Watt for speaker and Watt for power consumption, Class D and AB

[jst]

So in this day and age of higher energy prices and global warming class A is really not a good idea anymore, and class D is the way of the future. I would not bin it if I owned a good class AB design, but the next one would surely be a class D.
For us, this is precisely what we are doing each time we buy a new replacement appliance of one kind or another. Our new vacuum cleaner consumes only half of what the old one from a well respected brand did, is quieter, and works better. Current refrigerators consume about a quarter of those from 15 years ago, and my new desktop computer is ultra efficient as well (and efficient enough not to need a fan). Of course, in absolute terms audio equipment does not consume that much, but it is the sum of all these little things.

I didn't actually understand much about what's going on inside an amp, but I was shocked when I read my azur640a can consume 600 watt while it's only producing 75 watts @8 ohm. I also didn't understand class AB work like that, but now that I know I prefer class D. It's not like I can hear any huge difference from the class design.

You answered your own question. The efficiency range of class AB is between 39.3 and 78.5%, depending on the bias point. If a class AB amplifier pulls 600 watts from the wall, it can never output more than 471 watts continuous. Peak power can be higher, if enough capacitance is available.

I only just discovered that lately though, glad that I answered my own question there coz I am still grasping how this wattage works lol. So power consumption will always be higher than watt to speaker and even lower for higher than class D since the efficiency is much worse.

The idea that one had to distill a lot of "dirty watts" from the power lines to produce a few "clean watts" had a lot of appeal in the audiophile community of the 80ies. It still has I guess. Jean Hiraga (again) was partly to blame.

So that's probably why the power is always drawn less than from wall socket ? it's 110v in the US and 220v for others, but transformers/dc always use less like 12v 24v 32v 36v 42v 48v 51v 60v etc.

The transformer rating is probably does as much about avoiding overheating. For short periods of time I'm sure it could push out more power than the rated 600W.

It says 60v-0v-60v , why is 60v written twice ? is it 60v x 10A or (60v x10A)*2 ?

 

[DVDdoug]

I read my azur640a can consume 600 watt while it's only producing 75 watts @8 ohm.

Remember that regular program material is dynamic so if the amp is putting-out 75W on the peaks the overall-average is typically around 1/10th of that.

It says 60v-0v-60v ,

It's center-tapped( "CT"). The two 60V outputs are out-of-phase so you have 120VAC if you measure across both of them. They can be rectified to give you positive & negative DC supplies. That allows the output to swing positive & negative without an "DC blocking" output capacitor on each channel. (Most amps are made this way.)

 

[kchap]

It says 60v-0v-60v , why is 60v written twice ? is it 60v x 10A or (60v x10A)*2 ?

It's center-tapped( "CT"). The two 60V outputs are out-of-phase so you have 120VAC if you measure across both of them. They can be rectified to give you positive & negative DC supplies. That allows the output to swing positive & negative without an "DC blocking" output capacitor on each channel. (Most amps are made this way.)

Very good point 60V + 60V 10A. That's 1200W!

 

[jst]

Very good point 60V + 60V 10A. That's 1200W!

So transformers really work like that ? coz even the boxy trafo also has 2x voltage written to it, and a few other voltages, it draws power from that too if used ?
Like this

<- does this mean it's (35x20)*2=1400w ?


Other than that there is also elco or electrolytic capacitor. I notice even if Aiyima A07 is bridged and outputted as mono, then add another Aiyima A07 bridged as mono too, and produce 300watt x2, the elco even in both of them is only 4x1000 = 4000µF, while the pa350 here has four 6800µF elco = 27,200µF

Spoiler: 4000µF

While in that PA350 amp, the elco is 6800µF*4 = 27,200µF

Spoiler: 27200µF

So even if Aiyima a07 per ch plays 300 watt and pa350 plays 350 watt, only 50 watt difference, in reality the sound from pa350 will be more powerful coz it has bigger elco.

From what I gathered, Elco is used as a reservoir for power, an electrical engineer ever told me, when a sound is played it draws power from this elco, so it needs to be quite huge in numbers, that's why if an amp gets upgraded elco, the bass becomes more powerful because there's more power to be drawn. Cmiiw though about how it actually works. Most people buying new amps (especially diy-ers) here usually upgrade this elco to higher capacity because of that. Is that thing with elco capacity myth or fact ? Should Aiyima A07 be modded for its elco ? because I've seen pics of other tpa3255 design with 4700µF*2

=============

After further reading turns out voltage written on a transformer is in VAC, in VDC it's multiplied by 1.414 , so 60V would mean 84.84VDC. Watt to speaker is VDC*VDC/Resistance , so 8 ohm = 84.84*84.84/2*8 = 899.7282 watt ~ 900 watt, dunno whether this is per channel or stereo, and dunno whether 60-0-60 means 2x 84.84 or just one. I can't find any info whether CT = 2xVAC.

