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Questions about Ohm

post #1 of 11
Thread Starter 

Hi All,


I hope I'm in the right place.

I've got a few questions about ohm, and since I'm not that big of an audiophile and never studied anyhting like engineering of some sort.

I've been trying to learn a bit more about ohm, and so my first question is, and this is more related to connecting a set of speakers to a receiver. Is it better to have (for example) speakers which are 8 ohm and a receiver which is 4 ohm than it is the other way around?

Because I've got a Fiio E11 with 32 ohm output and my Shure SE215 only need 20 ohm.


The second thing I heard was about an ohm cable which people use between their source and their listening equipment. Could it improve the quality of my sound if I put an ohm cable between my Fiio and my Shure?

My source is an iPod Classic 80GB 1G.



- Alexander

post #2 of 11

Originally Posted by Dutch-Guy View Post


Is it better to have (for example) speakers which are 8 ohm and a receiver which is 4 ohm than it is the other way around?


Yes, if the load (speaker) impedance is too high, the only potential problem is usually that it will not be loud enough without clipping. On the other hand, connecting low impedance speakers to an amplifier that is not designed to drive them, and listening at high volume may even damage the amplifier in some cases.

post #3 of 11
Thread Starter 



But would you say it's the same with my Fiio and Shure?

And do you know something about an Ohm cable?

post #4 of 11

The E11 doesn't have a 32 ohm output. It's output impedance is below 1 ohm (specified as < 0.3) which means you can drive even picky IEMs without changing their frequency response.


The spec output power (180 mW@32Ω) just tells us how much power the amp can output into a 32 ohm load, but the load can be pretty much anything ranging from <16 ohm IEMs to >600 ohm full-size headphones.



edit: With "ohm cable" I'm assuming you mean a cable or adapter with resistors in series. This will effectively increase the output impedance and reduce the volume of your in-ears. Since the impedance of your Shures is almost a flat line it won't change the frequency response.

Edited by xnor - 5/25/13 at 9:02am
post #5 of 11
Thread Starter 

Ah silly me, I see it now too, must have looked in the wrong place.

No there appears to be a cable with no resistors of any kind. And if I were to connect it to my AKG K450 which needs 32 Ohm, would that make a difference?

post #6 of 11

I think there's a confusion of terminology.


The headphones (well, each side) has its impedance, which is a function of its electromechanical design—mostly of the wiring of the voice coils.  The amp has an output impedance, which is a result of the electrical design.  It's kind of something of an electronic circuit analysis abstraction, a description of behavior.  For some or most headphones, it doesn't really matter, but usually the by-the-books suggestion is to make sure the amp output impedance is significantly less than (say no more than an eighth of) the headphone's impedance.


The AKG K450 doesn't "need" 32 ohms.  Its impedance is 32 ohms; it doesn't need anything in particular.  FiiO E11's output impedance is pretty low, something like 0.5 ohms.


I'm not sure what you're talking about when you refer to an "Ohm cable" if it's not what xnor described.  What's it do?  What's it look like?  Description?  Link?

post #7 of 11
Thread Starter 
post #8 of 11

The cables have impedance (unit of measure is ohms) themselves.


ER4P to ER4S adapter cable has resistors inside, which effectively filters and alters the frequency response the headphones themselves see if they have impedance that varies over the audio band. See earlier xnor response.


The coax cable for digital (high-speed, so high-frequency) transmission is referencing the characteristic impedance; 75 ohms is a typical standard value for that. Characteristic impedance describes the behavior more so for a relatively uniform transmission line, which is mostly considered when the effects deviate from lumped-sum models, which happens when line length or signal frequency is high (really, when line length is long enough relative to signal wavelength). This doesn't have to do with connecting headphones at all. The actual analog signals driving headphones don't have frequencies that high.


Which one do you mean, or do you mean something else entirely?

Edited by mikeaj - 5/27/13 at 6:26am
post #9 of 11
Originally Posted by mikeaj View Post

The AKG K450 doesn't "need" 32 ohms.  Its impedance is 32 ohms; it doesn't need anything in particular.
Doesn't it need to be paired with an amplifier that has less than 4 ohms output impedance?

I have a question: what is 30ft of extension going to do to impedance?
post #10 of 11
Originally Posted by StudioSound View Post

Doesn't it need to be paired with an amplifier that has less than 4 ohms output impedance?


Sure, I guess, if you want to follow some (arbitrary) one-eighth rule of thumb. Its impedance is pretty similar across the audio band, say 35 to 42 ohms, apparently. Some moderate amp output impedance wouldn't make much difference.


Originally Posted by StudioSound View Post

I have a question: what is 30ft of extension going to do to impedance?

It would reduce the signal the headphones get by a slight amount depending on the resistance there, which depends on the thickness of the wire used. Not by much. I'm bad at eyeballing stuff, but let's suppose it's 26 AWG. If it's 30 ft of 26 AWG (30 one way, 30 the other), then that'd be 2.45 ohms of resistance. Effectively the headphones see that as some additional amp output impedance.


If the amp is a bit unstable, the capacitance of that long extension could possibly make it misbehave a little—oscillate in the worst-case scenario.

post #11 of 11

The above answers are well thought out and true. But if you are still worrying about "ohm" cable  the only thing I can think of  is the midget US radios that were imported to the UK after the war and had to be used with a resistance "line cord" to drop the voltage to 110V . When it wore from use people used to cut off bits but that just  increased the voltage and eventually blew all the heaters in the radio--series connected. So you can get special high resistance cord but as said above your going to loose power[peak volume]  If you are thinking of tubes with an output transformer it works best into an impedance of the same value unlike SS which DEPENDING on the output circuit can INCREASE its out put into a lower loudspeaker impedance-eg-4/2 ohms BUT not all designs act like that some SS actually decrease into a lower impedance its down to design.    The old NAD 3020 I bought last week looks small and weedy -its not 20W into 8ohms BUT 40W into 4ohms and even more into 2 ohms. This is a test of a good SS amp. A lot fail this test.

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