Watts vs. current

March 18, 2021
 by Paul McGowan

I am so often asked to explain the difference between high current and high wattage that I am convinced these are confusing terms.

Most audiophiles understand wattage and current are connected, but how many actually understand the idea they are forever entwined like thunder and lightning?

Wattage is an expression of current and voltage. Think of it as a hurdeler. The voltage is the height of the hurdle while current is the power needed to clear it. Lots of power is useless if there’s no high hurdle to jump in the same way a hurdler won’t clear the obstacle if there’s not enough power from which to spring.

The higher the jump the more wattage is needed.

Wattage is the term we use to describe two interlocking events.

A preamplifier produces voltage but almost no current which is why we don’t rate preamplifiers in watts. A power amplifier has two jobs: raising to a higher level the input voltage from the preamplifier and then providing the horsepower to keep that voltage high in the face of opposition from the loudspeaker. That opposition is called impedance. Oddly enough the lower the impedance number the more horsepower required to overcome that obstacle.

Hope that helps.

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43 comments on “Watts vs. current”

  1. OK, so the only thing I know except don’t touch the brown wire, think garden hoses and water pressure (voltage), hose thickness (current), rate of flow (power) and how much water ends up in the wash bucket (socialist energy) or swimming pool (capitalist energy). Think impedance as socialist pipes, offering resistance, the more socialists (the higher their frequency), the more resistance.

    As to amplifiers, think of comrades distributing loaves of bread from the back of a truck to the proletariat. You need comrades strong enough to throw loaves to the back of the gathered masses, but also sensitive enough to notice the little workers at the front. If they are too strong and the loaves sail over the heads even of the people at the back, those loaves are wasted (too much headroom, wasted power) and the ones at the front get left hungry as the (insensitive) comrades show off their throwing power. The larger the truck the more get fed (capacitance) and the more different sizes of loaves the better they get fed (dynamic range).

    The upper classes (A and B) think they know best, but waste energy and are more noisy, but switch mode to the lower classes (D) and they are more efficient and quiet, they cost less and take up far less space. What’s not to like?

    1. I also liked your original post on this topic, from a couple of days ago. However this one was also amusing. You’ve obviously had time to expand on the subject 🙂

      1. So it’s not only English spinners that keep you amused.

        As engineers seem almost universally incapable of explaining anything to the ignorant masses (me), I had to have a stab at it myself.

        Is there an analogy for inductive reactance, or is it reactive inductance?

          1. Everyone knows that only equipment that measures poorly sounds great. Equipment that measures well is crap, unless it’s 1970’s Japanese midfi; then, it’sthe greatest thing ever made.

            All of this engineering talk about voltage ‘n’ wattage ‘n’ current is wrong, cause it’s just engineering talk, ‘n’ everyone knows engineers can’t hear, ‘n’ only audiophiles can hear.

            The guy who posted a reply to Paul’s Post a couple of weeks ago, sayin’ dat Covid-19’s a hoax was correct. It’s all just a ruse to take down the greatest human ever made.

            Science is a lie. There ain’t atoms, or molcules, or nuttin’ like dat. Their just teachin’ you ‘n’ your kids dat cause they want to control yer mind. That’s how they control you; with science. And, 5G. You have to science-proof yer family. The earth is flat. Reptilians run the world, and eat childrens.

            Rock on.

            1. Rock on indeed!
              Wow Neward I’ve never read so many truths in one reply on ‘Paul’s Posts’
              You are a true Oracle of wisdom sir.
              You’re referring to Donald A. Hump, right?

  2. Oooh, this new site is so clean & modern. I feel like I’ve just moved into a new apartment.
    I better not upset the neighbours.
    I bet that the common walls are paper thin.
    I probably wont be able to turn my subwoofers up as loud 🙁

    The ability for an amplifier to supply a lot of current instantaneously is important for crescendos & musical peaks, like the headroom that Paul is always banging on about. Basically, the lower the resistance, or impedance, the more current the amplifier must be capable of supplying; remembering that impedance varies along the frequency range.
    You can devise whatever analogy you want to create to explain current, voltage & power but in the end all your audio system has to do is to sound terrific…separate components don’t even have to ‘measure’ well 😉

    1. Clean and modern looking site, I will agree with that. I don’t mind it although I have seen others who do.

      I realize I no longer receive email notices of this daily post nor replies to my comments, and my avatar is gone (although on the forums the avatar is still there). A work in progress certainly.

      1. Larry, I am hoping that some day soon we will again get email notices of Paul’s Post since there is still a place on the page (upper left) were one can sign up to receive Paul’s Post.

        1. Yes, sorry guys. The new website isn’t working with our email service and thus no posts are being mailed out. Sigh. The engineers are working away at whittling down the list of problems to be fixed.

          1. Like stimpy2 I’ve signed up again and got a mail today, later. Hope I now don’t get two mails when the issue is sorted. When it comes to mails I prefer mono.

