RedwoodPill - 50 W Teak Wood Bluetooth Speaker

Welcome to my first Instructables.com guide! I really love the content on this website and I am happy to contribute to the community with this project I've recently finished. I will walk you through my process of making a portable Bluetooth speaker out of teakwood and aluminium.

This guide will briefly walk you through the design process so that you can modify the product to your liking. I made my speaker in India, using locally available components and makerspace level equipment such as a CNC router and SLA printer. Speakers can be built in all sorts of shapes, sizes, and materials, so I would love to see you come up with your own creative versions.

Special note for the One Board Contest 2022:

The wooden enclosure, along with the aluminium frame, is the most prominent design feature of the speaker and can be machined out of a solid wood board similar in size to a framing stud. The minimum size of wood stock required to machine the wooden enclosure halves is 28.5 x 120 x 650 mm (1.12" x 4.72" x 25.59").

List of components:

(Links lead to Indian e-commerce websites. Look for an equivalent for your country)

Components to Buy:

1. Peerless by Tymphany TC8FD00 3" Full Range Speaker Drivers x 2 (Link)
2. Passive Radiator x 1 (Link)
3. TDA7492P 50 W Amplifier+Bluetooth Receiver Board x 1 (Link)
4. 3S1P 5000 mAh Lithium Ion Battery w/ BMS x 1 (Link). Ask for one with a female DC connector.
5. Metal Push Button Latching Switch x 1 (Link)
6. Boost Convertor x 1 (Link)
7. Buck Convertor x 1 (Link)
8. 3S Lithium Battery Indicator Module x 1 (Link)
9. 12V 2-4 A DC Power Supply with male 2.1 mm DC pin x 1 (Link)
10. 12V Blue 5630 LED strip. I use 6 LEDs (Link)
11. MacBook replacement rubber feet x 4 (Link)
12. n-type MOSFET IRFZ44N (Local)
13. M5 x 8 mm Brass Insert x 4 (Link)
14. M5 x 65 mm Socket Head bolt x 4 (Link)
15. M3 x 4 mm Brass Insert x 4 (Link)
16. M3 x 10 mm screw x 19
17. M3 locknut x 8
18. Silicone/Rubber o-ring 2mm OD x 2m long
19. Wiring

Components to Procure/Fabricate/3D Print

1. Front Board x 1 (Router , Teakwood)
2. Back Board x 1 (Router, Teakwood)
3. Aluminium plate x 1 (Milling, stock of min. 25 x 120 x 320 mm) Anodize to colour of choice.
4. Control Button Pad x 1 (SLA, Elastic 50A)
5. Battery Indicator Button x 1 (SLA, Elastic 50A)
6. PCB Mount x 1 (SLA, Standard Clear)
7. Top Button Mount x 1 (SLA, Standard Clear)
8. Bottom Button Mount x 1 (SLA, Standard Clear)

Local sources for routing, SLA printing, milling, and anodizing.

Files are provided in Step 4.

The speaker driver converts electrical signals to acoustic waves. The analog audio signals sent to the drivers are alternating currents are made up of frequencies typically in the audible range of humans (20 Hz – 20,000 Hz). The performance of the driver is evaluated by how closely it can translate the electrical signals into sound waves at different frequencies, as illustrated by the frequency response graph.

A single driver is usually not capable of accurately reproducing the entire audible range, which is why many speakers incorporate multiple types of drivers specialised for different frequency ranges. The electrical signals are passed through crossover networks which divide the unfiltered signal according to a predefined upper or lower threshold, supplying each driver with the signal range it is designed to best reproduce. Subwoofers play low bass heavy tones (around 20-200 Hz), mid-range drivers handle around 200-2k Hz tones and tweeters handle high frequency tones of 2k-20k Hz.

This speaker design uses 2 full-range drivers, which can reproduce 100-20k Hz well, with some drop in performance at the low and high ends. Two drivers will provide stereo sound, which gives some "depth" to the sound over a mono speaker, just like how two eyes provide visual depth perception. In order to improve the bass performance, I added a passive radiator, which is a diaphragm tuned to resonate at low frequencies from the sound pressure inside the enclosure.

The chosen speaker driver, the Peerless by Tymphany TC8FD00-04, are full range drivers with a power rating of 25 W, which matches the output of our amplifier board. Higher power drivers will be louder but will require a large enclosure and reduce battery life. You can find the driver parameters of most speaker drivers on LoudspeakerDatabase.com (ex: TC8FD00).

