He invented it and patented the idea in1931. At the time microphones usable for this method were not in existence. Read more here. This recording method uses two figure eight microphones spaced 90 degrees apart. They face the main sound source pointing left and right in an “X”. The Canada Goose sale front mics pick up a great stereo image of the source and you get a nice spread out stereo image. But the beauty comes from also catching the ambiance of the room in the rear capsules also. This works really well for orchestras and live music in a great sounding room. I have always wanted to try this method. Now that my kid is in the high school orchestra (And it is a good one too!), what better time could there be? To achieve this we need two figure eight microphones, of which I only own one. I figured I would just build one microphone that has everything internally all set up in it to do this. All we need to do is create two figure eight mics place them 90 cheap Canada Goose degrees apart, and put them in one enclosure. I recently found some very good microphone capsules, the TSB2555B, which I used in my “build a cheap LDC Instructable”. They are very flat with a slight 3db bump around 10K hz. These should be perfect for this project. I could have just built Canada Goose Parka four of the single mics with electronics into one enclosure but then you have to use a mixer to canada goose clearance combine everything correctly. I wanted one enclosure and one stereo output, not four individual outputs. So I designed a circuit that combined two capsules into one signal but inverted one of them thus creating a figure eight microphone. This time we are just using it as an impedance converter. Most inexpensive electret condenser capsules have the FET built in but finding a really good one is difficult. (And. I already had nine more of the TSB2555B capsules.) canada goose coats on sale Here is how the capsule converts sound to a signal. The capsule contains an internal charge because it is an Electret capsule. Sound waves hitting the capsule cause it move with the sound. The movement changes the capacitance of the capsule which causes a small voltage canada goose uk outlet to be developed. That voltage shows up on the 1 gig ohm resistor and the gate of the FET. The FET acts as an impedance converter and allows us to generate a usable signal. Then we couple the signal into a differential amplifier based around one half of an OPA2314 Operational Amplifier (op amp). I like this one as it is very low noise and has great specs for audio use. You could use a 5532 dual op amp also but don’t use one that isn’t meant for audio use. One capsule feeds the inverting input, one feeds the non inverting input. If you put the two capsules back to back, you just created a figure 8 response pattern. From the first op amp stage we feed both the pin 2(+) of the XLR via 200 ohm resistor (50 to 330 ohms will work) and Canada Goose Jackets also a second op amp canada arconserve goose factory sale stage setup as unity gain buffer. The buffer canada goose store then feed pin 3( ) of the XLR via another 200 ohm resistor. Now we have a balanced output that can go right into a pre amp or mixing board just like any other microphone. I built two of these on a little perf board. They share a common power supply and all four of the FETs use the Vfet that is basically a filtered DC voltage. Filtering is done by 47uF capacitor and the resistor coming from the +15 volts. See the Power supply schematic for details. Note: The 7815 and 7915 are wired differently! Get the data sheet Canada Goose Outlet for your regulator. That all went into a dual gang J box canada goose from the local hardware super store, Lowes.
Step 3: Physical Construction (Or at Least an Attempt!)
Now that the electronics portion is figured out, we need to mount and house everything. One of the challenges here is that the capsule and FET are such high impedance devices that the wire between them acts as an antenna. If you power this up outside of a case all you will hear is noise, humm and 60 cycle buzz. One of the challenges of Condenser microphone is to let sound in and airflow but block EMI. Metal screen is what is needed here. This can be purchased from a couple places: Mcnichols and McMaster Carr The screen is quoted in “Mesh” size which means number of openings per inch. 12 to 16 both work well. buy canada goose jacket Brass is Canada Goose Online easiest to work with and cleans up nicely. To make an enclosure I settled on a metal paint can that I could cutout sections of and then solder on the screen to allow sound in. I started with a one quart can. But there were canadian goose jacket problems. Mainly with getting everything inside and not touching. Plus closing the lid. Lets just say I had to cut slots in the can to get buy canada goose jacket cheap the PC board to go in. Then I bent the thing trying put the lid on. Not a good day for me. But, I did prove the concept! And decided to buy a gallon paint can. Who builds a microphone that big? I did. Thinking about it, for what it was going to be used for it wasn’t like it needed to be right above a snare drum or having a harmonica player cup it. It was going to be on a stand above and in front of the Orchestra. Why not a bigger housing?Step 4: The Capsule Holder
The next thing I had to sort out was mounting the capsules. Not just mounting them but positioning them too. These are pretty delicate and required some thought on my part. canada goose clearance sale Normally they are mounted in a saddle or gently pressed into a holder. I thought about this and realized the capsules are 25mm in diameter and that 1″ PVC pipe is nominally one inch in diameter internally. So I cut a small piece and then cut out a small section. Basically making big letter “C”. The piece closed up slightly when the small cut section was removed. And, a capsule fit in snuggly. This was a huge win for me as I can see using this capsule in a multiple designs. (yea! more instrucables!) Now to hold four of them in the correct position, I cut a 1/2″ piece of 2″ PVC making a ring that I could glue the four capsule holders too. I actually bought just a 2″ PVC fitting and cut the ring from it. I used a hand saw and a miter box to make a clean straight cut both for the 2″ piece and the capsule holders. uk canada goose outlet After cutting them I cleaned them up bit with sandpaper and washed any dust off with soap and water. Then I used PVC glue to mount the holders to the base ring. The glue is pretty quick acting. I pressed the two pieces together for about a minute then moved on to the canada goose coats next. Solder the 1 gig resistor between the center terminal and ground. canada goose black friday sale When you have done this with all four capsules carefully press them into the holder. I then used a couple drops of Hot glue to lock them in place. Now take 8 or more rubber bands and place them diagonally across the capsule holder. We will use these to hold the assembly to the long bolt on the paint can coverStep 6: Mounting the Capsule Assembly
Now how to mount the whole thing. As mentioned before, I started with a 1 quart canada goose uk black friday paint can. And, it didn’t quite work out. It did however prove the concept and provide me with housing for testing other designs. Not all was lost. like web One of the challenges of the original paint can was positioning the capsules without touching anything. We want to isolate them from bumps and thumps. To get it all to fit the capsule assembly touched the PC board. That picked up too much rumble and thumps. Using the larger paint can did work.
I took off the lid and drilled a hole right in the middle, two other holes for the cables (one for audio and one for power) and two to mount the PC board. For the wire entry, I used rubber grommets to protect the wire. Lowes sells those too. To mount the capsules I used a 20 eye bolt. I could only find one that was 2″ long. So I then added a 20 standoff as an “extender”. This with a 4″ carriage bolt allowed me to put the Canada Goose Coats On Sale capsule assembly above the PC board and isolate it canada goose uk shop with a bunch of rubber bands. We want to float the gate leads so that we can connect it to the capsule without touching the PC board. Please double check the data sheet for your FET. I got mine here:
I misread this the first time when using the FET and got the leads backwards For mounting to the can I used a couple of these 4 40 angle brackets Once you have the board finished take a break uk canada goose and check your work. I typically use water based flux solder. It says “No Clean” but I wash the bottom of the board with a toothbrush, soap and water. Then let the board air dry. A really good method for drying Canada Goose online is to set your oven to 220 degrees. When it reaches that temperature and beeps, turn it off an put your PC board in. When it is dry, mount it on the paint cheap canada goose uk can lid.