> what I think was called a Cooper time cube delay/reverb.
You're giving me flashbacks.
Very funky, very useful for a very short period. Many studios have one in storage/junk-room.
Nothing to it. True DIY stuff.
Find a discarded garden hose. Cut off about 20 feet without big leaks.
Cut a 2x6 board about 6" long. Drill the center so the hose just fits.
Nail a 4" speaker over the hole. Stuff a wool sock in a heavy cereal bowl, butter the edge with goop, and drop it over the speaker. (Actually, you should run wires out of the speaker before you glue the back-chamber permanently...)
Get several 6mm Panasonic mike capsules. Drill 1/4" holes in the hose at odd intervals: 6', 10', 17'. Goop the capsules into the holes.
The signal off the mikes will be high, you may not need a preamp. You can probably just passive-mix the mikes. You do want to get a stereo mix, that's maybe the best use of the Time Cube.
Try leaving the far end open, sealed, or loosely stuffed with cotton.
Drive the speaker with any handy small amp. Probably does not need 1 Watt to get a heck of a level at the mikes.
Mix the mike signals with the original: they amount to "echoes", delayed and un-flat. You may need a heavy bass-cut to correct the speaker's rise when not not trying to drive the whole world, just a pipe. You may want some treble boost: the front-chamber is a ~800Hz low-pass. These EQs should probably be in the speaker-amp.