Portable Bluetooth Speakers

The main objective of this project was to create a speaker that mimicked Bose’s $200 Soundlink speaker quality at a fraction of the cost. While we were on a strict time schedule and often had to forego cheaper parts from China for more pricey units with faster shipping, we were still able to produce an excellent, 360-degree sound, portable, bluetooth-enabled speaker for less than $50. For those who are able to wait 4-6 weeks for parts to ship, however, it is feasible to reproduce this exact project for a third of the cost.

Our speaker is bluetooth-ready, long-lasting on a battery, and easy to use. We packed four 3W, 4Ω speaker drivers and a 3000mAh battery into a unit roughly 5.5” x 4.5” x 2” and weighing less than half a pound. By tearing down a cheap, low-power bluetooth speaker unit, we were able to extract a bluetooth module that was already configured to work with virtually every bluetooth-enabled device, as well as a pre-wired panel of buttons for standard music control functionality. Topped off with audio in, out, and micro-usb charging jacks, our speaker is small in size and budget but big in capability.

You needn’t be a seasoned electrical engineer to make your own powerful bluetooth speakers! But what you do need is...

Electronics

• Cheap bluetooth speaker for teardown
• Li-Po battery (3000mAh, 3.7V)
• 4 of 3W speaker drivers (40mm diameter)
• Passive radiator (optional for improving bass)
• 5V 4-channel output amplifier
• 5V step up converter
• Assorted colors of wire
• Simple on-off switch
• Micro-usb charging module + cable

Casing

• Electronics box, 2” thick, any shape (to be cut to 5.5” x 4.5”)
• Cardstock, construction paper
• Thin foam

Tools

• Soldering iron + solder
• Rotary tool (dremmel)
• Deburring tool
• Drill
• Band saw for cutting electronics box
• Hot glue gun
• Wire stripper + cutter
• Scissors
• Paper cutter
• Super glue
• Ohmeter, voltmeter, oscilloscope (optional)

Other

• Enthusiasm! (optional)
• A bluetooth-enabled device

Our speaker project was inspired by that of ASCAS (see here).

Bluetooth modules come in many different shapes and varieties and can often cost you a pretty penny. On top of this, their specifications are often so esoterically written that it is impossible to tell if they will even work with your standard iPhone or Android device. A really cheap and convenient way to get a bluetooth module that is guaranteed to work with the devices you want it to is to buy an inexpensive, low-quality bluetooth speaker fully assembled off of Amazon or eBay and extract the bluetooth module from it for repurposing. Just make sure in the speaker's description it mentions the full range of compatible devices you are looking for (virtually all will).

We went with a SoundBot speaker that came with a useful assortment of buttons and audio in/out jacks, thinking we could recycle more than just the bluetooth module. But first thing's first: let's get a working module!

After testing how the speaker worked with our mobile devices, we opened it up and identified the bluetooth module, recognizable by a small chip with a lot of connections running into and out of it. We carefully desoldered the connections to the other speaker parts, noting what went where, and removed the board. The first and easiest thing to do at this point is hook up the new battery. After all, everything that comes after this will need the battery power before we can test if it works. We desoldered the wires to the original battery and connected those of our own, bigger battery.

Depending on the speaker you buy for teardown, your bluetooth module and the board it comes on will look a little different. However, most speakers will come furnished with their own amplifier for feeding a more generous signal to the speaker drivers than what comes straight out of the bluetooth chip. Our amplifier was located on the underside of the same complex board that the bluetooth chip was on. It is identifiable by the original speaker's drivers, which protruded from the same spot on the board. This amplifier will not be as loud as we would like, nor does it service more than two speaker drivers, so we will be replacing it.

Take care desoldering this amplifier so as not to mess up the rest of the board. Next, look up the documentation of the amplifier to determine which pins correspond to the two input channels and ground, as we know the signal from the bluetooth chip will reach there first. We tested the two pins with an oscilloscope to make sure the signal was making it there. Our amplifier was model number CS8563S. Be sure to solder the three new wires to go to the new amplifier before you forget the pins!

We opted to go with a two input (+/- for both), four output channel double amplifier. Fortunately, stringing the signal along from the first input to the second so that the two amplifiers can run in parallel did not significantly impact the output signal strength.

