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Thread: Amp Headroom vs Efficiency (and quick question about dyno vids)

  1. Back To Top    #11

    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Quote Originally Posted by dumdum View Post
    Sorry must pay attention... it’s a dynamic test with a dynamic signal vs a test tone that rises steadily until clip... the former reflects music more
    Both time stamps show the AD-1 on Certified Dyno Run for me. I've not heard him mention about a different test tone on certified runs (though I know there is a separate dynamic test). Maybe I'm missing something here.

  2. Back To Top    #12
    Noob Jdunk54nl's Avatar
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    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Quote Originally Posted by Stealth1 View Post
    Both time stamps show the AD-1 on Certified Dyno Run for me. I've not heard him mention about a different test tone on certified runs (though I know there is a separate dynamic test). Maybe I'm missing something here.

    I can't see what model the multimeter they were using, but usually these are pretty crappy devices to get a true estimate, especially on peak runs at frequencies outside their capability.
    2014 F150 Limited -> Kenwood DDX-9907xr -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 mki in Valicar Stuttgart Pods, Rear SB17's, Sub SI BM MKV's in MTI BOX. Alpine PDX-F6 -> SI Tm65 mkIV, SI M3 mkI in Valicar Stuttgart Pods

  3. Back To Top    #13

    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Quote Originally Posted by Stealth1 View Post
    Both time stamps show the AD-1 on Certified Dyno Run for me. I've not heard him mention about a different test tone on certified runs (though I know there is a separate dynamic test). Maybe I'm missing something here.
    I see what you mean, the amperage is different on the still shot of the test... I don’t know... ask him... he normally answers questions... infact I will ask...

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    BURNED OUT Hillbilly SQ's Avatar
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    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Quote Originally Posted by dumdum View Post
    They are at two different impedences, the power supply is closer to its maximum output with a two ohm test vs a four ohm test, no other reason

    why would anyone test at a random number in the middle of an amps power delivery, heat figure should it be done at?

    using amps to have headroom is not even a reason to get a bigger amp, distortion drops as you get near the clip point, so you ideally want to be in the top 25% of the amps performance to get the best power vs distortion figures
    So basically the only reason to run way more power is to allow the amp to be less stressed to hopefully increase its service life? And to think all these years most people were putting several hundred watts to each speaker for the wrong reason?
    They might say "don't try this at home" but nothing about not trying it at your friend's house.

  5. Back To Top    #15

    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Most music has a crest factor around 12-18 dB.

    So if the RMS wattage is 1W, then the peak wattage is between ~ 20 to 50W (which represents 13-17dB)
    On a tweeter that is a lot of sound.

    When we get to woofers and even more so to subwoofers, then crest factor become better envisioned as closeted to 3dB when the bass notes play, and then gaps of no sub notes.

  6. Back To Top    #16

    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Quote Originally Posted by Hillbilly SQ View Post
    So basically the only reason to run way more power is to allow the amp to be less stressed to hopefully increase its service life? And to think all these years most people were putting several hundred watts to each speaker for the wrong reason?
    Lots of people do lots of things for reasons with no actual legitimate reason to do it...

    and I made no reference to service life? It all depends how loud you want it and how your drivers stand up to some extra hammer

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    Noob Jdunk54nl's Avatar
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    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Service life might actually be worse at lower levels too. The amp is less efficient so could be creating even more heat.
    2014 F150 Limited -> Kenwood DDX-9907xr -> Helix DSP.2 -> Alpine PDX-V9 -> SI M25 mki in Valicar Stuttgart Pods, Rear SB17's, Sub SI BM MKV's in MTI BOX. Alpine PDX-F6 -> SI Tm65 mkIV, SI M3 mkI in Valicar Stuttgart Pods

  8. Back To Top    #18

    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Quote Originally Posted by Jdunk54nl View Post
    Service life might actually be worse at lower levels too. The amp is less efficient so could be creating even more heat.
    I doubt it...

    The eficieent at zero output is not overly important
    ...but my amps are biased.

  9. Back To Top    #19

    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Quote Originally Posted by dumdum View Post
    There is nothing wrong with a little headroom... but people who use 500wrms amps on tweeters are not really using there noggin...

    two secs I’ll find you an illustration...

    this is a purifi et400 I think it was...

    note how the distortion gets lower and lower as power increases, and is lowest just before clipping kicks in and the distortion goes north once more, so using this amp at 30watts on a set of tweeters would likely have more distortion than a smaller amplifier with power that’s more in keeping with what the speakers actually need, if you need 50watts use maybe a 75w amplifier

    i use a 150.6ap for sq, rather than 6x150rms I’d much rather have 2x75, 2x125 and 2x250 as that would be far nicer and actually lower distortion than 6x150rms I have now
    I agree that "literally" that is what the chart shows, but I think there's a lot also to be seen there that should have you questioning what's really being measured:
    Click image for larger version. 

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    The first point - the volume knob. You aren't sending 250 watts to the speaker with that amp. That's simply the most that COULD go to that speaker on big -0dB level peaks in the music...

    If you are listening loud at 95dB on a 50w amp - that mid is getting maybe 20 watts, the tweeter maybe 5w, 10w.

    If you are listening loud at 95dB on a 500w amp - that mid is still getting 20 watts, the tweeter still 5 or 10.

    So now let's go to that chart...
    At 20w it's something like 0.001% THD.
    At 1w it's something like 0.015% THD.
    At 0.1mw it's something like 0.02% THD.
    And yeah - at 200w it's 0.00001% THD.

    First point - these numbers are so low, they are below the threshold of human hearing.
    Second point - even if they weren't, the difference between any of those is too small to hear.
    Third point - when that kick drum hits for that 0.1 second burst, you are even less capable of perceiving a 0.00001% THD - or even 1% THD.

    Then, this is the measurement for this particular amp. Is that necessarily true for ALL class A/B amps? Might there be ones where the power supply falls short, and the distortion accordingly increases at some point before rated power?

    And even if it WERE true for all class A/B amps... What about other amp classes? Class D in particular - it clips ugly. With class A/B amps we could get close to clipping and most people wouldn't notice if the needle got a little into the red on extremes.

    But with class D, if you had an amp with this much power, it WOULD be smart to use the gains to conservatively guarantee you never hit clipping at all - maybe even limiting the amp to half capacity. Those amps might "only" have distortion as low as 0.03%...
    Technically "worse" than this Purefi amp...
    ...but that's comparing 0.003% to 0.03%

    Not only are those both below human (or dog) hearing accuracy limits, but to put it in proportion, let's compare it also to another spec that fluctuates with your usage...
    Would you buy one car over another if one got 30mpg and the other got 30.01... in theory, as measured in a lab?

    Final point - even if the measured numbers were closer to the human hearing threshold, I think having that headroom available (both amp and power supply side) and amp efficiency improvements of running a more powerful amp conservatively low both are more important to actual performance than the difference between literal fractions of distortion percentages - especially when you consider the speakers will (WILL) have higher THD than the amp.

    Phew. That took too long on this little keyboard.

    Sent from my LM-G820 using Tapatalk
    Last edited by geolemon; 04-28-2021 at 12:58 PM.

  10. Back To Top    #20
    Noob KillerBox's Avatar
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    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Geolemon, I tend to agree. Everyone talks about the amp specs of .1% or .0001% distortion but, no one talks about speaker distortion specs. So if your speakers have 10% distortion levels are you going to truly hear the difference of .1% compared to .0001%?

    Myself I like bigger amps within reason. The bigger amps run cooler because normally they are built to dissipate more heat. So I can run all day long and never have to worry about the amps overheating or clipping.

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