2. amps-preamps
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Amplifier stability with very low impedance, high efficiency mid/tweeter section???

I've been looking for this information everywhere but can't seem to find a clear cut answer.  I understand that a very low minimum impedance like 2Ohms is a very difficult task for most amplifiers to drive and may even damage it.  But it's also my understanding that this is a current, not a voltage problem.  In other words, say we had an MTM speaker that was used ONLY as a midrange from 200hz up, so it wouldn't have to play bass where most current is required.  And say it also has a very high efficiency of 97db but also a very low impedance of 2 ohms.  Would this be a problem for most amps?  Could it damage the speakers? I'm thinking no since the amplifier wouldn't have to put out much voltage or current to output sufficient SPL.  But what's the actual answer????

poseidon1500
millercarbon's avatar
millercarbon
12,531 posts
 

I am old school. If your amplifier cares about the speaker I say look, you're an amplifier, this is your job, tough luck. If you want it easy go back to school, learn how to be a AVR, nobody cares as long as you have a lot of knobs and switches and stuff. But for now, get on with it.

I did lose one to Amplifier Protective Services but that was before I learned to not let them have a cell phone. Take my advice, make an example out of one, word gets around fast, you won't evert have any amplifiers whining about how hard you work them. Trust me. Haven't heard one word of complaint in 20 years at least now.

erik_squires
16,186 posts
 

To understand this better you need to understand what happens when you have an ideal voltage followed by two impedances.  One of the amp, one of the speaker.

 

V ---> Z(output) --> Z(speaker)  or for simplicity in a DC world:

V--> Ro --> Rs

You need to understand a little about how the varying Z (or R) will affect the voltage at the speaker.

You also need to understand that Zo/Ro is almost never flat, so the amplifier's output impedance is also changing.  The inability of an amplifier to double it's output as impedance is halved is related to this.

So a 100W amp that can't double all the way down to 2 Ohms will also probably not be able to double at 1 Watt output.

poseidon1500 OP
15 posts
 

Lol MillerCarbon.  

Erik, I've looked at a bunch of other stereophile measurements of amps.  They all fluctuate in impedance but but it's not by very much, at least most of them.  I guess you would need an amplifier with an output impedance of less the .2 ohms across the spectrum and a beefy power supply/enough output deviced to drive a 2 ohm load safely.  

russ69's avatar
russ69
3,520 posts
 

...low impedance of 2 ohms.  Would this be a problem for most amps? 

It can be a problem. My rule is that if the loudspeaker gets into the 2 ohm range I would want to match that with a very robust amp that boasts about its low impedance performance.  

erik_squires
16,186 posts
 

Erik, I've looked at a bunch of other stereophile measurements of amps.  They all fluctuate in impedance but but it's not by very much, at least most of them. 

 

Yeah, but that's wiht a simulated 4 Ohm speaker. :) Lower speaker impedance = more fluctuation.  I'm not saying it will be unbearable. Just explaining how a more robust amp with a lower output impedance would behave.

In some cases the interaction could be euphonic.

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