DIY boombox plans – 2 x 100 watt – 12 hours playtime
How to make your own boombox
In this article you will find the DIY boombox plans for a portable speaker that is designed to play loud and last a long time on battery power. The keyword here that you want to look after is portable, and how do you define it. This speaker will have a respectable weight. It’s not meant to be carried all day. Instead, this boombox is more useful at a barbecue, at a pool, or at some party on the go, where you stay in one place for a long time. It definitely goes loud enough for a small party, especially indoors.
The components and parts list
You will find in a previous article all the components for the amplification side.
This schematic will be in the mentioned post, but for completeness sake, I’ll re-post it here. Besides all these electrical components, you will also need some speakers. The boombox contains two 4″ woofers and two 1″ tweeters :
- Peerless HDS-P830992 – 4″ mid-bass
- If you are having trouble finding this driver, you could try and use Peerless 830870. I haven’t tried it in this setup, but if you look at the spec sheet they are nearly identical
- Peerless XT25SC90-04 – 1″ tweeter
These are great drivers. The only issue I have with these mid-bass drivers is that they don’t use neodymium magnets. This will increase the weight of the whole boombox. I tried some Dayton Audio speakers with neodymium magnets, but they are miles away from the Peerless performance.
DIY boombox plans
To make this portable bluetooth speaker, I used 10 mm MDF (3/8″ MDF). The enclosure is bass reflex and for speaker protection a metal grille is in the equation as well. Here is the list for all the panels (dimensions in mm) :
- Front and Back – 395 x 110 – 2 pieces
- Top and Bottom – 415 x 215 – 2 pieces
- Sides – 215 x 110 – 2 pieces
- Port – 350 x 110 – 1 piece
To get an idea on how the panels fit together. Here are some schematics :
Here is how the box should look like with all the components in place.
These are all the components of the boombox. In this diagram you don’t see the crossover parts. We will get to that soon enough.
These are the dimensions of the front baffle. Just some standard circle cutouts into the board.
This is the most complicated panel. I used a jig saw and free hand cut the rectangle for the battery indicator. The button holes are simply drilled. The tricky part is that the rectangle which servers as a frame for the buttons, needs to be recessed from the inside. Use a router to make a recess of 5 mm on the marked area. This is because some buttons are not long enough, and you can’t tighten the nut from the inside.
The next thing that might pose some questions, is where to place the port. The answer is in the above illustration. The port is 40 mm wide and 110 mm tall. You can also see that the front panel (baffle) is placed 20 mm to the back. This is to make room for the metal grille.
DIY portable boombox build
Now that you have the DIY boombox plans, I will show you how I did it with a series of images. Comments inside the pictures.
Now all that is left to do is to connect the speakers, put them inside and put the grille in place. However, we haven’t talked about the crossover section.
Since this a 2-way design we need a 2-way crossover. As a result, we have to include this into our DIY boombox plans. Here is the circuit diagram:
If we analyze the circuit, we can see that we are dealing with a simple 2 way crossover. The resistor R2 is just an L-pad without the series resistor and it’s meant to reduce the output of the tweeter.
Let’s talk about the capacitor C3. The purpose of that capacitor is to filter the very low frequencies. Even though the speakers are full range you don’t really want the very low notes to play through a 4″ speaker. However, if you plan to play this boombox at moderate volume levels, you can ditch this capacitor and have more bass response. Here you can play with this aspect depending on your needs. A higher value capacitor will filter less bass but also provide less protection. Do whatever you feel like. The 220 uF cap feels like good compromise.
How to design loudspeakers - video courses
Since all the capacitors and inductors have small values we are going to use air core inductors and film/foil caps. Except for the 220 uF one. That will be an electrolytic. Here is the parts list :
- 2.7 uF capacitor
- 8.2 uF capacitor
- 220 uF capacitor
- 0.1 mH inductor
- 0.27 mH inductor
- 10 Ohm 10W resistor
The available space for crossover components is kinda cramped. As a result, make sure to use higher wire gauge (smaller diameter wire) for the inductors. This is acceptable because they have few windings, so resistance is no issue. Furthermore, we don’t need them to handle a lot of power.
Quick recap : Small value capacitors – film and foil, 220 uF cap – electrolytic, all inductors air core with 18-20 AWG wire (0.8-1 mm).
First, let’s look at the boombox with speakers and grille in place.
Now let’s look at the frequency response. The frequency response measurement was taken in a test box with nothing inside it (more volume). Therefore, I excluded the bass response which is not representative. I can’t measure it now that it’s finished, because I have no means to connect via bluetooth to my computer. So we are going to analyze only the 400 Hz – 20 kHz response.
You can see that the response is dipping towards the end of the spectrum. I’ll explain why in a bit. Since the baffle is a bit inside the box, you have 2 cm of perpendicular edges around the baffle. This creates some diffraction issues. The fact that the tweeters are not that far apart doesn’t help either. When you measure the tweeters (without the crossover) you will see significant dips (cancellations) at 3.7 kHz and at 18 kHz. The dip at 3.7 kHz is solved in the crossover by allowing the mid-bass to play in the higher octaves. The 18 kHz cannot be solved and it shows in the frequency response chart. It’s not the end of the world as most people cannot even hear those frequencies anyway.
I’m quite pleased with this portable bluetooth speaker. Probably one of the loudest battery powered boomboxes out there. Definitely in the big boys league. Here are some specs :
- Amp rated at 2 x 100 watts. In this setup it will deliver 30-40 W per channel of clear, undistorted signal (that’s what matters).
- Impedance of 6 Ohm.
- Crossover point at 6.5 kHz.
- Bass reflex design.
- SPL measured at 1 meter, volume at 93%, boombox placed on a table : Consistent 104 dBs. Peaks of 107 dBs.
- Weight of 6.2 Kg (13.6 lbs).
- Battery life of 12 hours at 80% volume.
The project is easy to follow, but the difficulty is to cram all the parts inside and connect them together and then finish the box into something that looks at least decent. Here you can do it however you like. Veneering is what I am comfortable with. But you can paint it. wrap it etc. You have the DIY boombox plans. Start building! Good luck!