Watts manufacturers doings to us - RMS vs Peak - it’s time to take a stand

[Chienmortbb]

On 12/12/2018 at 01:44, Count Bassy said:

RMS can also be used for current, and can be used for power as long as you take account of the  power factor.

Hopefully not patronising note to those who don't know: Power factor takes account of the phase difference between the voltage and the current. In a pure resitive load load this is '1', but when you get inductance and capacitance involved it is usually less than one. Fairly easy to calculate, or measure, with sine waves, but very complicated when you have a 'random' signal as in audio. It can never be more than 1.

 

The reason you use s resistive load is to take power factor out of the equation. 

[agedhorse]

39 minutes ago, itu said:

OK, so if the amp has linear power, the situation is totally different than with switching powers? My understanding may be outdated, because SMPS has pretty much different behavior compared to linear, transformer-based supplys. I would say, that linear needs quite a lot of power to produce the claimed numbers - in RMS.

I have an old HiFi amp from the 80's that can push 2 x 110 W RMS continuous to 8 ohms (tested) and its maximum input power is 650 W. I understand losses and the power consumption of the other components, so the amount of input power makes sense. But if an amp says 1 kW and the input power is 200 W, I feel like I have fallen from the train. Sir, please, open up this a bit more; I do not have reasonable access to that standard, as it costs 300 € + VAT. Can this SMPS class-D amp push continuously 1 kW RMS to 8 ohms or not?

It's no different between a line frequency based supply and an SMPS (with a bit of a distinction for PFC based supplies).

It's all about total efficiency, the higher the efficiency the lower the input power that's needed to achieve rated power. 

Taking your hi-fi amp as an example, if it's rated at 110 watts/channel (RMS metrics), then it's going to be roughly 160 watts/channel at 4 ohms. The calculations would be as follows:

Total audio power at lowest rated impedance is 2 x 180 watts (total of 2 channels) = 320 watts. The NRTL agency testing power will be (320 x .125) = 40 watts total.  Say the efficiency is 35% for the amp and 75% for the power supply, the rated average power being drawn will be 40W/(35% x 75%) = 152 watts which is what the agency will be looking for as the "rated average input power".

There's another number that can be included, it was more often used on hi-fi and more commonly used a while ago, but that is "MAXIMUM" input power which is of little use unless you are operating the amplifier continuously with a sine wave signal (your speakers may not appreciate this).  Here, the calculations will be a little different in that instead of the 1/8-rated power specified by the safety regulations, you would use the total rated power at the lowest rated load impedance. Note that the efficiencies are typically higher in full rated power testing) In this case it would be ~320W/(45% x 85%) = 830 watts (this is higher than your given number, I suspect that my assumption of 4 ohm power is on the high side OR the amp is not rated for 4 ohm operation.

With class D, you can run the same calculation but substituting the average efficiency of about 90%, and with an SMPS the average efficiency is typically about 92%. Thus: 40W/(90% x 92%) = 48 watts rated average input power. 

There is not a "something from nothing" scenario here, it's all about how the regulations require that we state the input power, and in reality the 1/8-rated power is not too far off until we get into heavily overdriven or compressed tones where the crest factor (an expression of the ratio of peak to average content of the signal) decreases. IF the amp is designed specifically to support such operation, especially if it is advertised as such, the 1/8-power factor may be increased to more accurately reflect the expected operation of the amp. Note that different countries have slightly different requirements for testing and labeling (called "national differences", but this is by far the most common way it's done.

Hope this helps.

[Guest gazzatriumph]

17 hours ago, Phil Starr said:

That's why I specified the same speaker. 

 

But it would still depend on what speaker used wouldn't it.

[itu]

10 hours ago, agedhorse said:

Total audio power at lowest rated impedance is 2 x 180 watts (total of 2 channels) = 320 watts. The NRTL agency testing power will be (320 x .125) = 40 watts total.  Say the efficiency is 35% for the amp and 75% for the power supply, the rated average power being drawn will be 40W/(35% x 75%) = 152 watts which is what the agency will be looking for as the "rated average input power".

...

With class D, you can run the same calculation but substituting the average efficiency of about 90%, and with an SMPS the average efficiency is typically about 92%. Thus: 40W/(90% x 92%) = 48 watts rated average input power. 

...it's all about how the regulations require that we state the input power, and in reality the 1/8-rated power is not too far off until we get into heavily overdriven or compressed tones where the crest factor decreases. IF the amp is designed specifically to support such operation, especially if it is advertised as such, the 1/8-power factor may be increased to more accurately reflect the expected operation of the amp.

This sounds reasonable. If I use the stated 8 ohm power level of 110 W per channel, I get 220 W / (.45 x .85) = 575 W which is in line with that 650 W input power.

Those regulatory bodies have done something that I was not aware of - at all. Your examples and notes clarify this issue, also in a scientific manner, thank You, Sir. I think this power level comparison between amps could be more clear to help us customers. At least I like to make decisions that have something to do with reality, not only marketing based jargon.

[Phil Starr]

1 hour ago, gazzatriumph said:

But it would still depend on what speaker used wouldn't it.

I'm assuming this is a serious question. The only fair test is to change only one variable at a time so if all you want to know is what the amplifier does then that's the only bit you'd change. If you change both the speaker and the amplifier you won't know which may have contributed to a change in volume. So long as the speaker can handle the signal without compressing you should get your 4.77dB extra. If you change to a speaker with a lower sensitivity it will be quieter with both amps but you'll retain the just under 5db difference, just at lower levels. 