Also I read that 60-0-60 , if using 60 and 60 = 120, then the ampere is halfed.

 

[kchap]

So transformers really work like that ? coz even the boxy trafo also has 2x voltage written to it, and a few other voltages, it draws power from that too if used ?
Like this View attachment 160024 <- does this mean it's (35x20)*2=1400w ?


Other than that there is also elco or electrolytic capacitor. I notice even if Aiyima A07 is bridged and outputted as mono, then add another Aiyima A07 bridged as mono too, and produce 300watt x2, the elco even in both of them is only 4x1000 = 4000µF, while the pa350 here has four 6800µF elco = 27,200µF

Spoiler: 4000µF

View attachment 160043

While in that PA350 amp, the elco is 6800µF*4 = 27,200µF

Spoiler: 27200µF

View attachment 160044

So even if Aiyima a07 per ch plays 300 watt and pa350 plays 350 watt, only 50 watt difference, in reality the sound from pa350 will be more powerful coz it has bigger elco.

From what I gathered, Elco is used as a reservoir for power, an electrical engineer ever told me, when a sound is played it draws power from this elco, so it needs to be quite huge in numbers, that's why if an amp gets upgraded elco, the bass becomes more powerful because there's more power to be drawn. Cmiiw though about how it actually works. Most people buying new amps (especially diy-ers) here usually upgrade this elco to higher capacity because of that. Is that thing with elco capacity myth or fact ? Should Aiyima A07 be modded for its elco ? because I've seen pics of other tpa3255 design with 4700µF*2

The PA350 does not have a regulated PSU; the standard approach for a class AB amp. Capacitors must be large enough to maintain the rail voltage even under high transient currents. It's not mandatory but most class D amps go for SMPS. Smaller, lighter and less heat. Smaller capacitors.

 

[jst]

The PA350 does not have a regulated PSU; the standard approach for a class AB amp. Capacitors must be large enough to maintain the rail voltage even under high transient currents. It's not mandatory but most class D amps go for SMPS. Smaller, lighter and less heat. Smaller capacitors.

So Aiyima A07 does not need high capacitors because it's using smps ? So even if I buy meanwell lrs-350-48 (350watt, 48v 7.3A) , it can be utilized with no drawback and will work as it should, even with only 2000µF elco ?

SMPS has its own elco ? is black brick adapter smps ?

 

[kchap]

So Aiyima A07 does not need high capacitors because it's using smps ? So even if I buy meanwell lrs-350-48 (350watt, 48v 7.3A) , it can be utilized with no drawback and will work as it should, even with only 2000µF elco ?

SMPS has its own elco ? is black brick adapter smps ?

Most of the regulation is be done by the external brick. I'm wondering if the Aiyima has an onboard regulator or just the larger capacitors are to decouple the external regulator.

 

[jst]

Is Amplifier watt output determined from its VOLTAGE ? (v peak = dc = rms, dc=1.414*vac)

Like with Aiyima A07 , if I use 32v adapter (this is already DC ,right ? so no need to multiply it by 1.414 ? ) and 8 ohm speaker, then max watt is 32v * 32v / 16ohm (stereo 8ohm) = 64 watt, that's max I will get using a 32volt adapter. While 32v 5A adapter can supply 160watt, so it's enough for 64 watt *2

If I use 48v adapter and 8 ohm speaker, then max watt is much bigger 48*48/16=144 watt per channel speaker or 288 watt in total, but since 48*5=240 watt only, so using 48v 5a is actually a waste, on top of that build quality usually not that good, so it cannot supply power needed for the amp to output 144 watt per channel it's supposed to. That's why even if I use 48v * 20Ampere , it's wasting it coz 7.5A can supply enough even with efficiency factored in.

So for a 5A adapter (seems max in black brick adapter) 42v should be the sweet spot. 42*42/16=110 watt per ch, total 220 watt, while 42*5=210 watt, so it's close, but since black brick efficiency is somewhat questionable then maybe 42 or one notch lower is the sweet spot using black brick adapter for Aiyima A07.

