lm386-powered amplifed porch-board bass drum idea

[darwindeathcat]

Yes, the LM386 is cool that way. You can easily use it with a single supply... I am going to the thrift shops this afternoon to scrounge up some speakers. I want to get a pretty big one (8-10 inches), but which is fairly light weight (smallish magnet). The idea is to keep the weight down for portability, but have a big surface area to make a nice deep bass drum sound. The 6" subwoofer I have is too damn heavy and actually sounds less deep than my nice vintage 8" organ speaker. I don't want to use my nice vintage speaker for this thing (save that for my next amp!), so I'm off to find a cheap one at the thrift shop. Once I get the speaker, then I can continue to fine tune the drum voice by fooling with the cap values. The idea will be to tune the drum sound to the speaker I end up buying, so that sound will be the best it can be for whatever speaker I end up using....

[darwindeathcat]

Okay, so I a chance to head to the Goodwill, and I got what I think will be the perfect speaker. It's an 8" 8ohm Kenwood hifi. The magnet is on the smaller side, so it's nice and light (MUCH lighter than my good vintage 8-incher). I think in this case that's a good thing. I don't need a speaker that can take sustained loud playing. I just need a nice speaker that can deliver good low end without any need for a heavy, over-spec'd, super-beefy magnet. I don't have time tonight to try it out all together, so I will report tomorrow on how it sounds...

[darwindeathcat]

I tried out the new speaker, and it sounds really quite good! Interestingly, I think it sounds more "bass drum-like" if I turn the speaker upside down so that the cone is against my desktop. Probably this is because doing so really mutes out the higher frequencies. Also, my desktop might now also be acting as big extension to the speaker cone, helping those low frequencies come through. I haven't fooled around with capacitor values yet, but it I'll probably try a few before I take it off the breadboard and put it onto perf.

  Now I have to think of how to build the housing. The circuit is quite sensitive to the amount of surface area on the trigger. The sound changes depending upon how much of the trigger pad is touching ground. JM's suggestion of two thinnish pieces of plywood kept a couple of mm apart is a good one, as I could then vary the amount of the trigger that is in contact with the ground pad via "stomping pressure". I've got some aluminium tape (the kind used to repair holes in your air ducts) that I'll line these pieces of plywood with to make the trigger and ground pads. I'll keep the boards separated by a few mm with some double sided foam mounting tape. I'd like to attach the trigger pad to the housing for the speaker and perf board with some sort of hinge so that I can fold the thing up and take it with me. I think I'll have only one control (a pot with a built in SPST switch), and I'll probably mount this to the board (PCB style). I guess the speaker will be facing down onto a thin piece of plywood so that I get that bass boost effect I was talking about. I'm not sure if I'll build a box to cover the back of the speaker (more complicated, but safer), or just let it all hang out (easier, but potentially exposes speaker to damage). I'll sketch some ideas out, and see what I end up with, but any suggestions would be appreciated!

[J M Fahey]

Hi Darwin.
Just use the speaker facing the floor.
Mount 4 rubber feet on the front of the speaker box so it stays , say, 1/2" from the floor so the sound can come out.
The box should be closed.
I use a similar arrangement on my Wonder Mini Bass Cabinet, with a 10" full range facing front and another 10", subwoofer type, facing down.
*Nobody* believes the bass and clarity in such a small cube.

[darwindeathcat]

Thanks JM, that's a good idea. I'll build a box 8.5" square, by 4" deep for the speaker, with the speaker facing down. I'll stick the PCB in this box too, with control pot/switch sticking out the side. I have the little rubber screw-on feet that I can use to keep the speaker opening off the floor. I'll attach the trigger pedal with a gate hinge off one side so that it will extend out with a slight angle to rest on the ground, and can be folded down across the speaker opening for stowage and transport (which will also protect the cone). I'll build it out of 1/4" plywood. It'll take me a couple of days, but I'll post pictures/sound clips/videos when I'm done...