[Luxey]

�реда, 21. октобар 2015. 21.28.59 UTC+2, је напи�ао/ла:
On Wednesday, October 21, 2015 at 12:09:17 PM UTC-4, JackA wrote:
On Wednesday, October 21, 2015 at 11:23:03 AM UTC-4, wrote:
What is being measured is average power.
If you
take RMS current and RMS voltage and multiply, you get average power, not
RMS power. People call it "RMS power" but it isn't.



+1 exactly correct
Mark

I say it's "apparent" power, since it is AC, reactive.

Jack

If the phase angle between the voltage and current is 0 deg, (resistive load) then it is REAL power measured in Watts.

It the phase angle is 90 deg, then it is apparent power measured in VARs.

In between is a combination of both.

Mark

Once I had Eastern German guitar combo and it was rated in VAs,
I think it was 25VA.

Actually, I still own it, just can not remember to whom I've lent it and where
it is at the moment. Perfect clean sound, trust me. Very simillar to this one,
but not exactly the same, I think: http://goo.gl/lGc4Iq

[geoff]

On 22/10/2015 4:22 a.m., wrote:
What is being measured is average power.
If you
take RMS current and RMS voltage and multiply, you get average power, not
RMS power. People call it "RMS power" but it isn't.


+1 exactly correct
Mark
I guess the reason RMS became used was to differentiate from
more-misleading 'peak' measurements.

geoff

[JackA]

On Wednesday, October 21, 2015 at 3:28:59 PM UTC-4, wrote:
On Wednesday, October 21, 2015 at 12:09:17 PM UTC-4, JackA wrote:
On Wednesday, October 21, 2015 at 11:23:03 AM UTC-4, wrote:
What is being measured is average power.
If you
take RMS current and RMS voltage and multiply, you get average power, not
RMS power. People call it "RMS power" but it isn't.



+1 exactly correct
Mark

I say it's "apparent" power, since it is AC, reactive.

Jack

If the phase angle between the voltage and current is 0 deg, (resistive load) then it is REAL power measured in Watts.

It the phase angle is 90 deg, then it is apparent power measured in VARs.

In between is a combination of both.

Mark

Let's target unity power factor!

Jack

[Phil Allison[_4_]]

thekma...


The nice thing for you(or Scott, et al) to do is explain WHY
RMS isn't relevant. I know that RMS doesn't take into
consideration the frequency range of what's being measured,
but that's as much as I know so far.



** It all started back in the 1880s, when AC power competed with DC power for home and business lighting. Edison light bulbs operated at 110V, matching their DC system voltage and in order to compete the Westinghouse AC system had to be compatible. So the AC voltage was adjusted to give the same light output
as 110V DC and became known as 110V AC.

A bit of calculus showed that when this occurs, a sine wave AC voltage has a peak value 41% higher than the DC voltage. That math uses the heating effect of sine wave current to derive the equivalent DC value - forever after known as the RMS value.

The frequency of the sine wave does not affect the calculation and the concept was so useful it was adopted everywhere to describe the magnitude of sine wave voltages and currents.

When measuring the power output of an audio amplifer, using sine waves and resistive loads is an automatic choice and the calculation is made by squaring the RMS voltage reading and dividing that by the ohms reading of the load. The answer is simply watts.

To emphasise that the power figure being quoted was measured in this way, some makers added the term RMS after the word watts - making "watts RMS".

So an amplifier's power spec might say "Power output: 50watts RMS".

The next simplification was to write "RMS power: 50 watts".

Then some fool asks, " What the heck is an RMS watt? "



.... Phil

[Luxey]

On Thursday, October 22, 2015 at 7:12:42 AM UTC+2, Phil Allison wrote:
thekma...


The nice thing for you(or Scott, et al) to do is explain WHY
RMS isn't relevant. I know that RMS doesn't take into
consideration the frequency range of what's being measured,
but that's as much as I know so far.



** It all started back in the 1880s, when AC power competed with DC power for home and business lighting. Edison light bulbs operated at 110V, matching their DC system voltage and in order to compete the Westinghouse AC system had to be compatible. So the AC voltage was adjusted to give the same light output
as 110V DC and became known as 110V AC.

