what i the difference when a speaker is listed at 8 ohms vs. 6 ohms?
is one better than the other? does this number have an effect on preformance? i have seen both for sale and want to know if they will work together?
thanx,
Max
IIRC the lower the impedance, the more efficient the speaker can be. That is if everything else is equal it will take less wattage to produce a given sound level. That’s why companies like Bose, who make make very low impedance speakers (1 ohm and lower) refuses to use wattage in thier advertising. Wattage really dosen’t relate to sound pressure level because you can play games with the electronics and have (literally) a hot speaker with crappy sound level performance.
Also you need to know what your systems amplifier is geared for, most aftermaket systems are meant to be used with 4 or 8 ohm speakers. Lower impedance speakers will not work properly with them. Speaker impedance is only one part of the equation to a decent sound system.
For maximum transfer of power from the amplifier to the speaker the output impedance of the amplifier should equal the impedance of the speaker. Your amplifier should be labeled as to what the speaker impedance should be.
Speaker quality is affected to some extent also if the amplifier output impedance is wildly different from the speaker impedance. Speakers sound best when their input is connected to the correct impedance so as to provide proper damping to prevent such things as ringing after an impulse of sound and to allow the proper rise time in case of a sudden impulse, such as with a cymbal, or a stattaco trumpet.
On looking this over once again, I’m sure I meant “staccato trumpet.” I have no idea where “stattaco” came from. I’m not even sure it’s a word.
It means you’re in a hurry in a Mexican restaurant.
Modern solid-state amplifiers use negative feedback to try to make the output impedance as low as possible to increase the damping factor (the ratio of speaker impedance to amplifier output impedance) while still having unconditional stability for all likely loads and signals. Typical power amplifier output impedances are in the range of a fraction of an ohm, i.e. nowhere near equal to the speaker’s impedance, and lead to damping factors in the tens or even hundreds. Higher damping factors do indeed (up to a point) improve control of transient music signals such as cymbals.
Yeah. There is more to life than matched impedances and maximum transfer of power. In fact, the efficiency of power transfer, *i.e.*power in the load divided by total power in the source is high when the load impedance is much bigger than the generator output impedance. In the case of matched impedances the efficiency of transfer is 50%, half the total power in the load and half in the output impedance. It’s just that with a high load impedance you can’t develop as much power as in the matched case. In audio amplifiers that is immaterial because the capability is there to develop as much power as is needed in all cases.
Negative feedback does other good things besides reduce output impedance. It also greatly reduces distortion and stabilizes the amplification of the system. And that was true, and widely used, even back in the antediluvean age of vacuum tubes.
It means he’s dying for Mexican food.
Now cut that out.
(With apologies to Jack Benny)
Most home speakers are listed normally as 4, 6, or 8 ohm. However, lower or higher does not affect performance. I’ve seen Cerwin Vegas that were 4 and Infinitys that were 8 that were both great speakers.
While most receivers out there can handle a 6 or 8 ohm speaker you do need to be careful if you go with 4s. Most receivers that can’t handle a 4 will state directly on the back of the receiver “for 6 ohm or higher only”. If you hook up a 4 you will either blow a fuse in the receiver or send it into protection mode (shut down).
Don’t know if it still is true today but amps that could handle 4 ohm speakers used to be known as “high current” amps.
From my listening ears, lower impedance speakers do sound louder than higher at the same volume setting.
As pointed out by Antonius Block, this is incorrect.
Lets say I have a 12 V battery with an adjustable source impendence. And let’s say my load is fixed at 10 Ω.
If I want maximum power to be delivered to the load, what should the source impendence be set to? Should it be set to 10 Ω?
No. It should be set to 0 Ω.
You’re thinking of the opposite scenario, where the source impendence is fixed and the load resistance is adjustable. In this case, the load resistance should be adjusted to match the source impendence for maximum power transfer.
2 Ω. 
No. As others have mentioned, speaker impedance in-and-of-itself has nothing to do with sound quality or efficiency. But having said that, you do need to be careful when using low-impedance speakers, as they will draw more current from your amplifier vs. higher-impedance speakers. All amplifiers are specified to drive speakers at or above a certain load impedance.
When you find a source with 0 output impedance write it up or Proceedings of the IEEE. In all cases sources have output impedance and if you want maximum power possible you have to match it. In many practical cases the source can’t deliver that much power and blows a fuse.
