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Clamp Testing

Q : What is Clamp Testing, and Why should I do it?

Clamp testing is the way to calculate your amplifiers true output power and the actual impedance being driven, in it's real environment. Clamp testing, and understanding the numbers it gives, is a must if competing in SPL or interested in getting more performance out of any system.
How to Calculate Amp Power and Impedance:

You will need a Digital Multi-Meter, AC Amp/Clamp Meter and Test Tones/Signal

The Volt-meter/Multi-meter test leads should go directly to the speaker leads from the amplifier. Pick a (-) and (+) to pierce your test leads into. Set your Volt-meter/Multi-meter to AC Voltage and turn on the Peak Voltage feature. 

The Ampmeter/Clamp-meter should be clamped around only the (+) speaker wire coming from the amplifier outputs. Set the clamp meter to AC Amperage. Turn on the Peak Hold feature. Do not use the test leads of the Ammeter/Clamp-meter in this process.

When testing the system for output power and impedance at one specific frequency, test using that single frequency. To know the impedance curve and power curve, test tones from 70Hz down to 20Hz in 5Hz increments.

If you don't have a way of generating tones from 70Hz down to 20Hz, you can download the wav files we have created.  70Hz-20Hz ( in 5Hz increments)

If power and impedance numbers for a daily driving system are needed, we suggest warming up the subs and amp to get readings congruent with how the system is normally played, SPL competitors should take readings with coils/amps at room temperature.

Roll up the volume at the head unit that is just under clipping indication on the amplifier.

The Voltage and Amperage numbers are simply multiplied together to get your Wattage. (P=VI or Power equals Voltage times Amperage).

To find out what impedance the amplifier is seeing, simply divide the Voltage by the Amperage. (R=V/I or Resistance equals Voltage divided by Amperage).

To plot a power or impedance curve, repeat the previous test for each frequency, i.e. 70, 65, 60, 55, 50Hz etc. 

The commonly used term "Box Rise" is the sum of the subwoofer(s) impedance and the additional acoustic impedance added by the enclosure and the vehicle.

For example, 4 subs wired to a 1.0 ohm load, after running an actual impedance curve, may present a load over 4 Ohms to the amplifier. That 1000w amplifier may be pushing between 200w and 400w of real power.

An informative experiment would be to test the box in its normal position, then change the position in the trunk or cargo area. Try moving the port and speaker about 2" away from boundaries in the cargo area and test it again. The numbers will come out different due to changing acoustic load presented by the new location, affecting the SQ and SPL of your system.

For an Ohm's Law Calculator and other useful tools, try the follwing link.