A bit of calculus showed that when this occurs, a sine wave AC voltage has a peak value 41% higher than the DC voltage. That math uses the heating effect of sine wave current to derive the equivalent DC value - forever after known as the RMS value.

The frequency of the sine wave does not affect the calculation and the concept was so useful it was adopted everywhere to describe the magnitude of sine wave voltages and currents.

When measuring the power output of an audio amplifer, using sine waves and resistive loads is an automatic choice and the calculation is made by squaring the RMS voltage reading and dividing that by the ohms reading of the load. The answer is simply watts.

To emphasise that the power figure being quoted was measured in this way, some makers added the term RMS after the word watts - making "watts RMS".

So an amplifier's power spec might say "Power output: 50watts RMS".

The next simplification was to write "RMS power: 50 watts".

Then some fool asks, " What the heck is an RMS watt? "



... Phil

Which is all fine, but putting label "RMS Power" on value of measured level
of a digital audio file?! What is the claim? Are they saying: "The actual
measured average output power, usually labeled RMS Power, of an amplifier
would be "this much" lower in dB(?)than peak level, on playback of this file
through that amplifier."?

[Gray_Wolf]

On 10/21/2015 3:45 PM, geoff wrote:
On 22/10/2015 4:22 a.m., wrote:
What is being measured is average power.
If you
take RMS current and RMS voltage and multiply, you get average power, not
RMS power. People call it "RMS power" but it isn't.


+1 exactly correct
Mark
I guess the reason RMS became used was to differentiate from more-misleading
'peak' measurements.

geoff

I think so too. There was the "Instantaneous Peak Music Power" that brought the
trade board into laying down the law.

[Mike Rivers[_2_]]

On 10/22/2015 4:59 AM, Luxey wrote:
Which is all fine, but putting label "RMS Power" on value of measured level
of a digital audio file?! What is the claim?

It's like "Output Level: +4 dB" - meaningless to people who don't
understand. But you care, I care, Scott cares, and unless it's from an
unreputable source (in which case I wouldn't care) we both know what it
means. What we don't know (and what some of us care about) is what the
maximum undistorted level (or with a specified amount of distortion) is.

--
For a good time, visit http://mikeriversaudio.wordpress.com

[Mike Rivers[_2_]]

On 10/22/2015 6:51 AM, gray_wolf wrote:
There was the "Instantaneous Peak Music Power" that brought the trade
board into laying down the law.

I once saw a set of powered computer speakers that said on the carton:
"200 watts." They were powered by a wall wart with a rated output of 12
v at 700 mA.

--
For a good time, visit http://mikeriversaudio.wordpress.com

[Randy Yates[_2_]]

Mike Rivers writes:

On 10/22/2015 6:51 AM, gray_wolf wrote:
There was the "Instantaneous Peak Music Power" that brought the trade
board into laying down the law.

I once saw a set of powered computer speakers that said on the carton:
"200 watts." They were powered by a wall wart with a rated output of
12 v at 700 mA.

Maybe that just charged a car battery...
--
Randy Yates
Digital Signal Labs
http://www.digitalsignallabs.com

[JackA]

On Thursday, October 22, 2015 at 8:12:51 AM UTC-4, Mike Rivers wrote:
On 10/22/2015 6:51 AM, gray_wolf wrote:
There was the "Instantaneous Peak Music Power" that brought the trade
board into laying down the law.

I once saw a set of powered computer speakers that said on the carton:
"200 watts." They were powered by a wall wart with a rated output of 12
v at 700 mA.

Seen that often. Bought a set of Jensen computer speakers (w/ bass & treble controls) when they had computer shows, maybe only $10. But the speakers had a massive linear DC power supply!!

Probably why Boss OFFERS NO SPECIFICATIONS!!

Jack

--
For a good time, visit http://mikeriversaudio.wordpress.com

[Phil Allison[_4_]]

Luxey wrote:



** It all started back in the 1880s, when AC power competed with DC power for home and business lighting. Edison light bulbs operated at 110V, matching their DC system voltage and in order to compete the Westinghouse AC system had to be compatible. So the AC voltage was adjusted to give the same light output
as 110V DC and became known as 110V AC.