I think a little more information on impedance matching for power is needed. And, as I said, matching for maximum load power isn’t the be-all and end-all of electronics for audio use, loading the speaker properly for best sound is much more important. And as Antonius Block pointed out, speaker impedance varies all over the place and you can’t really match for max power out except maybe at some particular frequency. In addition by its very nature, the negative feedback used in all high quality audio amplifiers results in such a low output impedance that you probably couldn’t match it anyway, even at one frequency.
That being said let’s look at the world of impedance matching and power output.
Alpha, the ratio of load resistance to source resistance varies from 0.1 to 10. At the 0.1 end the total power curve shows that there is lots of power being generated by not much of it is delivered to the load. Over at the alpha = 10 end almost all of the power is delivered to the load but there isn’t much power being generated. In the middle where alpha = 1 the source and load resistances are equal and 1/2 the total power is delivered to the load and this is the most you can get.
Audio power amplifiers operate over at the right end of the chart with less than maximum power being generated but with almost all of it going to the load.
A couple points:
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Regulated voltage sources, even the jellybean variety of 78XX voltage regulators, have (essentially) 0 Ω of source impedance within a given operating range. In other words, below a certain output current, and below a certain slew rate, a regulated voltage source has (essentially) 0 Ω of source impedance.
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Maximum power is transferred to a load when the load impedance equals the source impedance. But there are exceptions to this rule, namely:
a. If it’s a regulated voltage source, which means the source impedance is (essentially) 0 Ω within a given operating range, a 0 Ω load (e.g. a superconductor) will not give you maximum power transfer. This is for two reasons: i) a 0 Ω load cannot dissipate any power (P = I[sup]2[/sup]R = I[sup]2[/sup] 0 = 0), and ii) The current spike will cause the power supply to operate outside of its operating range, and the source impedance will no longer be 0 Ω.
b. The source impedance may not be constant with current; for many sources, as the current goes up the source impedance also goes up due to self-heating and a PTC. If this occurs, maximum power to the load is achieved when the load impedance is somewhat higher than the source impedance.
Whilst I appreciate the point you’re trying to make, the reasoning here is a bit faulty. You’ve stipulated a regulated source with a zero source impedance. The correct way to analyse the power dissipated in the load is to note that V is constant for the regulated source. Power in the load is V[sup]2[/sup]/R, and as R approaches zero, P approaches infinity. At the point where R actually is zero, the equations take on undefined values. It’s not correct to assert that P = 0 in this instance. P is undefined.
Yes, it’s undefined of course. But I think you understand what I was driving at…
Amplifiers are limited by thier power supply as to how much power they can deliver to a given load impedance. If you reduce the load impedance, you can use a lower power supply voltage for a given power level. This is why automotive speakers evolved to a lower nominal impedance (4 ohms) vs. home audio (8 ohms).
In the old days it was very difficult to raise the nominal 13.8 V. car electrical system to any higher voltage. So with an 8 ohm speaker you could only make ~ 8 W/channel (bridg tied load) but with 4 ohm speakers you could double that to ~16.
This improvement comes at the cost of doubling the current drawn from the amplifier output. For automotive use this was a good trade-off.
If your amplifier can handle the lower impedance, then you can get more power out of the same amplifier by using lower imepedance speakers.
As mentioned above, though, the damping is reduced, so in a grid-tied setting where it is simple to raise the supply voltage, 8 ohms speakers are still the norm.
Regulated power supplies are one thing. Audio amplifiers are another. And in order to have 0 output impedance the power supply would have to have perfect regulation. That means a position regulating servo system of type1 which can produce an output with no position error. In this case “position” is output voltage. Any ordinary regulating supply will be a servo of of type 0 which requires some small error in order to produce an output. In that case there will be a slight decrease in output with increasing load. That decrease will depend on the gain of the servo and will represent a small output impedance.
You make a theoretical quibble. You say a 0 ohm load can’t dissipate any power. You overlook the fact that for 0 impedance the current is infinite (if you can deal in impracticalities so can I) and their product is undefined. Neither of us can say anything meaningful about the answer.
And in addition. Even playing the hypothetical game of ideals, even with 0 output impedance you are still not getting maximum power out of the source with any load higher than zero. You are operating way over on the right hand end of the curve where the majority of the power (all of it in the ideal case) is going to the load but that is still not the maximum theoretical power available.