how to compute the rms output of audio amp

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
what is your rail voltages?

in case of a single supply, devide rail voltage by two, to the qoutient, subtract about 3volts for output saturation, subtract again another 10% for voltage sag under full load, finally to the result multiply by 0.7071 to get the rms voltage,and finally with the result, you can calculate the power into an 8, or 4 ohm load.
this is just my way of ballpark calculating the capablity of an amp given its rail voltage.
 
Re: ...another one:

janneman said:
Climb the stairs in the building, and put marks on the walls for every "barometer height" as you climb. At the top, go back down and count the marks. Multiply with the barometer length, gives you the building height.

Another one, anyone (yes, this is a challenge)?

jan Didden

Drop the barometer off the roof, hitting an innocent bystander. Read the newspaper the next day where the accident is described. They'll certainly point out the height from which the barometer was dropped.

BTW, the RMS formulas given here are only valid for sine waves.
 
AX tech editor
Joined 2002
Paid Member
Petter said:
.707 is actually 1 / sqrt(2)

As far as I have been able to see, there has been some confusion in previous postings on this thread, but as of late, it has started to shape up (I even forgot to put the squared for Vpk myself). To recap:

Vrms=Vpk*1/sqrt(2)

Vrms^2=Vpk^2 * 1/2 = Vpk^2/2

"Power" is thus = Vpk^2/(2*R)

Petter

Sorry to repeat myself, but again, this is only valid for sine waves!! Not for square waves, triangles, music. So, if you test your amp with sine waves and you get, say, 100W RMS, that doesn't mean that with music it will or can deliver 100W RMS when driven to max level. It will be much less. Read up on "crest factor".

Jan Didden
 
janneman said:


Sorry to repeat myself, but again, this is only valid for sine waves!! Not for square waves, triangles, music. So, if you test your amp with sine waves and you get, say, 100W RMS, that doesn't mean that with music it will or can deliver 100W RMS when driven to max level. It will be much less. Read up on "crest factor".

Jan Didden


Since we are all getting somewhat pedantic ...

The term "Power" is not in fact valid at all unless you have very strange speakers. I think that syntentic RMS calculations are perfectly fine and much less of a problem than the validity of power as such. Also, it is not true that this is valid ONLY for sine waves - it is possible to construct an infinite number of waveforms that have the same relationship between RMS and Vpk.


Petter
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.