Why watts rms is not valid for audio amplifier power measurement

[@JohnAudioTech]

After reading some of the comments left here, I can see that I was not clear in my explanation. The help to clarify this, I have made a new video: kzbin.info/www/bejne/gpKkeoKahrmFgK8 It also has links in the description that may be worth checking out.

[@tonep3168]

Watts RMS was never meant to be “the best way” to measure actual power output, but the RMS standard came about due to the crazy ways that audio equipment was measured. RMS was aimed at stopping buyers from being ripped off when choosing an amplifier.

[@StringerNews1]

Nice subject to tackle! You are correct that "RMS Watts" would not be an engineering spec. That's because it's a _measurement_ spec that's been simplified so that people who have a fair understanding of DC theory but can't grasp the finer points of AC theory (with reactance in imaginary numbers and so forth) can see why average power is a desired measurement. It all hinges on testing with a completely resistive load, so even with complex waveforms, Ohm's Law can be used instead of integral calculus. Frankly in 2018 it's pretty amazing that the FTC had that much confidence in the buying public to deal with square roots and mean values 40 years ago, when scientific calculators were not commonplace! As we see from your graph, if we calculate power based on peak-to-peak voltage of a sine function, we get a number that's more than 40% greater than the mean. That's great news for marketing departments, but not so great for a consumer who just wants a number that correlates to listening to music. When the Institute for High Fidelity was formulating testing criteria that better reflected real world conditions, the gamut of reactance for the range of available speakers stood in the way of some standardized reactive test load. Dynamic speakers tended to be inductive loads, electrostatic speakers were mostly capacitive. The only fair measurement was one that took all reactive components out of the equations. That allowed the continued use of resistive test loads, and while not perfect, it was a pretty good compromise. Power that's derived from RMS voltage over a near-infinite time period is a tough but fair test, while peak power is designed to make big numbers. Given a choice of single scalar numbers to base my decision on, I know which one I'd pick as a customer!

[@jp-um2fr]

I could not agree with you more. It seems that any old system that gives BIG numbers is the one to use. One idea was 'music power' and to be honest that seems to have been dragged up again. In the UK we used to joke about 'Dixon's watts'. Dixson's is a electrical retailer that went through the telephone directory for really big numbers. RMS may no be entirely suitable for music but it's a solid standard that makes a good comparison between amps - unless you are stupid enough to quote 10% RMS distortion. It's bad enough the U.S. using pounds to weigh lorries, what will they do if they ever go metric, use grams. Use tons or tonnes they are almost the same. I'll get off my soap box now.

[@StringerNews1]

The bottom line is that any true Watt is a Watt subscript RMS. The whole reason why we have Watts in the SI is to measure the rate of energy transfer. It only follows that a rate that cannot be sustained for any length of time has problems. The people who use the synthetic "peak power" are the ones who are gaming the system. It's because of them that we have to discern between real Watts and fake ones in the first place. Nobody listens to anything a peak at a time.

[@janprinsloo]

Finally get it after so many years. Thank you John!

[@lawrencel3188]

Watts RMS is the equivalent AC power as DC watts, as both deliver the same heating value to a fixed load, so it was as good as any standard as any to keep the shady advertisers from inflating their specifications as they continue to do to this day.

[@kingsman428]

Yep, that's how it was taught and how we analysed it at college.

[@1959Berre]

A speaker is a variable inductive load depending on the frequency. The power delivered by the amp to the speaker will vary accordingly.

[@chrisbauer1925]

True, though power into a resistive load is a reasonable spec, as long as it is stated to be the load in the specs. Ideally the amp can also handle the same voltages into the same impedance magnitude at a 60 degree inductive angle, because that's a pretty extreme for speaker inductance.

[@mbaker335]

I remember when amplifiers were advertised with 'total music power'. They would drive an amp to 10% distortion, take the peak power and then multiply it by two because the amp was stereo. I far prefer an RMS figure which is a bit more honest.

[@1pcfred]

Remember when all audio specifications were bullshit? Pepperidge Farms remembers.

[@BobOberan]

John - Thank you! Having been an electrical engineer since I was born, it is good to see some common sense. I worked in the audio biz back in the 70s and 80s and since then in telecom and datacom. As you stated, one can take any signal, square its waveform, take the mean, and then take the square root. But with power it is silly and wrong. For voltage and current it is sensible - because the power that is produced into a constant resistance is proportional to the SQUARE of that signal. I've only seen RMS POWER used in audio products' literature. It is WRONG. Power is power.

