
What's worse: 4 or 12 ohms
Whats worse or harder on a receiver/amp that's rated solely for 8 ohms out to the speakers: 4 or 12 ohms speakers?

Re: What's worse: 4 or 12 ohms
all things consider if it is a solid state amp 4 ohms is worse. My tube amp knowledge is lacking to give a decent answer.

Re: What's worse: 4 or 12 ohms
High impedance you're limited by voltage, low impedance you're limited by current.
As stated above, the current limit will stress the amp more, thermally as well. 12 Ohm speakers will not stress the amp at all, but it will clip at a lower power level.

Re: What's worse: 4 or 12 ohms
ya.. I should of stated SS.
Opening up a can or worms here for discussion.
WHAT exactly is happening, say, for the 12 ohms speakers on a 8 ohm rated SS amp/receiver? I could never logically figure it out I always would of thought 4 ohms had less resistance and should not stress the amp more... but it's the other way around.

Re: What's worse: 4 or 12 ohms
Yes less resistance = more conductance = more current.
Think of it this way...if you had just a wire, it would be called a short circuit, and would be near 0 ohms.
I explained above what is happening. The very basic way to look at it is with Ohm's law. Your amp has voltage rails, it will not output a voltage above this limit. It's rated thermally and by the capability of the output devices of the amp. Amps have protection circuits to limit this current so the output devices do not burn.

Re: What's worse: 4 or 12 ohms
Since the amp's voltage limits come into play when the speakers impedances are higher than the amp is rated for, the only "problem" will be the amp won't be able to drive the speakers as loudly. In this case with 12ohm speakers, the amp will be putting out about 67% of its rated power.
Paul
Originally Posted by HuskerNation
ya.. I should of stated SS.
Opening up a can or worms here for discussion.
WHAT exactly is happening, say, for the 12 ohms speakers on a 8 ohm rated SS amp/receiver? I could never logically figure it out I always would of thought 4 ohms had less resistance and should not stress the amp more... but it's the other way around.

Re: What's worse: 4 or 12 ohms
If you need a good way to power a 12 ohm load, you could use a stereo amp that allows bridging. When running in bridged mono, a 12 ohm load is equivalent to running two channels at 6 ohms each.

Re: What's worse: 4 or 12 ohms
Originally Posted by HuskerNation
Whats worse or harder on a receiver/amp that's rated solely for 8 ohms out to the speakers: 4 or 12 ohms speakers?
Another way to look at it is that, current is what makes the voice coil and the cone of the speaker move. So to get a certain cone deflection (loudness) will take (approximately) the same amount of current from the Amp for both the 4 and 12 ohm speakers.
However, the voltage drop across the 4 ohm speaker will be 1/3 the drop across the 12 ohm speaker when drawing the same amount of current. For the 4 ohm speaker, the extra 2/3 voltage drop will get dropped across the Amp, increasing its power dissipation and causing it to run hotter.
Louis

Re: What's worse: 4 or 12 ohms
Originally Posted by philiparcario
all things consider if it is a solid state amp 4 ohms is worse. My tube amp knowledge is lacking to give a decent answer.
There are no universal rules for tube amps either. Read the manufacturers recommendations, specifications.
Some (tube amp) output transformers have taps for 4, 8, 16 and even 32 ohms!

Re: What's worse: 4 or 12 ohms
Originally Posted by Æ
There are no universal rules for tube amps either. Read the manufacturers recommendations, specifications.
Some (tube amp) output transformers have taps for 4, 8, 16 and even 32 ohms!
yeah the taps for higher impedance are what through me off.
my question would be if my tube amp has 3 taps 4, 8, 16 ohms and a put a 12 ohm speaker on the 8 ohm tap what happens?
since the truth is I don't have much experience with tubes amps I left them out in my answer.

Re: What's worse: 4 or 12 ohms
Originally Posted by HuskerNation
Whats worse or harder on a receiver/amp that's rated solely for 8 ohms out to the speakers: 4 or 12 ohms speakers?
If you're trying to tweak out the last few dB out of your amp for the best possible spl, 4 ohms will be better as long as your amp will handle the load.
If you want better controlled bass and better dynamics, your damping factor and rail stiffness will be better with 12 ohms.
With most of todays mid level multichannel receivers ($1000 or less), I would prefer and recommend 12 ohms.
Phil

Re: What's worse: 4 or 12 ohms
Originally Posted by philiparcario
yeah the taps for higher impedance are what throw me off.
my question would be if my tube amp has 3 taps 4, 8, 16 ohms and a put a 12 ohm speaker on the 8 ohm tap what happens?
since the truth is I don't have much experience with tubes amps I left them out in my answer.
It kind of depends. . . .
But there is an impedance mismatch.
I would imagine that if you use a lower impedance output tap than the impedance of the loudspeaker the onset of distortion would be sooner and if you selected a higher output impedance tap the power available/delivered would be lessened.
I'm fairly sure that using the higher impedance tap would be the safer approach. I'd try it both ways just for the sake of it to determine if there were any audible differences and go with the one that avoided audible clipping/compression.
Last edited by Æ; 02122010 at 04:56 PM.

