Is Minimum Continuous Power the Same as Rms

1. What is "Minimum RMS"?

   I've done some Googling but nothing definitive, except a general concept of continuous average power of output measured- the power is at a minimum rated for the published RMS. My Soundstream DA-1 manual states:

   "Conservatively rated at 200 watts minimum RMS continuous per channel, 8 ohms, 20Hz-20kHz, with less than 0.05% THD".

   So I assume that it "idles" at 200 wpc RMS- but can actually provide more "peak" power- or "maximum" RMS for short periods, if so driven (which I would never do). It's not a critical need to know here, but if I ever switch speakers to some that need the extra power, it would be good to know.

   Thanks!

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2. 

   Fisherdude Regular Dude - Super Mod Staff Member Super Mod Subscriber

   Oh, what a difference a comma would make!

   I'm guessing it meant "a minimum of 200 watts output, continuous RMS power..."

3. well ..r.m.s is short for "root mean squared " and is a calculation of voltage and ohms with the output just at dc clipping . so i suppose minimum could be zero r.m.s ..
   i think in your case the r.m.s is calculated well before dc clipping .so there is some overhead .

4. 

   Fisherdude Regular Dude - Super Mod Staff Member Super Mod Subscriber

   Continuous power

   Continuous power ratings are a staple of performance specifications for audio amplifiers and, sometimes, loudspeakers. Continuous power is sometimes incorrectly referred to as RMS power and is derived from Root mean square (RMS), a method for measuring AC voltage or current.

   In its 1974 Amplifier Rule meant to combat the unrealistic power claims made by many hi-fi amplifier manufacturers, the FTC prescribed continuous power measurements performed with sine wave signals on advertising and specification citations for amplifiers sold in the US. Typically, an amplifier's power specifications are calculated by measuring its RMS output voltage, with a continuous sine wave signal, at the onset of clipping—defined arbitrarily as a stated percentage of total harmonic distortion (THD)—into specified load resistances. Typical loads used are 8 and 4 ohms per channel; many amplifiers used in professional audio are also specified at 2 ohms.

   Continuous power measurements do not actually describe the highly varied signals found in audio equipment but are widely regarded as a reasonable way of describing an amplifier's maximum output capability. Most amplifiers are capable of higher power if driven further into clipping, with corresponding increases in harmonic distortion, so the continuous power output rating cited for an amplifier should be understood to be the maximum power (at or below a particular acceptable amount of harmonic distortion) in the frequency band of interest. For audio equipment, this is nearly always the nominal frequency range of human hearing, 20Hz to 20 kHz.
   In loudspeakers, thermal capacities of the voice coils and magnet structures largely determine continuous power handling ratings. However, at the lower end of a loudspeaker's usable frequency range, its power handling might necessarily be derated because of mechanical excursion limits. For example, a subwoofer rated at 100 watts may be able to handle 100 watts of power at 80 hertz, but at 25 hertz it might not be able to handle nearly as much power since such frequencies would, for some drivers in some enclosures, force the driver beyond its mechanical limits much before reaching 100 watts from the amplifier. The continuous ("RMS") value is also referred to as the nominal value, there being a regulatory requirement to use it. (From Wikipedia)

   http://www.hifi-writer.com/he/misc/rmspower.htm

   http://www.n4lcd.com/RMS.pdf

5. RMS may be imprecise to the layman, but it's the most useful way of comparing different amplifiers, and also of gauging the current capability in multi-channel amps. The closer the RMS power of a single channel driven is to all channels driven, the better the power supply's capabilities. Far better than "music power", which tells you...well, not a whole lot.

   Personally, I always liked ILS power - "If Lightning Strikes".

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6. Watch out for specs quoted as " xx watts RMS".

   There is no such thing as 'watts RMS'.

   Watts are watts, nothing more, nothing less. It is a measurement of power.

7. Maybe best breaking this down to simpler terms. An AC sinewave, spends a certain time at the top (+) peak of the waveform, a certain time at (0), and a certain time at the bottom (-) peak of the waveform. RMS, is basically an averaging formula between the two, aproximating continous DC equivalent, and usually about half the peak to peak value. Household electricity is actually 230v peak to peak, but rms value is 115v. The minimum rms value stated on amps, is what the amp will at least do. Can usually do a little more than rated though.

8. 

   Fisherdude Regular Dude - Super Mod Staff Member Super Mod Subscriber

   With all due respect to Renzor, in an attempt to make sure that we try to give accurate information to folks who are trying to learn, none of the above is correct.

   The RMS value is NOT the average of the top and bottom peaks. The average of the top and bottom peaks is zero.

   The RMS equivalent of a sine wave is NOT half the peak-to-peak value, it is 0.707 times the peak value. This is the DC equivalent of the varying voltage (or current) in a pure sine wave. The clearest way to imagine this is to visualize the top half of a sine wave made out of string, and attached to the horizontal axis of the graph at the zero points. Put your fingers inside the string and pull outward until you turn the sine wave into a rectangle. Your fingers in the corners will be 0.707 of the height of the original sine wave's peak.