[@victorjohnson7512]

RMS (root-mean-squared), is the "average" power over the 360 degree sinewave

[@ebarbie5016]

That would be average not root mean square. No physical meaning to taking RMS of v*i. You can only take an average of v*i over one fundamental cycle.

[@peterscrace3530]

There is nothing wrong with amplifiers being rated in R.M.S watts as opposed to P.M.P.O for example, however R.M.S power ratings mean nothing with considering the impedance of the load and over what frequency bandwidth and not just 1 specified frequency usually 1Khz. The proper way to express power output would be something like 100 Watts R.M.S per channel both channels driven into 8 ohms from 20Hz to 20Khz with 0.001% distortion, home theatre amps never have their power outputs expressed this way because none drive all channels at the same time at their rated single channel output which is very misleading for the average consumer. In terms of perceived volume speaker efficiency also plays a big part.

[@martinda7446]

There once was no issue, but in the late 70s and 80s people started advertising amplifiers the size of peanuts with stratospheric power. How they arrived at that power was with some sleight of hand and some artful use of the truth. It had to be explained to consumers that to arrive at the real power an RMS value of the voltage supplied to the load - (assuming the usual 1khz single tone as a test source) - was necessary, and the advertised 1000W suddenly became 5W ''RMS'' . It sort of stuck from there to show they were 'real' watts. Then of course some engineer got snooty and rightly said 'It's just WATTS' and so on. The law for false advertising and consumer protection was enforced with regard to power specifications. . Originally it was as John says the heating effect - equivalent to match DC. To heat water from 0-100C took 60 secs with 200V DC and took the same with 200V AC (RMS derived). All AC has historically been rated in RMS for that reason. The mains in the UK is peak to peak 678V measured, yet has a DC heating value of 240V. Amplifiers are specified into 8ohms unless told otherwise and have often two channels for stereo, but the specs are usually for a single channel driven into the load. Often the power with both channels driven will drop due to sagging of the power rail. Which can be significant as power is derived from the voltage squared. Hence two channels driven in mono antiphase with outputs taken from the positive terminals can give a four fold increase in power. Bridging is sort of a 'free' lunch.

[@victorjohnson7512]

Root/Mean/Square wattage (RMS) is exactly: 0.707 of the positive peak voltage of a waveform, multiplied by the mesured current. It is intended to represent the "average power" of the output signal applied to a given load (like an 8 ohm speaker).

[@JohnAudioTech]

It should be called continuous average power then because RMS watts is incorrect.

[@EVnewbie]

Good video as always John! I understand why the FTC did what they did--they needed some form of standard...heck, any standard back in 1973 to protect the consumer. They finally lightened up on wattage then--just because the world is funny, then home theater and EDM with very loooooong bass drops became a "thing". Now that wattage is rated for music such as kick drums and other short bursts, now movies have very long sound effects that hammer subwoofers relentlessly without a break for 10 to 30 seconds. Some EDM has bass drops that just rumble away. For that level of insanity, then RMS ratings continous sine wave testing would make sense. Funny how that works! I've seen professional amps rated at 1KHz pulses for 40mS bursts--marketing takes full advantage! People will bench test that amp and notice actual output power for 10 seconds of sine wave testing causes massive current limiting as the power drops 25 to 50 percent. So, always get full testing of an amp and for subwoofer use for EDM and home theater use, go for the one that has a power supply that holds up under sine wave testing. The 1KHz testing stuff should be OK for mains--be careful out there!

[@pafoofnic]

The R.M.S. standard was and is a good one. Are the past I.H.f., peak music power, P.M.P.O., I.P.P and other strangely calculated wattage powers forgotten? That's how they arrived with such an excellent system.

[@StringerNews1]

When I was a teenager and the hi-fi business was really taking off in the US, the IHF test suite was the consumer's best friend. Whether it was a FTC mandate or just a convention among reviewers was never clear to me. What I do recall was that makers of car stereo components were exempt, and their numbers were based on peak power and testing methods best described as "destructive". If any car amp actually made such an inflated number, it would be the last thing it did.

[@JohnAudioTech]

The 1974 FTC mandated standard is a very good way of representing amplifier power. I have no arguments against it other than they should have not used watts rms because it is technically incorrect. They should have said "continuous average power", which they eventually changed to.

