Introduction: Computer Subwoofer System Retrofit Into Jeep and Audio Upgrade

About: I love building things, and I'm a twin, we both are electrical engineers and inventors. Feel free to ask anything else
Awhile ago I was given an Alpine headunit from a neighbor and not thinking I had much use for it, I just tossed it in the back and there it sat till recently when I took a second look at it and realized how nice it was compared to my current Pioneer headunit. After hooking it up, it sounded so much better and looked nicer too but the Jeep still lacked some bass. I remembered I had a set of  Cyber Acoustic computer speakers with a subwoofer on them. I wondered if I could hook that up and use those to get me some more bass, so thats exactly what I did and thats whats ill show you how to do from installing a new headunit to the sub system,

Step 1: Ripping Out the Old Unit

  Perhaps one of the more fun parts of doing audio is removing the old radio to make way for the new better equipment. the radio I took out was a Pioneer CD player unit from 2004 or so. It did the job but didnt have anything special about it, and it didnt have an AUX input either. 
  To get the radio out you have to remove a few parts of the dashboard that are in the way. On Jeeps it isnt too hard, there is just the instrument panel bezel that has two screws and clips. I was able to take it off in about three minutes. 
  The radio itself was held in place with two scews, so taking those off, it slid right out. Thankfully the previous owner used an after market wire harness adapter on here to put the old radio in so wiring it up will be a breeze. it just unclips off the harness, pop the antenna wire off and out it comes. (your experience may differ as more is involved with newer vehicles)

Step 2: Adding the Aux Input to the Alpine Headunit

  Somewhat like the other radio but not really, this radio doesnt have a useable input unless you go online and buy an expensive plug for it. I wasnt about to do that so I decided to make my own and solder it onto the board underneather the plug.
  To get to the pins on the board i needed to remove the casing, but unfortunately the bottom panel I needed to remove could only be taken off if I dismantle the entire unit and take out the board to get to the pins. I wasnt about to do that; just take a pair of tin snips and cut the metal around the pins to gain access to them.
   Step two is to figure out what pins are the audio inputs and which ones are power supply to the aux unit. (this input is meant for a cd changer or XM) I hooked up a 12 volt 10 amp regulated power supply to the radio and a couple of speakers. I then took a voltmeter and measured the pins while the radio was on to figure this out and pretty much every pin had 13.3 volts on it except for two. The board had a L and R under a pin but these had voltage too.
   I used a portable cd player and a scrap headphone plug to test the two inputs I found. I put the common input wire from the portable cd player to chassis and touched the other two wires to the pins and music was heard perfectly from the headunit. So now that I know what pins are the inputs I simply soldered them on and soldered the common wire onto a negative pin on the board and it works perfectly. to keep it in place I zip tied the wire to the antenna wire. this method was free to do versus buying a plug to use for it, and more fun.

Step 3: Making a Mess and Testing the Computer Speakers

  This is what my dining room looked like for a couple of weeks as my project moved forward. I am able to test the radio and computers speakers inside with the power supply and fine tune it.
  Using ampified speakers from a computer in theory is not that much different than a car sub system as far as both have an amplifer and some controls to do fine tuning. A car amplifier has controls to tune the amp and sub to the radio. This computer system has a volume control and bass control which is similiar to the gain and bass boost controls on a car amplifier. The only real downside of computer subs for a vehicle is that the amp and speakers arent much wattage. mine might be 30 watts if im lucky, so it wont put too much bass out but I dont want that much so its all good.

    I got a scrap usb/ speaker input board from work to connect the computer speakers to the subwoofer output of the radio using half an A/V cable. By using the input board I can later add more speakers if I so choose, and make for a quick disconnect to remove it. also its one less thing I need to hack. 

    To power the speaker system, it needs to be able to run on around 11-14 volts. the system runs on 9 volts 700 milliamps which is converted from a wall transformer plug. All I need to do is reduce 12 volts down to 9 volts. An easy way to do this would be to buy a voltage regulator circuit or even a cheap power inverter to keep the 120 volt plug. The way I did it was use two 8 ohm resistors in parallel to make it 4 ohms resistance. which if i did the math right gets the current down to 700 ma constant. but It didnt change the voltage unless there is a big current draw. Resistors arent good for this application because of that issue and automotive power systems are never constant. so the voltage and current will vary from 11-13 volts. the speaker amp doesnt seem to mind as I tested it hard for a straight week like this and never overheated.

Step 4: Wiring the Harness to Alpine Radio

  This is an after market radio harness to connect an after market radio to your vehicle. The first picture has part of the old radio harness on it so that will be removed.
   All the wires on the aftermarket harness are color coded to the Alpines radio harness so wiring it up was a sinch. You will also want to run two wires from the 12 volt positive wire (red) and also the amp turn on wire (blue w/ white stripe) which will go to the sub speaker amp and soon to be installed relay to turn on the sub speaker when the radio is turned on.

