The Magician's Assistants

July 2010 Portable PA for The Prestidigitator Lou's Home Page

Design Considerations

One of my best friends has become a pretty good stage magician. He does quite a few gigs for charities, kids groups, and small corporate gatherings. One thing he's figured out is that he can't always depend on having a PA system that works with his wireless lavalier microphone. His son has 3 passive boxes ( a Titan 39, a half size Omni 10 and a DR-250 all Bill Fitzmaurice designs). But those aren't very portable and still need power and they don't fit in the trunk of his car.

I looked around my stash in the garage and found a pair of Hammer 8F buyouts from Parts Express (basically Eminence Beta 8's). I threw them in a box model and found a 7 liter sealed box would give an F3 of about 120. Since he's not James Earl Jones, I thought that ought to do fine. I had a box of piezo tweeters (I was going to do a DR200) so we had drivers. The power come from a little 25 WPC Dual plate amp I got from Apex Jr years ago. It used be my testing amp. Cool little guy. Two sets of RCA inputs + a 3.5 mm microphone plug with a built in mixer.

To accomodate the plate amp, its power tranformer and a little control panel, I would up with the box on the right. 14.5" high, 7.5" deep, 15.5" wide. The woofer is on a 9" X 9" baffle. All 1/2" Baltic Birch. Since piezo tweeters are PITA to mount and seal, I just glued the tweeter to it's own baffle and left the space open behind it.

I recessed the amp 1" to protect it, and cut up a little project box on my bandsaw to hold the volume and balance control. The amp is directly connected to the left channel of the amp. The right channel comes out of the bannana jacks ar the bottom. I made matching passive box (10.5" wide) so all he needs is some speaker cable to tie them together. Or he can just take one box for small gigs. For grills, I used black hotmelt and glued some pet screen to the boxes. I covered that with a bit more hot melt and some 1/4" baltic strips for molding.

There's no crossover at all on the Beta 8. I wound up with a 40 ohm series resistor on the tweeter to pad it down to a decent balance. Took away most of the grit everybody seems to complain about. I ran some tunes through these, and all in all they are pretty listenable. The Beta 8 is actually a pretty nice mid, vocals are clear and clean. 25 watts actually pushes them to painful levels in the garage. Not a lot of real bass, but overall pretty balanced. I could live with these as patio/party speakers just fine. Throw in a tuba or titan sub, and you could rock the house.