DIY a portable Bluetooth speaker

In this tutorial, I'll walk you through the steps of making a portable (Bluetooth) speaker from scratch. This sounds like a daunting project for a beginner, so my goal is to help anyone who wants to try this by explaining things as simply as possible without missing any important steps.

I think the most basic tools you need to make a speaker are a drill and jigsaw, along with a suitable blade, drill (I also recommend a step drill), and measuring tools. Yes, you can use some straight pieces of wood as side guides to make straight cuts with a jigsaw; obviously if you want to upgrade your equipment, a table saw and router will be your best friends (although I still don't own one). You'll also need a soldering iron and some tin to solder all the wires.

Other supplies you will need include: Copper wire (both red and black speaker wire will work, black and red will help easily distinguish between positive and negative), screws (wood or metal screws depending on the material), wood glue (for wood speakers), glue gun and silicone (for joining and sealing things), (optional) heat gun (in case you want to open and bend the pvc pipe used as a bass reflex port), a switch, a 2.1x5.5 (or preferred size) barrel jack (depends on charging system), some kind of protective feet (I use rubber ones), handles, some LEDs if needed.

Step 1: Budget Adjustment

You should start by determining how much money you want to invest in the project, since staying on budget requires some balancing (you can't spend 90% of your budget on speakers alone because you won't have the rest).

If you're on a really tight budget, my advice is to reuse stuff you already have: whole speaker boxes from old speakers or tiny hi-fi systems, recycled batteries (more on that in the battery section), leftover wood.

Step 2: Materials and Making Box

You can basically choose any material for your speaker box, but obviously not all will be enough for a variety of reasons.

My advice is to use plywood: choose a variety that has a good compromise between stiffness and weight, as both are equally important in portable design. You can prime, sand, and then spray paint to get the color you want, or simply use wood paint to maintain a wood look.

Another widely used material is MDF, which is a good compromise. It must be treated with sealant and not used as is as moisture will destroy it. As for thickness, I'd say the same as above: don't make it too thick because of the weight, don't make it too thin because the panel will vibrate. I tend to use plywood between 10 and 20 mm thick.

In case you find that the material you choose vibrates a little, you can always strengthen it by making internal braces.

General materials: metal (easy to work with, but will vibrate if thin, for ammo box speakers I recommend building a wooden box with an interior), particle board (wouldn't intentionally buy it, but if you can use it already), plastic (sort of Like metal, plus all commercial products are plastic, why not do something different ;))

I've attached some photos of painted plywood (made by my woodworking cousin), treated plywood, and a metal box for reference.

Build your box the way you like, making sure to secure everything with glue and nails or screws.

Step 3: Speaker Type

This is a trivial part: What kind of speakers should I use? What if I don't know much about speaker construction?

Let's start with the car audio speakers (coaxial, 2-way, not subwoofer). These are very attractive for people who don't want to spend too much time doing dividers, calculating box sizes, etc. The problem with this is that you can't predict how the speakers will sound at all, because most of the time there's no information about them other than sensitivity, power, and (mostly useless) frequency response maps. My advice: if you're on a budget and have some left over, use them. Don't try to make a ported box because most of the time it will sound terrible! Make a good sized closed box and they will play well. Just don't expect too much bass from them. For a rough estimate of how much volume you need, check out this website (it's in German,

For the best possible results, you should purchase high-fidelity (non-car audio) speaker drivers that have documented specifications (called Thiele-Small parameters), frequency response, and impedance charts. For those who don't know much about crossovers and box design, my advice would be to look for projects that have already been completed (either free or paid build plans), as the bulk of modeling and designing crossovers and box sizes/types has already been done And tested and proven to be good. Otherwise, an easy starting point are "full range" speakers, usually 3-4 inches in size: they cover most of the frequency spectrum, so no crossovers are needed (*), and some of them can when placed in adequate enclosures Achieve nice bass. You can design the enclosure based on driver Thiele-Small parameters by putting these parameters into a box modeling software like WinISD or VituixCAD2 (or SpeakerBoxLite online).

I can give you some advice on tutorial box modeling and crossover making from the YouTube channel Toid's DIY Audio, Impulse Audio, DIY Audio Experts. There are many websites to check out for projects that have already been done; one of them is Paul Carmody's website.

If you want to take your speakers with you, I recommend using speaker grilles, as this will protect the drivers from accidental contact with external objects, which could damage them.

If you plan to reuse a speaker you've already made, you can skip all of the above and just open the box and put the electronics inside. Usually this only requires unscrewing and removing the larger speaker from the box.

*Some kind of crossover is usually always needed to compensate for several diffraction related issues, but for beginner projects these can be set aside for now as they require some knowledge of crossover production.

Step 4: Sensitivity, Power, Impedance

We need to understand these things as they are critical to determining baselines/goals in speaker design.

