The Silent Microphone II
PARTS:
- 1 - 3M 6000 Series™ Half-Mask Respirator - LARGE
- 5 feet - vinyl tube 3/4"outer diameter (1/2" inner diameter)
- 1 - Shure R93 microphone cartridge (Shure has stopped selling this item by itself. You may have to purchae the shure SM10a or Shure 512 headset mic just to get the R93 cartridge)
- 4 lbs - Plaster of Paris
- 10 feet - Low-profile microphone cable (2 conductors and shield)
- 1 - XLR male collector
- 1 pint - Noxudol 3101 acoustic paint
TOOLS:
- razor blade to cut the tubing
- black sharpie fine point permanent marker
- Stanley Surform Pocket Plane
- a dozen No.2 pencils
- A ruler to measure the pencil length and tube length
- small hacksaw to cut the pencil to length
- a throw-away plastic bowl to mix the plaster of paris
- several throw-away plastic knives to spread the plaster of paris and paint
- pruning shears to snap the pencil in half for removal
- coarse grade 60 sand paper
- a hammer
- wire cutter/stripper
- soldering iron & solder
- electircal tape
- small flat screwdriver or small clay carving tool
- super-sticky adheisive tape.
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1. Strip the Mask.
Gently pry off the straps, the front hole cover and the round rubber film washers.
2. Create Hole Protectors.
Cut two 2" sections of tubing. Use the razor blade to make the cut. Mark one end of each tube with an arrow indicating the prepared end. Use the pocket plane to make the prepared end 90 deg perfectly straight (the plastic opening on the face mask that grips the tube end is only a few millimeters deep), and then slightly round off the outer edge of the tube opening so it will easily slide into the two side holes of the mask with a little twisting. The purpose of the hole protectors is to keep the holes clean while the plaster of paris and paint is applied, but at the same time not getting in the way.
3. Adjust the Opening of the Face Mask.
Use the ruler and sharpie to precisely measure and mark two pencils. Mark one for 5.25 inches from the eraser tip, mark the other for 5.0 inches from the eraser tip. Use the hacksaw to cut the pencils. Gently jam the cut end against a firm surface to blunt the end. Make sure there are no sharp parts on the cut pencil ends. Place the 5.25" pencil inside the vertical opening of the mask. Place the 5.0" pencil inside the horizontal opening of the mask. The pencils will keep the opening at a proper fit while the plaster of paris is hardening.
4. Start Applying the Plaster of Paris.
Insert the two placeholder tubes firmly in place in the side holes. Mix the plaster of paris in the small throw-away bowl and use the throw-away plastic knife to apply a thin layer of plaster of paris at the outer edge of the face opening and around the outer side holes. After it sets (about 20 min) apply a thicker layer to the face opening and around the outer side holes. The placeholder tubes should be immersed on the outside with at least a half inch thickness of plaster of paris.
5. Check the Mask Fit.
After 30min from the latest plaster of paris application remove the pencils by using the pruning sheers to snap the pencils in half. Check the fit by pressing the mask over your face and similuating singing lip movements, especially wide-open-mouth singing. Make minor adjustments by shaping the hardened plaster of paris with the coarse sand paper. If major adjustments are needed start all over by firmly tapping the plaster of paris with the hammer to crack it and then use different pencil lengths to better fit your face.
6. Finish Applying the Plaster of Paris.
After you confirm that the fit is proper, continue applying more layers of plaster of paris. The outside of the tube placeholders should be about an inch deep in plaster of paris and the center hole should be completely covered with a thick layer of plaster.
7. Prepare the Plaster to be Painted.
Remove the two placeholder tubes. Use the coarse sand paper to smooth any rough spots on the plaster surface. Rinse the entire mask in water to remove any plaster dust and let dry overnight.
8. Paint the Plaster.
After you open the can of the Noxudol 3101 acoustic paint and stir it with the plastic knife for the first time try to memorize the viscosity of the paint. In the future when the paint in the can begins to dry you can add water to make it thinner. The paint is water based. But you don't want the paint to be any thinner than its original viscosity or else the acoustic properties might be diminished. Protect the two holes with the placeholder tubes and use the plastic knife to add several layers of paint to the plaster, allowing the paint to partially dry in between layer applications.
