Quick and Easy Do-it-Yourself Mod for Popular Low-Cost Dynamic Microphone
Here's a way to get some different sonic flavors out of the popular ES-58 dynamic mic and learn something about mics and modifications in the process. Don't have one these SM-58 copies? Don't worry, they're pretty cheap and easy work on. Let's get started!
Did you ever notice how an SM-57 or SM-58 can have too much upper midrange presence on some sources? That's because these mics are designed with a presence boosting feature built in - an acoustical resonance disc.
The acoustical resonance disc is a round plastic plate with a series of perforations around its perimeter and in the center of the disc. The disc allows sounds waves to reach the front of the diaphragm through the perforations but also causes sound to be reflected back and forth between the solid area of the disc and the diaphragm.
Cup your hands around your mouth as if to shout out to a friend and speak. The reflective chamber created by your hands reinforces your voice at certain frequencies and makes it louder. Not necessarily very natural - but definitely louder. The acoustical resonance disc in front of the ES-58 diaphragm (and many other dynamic microphones as well including the SM-57 and SM-58) performs a similar function - to make transduced sound louder in the upper midrange frequency range.
But sometimes it can be more pleasant to hear a source recorded with a dynamic microphone with a flatter frequency response. If you'd like to try this out, and be able to reverse the changes at will very quickly, read on.
The first step is to unscrew the pop filter ball and place it to the side. Once the ball is off you'll notice the capsule is wrapped in an acoustically porous fabric. Find the seam in this fabric and gently unwrap it from the capsule to reveal the structure as shown below.
Unwrapped capsule ready for resonator removal
The disc resonator of the ES-58 can be removed by gently inserting a small jewelers screwdriver into the seam shown in the picture above. Gently work your way around the circumference of the capsule by inserting and prying the disc resonator cap up and off the main body of the capsule.
Main capsule assembly, perforated resonator and foam filter
Hear mod'd MK-219 against Neumann M149
Once you've worked your way around the circumference of the resonator it will lift off the main assembly. Be very careful not to puncture or distort the very fragile moving coil diaphragm.
Notice there is a small key on the main capsule body that mates with a slot on the resonator cap. You'll need to line up these two features if you want to replace the resonator cap later.
When the resonator capsule is off, you can pry off the little foam disc to reveal the series of acoustic perforations in the cap. At this point you can simply re-attach the pop filter ball to protect the fragile diaphragm and try out your modified ES-58. Notice it no longer has the sharp upper midrange boost heard in the stock mic.
Resonator Disc Mods
Resonator disc with perforations partially closed
Once you've heard what the ES-58 sounds like with the resonator cap completely off you might like to experiment with partially closing the perforations. This has the effect of closing the acoustic chamber, reducing its cubic volume and thus raising the resonant frequency of this acoustic space in front of the diaphragm. If you use bits of electrical tape or gold stars from your kids craft box you can experiment with different open area effects.
So you see its an easy task to tune the resonator disc and install it, or just leave the resonator disc off. Have fun experimenting and recording with your modified ES-58 dynamic mic!
Ps - Just follow the text and pics carefully, this mod is really easy to do. Good luck because unfortunately my schedule doesn't allow the time to answer any questions about the pics, text or process. Best, Michael
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