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
    Joined:
    Apr 16, 2004
    Messages:
    172
    Likes Received:
    1,621
    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
    Joined:
    Nov 26, 2003
    Messages:
    11,235
    Likes Received:
    3,052
    Location:
    Joisey and Texas
    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
    Joined:
    Jan 19, 2006
    Messages:
    540
    Likes Received:
    144
    Location:
    Waterloo Ontario, Canada
    Great article, it's very interesting how far they go to pump up those numbers.
  4. kevon27 Annoying Poster

    kevon27
    Joined:
    Apr 11, 2009
    Messages:
    92
    Likes Received:
    8
    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
    Joined:
    Apr 21, 2016
    Messages:
    2
    Likes Received:
    0
    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 Spartan

    slipperybidness
    Joined:
    Jul 24, 2011
    Messages:
    5,553
    Likes Received:
    1,238
    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!
    • Agree Agree x 1
  7. PENG Audioholic Warlord

    PENG
    Joined:
    Oct 23, 2004
    Messages:
    9,793
    Likes Received:
    2,654
    Location:
    Ontario
    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 Spartan

    slipperybidness
    Joined:
    Jul 24, 2011
    Messages:
    5,553
    Likes Received:
    1,238
    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.
    • Agree Agree x 1
  9. Mr Moscode Audiophyte

    Mr Moscode
    Joined:
    Oct 22, 2016
    Messages:
    2
    Likes Received:
    1
    I sold stereos at a Lafayette store in Ithaca, NY the summer of 1970. At that time there were FTC rules that prohibited lying about power ratings and only RMS values were permitted.

    However the forces of commerce found their way into undoing truth in advertising, as they have found their way into undoing truth itself. Now you can say anything about anything. I say this as I listen to my 5kw cell phone. Which is better than a 4kw cell phone.

    That said the most brutal, power wise, test of an analogue amp is 1/3 power as it creates the most waste heat in the output stage. My Moscode amps could always do any output all day long with normal cooling. I never liked to over rate the amplifiers. The Moscode 300 actually does 165 wpc into 8 or 330 both channels driven. RMS, of course.

    I see plenty of cheap car amps that claim to put out more power than the fuse lets in. A shame, really.

    Class D - Digital amps - that's a whole other world of misinformation. If you really want to know what is what you have to read the paper that comes with the modules that the companies use. One of your other articles mentions IcePower and points to that.
  10. M Code Senior Audioholic

    M Code
    Joined:
    Oct 26, 2009
    Messages:
    643
    Likes Received:
    177
    Location:
    Joshua Tree, CA
    What is pertinent for an audio amplifier be it analog or class D..
    Is "What are its output capabilities as the load impedence decreases..."
    Note that loudspeakers are not like the load resistors (only resistance) used in a lab test, as the impedence decreases as the amplifier is drawing more current.. So the power supply and its capabilitites must be capable to deliver enough voltage/current to support teh amplifier stage or else the resulting power output drops big time. The other part of the equation is @ what frequency is the amplifier being asked to deliver and for how long.. The lower the frequency and the longer the time is demanded of the output amplifier/power supply the more demanding the requirements..

    Just my $0.02... ;)
  11. Mr Moscode Audiophyte

    Mr Moscode
    Joined:
    Oct 22, 2016
    Messages:
    2
    Likes Received:
    1
    In general, you are right.

    There's more to it than that. Electrostatic's impedance drops the most at high frequencies but there usually isn't that much power demand in the upper 2 octaves. Efficiencies of speakers in general are not measured broadband so that info is a missing variable.

    Some speakers like Magnepans are essentially resistive loads.

    Usually the impedance goes up as you approach the resonant F of the speaker.

    There are so many things against music being rendered realistically it's amazing it works at all.
    • Like Like x 1
  12. zapzap Audiophyte

    zapzap
    Joined:
    Apr 21, 2016
    Messages:
    2
    Likes Received:
    0
    Yeah, with most manufacturers it doesn't matter whether they spec PMPO or average power; they're both lies. :D

Share This Page

  • RBHsound.com
  • BlueJeansCable.com
  • SVS Sound Subwoofers
  • Experience the Martin Logan Montis
  • CEDIA