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Headphone Impedance?

post #1 of 11
Thread Starter 
What *exactly* does impedance mean? I did several searches on it and did not find a straightforward, plain-English answer. I originally thought it was related to the ease of driving - i.e. if the headphones have lower impedance they're easier to drive. But i've been looking at the SR60 (called low-impedance headphones) versus iM716 (hard to drive headphones), and the iM716 has a 16ohm impedance compared to a 32ohm impedance... what does it all mean???! I was wondering how impedance ties into amping, but first and foremost I'd like to find out what it is.
post #2 of 11
I think you are spelling it wrong.
There was a discussion thread just a few days ago.... I found it pretty plain-jane English.
post #3 of 11
Impedance is the total opposition to the flow of current that is presented by a circuit.

Impedance is different from resistance because it also counts all reactive components (capacitive and inductive).
post #4 of 11
Just think of it as resistance to flow of current. Technically, Impedance = Resistance + Reactance but don't worry about it. Basically what happens is you have a source of music sending some current to your headphones. The circuitry and wires leading up to your headphones have some impedance and your headphone wires along with the other circuity in the headphones have another impedance (remember just to think of all this as resistance to flow of current ...just like a thin garden hose resists water flow more than a wide hose). When the current travels from the source and hits the boundary of the headphones you have some current bouncing backwards and some current that keep going through and getting to your headphone drivers. If the impedance of the headphones is high then a lot of this current bounces backwards instead of going through and so not much current drives the headphones. This is a problem because you have less power output. If you have a matched load that means that the impedance of both the source and the headphones are the same. The current doesn't know the difference when it reaches the boundary between source/headphone so you have optimum power throughput.

I guess one analogy is to think about this: If you punch a bag, then the momentum from the forward punch can be the source current. If the bag is really heavy and hard (like high headphone impedance) then when you hit it your arm is going to bounce back. If the bag's lighter (lower impedance) then you have a good boxing workout. If the bag is as light as a feather you end up wasting a lot of energy and probably throwing out your arm (this is why very low impedance headphones can suck a lot of battery life from portable sources like mp3 players. the source is basically throwing a lot of current at it and so the battery dies quickly). Not a perfect analogy but it sort of works.
post #5 of 11
Impedances under 60 ohms are usually considered low.

The volume pot on an amplifier is basically a variable resistor, to control how much current goes out to the headphones. Lower-impedance headphones won't need much current to get loud, while higher-impedance ones will. So the higher the impedance, the more current a headphone needs to attain volume.

Even equal-impedance headphones aren't made the same though, so sometimes you'll find two (or more) headphones at a given impedance that actually require varying levels of current to achieve the same volume.
post #6 of 11
Quote:
Originally Posted by Aflac
..........and the iM716 has a 16ohm impedance compared to a 32ohm impedance...
I copied this from an earlier post regarding the iM716, thread: "Altec Lansing IM716 equals Ety ER4s" op, Old Dave. In short, in the HD mode the impedance is 68 Ohms.


Back for a moment to the impedance issue from earlier in this thread:

Although the interest in this topic has waned, it is an important issue that has not yet been addressed.

I pulled out my old VOM, replaced the batteries, and quickly checked the DC impedance of the iM716’s, and a couple others, as per the suggestion of gremlin. I don’t know what happens to the impedance over the frequency spectrum, sorry Head-Case.

Senn HD580: I get approx. 320 Ohms, it is rated at 300 Ohms.

Senn PMX 60: I get approx 27 Ohms, it is rated at 32 Ohms.

Sony MDR-J11G: I get approx 16.5 Ohms, it is rated at 16 Ohms.

Apple earbuds: I get approx 34 Ohms, it is rated at 32 Ohms.

So, the quickie DC readings are all pretty close to rated specs. On to the iM716:

iM716: (PCMag.com listed at 16 Ohms, mode unspecified. From my readings this may have been a missprint and is probably the iM616 which is a clone of the ER6i)
HD mode: I get approx 68 Ohms
Bass mode: I get approx 37 Ohms


Ety Research (@ 1 kHz; from their web site):
4S model: rated at 100 Ohms
4P model: rated at 27 Ohms
6 model: rated at 48 Ohms
6i model: rated at 16 Ohms


My readings were later verified by others.
post #7 of 11
Quote:
Originally Posted by Aflac
What *exactly* does impedance mean?
A measurement of the resistance to the audio current by the voice coil of the driver.
post #8 of 11
How is the impedance changed for the same drivers in headphones? ie: what is the difference between a Beyer 880 250 ohm and a 32 ohm version? Same drivers? How is the resistance made less? Anyone know?

Ian
post #9 of 11
Quote:
Originally Posted by Aflac
What *exactly* does impedance mean? I did several searches on it and did not find a straightforward, plain-English answer. I originally thought it was related to the ease of driving - i.e. if the headphones have lower impedance they're easier to drive. But i've been looking at the SR60 (called low-impedance headphones) versus iM716 (hard to drive headphones), and the iM716 has a 16ohm impedance compared to a 32ohm impedance... what does it all mean???! I was wondering how impedance ties into amping, but first and foremost I'd like to find out what it is.
Yeah, I made a thread like this last week..You can search for it if you like..Great responses..
post #10 of 11
Impedance can vary throughout the freq spectrum for a driver. Most measurements are generally DC impedance, unless otherwise stated.

The only thing you really need to know is how that impedance will mate with your source (amp). For example, home Hi-Fi will generally interface better with a high impedance phone (say 300 Ohms), whereas a small portable source will require a low impedance phone (say 16 Ohms) for its tiny amp to drive.

If you plug your 300 Ohm cans into a DAP, it will not get very loud, and suck up your battery. If you plug your super efficient 16 Ohm portable phones into your home Hi-Fi you may hear hissing, or other such sounds. You can stop the hissing by adding resistance in-line, such as a volume control, or just straight resisters wired in-line, to increase the impedance.

Pretty plain Jane.
post #11 of 11
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