[@StringerNews1]

I sure miss those testing standards, as well as some evolutionary changes that the AES has written but can't mandate. I especially like terminology such as "continuous average power per channel, all channels driven" and other specifics about how the test was conducted.

[@SJMessinwithBoats]

StringerNews1 I didn't know that about exempt car audio! Sanyo had a lot of bi amp stuff. Speakers, amps. The "audio spec" series had this "x watts into, ohms, no more than, x. distortion" loved that stuff. But what is "slew rate" exactly?

[@StringerNews1]

Brian David, all I know for sure was that car stereo amps were being sold with ridiculous power claims at the same time that home stereo amps made more reasonable claims. The statement "_x_ Watts minimum into 8 Ohms from 20 Hz to 20 kHz, both channels driven at (rated) THD+N" was a very precise statement designed to be as honest as possible. Car amps of the same era often said only "200W!!!" What that usually meant was a number calculated with a DC input voltage far higher than what a car alternator would make, only one channel driven by a single cycle of 1kHz at full clipping. They'd then plug the peak-to-peak voltage into Ohm's law to further exaggerate the number without technically lying. But to use anything but RMS voltage in Ohm's law is inherently wrong and usually dishonest. Slew rate is the rate at which voltage changes. When you see square waves used to test amplifiers, they're usually measuring the slew rate. Amps that limit the slew rate at as power and/or frequency increases are less versatile than those that can pass an undistorted 20 kHz square wave at rated power.

[@anorris1212]

Is the "CAT BREAK", a paid endorsement?

[@89.8kiwifm9]

Voltage across resistor x current through resistor = cat.

[@georgebliss964]

Watts RMS is good enough for me. It gives a yardstick for comparing the loudness potential of different amplifiers.

[@1pcfred]

Loudness is more often down to the speakers than the amplifier. I really don't care how many Watts an amp can push. Because if your speakers can't handle it you're not going to get the sound anyways. Highly efficient speakers are pretty loud at just a Watt too. 92+ DB sound pressure is not unheard of at even that level.

[@tomterrific9459]

Watts RMS is an incorrect term.

[@swinde]

Here is a little background explaining why the regulating authorities made rules to have a standard means of measuring audio amplifier power. Before this ruling companies used a term called "music power" which had another term but I forget the acronym. To acquire this rating the unit under test would would have its standard power supply replaced with a more "ideal" power supply. They would also used the "Peak Power" measured with this configuration. Some even used "peak to peak" numbers for their rating. Most of the time, an amplifier with 20 watts rms would have more real power than an amp rated at 50 to 100 watts using these deceptive types of measurement. Remember that the Power Supply is the heart of an amplifier. The tubes or transistors are just "valves" that control the power supply to amplify the input signal.

[@Centar1964]

RMS power is actually average power derived from the RMS voltage times the RMS current and is only valid for a sine wave...and seeing how most specs are rated using a 1000 hz sine wave it makes for good a measure to compare amps, etc. regardless if they call it RMS or average...average power would be the correct term to use but doesn't RMS sound better? ;-)

[@StringerNews1]

Craig, since the resistors were a known quantity, it was usually P = V^2 / R. No need to try to measure current, which can get tricky.

[@johnyang799]

StringerNews1 Current is very important aspect of amplifier you can't just ignore current!

[@jimmurphy5355]

High quality ac voltmeters are NOT reading the average voltage. They use a variety of methods to compute the actual RMS value of a complex waveform, and will give the correct answer (power delivered to the load) for any waveform, not just for sine waves.

[@tomterrific9459]

Average and rms are not the same value. They are not interchangeable terms.

[@snaprollinpitts]

very good explanation!!! thanks John.

[@ford1546]

For example, many factories or sellers write 200 watts on an amplifier to no more. often 200watt is max peak watt to not constant watts. Therefore, we need the word max and constant and can not only use watt.

[@supersilve]

I have been reading all the comments below but now I am still confused of what and how to measure the average power of a PA. I know that most of the power supplies used in audio are not regulated so the supply voltage will sag under load according the intensity of the music at that instant. I guess it will also depend on the type of music played. There must be some kind of procedure to check for at least taking the average power of a particular PA system. Can someone explain how to measure it?