A bit of calculus showed that when this occurs, a sine wave AC voltage has a peak value 41% higher than the DC voltage. That math uses the heating effect of sine wave current to derive the equivalent DC value - forever after known as the RMS value.

The frequency of the sine wave does not affect the calculation and the concept was so useful it was adopted everywhere to describe the magnitude of sine wave voltages and currents.

When measuring the power output of an audio amplifer, using sine waves and resistive loads is an automatic choice and the calculation is made by squaring the RMS voltage reading and dividing that by the ohms reading of the load. The answer is simply watts.

To emphasise that the power figure being quoted was measured in this way, some makers added the term RMS after the word watts - making "watts RMS"..

So an amplifier's power spec might say "Power output: 50watts RMS".

The next simplification was to write "RMS power: 50 watts".

Then some fool asks, " What the heck is an RMS watt? "



Which is all fine, but putting label "RMS Power" on value of measured level
of a digital audio file?! What is the claim?


** Looks to me they are claiming that levels in dB are based on an RMS computation of the music signal over some interval.

This is easy to do with a digital data stream and the result can be different from the common rectified and averaged levels as seen on VUs and LED ramps.

Since dBs measure *power* relative to some reference, I guess using RMS values is justifiable, but when dealing with signal levels in a recording system the peak value at a point in time is of more interest than the heating effect.



.... Phil

[Luxey]

On Friday, October 23, 2015 at 6:37:48 AM UTC+2, Phil Allison wrote:
Luxey wrote:
Which is all fine, but putting label "RMS Power" on value of measured level
of a digital audio file?! What is the claim?


** Looks to me they are claiming that levels in dB are based on an RMS computation of the music signal over some interval.

This is easy to do with a digital data stream and the result can be different from the common rectified and averaged levels as seen on VUs and LED ramps.

Since dBs measure *power* relative to some reference, I guess using RMS values is justifiable, but when dealing with signal levels in a recording system the peak value at a point in time is of more interest than the heating effect.
... Phil

My question was rather rhetorical.
It is obvious what their value is, but it is not obvious why they chose to
label it "RMS Power".

Of my concern was not "RMS" part, but "Power" part.

In dB is expressed ratio of 2 quantities of the same quality.
If one quantity is of "Amplitude Level" than other can not be of anything else,
including RMS Power.

[Luxey]

In response to my self ...

I've just decided to Google for the topic and found out very similar discussion
from the January 2009, with many of the participants being the same as in this discussion we are having now, here on RAP.

The discussion is located he
http://alturl.com/jf2zi

And what I tried to say here Mike Rivers is telling there, in post #7:
http://alturl.com/ffb2g

[Scott Dorsey]

In article ,
Luxey wrote:
In response to my self ...

I've just decided to Google for the topic and found out very similar discussion
from the January 2009, with many of the participants being the same as in this discussion we are having now, here on RAP.

The discussion is located he
http://alturl.com/jf2zi

And what I tried to say here Mike Rivers is telling there, in post #7:
http://alturl.com/ffb2g

Yes, and my suspicion is that if you look more carefully you will find the
same discussion over and over and over again going back to 1990, probably
with the same people saying the same things too...
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Angus Kerr]

I rather like knowing the power output of an amplifier quoted in Watts r.m.s. It may be a misnomer, but it is a universal standard, and gives me a nice fuzzy feeling. You can't really spin this figure, it tells the whole story.

How do we get r.m.s.? It comes from the following:

In ac systems, the voltage waveform is sinusoidal, so the instantaneous power delivered into a load pulses instead of being constant over a complete cycle. If one calculates the instantaneous power, it is proportional to the square of the voltage. If we plot the power curve over time, it produces a waveform that looks like a fully rectified ac waveform. Not to bore you with the maths, but in order to get what the average power dissipated in the load is, we have to integrate the instantaneous power over at least half a cycle to get the total energy, and then divide that by the time of the half cycle. What comes out of all of this is that the r.m.s. voltage of an ac waveform is the equivalent d.c. voltage that will cause the same average power dissipation in the load. If you do the math, it works out to the peak voltage divided by the square root of 2. The rms "power" is just the average power being dissipated in the load, as mentioned above, calculated by the rms voltage divided by the resistance (or more accurately, impedance).

