The Truth About Amplifier Power Ratings

Discussion in 'Amps, Pre-Pros & Receivers' started by admin, Apr 27, 2009.

  1. admin Audioholics Robot Staff Member

    admin
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    Ever wonder why the boom box you bought at Best Buy has a higher power rating than your dedicated two-channel power amplifier? Amplifier power ratings are usually honest in Hi-Fi equipment, but become very silly when it comes to the 'mass market' systems and even some of the latest Class D amplifier offerings. Few amps have a dynamic headroom of better than 1 or 2dB, and the greater the headroom, usually the cheaper the power supply for the rated power. This article explores the history of power ratings for consumer audio and also busts the myth about 'RMS' power.
    [​IMG]

    Discuss "The Truth About Amplifier Power Ratings" here. Read the article.
  2. markw Audioholic Overlord

    markw
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    Putting this in one bite sized capsule is long overdue. It should be required reading for anyone in this hobby.
  3. Wayde Robson Audioholics Anchorman

    Wayde Robson
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    Great article, it's very interesting how far they go to pump up those numbers.
  4. kevon27 Annoying Poster

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    You need to do an article featuring the other side --- Ultra high End Gear. How much of their claims are true?

    This is from Goldmund, describing their Telos 2500 amp.

    Telos 2500
    MonoPowerAmplifier

    A new monster is born. Many of our faithful customers have already successfully adopted the Telos 600, which was received with unanimous acclaim as the best amplifier ever made. However, a few also regretted the extraordinary work of art we made in the Millennium Mechanics and the corresponding authority provided by the ultimate "Mechanical Grounding" construction.

    As powerful as it is, the Telos 600 with its incredible dynamics, only tempted users of ultra-low impedance speakers where the current capability of the new amp seemed insufficient.

    Now, both have their dreams come true with the new and ultimate Telos 2500 from Goldmund, adding to the incredible accuracy of the Telos 600 much more power on low impedance speakers and the exact mechanical construction of the famous Millennium amplifier. The Telos 2500 is the same size and same finish as the Millenium amplifier, except for the conventional front screen. The Telos 2500 has the final sonic authority given by the most advanced "Mechanical Grounding" construction ever made by Goldmund. And it can play louder.... And better.... A dream come true.
    KeyFeatures

    * 2500W on 1 Ohms FPP (Fast Pulse Power before clipping) Mono Power Amplifier.
    * High-Power newest JOB 5 high-bandwidth circuitry.
    * Thermal Grounding full implementation with much increased gold-plated copper buffer plate.
    * 12 separate high-power transformers and separate power supply for the safety circuitry.
    * Balanced and unbalanced analogue inputs and RCA digital input/output.
    * Alize 6 input D/A converter with improved linearity and static protection.
    * Full DC, HF and overload speakers and amplifier protection.
    * Input attenuation adjustment (-9dB, -6dB, -3dB, 0, +3dB, +6dB, +9dB).
    * 3 x Goldmund coaxial speaker cable and 3 x 5-way binding post connectors.
    * Millennium amplifier chassis with Goldmund ultimate mechanical grounding.
    * Unique circuit time accuracy : better than 100ps.
    * Size and weight: 460 W x 515 D x 330 H, 75kg.
  5. zapzap Audiophyte

    zapzap
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    Well I'll give it a try: "Peak momentary power output" is a perfectly meaningful and useful term.
    • "Peak power" refers to the maximum value of the instantaneous power waveform.
    • "Average power" refers to the average value of the instantaneous power waveform (often incorrectly stated as "RMS power").
    "Peak power" is easier to measure accurately and more comparable than average power, since it doesn't require a THD qualifier. The peak of a full-scale square wave and a full-scale sine wave are the same value. Average power ("RMS power") suffers from the flaw of being measured at 0.1% distortion by some people and 10% distortion by others, inflating the values.
    • "Continuous power" refers to the maximum output that can be sustained long-term, limited by the rate at which heat can be removed from the amp or speaker.
    • "Momentary power" refers to the maximum output that can be sustained short-term, in which heat build-up is not a concern.
    Since nobody except Merzbow listens to continuous full-power waveforms, "momentary power" is actually the more musically-meaningful measurement. Real music has a crest factor of at least 6 dB, or a peak-to-average power ratio of 4, so "how loud does it get?" is determined by momentary power, not continuous power.

    So, yes, if measured honestly, PMPO would be a better measurement than "continuous average sine wave power". That the value is usually pulled out of thin air does not invalidate the concept.
  6. slipperybidness Audioholic Ninja

    slipperybidness
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    I agree with most of what you say here, and you obviously understand much of the technical aspects of electronics in general and measuring output in particular.

    In my opinion, and the opinion of many authors of books on building and designing audio power amplifiers (Sloan, Cordell), the CONTINUOUS POWER is the design parameter that will give you the best representation of amplifier performance.

    When I design an amp power supply, I design it to be robust to be able to supply continuous power.

    Edit--Good luck getting an honest or any continuous power spec from a vendor! You will almost certainly have to measure this yourself!
  7. PENG Audioholic Warlord

    PENG
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    You got that right, most lab measurements found online referred to continuous power as sustained power for a short duration, 1 minute to a few minutes, may be ten? I am not sure but not truly continuous for sure. I suppose there are a few manufacturers that probably do rated their amp correctly, or almost correctly as "continuous", Krell is likely one of those. Emotiva, Parasound, NAD and Anthem's, definitely not. In real world, even continuous for a couple of minutes is good enough to pass the point of diminishing return for normal hifi music enjoyment.
    PENG,
  8. slipperybidness Audioholic Ninja

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    Yeah, to be clear, driving an amp with a sine wave is going to be way more strain on an amp than any real world program material.

    And, when you are doing that, you are almost always driving the amp right up to the point of clipping, that's kind of the point of that test measurement.

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