320 watts

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luke warmwater

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My buddy thought he was getting a kickin' new stereo.

The box stated 320 watts.

Then in the paperwork fineprint, he finds out that it is 320 watts at 100 hz. :eek:

I'm having trouble finding a formula to figure out what the wattage might possibly be at 60 hz.
 
Re: 320 watts

Todd.

That's 100 Hz. out of the speakers.

And my guess is that because they're being so specific about it, you wont find the promised wattage anywhere.

I used to be able to actually believe stereo specs. Many, many years ago. I'm sorry to say that now-a-days, stereo specs are more likely an attempt to decieve.

A once great country we live in.

Edit: In the old days, 20 years ago, the specified wattage was "each output".

Now, you'll be lucky to devide the wattage by the number of output channels and have that match what those channels will actually deliver.

Edit again: If you actually ask the thing to perform as you've been told it would, DUCK, it'll probably explode.

Don't blame China either.

[ May 11, 2005, 12:13 AM: Message edited by: physis ]
 
Re: 320 watts

Sam, thanx for the input.

With today's marketing schemes, I believe it would probably not be possible to figure out the actual rating (using math and their supplied ratings).
 
Re: 320 watts

You can if you feed it a signal and wait for it blow up. Now I'm just kidding. :D
 
Re: 320 watts

Todd
I have tried to use every known formula that would show where they are even getting these ridiculous figures from? :D
Hooked it up once in the house. It cost me three windows. :p

[ May 11, 2005, 03:05 AM: Message edited by: hurk27 ]
 
Re: 320 watts

is this a sub-woofer amplifier? You cannot determine anything without knowing frequency response curves which is expressed + or - db vs frequency. Anyway my bet is the wattage is really peak power which tanslates to 80 watts RMS @ 100Hz into 4-ohms.
 
Re: 320 watts

Why would you want to know how to do any type of conversion from 100 hertz to 60 hertz? I think you are mis-reading the paperwork.

I may be wrong about this, but I am reasonably sure they were not talking about 320 watts, given a power input source of 100 hertz, forcing you to figure out how many watts you get if you supply power at 60 hertz. Rather, what they are saying is that if you play a CD that includes the sound of a trombone, or the sound of me singing (heaven help you then ;) ), or some other relatively low tone, a tone that travels through the air to your ear at an air vibration frequency of 100 hertz (this would be close to the ?A? note in the second octave below ?middle C?), then the stereo system can blast that note out at a power level of 320 watts.

Are you asking at what power the stereo will blast out a note of 60 hertz (about the next note ?A flat? an octave below the ?A? note I describe above)? My response, again, is why would you want to know that?

[ May 11, 2005, 10:52 AM: Message edited by: charlie b ]
 
Re: 320 watts

There are many receiver specs out there that give a power rating in a range of frequencies say from 20 Hz to 20 KHz.

Luke, Charlie I believe is correct in his interpretation. The 100 Hz is referring to the frequency of the output sound. I apologize if I have also misinterpreted your post. :D
 
Re: 320 watts

If you really want to know what it will do you will have to do some testing. There is no "formula".

What you do is put the amp on the bench, connect an audio signal generator to an input and connect an oscilloscope, an AC voltmeter and an 8 ohm load to the output for that channel. The 8 ohm load needs to be a large non inductive resistor with a power rating in excess of what you expect you are going to get out of that thing. It should get hot.

Feed it a sine wave signal, 400Hz is a good starting point. Keep the level low. Set you scope to display a couple of cycles of the waveform. It should be nice and clean, no clipping etc.

Now crank up the level from the generator until you see the sinewave just start to clip. Note the voltage on the voltmeter. Use the formula P=E*/R to figure the power in watts. Where P= power in watts, E= voltage and R= 8 ohms.

Do this for other frequencies between 20Hz and 20KHz. You can plot a little graph on some graph paper or use Excel to give you the frequency response curve of the amplifier channel. This is the continuous RMS output which is the only thing meaningful.

Other tests would be with a 4 ohm load and with both channels driven to full output. Don't be surprised when the power supply sags badly with both channels driven and limits the outputs.

-Hal
 
Re: 320 watts

I read in a trade mag a couple years ago that one way they are getting there ratings is by using the SPL @ 1 meter Of an equivalent amp fed with a white noise signal that produces the same SPL of this amp that is only fed a very narrow frequency band. Then using the peek rating of that figure. A white noise generator produces the sum of all frequency's in the audio spectrum. Hence the 20hz to 20,000hz rating that was used in the specs a few years ago. When an amp spreads it's power across the full spectrum the SPL of a given frequency is much lower than if a very narrow band is used. So a amp having a 320 watt rating @ 20hz-20khz would produce the same SPL of a much lower rated power amp that was only amplifying just 100hz. This is a very bad way to make people think their getting more when there getting less. :mad:

By the way "SPL" stands for "sound pressure level" and is measured in Decibels, and for every increase of 3 DB's is a double in power. Peek is 6 DB's over RMS which means a double in power twice. An amp that has a 100 watt RMS rating will have a 400 watt peek ratting and the level for clipping would be the same but at the true RMS rating.

Just thought I would throw that in.

