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

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

    Greetings,

    Can anyone point to resources that help explain the relationship between headroom and efficiency?

    Currently looking at some class D amplifiers, and I recognize that efficiency tends to drop off significantly as one approaches maximum wattage prior to distortion. However, I'm considering amps that have more headroom and it seems tests for efficiency at 75% of maximum wattage before clipping, for example, are hard to find.

    Also, just a quick question about dyno tests. On this video, for example, we see an efficiency rating given at 5 minutes and 27 seconds:

    https://www.youtube.com/watch?v=HSwWYtkvbm8

    Can someone please explain why that efficiency figure is so different from the one that would be calculated at 4 minutes and 41 seconds into the video, for a seemingly identical test? I have watched a number of these videos, and this is very common.

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

    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

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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
    The last part that I put in bold is something I have never heard before. Do you have any books or articles that you can recommend to learn more about it? I have been dreaming of getting bigger amps some day for the headroom but now I want to see if I have been on the wrong mental track from the start.

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

    Quote Originally Posted by Fernpatch View Post
    The last part that I put in bold is something I have never heard before. Do you have any books or articles that you can recommend to learn more about it? I have been dreaming of getting bigger amps some day for the headroom but now I want to see if I have been on the wrong mental track from the start.
    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
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    Quote Originally Posted by Stealth1 View Post
    On this video, for example, we see an efficiency rating given at 5 minutes and 27 seconds ....
    .....so different from the one that would be calculated at 4 minutes and 41 seconds into the video, for a seemingly identical test?
    Those two timestamps don't make sense. The measurements on the AD-1 are exactly the same but the max current measured on the Fluke multimeter are different. This seems to be a bad example of what you're trying to ask, or maybe I don't understand what he's doing in the video.

    Here's a better answer for your question:
    screenshot from the Texas Instruments TPA3221 class-d amplifier datasheet:

    Name:  tpa3221 efficiency vs output power.PNG
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    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Amp Headroom vs Efficiency (and quick question about dyno vids)

    We are also missing the point laid out here:
    https://www.caraudiojunkies.com/show...utput-in-volts

    The RMS power of the amplifier will never be delivered to the speaker while playing music because music has loud AND soft sounds.
    .....unless you clip the snot out of it.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

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    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
    Thank you good sir. I found that graph to be very interesting indeed as it could explain a phenomena that I have been trying to understand where the more subtle parts that make the music richer and sweeter seem to get better and more pronounced as system volume increases until a tipping point is reached and than the louder you go from there the sound changes and starts getting tighter and thinner and loses the rich details. I have been debating what is causing that effect to happen and now I am wondering if what I am hearing is the onset of clipping?

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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

    The two timestamps I listed reflect different impedences for you? For me those two timestamps show the exact same readout on the AD-1, with a different multimeter readout (as Justin Zazzi noted as well).

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

    Quote Originally Posted by Stealth1 View Post
    The two timestamps I listed reflect different impedences for you? For me those two timestamps show the exact same readout on the AD-1, with a different multimeter readout (as Justin Zazzi noted as well).
    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

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

    Quote Originally Posted by Fernpatch View Post
    Thank you good sir. I found that graph to be very interesting indeed as it could explain a phenomena that I have been trying to understand where the more subtle parts that make the music richer and sweeter seem to get better and more pronounced as system volume increases until a tipping point is reached and than the louder you go from there the sound changes and starts getting tighter and thinner and loses the rich details. I have been debating what is causing that effect to happen and now I am wondering if what I am hearing is the onset of clipping?

    You can also go here and see all of the graphs of amps measured via the Audio Precision device. Most of the well designed amps produce the best output (across many graphs) as they are right at their max output.

    https://www.audiosciencereview.com/f...pment_Reviews/
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