I would recommend a single Alpine SWR-8D4 8" DVC (4ohm +4ohm) dual voice coil subwoofer, wired in parallel for bridged 2ohm configuration to compliment the R-S65C Alpine components.

I'd put the sub in a sealed enclosure to get the deepest note possible. The enclosures inside airspace should be about 0.50 cubic feet taking into account; the woofers displacement. A larger (0.80 cu.ft., for this model sub), ported enclosure would give you a 2-3dB peak at around >40Hz, but sacrificing some -5dB loss at around 20Hz. You can, however, gain that +3dB bump in the sealed enclosure, with the aid of the Alpine headunits parametric EQ, if you so desire. Bass output will be loud enough that you will able to hear your car from inside your house at 50ft away, so be aware with your city's noise ordinance to avoid any noise violations.

I would configure the amp for 2 front speaker bridged @4ohms/1 sub bridged @2ohms output mode. Connect the Front L&R RCA output from headunit to amplifier channels 1,2,3,4 via pair of "Y" adapters and connect L&R Subwoofer RCA output from headunit to amp.

As a safeguard to the mids and tweets, at the amplifier, set the high pass crossover point at 50Hz (HP Filter ON). Then set the low pass crossover point at 50Hz also. The amplifier owners manual says to set filter off, but it won't hurt the speakers when the filter is on either. Final crossover setting is configured with the headunit controls. From the head unit, set the front speaker HPF at 63Hz @12dB / octave slope and set the subwoofer LPF at 50Hz @ 12dB/ octave slope.

To set the amplifier front and sub channel gains, first set the input selector CH-3/4 to 3/4 and SUB W. to SUB W. Then, follow the input gain adjustment control as instructed by the amplifiers owners manual.

Although the amps front L&R bridged RMS output is slightly greater than the speaker components maximum RMS power capacity, this configuration will allow you to safely set the appropriate gains, crossover settings and subwoofer phase from the headunit.

To fine tune and set the subwoofer level, play a dynamic high-quality digital recording, press the headunit AUDIO button repeatedly unti you get to Subwoofer Level then turn the rotary **** to get to the desired setting. The perfect setting would make you believe sub bass is playing through the kick panels.

Now, you can set the Time Correction parameters from the headunit by delaying the drivers side speaker output to give you a wider soundstage and a defined center image.

As for amp power, run the recommended 4 gauge wire through the firewall rubber grommet located under the battery tray and terminating with an AFS60 or Midi 60 amp fuse at the constant 12v power block near the battery.

There is an available slot (F1) in the power block for a midi fuse but the bolts to hold the fuse in place did not come with nuts from factory. Use a couple nuts with 10-32 thread pitch for the fuse mount. I prefer using an AFS fuse because they have an open-end spade opening on one end which would make it easy to change a blown fuse. To install a fuse, just loosen all the nuts on the buss bar and insert the spade end under the F1 slot of the buss bar, then re-tighten all the nuts according to the torque recommendation on the fuse cover. Often, midi fuses have only mounting holes on each end which would require more work to replace properly.

A generous amount of sound deadening material, like Dynamat, is recommended for the doors just because your amplifier output has the potential of loosening things with those 6-1/2" mids. While working with the door panels off, go ahead and epoxy the tabs at the backside of the silver, mid speaker, trim ring because they have a tendency of falling off unexpectedly.

I recommend installing the 1" tweeters at the "A" pillar, at eye level, for a more realistic soundstage. (see my post on modifying for 1" tweeters on the "A" pillars) You may have to use a 15 or 20 ohm resistor in-line with the tweeters to keep them from being too "hot" or overpowering. You will enjoy better center imaging of vocals and instrumentation clarity when installing the tweeters up high at the pillars.

While working on the pillar tweeter project, I would go ahead and custom install the hands-free microphone that came with the headunit, high up-top on the drivers side "A" pillar.

These recommendations are just some of the basic stuff but I hope it will help you somewhat in putting together a kick-*** system.

Thank you for the well thought out reply. It is very helpful and I appreciate your input. I will read up on the tweeters and I’ll definitely dynamat the doors.
Obviously I will bridge the output on the amp to two channels for the doors. Would it be better to split the front channel rca from the head unit to both pairs on the amp or just run the front and rears (all 4) and leave the fader set to the center?

Perfect I will pick up a splitter. Thanks.
Would this sub be a good choice then?
https://www.crutchfield.com/p_500SBR...-S8-4&skipvs=T

Excellent. I think I now have everything I need incoming other than a few pieces of hardware and I have to pick up some bigger shrink wrap. Once it all arrives I just need to find time to do it. I have some spray on lizard skin brand sound deadner but I lent out my gun for it and didn’t get it back.
I haven’t made a decision on tweeter placement yet. I may just put them in the stock location for now and see how it sounds. I have two gauges in my driver side a pillar already.
I truly appreciate all the input. The knowledge shared will save me time, money and regret. The head unit I have now is a blaupunkt with the rest factory components. I separated the factory amp to have the subs as rears so I can adjust them with the fader. I have a blown sub and a blown door speaker. It also has poor fm reception and picks up ignition noise. I’m hoping the interference issue and poor reception goes away. This upgrade is long past due.

Here was my last crossfire build. How was that 12 years ago???
a tree fell on that car and smashed it flat.
I have no desire to make a double din again but it was cool.
https://www.crossfireforum.org/forum...r-avic-z1.html

Moving along. I got the head unit and amp wired up and mounted . I need to do the door speakers. I’m going to work on that today. I’ll post some pics soon.

I have everything installed. I set the amp and gain levels. I just need to finish tuning it and mount the sub enclosure so it doesn’t slide around.