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Thread: Wattage Overkill?

  1. #1
    Low Bitrate Linus's Avatar
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    Wattage Overkill?

    I bought a wattmeter (the Kill-A-Watt) the other day, and one of the things I plugged it into was my home stereo amplifier. It's rated at 100x2, but even at what I consider maximum volume, it registered a little over 20 watts. I've heard that more "headroom" in your amplifier will clean up the bass and generally make for a higher-quality listening experience, but where do you draw the line?

    The lowest-power amplifier I have is my current head unit in my car. 23x4 watts RMS and 47x4 peak, driving factory Honda 6.5"s in the front and 6x9"s in the rear. I get a little distortion in bassy tracks when with the volume just under my "max", but I think it's due to speakers - upgrading from whatever the stock unit was (5x4?) to the 23x4 made little difference.

    So why have more than about 30 watts per channel? I can only think of two reasons: clarity at rediculously high volumes and bragging rights. Frankly, I'm not interested in either.

    Am I missing something here?

  2. #2
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    You have to remember that you measured 20 watts at 120volts feeding your home amplifier. That is different than the output of your amplifier that feeds your speakers.

    Power (wattage) can be calculated Power = Voltage x Current. (where power is in watts, voltage in volts, current in amps)

    The voltage of the output to your speakers is alot lower than the 120 entering the amplifier, but might be at a higher current. Those calculated together will yeild a higer wattage than the input at 120v.





    Maybe someone else here on this forum can help better explain this.



  3. #3
    Low Bitrate Linus's Avatar
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    Whoa, wait a minute. I thought that a watt is a watt, no matter what the voltage (?). 20 watts at 120V gives a current of 167mA and 20 watts at 12V is 1.67A, right?

    I could understand if one kind of power required conversion that it might require a little more power to get the same signal amplitude to a speaker. Are these things fundamentally AC or DC?

  4. #4
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    Are you sure your amp is rated at a 100x2? It's probably peak power not RMS which is why you are probably only seeing a 20 watt draw. Basically a watt is a watt. The reason why you would need a lot of power from an amp is for clarity at both low and hi volume. It's all relative to the listener. Frankly I wouldn't be able to stand the sound quality that you are used to with your stereo/speaker setup it would drive me nuts. Basically you are missing out on a lot of music with a low power stereo and speakers just go to your local electronics store and try out the different amp/speaker combos listening to the same music on all of them and you'll hear why more power is better.

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    FLAC cproaudio's Avatar
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    oh oh I feel a "Does using pc's in your vehicle cause increased fuel use?" discussion coming on. Where did you get the reading of 20 watts from? how does your killatwatt meter work? I use a Craftsman 82289 meter/oscilliscope for all my electrical measuring. I doubt your home amplifier draws only 167ma. Are you measuring the AC power input of your amp or are you reading the output of the amplifier? Dynamic headroom is the difference between the lowest audio passage and the highest audio passage. Rock musics have little or no dynamic headroom because there's little or no difference tween the loudest spot and the softest spot. Classical music is the opposit. Music is fundamentally AC.
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    Low Bitrate Linus's Avatar
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    Quote Originally Posted by nixapatfan
    It's probably peak power not RMS which is why you are probably only seeing a 20 watt draw.
    I think they report different specs for home stereo equipment than for car audio stuff. Usually it's given as a watt output at 8 ohms and a particular total harmonic distortion (THD) and bandwidth (usually 20-20,000Hz). So I don't know whether that number corresponds to a peak or RMS value.

    I also have a Klipsch ProMedia 2.1 setup, which claims 130 watts RMS for the sub and 35x2 RMS for the satellites. It draws nearly the same power as the Sony at the same volumes, which makes sense to me - why would a "higher-power" amp draw more power for the same amplitude output?

    Quote Originally Posted by cproaudio
    Where did you get the reading of 20 watts from? how does your killatwatt meter work?
    You can press various different buttons to display the voltage, current, wattage, or watt-hours. I assume the wattage is simply the voltage times the current and the watt-hours totals up wattage at some recording interval.

    Quote Originally Posted by cproaudio
    I use a Craftsman 82289 meter/oscilliscope for all my electrical measuring. I doubt your home amplifier draws only 167ma.
    Well, that's about what the Kill-A-Watt reports. About 23 watts and 190mA at my usual volume levels. I played with the Klipsch's a bit more, and was able to get the wattage to peak around 75, but that was considerably louder than I would ever intentionally listen except when showing off speakers or something.

    Quote Originally Posted by cproaudio
    Are you measuring the AC power input of your amp or are you reading the output of the amplifier?
    Input to the amp. Obviously the output would be lower.

    Quote Originally Posted by cproaudio
    Music is fundamentally AC.
    That's what I thought. Does that mean a DC amp would draw just a little more power than an AC one (due to losses in conversion)?

