Minimus 77 Rebuild
Project completed April, 2008
This was the first project I tried after spending an inordinate amount of time on Rod Elliott's site, learning about amps and speakers. While speaker system design isn't the focus at Rod's site, figuring out how to do things is.
I was using these for my computer's sound system, they were satellites connected to the L-R channels of a Logitech Z560 4.1 channel computer sound system. They sat on either side of my second monitor, a 32" LCD TV. This puts them firmly in the near field monitor category as I sit about 30" to 40" from them. I use the system as a simple 2.1 stereo set up, leaving the rear channels disconnected. The tweeters were completely dead and the little woofers looked tired too, so I installed
Dayton Classic 1 1/8" tweeters
HiVi B4N mid-woofers
in the original Radio Shack Minimus 77 enclosures and made new crossovers.
The crossovers for these were designed with an audio signal generator, a multimeter, and a spreadsheet. It's old school all the way, and it worked surprisingly well. The background for the methodology and the spreadsheet is located here: http://sound.westhost.com/lr-passive.htm
I imagine this is very close to how professional designers were doing things into the 80s. Until CAD packages were developed that could look at most of the variables simultaneously and continuously across the frequency spectrum, you had to work from "snapshots" of the drivers' impedances at critical points.
This was really fun, and when I looked at the results with a couple of measurements using SoundEasy, I was amazed at how well it worked out.
This worked well, and definitely put new life into a 25 year old pair of mini monitors. The results are usable and listenable. This pair is being used by my dad in his stereo with a little Yamaha sub, and the sound is pretty good for casual use.
Be warned though, for accurate sound reproduction the HiVi B4N driver is just too large for cabinets this small. These guys have a broad 5 dB peak centered between 100 Hz and 250 Hz. For casual listening/computer monitor use some may find they prefer this if they are used without a sub woofer.
For use with a sub, I wouldn't recommend the B4N for the Minimus 77 enclosure. I've moved on from this project, but I suspect there are several 3" drivers that would work better (the Dayton ND90 would be my first choice now).
Jay R. Taylor
02/21/2010