Car Stereos: Need help with amp settings, using a digital multimeter, dual voice coil

Question
Hey Brian, I have the following equipment:
Head unit: Kenwood KDC-BT838U
Amp: Rockford Fosgate P500-2
Subwoofer: 12" Alpine Type-R

I need help with setting the correct frequency and gain controls on the amp, and if applicable, any settings on the head unit that affect the subwoofer as well.

Any suggestion is appreciated!
Thanks

Answer
Hi Jon,

I want to apologize for the long delay in answering your question. I didn't realize how long I'd let this one go.

The P500-2 amplifier is a good match for an Alpine Type-R subwoofer, but only if you have the dual 2-ohm version of the sub.  This is a dual voice coil sub, so if you have the 2-ohm version, you can wire the coils in series to make a 4-ohm load.  This would work very well with the 2-channel amplifier in "bridged" mode.  On the other hand, if you have the (more common) dual 4-ohm Type R, you have the option of wiring the coils in series for an 8-ohm load, or in parallel for a 2-ohm load.  The amplifier isn't meant to be used with a 2-ohm load while bridged, but if you connect it to an 8-ohm sub you'll reduce the output power substantially.  If you're using the 4-ohm DVC Type R, you'd be much better off with a mono amplifier like the P500-1BD.

The gain setting is meant to match the amplifier's input level with the head unit's output level.  The Rockford amp's gain dial is a variable setting between 150mV and 5V; the Kenwood head unit's RCA output spec is 2.5 volts, so you'll probably end up with the gain set near the middle.  The amplifier owner's manual gives some instructions for gain setting on page 9.  If you want to be very precise with the gain setting, you can find tutorials for using a digital multimeter or even an oscilloscope, but personally I don't have a problem with setting it by ear.  Make sure that your head unit's bass boost is turned off, and the EQ set in a flat position, before going through the gain setting procedure.

Your crossover switch should be in the "LP" position; this will send only bass to the subwoofer.  The frequency setting will depend partly on the other speakers in your system; it usually ends up around 80-100Hz.

Finally, the "Punch EQ" feature can be set to your taste, to give you a little more low-end punch.  Don't use it to just make the sub louder, though; if you boost the Punch EQ, you should reduce the gain slightly so that you end up around the same overall volume level.

Hope this helps!

Brian