What is the name of the tool?

Forgive my absence of knowledge, but what is the name of the tool that one uses to measure the wattage coming out of ones speakers. I called it a watt meter to my family and got something that measures the watts and current coming from the outlet to the powered device I was using instead, for Christmas.  
Again, forgive my ignorance. I want to measure the Watts my amp puts out, not the speakers and I misspoke. I have no meters on my power amp so I want to know how many watts I am sending to my speakers at any given time. I hope that makes more sense. The decibel meter would be something I would be interested in as well, though. Thanks.
Amps don’t put out watts, they put out voltage. Speaker cables deliver voltage to speakers where it goes through crossover and coils all of which adds impedance, or resistance, which is good since without it the circuit would be a dead short and fry the amp.

So we have voltage, and we have resistance, which is good because this means we have amps which is current flow.

Which brings us to watts. You wanted to know about watts. Watts are units of power or work. Volts times amps equals watts. Its a silly thing invented by a guy James Watt who wanted to quantify the power of his new invention called the steam engine. Started with horsepower, how many horses it could replace. Wouldn’t happen to be interested in measuring that, would you? Too bad, its a fascinating story. They all are.

Anyway, watts changes with impedance. Speaker impedance varies from speaker to speaker. Impedance even varies within the same speaker depending on frequency. You see the problem, surely? In order to measure watts in any meaningful way we are going to have to know the impedance. Now you know why every amp power rating is such and such watts at such and such ohms. Its never just watts. Its always watts into ohms.

How in the heck are we gonna measure that?! Well, we’re not. We’re gonna measure the voltage and call it good. Which is what they do. Because really when it comes right down to it none of this has the least little thing to do with sound its all about cool stuff for guys who drool over cool stuff to have something to drool over.

So you hook up a volt meter across the speaker wires and watch the needle swing. The more old-timey the meter the better. And there’s a whole lot of things in this world I know, more even than you can imagine, but why guys drool over these meters is one I never will understand. They just do. And the more old-timey the better. The current gold standard for old-timey is Steampunk, which if you can nail that you can get a cool five figures for your three figure amp just like Danny D'. So go for it. And don’t forget to regale everyone with your new found encyclopedic knowledge of speaker power measurement. Preferably sans drool.
Hey Ricky,

They did sell them a long time ago at your average Radio Shack. Terms to search for are "RMS Power meter" or "speaker power meter"

Today your chances of finding one are best if you DIY them.

You may also want to see this thread:


It is true that for the most part, the accuracy was questionable due to the varying impedance of loudspeakers. Even built-in amp meters assume (incorrectly) that the speakers are perfect 8 Ohms, and extrapolate from the output voltage. The only way to make an accurate watt meter, without significant computing and speaker measurement, is to put some resistor in series with the speaker. Anything that connects in parallel will only offer an approximation.

On the other hand, these meters are usually good enough to tell you how close you are to exhausting your amp's output, so long as your speaker impedance isn't too low for the amp.  The limits of amps at high speaker impedance is voltage.  They cannot exceed their voltage rails.  So if you have a 100 W amp, and you have a meter (inaccurate as it is for Watts), keeping the amp from reaching 100 W on output will keep you from exceeding the voltage rail limits.

"Good enough for jazz" as they say.  It is a good experiment though, I think for most music playing you'll be surprised at how little power you use most of the time.


It’s called a VU power meter. Realistic APM-100 or Realistic APM-200. They were popular many moons ago. You might find one on Ebay if you do a search. This video shows how it works. Happy hunting!
Analog VU Power Meter Realistic APM 200 Review - Bing video

VU meters are a guess at best. Watts are frequency dependent and the real measurement includes the frequency and distortion levels, This requires expensive testing equipment. I have had amps with and without power meters and to tell you the truth, you don't need them. They are just cool to look at but they don't add one bit of useful information. When you clip your amp, you'll know it. If you have a high power unit, you'll break your loudspeakers first before the amp gives up. Plus it's not a good gauge to judge if you are near the limit, your ears or your loudspeaker fuses will catch it before your meters tell you anything. 
I have had amps with and without power meters and to tell you the truth, you don't need them.

Thank you guys very much for you answers while not being arrogant. This is why a newbee like me wants to stick around.

