Axiom Home Page Forums General Discussion Advice from Axiom Owners Difference between impedence specs

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?

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.

Resistance is actually futile.

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

Women proved me wrong when I told them that.

You've both talked with women?

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.

You may have noticed that the treadjacking impedance of this forum is very low. As Mark wrote, resistance is futile.

I'm blaming it on brain parasites.

I always blame Mark. No point starting a new trend.

Maybe Mark has a brain parasite?

Maybe Mark is a brain parasite.

I'm blaming it on cat feces.

Maybe Mark is cat feces?


Oh.

Wait.

The cat feces made a very funny post there!

Is that why your head is so big and shaped like a football?

That is to counter the standing waves in his room.

That's to increase apparent stereo separation. To me, everything sounds like a Hendrix recording.

But when you play Hendrix, the flux capacitor reverses and it sounds like Lawrence Welk.

Punisher, if your looking at speakers that are 2 ohm's you will need a serious amp to power them. The way that amplifier companies make the amp stable to a lower impedance is by adding transistors, the more transistors the more power and the lower the impedance the amp will be stable to.

Depending on the speaker manufacture, some label the normal impedance, others will give you the normal, and minimum at the frequency that the minimum occurs at.

Any average receiver will have a onboard amp powerful enough to power a 6 or 8 ohm speaker. Some receivers can power a 4 ohm load, Denons are popular.. for a 2 ohm speaker, most receivers will not have an amp powerful enough to power those, you will need to find a dedicated amp that is stabile to 2 ohms. Plan on spending some cash for one.

Maybe I should have Mark talk to the women for me.

Thanks for the responses. Not quite clear about the explanations. I should probably explain the issue I'm having - I have a pair of Senheisser HD650 cans that are rated at 300ohms. I have Logitech Z5450 speaker which I sometimes listen to through my headphones.

The problem is I have the volume turned all the way up and it's not loud enough (sound is about average volume but not loud enough for me) through the headphones. Its probably because the Z5450 has a crappy amp for the headphone jack (even my iPhone is louder at higher volumes).

So presumbly I need a headphone amp to boost the volumes. And I'm trying to figure the proper impedence I would need on the amp. The nominal impedence on the z5450 is in the 1000s. But this won't drive those headphones.

So going back to my original question I am confused about how impedence is measured? Speakers in general are rated in single digit ohms. My headphones are rated at 300ohms. My speakers nominal impedence is rated in 1000s. Why is the metric so vastly different for different devices?

Yeah, sometimes it helps to actually ask what you want to know.

Here's something from a website:


So basically the amp can't drive the higher impedance of the semi-pro phones to the volume level you want. You need to get an amp designed to drive higher impedance levels.

I am not sure why you are looking at the input impedance on your Z5450 when you are looking to drive(output) to your headphones, 2 different things.

I will guess the Z5450 headphone jack is a very low line level voltage(0-3V) out for headphones and not passed through it's amp at all. So yes, you could use a headphone amp.