Step 5: Installing the Radio Unit

  Installing it is almost as easy as taking it out. Since its on a harness, all that is needed to do is plug it in and shove it in the hole. You might have to play around with the position of the wires to keep them out of the way so the radio fits in good.. since we are having the sub system on it, dont forget to run the wires through the dash. The power wires and sub out audio wire. Mine were just long enough to make it to the front seat which is what I wanted for this point. also run the aux input out of the dash wherever you want it to go.

   The mounting bracket that holds the radio to the dash board got bent when removing it off the old radio so thats why my new one is sideways, not because of the aux input wire.
   At this point I tested the radio to make sure all the speakers and connections are working before putting the dash together. this way you wont have to remove it all again if you have a speaker thats not working, or forget to plug the antenna in.

  After its installed, go ahead and put the dashboard back together, which again was easy in my case.

Step 6: Running Wires

  I used two scrap computer power supply cables I got from work for the power from the radio to the amp. I spliced them with those little red couplers and taped them up real good to prevent exposed wires. the blue wire comes from the amp turn on wire from the radio. and goes to the relay, the brown wire is for the power negative going to the relay which I will explain in the next step, and the green is power positve going to the relay for power supply to the amp. so all three of these wires are going to the relay.

  The audio cable is just two wires. Just splice the two coming from the radio to two wires going to the usb/ speaker board which is connected to the speaker system audio input. I used just plain speaker wire which will work fine for this.

Step 7: The Relay

  We need a relay for this setup for two reasons:
1: to switch the system on and off from the radio
2: a more safe and reliable power source
  This particular relay is a 12 volt headlight relay from a hyundai which is perfect for this. The three power wires coming from the radio meet up here and then one goes on the the sub system. Here is where i soldered the resistors to reduce the power going to the sub. The relay works like an electric switch to turn the power on and off to something. It has two circuits inside it. one circuit is the switch itself which is a small solenoid that when has power applied to it will close the circuit of the other one, therefore allowing power to go through it. there is one negative wire on the relay which is for the solenoid so the circuit can open or close (off or on) when voltage is applied. the power for this comes from the amp turn on wire from the radio. The power for the other circuit which will supply power to the amp comes into this second circuit and doesnt turn off, its always hot. the two are not connected in any way.
  Just as in a car audio amp, when the headunit is turned on it sends 12 volts to the relay which energize and close the circuit of the other part and allow the amp to turn on. when the radio is turned off the relay will not have power going to the solenoid anymore so it will open the circuit and turn off the amp. 
  You dont need one of these, you can wire it directly to the radio amp turn on wire to supply the full power. It does work the exact same way as the relay would.  I tried it but I decided to use a relay so the radio circuitry wouldnt be overloaded. I also went an extra step to wire the main power wire into the main power for the radio (red wire) so nothing will have power when the ignition is off. 
Now that i explained how the relay works, the power positve from the relay will now go to the computer speakers.

Step 8: Wiring Up the Audio to the Computer Speakers

  Now we can start to wrap up the install. The two audio wires coming from the radio will now be spliced into the speaker/ usb board. Since all I really want is the sub to work and not so much the speakers on the system, I just wired up the headphone jack to do mono. Since I have no use for the usb part...yet i will just leave it alone for now. After I spliced the wires in, I just needed to simply plug in the jack. It was make for a quick disconnect this way.

  All that is needed to wire now is the negative wire from the computer speakers. I originally tried to have the negative that also powered the relay come to power the sub but it was humming too much. To fix that I removed it from the relay and grounded it to the vehicle chassis with a screw and problem solved. Everything is now hooked up and ready to go!

Looking at the second picture, you can see the advantages of this setup:
1: small, compact so it saves space
2: the way its setup is now removeable
3: nobody will steal it lol

Step 9: Final Steps and Testing

  Only a couple things left to do, hide the wires and turn it on! Hiding the wires was simple, All i did was tuck them under the center console and put the relay under the back seat out of the way.
 I turned the radio on and as planned, the relay energized and turned the computer speakers on. I didnt need to do any fine tuning other than adjust the bass on the headunit. The little sub hits pretty hard. its only 3 inches or so but it sounds really decent. It adds enough bass to do what I want and doesnt suck a load of power like a typical car audio system would which is a plus.
  I also tested the AUX input I soldered in and it works perfectly still, sound comes from all the speakers and in stereo! All the speakers hit really hard compared to the older Pioneer CD player I had in it before also.
  So if you are looking for a budget system that sounds really decent; consider looking around your home for parts you dont use much. this upgrade costs me literally nothing other than the computer speakers which I paid $30 for 5 years ago! It sounds great too!
Car Audio Challenge

Participated in the
Car Audio Challenge