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Difference between impedence specs
#298249 03/24/10 05:26 PM
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I've seen impedance on speaker specs rated at 8,6,4,2 ohms and high end headphones like the HD650 that have an impedance 300 ohms. Then on amps that have input impedance at 9500 ohms.

What is the difference between these different impedance specs and what do they mean in layman terms?

Re: Difference between impedence specs
punisher101 #298254 03/24/10 05:55 PM
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Impedance is the resistance* to the flow of current. High power amplifiers are rated to be stable into some impedance. If have nothing connected to the output of an amp, that air between the terminals presents nearly infinite impedance. On the other hand a piece of wire running between the terminals would be next to 0 impedance.

An amp doesn't like to have it's terminals shorted, but the reason may not be immediately obvious. What actually happens when you connect a current source to ground is the flow rate gets so high the electronic parts making up the device can't handle that much, so they overheat and fail.

So amps are rated for the minimum impedance which they can support. At the other end, a higher impedance doesn't really hurt anything, it just decreases the over-all efficiency of the speaker, thus requiring more power to play at the same volume level as another similar speaker of lower impedance.

I don't follow headphone specs too much, but the same applies there, just the amps are designed to run into higher impedance drivers while still presenting high enough listening levels.

As for the input impedance of a device. With some equipment, the output when connecting to another device must have a "matched impedance". This doesn't apply for the output of an amp driving a speaker, where the output is in the kΩ range (although it may have some effect on the dampening factor). But when connecting the output of a pre-amp to a power-amp, those two should be matched. Without getting too technical, it's basically like they have to be speaking the same language to communicate effectively. It isn't something really to worry about in consumer gear as everything with RCA jacks will work together.

*Resistance is actually the measurement of voltage loss through a circuit.


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Re: Difference between impedence specs
ClubNeon #298266 03/24/10 06:35 PM
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 Originally Posted By: ClubNeon
*Resistance is actually the measurement of voltage loss through a circuit.

Resistance is actually futile.


::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::
Re: Difference between impedence specs
MarkSJohnson #298267 03/24/10 06:38 PM
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 Originally Posted By: MarkSJohnson
Resistance is actually futile.


Women really don't like it when I tell them that.

Re: Difference between impedence specs
CV #298269 03/24/10 06:45 PM
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Women proved me wrong when I told them that.


Bears, beets, Battlestar Galactica.
Re: Difference between impedence specs
medic8r #298281 03/24/10 07:23 PM
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You've both talked with women?


::::::: No disrespect to Axiom, but my favorite woofer is my yellow lab :::::::
Re: Difference between impedence specs
MarkSJohnson #298287 03/24/10 07:53 PM
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It is also worth noting that speakers are rated at a 'nominal' impedance: an average of sorts. The actual impedance of a speaker varies with the frequency being produced.

Practically it doesn't mean much except when you have speakers with a low impedance. Very cheap receivers, or those with an overly active protective circuit will shut down with low impedance loads.

Not all receivers play nice with the M80. Thing is, there are enough receivers out there that do, that it is not much of an issue.


Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!
Re: Difference between impedence specs
fredk #298288 03/24/10 07:56 PM
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You may have noticed that the treadjacking impedance of this forum is very low. As Mark wrote, resistance is futile.


Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!
Re: Difference between impedence specs
fredk #298289 03/24/10 07:57 PM
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I'm blaming it on brain parasites.


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Re: Difference between impedence specs
ClubNeon #298291 03/24/10 08:09 PM
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I always blame Mark. No point starting a new trend.


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