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Discussion Starter #1 (Edited)
This article is a guide on how to convert your early model Mustang Rear Deck 6x9 Speakers into a High Fidelity Music Machine

The Problem
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.

Background Information
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.


Construction Solution
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.







Installation
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.


Final Thoughts
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.

Parts List
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
 

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Re: Louder then My Engine.....

Did you wire the 330Hz woofers out of phase with the 60Hz woofers? Since the sound coming out the port is 180 degrees out of phase with the woofer below resonance, your ports would be completely out of phase between 60Hz and 330Hz. Reversing the phase would cause them to be out-of-phase only below 60Hz, but since you say this isn't a subwoofer, that shouldn't be a concern. If you haven't tried it, just give it a shot, and if you have a DB meter use it to quantify the difference... it could suprise you.

Also, did you consider mounting the box the opposite direction, so the woofers are facing the passenger compartment? Overall it's a very cool and interesting design! What made you decide to go this route vs. a 10" woofer in a similarly sized ported or bandpass enclosure?
 

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Discussion Starter #3
Re: Louder then My Engine.....

Good Questions Motorhead, I will try to address them.
Thanks for the nice notes too.

The speakers are facing the trunk to take advantage of the trunk space as a resonance chamber. The trunk is actually part of the acoustical design. I was not sure how much power I could get from just 6 inch drivers, so I counted heavily on the trunk to act like a sonic amplifier, ad I hit that goal 180%.

Secondly, I can open the trunk when I want to hear the music away from the car..... Thirdly,it looks cool....(smiles)

If they were facing the seat, it would actually take away some of the resonance and soften the sound a bit.

I gatta tell ya, this thing kicks butt....with just 50 watts.


The 80 hz and 300 hz chamber speakers are in phase with each other. It is a little difficult to understand how the system of baffels in this cabinet work without seeing it in 3D. but by the time all 4 of the chambers combine the sound from both left and right, high and low, at the exit portal in the top of this enclosure, they are in phase.

The phase matching I mentioned in the article are between the 4 woffers and the two midranges on the top deck. Those and the tweeters need to be out of phase by 180 degrees. I should have been more clear on this. I tried to keep the scope of this article short, and without writing a novel about it....

I think the concept of an approach like this is the more important issue.

I am sure this will work for the Falcon and other simular vehicals.... Just gatta change the external dimensions to mount it properly.

I like to think outside of the box, (pun intended) went away from off the shelf speakers, and created this.

It actually works (and sounds) a lot better then I thought it would. I have been around music for a long time, and I have never heard a stereo in a car sounding like this.
 

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Re: Louder then My Engine.....

Thanks Mike, I noticed the unique chape of the low-frequency chambers, how they wrap around the box... that would definitely have an effect on the sound and phasing, that would make it perform differently than a normal ported enclosure. That's definitely a design that I haven't seen in any of my books, and it sounds like it's working great for you!

I understand what you're saying about the woofers facing the trunk vs. facing the seat. In my Bronco I built a custom box that buts up against the back of the rear seat, with the four 12's facing the rear, to accomodate more cargo space. Just for grins, I used my DB meter to compare the volume and my ears to compare the sound with the subs facing rear vs. against the tailgate facing forward, and there was a 1-2db improvement with the subs facing rearward, plus it seemed to have a richer sound with stronger low-end bass. Woofer systems design and performance can get very interesting when they are installed in small spaces like inside a car vs. in a theater or large room.
 

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Discussion Starter #6
Re: Louder then My Engine.....

Hey Motorhead,

Good grasp of 3d imaging from looking at the photos.....your correct, it is a folded resonance chamber design. The tricky part is keeping all of the different chamber volume's (area) at the correct porportions.

This speaker I designed last year, has a lot of the same folded chamber designs inside of it. This design actually has 5 resonance chambers all tuned for different aspects of the spectrum.

This speaker cabinate, proabably emmits and can handle the most bass I have ever heard in a home stereo system.

Playing Darts in the Cellar, and just a 20 watt amplifier hook up, most folks say it is the cleanest, deepest, and loudest speaker set they have ever heard.

I have had my 260 watt home amp on it, they will take full power, but only in the winter time, since sound travels in the summer.
 

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Re: Louder then My Engine.....

Mike, Why did you use plywood vs. MDF?
 

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Re: Louder then My Engine.....

Mike, Why did you use plywood vs. MDF?
Not sure what MDF is, unless you mean particle board/ pressed wood. I have been building sound transducers for 25+ years, and there is no better sound then plywood. The particle board, is used in a lot of production speakers, cause it is cheaper for them, and it is easier to get reproduction quality the same. ( meaning, no wood knots ). There is no acoustical advantage, only manufacturing advantages.

Plywoods is also stronger, and in a car that is subjeted to high torque stress, composite wood will shatter.

Trust me, with these little 6 inch woofers I used, there is more bass then then any 12 inchers, and it is a richer sound across many different resonance bands instead of a single resonance like the larger speakers.

This design has carfully placed resonance chambers inside of it, to create many different resonance frequencies. The wood type has a lot to do with this too.A hollow box design has only one resonance frequency, and has can only have strong bass at that frequency. Open chambers also cross cancle sound from ajacent speakers.
 

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Re: Louder then My Engine.....

Its not particle board. Its Medium Density Fiber board. It isn't as "loose" as particle board or plywood.

I can't believe in over 25 years you never heard of it! Man your missing out! It isn't always easy to find, But it is getting easier.

MDF FAQ - Tutorial (a quick search)

I have built plywood and particle board enclosures over the years. Ported, chambered etc. MDF is the way to go. (this is my humble opinion)

I love that your using the smaller drivers. So many people jump right to a 12"..
I personally do not like the freq. that 12's put out. 6.5"-8"-10" or even 15" (when I was younger!) are much better then a 12". But my idea of good bass is deep and solid. Not hollow like a 12".

Shoot, I feel that the SAS Bazooka tubes are a great buy for someone not wanting to build a box and add a lot of weight to their car. That is if the interior drivers and head-unit are up to snuff. I am a non-believer in running an amp to dash/door/deck speakers.. But that is just me.


And BTW. I LOVE your design!!!!! It took a couple of scrolls with the mouse to visualize it right. But I see it. :cool:
 

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Just came across your thread and interested in doing something similar in my 1965 Mercury Comet. I believe I should be able to replicate the process since the vehicles are very similar. I was wondering that since you have completed the project if there is anything you would change and also could you provide some more specifics on the stereo equipment (woofers, amps, etc.) that you used or would recommend.
 
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