3D Printed Spring Reverb Microphone

Spring reverb, the slinky progression of natural reverberation has been used in the music industry for decades. From standalone units that used physical sloppy springs to virtual facsimiles squeezed into guitar pedals and software, spring reverb is one of the most widely used instrument and vocal effects.

Units that contained physical springs were susceptible to a plethora of different ailments, undesirable sounds in most musical contexts, but ultra-rad ray gun sounds in other contexts. Bumping, nudging, smacking or even walking heavily near one of these physical spring reverb units set them off, which is why most were replaced by synthesized approximations. 

Regardless of technological advancements, purists know that the only spring reverb worth using is one that sends the signal spiraling through spring steel. Hence the desire to create a microphone with a built-in physical spring reverb effects unit!

What you'll need to recreate this project:

• Access to a computer with internet access
• Access to a 3D printer (don't fret if you don't have your own yet, check with your local library, college or makerspace )
• Piezo element (can be had online for cheap or salvaged from all things that BEEP )
• Small gauge wire (shielded if you're an audio purist )
• Soldering iron (any will do, but a quality soldering station is a worthy investment )
• Set of small machine screws with matching bolts (I'm using some old brass ones )
• Music wire, piano wire, or a medium gauge guitar string (I used a G string... )
• 1/4'' audio jack or equivalent for your setup (rip it out of something that no longer works [an old guitar tuner in my case ] )

*To simply nab the .STL files and run, skip ahead.

Before jumping into 3D modeling the design, I’ll explain how the microphone is theoretically supposed to work. At its core, the 3D Printed Spring Reverb Microphone is a membrane microphone design, in which a piezo element translates vibrations felt on a thin membrane into a workable signal. This design: however, has a sloppy spring suspended between two membranes and affixed to the second is the piezo element. 

The theory is: the first membrane undergoes a sonic barrage causing it to vibrate, the vibrations are then lazily carried by the spring to the second membrane, to which the piezo element is attached, and the delay caused by the inherent process causes a simple spring reverb effect. Theoretically. For an added challenge, I wanted the microphone to be almost entirely 3D printed, including the membranes! 

First let’s measure twice and model once. A cheap pair of calipers aids immensely during this process, but a ruler will also work. 

With the intention of designing multiple parts that needed to be affixed to each other, I started my design process by measuring the fasteners I intended to use (small machine screws and nuts) and scaled the rest of the design around them. I also measured the diameter of the ¼’’audio jack I intended to use. 

I decided to make the body of the microphone cylindrical. *It should be noted that when creating a cylinder, tube, or cone in Tinkercad, it’s good practice to bump up the default side count to 64 before continuing. When trying to calculate nesting tubes, I use an online calculator. Which is exactly what I used to calculate the bottom and top halves of the microphone body. 

The rest of the modeling isn’t complex, just basic geometric shapes juxtaposed together, but I do cover some 3D modeling tips and tricks in the next step! 

With the 3D modeling done, it's time to export the .STL files and import them into your preferred slicer software. Once sliced to your specifications, send it off to the printer and wait patiently...OR remain productive by making the spring and sorting out the electronics!

*Be sure your print head is well calibrated and that your print bed is well leveled before attempting to print the membranes!

*Please note that the included .STL files are a revised and improved version of this first prototype.

3D Printed Spring Reverb Microphone in Tinkercad

This instructable assumes prior 3D modeling experience; however, I thought I'd offer a couple tips and tricks.

Polygon Tool: The polygon tool was used to create the hexagonal bolts in the design. PLEASE NOTE: Tinkercad’s Polygon Tool could be improved by having the flats of the polygons be square to the grid instead of their corners but…a simple work around in our case is to rotate the hexagon by 30 degrees before using it. (see animated .GIF above ) 

Hollow Cones: Create a cone that has the dimensions you’re after, use the Mirror Tool to flip it vertically, then use the Duplicate and Repeat Tool to make a copy. Whilst the copy is selected, turn it into a hole shape and use the Z axis Arrow to raise it by the desired thickness of the hollow cone, 2mm for example, and then use the Group Tool to group both shapes together! (see animated .GIF above )

Bolt Pattern Layout Trick (for cylinders ): Use the Align Tool to align the nut or bolt hole with the center and top of your cylinder. Change the increment distance to reflect how far in you want your nut or bolt to be, select it and then use the arrow keys to move it down by one increment. Next, use the Duplicate and Repeat Tool to make a copy of the nut or bolt hole. Select the second nut or bolt hole and the cylinder and use the Align Tool again to align it with the bottom of the cylinder (make sure the cylinder isn’t the object that is moving ) and use the arrow keys to move it up by one increment. Then select both nut or bolt holes and use the Group Tool to group them together. After they're a grouped pair, use the Duplicate and Repeat Tool to make a copy and while that copy is selected, rotate it by one of the preset angles. Last step is to keep pressing the Duplicate and Repeat Tool until the pattern makes it all the way around. (see animated .GIF above )

After getting your hands on music wire, piano wire, or a medium gauge guitar string (what I used), start searching for an appropriately sized shaft (preferably metal). I had this headless screwdriver kicking around and decided to convert it into a dedicated spring making tool. (Am I the only owner of headless screwdrivers?)

