How to 'measure' subs

Rog Mogale wrote: If you only want to do a frequency plot of your subs, then the mic must be on the ground with the element physically touching the ground. The sub cab must also be on the ground and you will need a hard surface like concrete or tarmac to do perform the test. Use a distance of 2 meters from the mic to the front of the sub cab and if its 8 ohms drive with 2.83V. For a 4 ohm load use 2.00V The stimulus should be a swept sine wave from high to low. You will also need to perform this test outside with no wind present and on a very large surface at least 30 x 30 meters to any boundary if it’s going to be at all accurate. If you have a bit of ground larger than 30 x 30 meters then its possible to do the test out at 10 meters with a higher input levels. Although I find this useful I don’t advocate it for real 1w/1m measurements.


Rog.

What smoothing is suggested to be used?

For subs I prefer none

Confused about setting the output to 2.83 V. 2.83V of what? Can't set it to 2.83V of pink noise because the wave keeps fluctuated with in turn makes the voltage fluctuate. I can't set it to 2.83V with 50Hz easy enough, but what good is that?

I always heard that Voltmeters have trouble accurately reporting voltage if the frequency is not set to 50hz. I would just callibrate the level at 50hz and then do your testing at that level. That is what I always do.

Will be watching this thread to see if someone else has a better suggestion.

Ok, thats what I thought too. I set the voltage to 2.83V with the 50hz, but then I was put off when I put the pink noise through right after and the voltmeter was showing way more than the 2.83 etc.

Also on a slightly different note......when RTA'ing pink noise with Smaart what averaging should I have it on? I was putting it on 10sec averaging and waiting almost a good minute before recording the wave. Good? Bad? Suggestions?

I don't know about any of the measurement software, my tests have been done with an ableton test tone, an RTA mic and a hand graph on graph paper. Ghetto, I know but it has answered the questions I needed answered.

One thing to make sure of when you are calibrating the voltage is to make sure that the amp does not have a high pass filter on when you calibrate. If you had a filter on then the voltage at 50hz would be misleading.

To measure the voltage of any other signal than a sine wave you will need a True RMS Voltmeter.
So the best thing you can do is to calibrate with a sine wave as you do.

Dref do I need a true voltmeter for sine sweep measurements?Also, is REW V5 ok for this?

Nop. Just calibrate with a 50 Hz sine signal using your standard volt-meter. And then do the measurement without changing any gain settings.

You can even just do a measurement and then adjust the data to the correct dB level later.

I am using REW V4,11. But I am sure that V5 should be at least as good.

What voltage for a 4 ohm cab was it?