[@StringerNews1]

Silvio, when you get into PA systems things can get really complicated really fast. There are also differences in what's desired compared to home audio gear. Here's a primer on what has been discussed from a PA perspective: www.prosoundweb.com/channels/av/understanding_the_nuances_of_crest_factor

[@supersilve]

Thanks very much for your reply, now that info is getting me to more understanding

[@StringerNews1]

You're welcome, Silvio! Happy to be of assistance.

[@CJWarlock]

Good explanation. The "cat break" was very funny. :) Thanks. Cheers!

[@62stormm64]

Could you help me figure something out with an amp?

[@mikedrz]

Umm I'm confused here, so are you saying they just changed the name to average but its still RMS? Because if you use rms voltage and current your power calc would also be in RMS?

[@StringerNews1]

The mean and average are very similar, but mathematically different when it comes to doing the calculation. For the end user it's safe to use them interchangeably most of the time. Think about this: the average voltage of a sine wave with equal positive and negative swings is always zero. In this context, you need to operate on the absolute value of the voltage to get a meaningful number.

[@mikedrz]

Thanks for the explanation. I think I missed that math class. Never fully understood SIN wave functions. I will have to continue using the same formulas, and explain the parts I don't understand as so sorcery.

[@StringerNews1]

mikedrz, it works with _any_ waveform. Thanks to Joseph Fourier we can break down any function into many sine functions. Just remember that you should never use Ohm's law to solve AC equations, and if you do, only RMS values will yield a truthful answer.

[@mikedrz]

StringerNews1 Ah yes good ol fourier analysis. I'd really have to dust off the textbooks if I wanted to revisit that.

[@StringerNews1]

mikedrz, you still have your textbooks?

[@bobwalker6756]

It's the amount of HEAT developed in a resistive load. That amount of heat is the same when the RMS value of ac voltage equals the equivalent DC voltage. In other words it takes 10/.707 or 14.14 peak volts of AC to create the same amount of heat in a resistive load as feeding 10 volts straight DC into it.

[@logiticalresponse9574]

The infamous rogue cat strikes again for the 1st time

[@SJMessinwithBoats]

My opinion is to look at the ratings. Then look at the device UL rating on the back of the amp. 120v 480 watts, is power consumered, max. So all maxed out the unit couldn't consume more than that. If an amp specs says 2400 watts, and then you look at the rear and it says 120v 200 watts, then you know that sucker isn't going to do 2400 watts except for a nano second.

[@jimdavis5230]

When you have an amplifier producing a clean sinusoidal output voltage and you connect it across a non-reactive load, you get a sinusoidal current flowing in the load which is in phase with the voltage across it. Now if you plot the power developed in the load it's not sinusoidal. The power waveform is very strange and never goes negative because you can't have negative power. I think that amplifier output should be expressed as an RMS voltage across a stated load before the onset of clipping.

[@chrisbauer1925]

AKA an average power in a stated load. It's equivalent. Either way the term "RMS Power" is pointless at best, flat out wrong at worst.

[@antoniograncino3506]

My kitty gets involved in my work also. But she is banned from the shop when I have open live electronics on the bench, for the obvious reasons.

[@glpilpi6209]

As others have pointed out it seemed a good idea to remove a lot of complicated mathematics and state the power in a simpler form that is understand by everyone and applies to all pieces of equipment .

[@chrisbauer1925]

I completely agree. It simply should have been labeled the max average output power, literally the same values. They were just incorrectly labeled RMS instead of average. The standard itself is fine. Its the mislabeling that is wrong.

[@kisspeteristvan]

it makes zero sense to me . can someone explain to me how can an amp that draws a max power of 300w from the wall deliver 7*165W ???? , it makes absolutely no sense( to me 40w seems real )

[@whocares3132]

Hi i have a question, Can you please tell me if 50watt per channel amplifier is enough for me?

[@flhusa1]

is there a meter or device than can actually measure watts hooked up inline to a speaker? thanks

[@1pcfred]

It is semantics though. Within the limited context of audio amplifiers RMS can have its own meaning then too.

[@chrisbauer1925]

Except that RMS is short for the mathematical expression root mean square, which is not what is being done to the power waveform for the rated power spec. It seems as though some people see it to mean continuous power, but it's literally just an incorrect way to describe the power.

