Originally appeared in the November/December 1990 issue of Car Stereo Review magazine.
If youve ever attended a sound-off contest or flipped through the pages of CSR, you have probably run across a system that has amplifiers and other components mounted on a panel in the hatch or trunk. This panel, commonly known as an amp rack, is very popular in high-end auto sound circles these days.
There are many good reasons for using an amp rack, but the primary factor is cosmetics. Even simple racks make an otherwise ordinary installation look sophisticated, and features such as forced-air cooling, motorization, and custom upholstery can transform a simple rack into a work of art.
There are practical reasons for using an amp rack, too. When a rack is properly designed, it makes installation much easier and greatly simplifies system maintenance – it can be a big time-saver when you need to change a fuse or run new speaker cables, for example. In addition, the fewer holes you drill in your car, the better (at least from a resale-value point of view).
Before we get down to business, there are a few general points to keep in mind concerning the design of an amp rack.
Where to Put It
In most cases, the type of vehicle you own will dictate where you should install the rack. In sedans, the trunk is the most logical place. In hatchbacks, your best bet is to install the rack in the hatch. Some cars, including Corvettes and Trans-Ams, even have small storage wells in the hatch area that can be modified to accommodate an amp rack, although it takes a little ingenuity and a whole lot of craftsmanship to pull off this space-saving option.
If you own a pickup truck, youll probably want to relegate the rack to the often cramped space behind the seats. If the size of the components you intend to mount on the rack allows, however, or if the truck is an older model, you just might be able to squeeze a rack underneath a seat. You could mount the rack to the bed of your truck, but youd better have one heck of a security system – and a weather forecaster whos more accurate than mine.
In the end, finding a home for your amp rack boils down to the type of vehicle you have and the size of the components you plan to use.
Common sense is the only thing you need when it comes to planning the dimensions of your amp rack. Plain and simple, the size of the rack will depend on the size and shape of the components you plan to use and the layout of the mounting spot youve selected. One not-so-obvious thing to keep in mind is the possibility of future upgrades. If an additional amplifier may be in the cards, for example, be sure to design your rack with that in mind. You may also need to leave room for accessories like power-distribution blocks and panels for fuses.
The trick here is to envision what the finished amp rack should look like in your vehicle. Will it be concealed under a secret panel? Will it be exposed, sporting a colorful but carefully arranged array of cables? Will it be painted or covered with carpet, vinyl, leather, or some other exotic material? Basically, your rack can look any way you want it to, and its a great opportunity to show off your personal style.
Maintaining an adequate flow of air over your rack-mounted amplifiers is important for reasons of performance and reliability. The problem is that most car stereo amps (the component most commonly mounted on a rack) are only 50-percent efficient, which means they generate a substantial amount of heat when you crank them up loud. If their temperatures get too high, electronic components inside the amplifiers could be damaged. The idea, therefore, is to keep the amplifiers as cool as possible.
The most common ventilation method, convection cooling, also happens to be the simplest – and provisions for it are built into most car amplifiers. Convection cooling works like this: As the tiny electronic components inside an amplifier heat up, warm air is transferred to cooling fins, usually part of an aluminum heat sink on top of the amp chassis; the fins radiate the heat into the air, where it dissipates. As the warm air rises, its replaced by cooler air thats sucked upward from beneath the amplifier, and it is this continuous circulation of cool air that prevents the amp from overheating. Convection cooling works fine as long as the warm air can dissipate and cool air can move in. Thus, amplifiers should never be mounted in an air-tight enclosure. Instead, mount them on a vertical surface (when possible) in an open space, preferably with their fins running vertically rather than horizontally.
Another popular cooling method relies on a small electric fan (or more than one) to move air over the amplifiers heat sinks. The benefit of this approach is a dramatic threefold increase in cooling capability; thats why many high-power amplifiers are equipped with built-in thermostatically controlled fans. If you want your rack to house several convection-cooled amplifiers, its worth the extra effort to install this kind of "forced- air" system – the cooler you keep the amps, the longer theyll last. And if youre designing an enclosed amp rack, one or more fans will be a necessity. Since most accessory fans run on 12 volts DC, powering one is simply a matter of wiring it into the source units remote-turn-on lead so that whenever the system is turned on, the fans kick in along with the other components triggered by the lead. Fans are sold by Radio Shack and other electronics distributors.
