What happens to an amp below 2 ohms?

It depends on the amp. What is the particular amp you have been reading about?

The lower the impedance, the more current the speaker tries to draw from the amp.

With transistor amps, this will certainly result in more heat as the current has to come through the output transistors, even if the amp is class D. Some SS amps have enough current rating in their output sections to support this and others do not.

Tube amps will not produce any more current at all- usually they will put out less power as a result, although with a set of ZEROs http://www.zeroimpedance.com installed, they may be just fine.

Now for the *effects* of a low impedance like that (IOW: the bad news). No matter what kind of amplifier you have, if sound quality is your goal, it will be at a disadvantage driving a load like this, even if the amp has the current to do it. OTOH if *sound pressure* is valued over sound quality, then this *might* be OK, but if that is the case you are often better off seeking a speaker that is higher efficiency that might be a little easier on the amp.

The reason SS amps don't sound their best into lower impedances has to do with internal capacitances that exist in the junctions of the output devices. In most cases, this capacitive element is non-linear. It is magnified by increasing the current through the device- precisely what happens when you use a lower impedance load. This results in greater odd-ordered harmonic distortion, making the amp sound harsher and less transparent.

If you prefer a smoother, more transparent sound then you will find this a good argument to seek a speaker that has a higher impedance.

Another way to look at it is to search for the few, underline few, amps that can comfortably and reliably,heavily underline reliably, drive the Apogee Scintilla which goes down to 1 ohm. Looking at those amps will tell you what is necessary for an amp to handle such a load.

Very few amps will handle such a load but I know of only 2 speakers myself that go below one ohm: the aforementioned Scintilla and the Quad 57. The latter does this in the top end so is not nearly as difficult a load to drive as the Apogee. In a perfect world the impedence curve would stay above 6 ohms but in our world some very good speakers have difficult curves. My Gamut L5s go down to 3.2 or so and my friends Sasha to below 3. The amount of work my CJ 350 has to do driving the Gamuts is considerable, gets quite hot driving them to a good volume in a long session. On the other hand it gets barely warm driving my Spendor S 100s to a similar volume. A good reason why you should always buy the speaker first; then you know what your amp requirements will be.

The Krell KSA and MDA are noted for playing the Apogee line of speakers with aplomb. In fact Krell put themselves on the map by building amps that could do this and were the amps of choice for Apogee to demo with. I'm not sure if some of the latter Krells could still do this but I'd be surprised if they couldn't.

The benefits that some speakers that have low impedance's provide, outweigh the disadvantages of that low impedance. Buy the speakers you like best, then buy an appropriate amp.

They blow up and make a mess!

Buy amp and speakers as a unit...and than after a nice test listen. If you are really after a 2 ohm stable amp, and they are few/farbetween, leave out ALL the 'd' amps with ICE modules. The data sheet says the limit is 2.7 ohms. I'd be inclined to listen to 'em.

I'm not even gonna touch the 'need' for a 2 ohm speaker. What I will say, is that if it were pure resistive, you'd have better luck. Since it isn't, you have to deal with reactance. bad juju. You may get lucky and it won't be too awful, but in more extreme cases of large phse angles (highly capactivie or inductive) you're gonna suck up amp power like you own stock in the power company.

Hi sensitivity would also help, but only so much. Less phase shift would buy you more than a sheerly high sensitivity number. especially if you knew such phase shift peaked at or near the impedance minima.

In general, however, there's no need for such a wacky load.

They heat up and may blow up.Not mine i have ROWLAND 8T a great amp.

For some speakers there is no appropriate amp. As Ralph mentioned previously regarding the effects of low impedance speakers.
"No matter what kind of amplifier you have, if sound quality is your goal, it will be at a disadvantage driving a load like this, even if the amp has the current to do it."
Isn't sound quality everyone's goal?

Isn't sound quality everyone's goal?

Surprisingly, no. Many audiophile revel in that fact that they can weld with their amp, or drive loads like that, even though there is no sonic benefit whatsoever in doing so.

Depends on the amp and how it was designed. When designing amplifiers, one design criteria is the load that it must be able to drive in a stable manner. This is one of many extensive equations that help determine the values of components in the circuitry. it is not magic. It is designed by calculations and one can determine how stable the amp would be for particular loads. This is basic Electrical Engineering. However, there are compromises for each piece of equipment. First is price point. If price is no object, a competent Engineer can design an amp to drive basically any load and not oscillate or fail. This is why you all see different amps from the same manufacturer. price point design. Good, respectable manufacturers stated specifications are true and accurate. Other's specs are not quite true. But to answer your question, it totally depends on the amp, the design characteristics, such as input impedance, gain, load driving capability, transfer function, phase, stability, heat, power output, voltage, etc. All of these result in equations for the circuit that determine the values of the resistors, capacitors, etc. within the amp. compromise any of these and the characteristics of the amp are changed. If your speakers have load characteristics that drop to 2 ohms or so over frequency, then you must purchase an amp that is stable within that power band at that load. Typically, you are talking about a seriously designed and built amp. This is where you really do get what you pay for.

One reason why some powerful amps have lots of pre-drivers and output drivers sharing the burden.

If you can get your hands on the stability charts of the amp over frequency, load and power range, you will see for yourself how stable the amp is.

enjoy

No matter what kind of amplifier you have, if sound quality is your goal, it will be at a disadvantage driving a load like this, even if the amp has the current to do it....