[@octavmandru9219]

So how do we calculate the wattage of an audio amplifier then? The load is not resistive (can a speaker be considered inductive load?), the signal is not necessarily sinusoidal... I am more confused now

[@JohnAudioTech]

Speakers are reactive loads and are different from one to another of different models. It is easiest to use a purely resistive load for the power measurement. Due to the variations in the music signal, it would be difficult to use it to get a measurement, so it makes sense to use a pure sine wave.

[@1pcfred]

You can test an amplifier with a purely resistive load. No one says you have to drive a speaker then.

[@magottyk]

Watts RMS, or to put it more succinctly Watts (RMS). RMS is signifying what watt is what in this case. Watts is derived from AC Voltage at the RMS Value of that voltage and not peak nor peak to peak. If we use simple ohm's law VIR, what value is the Voltage? The only real value is V RMS. The current value is I RMS while the load is purely resistive R and not RMS for the standardised measurement. Once you start calculating inductance etc, you've got a whole host of potential variation and have created complexity where none is needed. Watts RMS is a consumer measurement that standardises the voltage and current used in the claims. While watts is watts and watts RMS is still watts, the inclusion of RMS tells us that there is no hype being applied to the claims. Whereas just using watts tells us nothing about how the claim was derived. I hate to break it to you, but marketers aren't electrical engineers and they have a fond habit of using partial truths in their claims. Like PMPO is the amount of power a system will survive measured in milliseconds or less, whether or not that system can deliver that power. Also is power or continuous average power the correct term when what is being measured is the VRMS into an 8 OHM load before clipping occurs. VRMS is what is measured but as the load is a fixed resistive load with voltage and current in phase, whatever the voltage is, will determine the current and that voltage times that current gives you power in watts. If V=32 and R=8 then I =4. If P= 128 and R=8 then I= root 128/8 (16) and V=IR. so for a 200 Watt RMS amp, that tells us that I=5 (root 200/8) and thus V=40 RMS before clipping. But of course 200W RMS sounds better than 40V RMS and no one wants a 12V RMS if they can have an 18W for the same price. Heck 16V RMS is only 32W and 20V RMS is only 50W, it's only 8 more V's but it's 32 more W's. All the RMS is telling you is that the claim is to a fixed standard of measured voltage whether the consumer understands that nuance or not, whereas continuous average power????? If continuous average power = the same watts measured with voltage RMS then isn't 200Watts RMS equatable as a real measurement when we can determine the RMS voltage from the watts nominated into a standard 8ohm load? Or if 4 ohm then the equations remain the same just the label would be 200W RMS 4ohm, with less voltage but more current. (v=28.3 I=7.07 ironically)

[@JohnAudioTech]

Most consumers don't know what RMS is anyways, so why use a nonsense measurement label for power? The FTC should have used continuous average power from the beginning. You don't see watts rms used in any books or papers published by electrical engineers because they know better.

[@magottyk]

Most consumers do know what RMS signifies even if they don't understand what it means. Everyone has a period of naivety before they learn about what they are buying, and if all they learn is that RMS is real and without it you cannot trust the rating, then that's all they need to do comparative shopping. Most salespeople selling quality components will happily explain RMS in simple understandable terms and most people looking for a quality sound system will do some research even if it's on the fly as they shop around. You hark back to electrical engineers and what they publish, yet fail to recognise what I said in my post regarding Watts (RMS), the bracketed term is a relative comparator. Watts RMS without the brackets is shorthand. If you want to get technical then continuous average power is just as wrong as that is never what is actually measured but is implied from the VRMS measurement through maths. You assume that watts RMS is a nonsense measurement when I clearly showed that from that "fake" measurement I can get real answers. You also fail to account for the fact that Watts RMS is actually representative and not a made up number and that RMS is used in the measurement protocols. Why do we have multimeters and "true RMS" multimeters? What does "true RMS" signify in that instance. One word TRUST. Watts you can trust is what watts RMS signifies to the common consumer

[@philvincent3157]

From a person that used to design & build audio power amplifiers in the 70's. Everyone knows that RMS = Really Macho Sound. On a serious note, you failed to mention frequency. Most folks used to quote X RMS @ 1Khz which was an average across the audio spectrum. It obviously changes with frequency as does the impedance of a speaker. I still believe that speakers should be marked with a 'z' for impedance & not the omega symbol.

[@GeorgeTsiros]

you're looking for the T&S parameters of the speaker, then :)

[@craign8ca]

I got a good laugh from the cat crossing.