Looking at that, upgrading from 32v (64w/ch@8ohm) to 48v(144w/ch@8ohm) is like doubling the power.

 

[kchap]

Is Amplifier watt output determined from its VOLTAGE ? (v peak = dc = rms, dc=1.414*vac)

Like with Aiyima A07 , if I use 32v adapter (this is already DC ,right ? so no need to multiply it by 1.414 ? ) and 8 ohm speaker, then max watt is 32v * 32v / 16ohm (stereo 8ohm) = 64 watt, that's max I will get using a 32volt adapter. While 32v 5A adapter can supply 160watt, so it's enough for 64 watt *2

If I use 48v adapter and 8 ohm speaker, then max watt is much bigger 48*48/16=144 watt per channel speaker or 288 watt in total, but since 48*5=240 watt only, so using 48v 5a is actually a waste, on top of that build quality usually not that good, so it cannot supply power needed for the amp to output 144 watt per channel it's supposed to. That's why even if I use 48v * 20Ampere , it's wasting it coz 7.5A can supply enough even with efficiency factored in.

So for a 5A adapter (seems max in black brick adapter) 42v should be the sweet spot. 42*42/16=110 watt per ch, total 220 watt, while 42*5=210 watt, so it's close, but since black brick efficiency is somewhat questionable then maybe 42 or one notch lower is the sweet spot using black brick adapter for Aiyima A07.

Looking at that, upgrading from 32v (64w/ch@8ohm) to 48v(144w/ch@8ohm) is like doubling the power.

With the TPA3255 it's a bit confusing; it runs off a single rail single rail but uses bridge mode. The single rail voltage can be between 14 and 53 Volts. A max of 48V is recommended by Aiyiama

The principles still apply; your pk voltage, pk Current and therefore Pk power is determined by the rail max voltage plus losses and for a sine wave, the RMS voltage / Current will be 1/√2. A handy shortcut for sine waves, the rms power is half pk.

(V*1/√2) * (I*1/√2) is = V * I * 0.5

With 8Ω, Pk Current is 4A. 32 V * 4A = 128 Wpk. This makes the rms power 64W. The switching efficiency of class D combined with 2000μF capacitors the Aiyima A07 can push out around 60W a channel, both channels driven, when using a 32V 5A PSU. A lower impedances, 6 to 2Ω, the the 5A supply will be the limiting factor.

With the recommended 48V 7.5A PSU it's 48V * 6A = 368W Pk, 186W rms. But! 1) losses and the chip's own protection circuitry mean the best case is probably 150W; 2) both channels driven maybe 100W and 3) The power into a 4Ω load power will still be around the 100W mark, maybe a bit higher, both channels driven. The 7.5 amp limit is the issue for points 2 and 3.

The Aiyima A07 is a nice little unit but do not expect much more than 100W continuous both channels driven with the 48V 7.5A PSU.

 

[jst]

With the recommended 48V 7.5A PSU it's 48V * 6A = 368W Pk, 186W rms. But! 1) losses and the chip's own protection circuitry mean the best case is probably 150W; 2) both channels driven maybe 100W and 3) The power into a 4Ω load power will still be around the 100W mark, maybe a bit higher, both channels driven. The 7.5 amp limit is the issue for points 2 and 3.

Sorry, did you miscalculate 48v*6a = 368w or is it calculated using other method ? if it is 48x6, then it shld be 288, halfed then it's 144, per ch is 72.
You use 6A for 80% efficiency ?

Kinda disappointing only 72watt /ch. I thought I can get closer to 150w/ch.
If it is halfed because of the single rail , then it's like less than 50% efficiency on top of the -1.5A from before ?

I'll buy kwh meter, I'm curious. 72 watt is so disappointing.

Before using this Azur 640A I used a diy amp with high watt, 12 inch woofer, and I could feel the bass on my chest, now I use 10" , and I cannot feel the power not even the slightest lol, sure the bass is there, it's deep and tight but the vibration is just not there. If it's a low power amp then I won't invest more money buying adapter/psu , I shld get a spl amp with high watt.

 

[kchap]

Sorry, did you miscalculate 48v*6a = 368w or is it calculated using other method ? if it is 48x6, then it shld be 288, halfed then it's 144, per ch is 72.
You use 6A for 80% efficiency ?

Kinda disappointing only 72watt /ch. I thought I can get closer to 150w/ch.
If it is halfed because of the single rail , then it's like less than 50% efficiency on top of the -1.5A from before ?

