3D Printing Speaker/Amplifier Design
Project Info: Summer Internship, Personal Side Project
Project Timeline: 1 week (August 2022)
Skills and Techniques: Ideation and rapid prototyping, Solidworks CAD modeling, 3D printing, surface finishing
OVERVIEW
Background and Inspiration: I wanted to do a personal side project in my extra time during my internship and apply the knowledge I gained regarding optimizing orientation, support material usage, and surface finishing a 3D printed object.
I wanted to print a passive speaker/amplifier with no electronic components or drivers. It would act as a natural sound amplifier for a mobile phone speaker already playing music. I was inspired by the concept of putting a phone (the speaker end) into a bowl or a cup to increase the volume and help it resonate.
Design Process: Shape and Material
Shape & Enclosure
I did some research online on the effect of shape on acoustic performance and sound amplification. The summary of my findings includes the following:
Close-knit material with high stiffness and strength → prevents the device from vibrating
Well-insulated casing → prevents the sound from escaping
Airtight processing → prevents the sound waves from escaping through any cracks
I then compared spherical (curved) vs. square speaker designs and found that speaker with curved edges has increased benefits, which are shown below:
Due to the rounded form, the sides are the exact opposite of each other, which means that the sound is constantly circling round rather than being stuck in a corner.
Curved speaker better distributes sound into a room. The sound can be perceived in more places.
The walls of a curved speaker require less vibrations than the walls of a square-shaped speaker.
It is aesthetically pleasing
Material
Should be a fairly rigid material resistant to vibrations
At some thicknesses and by using the correct composite materials, rigid plastic speaker enclosures flex less than very thin wood enclosures. They're also more durable than wood and more cost-effective in high manufacturing volumes
ABS (Acrylonitrile Butadiene Styrene)
the primary material for Stratasys FDM printers and is low-cost
great mechanical properties like toughness, hardness, and rigidity
high impact resistance and surface hardness at high and low temperatures
easy to post-process
high aesthetic qualities due to its natural opaque and ivory tones, easily modifiable into vibrant, colorful parts with variable gloss levels
Note: We did not have PLA available, which could also be an alternative materi al with high stiffness and strength and is biodegradable and environmentally friendly.
Cross section of a nautilus shell
Spiral Shape
I like turning to nature when in design and when brainstorming ideas. Exploring and researching different shapes in speaker design, I came across a nautilus-like spiral shape, which happens to have increased sound properties. The logarithmic spiral is found abundantly in nature, with examples like spiral galaxies, human cochlea, and nautilus, a marine mollusk. There is a mathematical and geometric correlation between the cochlea and natural spiral objects, and the same functional reason for their formation.
Anatomy of inner human ear
Curved speaker enclosures, which taper exponentially and are in the shape of a logarithmic spiral are designed and produced by speaker companies at high quality. Some examples include Deeptime's “Spirula” and the nautilus speakers of Bowers & Wilkins.
Iphone Opening '
I created the thin rectangular opening based on the iPhone models that have the largest width and thickness to fit all sizes, small or big.
largest width: 3.07 inches = 77.978 mm
largest thickness: 0.31 inches = 7.874 mm
Modeling
I modeled on Solidworks. I used the helix/spiral feature to create the spiral path and then swept a circle along the path. I then used lofted the end with a wider circle and created a cut for the iPhone opening.
Challenges
The iPhone cut does not overlap with the curve
Size of the design: I realized that the model was too large to print which would take more than half a day. Considering it is designed to hold an iPhone, it would have been unnecessarily large and not sustainable to use up more material. I then adjusted the size of the design, and the spiral path accordingly. I played with the pitch size and the start angle, with the pitch set to 160 mm, and the start angle to 60 degrees.
Placement of the cut: Playing with the spiral size ended up making the area where the rectangular iPhone cut is located smaller, with a reduced width. That's why I had to extend the cut to where the spiral curls, which is non-ideal considering the flatness of the iPhone.
Design Process: 3D Printing & Finishing
Settings
The high printing temperature and slow speed combined for better layer adhesion and adhesion to the build plate. This prevents any lifting of edges or corners of the 3D print.
I decided to break the design into 2 equal parts and print on 2 different printers. This would allow for faster print time and the use of less support material. If I were to print the whole piece, the inside of the spiral would all be filled with support material which would also be hard to remove due to its intricate shape and curling. This would be time-consuming, would create more material waste, and would have a lower surface quality.
Orientation: I placed the model on the 3D printing bed horizontally, which only needed support material for below the curves as a base, however no support material inside on the top.
Locking Parts: Utilizing Materialise Magics, the STL Editor Software, I added a locking mechanism to the edges to be able to assemble two parts. Lap joint cuts at the inside would allow two parts to click and stick into each other smoothly, without being visible on the outside.
Build time: 6:19h, ABS-M30 17.1 in3
Assembly
After cooling down when the print was done, two parts did not merge as smoothly and effectively as I expected. That's why using a hammer carefully was helpful to ensure the two parts merge tightly, without any cracks or gaps. This was important for better sound quality.
Surface & Coloring
Using a spray paint gun, I painted the outside of the speaker blue, building up thin layers of even paint in multiple coats.
NOTE: I did not prime, sand, and polish the surface as I did not have enough time. If I had more time, I would first sand the print with a sand paper for a smoother surface finish and then apply a primer to create a clean and smoother surface, which would will seal the part surface and prepare it to receive the paint. It would also fill in small cracks and holes, which is even better to prevent the sound from escaping. I would then apply a clearcoat for a polished finished surface that would form a glossy layer.
Reflection
I really enjoyed doing a personal project and 3D printing a design that I would use in my daily life. It was a fast-paced project I did during my last week. I am able to use the amplifier with my iPhone and it does succeed in amplifying the music. If I were to redesign, I would have included a smaller section for inserting the iPhone, which wouldn't be rectangular. This is because, in iPhones, the bottom speaker used for music and audio generation is located at the bottom right corner. Designing an appropriate-sized opening would have allowed to transmit the sound from a narrower space and allowed for fewer sound waves from escaping. Because I designed for the largest width and thickness, this makes small-sized iPhones have more space at the sides, which are gaps that allow sound to escape.