Difference between "Watts" & "Currunts"?

Someone will probably refer you to a good book, but...Voltage is electrical potential or "pressure" provided by a source such as a battery, generator supplying your wall outlet, or an audio amplifier and is usually denoted as "E". When some load is connected across this source (e.g. light bulb, speaker) making a complete circuit from source terminal to source terminal, electrons flow in that circuit and that is current, usually denoted as "I".. Current is measured in amperes. The load offers some "resistance" to the flow of current depending in its physical characteristics, and is denoted by "R". Resistance is measured in ohms. By definition, 1 volt of potential applied across a resistive load of 1 ohm will cause 1 ampere of current to flow. The basic relationship is I=E/R or however you might want to transform it algebraically. The polarity of a battery does not change, so it is said to supply direct current (DC). The polarity of the voltage at an outlet or the output of your amp varies and is said to supply alternating current (AC), I must say at this point that there are differences between a DC source with a purely resistive load and an AC source with a load like coils (inductors) and capacitors (like in xovers) and speaker magnets. The AC scenario is much more complex. A capacitive or inductive load is said to have "Impedance" rather than resistance, although it too is measured in ohms as you know from looking at speaker spacs. However, using a DC case will show the basic relationships. The power, measured in Watts and usually denoted as "P" supplied to a load is calculated by the formula P=EI or P=I2R (2 = power, ie "sqaured). For example 10 volts across a 2 ohm load will cause 5 amperes to flow I=E/R). The power in the load is 10x5=50 Watts or 5x5x2=50 Watts. Let's look at an amp and speakers, but simplify by using DC considerations. Suppose your amp can supply a 24 volt audio signal at its output terminals. This depends on internal power supply and circuit design. Although speaker impedance varies across the frequency range, let's just consider the typical "nominal" value of 8 ohms. That means your amp could be asked to supply 24/8=3 amperes to the speaker. If it can only supply 2, because of internal power supply limitations, it will "clip" or "cut off" at 2, causing problems for your speaker. Say it can supply 4 (a rating of 4x24=96 Watts), so it is ok at 8 ohms load and the power delivered would be 24x3=72 Watts or 3x3x8=72 Watts. Now use a 4 ohm speaker. 24/4=6 amperes, 2 amperes more than your amp can supply. If you crank it, the current limitation of your amp will cause "clipping" and may well do in your tweeters. If you keep it under control, your amp can supply 72 watts to this speaker also. Now use a 16 ohm speaker. 24/16=1,5 amperes and the power delivered is only 24x1.5=36 Watts or 1.5x1.5x16=36 Watts, even though your amp is capable of more with a different load. When amp manufacturers specify power capability with different loads, you can use that to roughly calculate the current capability. Use the power specified for the lowest impedance load and P/R=I2 (squared). So, if an amp can supply 100W to a 4 ohm load (assuming 4 is the minimum specified), it can supply roughly 5 amperes (100/4=25, sqrt 25=5). Also implied is an output voltage of about 20 volts. If you used a speaker whose impedance varied considerably below that, you may run the risk of current limitation problems. Again, this is a simpistic analysis and noone should complain to a manufacturer about a design based solely on these examples as the current capability is only "implied" from such specs.Thank you. Hope this was not totally boring. :)

