[mapleleafs]

I know what an amp is, but what exactly is an ohm adaptor, and what does it do? I've heard many people make reference to such devices e.g. "The headphone sounds much better with a 75 ohm adaptor", and I would just like to know more about them. Thanks, and sorry if this is a nooby question.

 

[angler31337]

Don't worry about asking stuff like this -- everyone is new to headphones at some point. (Please, no one ask me to prove this rigorously.)

When someone says "75 ohm adapter," what they usually are referring to is a short cable that adds 75 ohms of impedance to the headphone input. Adding extra impedance to the input makes the headphones a little harder to drive, and so can make them "play" better with some equipment. A lot of times, people find that "hissing" sounds can be eliminated by adding extra inline impedance. I think the classic example of such a cable is the one etymotic sells for their ER-4p (which is just a 73 ohm impedance cable).

-Angler

 

[nightfire]

Yep.. what Angler said.

It's worth noting that in addition to helping play better with certain equipment, they can also change the sound signature of some headphones (ie. the ER4).

Essentially, a higher impedance means a higher voltage is required to produce the same current flow (amps = voltage/impedence). By extension, this means a higher voltage is required to create the same wattage (power = volts * amps).

SPL (sound pressure level) is related to the amount of power running through the speaker; the measure is called sensitivity (dB/W).

Why is all this relevant? It turns out that some drivers produce a stronger vibration at certain frequencies (usually treble) when the voltage:amperage ratio is higher. High voltage "stimulates" the treble more than the bass.

Increasing the impedance with an adapter will mean more voltage is required to generate the same SPL, and hence will change the sound signature, but not the overall loudness per watt. But only in certain headphones.

Whew.. beat that one to death.

 

[angler31337]

Quote:

Originally Posted by nightfire Whew.. beat that one to death.

It's not worth beat'en if you ain't gona kill it.

-Angler

 

[Gibo]

We were all n00blettes once

 

[skyline889]

So basically they're getting overpowered so your adding more resistance to them? How come no one ever has this problem with the Grados? They're all 32 ohms right? And some people use them with monster amps and receivers.

 

[bhd812]

I need one for My sensa's...

Raptor and Sensaphonics no play nice together, this may or may not be the key

 

[milkpowder]

The Ety adapter definitely changes the sound signature. I find that the adapter is very good with the PX100 and ER-4P. With my SR-325i, the adapter makes the 'phones sound a little restricted. No longer is the sound airy like before. Try putting your hands partially over the cups of the SR-325i while listening to music. The sound becomes muffled and less bright. It's good that the Grados are less bright, but the slight muffling is not good. It is true that some of the noise is removed.

 

[nightfire]

Quote:

Originally Posted by skyline889 So basically they're getting overpowered so your adding more resistance to them? How come no one ever has this problem with the Grados? They're all 32 ohms right? And some people use them with monster amps and receivers.

Well, not overpowered exactly.

The only situation in which a headphone is overpowered is if it starts to clip or distort. This comes either as a result of insufficient peak current (distortion) or voltage (clipping). Or overwhelming the driver material.

If your amp is low voltage (running off batteries?) then low impedance is good. It will get you the most clean volume per volt.

If your amp is current limited (output of a cheap home receiver), then high impedance is good.

Aside from changing the sound signature, the main benefit is lowering the noise floor. Since all amps have some defined signal to noise ratio, even with no signal present, raising the impedance will lower both the peak volume, and the white noise itself. The noise just won't have enough presence to be audible.

The reason it's not a problem with Grados is probably because they're open cans. It's harder to hear amplifier noise against a noisy background. They also have a lower sensitivity than IEMs. In any case you can only overpower headphones if you turn up the volume too loud.

 

[Mr.Shadow]

Very helpful comment I must say, its a keeper thats for shure !!!
Thanks for a very detailed but yet easy to understand explantion

 

[wakked1]

Listening to the HF-1 through a 120-ohm adapter changes the sound, for the better imho. Tames the brightness a tad. The SR60 sound MUCH better through the adapter, almost a different phone.

 

[jrosenth]

I found that the Koss ksc 75 became really, really nice with an adapter - wonder if it does something similar to the senn 100 (which I found a touch boomy)

 

[fewtch]

I found no relevant difference using a 75-ohm adapter with Koss Portapros.

Also, I really don't understand the point of raising a headphone's impedance, from a SQ perspective (except a special case like Ety ER-4). I thought it was generally understood that there's no direct relationship between sound quality and the impedance of a headphone. Give me a break, just adding two resistors into the signal path greatly improves a pair of cans?

 

[Naris]

Where can you get these adapters from (in varying resistances)? I knew about the Ety one, but where are you getting the 75-ohm and 120-ohm stuff? And I guess there's not problem with using it on all headphones (sounds silly I know, but I was concerned)?

 

[ckhirnigs113]

Radio Shack sells a $5 in-line variable impedance adaptor that works quite well. I use it with my UM2's to eliminate all the hiss that comes from the iPod.