Is there any device to measure the output watts from a reciever? (1 Viewer)

[Pablo Abularach]

Hi,

I'm just concern about all the reviews I have being reading about manufacturers don't delivering what they promise or advertise (watts per channel)

So I'm searching for something to measure it. Do anyone know a gadget or instrument that I could use (like the radioshack DB meter), but for watts.

Thanks,
Pablo Abularach

 

[John Garcia]

Personally, I am tired of hearing this discussed. FORGET what the manufacturers say, forget what the magazines say, and go LISTEN to the receivers. Your EARS should tell you if it is good or not.

What really matters is that you match the receiver's power potential to the speakers you have or will buy. The amp should have sufficient power that it will not clip when driven at calibrated reference level with your speakers. If the amp can do this, it doesn't matter how much it actually puts out. I can tell you from experience, the 5200 has a very respectable power output, unless you will be driving large speakers, in which case I might opt for the 6200/7200.

 

[Matthew Speed]

Output on equipment is rated in watts because the FTC requires it be rated in SOMETHING. If watts mattered, than they would be called wattifiers, but alas my equipement has AMPlifiers... Additionally, the manufactureers have about 30 different tricks to get the output they desire for watts, THD, etc. If a manufacturer can get an amplifier to hit 100w for a split second before it blows, it gets a 100w rating. Most of the time, they are only driving one of the five amplifiers off the power supply anyway. Sound shady, it gets better; By rerouting the speaker output back into the input of the amplifier they can achieve rediculously low THD numbers at high outputs. Sometimes they do this on a narrow frequency. Never mind that they occasionally use 6 or 4 ohm speakers. Trust your ears but if you like spec sheets look for things like Sony's specs on ther TAN-1 ES power amp "200 watts per channel, both channels driven into 8 ohms, 20 to 20,000 Hz, at 0.005% THD" How rare are such candid descriptions? Very.

 

[GordonL]

I have being reading about manufacturers don't delivering what they promise or advertise (watts per channel)

Actually, the manufacturers usually do deliver what they advertise - it's how they advertise it that is the point of contention. The specs are worded in such a way that a casual reader could easily be misled. You just have to learn how to recognize what they mean. As far as amp output, if the specs don't specifically say "xxx wpc, all channels driven simultaneously", don't expect it to. It may or it may not. IMO, this is one area where having a THX certification is useful for lower end products because being able to drive a hard load is required to get certified.

 

[Jon W (NoVA)]

Sure. They're called watt meters, plus you'd need an 8 ohm, 100+ watt dummy load as well.

But if you're willing to risk destroying your speakers and/or your ears you can always convert the SPL to watts.

All you need is the sensitivity rating of your speakers. You can also measure this with a volt-amp meter.

But still you don't know how much distortion there is ... so you'd have to hook up a real time spectrum analyzer (you can use s/w on your PC and a sound card) or use an oscilloscope.

 

[Michael R Price]

This might work. I haven't actiually tried it though.

Get a set of dummy load resistors and wire them to your receiver. Run the B output of one channel through a large resistance (like 300k) into your computer, or into an oscillioscope. Play a 1 kHz tone and watch the waveform as you increase the volume. As soon as the tops of the wave start to get clipped off, you have reached the amp's limits. Measure the voltage across the dummy load in AC volts RMS. Wattage = voltage squared divided by resistance.

 

[Mike Veroukis]

Just the other day I came across an interesting article on www.audioholics.com.
Let me just cut & paste the important section here... It's rather interesting I think and goes to show it's not just the lower-end receivers that make misleading power claims.

 

[Greg_R]

A multimeter and a few resistors should work (for measuring power delivery). I think Pablo understands that all amp specs are not equal (that's why he wants to measure).

...unless you will be driving large speakers...

Size has nothing to do with it. The speakers sensitivity & impedance control the amount of current required to drive the output to specific levels. Also keep in mind that speakers are not purely resistive loads. In particular, planar & ES panel speakers have a significant capacitive element.

