Audio Speakers by Oscar Jones

National Electronics Competition Student Members’ Projects Arkwright Engineering Scholarships

Big Stereo Speakers

This was the first complete pair of speakers I ever made, making the first one when I was about 12, then completing the stereo pair a few months later. My interest began not too long before when I was in Maplin with my Grandad buying parts for a computer he was building. I happened to see a shelf of speaker components, and fancied trying to put one together. So, we bought the speaker drivers, an amplifier module, and the other parts we thought we’d need. It took a few days of experimenting to make it work, and a few more trips to Maplin, but eventually we made a working system, speakers wired up and enclosures made. This worked ok, but now having tried and learnt, I knew it could be done better. And so, I began to make the big speakers. Speaker front
The original plan had been to make one unit with many drivers in it, however the local Maplin did not have enough speakers, so I settled for fewer, three, and ended up with the speaker pictured here. It was an active speaker, with audio and power inputs and volume control on the back, and a mini amplifier and crossover board inside to split the sound to the high, mid, and low frequencies for the three speakers. This worked well, and soon I made another one with a mirrored design to create a stereo pair.
Speaker back Over the years I learnt more about speaker design and how they are made, using my growing knowledge to improve these speakers. Improvements I made included making the speaker air tight to improve bass response, by lining the inside joins with glue and fitting draught excluder to the removable back panel. Isolation feet were also added, raining the speaker off the ground and improving the definition of the sound. I also bought a large HiFi amplifier to power the speakers, removing the mini amplifiers in each speaker and gluing up the holes for their inputs. This greatly improved their sound. These changes took place over a few years, leading to the speakers I now use on a daily basis in my room.
They measure 20″ tall, with a 10″ x 10″ footprint, and feature an 8″ woofer, 4″ midrange and 1″ tweeter. They are powered by a 60 Watt per channel stereo amplifier and can play loud down to about 45Hz.

Small Speakers

Speaker front This is a small mono speaker I quickly put together to play music relatively loud in portable situations, with a mini amplifier contained inside with audio and power jacks on the rear. I left the speaker with a rough finish as it would mainly be used in the shed in not so tidy conditions. The sound is adequate for its small size and simple design.
It uses a 5-1/4″ driver with a 20 Watt mono amplifier.
Speaker back

GCSE Speaker Project

Speaker inside This speaker was created for my GCSE Electronics project, completed over the course of about a year. It was made completely from scratch, with the amplifier design from an amplifier construction book photocopied onto acetate and etched onto PCB, and all the 80+ discrete components soldered on by myself. The amplifier was powered by a +/- 42V 5A power supply, and was rated for 200 Watts. The construction process of the electronics was long, with the board taking about two weeks to finish, then some further time securing it to the heat sink with bolts through cut and bent aluminum strips.
The power and audio inputs and power outputs where soldered to the board, and the necessary input components mounted to the enclosure. The enclosure consisted of a laser cut plywood front and back, with the front layered up to effectively countersink the speaker drivers. The curved shell is two layers of flexiply, all glued together. The back panel is also multiple layers, the inner most slightly smaller to allow the back to fit into the shell like a plug. The front is the same, however was never fixed to the shell, as access was needed to the inside to assess the project. The speakers are simply bolted in place, with some grey tape used to give the subwoofers an air tight seal. Speaker back
Speaker box front The speakers used were two 6-1/2″ subwoofers and two 4″ full range drivers, with a 100Hz crossover network. The system did indeed work, and I achieved a grade of 100% for this coursework part of the DT GCSE. After this though the performance of the amplifier board deteriorated, and I removed the speakers to be used elsewhere as I am yet to fix the board. My suspicions are that one or more components may have burnt out. However, the unit still sits proudly in my room. Speaker front