Make a Rotating Microphone

This Instructable describes how I made a rotating microphone using just a few basic electronics and some common household items. You can use a rotating microphone to simulate the doppler effect like that of a leslie speaker cabinet. The rotating microphone is the inverse of the rotating leslie speaker. My design is a microphone installed at the center of a lightweight wooden "turntable." The microphones capsule is connected electrically to the back side of a female 1/4" TRS connector that is affixed to the turntable. The male end of the Male 1/4" TRS --> Male XLR adaptor is used as the axis of rotation for the turntable and also functions like a slip ring by maintaining an electronic connection while the female 1/4" TRS spins around its axis. The turntable has rubber gears installed along its edges that are in turn moved by the gears on the DC motor. The microphone requires an external power supply that is seperate from the motor and turntable.

You will need the following items to make the rotating microphone work using my methods:

1 Electret Condenser Element (for this application a unidirectional capsule will work best)
1 Male XLR Connector
1 Female XLR Connector
1 Male 1/4" TRS --> Male XLR adaptor
1 Female 1/4" TRS plug
1 DC Motor (9V) with gear
1 Circular lightweight piece of wood (I got mine at Hobby Lobby)
1 Drill
1 Rubber Gear Strips (long enough to cover the circumference of the wooden circle; matched to motor gear)
1 Glue (Gorilla Glue or something like it)
1 Wood Glue (used for the rubber gear strips and the wooden circle)
1 H Bridge
1 10k resistor
1 2k resistor
1 1000pF capacitor
2 10uF capacitor
1 Analog or digital switch
1 Potentiometer (50k-100k will work)
1 Arduino microcontroller (I am using the Diecimila) including a computer or other way to program the board. You do not need a computer to use the rotating microphone once the Diecimila is programmed and has 9V of power coming in (center positive).
1 9V power adaptor (center positive, not exceeding 300mA)
1 9V battery or 4 AA batteries in a 4 AA Battery Cell Holder
1 breadboard for motor circuit
1 perf board for the mic powering circuit
A good bit of wire and alligator clips
small plastic clamps
electrical tape
Soldering iron with solder
small lightweight plastic bottle with screw on cap (I used a small bottle of Dr. Bronner's Magic Soap)
large plastic bottle cap (to hold the motor in place)
mic stand
small mic clip

optional:
rubber mount for electret capsule (I used one that I stripped out of an Apple PlainTalk microphone)

Step 1 Make the microphone powering circuit

First off, make the powering circuit for the "Tape Op" microphone as shown on this site:

http://www.prosoundweb.com/recording/tapeop/buildmic/buildmic_16_1.shtml

You can also power the microphone using four AA batteries in a four AA battery cell holder.

I chose to make mine with XLR in/out as XLR is usually the type of mic inputs that I'm using.

I went ahead and made the circuit on a perf board- it's much easier to do on a perf board that has some connecting strips for ground, etc.
The microphone circuit that is also shown on the web page will be used later on so bookmark the page for future reference.

Comments

[onlinemastering]

Wicked instruction, classic sounds DIY style, thanks for posting it up.

online mastering

[NARCO-POLO]

check out my vid its along the same lines but backwards. youtube title, dumpster leslie speaker

[sn3102]

If you decide to take this with you anywhere, I would make a heavier platform (detachable) for support and stabilization.

[bobwantzanapple]

video?

[C0D3914]

hey man r u sure ur plan works? if i try it will it work?

[PS118]

Alternative idea: Instead of trying to get the doppler effect, would is be possible to subtract off the motor rpm in order to get a 360 degree ambient sound? Then maybe you could re-construct the sound for a given direction (and again for 180deg) after the fact. The thought being like, for instance, those Quicktime VR images, only you can pan around audibly instead of visually... Like you'd be able to play back a recording of a band and you could rotate and explore by "turning your head" to hear differnt instruments... Then in the ridiculous extreme... if you somehow figure out the vecor AND a magnitude you could like re-create a stored 3d space to walk around in. Again, not sure how to do that. Smacks of algebra tho, and I just woke up. :)-

[noxidgerg]

These are some great ideas and right in line with my thoughts on why I wanted to build something like this.

There are now some really interesting surround sound and ambisonic microphone options that allow you to do just what you are describing by decoding a 4 channel Soundfield B format microphone signal.
Soundfield- http://www.soundfield.com/soundfield/soundfield.php

Also, check out this more affordable option from core sound:
http://www.core-sound.com/TetraMic/1.php

In order to simulate turning your head, with a neck that can rotate 360 degrees (!) you could utilize two microphones in a stereo configuration and rotate both of them at the same time.

