RMS wattage Calculation

[SpeakerBoy 64]

Can someone throw me the calculation for RMS wattage, i think it's something about the fuse rating times something else. I Have a Kenwood 4ch amp, with a 15amp fuse wanted to know roughly how much i could possibly expect.

Half of all websites arent working at the moment. School server is being funky with the blocking, i think Mr.B needs to reset the filters.

[CrazyKenKid 64]

i thought it was fuses times 12! so 15x12= 180rms

but that is how you do it for a class d amp i don't know about a/b or rather a 4-channel amp.

[///M5 2,833]

Read the damn manual and expect 80%. No bs formula necessary.

[SpeakerBoy 64]

Read the damn manual and expect 80%. No bs formula necessary.

I don't have the manual, bought it used.

Never mind.

[///M5 2,833]

Then look on the internet. Really simple.

[Impious 1,476]

Can someone throw me the calculation for RMS wattage, i think it's something about the fuse rating times something else. I Have a Kenwood 4ch amp, with a 15amp fuse wanted to know roughly how much i could possibly expect.

Half of all websites arent working at the moment. School server is being funky with the blocking, i think Mr.B needs to reset the filters.

The fuse rating will tell you absolutely nothing about the power output of the amplifier. Some people incorrectly try to use it as a basis for determining power output. But it's really meaningless.

The only true way to know the actual power output is to bench test the amplifier.

[SpeakerBoy 64]

Can someone throw me the calculation for RMS wattage, i think it's something about the fuse rating times something else. I Have a Kenwood 4ch amp, with a 15amp fuse wanted to know roughly how much i could possibly expect.

Half of all websites arent working at the moment. School server is being funky with the blocking, i think Mr.B needs to reset the filters.

The fuse rating will tell you absolutely nothing about the power output of the amplifier. Some people incorrectly try to use it as a basis for determining power output. But it's really meaningless.

The only true way to know the actual power output is to bench test the amplifier.

Can i test with a DMM?

[Impious 1,476]

No, you couldn't test it solely with a DMM.

You would also need a test load and oscilloscope at minimum to actually do it correctly.

[SpeakerBoy 64]

No, you couldn't test it solely with a DMM.

You would also need a test load and oscilloscope at minimum to actually do it correctly.

I think I know someone with an O-scope. Test load, like having speakers connected?

[bigrank916 72]

Damn. I know an assload of people that are thinking wrong then.

[///M5 2,833]

No, you couldn't test it solely with a DMM.

You would also need a test load and oscilloscope at minimum to actually do it correctly.

I think I know someone with an O-scope. Test load, like having speakers connected?

Should have a linear load or something more quantifiable than a speaker. It "can" be done with a speaker, but you need to know a lot about that speaker.

Again, just look on the internet and multiply the number by 80%. Really simple.

[///M5 2,833]

Damn. I know an assload of people that are thinking wrong then.

Curious as to why they would ever think that some RMS calculation is possible. Hell even clamp meters aren't very accurate.

[KU40 173]

One question is, why does it even matter? The power output to your speakers will vary widly anyways just due to impedance fluctuations with different frequencies. Plus what's really the difference between like 100 and 120 watts? What will you do with that information?

Chances are that amp puts out about 20-25 x 4 @ 4 ohms.

[bigrank916 72]

Damn. I know an assload of people that are thinking wrong then.

Curious as to why they would ever think that some RMS calculation is possible. Hell even clamp meters aren't very accurate.

Just something that was thought to be true. Personally, I had been told this by many audio shops as well as car audio boards. Multiply the total of the fuses on the amp by the voltage it receives and you will get a figure for the rms wattage.

How accurate are they?

[Impious 1,476]

Damn. I know an assload of people that are thinking wrong then.

Curious as to why they would ever think that some RMS calculation is possible. Hell even clamp meters aren't very accurate.

Just something that was thought to be true. Personally, I had been told this by many audio shops as well as car audio boards. Multiply the total of the fuses on the amp by the voltage it receives and you will get a figure for the rms wattage.

Nobody with any understanding has ever thought it to be true. One of those myths perpetuated through the ignorant masses.

[bigrank916 72]

Damn. I know an assload of people that are thinking wrong then.

Curious as to why they would ever think that some RMS calculation is possible. Hell even clamp meters aren't very accurate.

Just something that was thought to be true. Personally, I had been told this by many audio shops as well as car audio boards. Multiply the total of the fuses on the amp by the voltage it receives and you will get a figure for the rms wattage.

Nobody with any understanding has ever thought it to be true. One of those myths perpetuated through the ignorant masses.

Ok. Glad to know this. How would you go about debunking this myth in a science method? Just curious.

[KU40 173]

Damn. I know an assload of people that are thinking wrong then.

Curious as to why they would ever think that some RMS calculation is possible. Hell even clamp meters aren't very accurate.