[@passionearmiariacompressa883]

this is why in my early audio experimentation and technical articles on electronic magazines I used to measure amplifiers output as Vpp or Wpp (peak to peak): this is the real voltage swing on the load, this is what you see on your oscilloscope. Then someone told me this can make confusion and I started to use the standard, converting peak-peak power to RMS. But for me this remains un unsolved question

[@jeffmassey4860]

RMS wattage is good only for a sine wave. Who listens to tones,anyway? Square waves,as in a synthesizer,would "sound" louder and pull more juice out of the amplifier stage. But I guess having a standard that every MFR adheres to is good.

[@StringerNews1]

"RMS wattage is good only for a sine wave." That's not true. In theory any signal that causes a resistor to make heat is valid. When the math was done by hand, it was easier to do sinusoidal functions. As computing capacity increased, more complex test signals such as a sweep from a low frequency to a high one replaced steady state tones. They were in turn replaced with bandwidth limited pink noise for some of the best tests. All you had to do is use a calorimeter to accurately measure the heat output. Square waves were used to measure slew rate, mostly. Some reviewers made a big deal over the "tilt" of a square wave coming out of an amp, but that was a pseudo-scientific analysis.

[@amb3cog]

"Who listens to tones anyway?" Me. I like Tone Loc, and The Deaftones. 😁

[@StringerNews1]

No love for the "Tone" in "Tony! Toni! Toné!" eh, HH?

[@amb3cog]

StringerNews1 Nah. Not my bag man. :)

[@StringerNews1]

LOL, not mine either! I have no idea how that factoid made into my brain. That's all I got though. Cheers!

[@rogeronslow1498]

John you are dead wrong. Specifying the RMS output power into a certain load is ideal from an engineering point of view. It allows an engineer or knowledgable enthusiast to evaluate the amplifiers capability under steady state conditions. It is also done in all other areas of electrical engineering when evaluating electrical equipment. If the audio amplifier is able to output so many Watts RMS continuously then an engineer can determine many things about the amp. In the past shrewd marketing allowed companies to claim ridiculous output powers from tiny radios/amps. They justified this by saying that the instantaneous power at the peak of a drum beat represented the quoted power. This made the amps seem much more powerful than they really were. Marketing nonsense. By insisting on quoting an RMS output power it eliminated the marketing nonsense and established a standard that was easily reproduced in any test lab.

[@JohnAudioTech]

I think you misunderstand what I was saying. The FTC standards is great at giving us the proper power figures, but they stated it wrong. They said "watts rms". They should have said "continuous average power" in watts. Stating watts in rms is meaningless.

[@johnyang799]

JohnAudioTech Oh then why imply such thing in the title? Why not say that Saying watt rms is wrong or there is no such thing as watt rms?

[@johnyang799]

JohnAudioTech If you are reading some some what professional audio equipment datasheet you will see Pa meaning power average Ua Ia etc, with the a in the right bottom corner.

[@tomterrific9459]

Watts rms is an incorrect electrical engineering term. *_Watts are Watts_* . Watts (continuous) is appropriate, Watts rms is something somebody made up.

[@1101nz]

RMS is not the same value as average . .707 & .637 True average voltage is of course zero in AC :-)

[@jo2lovid]

That depends if the AC wave is referenced at zero volts. But AC can float above 0V and might not even need to pass below that, and will still be AC

[@kenfoland]

Joanne, please correct me if I am wrong. But, wouldn't that actually indicate an AC wave riding on a DC offset. If measured ignoring the DC offset, shouldn't the AC amplitude still average to be 0 over time?

[@ryangatling2973]

That's why it is called root mean square. Squaring the output removes the negative component ( remember negative times negative is positive). The you take the square root which will be negative and the average is of the area under the curve is 1/SQR (2).

[@Synthematix]

Watts are a mathmatical equation and end result of power, (amps and volts) you dont hear watts you hear decibels and sound waves

[@SJMessinwithBoats]

Same thing for car stereo. A 5 amp fuse and a 1000watt rating is just wrong. The rms ratings have worked for me, for 40 years, better than overinflated peak values, going down hill with a tail wind, sort a speak.

[@1pcfred]

If your amplifier runs at 200 Volts 5 amps gives you 1,000 Watts. One thing I have noticed working with audio amplifiers is that for any output running voltages seem to track that too. What I am saying is higher wattage amplifiers generally run at higher voltage than lower powered amplifiers do. That is to keep current at a manageable value. But your example is a bit off the beam in general application. 1,000 Watt amplifiers would be around 100 or so Volts. That lands you more in the 10 amp range then. There's practical reasons why these values are normally traded off.

