the output stage.

Low Impedance means the phones will need bigger currents to get the same power into them. Here, hard to drive means that the amplifier cannot supply the required current, the result of which is that louder passages and low frequencies don't sound good. Amplifiers that cannot provide the required current are suffering from whimpy output stages (small transistors, perhaps), or soft power supplies that can't keep up with demand.

There is more detail to how these things work (like the idea of amplifier output impedance) but that's the general idea.


When discussing cans that are "hard to drive," I propose that we try to always try to say which of the three reasons is the culprit. That may clear things up.




Power hungry = low sensitivity

Voltage hungry = high impedance

Current hungry = low impedance




Example: HD600's are hard to drive because their high impedance make them voltage hungry.

Grado's can be hard to drive because their low impedance makes them current hungry.

E2's aren't hard to drive even though they have low impedance, their high sensitivity makes up for it.


Etc.


-Bandit

 

[bandit1200]

Because someone asked:

Power is not equivalent to voltage. Or to current.

Power is Voltage times Current. (The combination of both!)


So high power can still be low voltage if there is lots of current.

And high power can also be low current as long as there is lots of voltage.


Sensitivity is a measure of Volume per unit of power. That's why is measured in dB/mW (decibel per milliwatt).

-Bandit.