This page documents the process of designing and fabricating a bluetooth speaker. The idea originated from the YouTube channel DIY Perks, although design changes were made to their design to optimize for our personal preferences and capabilities. The electronic circuit shown later in figure 3 was composed of components bought online and soldered together to develop a cohesive working system. The speaker drivers of the circuit were embedded into a wooden front panel which was then housed in a curved concrete casing. While the speaker concept is technically portable, due to the size and weight it is more likely to have a designated spot in somebody’s home which was the purpose that was intended for this speaker. To complete this project, advancements were made in several different areas at once. Circuitry work needed to be completed while the physical construction was also being developed.
Design and Results
Physical Design
The complete design focused on two discrete areas—electrical circuitry work and physical construction work—which were unified at the very end of the project to complete the speaker. The physical construction began with developing AutoCAD files for several components. The first components that were designed were for the mold that the concrete could be poured into. Design modifications were made to the mold such as removing a slot for batteries and adding in a slot for the USB-C port which will be discussed more later. These AutoCAD files can be seen below in figure 1
Figure 1: AutoCAD files for the concrete mold
Different components shown above were cut out of a large piece of MDF plywood with a CNC machine and then glued together to create an inner and outer mold such that a concrete shell would be produced. Progress of the outer portion of the mold can be seen below as figure 2:
Figure 2: Outer mold and faceplate drying after being glued together
Once the molds were constructed, clear acetate sheets were cut to size and wrapped around curved portions of the mold to allow a smooth curve of the concrete structure. Additional AutoCAD files were created to produce the wooden face of the speaker, the housing for the speaker drivers, and additional support for the concrete mold. These AutoCAD files can be seen below as figure 3:
Figure 3: AutoCAD files for concrete bracing cutout and front panel cutouts
These files were also cut out using a CNC machine and several wood types were used. Only the front panel required a high quality finished wood and so rustic walnut was used with stain applied to it post-processing. The other wooden pieces were structural in nature and hidden from view and so MDF could be used for those pieces as well. Additional materials such as caulk, sound damping foam, and hardware were also purchased.
Electrical Design
The first thing to consider, which affected the physical creation of this project as well, was that I didn’t want to use a series of batteries and instead opted for a simple usb-c connection port to supply the speaker with power.
With that design feature in mind, a few things about the circuit had to change. Firstly, since the voltage delivered would no longer be the amount of voltage necessary for the amplifier board, I thought of using an op-amp to achieve the desired gain, bringing the 5V input up to 12V. After some consideration and circuit analysis, I realized that using an op-amp would not work for the design, so instead decided to go with a voltage booster.
All of the components of this project were chosen to work well together, and the final list of circuit components were as follows:
-
5V-5V DC-DC isolating converter: This component was chosen to limit something called ground loop interference, which can create a static noise when no music is playing.
-
USB type C female and male boards.
-
DC-DC adjustable voltage power converter/boost module: This voltage booster has variable input and output voltages, and I calibrated ours to boost 5V to 12V by turning the potentiometer and taking measurements with a DMM.
-
OEP30W TDA8932 Audio Module class D digital power amplifier: Used to increase the current coming from the source, amplifying the frequencies from the bluetooth module and outputting to the speakers. Also responsible for the left and right channel controls from the potentiometer.
-
50 k-ohm dual gang potentiometer: Used as the volume control knob.
-
5V wireless bluetooth receiver board.
-
2x Dayton Audio ND65-8 2-½” aluminum cone full-range drivers - 8 ohm: Main speakers for the setup. The speakers deliver a deep punchy bass, nice treble, and smooth midrange sound.
​Before ordering all the parts however, a block circuit diagram was necessary. After the diagram was finished and the parts were in hand, the process of soldering all the components together did not take much time. Most of the time spent during this phase went towards design consideration, and ensuring everything could fit well within the speaker.
Figures 4, 5, and 6: Circuit diagram and physical circuit soldered together and mounted into faceplate
In summary, this project served as a profound learning opportunity both from the mechanical and electrical design aspects. As a mechanical engineer, this project had a healthy blend of everything, except perhaps software. Some of the project difficulties I ran into included soldering issues and electrical component failure. Early on in the project the bluetooth receiver board burned out due to improper soldering techniques, and rendered the speaker useless for the presentation. I later bought another bluetooth reciever and fixed the circuit with improved soldering.
Figures 7 & 8: Poor soldering job (left) vs. improved technique (right)
Aside from the project difficulties, there were actually more successes than failures. I successfully learned how to use a CNC cutter, and refined my CAD skills in the process. I also both learned how to work with concrete and how to solder. Utilizing techniques like DFA and DFM (design for assembly and design for manufacturing), I gained lucrative skills that field mechanical engineers have to learn.
The value of proper research and preparation was a big lesson for me, and considering this, I came up with various ways I could improve this project in the future.
If I were to start this project over from scratch, I would devote more time researching and improving my design techniques before using tools on the components. In terms of powering the speaker, I know that if I were to do this again, I would probably go with a simple USB-A connector or a battery pack that delivers the correct voltage and power to the circuit. I believe I did well when it came to time management, but I know that with more considerate planning, I could have had a much smoother project execution.