Re: What's worse: 4 or 12 ohms
Originally Posted by HuskerNation
I always would of thought 4 ohms had less resistance and should not stress the amp more... but it's the other way around.
In a certain sence that can be true. But it is what causes the problem.
The lighter load(4ohms) allows more current to pass through the amp easier. Power in this case is measured in watts. The voltage remains the same but the current increases, thus the wattage(heat) in the amp increases. Many of the amps internal components are rated at 1/2 to 1 watt. With the increase in current the wattage increases past the rated components ability to disapate heat and they burn.
The higher load(12ohms) decreases the amount of current the given voltage can push through the circut. The same voltage and less current through the amp produces fewer watts in the components in the amp. Thus, they do not burn.
I better stress this is a BASIC explaination. I'm sure someone will correct terms or add to it as the trend is to be technical.

Re: What's worse: 4 or 12 ohms
Originally Posted by Æ
There are no universal rules for tube amps either. Read the manufacturers recommendations, specifications.
Some (tube amp) output transformers have taps for 4, 8, 16 and even 32 ohms!
Man, I realize this believe me! Not concerned about tube amps in this instance. Just about SS which I really have never technically educated myself about.
One of my grand dad's classic tube amps I have now has the taps for 32 ohm LOL.

Re: What's worse: 4 or 12 ohms
Originally Posted by Ludo
Another way to look at it is that, current is what makes the voice coil and the cone of the speaker move. So to get a certain cone deflection (loudness) will take (approximately) the same amount of current from the Amp for both the 4 and 12 ohm speakers.
This is not correct. The voice coil is driven by magnetic field, which is in turn determined by ampereturns. The high impedance voice coil will have more turns, and draw less current for the same field strength.
Solid state amplifiers have higher distortion at high current because output stage gain falls as emitter current increases. That reduces negative feedback (output stages typically have an overall voltage gain of 1 . . . all the stage gain is used for distortion reducing feedback). Douglass Self discusses this in some detail in "Audio Power Amplifier Design Handbook", but any amplifier design book will tell you the same thing. In addition, the power supply may not be able to deliver the higher current demanded by a low impedance load, placing yet another limit on the amplifier output.
The flip side is that with the higher impedance load the amplifier will become voltage limited (clip) sooner, also reducing maximum power output. But you will probably experience less distortion as you approach the voltage limit than you will approaching current limiting, and the higher impedance speaker will be "easier on the amplifier". That doesn't necessarily mean that the *system* will sound any better, though . . . there are too many other variables to make a blanket statement.

Re: What's worse: 4 or 12 ohms
Originally Posted by Deward Hastings
This is not correct. The voice coil is driven by magnetic field, which is in turn determined by ampereturns. The high impedance voice coil will have more turns, and draw less current for the same field strength.
Yes of course, magnetic field strength is a function of ampere turns, but there is nothing preventing the use of larger guage wire for the 4 ohm coil to get the same number of turns as the 12 ohm coil. There will be other effects that will create differences between the two, but as I said this is an approximation.
Louis

Re: What's worse: 4 or 12 ohms
Originally Posted by Ludo
there is nothing preventing the use of larger guage wire for the 4 ohm coil to get the same number of turns as the 12 ohm coil.
There are a number of practical reasons for not doing that, and it is not in fact what *is* done. Low impedance voice coils have fewer turns, and draw more current for the same field strength.

Re: What's worse: 4 or 12 ohms

Re: What's worse: 4 or 12 ohms
Originally Posted by Deward Hastings
There are a number of practical reasons for not doing that, and it is not in fact what *is* done. Low impedance voice coils have fewer turns, and draw more current for the same field strength.
There's also the case where drivers are connected in parallel.
Take a single 12 ohm driver drawing an rms current of 1A from a class A/B amp with +/60V rails. The power dissipated in the amp due to the 12 ohm load will be 48W.
Now parallel 3 of the same drivers to get a 4 ohm impedance and the voltage sensitivity will increase by 9dB while the current sensitivity will stay the same; so 1A will produce the same loudness. In this case the power dissipated in the amp due to the 4 ohm load will be 56W.
I'm not saying its a universal rule, but in general a lower impedance speaker will make an amp work harder to generate the same loudness.
Louis

Re: What's worse: 4 or 12 ohms
Originally Posted by Æ
4 ohms is worse.
LOL now that's a direct simple answer (and what I thought).
Nice discussion fellas...
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