Audio terms BS and not BS

[Irvrobinson]

I totally get your point, Irv. I'm just adding that once you know how things should work, then it's easy to see through a trick like the one you first described... as long as there are three data points.

Electrically speaking, output should double when impedance halves. That's what we call an "expected result" under Ohm's Law.

Provided the power and output stages of an amp are of good design, then there's no reason why Ohm's Law shouldn't apply. But most often they are not. That doesn't stop the application of Ohm's Law and the interpretation of manufacturer specs.

Honestly rated gear may not double with halving of impedance but it will still increase power inversely proportional to impedance eg. 120W @ 8 ohms, 240 @ 4 ohms, 480W @ 2 Ohms.

What it can't do under Ohms Law is deviate from proportionality (eg. 120W @ 8 ohms, 240W 4 ohms, 400W @ 2 ohms) without some reasonable explanation that tells us where the watts went between 4 and 2 ohms. Manufacturers who don't make it clear where the power went can be legitimately accused of having a design with some shortcomings. Typically, this occurs from limitations connected to the power supply, output stage, or heat sinks (electrical resistance in metals increases with heat).

The real crime, however, is when there is an unproportional increase of power when impedance decreases (120 --> 240 --> 500). This is a clear violation of the laws of physics and, in almost all circumstances (except the one I outline below) evidence of a serious mistake or purposeful misdirection. Why? Because it makes no sense whatsoever that output should increase disproptional to impedance.

This only holds true when comparing like things (ie. 2 channels driven OR 1 channel driven). It doesn't necessarily apply when comparing two different things, like 4 ohm --> 2 ohm output @ 2 channels driven versus 1 channel driven @ 2 ohms in a bridged amp. Why? Because comparing two unlike things equally ignores the possibilities of efficiency gained through bridging.

So whenever I see stats that deviate from Ohms Law in any logical or meaningful way, I question whether the data is valid or invalid.

I hope this clarifies my previous post... it wasn't as much about what you wrote as the principles under Ohm's Law can be easily used to spot industry flummery.

I don't know who you're lecturing, Grim. Or perhaps you just like to do the forum equivalent of hearing yourself talk, and it's my post you happen to reply to. Whatever. You're being as tedious as a treadmill in this case.

 

[VonMagnum]

I saw that. Nowhere it mentions RMS power or how it is derived. Obviously you cannot tell me how, what products are used like Vrms or Irms.
I see that Vrms is .707 of Vpeak so the current must be the same.
I guess I could get peak power just by Vpeak x Ipeak. Would that be used to get RMS power? Or is there are secret function?
Could you tell me what is the power with 10 Vrms and 10 Irms is? Or that is , 100W but is that RMS or just continuous .5 of peak power? After all, RMS has a fixed function for sine waves. I can tell you that power is not .707 of the power peak so it cannot be RMS.
View attachment 28737

I'm not a calculus teacher (I last took Calculus 2 around 1997). But Google is your friend. It would take you five seconds to find what you're looking for (https://masteringelectronicsdesign.com/how-to-derive-the-rms-value-of-a-sine-wave-with-a-dc-offset/).

Edited (for accuracy):

RMS is a math concept used to find the DC equivalent of waveform. For a sine wave it's 0.707 of a waveform value, V or I. Average power is derived from Vrms and Irms values (P=Vrms x Irms). Amplifier advertising regularly states power values in "RMS" but these are not "RMS Power" but "Average" or "Continuous Power" values to not be confused with peak values often used to inflate numbers. (See: https://en.wikipedia.org/wiki/Audio_power#Continuous_power_and_"RMS_power"). Average power is the RMS Voltage multiplied against the RMS Current. Thus "100 watts RMS" means 100 watts average power not "RMS Power" as I gather this is what you're actually getting at as opposed to peak power ratings used to inflate sales numbers.

 

[GrimSurfer]

I don't know who you're lecturing, Grim. Or perhaps you just like to do the forum equivalent of hearing yourself talk, and it's my post you happen to reply to. Whatever. You're being as tedious as a treadmill in this case.