9. Construct the Long Tubes.
Cut two 2' tubes and prepare one end of each tube the same way you did for the 2" placeholder tubes. Make sure to use the permanent marker to indicate which end has been properly leveled and rounded.
10. Construct the Microphone Assembly.
Cut the microphone cable to your desired length (anywhere from 5' to 25'). Solder one end to the Shure R93 microphone element (use an insulator covering or electrical tape to protect the exposed contacts). And then wrap it in tape so it can be handled without damaging the connections. Solder the other end of the cable to a male XLR connector. Below is the wiring diagram:
XLR Connector
(solder side)
_2 13
1 = shield (solder this to the cable braiding or its drain wire)
2 = mic signal (solder this to the red contact of the mic)
3 = mic ground (solder this to the non-red contact of the mic)
_ = connector case (wire this to 1)
11. Put it all Together.
Use a small flat-head screwdriver or a small carving tool to carve a groove line in the plaster of paris at the face opening. The depth and thickness of the groove should be slightly less than the thickness of the mic cable. This is so the mic cable can fit snug and flush with the face opening. Place the mic in the mask and keep in place with super-sticky adhesive tape. Firmly press and twist the two 2' tubes in the two holes.
12. Reducing the Paint Fumes.
After a few days when the paint has completly cured, remove the tape, mic assembly, tubes and gently wash the painted housing under warm running water. Let it dry overnight.
Microphone Assembly consisting of Shure R93 microphone element, Thin Profile Analog Audio Microphone Cable, and XLR connector.
2-inch placeholder tubes. Prevents holes from plugging up during construction, while being short enough to not get in the way.
2-foot vinyl tubes.
The hole of the finished housing.
The inside without the microphone assembly. The tan is the acoustic paint. The white is the plaster of paris. The dark gray is the gas mask.
The inside with the microphone assembly.
The upside down inside with the microphone assembly.
The outside with the 2-ft tube pushed in firmly.Here are the numbers:
acceptable loudness at all hours: 60dB
loudest singing/shouting: 118dB
therefore, noise reduction needed: -58dB
standard sound booth: -32dB
silent microphone II: -36dB
whisper room double wall: -53dB
silent mic II inside a soundbooth: -68dB
Voice tips
Don't eat cheese or any dairy products for 1-2 hrs before singing
Sip on warm (not hot) lemon water to clear the throat
[squeeze 1/4 lemon into a cup of water]
avoid lemon juice with perservatives or sugar.
Keep hydrated by drinking lots of water.
Shure R-93 Top
Shure R-93 Bottom (The red-dyed solder is for the red wire)
A simple hanger for the Silent Mircrophone II (rubber bands, binder clips and a bathroom hanger)
The silent microphone II put away and ready for its next use.Simple Tricks to use on the Recorded Audio:
Removing Peak Clipping Distortion - Use an EQ or notch filter to remove around 320Hz only at the peak area.
Making the Audio Sound Louder - Add compression to the vocals.
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Silent Microphone 2 - Improvements to Do:
1. A More Secure Tubing Fit - Make the holes for the two tubes go all the way through the mask. Then push the tubes into the holes about 1/4" further in than when it was blocked. This will make it less likely for the tubes to get loose and fall off.
2. A More Manageable Tubing Ends - Tie the ends of the two tubes together so the ends curl within the same circular curve but with the openings facing the opposite direction. This will prevent the tube ends from flailing about while handling the Silent Microphone 2.
3. Add More Sound Absorption to the Tube Ends - You could wrap sound pads and sound foams around the ends of the tubes. This will, however, reduce the airflow through the tubes.
4. Add More Sound Absorption to the Tube Lengths - Paint the tubes with the acoustic paint. This will offer additional sound isolation but will make cleaning the tubes more difficult. Use masking tape to mask off x" on the insert end of the tube and mask off x" on the exit end of the tube. (This has not been tried yet)
4. Secure the Mic Cable - Wrap a #105 (5"x 3/8") rubber band around the outside of the mask near the face opening. This will clamp down the mic cable as it exits from the cable groove at the face edge of the mask. This is much more stable than adhesive tape in securing the cable.