          2. Another thing you might not be aware of. I haven’t looked at every product but of those I have close to the bottom of the page it states ‘This product is unavailable in your country.’ Do you no longer sell in the U.K.? I assume (always dangerous) it means it’s not available for direct sale from the website and that you need to click the “Locate a dealer” box. I just don’t think this is clear and a potential purchaser may give up there and then. Definitely not good for your bottom line.

  3. “Oddly enough the lower the impedance number the more horsepower required to overcome that obstacle.”

    Above is the line that jumps out at me. By having an amplifier that can handle a hard to drive speaker load without any compromise is important to some.

    Is there a definition of what a 2 ohm musical transient is?

    1. Mike. A speaker’s impedance is nominal and varies greatly over the musical range. The closer the resistance gets to zero, the closer it is to a short.

      1. rwwear,
        I certainly understand what you are saying about lower impedance getting closer to a short. So the tougher the load (lower impedance) the more current an amp has to produce while maintaining some voltage.

        My question of what is a musical transient of 2 ohms is hasn’t been answered. Is the transient a certain time? Or instantaneous? Or a number where someone doesn’t hear an amp falling apart?

        To those who don’t have low impedance loads then it doesn’t matter. It may matter to those whose speakers have the potential to drop to that level or below.

  4. A new neat and clean look…Nice Paul! PSA info all there, will just take a few days getting use to…”which way did they go”!?! 😉

    FR is correct…once it sounds terrific, a power analogy will be long forgotten!

  5. This post about Watts, Amps, Volts, Ohms has caused me to take a trip down “memory lane” where I briefly reviewed the history of Electricity and Magnetism (E&M) beginning around 1600 and culminating in 1873 with Maxwell’s equations. It reminded me how true geniuses made fundamental discoveries in the understanding of E&M and that practically every term we use in discussing electrical things today (Volts, Amps, Ohms, Watts,Galvanic isolation, etc.) is named after one of these great men.

  6. From my professional life I know that almost every new software (computer program) is rubbish without thorough testing.
    A lot of companies have the misconception that testing is not important (“programmers don’t make mistakes” – yeah right), so there is little or no testing. Result : a lot of “errors” (I am glad that my bank does a better job in this regard).
    Not a good thing that the big boss of the company has to say “sorry, but we are working on it” while the product has already been rolled out.
    Talking about audio products (devices) you could say that testing/quality control is very, very important.
    I am not convinced, from personal experience (I won’t go into more details) that PSA is always doing enough in this regard.

    1. Personally, if I’d been Paul, I’d have removed the history and recycled a load of them. As he says, this is only a little locker room/car talk for those idle moments when the coffee machine is warming up, etc. And occasionally I learn something.

      I hope PS Audio’s time is spent getting the Octave server software right. Personally, this new format to me is a bit lossy, as in lost space, a little too much spacing, so more scrolling. I don’t get the need for icons.

      What Paul should appreciate is that some of us read this by the coffee machine first thing in the morning, and his new full-size smiling face on the masthead is a bit much to cope with at that time of the day.

  7. Also the current needed to produce the same wattage varies depending on the mains voltage-as I discovered when adding a fuse for my 650 watt rated amp the other day in my (imported to Portugal) fused UK plugs.
    650 watts at 230v needs to draw just over 2.8 amps so I bunged a 3 amp fuse in (I know it’s fused internally but I’d rather open a plug than the amp if it goes) but with all other things being equal it’ll be 5.416 at 120v

    https://www.rapidtables.com/calc/electric/Watt_to_Amp_Calculator.html

    You get nothing for nothing as Mr McGowan has said on more than one occasion…. ; )

  8. The larger type of Paul’s post is hard to read on my 21″ monitor, which doesn’t have the contrast of my newer, laptop screen. Draging the window over to the 15″ laptop makes it easier to read, but that’s a drag (pun intended). The smaller type of the comments is easier to read on each screen, but is best on the laptop. Not sure I want to drag the window over to the laptop just to read this one email. I just went back to an older post to compare and the older format was a LOT easier to read. 8-(

  9. Please confirm if I am ok or wrong. Some thing I am missing….
    Voltage is equivalent to pressure of the water in the pipe and flow (ampers) is the equivalent to flow of water, quantity of electrons going through cables ( not exactly true). Wattage is presure x flow, or voltage x amps. So if the impedance of the speakers is lower why do you need more wattage? I thought it was the contrary, less impedance of the speakers less wattage required at the output of power amp.Actually always we read less wattage with higher impedance of speakers.

    1. Javier,
      Maybe this helps…
      Car analogies often work well. If the gearing (impedance) is high enough then your maximum speed (maximum output) is usually limited by the horsepower (voltage). But if you drop the gearing (impedance) then the revs (current) may limit your top speed. If you want more speed with high gearing you add horsepower, if you want more speed with low gearing you have to have higher revs. More power into high impedances requires a higher maximum voltage while more power into low impedance loads requires more current capability.

    2. Your confusion is due to a fundamental error in how Paul expressed himself.The issue is that he used “power” and “horsepower” colloquially while trying to explain the scientific meaning of voltage, current and Watts(power).