This is a place of knowledge. Ppl come hear to learn.

It doesn't work if nobody shares.

Critique noted. How's that handling issue going? Solved it yet?

 

[mtrycrafts]

I'm not a calculus teacher (I last took Calculus 2 around 1997). But Google is your friend. It would take you five seconds to find what you're looking for (https://masteringelectronicsdesign.com/how-to-derive-the-rms-value-of-a-sine-wave-with-a-dc-offset/).

RMS is a math concept for an average of the area under a sin wave or in other words the DC equivalent. It's 0.707 regardless of whether it's a voltage curve or a power curve. So yes, it's 0.707 of peak power. In other words, you tend to stay n the same units. If you measure a voltage in RMS, your power will be/should be in RMS also unless you convert. It's average/efficiency is not 100% because it keeps passing through zero, lowering the available power. This is one reason why three phase is used when more efficiency is desired (three phase spaces the sin waves of apart by 1/3 from each other so there is always a non-zero voltage available at all times).

Well, don't need all that calculus. And no, it is not RMS power. You still don't get it.
No need to invoke 3 phase or anything else.
All you have to do is do a simple, basic calculation that I have posted.
Here, let me help you:
10 V rms and 10 A rms will equal 100 watts. Now the question is what to call that.
Firstly, that 10 turns out to be 14.14 peak V and A. Better be.
Therefore peak power is 200 watts.
.707 of 200 watts is 141.4 watts. So, that 100 watt is not RMS, cannot be, period.
Here are two grabs from Hyper physics under RMS. No mention of RMS power but exactly what the above calculations proved, AVERAGE power.
RMS has only one meaning and it doesn't mean average.

P avg= V rms X I rms; average power, not RMS!

Yet, another. Since RMS is .707, guess what happens when you multiply .707 and .707 =.5 (average)

 

[VonMagnum]

Well, don't need all that calculus. And no, it is not RMS power. You still don't get it.

OK. I completely misread your questions as honest questions to understand RMS versus Peak values when it comes to an amplifier industry that regularly cheated on these numbers to make their products look better and sadly, I took time out of my vacation to try and point you in the right direction to find what I thought you were looking for even though I'm pretty rusty on the equations after 20+ years.

But in fact, it seems your sole purpose was to get me to make a mistake on 20+ year old memories of amplifier equations when I was quickly reviewing them (on my little vacation no less) so I "thought" I could help someone out. I didn't realize you were basically trolling. Well here here. You got me. I made a mistake (corrected above). Thanks for wasting my time responding and you can welcome yourself to my ignore list as I don't like wasting my time on mischievous hijinks.

 

[GrimSurfer]

Well, don't need all that calculus. And no, it is not RMS power. You still don't get it.
No need to invoke 3 phase or anything else.
All you have to do is do a simple, basic calculation that I have posted.
Here, let me help you:
10 V rms and 10 A rms will equal 100 watts. Now the question is what to call that.
Firstly, that 10 turns out to be 14.14 peak V and A. Better be.
Therefore peak power is 200 watts.
.707 of 200 watts is 141.4 watts. So, that 100 watt is not RMS, cannot be, period.
Here are two grabs from Hyper physics under RMS. No mention of RMS power but exactly what the above calculations proved, AVERAGE power.
RMS has only one meaning and it doesn't mean average.View attachment 28745View attachment 28746
P avg= V rms X I rms; average power, not RMS!

Yet, another. Since RMS is .707, guess what happens when you multiply .707 and .707 =.5 (average)

Ok. So where is all this leading then, cause as fascinating as calculus is I get the feeling there's a bigger punchline coming...

 

[TankTop5]

Obviously it’s more complicated but if you look at a receiver and it’s got a massive heat sink, huge capacitors and the side with the transformer weighs a ton it’s power rating is probably amazing. I bet if you looked at the specs vs weight you could almost graph the cost and value.