Ralph, I generally agree with your posts most of the time but I'm afraid that I have objections to this statement of yours.
Are you saying that people who have electrostatic or ribbon or planar speakers where the load impedance dips below 2 Ohms are not enjoying quality sound & that they are merely reveling in high SPL music environments in their respective homes?????
If yes, you know that that would be a load of BS on your part!

I've been reading some amplifier specs.

Ay-ya! That's the problem Mitch4t! you're wasting time reading amp specs rather than listening to music! ;-)

What happens if the speaker dips to 1 ohm or below?

the answer is: depends on the amp design as Minorl (& maybe some others) wrote.
The power amp is made to a certain price point so it has a certain power supply design that can support X amperes of output current. The manuf generally ensures that the output transistors do not leave the SOA (Safe Area of Operation) otherwise you are SOL! So, in such a case, when the load impedance dips below 2 Ohms, the power amp will run out of load current to supply the speaker to generate the SPL that set by your volume control. This means that the peaks of the music signal waveform will clip. This clipping is distortion (usually odd order harmonics) hence the amp will begin to sound harsh/brittle/piercing such that your mind will want you to turn down the volume. This clipping is not likely to damage your speaker 'cuz the amp is outputting a fixed amplitude at a certain non-zero frequency for (almost 100% of the time) a short duration of time. Short duration 'cuz it's the music signal & not some DC voltage. However, operating a semiconductor device at its extreme limit of safe operation is not good for the device; it can do some irreversible damage. Maybe not during the 1st or 2nd time but certainly as the number of such incidents recur because the clipping is fatiguing the device & it will finally give in.

In another case, if you attach an anemic power amp to a load that dips below 2 Ohms (an anemic amp would be an amp that, altho' specified to 2 Ohms, does not have a robust power supply i.e. high wattage output but ability to supply very little load current. Take an example: 500VA transformer with dual/two secondary voltages of 65VAC. Such a transformer can supply a grand total of 7.7A. Since there are 2 secondaries, each secondary can have 3.85A. If you calc the wattage of this amplifier you get 528W/ch into 8 Ohms. And, you look at this & go "wow! nice powerful amp!" Not! if you dig deeper - ~4A into a load that can dip below 2 Ohms is not a whole lot). Since this is not a high current amp, the heat sinks are likely to be puny. If you attach this to a load that dips below 2 Ohms & you start asking the amp to source current into this load, the output transistors will get very hot (as they'll be operating close to the upper limit of their SOA) & since the heat sinks cannot handle/dissipate the heat generated quickly, the output devices will likely explode/pop/destroy themselves & create a mess like Hifimaniac wrote.

Still another thing that could happen is that when the power amp is operating at its upper limit, the parasitic capacitances in the output devices could interact with the parasitic capacitances of the speaker cables + the speaker x-over & present an excessive capacitative load to the amplifier & the amplifier could go unstable & oscillate. This will manifest itself as harsh/brittle sound. Amps that are attached to electrostatic speakers often suffer this fate 'cuz the electrostatic speaker looks like a large/massive capacitor to the amplifier that it/amp might not have been designed to handle. Hence you find the likes of Innersound & Sanders Sound Systems offer their own power amps that match their speakers.

I'm sure that there are other ill-effects but these come to mind immediately. FWIW.

Are you saying that people who have electrostatic or ribbon or planar speakers where the load impedance dips below 2 Ohms are not enjoying quality sound & that they are merely reveling in high SPL music environments in their respective homes?????

No, what I am saying is that if those 'electrostatic or ribbon or planar speakers' were higher impedance the owners would be enjoying even better quality sound.

We can look at this from a very basic point of view. If a speaker has a reputation of being 'difficult to drive' due to low impedance, the reason that phrase is used has to do with the fact that the amplifier has a difficult task. Don't think for a minute that there is no price paid for that! The amp simply will not sound as good.

In addition, speaker cables get **critical!** when you are driving lower impedances. With higher impedances the cables are far less critical and can be run longer distances.

10-13-11: Atmasphere

No, what I am saying is that if those 'electrostatic or ribbon or planar speakers' were higher impedance the owners would be enjoying even better quality sound......

In addition, speaker cables get **critical!** when you are driving lower impedances. With higher impedances the cables are far less critical and can be run longer distances.

ah, I see! Thanks for the clarification.

If a speaker has a reputation of being 'difficult to drive' due to low impedance, the reason that phrase is used has to do with the fact that the amplifier has a difficult task.

Ralph, I did not understand this comment - amplifier has a difficult task & the use of phase. Please elaborate. thanks.

Ralph I am a soundlab m2 owner and have been wondering if using Ma1's with zeros would yield the same speaker performance as using the Ma2;my opinion would be the ma2's would control the panels better than the ma1's and result in a better sound;would you agree with that analysis?

my opinion would be the ma2's would control the panels better than the ma1's and result in a better sound;would you agree with that analysis?

correction! this is not an analysis - it's your opinion (as you correctly write at the begin of this sentence)....

Rleff, its a matter of power- in some rooms you have enough power with MA-1s on the big Sound Labs and in some rooms you simply need more. But you would not need ZEROs in any event.

Bombaywalla, the word was 'phrase', not 'phase'...

Phase is simply put, Power Factor. Another measure of reactance.
The larger the phase angle, the less power delivered to the load. A 1000 watt amp trying to drive a load which has a 90` phase angle will deliver exactly ZERO power at that frequency. cosine 90=0
A speaker which is a difficult load would, IMO, have large phase angles at the same frequencies where impedance dips occur. A double whammy.
My panels? Not a bad load, at all. low impedance, to be sure, but no wacky phase angles to suck up amp power.

Thanks Ralph;great review on the Ma2's !!!