I started by drilling a small hole at a 45-degree angle from the shaft into the handle of the screwdriver. I then fed the guitar string through the hole until the ball end of the string wedged itself into the handle side of the hole. Next, I attached a pair of the gnarliest, weld bead laden locking pliers I own to the other end of the string. 

After starting the first wrap around the shaft by hand, I let the pliers dangle from the end of the string as I held out the screwdriver handle in front of me and began turning it. The locking pliers have enough girth to them to keep the wraps taught enough around the shaft for our purposes. Keep turning until your locking pliers of a varying degree of hideousness kiss the shaft.  

All that was left was to unclip the grotesque locking pliers and to clip the ball end of the wire and the spring was ready!

The electronics for this build are quite basic, but I’ll admit that soldering to a piezo element can be a nightmare even for seasoned veterans and hams! If you buy your element from an online retailer, chances are that the lead wires will come attached. If you salvaged your element from something else (defective clip-on guitar tuner in my case) it may not have any lead wires.

Don’t fret, most people struggle soldering piezo elements because of their sensitivity to excessive heat but a simple fix is to solder to it on a heatsink, something that will wick away enough of the excess heat to prevent damage (I used the anvil of a stapler as it was sat on my desk, and I locked eyes with its strange little face). To mitigate other potential damage to the piezo element, limit the contact time of the soldering iron to the element. You’re aiming for just past a cold solder joint of contact time. Being conscious of those two things will hopefully allow you to solder to piezo elements successfully and with some practice, every time. 

Once you have two leads coming off your piezo element you can go ahead and solder them up to the corresponding lugs on your audio jack of choice. The justification for not using shielded/grounded cable is that this is meant to be a prototype and not a production model. With that, the electronics are complete!     

After the two main body pieces came off the printer, I discovered that my tolerances were spot on, but that the sound of the ridges of the print lines rubbing against each other was going to be a problem (unless I was aiming for a spring reverb guiro…). To remedy this without sanding, and sanding, and sanding, and sanding, and sanding, I decided to simply wrap and glue a piece of velum around the smaller of the two halves. When in doubt, wrap it. 

To install the electronics, start by gluing the audio jack into the end cone of the microphone, I used some CA glue for this, but adding some hot glue around the audio jack on the inside of the cone is suggested for increased longevity. Next, glue the piezo element to the back of the first membrane with some CA glue, then add globs of hot glue over both the piezo element and the soldered connections to act as a sort of wire strain relief. 

Electronics installation complete! 

This bit is a little fiddly. Start by using a pair of needle nosed pliers to bend a U shape in one end of the spring and feed it through the holes in the membrane as gently and carefully as possible. Once secured to the membrane mechanically, use some hot glue to hold it in place. Next, tuck the wires into the tail cone and feed the spring through the bottom half of the main body of the microphone, sandwiching the membrane between the lower body half and tail cone. Then, align the holes of the tail cone, membrane, and lower half of the body. While holding all three pieces aligned, insert a nut into one of the recesses and hold it in place with a fingertip (or tape). Thread a screw into that nut from the other side and finger-tighten. Repeat until all fasteners are installed, then tighten further with a screwdriver.

That's the lower half assembled!

Even fiddlier than the last step is attaching the spring to the other membrane. After sliding the top half of the microphone body over the lower half, pull the spring out past the mouth of the top half of the body. Carefully thread the spring through the second membrane in exactly the same way as the first after bending a U shape into the end with needle nosed pliers. Use a good amount of hot glue to secure the spring to the second membrane.

Maker Hack: Instead of waiting for a hot glue gun to warm up, wave a lighter under the end of a stick of hot glue until it begins to droop then smear the melted end where you need it. Not precise, but fast.

Now that the spring is attached to both membranes, start assembling the top half by aligning the holes of the vocal cone with those of the second membrane and top half of the body. Use nuts and machine screws to lock all three pieces together. Last step is to glue the grill cover cap on with a few dabs of CA glue.

With that, assembly is complete!

Overall, a successful proof of concept. I was immediately impressed by the performance of the 3D printed membranes especially. The microphone has great percussive potential from sloppy spring slaps to thick kick sounds. The sounds also change depending on the position of the microphone halves and how much tension is being put onto the spring.

Although the microphone works as intended, it would benefit greatly from some minor improvements. First improvement, barrel length. If the body of the microphone was much longer I believe the reverb would be closer to what I'm after. I'm not convinced that a 3D printed body would be the best option at that scale (3+ft) and would probably opt for some sort of off the shelf tubing of a similar diameter.

Next, the spring could be improved, either an off the shelf option cut to length (such as one from a storm door or from an actual reverb tank) or a miniature steel Slinky might be better options than the DIY method. The transfer of energy wasn't efficient enough from the DIY guitar string version which limited its sensitivity and sonic potential.

Third is something I already fixed in the 3D design, a way of limiting the travel of both halves as the prototype can come completely apart if not careful, which contrastingly adds to its sonic applications (as the spring is fully exposed and can be plucked). I'm sure that after more use I'll find other tweaks to make but as a prototype it is a fun new piece of kit to add to the studio/performance arsenal.

Here are some recordings of the 3D Printed Spring Reverb Microphone in action!