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[mtrycrafts]

OK. I completely misread your questions as honest questions to understand RMS versus Peak values when it comes to an amplifier industry that regularly cheated on these numbers to make their products look better and sadly, I took time out of my vacation to try and point you in the right direction to find what I thought you were looking for even though I'm pretty rusty on the equations after 20+ years.

But in fact, it seems your sole purpose was to get me to make a mistake on 20+ year old memories of amplifier equations when I was quickly reviewing them (on my little vacation no less) so I "thought" I could help someone out. I didn't realize you were basically trolling. Well here here. You got me. I made a mistake (corrected above). Thanks for wasting my time responding and you can welcome yourself to my ignore list as I don't like wasting my time on mischievous hijinks.

Trolling?
And, this has little to do with amps and lots to do with sine waves and calculating and having the correct terminology and about your professor and that new hole.
Wasting time?
Not if you realize and learned something. If not. then so be it.
Rusty? About simple RMS? Don't need those equations when you just remember .707 and 1.414. It is also one of those geometry functions of a 45 degree right triangle.
It is like knowing the multiplication tables, or a few decimals of pi, of sq rt of 2. Nothing complicated. Even used in carpentry by a good carpenter. Lots of places use that .707.
Even named an aircraft 707.

Ignore list? Yes, there is one on this board. Be my guest.

 

[mtrycrafts]

Ok. So where is all this leading then, cause as fascinating as calculus is I get the feeling there's a bigger punchline coming...

No punchline, just the use of correct terminology. So crucial for understanding and communicating.

 

[killdozzer]

Please list primarily common terms and somewhat not so common terms in the Hi Fi and AV world so that beginners like myself and others don’t get ensnared by marketing BS and recognize actual quality equipment when we see it. I’ll start with a term but lacking it’s meaning.


High order crossover:


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Just please realise that BS and Snake Oil more often than not comes from the utterance of an existing term. So it's very hard to distinguish among them. For example; "skin effect" real : "skin effect deteriorating your cables performance" Snake Oil.

This is the art of marketing BS; there has to be some truth to it and all else is distorted. Gold DOES conduct better - do you HEAR a golden conductor? Almost certainly not.

 

[PENG]

No punchline, just the use of correct terminology. So crucial for understanding and communicating.

Agreed, I wish people would recognize that making a mistake is not a big deal, just admit it, fix it or be corrected by others and move on without feeling upset. You have done so in the past afaicr, but I guess we cannot expect everyone to behave the same.

 

[VonMagnum]

Agreed, I wish people would recognize that making a mistake is not a big deal, just admit it, fix it or be corrected by others and move on without feeling upset. You have done so in the past afaicr, but I guess we cannot expect everyone to behave the same.

There's a difference between correcting a mistake or clearing up marketing terms and pretending to ask questions when you already know the answer. I'm wasting time looking up stuff I haven't looked at closely in 20 years while visiting relatives thinking I'm helping someone understand the marketing BS versus reality and they're playing ask 20 question games with terminology. Just spit your point out if you want to correct something. My time is worth something to me and I'm not on here to play refresher course games on things my current job doesn't typically use (I haven't even had to even use an oscilloscope in 18 years. It's usually not needed to repair the industrial equipment I work on. A multimeter and some circuit diagrams is normally sufficient).

 

[PENG]

There's a difference between correcting a mistake or clearing up marketing terms and pretending to ask questions when you already know the answer. I'm wasting time looking up stuff I haven't looked at closely in 20 years while visiting relatives thinking I'm helping someone understand the marketing BS versus reality and they're playing ask 20 question games with terminology. Just spit your point out if you want to correct something. My time is worth something to me and I'm not on here to play refresher course games on things my current job doesn't typically use (I haven't even had to even use an oscilloscope in 18 years. It's usually not needed to repair the industrial equipment I work on. A multimeter and some circuit diagrams is normally sufficient).

Okay I didn't realize you were asked a question. I have been here for a long time and I think I know mtry's posting style and am sure he meant well. This is most likely a case of misunderstanding.