I'll buy kwh meter, I'm curious. 72 watt is so disappointing.

Before using this Azur 640A I used a diy amp with high watt, 12 inch woofer, and I could feel the bass on my chest, now I use 10" , and I cannot feel the power not even the slightest lol, sure the bass is there, it's deep and tight but the vibration is just not there. If it's a low power amp then I won't invest more money buying adapter/psu , I shld get a spl amp with high watt.

Yes, you are right.

With the recommended 48V 7.5A PSU it's 48V * 6A = 288W Pk, 144W rms. But! 1) losses and the chip's own protection circuitry mean the best case is probably 150W; 2) both channels driven maybe 140W and 3) The power into a 4Ω load power will still be around the 140W mark, maybe a bit higher, both channels driven. The 7.5 amp limit is the issue for point 3.

The Aiyima A07 is a nice little unit but do not expect much more than 140W continuous both channels driven with the 48V 7.5A PSU.

 

[jst]

@kchap could you please comment on this amp ?

here's the pic of its transformer, toroid ct 22v-0v-22v , 5 Ampere

Spoiler: trafo

Elco is 2x 4700 35v (this is even lower than Aiyima A07 @50v elco but only1000uf)

Spoiler: elco

Spec says 150watt rms without saying per channel or total, do you think that's per channel or total ?

here is a vid of what's inside if you want to check

Spoiler: yt

Do you think it's higher watt than Aiyima , lower or more or less the same ? Price of this amp is 54usd, either I buy this amp or buy meanwell psu 48v 7.3A @34usd.


----
from what i learned from google, here's my calculation
22vac= 1.414*22vdc = 31.1vdc => 31.108² / (8ohm*2 speakers) =60.4 watt per channel. Is that right ? or since it's 22-0-22 = is that 22vac or 44vac ? But I read if using 22 and 22 (not using ct), it will be 44v but the Amperage will be halfed.

Power consumption from wall is 22v * 5A or is it 22v*2 * 5A ?

 

[pjug]

I think you don't need a 48V power supply with this bridged amp to give good power into 4 ohms. But if you want 150W avg power x 2 chan and 300 WPC peaks, then you need a lot of current. I think something like this would be pretty suitable (36V, 600W, 16.6A):

SE-600-36 - MEAN WELL - Order Today @ TRC Electronics

Order MEAN WELL SE-600-36 power supply on-line or call today for exceptional customer service. TRC is the USA stocking headquarters of MEAN WELL SE-600-36 Power Supplies. SE-600-36 is ready to ship today.

www.trcelectronics.com

 

[jst]

I think you don't need a 48V power supply with this bridged amp to give good power into 4 ohms. But if you want 150W avg power x 2 chan and 300 WPC peaks, then you need a lot of current. I think something like this would be pretty suitable (36V, 600W, 16.6A):

SE-600-36 - MEAN WELL - Order Today @ TRC Electronics

Order MEAN WELL SE-600-36 power supply on-line or call today for exceptional customer service. TRC is the USA stocking headquarters of MEAN WELL SE-600-36 Power Supplies. SE-600-36 is ready to ship today.

www.trcelectronics.com

I'm using 8ohm speakers, and the recommendation for Aiyima A07 is 48v 7.3a from its website. And Isn't amplifier output watt rated from its VOLTAGE ? P=V²/8Ω so using 36v would result in lower watt than 48v ? and 16.6A would be overkill if max watt is determined from 36v.

Like if P=36²/8Ω = 162 watt total or 81watt per ch , while 36vx16.6A=~600w, that would be overkill ? Unless I googled the wrong formula lol.

(This website I found told me to get a multimeter and clip it on the speaker cable, adjust volume till loudest without distortion and check how much Voltage coming out and use that formula if I want to know how much watt is my amplifier now with current adapter. I'll probably get it tomorrow with kwh meter coz i'm curious, I want to know how this works a bit)

How to measure amplifier watts using multimeter [English subtitle]​

 

[pjug]

I'm using 8ohm speakers, and the recommendation for Aiyima A07 is 48v 7.3a from its website. And Isn't amplifier output watt rated from its VOLTAGE ? P=V²/8Ω so using 36v would result in lower watt than 48v ? and 16.6A would be overkill if max watt is determined from 36v.

Like if P=36²/8Ω = 162 watt total or 81watt per ch , while 36vx16.6A=~600w, that would be overkill ? Unless I googled the wrong formula lol.