   Typical AC house supply of 120 volts RMS has a peak value of approximately 170 volts, and a peak-to-peak value of approximately 340 volts, NOT 230 volts.

9. On the face of it, a minimum power rating says to me that the unit will put out at least 200W RMS. It's kind of redundant since the reader assumes it will put out what they say it will put out, so why bother saying 'minimum'? Sure, any group of individual units will vary somewhat, some will manage 205 or 212. I guess they could claim the average of all the ones they tested as the rating, but instead they're guaranteeing 200 as a minimum for any unit.

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10. ^^^
    Right, no need to make it too complex. "200 watts minimum RMS", simply means the amp will put out at least 200 watts. Considering they clearly state it's conservative I'd guess the 200 watts is a sandbagged number, perhaps to give the appearance of doubling down at lower impedance. Not that that's necessarily bad, just that it's probably not really a 200W amp.

11. even further. The "200 Watt" spec is based on a certain sine wave voltage applied that yields less than some distortion value.

    Assuming you like to hear your amp below clipping, this is a reasonable way to compare an amplifier for a given application.

    If your amplifier applications are different, such as with 1 or 2 ohm loads, you need to select an amplifier that is rated for such an application.

12. 

    kirk57 Some guy on the Internet Subscriber

    Actually, you should watch out for specs that do NOT specify power in RMS watts.

13. Minimum RMS power is the minimum maximum the amp will put out at full power. The minimum the amp puts out is typically zero at Idle.

    All Amps list RMS or continous power output. All RMS power ratings or continous sine wave power can be converted to Peak power rating's by dividing by .707. RMS power is not the same as continous power. Peak power can be expressed in RMS terms, and RMS continous power can can be expressed as Continous Peak power if desired, changes nothing!

    The FTC Standard just happens to be continous sine wave or RMS. The problem is music isn't a sine wave. Short term peaks play a role and arent expressed in FTC Rating's. That's one reason some 100 wpc amps (like NAD and Harmon Kardon) can sound like other 140 wpc amps in AVR's with the same RMS Rating.

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14. I think the jist (sp?), though, is that the term RMS is not related to watts. It is related to a voltage waveform. There is no wattage waveform, just a power number, perhaps related to heating, or calories.

15. 

    Fisherdude Regular Dude - Super Mod Staff Member Super Mod Subscriber

    Rather than continue to get lost in semantic soup, let me try to tie this up:

    All three of the above gentlemen are correct.

    The term RMS only applies to the analysis (measurement) of sinusoidal waveforms. Power is a rate of conversion of one form of energy to another, and does not have a "waveform". Technically there is no such thing as an "RMS watt".

    However, as Mark Twain once said: "Figures don't lie, but liars can figure".

    As everyone who has ever tried to wade through an endless AK thread on the difference between old watts and new watts knows, hopefully, there is only one kind of watts, but there are sure a lot of different ways to come up with the ridiculous figure printed on the outside of the box.

    One of the ways for a manufacturer to try to convince potential customers that the manufacturer's specifications aren't inflated is to use RMS measurements of voltage and current in all power calculations.

    And that's what "RMS watts" really means: The voltages and currents used in the calculation of power were all RMS values.

16. At the risk of treading into the semantics thing Fisherdude is trying to avoid, no, not all amps list RMS watts / watts RMS.

    If you look at name brand pro audio amps intended for a (usually, IMO) more technically-focused client, I believe you'll find they don't use the misnomers "RMS watts" or "watts RMS", et al. The ratings will be listed as "continuous average output power" or similar.

    

    Last edited: Nov 17, 2014
17. 

    Fisherdude Regular Dude - Super Mod Staff Member Super Mod Subscriber

    Yeah, but those are RMX watts.

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18. Continous average power is the same as RMS power the way the FTC measures them. By stating either FTC or EIA they have effectively listed RMS watts. If they want to sell them in the US and Canada (FTC) or europe (EIA) they must. EIA Ratings are similer to FTC, but with one channel vs 2, and at one frequiency, typically 1,000 hz. vs a defined range like 20 - 20,000 hz.

19. The actual FTC rating method talks about "continuous average output power", which is what's listed. It makes no association to the term RMS with respect to the FTC continuous average output power method, although it does make reference to RMS, peak, music, and some other terminology used to describe amp output by various mfg. But, again, "continuous average output power" without reference to RMS, is the FTC standard description.

    You can read it for yourself by looking up the various FTC amplifier rule documents.

20. Your right, I'm only seeing Average Continous power, it would be same as RMS I believe. It seem's most amps use the term RMS though. In either case the point is if we use FTC ratings to compare amps, we have a pretty good idea of their power output.

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