I love meters. Mcintosh makes their own meters and takes pride in their accuracy. I’ve learned a lot from them, especially how little power is needed to make a decent amount of noise. Save up for them,their worth the extra money.
"...Mcintosh makes their own meters and takes pride in their accuracy..."
I just sold my Big Mac amp with those gorgeous power meters. But my Parasound A21 (or the JC1s for that matter) don't have any meters and they sound better to me. 

"... especially how little power is needed to make a decent amount of noise..."
So you are using the power meters to see how little power you are using? 1 watt goes a long way.....
Meters are too slow unless they are instantaneous peak reading with decay, read voltage, not power, and only if you know the amp voltage capability at all frequencies.

Most meters come under the classification of jewelry and are installed for appearance ONLY.

In the studio, we had a wall of amps, all without meters. Many studios have amps in separate rooms due to fan noise and the ability to duct in copious cold air to keep them happy. In million dollar+ studios, if power amp meters were of any use we'd have purchased them.

If you want to really know, use an oscilloscope. You can purchase an Android phone/PC based unit for under $100 Loto USB Oscilloscope OSC482M for Both Android Phone/Tablet & Windows PC, 2 Channels, 50M S/s, 20MHz (Bandwidth), 8~13 bit Vertical Resolution: Amazon.com: Industrial & Scientific

You won't know what the power is as you don't know the speaker impedance at the frequency in question, but by using Peak Hold function you will know how close you are to clipping. If you see an flat top peaks, you are clipping and your tweeters are probably not long for this world.

One caveat of using a scope on both channels at the same time is they must have a common GND terminal. Most amps do, but some use bridged outputs and may be destroyed by commoning GND.
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Meters are visual and distracting. I had meters on amps before. The ones with no meters usually sound better.

I prefer music following lights.

russ69 is all that.

Unless you can calibrate them, they’re useless.
If can you need a known resistance and a scope to allow them to tell you next to nothing.

You will get better use out of that KILL A WATT.
Sansui made a light display "watt" meter. I had one in the 70s hooked to my AU 717.
Meters on amps aren’t necessary or really useful but they can be pretty 
Ampzilla with decade meters-4 orders of magnitude. VERY useful for training oneself, lower decade readings quite sensitive. I am a scientist, these things fascinate me.
Here is what it says in the McIntosh 501 owners manual.

• Illuminated Power Meter
The Illuminated Power Output Watt Meter on the MC501 is peak responding, and indicates the true power output of the amplifier. The Peak Watt Hold Mode allows the meter to temporarily stay at the highest power output and then slowly decay. The Front Panel Meter Illumination may be switched Off at any time.

I believe the meters are accurate. What I’ve learned from having them is I was amazed at how little power is used for normal easy listening. 1-2 watts does go a long way. Also when you crank it up I was amazed at how fast it can jump up and use several hundred watts.

I looked at the Parasound amps. Looks like nice stuff, I’m sure they sound nice. To me, they look a little plain. 
I’ve used a 1 ohm load resistor in series with the speaker. I measured the voltage drop across the resistor with an HP rms volt meter while measuring spl at one meter on axis with a B&K spl meter. Source is a sine wave generator. I^2*R=power. 
Back in the day, Technics made a SH-9020 Power Meter.  I not only sold them, but personally used one for quite awhile.  Pretty accurate if I remember correctly.

The Illuminated Power Output Watt Meter on the MC501 is peak responding, and indicates the true power output of the amplifier
No, they measure voltage. Power would only be correct for a pure resistance. Examine loudspeaker impedance curves. Some of the more egregious ones have a 10:1 impedance ratio.
I'm curious as to why this is relevant. Obviously you are trying to measure this for a reason. Can you explain?
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Back in the '80's I had a VU/RMS LED display that 'tracked' either with reasonable accuracy.  Was 'bout 2"h.x9"w.x6"d. ....

VU was easy, a line input wherever you wanted to tap in.

RMS?  Forget how that was accomplished, but 30+ years wipes some details away....  But it did illustrate that 1 watt (average) into a living room could be loud enough....

The 'peak' readings, however, could be pretty substantial.  150 peaks could drive one out of the room...

Merry Post-New Year....
"....you're probably wondering why I'm here...and so am I...."


"...not that it makes a hellava lot of difference to you...."
I was going to write something rude. Instead why do you need a wattage meter?