I was also thinking about simulation of 3D spaces using a rotating sensor, it wouldn't have to be a mic necessarily. An ultrasonic range finder would perhaps work better. With the ultrasonic range finder you could send out a ping and measure the delay of the acoustic reflections in a 360 degree X Y planes, then do another rotation in the Z plane. With the combined data you could figure out the dimensions of the space and possibly start to come up with representations of the objects that inhabit that space.

[PS118]

Cool! Thanks for the links. Also, since I forgot to mention it before, thnks for making this instructible!

[Aud1073cH]

I may have to try this.

It looks like it wouldn't have the frequency modulation (doppler shift) vibrato of a rotating speaker, because the sound source isn't moving.
gmoon's suggestion of moving the mic to the outer rim may add the doppler shift. To sound more like a Leslie, two microphones may be used, set on opposite sides of the turntable. Then one is moving closer, while the other is moving away (like the Leslie horn).

Does adding a horn to guide the sound to the microphone change the sound much?
I find most cheap electret condenser capsule microphones from toys are fairly omnidirectional, so a horn may improve the effect.

[noxidgerg]

I really like your horn suggestion a lot and I think that would definitely improve the effect. You are right that many of the capsules from toys are the omni caps; I think they are much more common. The electret condenser elements don't have to be omni, however, and that's why I specify a unidirectional capsule. Theoretically, an omni cap would only pick up sound pressure changes and you would not hear any kind difference based upon the direction of the mic's capsule. In reality, they omni caps start to become more directional at higher frequencies. I was also think that you're on to something with moving the mic to the edge and getting greater distance displacement to simulate doppler effect. Thanks to you and gmoon for the suggestion.

[rimar2000]

I agree with gmoon. I don't know WTF is leslie effect.

[Aud1073cH]

The idea behind the Donald Leslie's roatating speakers was to add vibrato to the organ.
Wikipedia: Leslie Speaker

The baffles on the good leslies are simply light plywood (styrofoam just doesn't hold up as well). and played loud enough to cancel most motor noise.

[thelandlord]

The 'Leslie' effect is that doppler effect you hear on many Hammond organ solos - you sometimes hear it speeding up and slowing down too. One suggestion though, is based upon the way some 'real' Leslie speakers work... that's to keep the microphone still and avoid all the hassles inherent in a rotating connection. Instead, use exactly the same motor and speed control to rotate a baffle instead. The baffle in many Leslie speakers is made of styrofoam for light weight and low inertia so motor noise is less. The shape is rather like a drum with a piece missing from the underside, so the hollow 'horn' rotates over the speaker so the acoustic effect is identical to the actual peaker moving. Exactly the same principle would apply to a microphone replacing the speaker. Another possible refinement - again based on the construction of rotary loudspeakers - is to consider driving that drum through a belt rather than directly - that could lower the physical noise level by mechanically isolating the motor vibrations from the microphone. Yes, you guessed - I'm a keyboard player. ;-)

[noxidgerg]

Both really good suggestions! Thanks. :)

[thelandlord]

This is what's inside a Leslie speaker.

http://www.m0gdu.co.uk/leslie.jpg

This particular model combines both methods - there are a pair of treble horns that physically rotate at the top, and a larger bass speaker that faces downwards into a rotating drum baffle... if you look at the right hand side of the drum you can see the edge of the cut away portion.
What you can't see is that there's a small weight attached level with the cutaway to replace the missing mass so the whole assembly is balanced correctly - if you forget that the whole machine tries to walk across the floor!

[rimar2000]

Thank you very much for the explain. I remember to have seen a electronic organ whit a big oscillating speaker under the keyboard. ¿Have you some MIDI or MP3 files recorded by yourself? If you want send me any, my email is [e-mail]. Thanks newly.

[noxidgerg]

I'm going to try to put a movie up soon on YouTube so you can see what's going on (and how mechanically loud it is! Yikes!) Check back soon.

[thelandlord]

You have mail with 3 rapidshare links in. I hope you enjoy it. If you care to reply in kind that would be cool. :-)

[noxidgerg]

I didn't get your mail? I even searched through my spam filter but nothing turned up. Please try again.

[thelandlord]

You didn't get it because it was rimar2000 I sent it to. :-)

For anybody who is interested, I've uploaded some music here

http://www.m0gdu.co.uk/homemade.zip

It's a zipfile of around 37Mb and contains MP3s of several popular tunes played by myself.

http://www.m0gdu.co.uk/soul_limbo.zip

is a smaller download (under 3Mb) because it's a single track.
It features the use of a Leslie speaker on the organ - when you hear it you'll recognise it instantly... that 'swirling' sound is it.

[rimar2000]

I answered your email today in the afternoon. Now is night here in Argentina.

[gmoon]

Nice project! You should probably include an explanation of why you would want a rotating mic (leslie effect, etc.) Do you think that placing the mic element nearer the rim of the disk would increase the effect?