Wattage is a measurement of how much voltage AND current an amplifier can produce at a specific impedance. Most amps are rated with 8 ohms used as the reference level. This is a common rating for many speakers. While most amps would have no problems at that impedance, going down to a lower impedance like 6 ohms, 4 ohms or even 2 ohms can tell you a lot about just how beefy the amp is. Since there is less resistance at the lower impedance, the amplifier should be able to deliver more power. Theory dictates that because there is half the resistance when going from 8 ohms down to 4 ohms, you should have twice the power capacity. In other words, a 100 watt per channel (wpc) amplifier at 8 ohms should THEORETICALLY do 200 wpc @ 4 ohms and 400 wpc @ 2 ohms. Not many amps can do this. The common term for performance like that is referred to as "doubling down" since the amp doubles it's output as it goes down in impedance. Most amps are limited by how much current the power supply can feed the amplifier circuit and then again by how much actual current the output devices ( transistors or tubes, etc..) can actually pass before burning up. The closer that we can come to "doubling down" in terms of the rated output, the "beefier" the amp is. This is a generalization at best since there are ways to "fudge" the numbers and specs. While the power output or current capacity of an amp might not seem important with 8 ohm speakers, most speakers vary impedance quite a bit and therefore require the "extra muscle" that a high current amplifier offers. I have seen speakers rated for a "nominal 8 ohm" impedance that actually went down to about 2 ohms. This would mean that a "common" or "measly" amp could literally "buckle" under the pressure and start distorting, overheating or going into it's self protection mode if being pushed at all. Keep in mind that 0 ohms is a short circuit, so there isn't much resistance that the amp sees with only 2 ohms connected to it. For the record, i have a set of speakers that measure 1.1 ohm, so they require very sturdy amplifiers to operate properly. Some "exotic" speakers like electrostatic's, ribbon's, etc... can sometimes be "highly reactive" and be very low impedance. What this does is causes the amp to try to put out all it can while the speakers actually try to "push" power back into the amp. Having the extra "oomph" of the high current design helps to overcome this and controls the speakers better. It also comes in handy when running very large woofers with giant magnet / motor assemblies or quite a few woofers. Like the "reactive" loads mentioned above, these speakers can generate a lot of "backpressure" (reflected EMF) and the "beefy" amps can deal with that easier. True High current amps are usually noted for very tight and controlled bass output for this very reason. Tube amps typically don't do well with lower impedance speakers, putting out measurably less power and having poorer bass performance. Just like speakers, the amps actually have an impedance rating for their output. Since tubes are typically much higher output impedance than transistors, they tend to like higher impedance speakers for best results. That is why many tube amps have been characterized as having "mushy bass", especially when used with low impedance speakers. I hope that i kept this simple enough for you to follow and understand. While it was quite basic, it was a generalization at best. Keep in mind that there are exceptions to every rule and there are amps that don't fit into any of the above categories. Sean >

HAHHA.... Looks like we were doing this at the same time with both of us writing novels : ) Sean >

you guys! i thought a watt was a former secretary of the interior and a current a kinda berry used in preserves and pies. sure glad you explained things. woulda been embarassing had i posted first. ;<)

While watts describes electrical power in a dynamic sense, current (amperage) describes electrical force in an absolute sense. Watts and current as electrical concepts are vaguely similar to horsepower and torque in mechanical engineering. Strictly speaking, watts (total power) is simply voltage (pressure) x amps (force). Horsepower is the amount of torque (force) generated over a specific time period (torque x time);(1 horsepower = 550 ft. pounds of torque x 1 second). Like torque, current represents the level of electrical "force" without reference to a dynamic element. A simple analogy that is easy to visualize is that amperage is the width of a water stream flowing from a hose with voltage representing the pressure of the water flowing from it. The total water dispensed over a given time would be watts. A fire hose can potentially deliver far more force than a waterpik using the same amount of water per second (although the waterpik would conceivably cut steel at such pressures - much like a high voltage arc might). Just as water hoses are rated for maximum pressures, so are electrical insulators rated for maximum voltages (electrical pressures) and not amps. Conductor size, like the diameter of a water hose, determines maximum current. When you exceed a conductor's current capacity, you don't electrically defeat the insulation but the conductor overheats (and sometimes melts). This is how fuses work. Current is a factor in the mechanical control of a loudspeaker element. Current, like torque, has its value in the ability to overcome the inertial resistance of a load - sometimes referred to as "reactive power". All loudspeakers are in some form or another a movable mechanical element attached to a electrical "motor". Some driver designs have greater inertial values - a greater mechanical load - and require larger amounts of current (reactive power) to properly control their oscillations. This is reflected by the measured impedence specifications of the driver at various frequencies (expect a 4 ohm speaker to draw more current than an 8 ohm unit). The moving elements of low frequency drivers (woofers) tend to have much more mass than high frequency elements (tweeters) - and generate more inertial forces as they occiliate. The "motors" (voice coils) of woofers consequently need greater current (reactive force) to keep the bigger driver (load) from oscillating out of control. Imagine waving in your arms a sheet of paper vs. a sheet of 4x8 plywood and you'll understand the difference. This is why reproducing low frequencies uses so much more total power (watts) - because typically more current (reactive force) is required at any given voltage. Maximum amperes are typically specified for better power amplifiers. Controlled high amperage is typically more difficult to achieve with tube amps because vacuum tubes can only pass low currents at very high voltages, which then have to pass through a transformer (a device which lowers volts and raises amps, but which is not as electronically "responsive" - because it has its own form of electrical resistance called "inductance" - as a straight wire). This is why SS amps tend to exhibit crisper bass response than typical tube designs. I hope this wasn't too long or complicated, but amperage, watts and voltage are intimately related and to appreciate one you should understand all.