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Boosting Cell Phone Speakers

Mike Isley
Product Developer

May/June 2016


Introduction

On many occasions there is the need to boost the sound of a cell phone or an MP3 player for sharing music, podcasts, etc., with a group. This lab activity encourages students to think outside the box as they engineer devices that amplify sound from a phone or player’s speakers without any power assist.


Materials for a class of 30

  • 15 Long Cardboard Tubes (from paper towels)
  • 15 Short Cardboard Tubes (from toilet tissue)
  • 15 Paper Cups, 16 oz
  • 15 Plastic Cups, 10 oz
  • 15 Paper Cups, 8 oz
  • 16 Sheets of Construction Paper, 12 × 18"
  • 100 Pushpins
  • 15 Scissors
  • 15 Pencils
  • 15 Cell Phones or MP3 Players
  • Box Cutter
  • Glue
  • Transparent Tape
  • Cylindrical Food Containers (for oatmeal or chips, optional)
  • Assorted Bowls (glass, ceramic, plastic; optional)
  • Beverage Containers of Various Materials and Sizes (optional)


Background

For sound to be heard, 3 things must happen: something must vibrate, there must be a medium to transmit the vibration (solid, liquid, or gas), and there must be a receiver to receive it (such as an ear). Sound energy travels in longitudinal waves, which displace the particles of a medium in a direction parallel to the direction of the sound. Sound energy bunches these particles together into compression waves before returning them to their former random state known as rarefactions (areas of fewer particles).

The sound energy travels through the medium by forming one compression wave after another. See Fig. 1. Waves travel the fastest in solids because the particles are the closest together.



Figure 1  Compression waves.


Three properties of sound are loudness (amplitude), pitch (frequency), and intensity (pressure).

  • Loudness is changed by increasing the vibration energy (e.g., turning up the volume, blowing a whistle harder, or pounding a hammer harder). The wave has more energy and sounds louder even though the wavelength (distance between peaks) and frequency (number of wavelengths passing a point in 1 second) stay the same. See Fig. 2.


Figure 2  These 2 waves have the same frequency, but the lower wave is louder because of higher amplitude.


  • Pitch is measured in hertz (cycles/sec). See Fig. 3. For young adults, the range of hearing is 20 to 20,000 Hz. With advancing age, the range of hearing decreases, starting at the upper end. Dogs can hear in the ultrasonic (>20,000 Hz), up to 45,000 Hz, as can bats and dolphins, up to 100,000 Hz.


Figure 3  These 2 waves have the same amplitude, but different frequencies.


  • Sound intensity can be measured in decibels (dB). The faintest sound heard is given a value of 0 dB. A lawn mower produces values over 100 dB, which can damage hearing over a period of time. A chain saw creates 115 dB and a jet plane on takeoff may reach 150 dB.


Safety

Use caution when making cuts with a box cutter or razor knife on tubes and cups for students.


Teacher preparation

Set up 15 lab stations for groups of 2 students with the following materials:

  • Long Cardboard Tube (from paper towels)
  • Short Cardboard Tube (from toilet tissue)
  • Paper Cup, 16 oz
  • Plastic Cup, 10 oz
  • Paper Cup, 8 oz
  • Sheet of Construction Paper, 12 × 18"
  • 4 Pushpins
  • Scissors
  • Pencil


Teacher tips

  • You will measure the decibel output of each group’s sound booster by downloading one of the following smartphone sound meter apps:

    • Decibel 10th, free, App Store, iTunes®.
    • Sound Meter PRO, free, Android™ Apps, Google.
  • Below are photos of some sound boosters students may develop in the Design Challenge. See Figs. 4 and 5. Do not share them with students. Let them use their critical thinking skills to create original designs. One of the simplest and most effective sound boosters is a 16-oz cup, either upright or horizontal, with the phone or player placed inside.

  
Figure 4  Sound boosters made from tubes and cups. Figure 5  Sound booster made from construction paper.


Procedure

  1. Warm-Up Activity

    1. Take a toilet tissue cardboard tube and place a cell phone or MP3 player on top so that it is in the middle of the tube. See Fig. 6.


      Figure 6  Tube marked and ready for cutting.


    2. Trace an outline of the bottom of the phone or player on top of the tube.
    3. Have your teacher make a longitudinal cut on one side of the outline with a box cutter.
    4. Cut the remaining outline with scissors to form a slot for the phone or player.
    5. Place the phone or player into the slot. Place 2 pushpins on the back of the tube near the bottom to serve as feet.
      See Fig. 7.


      Figure 7  Completed sound booster.


    6. Take out the phone or player, turn on some music, move the volume button to at least 50%, and listen to how the speaker performs.
    7. Note the location of the speaker on your device. Some have the speaker at the top while others have it at the bottom.
    8. Without changing the volume, reinsert the phone or player into the slot. Orient it so that its speaker is inside the tube. Does it sound louder with better clarity?
  1. Design Challenge

    1. Do research on the shapes of speakers found on early radios, telephones, and record players. These early models relied on speaker shape rather than electronics to boost sound.
    2. Modify the sound booster you made or design a new one using materials provided (cups, construction paper, and cardboard tubes). Try with your modifications or new design to improve sound volume and clarity. Note: You may find that 2 different materials of the same design have the same increase in volume, but one has better clarity than the other.
    3. Your teacher will measure the decibel output for the same recorded song on each group’s phone or player with the volume set at 50%, first without any assistance, and then with the boosting device. Use the following data table to record the change in decibels for your design:

      Data Table

      Phone or Player Only dB
      Phone or Player with Booster dB
      Increase in Sound dB


    4. Your teacher will select the winner based on the largest decibel boost. If there is a tie, then the design with the best clarity will be declared the winner based on the teacher’s judgement.


Additional resources

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