(This website I found told me to get a multimeter and clip it on the speaker cable, adjust volume till loudest without distortion and check how much Voltage coming out and use that formula if I want to know how much watt is my amplifier now with current adapter. I'll probably get it tomorrow with kwh meter coz i'm curious, I want to know how this works a bit)

Oops, sorry. Somehow I got the idea that 4 ohms was being considered. You can also get MeanWell power supplies in 48V/12.5A

SE-600-48 - MEAN WELL - Order Today @ TRC Electronics

Order MEAN WELL SE-600-48 power supply on-line or call today for exceptional customer service. TRC is the USA stocking headquarters of MEAN WELL SE-600-48 Power Supplies. SE-600-48 is ready to ship today.

www.trcelectronics.com

That uses a fan though so I don't know how quiet.

Maybe someone else can say if these SMPS typically can give peak current higher than the rated current, in which case the 48V/7.3A supply might be more capable than what I am thinking.

Edit: looking at the datasheet (Note 7) it does look like it can deliver 150% of rated current for peaks, so then about 11 amps. So probably good in that case I would guess.

https://www.meanwell.com/Upload/PDF/LRS-350/LRS-350-SPEC.PDF

 

[jst]

Oops, sorry. Somehow I got the idea that 4 ohms was being considered. You can also get MeanWell power supplies in 48V/12.5A

SE-600-48 - MEAN WELL - Order Today @ TRC Electronics

Order MEAN WELL SE-600-48 power supply on-line or call today for exceptional customer service. TRC is the USA stocking headquarters of MEAN WELL SE-600-48 Power Supplies. SE-600-48 is ready to ship today.

www.trcelectronics.com

That uses a fan though so I don't know how quiet.

Maybe someone else can say if these SMPS typically can give peak current higher than the rated current, in which case the 48V/7.3A supply might be more capable than what I am thinking.

Edit: looking at the datasheet (Note 7) it does look like it can deliver 150% of rated current for peaks, so then about 11 amps. So probably good in that case I would guess.

https://www.meanwell.com/Upload/PDF/LRS-350/LRS-350-SPEC.PDF

Using the same formula, 48*48/8=288watt to speaker, while 48*12,5=600watt, so it's still overkill. 48v 7.A is actually enough, with Meanwell LRS-350-48

Here's how this guy measure his amplifier output.

Spoiler

at first he uses his multimeter to get the voltage running through the speaker cable and got 32v then he uses clamp multimeter and got 3.24A.
P=V*I=32*3.24=103.68watt

Spoiler

And he measures resistance from the speaker using the known variables and ohm's law R=V/I=32/3.24=9.8ohm~10.
If we calculate P using P=V^2/R, we get more or less the same watt or close, 32*32/9.8 = 104.4watt

Spoiler

So this calculation is quite accurate to use, so SE-600-48 with 12.5A is still overkill because 7.3A is enough= Meanwell LRS-350-48

 

[Raindog123]

@jst, here are a few simple but hopefully useful points about amplifier power:

1) An amplifier can output different power levels. They are defined by the volume knob, that is tied to an internal feedback loop that limits the output current at the desired volume [power] level. At every such volume, the amplifier outputs some current I.

2) As a sine wave, this current is I=Io*sin(ωt), with its mean value Irms=Io/√2.

3) For initial power estimation, it's fine to assume a purely resistive speaker load R (the number from the speaker spec - "4Ohm", "8Ohm".) [This resistive load is responsible for electric-current energy transfer to external - acoustic and heat - energy.]

4) So, for a given volume level the [per-channel] amplifier “continuous" output power P will be P=R*Irms^2.

5) Now, for a given volume, the amplifier output voltage (Vo and Vrms) is a fraction of its max output Vmax. [It's defined by the speaker R and the current from (1) per Ohm's law.] However, unlike a simple transistor, the output Vmax of a Class D amp is NOT necessarily limited by the input [power supply] DC voltage ("VDC") - as, eg, the amplifier can work in a "bridged" mode - internally doubling this input voltage.

6) Similarly, the amplifier input DC current (aka power supply output current , limited by PS' max [DC] current "rating") does not necessarily limit/relates to the amplifier output [AC] current [neither Io or Irms from (2)]. Instead, the only relation is through preservation of energy: R*Irms_max^2 <= VDC*Imax / 2 (2 channels).

 

[kchap]

Spec says 150watt rms without saying per channel or total, do you think that's per channel or total ?

