Microphone Array

Is it possible to direct a “beam” of sound with the use of an acoustic phased array?

Yes! This project uses a phased array to send sound waves further, and keep a cleaner airspace. This project is split into two teams: one team that creates the array of acoustic transmitters that will direct sound waves, and another team that wires and codes an array of acoustic sensors to detect whether the sound waves have been successfully directed in the expected angle. 

This instructable will cover the sound detection task, which will involve creating a sound dampened room for testing, and an arduino-based system to detect the angle of the sound “beam”.

To start off, you will need some supplies in the materials list below:

• Acoustic Panels
• Sound Damping Blanket
• Microphones (Arduino Compatible)
• Bread Boards
• Arduino Mega
• Tape
• Hot Glue Kit
• Arduino wires

Here is a summary video of our project!

In this project, we will be building a grid of sensors to detect and calculate the angle of waves emitted from the phase delayed speakers. This is achieved by detecting which microphone on the grid has the highest decibel reading then converted to degrees by the microcontroller.

Creating an effective sensor array relies on understanding the basic principles of sound waves and how it affects the microphones. It’s important to learn how to measure sound levels and intensity with acoustic waves, and examine the interactions that occur when waves meet barriers, restrictions, changes to the medium, and other waves.

Building a sound room is essential to dampen and minimize any reflections of interfering waves that can hinder the accuracy and reliability of the data from the sound array. Ensuring that the environment of the microphone is quiet allows us to minimize sources of error for sound waves to travel from the speaker to the sound array and ensure proper detection.

For the microphone array to work properly, it is essential to have a quiet space. If you have a small corner or area that you can block off to isolate from any background noise; try to follow this guide to get a relatively isolated environment.

• A space of your choosing with 3 walls
• Build a 4th wall with cardboard leaving about a foot wide gap for entrance
• Find space with minimum ambient noise
• Measure environment to estimate amount of panels needed (one panel for every square foot of space on the walls)

Our Sound Damping Room consists of 72 foam sound panels with a blanket on top with a width of 1.39m and a length of 1.16m.

• Prep Sound Panels
• Remove panels from packaging and soak in water to inflate
• Allow Panels to dry
• Use what you can to secure your sound panels to the walls of your chamber (tape won't work directly on the sound panels)
• We hot glued cardboard to the panels so that tape would stick to them

• Lay out sound dampening blankets draped over the roof and layed out across the floor
• Secure panels to the wall

Drape curtain over the chamber entrance and it's complete!

You will numerous microphones connected to an Arduino Mega microcontroller as shown in the schematic diagram (we used 10 for higher accuracy).

The microphones are connected to the Arduino Mega's analog inputs A0 through A9. The Arduino Mega is responsible for reading the analog signals from the microphones and converting them into digital signals that can be processed.

The Arduino Mega is connected to a computer via a USB cable.

The computer is used to control the Arduino Mega and to display the data from the microphones.

The code works by taking the analog values from the sensors and calibrating them so that it gives a rough estimate of decibels. It uses the dimensions of the array to then estimate the angle from which the sound is coming from. If you know the angle and distance between your sensors, you can do the necessary math to make your code output the angle of sound in degrees.

Using the real-world data known about your sensor array, you can calibrate the array to give you an estimated angle from where the sound is coming from.

The code stores the analog readings it receives from the sensors as an array with all the datapoints and then prints them all to the serial monitor where they can be recorded.

It uses a predetermined algorithm with minimum and maximum values to estimate intensity of sound detected by the microphones in decibels.

To eliminate outliers, the code also prints the average of the last five values, rather than just the most recent one.

• Gather material to build Array (we used scrap wood).
• Cut wood with a rounded shape depending on the angles you'll be measuring.
• Find the radius of the shape you cut out. That's the place your speaker should be put.
• Mount wooden studs  to the top of the array spaced out at the angles you want.

• Used double sided tape to secure the breadboards with the microphones to the Wooden studs.
• Ensure that the microphones are all mounted so that they would all be pointing at the center of your circle where you measured the radius to be.

Now it's time to test your microphone array!