What does Current mean in a power amp???

If your speakers impedance is rated (nominally) 4 ohms or less, or if certain frequencies dip much below 4 ohms, you will need a power amp that is rated into 4 ohm loads. The lower the impedance, the more current being drawn from the amplifier. Amps put out volts, the load draws current. I'm being very general here for the sake of brevity because there are many factors to consider, such as room size, how loud you listen, etc. There are other things to know about your speakers, such as minimum impedance dip, phase angle,
electrical sensitivity (sometimes referred to as efficiency) and such. Ask the speaker manufaturer.

Rwd,
What kind of speakers are you intending to drive?

"High Current" is a relative term. For a load with a given, fixed impedance, a higher powered amp will always deliver higher current INTO THAT LOAD. In other words, for a fixed 8 ohm load, a 200W amp will supply more current than a 100W amp. Therefor, based solely on current requirements, it could appear that using an amp with a higher rated power output would be the answer.

However, the rated power of an amp into an 8 ohm load is not really a good indication of the MAXIMUM current delivery capability of that amp. Most speakers do not have a constant impedance over the entire audio frequency range, and many have less than 8 ohms nominal impedance. As described in the post above, using ohm's law, into an 8 ohm load, a 100 watt amp would deliver 3.54 amps of current (assuming a 0 degree phase angle between the voltage and current waveforms, for you hardcore engineers :). If instead of an 8 ohm speaker, we were driving a 4 ohm speaker, then to deliver the same 100 watts, the amplifier would have to output 5.00 amps of current. If the impedance dropped to one ohm, to provide 100 watts of power to the load, the current delivered would have to be 10 amps, almost 3 times the current at the 8 ohm rated power output. The ability of an amp to deliver higher current into low impedance loads is influenced primarily by the design of the power supply, and the type and number of output devices. The ability to dissipate larger amounts of heat also becomes an issue as current delivery increases.

If you have difficult to drive speakers, such as Martin Logans, where the impedance drops as low as one ohm at 20kHz, it is important to have an amplifier that is designed to drive low impedance loads.

Therefor, it is probably more helpful for you to consider an amplifiers performance into low impedance loads, rather than zero in on the term "high current". As described above, it is possible to have an amplifier with a large power rating into 8 ohms that will have "high current" at 8 ohms, but may not be suitable for driving low impedance speakers. It is also possible to have an amp with a modest power rating into 8 ohms, and thus a modest current delivery at 8 ohms, that is capable of delivering much higher current, or even much higher power, into lower impedance loads.

In general terms, if you have speakers with an unusual characteristic impedance plot, you probably want to look for an amp with the ability to drive a 2 ohm load continuously. If a manufacturer won't put into writing that their design is capable of driving a 2 ohm load, then it probably isn't.

That said, if your speakers sound good to you with the amp that you are using today, and the amp does not appear to be running abnormally hot, don't mess with a good thing.

A minor clarification to my earlier response:

Ohm's law does not provide for a definition of power in an electrical circuit, rather it defines a relationship between the DC voltage, DC current, and DC resistance. When I stated "using ohm's law", I omitted that I was applying ohm's law, along with the basic power equation, to obtain the relationship of P=I^2*R, where P=power, I=current, and R=resistance.

Sorry for any confusion that may have caused,
Mike

Current is the rate at which charge passes a given point in a wire. If you were somehow able to count the charges as they went by in a wire carrying 1 ampere (1 A) of current, you would discover that every second an entire Coulomb of charge passes by.

Additionally, the "formula" provided in the first post is for a DC current. Since loudspeakers are designed to use AC current that formula will be of little use.

High current amps are typically big and heavy with large heat sinks. There are many but think Krell and Levinson.

Talk to a dealer that sells your particular speakers. He can best guide you in finding a good, quality high current amp that will satisfy your aural needs

Ohm's law has nothing to do with whether or not an amplifier can drive a speaker. While an amp may be able to sustain high power levels into low impedances, that tells you nothing about how well it deals with various amounts and types of reactance across a wide frequency spectrum. It is possible for a speaker to have sharp phase angles at several different frequencies all at the same time.

If you can picture a combination of a "slalom course" AND a "torture test" for amplifiers, that is what some speakers present. As such, you can have a speaker that is highly capacitive at treble frequencies, highly inductive at low frequencies and generates a high amount of reflected EMF ( electromotive force or "voltage" ) all at the same time. All of this can be independent of the amount of "pure" resistance that the amp sees at any given time or frequency. This is why speakers are a VERY complex load and why we don't have specific "tests" that show whether or not an amp can drive every load known to man OR maintain consistent sonic characteristics doing so.

Something else that is not commonly considered is that amplifiers produce LESS power as impedance is raised i.e. kind of the "reverse" of looking for high current into low impedances. After all, impedance raises at the point of resonance on a woofer. As such, power transfer is reduced right at the point that you need it most. Since vented systems typically have MUCH higher impedance peaks at resonance, you have even less power available to control a driver that is already lacking "damping". Even though most manufacturers do not offer power output specs into 16 and 32 ohm loads anymore, one might be able to make a more informed opinion about the overall build quality of an amp if we did know such things.

If you think that this sounds "crazy", take a look at the impedance curve of a vented speaker with a large woofer(s). It is not uncommon to see impedance peaks at resonance along the magnitude of 40 - 100 ohms. What kind of power transfer do you think an average SS amplifier is going to produce into a 50 ohm load ??? Let me tell you, not much.

Most "good" sealed designs keep the impedance of the woofers below 20 ohms, which results in much more accurate and controlled bass. This is due to the increased ability of the amp to transfer power and literally "muscle" the cone when it does not want to see any type of signal at all. After all, resonance is nothing more than the speakers' point of self oscillation. If excited at that frequency, it is literally contributing sound on its' own. It is up to the amplifier to "force feed" it at that point and damp / control the ringing that is taking place. Obviously, a lower impedance at resonance allows the amp to generate more power. This in turn can effectively work to control the speaker and produce greater accuracy.

Having said all of that, rms power ratings are WAY to easy to fudge given the way that the FTC has things set up. I think that measured power output at CLIPPING at various impedances is FAR more revealing of how "sturdy" an amplifier is. After all, this is the point of maximum long term stress for an amp. As such, it is the ultimate test in terms of how much TOTAL power the output devices can pass and how much current the power supply can sustain. If an amp can come close to "doubling down" at the point of clipping from 32 ohms down to 2 ohms, it can probably drive just about any load that you can throw at it. To do so would mean that the amp was as close to a pure "voltage source" as we are currently capable of making. Even if the amp is sturdy enough to do something like this, there is no guarantee that you will like the tonal balance or level of refinement & detail that the amplifier produces. Passing the aforementioned test simply shows that it is capable of "brute force" into just about any given load and does not necessarily mean that it will "sound good". It will however, drive the load that you connect it to. Sean
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