1. Amplifier+Bluetooth Board: The main component of the electrical circuit is the TDA7492P Amplifier+Bluetooth Board. The board can be powered with 8-26 VDC, providing flexibility with battery and power supply options. The integrated Bluetooth board uses a CSR8635 chip with Bluetooth v4.0, which is quite easy to connect to with most modern smartphones and laptops.
2. Battery/Power: The 3S1P 18650 Lithium Ion Battery pack provides a nominal voltage of 11.1V but will vary from 12.6 to 8V (see 1S Lithium-Ion Discharge Voltage vs State-of-Charge (SOC) graph). You can determine the playtime of your speaker by a simple energy capacity/power. My battery has a capacity of 5000 mAh@11.1V or 55.5 Wh. Dividing by the maximum power consumption of 50 W will give a playtime of only 1h7m. However, this assumes a constant max power consumption, which is usually not the case with the speaker playing music. The volume of the speaker will play a big factor on power consumption. During testing, the speaker ran for 4-5h on 50% volume, which is enough in most situations. Bigger capacity batteries are bigger, heavier, and more expensive - so the speaker playtime must be balanced against these factors of the speaker. It is best to test your set-up to get a more accurate estimate of power consumption and playtime. The battery is charged by a 12V-3A DC Power Adaptor (you can use 2-4A; higher amps will charge the battery faster but may reduce battery life). If you do not want to use a battery, you can directly power the amplifier board with a DC adaptor that can provide the maximum rated amount of power (for 50W and 12VDC, you need +4.2A).
3. Boost Convertor: This steps up and regulates the battery voltage to 15V, ensuring that the amplifier board always receives enough voltage to function.
4. 3S Battery Indicator: This is connected to the output of the battery to measure the voltage and determine the battery SOC. The LEDs light up for 2 seconds when the tactile switch is pressed.
5. Buck Convertor: Some power is diverted to the the LEDs for the buttons. I found that running the 12V LEDs on 9V reduced power consumption by 75%, with a slight reduction in brightness.
6. LED strip: These lights are wrapped around and hot glued to the button mounts to light up the buttons when the speaker is on, serving as a visual cue.
7. n-type MOSFET: This is used as a switch to only turn on the lights when the power button is turned on. The MOSFET only conducts through D-S when G is supplied with a voltage in the range of 2 to 4 V. Find a spot on the amplifier board using a multimeter that is 0V when the power button is off and 2-4V when turned on. The capacitor I connected to (see circuit) is one such spot but there may be others. An interesting side-effect of connecting to this spot is that the lights flicker to the music on high volumes, indirectly "dancing" with the music.
8. Push Button: This serves as a power button. Use a latching switch type (as opposed to a momentary one). I de-soldered the smd latching button that the board came with. Some boards do not have this switch, in which case you can connect the switch in series to the power supply of the board. In this case, you won't need the MOSFET and you can connect the LEDs in series after the switch. In hindsight, this is probably the better way to connect the power buttons and LEDs anyway.
9. Speaker Drivers: The two speaker drivers connect to the L-R stereo output of the board. You can ensure the speaker polarity is correct with a simple test.

There are different types of enclosure designs for speakers. The two most commonly used configurations are sealed and ported enclosures. An important parameter of the sealed enclosure design is the internal air volume. The materials used to make the enclosure are also important for the quality of sound as well. Some desirable material properties for speaker enclosures are high stiffness and good acoustic dampening, and from a practical standpoint – accessible manufacturing techniques, low weight, low cost, high durability, and appealing aesthetics. MDF is considered the best suited material for making speaker enclosures as it meets all the above mentioned criteria. Wood is another great choice as well but has slightly lower performance due to varying density, effect of humidity, and anisotropic stiffness due to grain orientation, but it looks much nicer.

I used Indian teak wood with an aluminium ring sandwiched between the two halves. The grain pattern of the stock wood was examined before machining it so that I could locate the best grain structure and plan where to cut out the front half of the wood from, as this face would play a major role in setting the overall speaker aesthetic. The aluminium ring serves as the mount for the control buttons and the power switch. The o-rings seal the enclosure and dampen most of the vibrations to the aluminium. The M5 screws hold the entire assembly together.

3D modelling and rendering was done on Autodesk Fusion360.

Wooden enclosure halves:

Find a suitable piece of hardwood. My version has a back cover piece, which has been eliminated, so there are only two pieces to machine. The wood is then hand sanded to up to 2000 grit and polished with Danish oil.

Aluminium frame:

Machine out of a block of aluminium. Anodize it to the desired colour. I went with Type 2 anodizing in gray.

3D printed parts:

All parts are can be printed using an SLA printer. I used a Formlabs Form 3.

Control Button Pad - Elastic 50A Resin (or Flexible 80A Resin)

Battery Indicator Button - Elastic 50A Resin (or Flexible 80A Resin)

Top Button Mount - Standard Clear Resin

Bottom Button Mount - Standard Clear Resin

PCB mount - Standard Clear Resin

Assembly Steps:

1. Connect the electronic components together as illustrated in the circuit diagram.
2. Epoxy glue in the M3 and M5 brass nuts to the slots of the Front Board.
3. Cut 2mm o-rings length to fit in the groove of the Front and Back Board.
4. Mount the speaker drivers with the M3 screws and locknuts and hot glue the passive radiator to the Front Board.
5. Complete the control button subassembly as shown in the above picture and attach the button mount and PCB mount to the Front Board using M3 screws.
6. Place the aluminium frame above the Front Board and mount the power switch to the frame.
7. Hot glue the battery, battery indicator, and battery indicator button to the Back Board.
8. Align the two wood boards and metal frame and secure down with the M5 screws. Ensure that there is an airtight seal between the wood and aluminium.
9. Glue on the MacBook feet to the bottom of the Front and Back board.

Congratulations! You have yourself your very own wood and metal Bluetooth speaker. Connect it to your phone or laptop to it via Bluetooth.

My speaker dimensions are 80 x 120 x 320 mm and it weighs 1.9 kg.

If you have any questions or comments, please do share them.

Have a good one!

-Simran