Uploaded March 2019 | Updated September 2026, 1 week ago
Note: this write-up is rather long and a work-in-progress. Old-school method I learned long ago.
Equipment needed: AC voltmeter with dB scale, load resistors, audio generator, unit to be tested, connection cables, and semi-log graph paper. Oscilloscope is optional using this method. Both the audio generator and the AC voltmeter have to have a flat frequency response over the range of frequencies to be tested. Best to use an older AC voltmeter rather than a modern digital voltmeter.
1. Obtain blank semi-log paper. All equipment is off.
2. Connect audio generator to aux input, not phono input (because of equalization you cannot use the phono input). Make sure generator output is turned down all the way.
3. Connect 8-ohm load resistors to speaker terminals of unit to be tested. Of course, if your amp/receiver needs a 4-ohm load, you must use 4-ohm resistors.
4. Connect AC voltmeter across one of the load resistors (dummy load).
5. Oscilloscope across other load resistor is optional, but I like to connect it across the other load resistor for monitoring purposes.
6. Turn volume on amp/receiver all the way down. Set function switch to aux. Make sure all tone controls, filters, loudness controls are in a neutral position.
7. Turn on all test equipment and amp/receiver to be tested and let warm up for 5 min or so. Longer if tube equipment.
8. Turn volume control all the way up and slowly bring up signal generator output until the AC voltmeter reads 2.82 volts RMS with an 8-ohm load. The waveform to be used is a 1,000 Hz sine wave. This is the reference frequency and the 2.82 or a close voltage (see below) is the reference voltage. I adjust the voltage so it is right on a DB mark of the meter since it is easier to do. For example, with my meter I can adjust the voltage so the pointer is right on the 0 dB mark, meaning it is not at 2.82 volts, but a little less. For a 4-ohm load the voltage would be 2 volts RMS.
9. Plot the reference frequency (1,000 Hz) and and voltage output (0 dB) on the chart.
10. Test at all other frequencies you want and mark on the chart.
11. Do other channel.
What we are looking for is a flat response, especially in the 20 to 20,000 Hz range.
Note: this write-up is rather long and a work-in-progress. Old-school method I learned long ago.
Equipment needed: AC voltmeter with dB scale, load resistors, audio generator, unit to be tested, connection cables, and semi-log graph paper. Oscilloscope is optional using this method. Both the audio generator and the AC voltmeter have to have a flat frequency response over the range of frequencies to be tested. Best to use an older AC voltmeter rather than a modern digital voltmeter.
1. Obtain blank semi-log paper. All equipment is off.
2. Connect audio generator to aux input, not phono input (because of equalization you cannot use the phono input). Make sure generator output is turned down all the way.
3. Connect 8-ohm load resistors to speaker terminals of unit to be tested. Of course, if your amp/receiver needs a 4-ohm load, you must use 4-ohm resistors.
4. Connect AC voltmeter across one of the load resistors (dummy load).
5. Oscilloscope across other load resistor is optional, but I like to connect it across the other load resistor for monitoring purposes.
6. Turn volume on amp/receiver all the way down. Set function switch to aux. Make sure all tone controls, filters, loudness controls are in a neutral position.
7. Turn on all test equipment and amp/receiver to be tested and let warm up for 5 min or so. Longer if tube equipment.
8. Turn volume control all the way up and slowly bring up signal generator output until the AC voltmeter reads 2.82 volts RMS with an 8-ohm load. The waveform to be used is a 1,000 Hz sine wave. This is the reference frequency and the 2.82 or a close voltage (see below) is the reference voltage. I adjust the voltage so it is right on a DB mark of the meter since it is easier to do. For example, with my meter I can adjust the voltage so the pointer is right on the 0 dB mark, meaning it is not at 2.82 volts, but a little less. For a 4-ohm load the voltage would be 2 volts RMS.
9. Plot the reference frequency (1,000 Hz) and and voltage output (0 dB) on the chart.
10. Test at all other frequencies you want and mark on the chart.
11. Do other channel.
What we are looking for is a flat response, especially in the 20 to 20,000 Hz range.
