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Old 14th December 2012, 11:46 AM   #11
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Thank's a lot for the replys, I found what you said Tandbergeren very interesting.

So if an amps ratings following the FTC-norm is 50W, is this RMS wattage? REAL continuous power into a 4 Ohm resistive load? One thing is that I can't remember seeing any manufactureres that explains what norm they are following when giving their wattage ratings I can't wait to measure the wattage of the amps I have

About this dynamic wattage by the way. If an amp is rated for let's say 50W coninuous avarage wattage then stepping over this value would either stress the transformer by drawing too much current, or the output would start clipping because of too low voltage. How are they then getting this dynamic power? Are they simply stressing the ratings of the transformer?

Last edited by Plecto; 14th December 2012 at 11:51 AM.
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Old 14th December 2012, 12:05 PM   #12
DF96 is offline DF96  England
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The most honest measure of power is continuous average power of one channel at a relatively low distortion. You can increase the number without actually telling any lies by relaxing each of those conditions.

Continuous:
Most amplifiers can produce more power for short periods between periods of smaller power, unless they have a stabilised supply. So take the highest power, perhaps after a few seconds of silence to allow the main PSU caps to fully recharge.

Average:
Average power is what you get by calculating from RMS voltage or current. Just to create confusion, many people call it RMS power. Assuming a sine wave, you can immediately double the power by specifying peak power instead of average. Note that this meaning of peak can be confused with the previous (non-continuous) one.

One channel:
Just multiply the channel power by the number of channels. In some cases it is not possible for all channels to deliver full power simultaneously, but ignore this.

Low distortion:
By going to, say, 10% distortion (whcih could be quite severe clipping and sound nasty) you can add maybe 20% to the power figure.

By combining all these measures you can boost amplifier power by a factor of between 5 and 10, without actually telling any lies.
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Old 14th December 2012, 12:09 PM   #13
AndrewT is offline AndrewT  Scotland
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Read the maximum unclipped voltage into your test load.
Convert that voltage to a power equivalent.
That is the simplest.
You need an oscilloscope, a voltmeter and a dummy load.

If you want to meet a specification then you need more equipment, as a minimum, a distortion meter
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Old 14th December 2012, 04:16 PM   #14
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Quote:
Originally Posted by Plecto View Post
Hi. I didn't find a better place to put this thread so I'm giving it a go here

I have allways wondered about the wattage ratings of different amplifiers. Some are giving off huge ratings, like 7x200W while others advertise "real watts" and then put out a more modest number. How do they find these wattage ratings? When IE. NAD talks about "real watts", are they talking about an avarage wattage into a 8Ohm load for an indefinite amount of time? Or are they still talking about some peak wattage that lasts for 1ms? The reason I'm asking is because I wan't to try and sell amplifiers in the future. It will be hard to compete with manufacturers that just picks a number out of thin air, puts a "W" at the end of it and paints on their amps. I wouldn't feel comfortable doing that :P
To explain a non technican user, how to understand a specified number of watts both at power amplifier and speaker is very difficult, because the value of these wattages depends on the following parameters:
1) output voltage
2) load impedance
3) internal resistance of power supply used in the amplifier (create the unwanted compression/modulation of the supply voltages depending of the individual output current flow).
Please note additional the follow:
- the load impedance isn't constant at the most speakers.
- the highest possible SPL is also depending of speaker's efficiency and not only from the RMS/program input power.
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Old 14th December 2012, 07:56 PM   #15
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Quote:
Originally Posted by AndrewT View Post
Read the maximum unclipped voltage into your test load.
Convert that voltage to a power equivalent.
That is the simplest.
You need an oscilloscope, a voltmeter and a dummy load.

If you want to meet a specification then you need more equipment, as a minimum, a distortion meter
Your existing amplifier power calculation takes no account of thermal compression speaker. Or in other words, do not take into account the power supply of the amplifier.
For example, if you apply the formula proposed in two separate cases:
a) 100W audio amplifier powered by one 150W PSU;
b) 100W audio amplifier powered by one 300W PSU;
in both cases, according to your formula, we obtain the same power (say, a maximum error of + / -1%), but it is not.

Now, let's clarify a few things that are misinterpreted theoretical - I think deliberately - by many manufacturers of audio amplifiers:

- Some manufacturers of audio amplifiers calculates the power amplifier taking into account the peak to peak value of the voltage on the speaker and not RMS value. A big mistake, unacceptable.