Sensitivity, in decibels, represents how loudly a speaker plays, measured 1 meter away from the microphone, when given 1W of power (or 2.83V of voltage, this is not always 1W but depends on the speaker impedance; the formula is power =voltage^2/impedance). If your sensitivity is 90dB, this means that sending 1 watt of power to the speaker will produce a sound pressure level (SPL) of 90dB. Now, if you double the input power, the SPL increases by 3dB (93dB at 2 watts), doubles it again, then another 3 (96dB at 4 watts), again (99dB at 8 watts), and so on.

The general rule is: doubling the power increases the sound pressure level by 3dB (10 times the power increases the sound pressure level by 10dB); doubling the cone area also increases the SPL by 3dB; doubling the number of speakers combines the above two, so the SPL That's a 6dB increase (and twice the power consumption).

These calculations are useful for determining "target maximum sound pressure level" and determining how much power you really need, as more power means less battery life, or the need for larger, more expensive batteries. For example: if I want to achieve 106dBSPL from a pair of 90dB speakers, I only need 2x10 watts of power (90dB+10 will take the power from 1 to 10W; if there are two speakers, we use 2x10W to go from 100 to 106dB power consumption); if the speakers If their sensitivity is 87dB I need 2x20W, if they are 84dB I need 2x40W and so on.

What maximum sound pressure level do I need? It depends on what you will be using the speakers for. Outdoor party? Shoots 100-105dB in a compact design and more in larger speakers. Indoor listening? You probably don't need more than 90-95dB, so less sensitive speakers are fine.

Regarding impedance: This is a parameter to consider along with the amplifier as it will determine how much power the amplifier can output. I wouldn't go above 8 ohms as this would complicate the battery system (requiring higher voltage). Most speakers are between 4 and 8 ohms anyway.

Step 5: Amplifier

The amplifier is the heart and brains of a portable speaker, so it must be chosen based on all the remaining components.

Since this is a battery powered system, it is natural to choose Class D amplifiers as they are more efficient than other amplifiers, so the battery will run longer and generate less heat.

There are a lot of boards that already include Bluetooth, so for simple designs you can use them, otherwise you'll need a separate Bluetooth module with a voltage regulator (as they usually run on 5V).

Once you determine how much power you need, you can choose an amplifier that can provide it.

For portable designs, my top choice is the TPA3116/TPA3118, which can be found cheaply on Chinese amplifier boards with or without Bluetooth; it can deliver over 50 watts to 4 ohm speakers and over 30 watts to 8 ohm speakers power. However, the maximum power of these amplifiers depends on the input voltage (see the datasheet, go to the graph called "Output Power vs. Supply Voltage", which is your battery voltage or the voltage from (for example) a boost regulator. For example, At 14V the tpa3116 can output about 20W in 4ohm speakers (1%thd, so not much distortion, ignore the 10%thd curve), but only 10W in 8ohm speakers if you need more power. The amplifier delivers higher voltages (obviously within the range of that chip). So pick a chip and from these curves you can determine the voltage going into the amplifier and therefore how you will make the battery system.

Also about impedance: all these chips have a minimum impedance specified in the datasheet. For example, you cannot connect a 2 ohm speaker to a regular stereo tpa3116 (called BTL mode), but you can do this in a mono tpa3116 (called PBTL mode). For example, 2.1 amplifiers put sub-channels into PBTL mode so they support impedances as low as 2 ohms, while stereo channels are limited to 4 ohms. As another example, the tpa3110 can only operate up to 16V (due to power limitations) when using a 4 ohm speaker, which is another thing you can see from the power vs. voltage curve. So always check the datasheet first!

Other chips available in this category are TPA3110 (lower power, but very similar to the 3116, less background noise), TDA7492, TDA7492P, TDA7498/7498P (for higher power)

Some good boards I tested: this simple tpa3118 stereo bluetooth, this tpa3116 which also has a subwoofer channel, tone adjustment and high pass for the left and right channels (if you want to make a 2.1 system), these various boards based on the tpa3116

PS: If building an ammo box speaker, consider soldering an external antenna to the existing antenna, as the metal acts as a Faraday cage, thus reducing the Bluetooth range. I'm using one of the older 2.4GHz Wi-Fi modems and it works fine because Bluetooth is also 2.4GHz (RF guys please don't be mad at me).

Step 6: Batteries

The last thing you need to design is the battery system.

My choice would be to use lithium-ion batteries: compared to lead-acid batteries, they are lighter, do not need to be charged all the time (lead-acid batteries degrade when discharged), and compared to nickel, they require fewer cells to get a certain Voltage-MH, also has a higher energy density than Ni-CAD and has zero memory effect.

A quick disclaimer since we're working with lithium batteries: Never short-circuit lithium-ion batteries, immerse them in water, heat them, and generally abuse them: they really don't like to be abused and can explode.

The most common form of lithium-ion battery is the 18650 battery, which is used in e-cigarettes, laptop batteries, and other electronic products. They come with helpful datasheets indicating their current ratings (continuous and peak), which we will use to choose the most suitable battery.