[@SJMessinwithBoats]

Paul Frederick , thanks, I was talking on a car amp. 12volt in. Yes I realize there is step up voltage inside. My 50wpc runs at 36+ and 36- rails. Push pull class AB. My point is for me, it is simple to look at the input rating (fuse)and figure out if it's inflated on the output watts.

[@1pcfred]

Yeah car amps are a particular brand of snake oil. A 5 amp fuse in a car suggests a max of about 67 Watts. But if everyone in the industry is full of it individual manufacturers have to follow suit in order to stay in business. The blame ultimately lies in the consumers though. Because by being ignorant they've allowed the situation to arise in the first place.

[@SJMessinwithBoats]

Paul Frederick, I hear ya on that. I worked as line mechanic at new car dealers most of the 80's. That biz is simular to audio of most types. Now, I work in rental property maintenance, a little better for me,

[@laurispeterisvejs4007]

@JohnAudioTech Hello! I'm here for a fast response and help. I have came to this video because this is the latest one. I'm here from your video " Connecting mono to stereo amplifier or stereo to mono amp?" The thing is that i have stereo speaker and stereo amplifier, but i have only 1 subwoofer. I have desk speakers that are connected to another amplifier. Im interested to use your first method of bridging the input signal from my pc. Is that okay that i only use 1 output chanel of my amplifier and leave the other one unussed? I can't to the second method, because the big amplifier is "Music Centre" (that means that its so complicated that i dont understand anything in it) Waiting for your reponse (:

[@1959Berre]

Cat says: "... couldn't care less..."

[@claycoates5056]

RMS is no more then a standard for a means for a delivered of power thing get neat when a high thrust small diameter magnet speaker can reproduce more sound then a high thrust big diameter magnet speaker the problem with high thrust small magnet speaker is that the talerence for any distortion OK RMS is poor for any true rating for am over amplifier speaker combination but RMS is still a definable stranded the one thing in the meserment of sound that is not defined is how the sound is produced and then reproduced from analog to digital thank you for your attempt to explain liked the video Dr. C

[@DruNicholsMD]

cat break made me laugh

[@Roderick_Legato]

RMS = root of the mean square, not root mean squared

[@JasonLeaman]

Good video !!

[@radu3g]

I don't understand what you mean by showing that .707from V peak is not RMS. Average is not RMS. Music is not always pure sine wave so the RMS value is can not be calculated as .707 x Vpeak. That's why good meters try to measure RMS value. If you want to use peak value of the AC signal then you have peak power. But so far, the only way to evaluate accurately the power of an amplifier is by running it with sinusoidal signal, with a known RMS value. Or we can go back to funny claims like PMPO, which gives more power output than input.

[@johnyang799]

radu3g As long as it's a standard, It's comparable and comprehensible. If not using rms or in this case 1khz sine wave rms, it will be a huge mess.

[@1pcfred]

Who says an amplifier has to be tested with a music signal?

[@jeddak]

I'd have to agree - watts *are* a mess.

[@gokulmahesh5757]

I bought sony htrt3 5.1 sound bar system the input power is given as 85 Watts and the RMS output was given as 600watts what it mean I have no idea but I think that in india 220v AC provided for single phase and now in this system I think by a rectifier or an SMPS might draw 12 volt and 7 ampere that total power is 84 Watts hence input power directly proportional to output power but limitation is losses in power like heat generated but what these companies say about their home theater systems by fooling people I don't know

[@Willam_J]

*** DOG BREAK *** kzbin.info/www/bejne/iaSudqpufN2Cms0 - That’s my pup. LOL

[@sachim3748]

Sir i have 4x55w speakers with 5 ohm impedence. Can i connect them to 1500 w pompo amplifier. . Please reply

[@Dazzwidd]

why? please reply...