      His first use is when he writes, “ The voltage is the height of the hurdle while current is the power needed to clear it.” Clearly, current is not power at all since in electrical terms power is voltage times current and has the unit of Watts. In this case Paul has used power to mean oomph or something like it rather than the technical meaning of energy per second.

      When Paul writes “providing the horsepower to keep that voltage high in the face of opposition from the loudspeaker” he can’t mean power in the technical sense since for a given impedance power is directly proportional to V^2. In effect, his statement means “the power to keep the power high” if we use the technical meaning of power. The sentence only works when horsepower is used to mean some nebulous idea, not the scientific meaning.

      In short, your understanding of the physics involved is correct and Paul’s explanation is unfortunately little more than handwaving because of his very imprecise use of terminology.

  10. I need to issue a complaint about the totally un-scientific “modern” typography of san-serif. Over a hundred years ago, the London Times PROVED that serifs increase comprehension and retention of textual information. Our eye mechanism has not evolved to reverse this conclusion.

    I can only conclude that the website manager wanted to obfuscate the facts of this channel like the rest of the “High End” press. (No, it was not “double blind”, only the cohort reading san-serif tests missed the information, so it was “half blind”.)

  11. OK, the problem here today and in general is that all the relevant parameters of audio are INVISDIBLE, whic is why so much effert and purple prose is erroneously lavished on purely cosmetic issues.

  12. Very interesting to read comments over the last 2 days. Apparently change is very hard for some. Myself for one had many of the same observations that have been posted so far, and a lot of the same initial thoughts.

    So a little change on my part became necessary. Having to go thru the home page to get here. A different look is all.

    The fact that so many have bristled with the new compared to the old just points out the reach of Paul’s influence in the world of audio. For that he should be proud. For all the posters… they should ask themselves why has reading and commenting here become almost a mandated ritual in their daily routine?

    Speaking for myself only I like the chance to start a day with some thought provoking, and these posts and replies help feed that desire. So thanks to Paul and all here!

    The kinks will be worked out over time and every one will get used to the new norm.
    ✌️

  13. OK, the problem here today and in general is that all the relevant parameters of audio are INVISIBLE, which is why so much effort and purple prose is erroneously lavished on purely cosmetic issues.

    Wattage, Voltage, Amperage, treble, bass, transients, timbre, spatial information – all are outside our visual acuity. Further, the synthetic environment is so laden with noise pollution that we have devolved into a visual dominance culture. Even poetry, perhaps the first sonic art form, is rife with “imagery”. “Seeing” has become a general term for understanding.

    I just read the introduction to “Sound Objects”, a collection of essays about the philosophical study of sound and meaning, and it was clear that 20th Century philosophers had hearing damage from the industrial soundscape – none of them appreciated the potential of music to synchronize and affect humans, and this is endemic to our culture which has commoditized and cheapened music to entertainment and masking noise.

    How much harder is it to instill appreciation for the physical properties of electronics. I came by this young, with a multi-meter. It could quantify the difference I sensed on my tongue between 1.5 Volt and 9 Volt batteries, and the 115 Volts that grabbed my arm. It could also measure the current and resultant Wattage of different Tungsten filaments as it turned into heat and light.

    When other children were playing cowboys and indians or learning ball sports, I was playing with lenses, magnets, and electric trains, making a relay, buzzer, and solar powered transistor radio, taking apart a TV (all tube) and learning what 10KV feels like.

    These multi-modal experiences inform the meaning of current, voltage, power, the differential of current and voltage into reactance and the integral of power into energy.

    I appreciate a liberal arts education (I was also hearing Shakespeare, symphony, piano and Frost and reading Voltaire by 8yo) – but we don’t even have a word for “lack of physics knowledge” analogous to illiteracy or innumeracy – and the former seems more prevalent.

  14. Regarding amps and volts:

    In a post (with the previous format) it was indicated that the current version of the IRS V had 6Kw of amplification per channel.

    This is a grandiosity, second only to the Crown industrial amplifier, model: Macro-Tech 10,000, designed for stadiums, which is powered by three-phase current to deliver “only” 10 kW with loads as low as 0.5 Ohm.

    In this 6Kw / ch PSA installation, in practice: How many watts will be used at most in an average listening session?

    Is so much power practical and necessary, even with inefficient speakers in a sound room not as big as the No. 1?

    Many audiophiles brag in front of their friends about the power of their equipment !!

    I don’t expect someone to answer these “awkward” questions.

  15. Speaker impedance always looks weird to me. It reminds me of doing smith charts in undergraduate Physics classes. While I don’t have a lot of new equipment, on mine, it’s not constant. So the poor amplifier might be complaining that at some frequencies it is drastically lower. But that’s what I get with Thiel 1.6s.

  16. For me watts is like water pressure while amps are the volume like as garden hose compared to a much larger diameter pipe used to fill a swimming pool at the same pressure.

    Similarily horsepower and torque relationship…

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