Truth in Amp Power Ratings

Discussion in 'Amps and Cabs [BG]' started by KPJ, Aug 18, 2005.

  1. KPJ

    KPJ Supporting Member

    Oct 2, 2001
    Methuen, MA USA
    I understand that different amp manufacturers use different methods to rate their amps output wattage (peak vs RMS) but I have a question for those in the know of how these ratings are determined. I have a mid-70's Acoustic Control Corporation 450 head. According to the owners/service manual, power output (continuous) across a 4 ohm load @ less than 5% THD output is 170 watts RMS ; peak power output (instantaneous) across a 4 ohm load @ 5% THD output is 450 watts. How does this translate to the way amps are rated now-a-days? If this amp was being marketed now, would it be listed as a 450 watt amp? My limited knowledge of amp ratings has come primarily from reading posts on this board, so I'm hoping someone here can clarify. From what I have read on Talkbass, it seems like Acoustic was merely describing how amps actually work, as in a 450 watt amp is not continuously pumping 450 watts into the speakers.

    Thanks in advance to anyone with some insight.
  2. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    I think ALL manufacturers now use the "RMS" power rating .

    It's mis-named, but standard terminology, since it is really "continuous average" power, which is based on RMS voltage and current values.

    There may be numbers added to that, Crown has had some forms of "single cycle" rating, as we have also. Those were intended to show the transient power peak capability, as in what it will produce as far as an "impact" with a single kick drum hit, or in our case, a single note struck. Those were still based on the "RMS" power.

    Others have had similar ratings.

    "Peak" power starts off being double the amp power, and as you probably meant, is just the power at the "peak" of a sine wave. Sometimes a bit extra is added because the measurement is done with a single pulse, and the peak is taken before the power supply voltages fall under load.

    Pretty much just a way to get a bigger number out there.

    It sounds as if that may be where the Acoustic's "peak" power rating came from. That 450W "peak" would be a reasonable difference from "RMS" if the "dynamic headroom" were a bit over a dB.

    Back then, it was common to "hype" the numbers as much as you could.

    That would be a 170W amp these days..... from pretty much any manufacturer.
  3. Lync

    Lync Supporting Member

    Apr 13, 2004
    "You can't handle the truth!!!!"

    -Amp Manufacturers

  4. I recently picked up an old Acoustic 370..and i know exactly what your'e talking about..this thing is loud...probably compareable to 900 to 1200 of "todays" watts