At this point, you should give some thought to the implications of mounting an amp rack in your vehicle. If the rack will be visible from the outside of your car (as in a hatchback install, for example), you could be tempting thieves. To prevent them from breaking into your car and parting you from your equipment, you should go with one of the following options.
First, you could make the amp rack removable. The advantage to this type of installation is obvious: If there is no equipment in the car, it cant get ripped off. Unfortunately, removing the rack every time you leave your car could become a real pain. A removable rack may be a necessity, however, if it will take up a lot of space and you want to use your vehicle for holding luggage or hauling large loads of such things as wood and groceries. Using wing nuts to fasten the rack will promote quick removability.
Another, more realistic solution is to make the amp rack invisible to someone looking in the car. The easiest way to accomplish this is to fabricate a removable cover that hides the rack from view. The cover can be anything from a piece of cloth to a piece of Masonite. The specific look and material is limited only by your imagination.
A good all-around security system should also be considered an essential in any high-end installation. The ideal install would incorporate all three of these deterrents. Removability would provide extra security when necessary and additional cargo area; the secret panel would provide the convenience factor; and the security system would provide a line of last resort.
After youve made the basic decisions, youll be ready to hit the shop. But before you get your hands dirty, take a few minutes to plot out a plan of attack in accordance with the following steps:
Design the rack on paper.
Acquire all of the necessary parts.
Fabricate/assemble the rack.
Upholster the rack (if your design calls for this step).
Mount the components.
Run all cabling.
Install the rack.
Grab a piece of paper and sketch out the general shape of the rack; then position each component on it. Arrange the components so that the connections can be easily made. At the same time, try spacing the components in a symmetrical fashion to provide a clean, balanced look; this is especially important if youre a participant in the sound-off circuit. Also, now is the time to take into account whether fuse panels or a power-distribution block will be mounted on the rack. Make a bunch of sketches if thats what it takes to come up with one youre satisfied with.
Next, measure the length and width of each amplifier. Using these measurements do a detailed drawing to scale (1 inch = 6 inches, for example) so you can see exactly how the rack will look. Label the sketch with FRONT and BACK legends, and make sure you arrange the components with thought to the location of their input and output jacks. The more accurate your drawing is, the better the finished product will be.
Finally, measure the designated mounting location to verify that the rack youve designed will fit. Its advisable to leave yourself a little breathing room.
Once you have an accurate "map" in hand, its time to round up construction supplies. Hint: Get everything you need beforehand. This will save you loads of aggravation later. Nothing is more irritating and disruptive than having to run to the store a dozen times while youre attempting to complete a project.
I recommend plywood as the basic construction material because its relatively light and easy to work with. Thats not to say that particleboard or another type of sheet lumber wont work – they will. Just make sure the wood you choose for the main body of the rack is thick enough to support the components you plan to use. Generally, 1/2 or 5/8-inch thickness will suffice unless youre going to load the rack down with a lot of heavy components. While youre out, youll also need to pick up some sandpaper, finishing nails, yellow carpenters glue, and wood screws. Along with the glue, youll use the screws to join the main pieces of the rack together.
Now decide how you want your rack to look and purchase the appropriate covering material if you plan to use some. If this is going to be your first upholstery job, I recommend using Ozite, an inexpensive felt-like carpet thats sold at most installation shops. Its available in almost every color of the rainbow and its very forgiving if you make a mistake.
Vinyl and leather are also viable candidates. Of the two, vinyl is less expensive and easier to work with. Leather, on the other hand, is costly and harder to apply. Either of these materials can be purchased at a fabric store or upholstery repair shop. Regardless of the type of upholstery you choose, youll need some means for attaching it to the rack. I suggest using spray adhesive (3M makes a good one) and an air stapler, both of which are available at a lumber yard or hardware store.