- Then, the PMPO power is calculated according to the value of filtering capacitor which accumulates energy and it can be downloaded in a certain timeframe. For example, suppose we have a filtering capacitor of 10000uF connected to a supply voltage of 35V. Capacitor that can play in 10ms about 600W. So, an audio amplifier is fed to 35V and has a capacitive 10000uF may 600W PMPO power. Some marketing departments calculated power reference to 1ms, to be more spectacular results. Another technique that is used to deplorable impress unsuspecting customers. Do not fall into this trap.

- Most manufacturers of audio amplifiers to render in stereo power specifications considering the measured power on a single channel. If you test an audio amplifier on both channels simultaneously, then resulting power per channel will be lower than if you tested only one channel. This was underlined by the user @DF96 above.
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Old 14th December 2012, 08:42 PM   #16
Pano is offline Pano  United States
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There are actually standards in place that are decades old. I've mentioned them above. Just like standards that exist in video, E.G. ANSI lumens for projector brightness. A standard that is well defined and easy to understand.

Whether or not manufacturers and their marketing departments wish to follow them is another matter. Cheating exists in all sectors of the economy.
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Old 14th December 2012, 11:11 PM   #17
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Standards have their own problems, such as enforcement, accessibility, national boundaries, manufacturer conformance and misrepresentation. They may have protected the consumer from a local manufacturer's false claims in some sectors of the audio market but somehow we now have more garbage numbers and worse confusion of the many, unqualified audio power ratings. These are applied differently across the entire audio/entertainment market, making it an unregulated mess of marketing hype and it's been that way since the term PMP was given legitimate marketing prominence decades ago, too. Big mistake, as now it is the only rating basis for many audio products!

We have had posts on this forum quoting 10,000 watt car audios and even my cheap little 2 watt powered PC speakers claim "90W" on the package! There is obviously now no need to qualify the audio rating standards used for consumer audio goods, because such masses of it sell globally without reference to any standard.

I think we (DIY amplifier enthusiasts) are in a small market sector that remains principally concerned with continuous, RMS sinewave power as one of many technical parameters for the serious assessment of amplifier performance. Well, we can understand, predict and reliably do the tests at least.

Unfortunately, standards and laws are only as good the authorities enforcing them but bigger numbers are always better, right?
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Old 14th December 2012, 11:17 PM   #18
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This has bugged me for a while with guitar amps. The most blatant I've seen was a "120 watt rms" amp that even printed "44 Vrms into 16 ohms" on the back panel. It used a quad of 6L6 tubes and was good for about 80 properly measured watts. All I can hope is that somewhere in their basement they have a vault. In that vault are 4 special 6L6 tubes that happen to conduct a lot better than any tubes you or I can buy. Those tubes are undoubtedly somewhat radioactive and actually generate their own power internally. If hit with a lawsuit they can install those tubes and say, "look, it does just what we say!" It's all marketing to sell against the more honest people out there. There oughta be a law.
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Old 14th December 2012, 11:58 PM   #19
forr is offline forr  France
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Default RMS power ? Peak power ?

RMS watts, or Root Mean Square, is a more reliable form of watts in an amplifier.

RMS power ?
Often stated, there is some misconception when mentioning RMS for Watts. They have no real meaning.
Just write Watts, nothing else.

Peak power ?
Speaking of Watts, many people forget that they are only calculated, the values which are really measured are Volts. And the conversion of Volts to Watts is is often misleading .

Lets say a sine signal of 8 V RMS voltage applied to an 8 Ohm load.
The power is 8/8 = 8 W
The instanteneous peak voltage is 8*2^0.5 = 11.3 V.
Can we say the the peak power is 11.3/8 = 16 W ?
I don't think so. Power needs some time to show its heating effect.
There is no reference of time elapsing in an instantaneous voltage.

Last edited by forr; 15th December 2012 at 12:09 AM.
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Old 15th December 2012, 12:11 AM   #20
WSJ is offline WSJ  United States
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My neighbor had a 30 year old stereo with 1,600 WATTS printed on front. It looked like a cheap chrome knob unit found at most yard sales for $10. I looked at the back and found the 120 VAC was rated at 1,600 WATTS. It sounded like a 5 W amplifier.
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