This article is a guide on how to convert your early model Mustang Rear Deck 6x9 Speakers into a High Fidelity Music Machine
When I picked up my 1966 Mustang with a straight 6 just 3 years ago, plans for this car followed the plans I had for all my other fast Fords I have owned. Make it FAST, make it LOUD, and have a KICK-ASS STEREO. Well, making a 66 Mustang go fast is like fishing in a barrel. I had a nice little 302 sitting in a basement for 10 years waiting for a car to go into. Making a 66 Mustang loud, is even easier. But what about that last requirement...?
After I got my car running fast and loud, I installed a pair of 6x9 speakers in the rear deck. Only problem was, this car is so loud, I could not hear the stereo, and the speakers had ZERO BASS. Shutting the stereo off when the engine is running, was not the plan I had in mind. Issue is, the trunk flooring is so thin, all the noise from the engine and street reverberate up into the speakers and make them flutter at the same rumble frequency as the engine. I needed STEREO SPEAKERS that were LOUDER then my ENGINE and could overcome the sound of the car rumble. Not having a loud car stereo did not sit well with me. So I came up with this neat little fix. I have been designing sound systems for the past 30+ years. Not my profession, just a wintertime hobby of mine. More to life then just working on Fords. I needed to design a speaker cabinet that was as non-intrusive as possible to the 66 Mustang and be LOUDER THEN MY ENGINE. The two important factors.
This is the rear deck on my 66 Mustang after I took out the 6x9's.
This is what the rear deck looks like with the seat and top cover removed. Notice all the holes from the factory in the rear deck. I have not modified any of these holes, they are still in stock configuration... no cutting here is needed.As a second concern was the street noise and the gas sloshing in the tank I could always hear. I installed a 1/4 inch thick rubber mat on the floor in the trunk. Great for anything you put in the trunk like a tool box, it does not slide or bounce around. Better still the rubber is a good insulator from damaging the gas tank.
The idea here is to create a lot of Bass, without major re-work to the car. This multi chamber speaker cabinet (in shown here in it's construction stage) use 2 small drivers per side to create the Bass I was looking for. Keep in mind, the install area this cabinet must fit in is very small. The top deck is only 10 Inches Wide. The total depth of this cabinet is 12.5 inches from the rear deck to the axle housing below it. The entire width in no more then 30 inches. As far as trunk space is concerned, I still have a complete trunk. This project did not intrude on any of the usable trunk space.
This photo shows where all the Bass sound is created. Behind those 4 small holes (2 inch diameter each) are large resonance chambers. These chambers in conjunction with 4 small 6.5 inch woofers is all that's needed for the Bass I wanted. 2 of these chambers are for Low 80 HZ frequency resonance (Left and Right) and the other two are for Higher 330 HZ Frequency resonance (Left and Right). These (4) 6.5 inch speaker holes are shown in this next photo. Keep in mind, this design fits very well, and does not use any of the already small trunk space. It can also come out, (un-install) and you would never know it was there. This cabinet looks big, but it really is not.
This photo shows the woofer compartments. Notice the large amount of screws I am using to hold this together. It is important since this cabinet will be installed in a car that will see a lot of torque stress, and we can not have a cabinet that will rip apart from being weak. All wood used was 1/2 inch thick ply-wood, high grade. $45.00 sheet. One sheet is enough wood for the whole project. I do not recommend composite wood. Different sound properties and it will shatter under torque stress. Will not assemble well either.
Below are some photos of the cabinet before final assembly. Please note there are two tweeters that I bolted on the side. They were only mounted temporarily while I was doing some acoustic testing. These tweeters will not be mounted in the cabinet, they will be mounted on the rear deck cover, after the speaker cabinet is installed. This first view is what would be mounted under the rear deck. Two speakers shown are 6 inch mid-range woofers that line up under the two existing holes in the rear deck. The center 4 small holes ( Looks like your looking down a 4 barrel) are the base ports. The 6x9 oval matches exactly the 6x9 oval in the rear deck.
Here is how it looks installed in the read deck.
Behind the seat, there was plenty of room to mount the power amp to the speaker cabinet. This is a 50 Watt, 2 channel amplifier. You will not need any more power then 50 watts, so plan for it. The speaker cabinet is mounted to the rear deck with 14 sheet-wall screws to keep it tight against the read deck. I also placed a strip of 1/8 inch thick rubber the whole length of the speaker box top to stop any vibrations against the metal. You can see the rubber just hanging down above the amplifier, and under the mounting surface. These screws will not support the box, only stabilize it. The support for the box is the 1 x 6 pressure treated decking I used under the speaker box. It holds all the weight of the box, and holds everything nice and tight up to the rear deck lid. Another Note: I did need to modify the rear deck just a little to mount this cabinet. The lip that overlaps the speaker box was cut at each end, and bent out to be flattened and create a surface that sits flush on the speaker box. Please note the decking block supporting the weight of this speaker shown in this next photo taken of the trunk. (later, I painted the wood to match the trunk... BLACK.)
This wooden support was a very tight fit, and I had to hammer it to get it into place. To date, 900 miles driven, many hard lunches, and this support has not moved at all. It is a pressure fit, no mounting screws were used. This last photo shows the seat re-installed, the rear deck cover, and the 2 tweeters mounted in the rear deck cover. I used a couple of old 6x9 grill covers to cover the holes, and the center hole for the base port is also a 6x9 hole, but I have not put a grill cover on it yet.
Without opening the trunk, you have no idea this car has a kick ass stereo. The results... This STEREO IS LOUDER THEN THE CAR. You have never heard 50 watts per channel so loud in your life. All the sound was designed to reflect off the rear window. The BASS is un-real, but not of that type found in those little Jap cars... this is not a SUBWOOFER. This does not sound like a Subwoofer. You do not need a Subwoofer. This is a tuned speaker cabinet.
I have done some racing with the stereo turned way up loud, and I could not hear the engine accelerate at all, even at WOT 6500 RPM's... all of the car sound was completely dampened by the stereo. Without looking at the tachometer, I would not know when to shift. You want an attention getter... your already driving one... you want to get their attention before you turn the corner... turn it up, they will hear you coming. Total cost for this project was about $350.00 with all the speakers. About 3 days to cut the wood and put it together. You should pick out your own speakers elements based on your music, and change the dimensions of the holes to match your needs. You do not need to go any bigger then 6.5" inch woofers. There is more Bass in this cabinet then you will ever need. Total weight is under 30 pounds.
Be careful about speaker phase. Sound cancels with one polarity and aids with the other. Try both ways to find which is best for your application. Here are the cutting plans for the wood. Cut all the pieces to these sizes, and assemble per the photos I have shown. The tiny reference letters shown in these drawings correspond to the reference letters in the following drawing. They show where each piece is placed. I think I have included all the information needed for this project. I have provided the basics, and I am sure other folks can do a much better job then I have done as I am not an expert cabinet maker. This should be enough to get your speaker project off the ground. Enjoy, and good luck.
1) 4' x 8', 1/2 inch thick Plywood Speakers purchased at Parts Express (ONLINE) 4) 6.5 inch Woofer, 4 ohms, 90 Watt $13.00 each 2) 6.5 inch Mid-Woofer, 8 ohms, 100 Watt $16.00 each 2) 3 Inch Bullet Tweeter, 8 Ohm, 60 Watt $12.00 each Please write me if you have any questions. Thanks, Michael Salerno (Mikes66) Salerno Family Racing