    I'll revise my hypothesis a bit. I think most people listen to music at volumes that correspond to less than 30 watts of power consumption. More than 100 watts of rated power seems like it would be hard to detect except for at high volumes (I'd test this out at an electronics store, but there aren't any in my area). Note: I'm not saying more power isn't necessarily better. Just not necessarily worth the money (for me, anyway).

  7. #7
    Low Bitrate stkdidy ntshidy's Avatar
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    damnit damnit damnit, i pressed back to look at the wording, and it erased my post in the "post new reply"...damnit

    anyway, i had a huge thing on how 220 watts is needed to actually make a speakers SOUND 2x as loud as 25w...3db is 2x as loud/2x the wattage/2x the cone area/etc, but the human ear can only hear 10db increase as a doubling of sound ...where its actually 2x2x2x1.1x the spl...so i therefore have no idea where you get this "rediculously high volume" from...it really isnt

    with that increase in wrms, however, your increase in sq and clarity, on speakers meant for that power of course, can not be compared to stock at 25 in any way/shape/form...just can't be done

    once you have the wattage to good speakers, you will understand, until then...

    "bragging rights" only refers to subwoofers...EVER...you don't hear teenagers going around bragging about "i have 150wrms to each side"...o ya i have 175...well i have a 200x2wrms amp and i give it all to the front stage...blah blah blah
    you will hear " i have 1500w on my sony's" "youre an idiot, sony's are rated at peak...you really only have 350wrms" "i have 3000wrms on my 2 RE 15xxx's" ...wait, that last one you wont hear cuz no teenagers know about good stuff like that


    add-ons:
    music is fundamentally ac...it is always changing in its sine waves
    most people listen to music at 30-50watts per front speaker, assuming its good equipment and the amps put out 100wrms (each side)...loud listeners with good equipment will have about 75wrms. a stock setup run off the deck will be at roughly 10-12wrms. subs are another story...a 1000wrms setup will usually put out 200-400w ave, 600ish for rap with peaks just below 1000...bass tracks will ave a little below the rms rating at full volume (~800). music with only really drumbeats will ave 100-200w ave at listening volume

    the numbers in this last paragraph are all either estimates or based partially on test numbers i have seen before...dont live by them
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  8. #8
    FLAC cproaudio's Avatar
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    First, you dont need to click back to look at the wording. All the replies are below the reply box you're typing in. Simply scroll down to read all the previous posts.
    Second, Finally somebody who knows what the hell he's talking about. Though I totally agree that it takes 10db increase in SPL for human ears to disdinguish twice as loud in audible volume, my basic rule of thumb is, twice as loud, add 10db in SPL or 10 times the wattage b/c it's easier to remember. if you use your previous example, to be twice as loud from a 25wrms system your way is 220wrms. My way is 250wrms. There's very very very little or no audiable difference between 220w and 250w. Of course this is all in theory and very hard to prove. Some people would consider +7db is twice as loud, some +12db in a hearing test. Fletcher Munson Curves also has alot to do with how human ears sentivity to different frequencies.
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    Low Bitrate stkdidy ntshidy's Avatar
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    ya..that back button gets me sometimes...i can get away with it over at sounddomain tho, and over there its easier to read the full page than to use the scroll box at the bottom. i just didn't think it would erase my post ...o well, i still got the point across

    btw, that is a decent rule of thumb for only calculating power...but its kind of hard to incorporate when, lets see, you compare on paper the output of 2 10's with 600w each sealed in a truck to 3 12s with 1000 each in a hatchback ported
    gotta incorporate ye ol' 2xpower/cone area/displacement/etc, add 3db...then add another 3-6 for the car...but the 10x thing seems to work with wattage.

    also, agreed, every person will hear 10db increase differently, but 10db will almost always come out to be approximately the ave when averaging a group of people...same as ideally a human ear can hear from 20hz up to 20khz as a rule of thumb, but some can only hear 25 to 19, others 20hz to 25khz...its all subjective but in that general area
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  10. #10
    Low Bitrate Linus's Avatar
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    Quote Originally Posted by cproaudio
    Finally somebody who knows what the hell he's talking about.
    Sorry if this thread has annoyed you. Part of the reason I posted was to see if I had things wrong (apparently I did) and get them right if I did (working on it).

    Quote Originally Posted by stkdidy ntshidy
    3db is 2x as loud/2x the wattage/2x the cone area/etc, but the human ear can only hear 10db increase as a doubling of sound ...where its actually 2x2x2x1.1x the spl
    This confuses me some. I understand that a 3dB increase doubles the volume, and it makes sense to me that people could only distinguish a 10dB increase. But you also need twice the cone area to double the volume? What's the 1.1x in there for? Your original (lost) post probably explained all of that better; if you could explain it again, I'd appreciate it.

    And can anyone explain why more power = more clarity? It doesn't really make sense to me that a 35 watt (RMS) amp drawing 23 watts would sound better than a 23 watt (RMS) amp drawing 23 watts. Is it because the peak level is higher, and it's able to "fill in" those dynamic peaks and valleys a little better?

    Again, sorry if I'm being a pain. I really want to understand this stuff to make sure my money is well spent.

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