Yor maths was right. It could be running in bridge mode but, I suspect it's 150W into 4Ω. You could not sustain 150W into 4Ω both channels driven. 22V * 2 * 5A = 220W.

What do want? A desktop amp to sit next to your PC, along with a pair of speakers or a basic hifi system where you would be sitting a few metres back from the amp and speakers?

 

[pjug]

@jst, here are a few simple but hopefully useful points about amplifier power:

1) An amplifier can output different power levels. They are defined by the volume knob, that is tied to an internal feedback loop that limits the output current at the desired volume [power] level. At every such volume, the amplifier outputs some current I.

2) As a sine wave, this current is I=Io*sin(ωt+ϕ), with its mean value Irms=Io/√2.

3) For power estimation, it's fine to assume a purely resistive speaker load R (the number from the speaker spec - "4Ohm", "8Ohm".) [This resistive load is responsible for electric-current energy transfer to external - acoustic and heat - energy.]

4) So, for a volume level the [per-channel] amplifier ["sustained, continuous"] output power P will be P=R*Irms^2. This is the formula for the amplifier output power.

5) Now, for a given volume, the amplifier output voltage (Vo and Vrms) is a fraction of its max output Vmax. (It's defined by the speaker R and the current from (1) per Ohm's law.) However, unlike a simple transistor, the output Vmax of a Class D amp is NOT necessarily limited by the input [power supply] DC voltage ("VDC") - as eg the amplifier can work in a "bridging" mode internally doubling this input voltage.

6) Similarly, the amplifier input DC current (aka power supply output current , limited by PS' max [DC] current "rating") does not necessarily limit/relates to the amplifier output [AC] current [neither Io or Irms from (2)]. Instead, the only relation is through preservation of energy: R*Irms_max^2 <= VDC*Imax / 2 (2 channels).

[Sorry @Raindog123 I meant to reply to @jst]
Here is what you have with the bridged amp running on 48V into 8 ohms, at the point of clipping (ignoring losses). Red and Blue are the single ended amp voltages fed to speaker + and -. The difference between these divided by 8 ohms gives the green curve, current. So you see your power supply is tasked with providing 6 amp peaks. When running L and R it will be 12 amps. However, after looking at the data sheet of the supply you want to use, I think it can give you those peaks or at least close to it.

 

[jst]

@jst, here are a few simple but hopefully useful points about amplifier power:

1) An amplifier can output different power levels. They are defined by the volume knob, that is tied to an internal feedback loop that limits the output current at the desired volume [power] level. At every such volume, the amplifier outputs some current I.

2) As a sine wave, this current is I=Io*sin(ωt+ϕ), with its mean value Irms=Io/√2.

3) For power estimation, it's fine to assume a purely resistive speaker load R (the number from the speaker spec - "4Ohm", "8Ohm".) [This resistive load is responsible for electric-current energy transfer to external - acoustic and heat - energy.]

4) So, for a volume level the [per-channel] amplifier ["sustained, continuous"] output power P will be P=R*Irms^2. This is the formula for the amplifier output power.

5) Now, for a given volume, the amplifier output voltage (Vo and Vrms) is a fraction of its max output Vmax. (It's defined by the speaker R and the current from (1) per Ohm's law.) However, unlike a simple transistor, the output Vmax of a Class D amp is NOT necessarily limited by the input [power supply] DC voltage ("VDC") - as eg the amplifier can work in a "bridging" mode internally doubling this input voltage.

6) Similarly, the amplifier input DC current (aka power supply output current , limited by PS' max [DC] current "rating") does not necessarily limit/relates to the amplifier output [AC] current [neither Io or Irms from (2)]. Instead, the only relation is through preservation of energy: R*Irms_max^2 <= VDC*Imax / 2 (2 channels).

I see, I usually only use Aiyima A07 at 9 o'clock, it's already too loud at times so that's the max watt I'll be getting then.

I'm getting a multimeter so I'll test it tomorrow how much voltage is running thru my speaker cable at 9'oclock volume.

Realtime I can be acquired using a clamp multimeter but it's quite expensive so I'll be using Resistance instead. The above example I posted shows that calculating P from known I or known R can result in more or less the same output.

But this is only calculating from adapter already owned, I'll just wait for the result and see whether I still want a meanwell lrs 350-48 after this. Or ask friar in other thread to do a test if he's willing coz he has 48v 7.5A industrial psu.