MCM Revised by Craig Schmidt In my last write-up I had decided not to build any speakers for a while. I thought this would be easy since I was getting such enjoyment from my Fostex FX200 project. Two things changed my mind. First, I was getting bored and second, a weird incident occurred. A fellow employee asked if he could borrow my MCM speakers for the weekend. It seems he was setting up a home theater system and needed a pair of rear speakers. Nice guy that I am, I said yes. I let a few days go by and then approached my friend about returning the speakers. He said (in a nice way) he could not return the speakers and that I had to sell them to him. Naturally I asked him why. He stated that the little speakers sounded great, even better than his front speakers and he had to have them. Egotistical guy that I am I said ok. This got me thinking that maybe I could build an even better version, so here we are. The little MCM driver (55-1870) is a good unit, especially for the $11.00 charge. I figured that if one worked well then maybe two would be better. In my opinion the driver has one minor flaw. It is slightly lacking in highs. Now I do not necessarily agree with the idea of adding 'helper' drivers to full range speakers, but what the heck. Maybe there is something to it. I decided to use two drivers and a low cost ribbon tweeter from Parts Express. (You can also get this unit from Apex Jr. for about $6.00). I decided to use 1" MDF for the cabinet. The idea of a crossover worried me. I wanted to be able to experiment with it. The crossover would have to be external and easy to alter. Now we are only talking about a capacitor and L-pad so what I did was put an extra set of speaker terminals on the back of the cabinet (wired it up in the circuit) (see picture at right) and was now able to literally screw the capacitor in and out of the circuit. I can now change the size even while the speaker is playing. (Cap sizes tried ranged from .68 to 3.0 uf. They were Solen's.) I thought this was pretty cool! I also installed a good quality L-pad. The absolute best one I could find was the Fostex R-80b. This unit costs four times more than the other units, but in my opinion they are worth it! It exudes quality, worked flawlessly, and had the least intrusion on the sound. The other two that I tried were not so hot. One had a sloppy feel to it and the other had poor tracking. You can get these pots from EIFL and other places. Now that I was set up with the crossover, I concentrated on the cabinet. I installed the usual fiberglass stuffing for the interior and used two plastic ports (2" diameter) from Parts Express. I used the KBapps program to figure the length and installed them on the top of the cabinet. (Now you might be wondering why I did that. There is a story behind it, which I will relate in my next write-up "The Return of the Holosonic (sort of)".) I cut all of the other holes and primed the cabinet. (I also used the Kbapps program to figure the spacing between the drivers.) I then painted the cabs with a spray-on stone finish. Rather than installing the drivers flush I decided to cover the face of the cab with a thin sheet of foam. I read somewhere that this was a valid alternative to flushing. (I am nuts). I wired up with my famous, cheap, and good sounding 18 gauge. (I know this could be argued till the cows come home but hey, I gotta be me!) I set these speakers up on wooden stands from Sanus. For what it is worth, I have given up on metal stands! They sound like crap. Prove it to yourself. Buy a pair of these low cost stands and put them next to your metal. Toggle the speaker back and forth. If you do not hear a difference, immediately go to your ear doctor. (Hopefully all you will need is a washout.) The Finished Speaker Now the BIG QUESTION: Do helper drivers, with simple crossovers, work? The answer is YES if used judiciously. You must adjust cap size and the L-pad level correctly. Kick the pad too high and you hear the tweeters. They stick out like a sore thumb. Set these two variables just right and they definitely improve the sound of this little driver. Which brings us to the final point. How do these speakers sound? I'm not telling. You have to build them to find out. I can say this. I am not selling these to anybody even though my wife says she is having a tough time walking around the house with all of these speakers lying around. Isn't she sweet? Top