Just something that was thought to be true. Personally, I had been told this by many audio shops as well as car audio boards. Multiply the total of the fuses on the amp by the voltage it receives and you will get a figure for the rms wattage.

Nobody with any understanding has ever thought it to be true. One of those myths perpetuated through the ignorant masses.

I would contend that it could give you a GENERAL idea of the power, but nothing specific. I mean obviously it wouldn't make much sense to put a 10 amp fuse on a 1,000 watt amp and vice versa, three 30 amp fuses on a 100 watt amp. I'd say maybe 20-30% possibility of being off either way of the fuse size x voltage x efficiency rating?

But I'd say if you really want to go through the trouble of finding out what the amp really puts out, it won't give you a close enough answer to satisfy.

[tejcurrent 13]

There are topics similar to this on other forums, the closest things you can do easily is with a clamp meter and 2 DMMS. It's not perfect- doesn't take into account or help find out if the signal is clipped. If you've already set with an O-scope I guess that wouldn't be an issue.

Put one DMM on the amp battery power + and - to find out DC voltage (not important for calculations, just nice to know).

Put the other DMM on the + and - speaker output of the amp, set to A/C voltage.

Put the clamp meter on the amps speaker output + set to A/C Amperage.

Throw in a test cd, do each frequency one at a time, write down the a/c voltage and amperage. Take the voltage and square it, then divide by the voltage divided by the amperage:

Amperage = A, Voltage = V

V^2 / (V / A).

Example:

30 hz: 152V / 31.2A = 4.87 Ohms

152v ^2 / 4.87 = 4744.15 watts.

Hope this helps, again it's not perfect but about the best the average person could do.

[bigrank916 72]

There are topics similar to this on other forums, the closest things you can do easily is with a clamp meter and 2 DMMS. It's not perfect- doesn't take into account or help find out if the signal is clipped. If you've already set with an O-scope I guess that wouldn't be an issue.

Put one DMM on the amp battery power + and - to find out DC voltage (not important for calculations, just nice to know).

Put the other DMM on the + and - speaker output of the amp, set to A/C voltage.

Put the clamp meter on the amps speaker output + set to A/C Amperage.

Throw in a test cd, do each frequency one at a time, write down the a/c voltage and amperage. Take the voltage and square it, then divide by the voltage divided by the amperage:

Amperage = A, Voltage = V

V^2 / (V / A).

Example:

30 hz: 152V / 31.2A = 4.87 Ohms

152v ^2 / 4.87 = 4744.15 watts.

Hope this helps, again it's not perfect but about the best the average person could do.

This helps a lot if that formula works in general. Thank you.

[Impious 1,476]

I would contend that it could give you a GENERAL idea of the power, but nothing specific. I mean obviously it wouldn't make much sense to put a 10 amp fuse on a 1,000 watt amp and vice versa, three 30 amp fuses on a 100 watt amp. I'd say maybe 20-30% possibility of being off either way of the fuse size x voltage x efficiency rating?

But I'd say if you really want to go through the trouble of finding out what the amp really puts out, it won't give you a close enough answer to satisfy.

It could only be considered useful in extreme situations where the fuse rating is nonsensical in comparison to the rated power......which is pretty much only an issue in brands already known to output far less than rated power.

[wof131s 10]

Read the damn manual and expect 80%. No bs formula necessary.

Just asking, not trying to start anything, but if this is so why is there such hate for the Hifonics amps that does 80% of their sad total wattage?

[corrie3232 8]

so now everbody that buy's an amp, has to go out and get a DMM meter and an o-scope just to prove the amp puts out what on the box , or maybe the amp manufacture would just throw those instruments in the box with the amp. what else does the consumer have to judge amp A to amp B. i really wanna know!!! Because you can never get a straight answer. ( so what i can't spell)

Edited December 22, 2009 by corrie3232

[brandonf 9]

so now everbody that buy's an amp, has to go out and get a DMM meter and an o-scope just to prove the amp puts out what on the box , or maybe the amp manufacture would just throw those instruments in the box with the amp. what else does the consumer have to judge amp A to amp B. i really wanna know!!! Because you can never get a straight answer. ( so what i can't spell)

I don't compete, so I could care less what my specific amp puts out. I do know my sundown saz1500d puts out more than 1500w at 12v (others rate at 14.4v) from seeing Jacob's benchmark test. Whether it's 1550 or 1580w from my specific amp, it's not audible anyway.

[corrie3232 8]

i heard that

[KU40 173]

so now everbody that buy's an amp, has to go out and get a DMM meter and an o-scope just to prove the amp puts out what on the box , or maybe the amp manufacture would just throw those instruments in the box with the amp. what else does the consumer have to judge amp A to amp B. i really wanna know!!! Because you can never get a straight answer. ( so what i can't spell)

Reliability. Is the amp going to last longer than 6 months? It's just like anything else electronics- cheap stuff burns out faster.