A little note on series/parallel connections. In a series connection, you connect the positive terminal of one battery to the negative terminal of another battery; the voltage measured between the unconnected positive and negative terminals is twice the battery voltage. In a parallel connection, you connect the positive terminals together and the negative terminals together, and the voltage you measure is the same as a single cell. Battery packs can be represented by the "xSyP" code: x is the number of modules connected in series and y is the number of cells connected in parallel that make up each module. A 4s1p battery has 4 modules connected in series, each module consists of 1 battery cell (a total of 4 batteries). A 5s2p battery has 5 modules connected in series, and each module is composed of 2 cells connected in parallel (10 cells in total).

Once you've determined how much power your amplifier will output and how much voltage you need to give it, you have to determine how many cells you have to put in series to reach that voltage: Given your target voltage, you just divide it by 3.7 and you'll Obtain the approximate number of cells (or modules) in series required. For example, if I'm targeting around 14V, I need 4 cells in series. Note that the maximum voltage will be higher because the battery reaches 4.2V when fully charged, so make sure the amplifier can handle the higher voltage.

To determine the battery's current rating and to be on the safe side, determine the total power drawn by the amplifier when the batteries are fully charged (4.2V per cell: 16.8V for 4 cells in series) and divide it by the voltage. For the tpa3116, at 16.8V you convert 2x30W into 4 ohms, so 60W total. 60/16.8 provides 3.57A current. Now amplifiers are not 100% efficient, so you can get the efficiency from the datasheet, or estimate a conservative efficiency of 80-85% for Class D. Divide the current by the efficiency and you get the actual maximum current, which in our example is 4.5A. So in theory any battery with a discharge rate higher than 4.5A can work. In practice, oversizing is important because batteries always have a voltage drop that is high near their maximum current capability and can cause distortion. For a project with a stereo tpa3116 and 4s battery, I would choose a battery with a discharge current of more than 6-7A. For higher power projects, get higher current batteries, or make multi-cell modules and wire them in series.

You can now calculate how many watt hours a battery has: simply multiply the nominal voltage of an individual cell by its capacity (as opposed to its current capacity, expressed in mAh) times the total number of cells. If we have 4 batteries in series, each with a capacity of 3500mAh, we will have 3.7V*3.5Ah*4=51.8Wh.

How long will my battery last? Considering that you never use full power very often (see Music Crest Factor), you can assume that the average power consumption is 10%/15% of the amplifier's maximum power. So to get the run time you divide the watt hours of the battery by 15% of the total output power, so in our example considering a 51.8Wh battery and 50W total output power we should get about 51.8/(60*0.15 ) = 5 hours and 45 minutes (5.75) at full volume. You can use these calculations to roughly determine how many Ah your battery will need.

When assembling a battery pack, be sure to always use the same type of batteries and never mismatch them!

Always buy batteries from reliable sellers as fake batteries do not match their claims and can be dangerous.

If you want to reuse old laptop/drill batteries, try to get information about them (they usually have the model number printed on the battery) and use the liitokalalii-500 or opusbt-c3100 (single battery charger and tester). Try to match them well and don't use batteries with large capacity differences, especially when connected in parallel (avoid doing this with old mismatched batteries)

How do I put the batteries together and connect them? I like to use battery boxes with spring terminals, otherwise you either have to solder the cells (not recommended) or spot weld them.

After selecting the number of batteries you need, you will need a protection circuit called BMS: This avoids overcharging, over-discharging, and short circuits; personally I always buy a balanced charging BMS circuit because it keeps the battery always charged Keep the voltages the same (they are "balanced"), like this one. "xS" indicates how many series "modules" you have: if you have four cells in series, your battery pack is a 4S1P battery pack, so you need a 4SBMS. If you have 5 cells in series, then it's a 5S and you need a 5SBMS. Always check that the BMS has the correct voltage, overvoltage protection (usually 4.3V per battery, not much). Get a BMS that can support the maximum current you determined earlier.

Finally, you need a suitable charger. Look for a charger (not a power adapter) that can do "cc-cv", is designed for lithium ion batteries, and fits your bag (if you have a 5s bag, buy a 5s charger, etc.). Choose your battery's maximum charging current based on its maximum charging current: lower or equal is good, higher is not recommended. I personally use it with a 4s1p battery; there are also some chargers with type C connectors.

Step 7: Wiring

Now everything is ready for you to connect the electrical system. I've attached a scheme for the complete system, with an on/off switch and a barrel jack for connecting an external charger (I usually use a 2.1x5.5 barrel jack; the inner tip is positive, the outer ring is negative; make sure to check polarity with a multimeter as some chargers may be reversed). I've also attached a scheme for the 4s battery connected to the BMS. You can get creative and add what you want.

Step 8: Assemble Everything

When building the electrical system, put everything inside your speakers. If your speakers share the same space as your electrical system, seal any possible air leaks with silicone or hot glue, as this is important to avoid noise and performance loss in sealed or ported systems.

Step 9: Done

If you passed all my instructions and made your own portable speaker, congratulations, you did it!

Now your favorite music will follow you wherever you go, and you can proudly answer "I did that" to people because you have a unique speaker.