Introduction: Surround Sound With Drive-In Movie Speakers
My wife and I were attending a local "Art & Music Night Out" on the town square of a small Texas town when I noticed in an antique store window a vertical pole with two drive-in movie theater speakers hanging from it. As old as I am I recognized it immediately. At the Drive-In theater the speakers would hook on a pole and when the movie goer drove up in their car they would roll down the window, unhook the speaker from the pole and hook it on their car window or door. Later the movie theaters changed to FM broadcasts because some people forgot to return the speaker back to the pole and drove off leaving a dangling cord.
They were a little pricey and I didn't know what I would do with them so I passed them by - but the thought of them stuck in my mind.
I was sitting around watching TV one night when an idea came to mind. How about using the drive-in movie speakers in my 5.1 surround sound system. I started looking around and searching on-line for some speakers at a reasonable price. As luck would have it, my wife was visiting friends in Chicago and found four speakers at a flea market for a reasonable price ($20 each). My wife wasn't too happy about lugging those heavy speakers home on the plane in her carry on luggage.
As you may have seen from my previous post about my Live Edge Desk, I am a fan of black pipe. So, I got to work.
Step 1: Speaker Disassembly
I had some small Sony speakers handy that I could use. The drive-in speaker housing is very narrow and the small Sony speakers would fit very snugly inside. I removed the screws from the back of the Sony speakers and carefully removed the front grill. The speaker and circuit board were attached to the front grill framework.
I wanted to use as much of the grill framework as possible to make it easier to attach the speaker inside the drive-in speaker housing. I also wanted to include the cone that was attached to the framework to help with the sound.
The wire terminals were pulled free from the connector on the back of the speaker housing. The speaker was removed from the grill, and the material that was glued on to the front of the speaker was pulled off.
Step 2: Plastic Surgery
Since the grill framework was too tall to fit into the drive-in speaker housing I had to do some surgery. I used a reciprocating saw to remove the acoustical horn and glued it to the side of the framework. I used cyanoacrylate adhesive and accelerator to glue the parts together. The adhesive and spray accelerator were used on all the plastic and acrylic parts for this project. The accelerator set the adhesive very quickly. You can see where I had to glue a piece of acrylic to the side of the horn to fill in one side after I had cut it off.
Step 3: Build the Speaker Framework
Next I built a framework of ⅛ inch thick acrylic panels to enclose the grill framework and mimic the box like enclosure of the original speaker. The ⅛ acrylic sheet was purchased at Home Depot.
Starting with a square acrylic base plate I drilled holes in each corner to accommodate screws that would hold the box to the front of the speaker box using the existing attachment points for the old speaker. I glued the framework to the acrylic plate then cut openings in the base plate using a Dremel to match the openings of the framework. Using strips of acrylic and cyanoacrylate adhesive I built a box around the speaker frame.
I cut the strips using a table saw, being very careful to move the sheet at the right speed – not too fast so as to fracture the acrylic or too slow to melt it. I used a Dremel cut off wheel to cut them to length.
Step 4: Speaker Installation
I installed the speaker and circuit board inside the enclosure. I wrapped the circuit board with electrical tape to keep it from shorting out against the metal.
Batting was added to fill the rest of the speaker enclosure outside the acrylic box.
Step 5: Speaker Housing Finishing Touches
Because there wasn’t much clearance between the speaker magnet and the back of the speaker housing I could not drill a hole in the back of the housing and run the speaker wire through the black pipe into the back of the speaker. I decided to use the connector from the Sony speaker. It was also a tight fit inside so I needed to plan on where the connector was going to be placed. I cut a square hole using a Dremel cutoff wheel to accommodate the wire connector. I epoxied the connector into the back of the speaker. I then reconnected the speaker leads to the connector on the inside of the housing.
I used a ½ inch black pipe flange to attach the speaker to the stand. Again, because of the limited clearance within the speaker housing I elected to drill and tap the holes rather than using nuts for the screws on the inside. I test fitted the screws and cut them with a pair of electrical pliers meant for this purpose – thread them into the hole in the pliers and snip off the ends. Because of the lack of room inside the speaker it was important to cut them short so that they didn’t extend into the speaker housing.
Step 6: Speaker Stand
I used ½ inch black pipe for the stand. Holes were drilled at the bottom and top of the pipe to run the speaker wire up through the pipe. Rubber grommets obtained from the local hardware store were used to protect the wire where it entered and exited the pipe.
The stand consisted of a ½ flange attached to the back of the speaker, a 90 degree elbow with the female end screwed into the flange and male end screwed onto the 30 inch vertical pipe. I experimented with several base configurations. I settled on a wider stance to keep the top heavy speaker from falling over at the slightest touch. The base consists of three tee fittings, four 2 inch pipes, two close fittings, and four end caps. It is still a little unsteady, so I may be changing out the four 2 inch pipe for 3 or 4 inch pipes.
The pipe was cleaned with Mineral Spirits and sprayed with satin polyurethane.
Step 7: Final
I converted four of the drive-in speakers and used them as the front and side speakers. The center speaker projects over 85% of the sound in a surround system and is a little larger. It wouldn't fit in a drive-in movie speaker. So there will have to be another Instructable on how I turned an old Philco radio into the center speaker.
I was surprised at the quality of the sound. One of the speakers rattled at first, but I fixed it by applying a little silicone on the inside to secure the metal screen that is on the front of the speaker. I have since found two more speakers and have them in reserve if I ever upgrade my receiver to a 7.1 surround sound system.
By the way, my wife loves the speakers and has forgiven me for making her lug them back to Texas.