Thursday, August 3, 2023

Tuning a sub with a multimeter

1)      Determine the voltage needed from the RMS output

The RMS output of the amp will determine the voltage to set. Take the stated RMS from the manufacturer and multiply that by the speaker resistance. The square root of that number is the voltage to set the output at.

Voltage (RMS) =√(〖Resistance〗in Ohms ×〖RMS Power〗in watts )

So if the Amp is 200 RMS and the Speaker is a 4 ohm speaker the desired output voltage is 200*4=800 and the square root of 800 is 28.28. The ideal voltage output would therefore be 28 volts.

The table below shows the voltage at 2, 4 and 8 Ohms for common RMS outputs. Find your RMS on the left and go to the column with the resistance of the speaker.

RMS

2W

4W

8W

150

17.32

24.49

34.64

165

18.17

25.69

36.33

175

18.71

26.46

37.42

200

20.00

28.28

40.00

225

21.21

30.00

42.43

250

22.36

31.62

44.72

300

24.49

34.64

48.99

350

26.46

37.42

52.92

400

28.28

40.00

56.57

450

30.00

42.43

60.00

500

31.62

44.72

63.25

 

 

2)      Next download a 50 or 60 Hz test tone. You can also just stream it if you find one online. The longer the better.

3)      Next set your volume to about 75% of the maximum volume. Turn your bass boost and  amp gain to 0.

4)      Take a multimeter and set it for A/C voltage. Connect the probes to the speaker wires coming from the amp.

5)      Play the test tone. Slowly turn up the gain until it matches the number from the table. The example above used 28 volts. At 28 volts the amp is putting out 200 watts RMS.

6)      Now hook the speaker wires back up to the speaker and play a familiar song. Listen to make sure there aren’t any unwanted distortions, hums, or buzzes. The system is tuned to about the maximum it will handle so don’t increase the gain any more. The bass boost can be adjusted now and the filters can be adjusted as well.