If we have a partially inductive load, the current will lag the voltage somewhat, and can be split into two components: one that lags the voltage (or leads in the case of capacitive load) by 90 degrees and one that is in phase with the voltage. If we calculate "power" of these two components, the component at 90 degrees is called IMAGINARY power (in power engineering it is measured in VArs) and the other that is in phase with the voltage is called REAL power, measured in Watts, and the combination of both is called APPARENT power, measured in VA.

Now, as I mentioned before, I like watts rms, because at least to me, I know what the amplifier can deliver. I'm looking right now at my newly purchased Behringer B115W powered speakers that have a big fat sticker on them saying '1000Watts'. Checking the fuse, it's a 3.15A, so I would guess that it probably consumes 2A max, so more like it draws 500VA. Assuming the amplifier is 100% efficient, which it isn't - it can't produce much more than about 400W, rms.

Also, if I know the rms output power and the impedance quoted, I can calculate the rail voltage being used. But even then, if the power supply doesn't have the beef, even the rail voltage will collapse under load.

-Angus.

[Phil Allison[_4_]]

Luxey wrote:


** Looks to me they are claiming that levels in dB are
based on an RMS computation of the music signal over some interval.

This is easy to do with a digital data stream and the result
can be different from the common rectified and averaged levels
as seen on VUs and LED ramps.

Since dBs measure *power* relative to some reference, I guess
using RMS values is justifiable, but when dealing with signal
levels in a recording system the peak value at a point in time
is of more interest than the heating effect.


My question was rather rhetorical.
It is obvious what their value is, but it is not obvious why they chose to
label it "RMS Power".

Of my concern was not "RMS" part, but "Power" part.

In dB is expressed ratio of 2 quantities of the same quality.



** A ratio expressed in dBs is always a power ratio - a difference of +3 dB always means double power.

A doubling of voltage is +6dB, because it represents a power increase of four times - long as other factors remain the same.

When calculating dBs, a factor of 10 is used with power levels and factor of 20 with voltage levels so that the dB figure always represents a power ratio.


If one quantity is of "Amplitude Level" than other can not be of
anything else, including RMS Power.

** Changing the name like that is confusing but not technically wrong.


... Phil

[Luxey]

�убота, 24. октобар 2015. 07.50.17 UTC+2, Phil Allison је напи�ао/ла:

** A ratio expressed in dBs is always a power ratio

Let's see what internet has to say...
https://en.wikipedia.org/wiki/Decibel
http://dictionary.reference.com/browse/decibel

Basicaly, they alll say "A unit used to express relative difference
in power or intensity, usually between two acoustic or electric signals."

I read it as: one, or another, usually.

- a difference of +3 dB always means double power.

A doubling of voltage is +6dB, because it represents a power increase of four times - long as other factors remain the same.

You can convert back and forth, as far as I'm concerned.

** Changing the name like that is confusing but not technically wrong.

IMO, confusion is wrong.

[Phil Allison[_4_]]

Luxey wrote:

Phil Allison

** A ratio expressed in dBs is always a power ratio

Let's see what internet has to say...
https://en.wikipedia.org/wiki/Decibel
http://dictionary.reference.com/browse/decibel

Basicaly, they alll say "A unit used to express relative difference
in power or intensity, usually between two acoustic or electric signals."

I read it as: one, or another, usually.


** There is a direct equivalence.

Sound intensity is measured as an electrical signal originating from a microphone and preamp inside a SPL meter.

The dB reading displayed represents relative power.



..... Phil

[Luxey]

Ok, so, you mean, since a in voltage expressed in dB, say 6 dB,
produces change in power expressed by the same number of dB, also 6 dB,
it doesn't really matter what the label is?

[Phil Allison[_4_]]

Luxey wrote:


Ok, so, you mean, since a in voltage expressed in dB, say 6 dB,
produces change in power expressed by the same number of dB, also 6 dB,
it doesn't really matter what the label is?


** Labels often matter, but not because the dBs are of a different type.

Be careful with dBs that have letters after then, like dBm or dBV - these are actual levels since a reference is quoted.


.... Phil