In addition to the above materials, youll need a few tools to build the rack. A saw is most important. If possible, use a table saw to cut out the base of the amp rack, since it will produce the straightest cut. Failing that, turn to a circular saw, a jig saw, or a hand saw – the hand saw being a last resort. Youll also need an electric drill, assorted bits, a hammer, a screwdriver, scissors, a rasp or file, and a razor knife.
Once youve gathered up all of the necessary tools and materials, draw a full-size template of the amp rack directly onto the plywood using a yardstick and a pencil. When youre absolutely sure that all of the lines are in the right place, carefully cut along each of the pencil marks using your saw of choice. Hint: Make the cuts on the outside of the line or the rack will wind up slightly undersized. Once the cuts are made, verify that the rack is of the correct size by holding the template up to it. As long as its within 1/8 inch of the template, itll be fine and you can begin sanding any rough edges; if an edge is really jagged, use a rasp or file first and then sand it. When youre finished smoothing things out, dust the rack off.
Place the amplifiers on the rack in accordance with your sketch. Once the components are positioned to spec, mark each mounting hole with a pencil. Also indicate where the power, speaker, and signal cables are going to pass through the rack if that is in your design. Now remove the components and set them in a safe place. Grab the pencil and write FRONT in huge letters on the front of the rack, BACK on its backside, and TOP on both of these surfaces, with an arrow pointing toward the appropriate edges. This may seem obvious, but nothing is more frustrating than "finishing" a project only to find that you must rip it apart to correct a major error.
Next, drill the mounting holes using an 1/8-inch bit; make sure each hole is straight and goes completely through to the other side. Use a larger bit to drill holes for the cables if theyre going to pass through the rack; the holes should be big enough so the cable slides through without hanging up. Sand away any splinters or burrs from each hole.
One of the secrets to professional-looking upholstery is preparation, so clean your workbench and cover it with cardboard or newspaper to keep adhesive over-spray from getting on the bench and other materials from sticking to the adhesive. Next, lay out the tools youll be using on a side table, including the razor knife (with a fresh blade), sharp scissors, a stapler (preferably air driven), and that can of spray adhesive. When you finally have everything organized, its time to begin.
Lay the amp rack (front side up) on the workbench and put the upholstery material (good side down) next to it. Using the razor knife, cut the material to size, allowing 2 to 3 inches of excess on each side. Now spray a liberal amount of adhesive on both the wood and the backside of the material; let it dry for a minute or so, until it becomes tacky to the touch. Then carefully pick up the upholstery material and turn it over. Starting at one side of the rack, slowly press the sticky side of the material to the rack as if you were applying a giant bumper sticker. You may have to hold the material with one hand while you smooth it down with the other (an assistant would be helpful here). Again, make sure the material hangs over the outside edges of the rack by at least 2 or 3 inches.
Before moving on to the next step, set the upholstered rack in a clean, safe location and replace any soiled cardboard or newspaper on the work bench. Now, flip the rack over and place it front side down on the bench. Using scissors, trim away the material that protrudes more than 3 inches beyond each side of the rack. Next, spray adhesive on the edges of the rack and along a 2-inch border on its underside; also spray the backside of the overlapping material. When the adhesive feels tacky, pull the overlapping material up and over the edge of the rack and press it firmly in place. If necessary, fire a couple of staples through the material to hold it in place while the adhesive cures. As a finishing touch, use the razor knife to make a diagonal cut in the overlapping material, moving from each corner toward the center of the rack; this will allow you to remove it.
Mounting the Components
When youve completed the upholstery job, youre ready to mount the components. Turn the rack over so that its bottom side faces up. Next, grab a handful of finishing nails and push one into the upholstery above each mounting hole. These nails serve as markers, so they should fit loosely in the holes. After inserting each nail, cover the bottom of each hole with a piece of masking tape to keep the nails from falling out; when youre done, the finished side of the rack should look like a bed of nails.
