Introduction: Micro-Sized Boom Box
This project was born out of the need of a simple, portable ipod speaker. I wanted something that could easily fit on my pocket, play at relatively loud volumes for its size, and run for hours on one battery.
Naturally, I chose an LM386 audio amp for my circuit. This amplifier has many benefits for this kind of application- it is small, requires no heatsink, can put out about .25 to .5 watts, and operates at 6 to 12 volts. I also chose the LM386 for my pocket-sized guitar amp here. Due to the staggering amount of information out there on the LM386 and sample schematics, I am not going to go into detail about how to build the circuit, but for this project the gain was set for max. Also, a 9 volt battery was chosen as the power source. Also,to simplify the circuit and save space, I decided to use the ipod headphone output as the signal source rather than the line level output. This means volume can be controlled from the ipod.
The drivers used are two oval drivers from a nv3 cell phone, and one inch wide driver that i had in my parts bin. The oval speakers each had an impendance of 4 ohms, and were wired in series, then wired in parallel to the 1 inch driver, which also had an impendance of 8 ohms. This gave a total load of 4 ohms.
The enclosure was the tricky part. It started as pressed cardboard that was about 1 mm thick. The enclosure has trapezoidal cross section, with the larger base housing the two oval drivers side by side, and the longer side housing the round driver. The circuit is mounted inside, while the battery is outside. The side opposite from the round driver has a magnet on it, so the speaker stays mounted on top of the 9 volt battery.
Once the enclosure had been assembled, .25 OD inch tubing was mounted around the drivers, so once the speaker cloth was added, it would not touch the drivers. The speaker cloth was wrapped around the entire thing, with the ends being bunched together on the sides and bottom. These areas were then covered by thin aluminum for aesthetic appeal.
Overall, the speaker turned out to be a success. It is plenty loud, and can easily be heard from a cross a room. There is also a surprising level of bass present, without there being any noticeable distortion. Since the amplifier is designed to operate at line-level input volumes, full volume is reached with the ipod turned up to half volume.