[Al Krow]

7 hours ago, Phil Starr said:

The only fair test is to change only one variable at a time so if all you want to know is what the amplifier does then that's the only bit you'd change. 

+1^^ exactly!

And you kinda need to assume a basic level of common sense here i.e. that you have a cab that can handle whatever both amps can throw at it. Seems kinda obvious: but there's no point whatsoever in first pairing a 250W rated cab with a 250W amp but then substituting a 800W amp and winging that the 800W amp doesn't sound any louder (or has blown your cab!) 

Edited December 14, 2018 by Al Krow

[Bill Fitzmaurice]

4 hours ago, gazzatriumph said:

But it would still depend on what speaker used wouldn't it.

It would, for the reason I already stated, you'd have to find one with linear response from 100w to 300w. Good luck with that quest. Thermal power compression alone will render the simple math null and void. For instance, consider the Beyma 12SW1300 Nd. It's rated at 1200w AES and has 10mm xmax, so on the face of it there's no problem with a 300w input. However, thermal power compression at 100w is 0.25dB, at 300w it's 1dB, so right there the 4.77dB increase you might expect with 300w versus 100w is closer to 4dB. That's with a premium driver, which has much lower than average thermal power compression. There's also mechanical power compression to take into account. With 10mm xmax that won't be much, but the 12SW1300 Nd is hardly a typical driver. Drop that xmax to a more likely to be found 5mm and mechanical compression can be just as significant as thermal. 

Edited December 14, 2018 by Bill Fitzmaurice

[LukeFRC]

1 hour ago, Bill Fitzmaurice said:

It would, for the reason I already stated, you'd have to find one with linear response from 100w to 300w. Good luck with that quest. Thermal power compression alone will render the simple math null and void. For instance, consider the Beyma 12SW1300 Nd. It's rated at 1200w AES and has 10mm xmax, so on the face of it there's no problem with a 300w input. However, thermal power compression at 100w is 0.25dB, at 300w it's 1dB, so right there the 4.77dB increase you might expect with 300w versus 100w is closer to 4dB. That's with a premium driver, which has much lower than average thermal power compression. There's also mechanical power compression to take into account. With 10mm xmax that won't be much, but the 12SW1300 Nd is hardly a typical driver. Drop that xmax to a more likely to be found 5mm and mechanical compression can be just as significant as thermal. 

Nice cheap driver there Bill! 

[Bill Fitzmaurice]

If I'd used a run of the mill driver as the example invariably someone would have said a better driver would have given a better result. Not that there aren't any drivers better than the 12SW1300 Nd, but they're few and far in between, and aren't going to be found in an off the shelf electric bass cab.

[LukeFRC]

3 hours ago, Bill Fitzmaurice said:

If I'd used a run of the mill driver as the example invariably someone would have said a better driver would have given a better result. Not that there aren't any drivers better than the 12SW1300 Nd, but they're few and far in between, and aren't going to be found in an off the shelf electric bass cab.

Is that driver used in off the shelf electric bass cabs!!! Ones mortals can afford 

[Jackass]

Hey guys. I rly need a schematic for pascal s-pro2, need to repair. If someone has it, please share, maybe for money

[Jackass]

Hey guys. I rly need a schematic for pascal s-pro2, need to repair. if someone has it, please share, maybe for money...

[Chienmortbb]

31 minutes ago, Jackass said:

Hey guys. I rly need a schematic for pascal s-pro2, need to repair. If someone has it, please share, maybe for money

You are unlikely to get a circuit diagram for Pascal/Icepower/|Hypex etc. They guard what they believe is their IP closely.

[Bill Fitzmaurice]

4 hours ago, Jackass said:

Hey guys. I rly need a schematic for pascal s-pro2, need to repair. If someone has it, please share, maybe for money

Did you happen to read the subject of this thread? And why did you double post? Trying to live up to your username? 

[Al Krow]

Duplicate post 😊

Edited April 11, 2021 by Al Krow

[Jackass]

4 hours ago, Chienmortbb said:

You are unlikely to get a circuit diagram for Pascal/Icepower/|Hypex etc. They guard what they believe is their IP closely.

thank you for your answer sir, but I heard that authorized services have access to schematic diagrams ... yes, I'm talking about not entirely legal ways to get information. I trust your opinion, and if you say that all employees of such services are honest and decent people who will never sell such information in any way, then I will believe you

[Jackass]

20 minutes ago, Bill Fitzmaurice said:

Did you happen to read the subject of this thread? And why did you double post? Trying to live up to your username? 

Bill, I'm glad I met the local guardian of the forum. I am so sorry but English is not my native language, so I didn't understand a bit how to delete the duplicated post 🙁.  I decided to write in this thread, since a couple of pages above the amplifier I was interested in was discussed.  I think it's better to ask a simple question here than to start a new topic, I apologize if it is not accepted here/contradicts the rules. 😥

 

p.s. yes, for the above reasons, I made myself such a nickname х)

[Jackass]

9 minutes ago, Al Krow said:

Bill that's a pretty unnecessary response to someone's first post on BC, and unlike you! 

@Jackass - welcome to BC. We are generally a pretty friendly bunch on here. 

I see, thanks for your friendliness

[Bill Fitzmaurice]

1 hour ago, Jackass said:

 I think it's better to ask a simple question here than to start a new topic

By posting in a zombie thread on a totally unrelated topic you appear to be a spambot, as that's typical of what they do, especially when it's their first post. You also greatly reduce the chances of someone who may be of assistance seeing your question.  Someone who has the schematic you need may have no reason to read a three year old thread about RMS versus peak watts.

[EBS_freak]

Ah. Another (a)”woke”(n) thread.