The image above shows where each set of connections happens on the amplifier board. They will generally be well-labeled. Our original amplifier labeled the input signal pins as IN-A and IN-B, so the L and R is essentially irrelevant. We tested the signal of each and saw no real difference. We soldered the first set of inputs and ground, and tested the signal on the output side, temporarily powering the amplifier with an external power supply. Once you can verify that one amplifier is functioning correctly, you can extend the input signal and power to the second amplifier.

We went ahead and soldered all of the wires to each of these pins first as it is easy to connect the other ends of them to their respective components later. Once all the wires are securely fastened, we encased the double amplifier set in hot glue to protect the soldering. We covered all the exposed pins on the integrated amplifers in hot glue, as well, to prevent any accidental contact with other wires from frying them.

Our battery supplies 3.6V, but the amplifier wants 5V. While it still works with 3.6V, the signal does not come out quite as strong, so we employed a step-up converter to provide the amplifier with the voltage it is intended for by making up the difference. This step up converter features an input, output, and ground pin. We soldered the input and output to form the connection to the battery and then connected the output and ground to the first amplifier. Keep in mind it doesn't matter which ground you use, so use the one that is easiest to make a solid soldering connection to. It is easy for the wires to come unattached during the construction process, running the risk of damaging the components of the speaker.

Once both sides of the amplifier are ready to go and you can read a signal on all four of the output channels, you can finish the circuit off by connecting the four speaker drivers' wires. You should be able to turn on the set up and produce an audible sound signal from the drivers now! Don't worry if they sound tinny and unimpressive -- a good speaker is 30% driver, 70% driver chamber.

Our SoundBot speaker was a bulky unit measuring about 12" x 6" x 4," but we wanted a more compact and mobile case. We took a standard electronics box measuring 8" x 4.5" x 2" and used a bandsaw to cut it down to 5.5" in length. We decided on this length by experimenting with fitting the different components into the box and seeing how we could get a fit that was snug but not uncomfortably so. Unfortunately, our passive radiator did not arrive in time to be incorporated into the speaker, but remember to leave room for this part as well if you choose to incorporate one into your speaker.

After sanding the edges and verifying that our choice of length worked, we used a 38mm diameter drill piece to cut holes for the speaker drivers, orienting two on each side. The speakers are 40mm in diameter, but we did not have a 40mm drill piece, so the deburring tool was used to widen the holes marginally more from 38mm in order to fit the drivers better and smooth out the edges of the holes. We also needed to cut holes for our jacks (which we arranged on the side) and our buttons (which we centered on the top panel). We found it easier to cut one long stretch out with the dremmel tool rather than individual holes for each button, due to their unique shapes. We cut more precise holes to fit around each component on the decorative material that we lined the entire case with as we could cut that with scissors. Be sure to take care of all of the cutting of the box before attaching any of the internal components.

Once you are satisfied with your holes, it is time to start gluing the parts in! It is important to make sure the drivers are airtight with their holes, so we used the hot glue quite liberally. We also glued in the jacks for audio and charging at this point. Our buttons were attached to the bluetooth module board.

Before inserting the lose components (bluetooth board, wires, amplifiers, step-up conveter, and battery) and sealing up the case, take a cushioning material like a thin sheet of foam or the anti-slip material used to line drawers and cut and paste pieces to form the backing of each of the drivers. This will help reduce vibrations if the drivers come into contact with the loose pieces. If certain components are particularly close together, fill the space between them with extra padding.

Due to our time constraints and some technical difficulties, we were unable to hook up our buttons, but one can easily attach them to the top panel of the electrical box with hot glue, as well. Our buttons and the skeleton they would have connected to are pictured above. We decided to include a hard switch for the battery, as well, because we were having an issue with the amplifier draining the battery even when the unit was powered off.

With the pieces hot-glued in, we can finally insert all the loose components and close up the case. The last step can take up a little time or a lot of time, depending on how much you care about the aesthetic of your case. We were not familiar enough with the tools needed to create a full wood or acrylic cover for the case, nor did we have the budget for nice wood, so we opted for faux wood printed on cardstock and black construction paper. The result is a very sleek and convincing retro wood look.

And there you have it! Your own portable bluetooth speakers, plenty loud and equipped to get you through any long outtings. Who needs to pay $200 for a brand name speaker, anyway?