Car Stereos: maximize my sony output, loudness controls, digital multimeter

Question
I have an XM-1652Z amplifier, that supposedly puts out 400RMS into 4 ohms.  I have uncoiled two 330W xplod subs with it.  I am wondering what the output level adjuster knob is referring to by how it is scaled, and what should it be set at for a max of 330W?

Answer
Hi Jesse,

The amplifier's level control is meant to let you match the amplifier with a head unit.  Different head units use different RCA output voltages, so a setting that limits your amp to 330 watts with one head unit might result in a completely different output with a different head unit.  In other words, I can't give you a setting on the level control that will keep your amp under 330 watts of output.

There's a way to use a multimeter to measure the amplifier's output voltage.  Using this, you can calculate the voltage that would result in 330 watts of power with a single 4-ohm sub, and adjust the amplifier's level control to that point.  However, the method isn't foolproof, for various reasons.

To do this, you'll need a CD with a test tone; a 60 Hz tone would be best.  You'll also need a digital multimeter with an AC volts setting.  Disconnect the sub from the amp, turn the level control all the way down, and connect the multimeter's test probes to the speaker output terminals.  Put the CD in the player; turn off any bass boost or loudness controls.  Turn the volume up to your normal maximum listening level (not the deck's maximum volume).  (You may need to disconnect the front and rear speakers to avoid damaging them during this process--test tones are generally tougher on speakers than normal music listening).  Go to the amplifier, and increase the level control until you see a voltage of 36 volts on the multimeter.  This level should result in an output of 330 watts to a 4-ohm sub.

Keep in mind that if you turn on the bass boost or loudness control, the result will be an increase in power to the subwoofer.  Also, not every CD may be recorded at the same level as the test CD; if you play a CD with a higher level, or another audio source, you may end up over-powering the sub this way.  However, this should give you an basic idea of where the limit is for your system.

In the end, your best option is probably to upgrade to a subwoofer that can handle the amplifier's full rated output.

Hope this helps!

Brian