Edit to add that SPL is = to ERP (effective radiated power) in the radio frequency spectrum. and manufactures are taking advantage of this newer way to rate equipment even in radios like FRS and GMRS handy talkies.
It's still all bull to me! :mad: :mad: :mad:

[ May 11, 2005, 06:51 PM: Message edited by: hurk27 ]
 
Re: 320 watts

It's unusual to see you out at this time of the day Wayne.

I think I'll have to consider you to be one of the resident audio experts.

That system you've described above, dude. :cool:
 
Re: 320 watts

You know the killer part sam?


I now live in a trailer in a trailer park! :(

I don't dare hook it up. :mad:

AHHH the temptation.......
buttrock.gif
 
Re: 320 watts

Well, since you probably wont be there long, you mind if I bring one of these over :D
 
Re: 320 watts

Originally posted by charlie b:

I may be wrong about this, but I am reasonably sure they were not talking about 320 watts, given a power input source of 100 hertz, forcing you to figure out how many watts you get if you supply power at 60 hertz.
Click to expand...
Charlie B, I think you are absolutely correct.

When he told me about it, I was thinking of the input source, and just had that stuck in my head.

Thanx everyone for their input.

Wayne that was some set-up.
I used to use a set of PA speakers (300watts@ 8ohm each) as my stereo years ago. Who needed surround sound? I would crank it all the way up to '2' and the sounds would bounce off all of the walls.
 
Re: 320 watts

hbiss forgot that you have to divide the voltage read from the oscilloscope by square root of 2 to get the RMS voltage.

Also, if the power supply has a Big F*$@ing Capacitor it could supply a very short burst of high power audio with relatively low average power through the cord.

Getting 800 watts out of power transistors is rather difficult. You need about 8 power transistors with 4 of them paralleled on each side of a push-pull class AB or B amplifier.

What also confuses the issue is that speakers were p!$$ poor for efficiency before personal computers. In order to get speakers to work directly off of a computer audio board the efficiency had to be vastly improved.
 
Re: 320 watts

Could someone give me a definition of "RMS power"? When the term first got popular in the 60's, I couldn't figure out what possible use that number could have in describing an audio amp performance. Forty years hasn't helped any. (sigh) :confused:

carl

edit: Along with the definition, how does one calculate "RMS power"?

[ May 12, 2005, 12:15 PM: Message edited by: coulter ]
 
Re: 320 watts

?RMS? stands for ?Root Mean Square.? The simple explanation is that it means ?average.? The more complicated explanation is that you take the moment-by-moment value of any variable (could be power, or voltage, or current, or the daily changes in the price of tea in China), square each value, calculate the average of this set of numbers, then take the square root of the average.

For things that follow a normal ?sine wave? pattern, it turns out that the RMS value is always 70.71% of the peak value. In other words, divide the peak value by the square root of 2 to get the RMS value.
 
Re: 320 watts

hbiss forgot that you have to divide the voltage read from the oscilloscope by square root of 2 to get the RMS voltage.

No, I didn't. Notice that I said to put an AC voltmeter on the output also. Should be an RMS meter. Read the voltage off the meter, why make things difficult.

-Hal
 
Re: 320 watts

I like the way some manufacturers give "peak-peak" power. I wonder if they actually take the "peak-peak" current and multiply by the peak-peak voltage.

Lets see, to get the real power, you would have to divide the voltage by 2, then by sqrt(2), and then same for the current. So 8 watts peak-peak is actually 1 watt RMS!!
 
Re: 320 watts

Originally posted by charlie b:
... you take the moment-by-moment value of any variable (could be power, or voltage, or current, or the daily changes in the price of tea in China), square each value, calculate the average of this set of numbers, then take the square root of the average.
Click to expand...
Originally posted by charlie b:
?RMS? stands for ?Root Mean Square.? The simple explanation is that it means ?average.?
Click to expand...
Yip, knew most of that. Had to look up some to remind myself. concerning power, I stumble on the differences between Average and RMS. My thinking is that RMS and Average are completely different.

For example, limiting to unbiased sine waves, audio amp output application, driving to a resistive load: average voltage is zero, average current is zero. However, as you said, RMS values are .707Vpeak, .707Ipeak. RMS values are much more useful than Average.

So, how does one calculate the power delivered to the load - I don't think it is an RMS power calculation.

In keeping with the above limits, and defining the power to the load as effective heating (ie: equivalent DC V and DC A) I'm thinking the power delivered to the load is Vrms X Irms - Which is Average Power.

And ... I'm seeing a bunch of blank stares looking back wondering what difference this makes.

Well, one approach is: The power delivered to the load is .707Vpeak X .707Ipeak = (1/2)(Vpeak)(Ipeak) = (1/2)(Peak Power) Not .707(Ppeak)

I'm thinking Madison Avenue in conjunction with Unamed Industry Audio Groups came up with the term "RMS Power". After all who wants their amplifer to only have "Average Power". "By golly, there ain't nothin average about our amplifiers."

So, are they saying, "Let's take the sustained power we can put to the load and multiply it by 141%." That would be the math definition of RMS Power. Or, "We know its 'Average Power', but lets call it 'RMS Power' cause that sells better." Of these two, the second sounds more plausible, but then again my brain doesn't function well in the MA/UIAG world.

Or is it some other secret definition known only to users of new math and fuzzy logic. On this issue, I'm clueless.

carl
 
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