 

[Kevin Parker]

I totally agree with gordonL, cause if we read the specification, they say that 75x5 which means receiver have the amplfiers for 5 channels whch can put 75w ot for each channel, but it doesnt say anything what happens when all the channels are being used. so guys I think our ear is the best tester ever produced

 

[Mike Veroukis]

Here's another interesting article from www.audioholics.com that shows how even Sound & Vision can make mistakes when measuring the power rating of a receiver. Just goes to show you can't believe everything you read!
- Mike

 

[Bob McElfresh]

Here is the real problem:
You cannot/should-not judge a receiver by just 1 watts-per-channel number.
Yes, the manufacturers try to push their unit so it stands out from all the others by putting 1 XXX number on the little display card.
Hopefully our members at HTF know:
- different frequencies of sound take different amounts of power.
- going from 2-3-4-5 speakers, changes the amount of power to the set.
- you CAN get more than the rated power from a receiver, but at the cost of higher distortion (and more heat)
- a receiver/amp actually stores a bit of power so it can output more than it takes in for a short amount of time.
Mike did a great thing by telling you the fine-print to look for.
I also really like this thread on Amp Power for Beginners .
But please: dont try and boil down all this complexity into a watt-per-channel number. You are better informed than that. And if you are not, do a search and then post to get some clarification. We will help you understand the issues.

 

[ThomasL]

I understand speaker sensitivity ratings but at what frequency is the test tone produced? I guess this follows up what Bob mentioned which is, it seems to me that it would be take more power to produce a lower frequency tone at 90db from one meter away than it would a higher frequency tone. Just the fact that more air is required to be moved. Does this make sense? This, I believe, is one of the reasons if you have a separate powered subwoofer, it shifts some of the burden off of your receiver/amp and onto the sub's amp and your receiver/amp is less likely to get "overpowered" pardon the pun
cheers,
--tom

 

[John Garcia]

Just the fact that more air is required to be moved.

It is not how much air is being moved, but how much power the driver uses to produce it's motion for a given frequency. You can have a large physical speaker with a small motor structure that might not draw as much current as a smaller driver with a much larger motor structure.

 

[ThomasL]

Thanks John for the explanation. I guess I should have qualified the frequency sensitivity question with the numbers that manufacturers state. i.e. are they required to use a sweep or is it 1khz?

And as far as how much power it takes to produce certain frequencies, it makes sense now. It will depend on just how efficient the driver is given the frequency it is trying to produce.

 

[John Garcia]

There are no requirements for how any manufacturer reports their numbers. I usually look for as much info as I can get. Often, better amps will list their ratings as a full bandwidth rating- XXXrated power @ 20Hz-20Khz. I believe that Sony even stopped rating their lowest model amps at only 1Khz. The whole debate of what actual power vs reported power is a debate that may never end, but I know that I just go and listen to a piece of gear and get the best idea of what it can do by hearing it do what it does.

 

[RichardMA]

If watts claimed meant anything, then my Yamaha RX-V2090
receiver rated at 100wpc(I used to have) wouldn't have been tripping it's protection circuit WAY before my Adcom 100wpc separate amps. If some company claims 120wpc across
6 or 7 channels and the receiver only weighs about 25lbs,
watch out!

 

[Jon W (NoVA)]

Actually, there is a FTC requirement for how manufacturers report their numbers, but it only applies to 2-channel stereo.

The FTC needs to get on the ball and setup some requirements for multi-channel too.

IMO, they should require minimally the following:

1) Power output to all channels driven, 20-20k +/- .xdB, xxx% THD, xxx% S/N

2) Power output to 2 channels driven, 20-20k +/- .xdB, xxx% THD, xxx% S/N

3) Power output to 1 channel driven, with other channels driven to typical home theatre levels, 20-20k +/- .xdB, xxx% THD, xxx% S/N

 

[ThomasL]

Actually, I was wondering if speaker manufacturers are
required to give speaker sensitivity numbers and at what frequency are those numbers reported? i.e. if it is 89db/1 watt/1 meter, at what frequency is this? i.e. is it true for the entire range that the speaker can reproduce?

thanks,


--tom

 

[Saurav]

Well, if you think about it, a speaker's sensitivity plot is the same as its frequency response plot. You're feeding it a fixed amount of electrical power at each frequency, and you're plotting the acoustic output, which is the same thing as plotting sensitivity at different frequencies. In most plots I've seen, the output at 1KHz is denoted as 0dB, and the rest of the frequency range maps out as +/- x dB around it. So, maybe the single 'sensitivity' number provided is measured at 1 KHz. Or maybe it's averaged out across the frequency range.
Interesting question. I do know that a speaker's sensitivity varies with frequency, because if it didn't, it would have a ruler flat frequency response.
Or I have this completely wrong

 

[John Royster]

I thought the sensitivity was the average over its rated frequency range. If you look at a frequency response graph you can generally draw a horizontal line through the plot...there's your sensitivity (approximated).

Don't know if the sensitivity is measured anechoic or not? Sometimes it is stated.