Homebrew Communications Speaker Project

I am taking a manufacturing class this quarter and our first "introductory" project is to build a box out of wood. This sounds pretty simple, but going with the manufacturing theme the box has to be designed (working drawings - dimensions, isometric), we have to have a bill of materials, and we need to lay out a plan of procedure for making the box. I have had this kind of stuff in the past and I am good with machines/building things so the project still seems a bit too easy.

I didn't just want to build a box. I wanted to put something in it. My first idea was to build a case for something. Then I couldn't think of anything to build a case for. Since I don't want a box to sit on my desk and look pretty or something to hold junk I tried to think of some function the box could have so I could USE it. Since I am a Ham radio operator I started thinking electronics. That's when the speaker idea hit me! I don't have a good speaker, and I don't have a whole lot of stuff that I have built in the station. So, it is a perfect project.


Since these are pencil drawings they didn't scan very well. This one gives you an idea of the finished product. It isn't an exact model/drawing though.

Gathering up the parts for the electronics has been a challenge. I don't want this to turn in to a really expensive project. I need to have some $$ to do my amp. I have spent the past 5 days or so on and off researching electronics kits to make this work.

I worked on the wiring diagrams all weekend. Let me tell you - this isn't a speaker box that you plug your wires in to a stereo and you get sound. Mine will have two speakers, a 10w/channel class AB stereo amp, switched capacitive filter (NEScaf) for bandwidth/shift control, a VU meter to monitor drive level (at the input), 4 mono inputs, and two stereo inputs. The 4 mono inputs can be switched individually to both speakers or one to one speaker and another to the other speaker. This way I can plug 4 radios in to it and switch between which ones I want to listen to. Only the mono channels can be routed through the filter board. The amp can be switched on/in or out/off so the line can be routed to a headphone connector on the front panel with the amp/speakers muted.


I just found one error on this - the dotted separation line should be above the power input on the right. I think I can work around that one.


I hope I can follow all those lines OK! It shouldn't be that hard, I understand how it is supposed to work.

I will work on the final drawings, bill of materials, and plan of procedure here and post my progress in the next couple days.

The speakers are 5" Dayton PA sound drivers. These aren't your average "speakers" - these are loudspeaker drivers. Note the price in the link there - $11.80 each, NOT BAD!! Now, why would I use loudspeaker drivers? Well, I am not trying to blow myself across the room when I tune in a signal on the radio. In fact, the speaker I am making isn't supposed to get loud at all. If you compare a PA sound driver to a car speaker the first thing you will notice is the ratio between the magnet size and the speaker size. The 5" Dayton drivers have a 4" magnet!!! This creates tighter, more hi-fi audio - which translates in to clearer sound. Car speakers are not as precise and would sound a little muddy or muffled. Same goes for "woofers". Although they have larger magnets, they are designed for low frequency response - below 600hz or so, usually (in a sound system the mid range takes over from here). This wouldn't do a communications speaker any good since the purpose is to hear the normal audio range of human speech - 500-2500hz or so (and tones, like Morse code).