Shortly after I revived this project back in 2018 I was contacted by Chris Yetter of AudioScape. Chris was interested in a reverb product and had heard great things about the MicMix MasterRoom XL-305.
I agreed to help Chris with the re-issue doing both the circuit design and teaching him how to cut springs to the original MIcMix timings. Chris and his team did the circuit board layouts and mechanical design. Now that he's shown it at NAMM I'm able to show the prototype he sent me for evaluation.
This is a pre-production prototype. I'm blown away by the execution and the many sonic improvements over the original I designed over 40 years ago.
More: https://proaudiodesignforum.com/forum/p ... =70#p16559
Update November 2018: We visit this decade-old idea and get down to the business of cutting some actual springs: viewtopic.php?f=6&t=213&start=40#p12050
A couple of posts later I provide a quick demo sound file: viewtopic.php?f=6&t=213&start=40#p12055
Beginning of original post:
How about a MasterRoom spring reverb clone? Accutronics graciously sent me springs and transducer assemblies to modify for the MicMix timings some time ago. After I dropped development on this in 2007 I received a number of e-mails asking "what happened?" I think I got bored counting spring turns and went crazy. The following is from my scrapbook capture of work done elsewhere.
Lets begin with this paper from Bill Hall of MicMix Audio who stumbled upon the invention while developing a pulsed acoustic intrusion alarm:
https://www.ka-electronics.com/Images/p ... Reverb.pdf
And the patent:
https://www.ka-electronics.com/Images/p ... 350845.pdf
The original brochure:
https://www.ka-electronics.com/images/p ... ochure.pdf
The MasterRoom spring mechanics were pretty simple - aluminum L channels screwed together forming a square cross section ran the length of the springs and held 4 Accutronics transducers at each end. The springs ran the length and were connected mechanically in series forming two pairs (x4) on each side. I think the drive transducers were paralleled and the receivers series-connected. The whole gizmo had spacers with bumpers on them to keep the spring assembly from hitting the sewer pipe. It was suspended by springs.
What might come in handy is, if I don't have the math right, a pulse response of the tanks. A soundfile of TDR pulse response might prove useful. What you do is pulse, say 1 KHz single-cycle click the tank. That's T0. You will get (in a stereo MR) first-order echos at T1, T2, T3, T4...T8. Those are the ones that really matter. The second-order echos are at 3T1, 3T2, 3T3, 3T4...3T8.
Why 3T? Because the second order echos have to reflect off of the receiver transducer at T1, go the length of the spring and reflect off the driving transducer (at T2 which is silent), and then return again through the spring a third time before being "heard" by the receiver at T3. Recursive delay lines are 2T systems and we had to re-write the patent to cover that.
Here are the schematics for the XL-305. These have also been posted over in Document. Nothing too special except for constant-current drive:
https://www.ka-electronics.com/MasterRo ... _Tile1.JPG
https://www.ka-electronics.com/MasterRo ... _Tile2.JPG
https://www.ka-electronics.com/MasterRo ... _Tile3.JPG
https://www.ka-electronics.com/MasterRo ... _Tile4.JPG
For the delay line timings (spring cuttings) I dug up the old log time-domain reverb formulas from mine and Bill Hall's original notes. These calculations are for a 6 or 12 spring system with an initial delay of 13.5 mS. The timings are equally spaced in the log domain. These calculations are in base e. For a six line/channel stereo reverb, the odd timings are assigned to the left channel, the even to the right. When mono'd they interleave.
I took the longest spring which equals the last line in the spreadsheet and worked backwards cutting the first spring at ~13.5 ms. Notice the difference in tension between the longest and shortest springs.