Speaker Driver Retrofitting

During the summer of 2020, I retrofitted a pair of old speakers with new drivers and a crossover circuit. I did this as an introductory project to design loudspeakers.

Planning The project started by looking for the perfect pair of speakers to retrofit on Craigslist. I found this pair of Fisher speakers from 1977 for that sweet vintage style. The speaker boxes and mesh are still in excellent shape, while the drivers themselves are deterred due to age. I learned that these were considered very average speakers even when they were new, but that's about to change quickly.

Building As soon as I got the speakers, I began to look for ways to make the best speakers out of these vintage boxes. The plan is to find new woofers and tweeters to fit the build and design new crossover circuitry to complement the new speaker drivers. For the new drivers, I decided to go with the Dayton Audio DA 215-8 for the woofer(8-inch) and the Dayton Audio RS100-4 for the midrange/tweeter(4-inch). I chose Dayton Audio because they are very transparent about their speaker specs and publish ZMA data files for crossover simulations, which will come in handy. For the crossover design, I used the data files published by Dayton Audio and used a software called XSim to design my crossover network. It can simulate the system acoustic response to help me align the phase of the speakers correctly in the crossover region. Here is what the simulation looks like:

The replacement woofer was slightly larger than the original, and can't fit back to the original hole. I made some laser cut filler piece to fit the new woofer in.

These speakers turned out great. So good when I sent pictures to the original seller on Craigslist, he offered me to buy them back. I hooked these up with a simple amp and bluetooth receiver, and they work great. I occasionally use them as external speakers for my small guitar amp, and they work great for that too. Looking at it toady, I think there are ways to improve it further. The woofer I used has a very low Qts, so a vented enclosure will give me better bass alignment. In addition, the 4'' full-range driver gets directional above 4kHz, so it will be beneficial to add a dedicated tweeter to achieve better directionality. These are not very difficult mods, so I think I will get to them soon.