This may be false logic- but how in hell can an amp ADVERTISED as 100 watts per channel only draw UL listed current of 100 watts from the wall? We should all be suspicious of ANY amplifier claims of output-no amplifier is 100% efficient and most tube amps are about 45% efficient and Solid state,maybe 50-60% efficient. If you look at the printed power requirements on the amp itself and it says 100 watts- only the most uneducated consumer would interpret that as its output power.To get the amps real output power under a DEFINED set of circumstances,as the LOAD from most speakers varies with frequency content and time constant,adding in capacitance from the feed wiring and crossover networks and resistance from the voice coil(s) A pretty tough job for any amp manufacturer,because he cannot be totally honest. It's true-Your Mileage May Vary.That slogan is good enough for the FTC.Just having 110 VAC or 120 VAC in your house wiring can make a huge difference in specs. But anything is better than some Chinese manufacturer advertising 1000 watts RMS on a $39.95 amplifier when some buyers will believe it.Some salesman will hook you on it. Now you are smarter than that Thanks,John for your videos and explanations.

[@voxpathfinder15r]

Power loss through a resistor is the square of the current multiplied by the resistance, you got lucky with your 1 amp current, but if it was anything but 1 your result would have been wrong.

[@JohnAudioTech]

First I showed the direct calculation to find power in watts knowing the voltage and resistance, E^2/R=P. Secondly, I used the indirect way to find the power by finding the current first. E/R=I and then E*I=P. I did NOT use I^2*R=P to calculate power (although I could have). I said voltage across the resistor times the current through the resistor.

[@voxpathfinder15r]

Voltage drop across resistor multiplied by current is kind of a funny way to do things. That's usually reserved for the seat of EMF i.e. E*i=P. I guess that can work - but you are talking about a circuit, which only contains a single element resistor apart from the EMF source. In that case you can't go wrong. I am thinking of circuits where you would have multiple items of resistance, capacitance, inductance, and a seat of EMF.

[@JohnAudioTech]

How is it funny? If you know the voltage, current and resistance, power can be calculated by using one of three formulas. No one is more or less correct than the other and certainly not "funny". A circuit dealing with complex impedance (inductance, capacitance, resistance) can have multiple ways of being solved mathematically depending on the known values. None of them will be more or less correct or "funny".

[@voxpathfinder15r]

I am not saying you are wrong - just not what I am accustomed to. Say you look at ohm's law V=IR and you want power you multiply both sides of that equation by i, and you get V*I= I^2*R - it's just natural how that drops out, the power for the seat of EMF of the circuit is E*I and the power losses for the resistive elements are I^2*R. But yeah, you're right alternatively you can think of the voltage drop of each independent resistor by going back to ohm's law and calculate V*I. I just say it's funny because for some reason I've never done it that way. In my mind when I think power loss of a resistor I automatically think I^2*R.

[@chrisvinicombe9947]

I miss din ratings.

[@kingsman428]

That's been replaced with *DIM* ratings

[@shaun9107]

thumbs up right there cat smart that was funny

[@brunobassi2440]

2019! I want a 100w x2 amplifier that will give me the power from 3.4 hom to 8 hom with a distortion of 0.01% from 0.1 watts to 50 watts and that never exceeds 0.2% .... this turned on for 1 week. bandwidth 10hz 80khz + - 0,25db 0,1 - 50 watt.... (+- 1db with phase rotations + - 60 degrees with 25 watts) otherwise we can remain in the stone age

[@89.8kiwifm9]

There's no such thing as watts RMS. Watts are watts, nothing else.

[@StringerNews1]

89.8 Kiwi FM, there is such a thing as real power vs. apparent power and reactive power. The radio station in your handle probably uses a Class C amplifier stage between the exciter and the antenna for efficiency. Because this class only amplifies about 90 degrees of the full waveform, it needs a reactive tank circuit to fill in the gaps. To make a long story short, it's the real power that does work on the antenna, and that is less than the apparent power. With audio amplifiers there's a similar situation where the maximum instantaneous "peak" voltage that the amplifier can generate ephemerally cannot be sustained. Because of that, the average (or mean) sustained voltage output is a more important figure in real world conditions. "RMS power" is a direct function of that sustained average voltage number. Neither measurement by itself tells you the whole story.

[@johnyang799]

StringerNews1 Electrical engineering student agree on that.

[@tomterrific9459]

You are exactly correct. Watts rms is an incorrect electrical term. Period. Full stop. If Watts rms is supposed to indicate what an amp can supply continuously, then it should be stated as Watts (continuous). Watts are Watts.

[@kdas4085]

Cat crossing 😂

[@whozaskin3639]

Record More Snickers

[@timonarthur]

Hahah beat cat ever

[@0x07AF]

Cat Break!!!!!!