ECE/ME 491 – Acoustics

ECE/ME 491 – Acoustics
Fall 2015
Project #3
Due: Tues., Nov. 3 at the beginning of class.
1 Guitar pickup
For this project, you will construct a guitar pickup from basic materials. You do need to use
the materials provided, but how you combine them is up to you.
2 Background
Sensors (i.e., transducers) are an important part of acoustics, particularly for sound transmission
and sound reception. For example, a guitar pickup detects the motion of a metal
guitar string, then the received signal amplified and transmitted. For this project, you will
build a pickup using magnets and magnet wire, as described in the sections below. Ideally,
we would like to use these guitar pickups to analyze the modal structure of resonating
strings, but realistically, building this sensor should be a sufficiently interesting project in
and of itself.
In this type of guitar pickup, as the steel string on the guitar vibrates, the field of the
magnet located very close to that wire is perturbed. This changing magnetic field induces a
current in the coil of wire that is wrapped around the magnet(s). For this project, there is
one magnet for each string on the guitar, where the poles are each oriented perpendicular to
the string, and all of the poles point in the same direction. You will wrap the 6 magnets (one
for each string) with a single coil of very fine magnet wire. This coil will contain hundreds
or thousands of turns of magnet wire.
3 Parts
Pick up the parts bag for this project in the ECE shop, which is located in 3234 EB. Each
bag contains magnets, epoxy (or super glue), and popsicle sticks/tongue depressors. Contact
Brian or Gregg in the ECE shop if you need additional epoxy or popsicle sticks/tongue
depressors. You will need to check out the spool of magnet wire – be sure to return the spool
to the ECE shop in 24 hours or less (we only have a few spools of magnet wire, and other
students also need to check these out). Expect to spend at least a few hours winding, plus
a few more hours on other aspects of this project (epoxy, etc.).
4 Hints
• The thinner magnet wire breaks more easily, but you can fit more turns into the same
space with thinner wire. Thicker wire is recommended.
• Scrape the enamel off of both ends of the magnet wire with either fine grit sandpaper
or with an X-acto knife.
• Check out a spool of magnet wire (for 24 hours only) the first chance you get. Don’t
wait until the last minute to check out the wire (only to find that all of the spools are
already checked out).
5 Constructing the guitar pickup
The instructions for constructing the guitar pickup are outlined in this section. If you would
rather figure this out yourself, quickly read the link on magnet safety (at the end of the
references section), and then read other sections below before working on the pickup.
1. Center one of the tongue depressors over the strings, and mark the location of each
string. These marks indicate where each magnet should be centered.
2. Use epoxy (or super glue) to attach each magnet to the tongue depressor. Wait until
the epoxy dries before attaching the next magnet. Be sure to align all of the poles in
the same direction. Use all 6 magnets – one for each string.
3. Epoxy a second tongue depressor to the top of the array of magnets.
4. Cut or trim the tongue depressors as needed. Don’t trim too much on one side – we
don’t want the pickup to fall into the guitar.
5. Before wrapping the wire, leave at least several extra inches (up to a foot or so)
exposed. This is important, because you will need to connect both ends of the winding
to complete the circuit for the guitar pickup.
6. Wrap several hundred or even several thousand turns around the magnets (in one large
loop around the outermost magnets). Be careful – this thin magnet wire breaks easily
– a drill will probably break the thin #43 wire. Expect to spend at least a few hours
winding. You can attach the pickup to the refrigerator, for example, to hold it in place.
7. Make an effort to count your turns while you are winding – include this information in
your report.
8. If the wire breaks while you are wrapping, you will either need to start over or carefully
splice the wire. The bottom line is: don’t break the wire!
9. When you are done winding the pickup, epoxy the outermost windings together (so
the pickup doesn’t unwind).
10. Strip the ends of the wires with sandpaper or with a utility knife. Don’t cut the wire
when removing the enamel.
11. Attach the exposed ends to a terminal block or a small screw/nut. Solder is optional.
6 Testing
Brian and Gregg made some test fixtures, including a speaker and a small amplifier. They
have also constructed a small signal amplifier if you would like to import your waveforms into
audacity ( Although not available for checkout, you can
quickly test your pickup with the guitar and amplifier. Demonstrations of your completed
pickups (using the test fixtures) can be arranged on any day when the instructor is available
after class.
All equipment for testing, along with the guitar, is located in 2228 EB. To access this
room between 8am and 5pm, stop by the ECE shop (in 3234 EB) and ask Brian or Gregg
to let you into 2228 EB to test your Acoustics project. This room is also staffed for ‘after
hours’ use – see the poster outside of 2228 EB for more information.
To enter 2228 EB, you need to have a pair of safety glasses. Also, be sure to turn off the
amplifier setup when you are done with it, and you of course need to clean up your work
area before leaving the room.
7 Project report
This is a one page report (more pages will be accepted, but no additional credit will be given
for more pages) that should contain the following information:
• the data collected
• analysis of the data (perhaps by interfacing to audacity)
• discussion, including any combination of the following
– answers to the following questions (but not limited to these questions – feel free
to pose your own questions)
* How does the sound produced change if the strength of the magnetic field is
changed (i.e., what will happen to the results if you use stronger or weaker
* What if the number of turns (wraps) in the coil of wire is changed? How will
this change the strength of the signal, and how will this change the frequency
response of the sensor?
* How does the position of the coil (closer to the end of the string or closer to
the middle of the string) influence the output of the pickup?
* how we might take this to the next level (i.e., what other objectives could be
– related projects or extensions of this project that you would like to pursue on
your own (i.e., need not be part of this class, but instead describe an application
that is of interest to you).
– comparison to a piezo-based pickup
– etc.
8 Honor code
Discussing this project, including materials and methods, with your classmates is acceptable.
However, you must complete your own project, and the ideas presented in the report must
be your own.
9 References
Much of the material presented here was obtained from the following link:
Other links:
One other link on safety – keep these magnets away from children:
10 Date
updated 11:29am on Oct. 19, 2015.

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