Now place the components on the rack, making sure that the rack is right side up before you do so. Lower each component down onto the rack so that the corresponding "nail markers" protrude through the appropriate mounting holes. When all of the components are in place, secure them to the rack using screws; I recommend #6 1/2-inch wood screws. To line everything up as accurately as possible, put one screw in at a time.
Depending on the number of components youre using, it may be a good idea to connect some of the cables directly to barrier strips on the rack. (The more components you use, the more time and effort this will save you later.) Since all of the speaker wiring will be connected to the barrier strip instead of the amps, it will be easy to make or break connections once the rack is installed. The bottom line: Wire as much of the rack as you possibly can before installing it in your vehicle; this includes fuse panels and power-distribution blocks if your design calls for them. But make sure youve accounted for these accessories at the planning stage, or you may not be able to fit them on the rack.
If the wiring on the rack will be exposed to view, you will want it to look as neat as possible. Route the cables from one component to another in a uniform fashion. Once theyre positioned, secure the cables in place using plastic cable-mounting clips available at Radio Shack.
Finally, were approaching that moment of truth – the actual installation. At this point, there are several important considerations to keep in mind. The first is clearance. If youre installing the rack in a sedan, make sure it doesnt get in the way of the trunk lid. And dont forget about the spare tire and jack – you just may need em one day!
In hatchbacks, clearance should be maintained around the hatch door and its pneumatic struts. Be especially mindful of the outer edges where the glass usually curves downward. As a rule, first try positioning the rack directly behind the rear seat and adjust it from there if necessary.
The only clearance problem that may crop up in pickups involves the seat. Unless you like driving with the steering wheel up under your chin, make sure you leave enough room behind the seat to allow for comfortable cruising.
Assuming that the design phase was properly executed and none of the above scenarios causes a last-minute panic, its time to secure the amp rack. The last thing you need is an amplifier that rattles around or becomes air-borne when you hit the brakes. Since every installation is different, there is no standard method for fastening the rack in your vehicle. There are a few general guidelines to follow, however: First, always fasten the rack to metal and not just plastic or fiberboard trim panels. Secure small racks using drywall or sheet-metal screws. If the rack is large and/or very heavy, use 3/8-inch bolts to hold it in place. Also, be extra careful when drilling holes in the vehicles chassis. You would be surprised how many people drill through the metal and into the gas tank or some other vital area. Thats not the kind of bang you want at the end of your job.
Going the Extra Yard
The sophistication of an amp rack is limited only by time and the amount of money and imagination you possess. While the rack described above (Figure 1) is simple in nature, there are a few things you could do to make it more exotic. One of my favorite add-ons is a facade or trim-plate (Figure 2), which creates a rack into which the amplifiers are partially recessed. The facade can be made from 1/8-inch fiberboard or Masonite and covered with the same material used to upholster the rack. The basic procedure involves constructing a wood border measuring an inch or so in height around the edge of the rack and cutting out a trim-plate that has the same size and shape as the rack. Then, you cut openings in the facade that match the tops of the components so they protrude through it when its in place. The result is a super-clean-looking installation that conceals all wiring while giving the amplifiers plenty of room to breathe.
Another favorite upgrade of mine is the Plexiglas shroud (Figure 3). Unlike the facade, the shroud covers everything, necessitating the use of a fan-type ventilation system. One popular method involves mounting a small exhaust fan (or two) in one of the racks sidepanels so it blows cool air from outside the enclosure across the amplifiers heat sinks. This forces the hot air to exit through an exhaust port youve fabricated on the opposite side of the rack; some designers go so far as to install two fans – an intake fan at one end of the rack and an exhaust fan at the other.
A clear shroud is perfect if youre a sound-off competitor and want to highlight wiring and other electrical aspects of your system. In addition to projecting a sophisticated, high-tech appeal, the shroud will serve as a trophy case that protects your systems power block from scratches and other damage.
Motorization is another option, although its usually very complicated to implement and way beyond the scope of this article. Racks that pop up, flip over, rotate, or spin are just a few possibilities.
Even the simplest rack is certain to improve the look and functionality of your system. And while I cant guarantee you a trophy at the next sound-off, a well-executed amp rack will certainly put you on the path to winning one.