 

[AcuDefTechGuy]

I don't know who you're lecturing, Grim.

Student: Why do we have to know all these physics formulas and concepts?

Physics Teacher: Well, duh, because once you graduate from college and have an actual career, you'll still be talking about RMS all day long on these audio forums!

 

[GrimSurfer]

I have two concerns with these sorts of discussions.

The first involves the tired old game called "stump the chump", where the intent of Q&A is intended to elicit a typo or small error so that the inquistor can then say "I gotcha... see, you don't know what you're talking about!". This is court room bull$hit and has no place in adult discussion because it assumes, without any evidence, that everything said up to the error was wrong.

The second is when such a discussion is intended to support a misleading conclusion.... such as, "if one can use calculus to determine RMS value from a waveform, then a peak or music power rating isn't misleading at all". That might sound good at first but it ignores time and frequency factors, when music power ratings are measured at a narrow frequency range over a vanishingly short time period. The first represents less of a challenge to transistors. The second makes it easy for capacitors to overcome poorly built power supplies or oversweep to be counted as meaningful output.

Not saying the intent of the posters was any of this, but rather trying to explain why parties get frustrated when threads take the turns they so often do.

I think it's best to say "I think you're wrong... and here's why" (there are many harder and softer ways to say this according to one's communication style) and be done with it. It's certainly more intellectually honest and makes for crisper discussion and better conclusions.

 

[Irvrobinson]

I have two concerns with these sorts of discussions.

The first involves the tired old game called "stump the chump", where the intent of Q&A is intended to elicit a typo or small error so that the inquistor can then say "I gotcha... see, you don't know what you're talking about!". This is court room bull$hit and has no place in adult discussion because it assumes, without any evidence, that everything said up to the error was wrong.

The second is when such a discussion is intended to support a misleading conclusion.... such as, "if one can use calculus to determine RMS value from a waveform, then a peak or music power rating isn't misleading at all". That might sound good at first but it ignores time and frequency factors, when music power ratings are measured at a narrow frequency range over a vanishingly short time period. The first represents less of a challenge to transistors. The second makes it easy for capacitors to overcome poorly built power supplies or oversweep to be counted as meaningful output.

Not saying the intent of the posters was any of this, but rather trying to explain why parties get frustrated when threads take the turns they so often do.

I think it's best to say "I think you're wrong... and here's why" (there are many harder and softer ways to say this according to one's communication style) and be done with it. It's certainly more intellectually honest and makes for crisper discussion and better conclusions.

I must be misunderstanding you, so perhaps you can clarify. Are you saying that the smoothing capacitors in an amplifier's power supply function as a supplemental energy source for audio output?

 

[GrimSurfer]

I must be misunderstanding you, so perhaps you can clarify. Are you saying that the smoothing capacitors in an amplifier's power supply function as a supplemental energy source for audio output?

Re-read what I wrote. Did I use the term "smoothing capacitors"? Nope.

 

[Irvrobinson]

Re-read what I wrote. Did I use the term "smoothing capacitors"? Nope.

Then which capacitors are you referring to?

 

[GrimSurfer]

Then which capacitors are you referring to?

I was talking about capacitors that form part of a charge pump in a power supply circuit. These operate like a reservoir, feeding power to a circuit when the transformer cannot fully meet a time-based or current-based demand.

What you refer to as "smoothing capacitors" sound to me like coupling capacitors used in the output stage of a transistor circuit to damp oscillation and transients.

 

[TankTop5]

Just please realise that BS and Snake Oil more often than not comes from the utterance of an existing term. So it's very hard to distinguish among them. For example; "skin effect" real : "skin effect deteriorating your cables performance" Snake Oil.

This is the art of marketing BS; there has to be some truth to it and all else is distorted. Gold DOES conduct better - do you HEAR a golden conductor? Almost certainly not.

Good point, I’m sure more often than not legitimate terms are misused intentionally by marketing departments.


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