Introduction: PUMBAA - Portable Bluetooth Speaker
I wanted a small and classy bluetooth speaker that wasn't made out of plastic so I decided to make my own! I named it Pumbaa after one of the most lovable "Lion King" characters...but also because this speaker can sing!
The enclosure is made out of 1/2" MDF, 3/4" pine, walnut, and wrapped in FR701 fabric, which is an acoustically transparent fabric. Packed inside are (2) 3" full range speakers in two equal volume ported chambers. The speaker is driven by a 2x30W bluetooth amplifier which is powered via li-ion battery pack or an 18V DC power supply.
The total cost of this build was around $100 USD but I had some of the building materials around. That cost may vary on your location and if you have to buy fabric & MDF in bulk. A full list of materials and tools which I used is below.
- Speaker & electronics kit: Parts Express
- (2) 1"dia. x 4"L flared port: Parts Express
- FR701: Acoustical Solutions (Sold by the yard but can be substituted for any fabric you like!)
- 3"W x 16"L walnut board
- 3"W x 36"L pine board
- 1/2" thick MDF
- Wood Glue
- Silicone Sealant
- Wood Stain
- Furniture Wax
- Rubberized feet
- Wood screws
- Circular or table saw (table saw works best)
- Miter saw (or table saw miter jig)
- Router (ideally mounted on a table)
- 3/4" Roundover router bit
- Rabbet router bit (various sizes)
- Flush trim router bit
- Pocket hole jig
- Drill or drill press + drill bits
- Staple gun
Step 1: Selecting a Speaker and Enclosure Size
Picking the right speaker for an application can be overwhelming. There are hundreds of options which can make it difficult to find what you are looking for. Here are some basic tips to help you decide.
Price range: there are lots of options in the $10-20 range which I think are perfect for portable/bluetooth audio. Since you will be limited in terms of output by the amplifier (typically 10-50W per channel), there's no reason to spend upwards of $100 on a driver which can handle high power.
Speaker Sensitivity: this parameter is very important when designing portable speakers since it's a measure of how loud the speaker can get with 1 watt of power @ 1 meter. Since the speaker is battery powered, you want to use as little power as possible. As a good rule of thumb, drivers with a sensitivity of 87 dB @ 2.83V/1m and higher are considered efficient drivers. At this rating, the speaker would produce over 100 dB with only 20W...which is quite loud!
Frequency response: the main reason why I chose the Dayton speaker above is due to it's low price, high sensitivity, and extended frequency response. This driver has a frequency response of 80 - 20,000 Hz, which means it is a true full range speaker. I wanted to avoid the complexity and cost of adding a tweeter and crossover network so this speaker fit the bill.
There are many other parameters that need to be considered when selecting speakers and designing the enclosure. The tips above are just that...tips. If you'd like to learn more about Thiele/Small Parameters and how you can use them to help achieve better results, here are some useful links:
In order to make use of these parameters, simulation software is usually required. For Windows users, WinISD is a good option. For Mac users, the options are limited...
For reference, I have included the simulation I generated which helped me decide on enclosure & port size. My priority was to extend the low frequency response without sacrificing SPL so I chose to tune the box to 85Hz, close to the speaker's resonant frequency (Fs). This configuration creates a +3dB peak at ~130Hz which gives this speaker a nice and punchy low end (read: not deep bass). It is possible to tune to a lower frequency but with this driver, it will result in diminished sound pressure levels.
Step 2: Building the Enclosure
I began by cutting two 7.5"x14" pieces out of a 2'x4' sheet of 1/2" thick MDF. This can be done via circular saw with guide or table saw. A table saw will provide much cleaner and more precise cuts. I used a circular saw and some hardwood as a guide...so if you don't have access to a table saw, don't fret!
I used a 3" fofstner drill bit to create the speaker openings. I then used a 1/2" rabbeting bit and a router table to create a rabbet around the perimeter of the opening. I set the depth of the rabbet to equal the linear excursion of the speaker + the depth of the speaker flange + a couple of millimeters as a safety factor. This allows for the speakers to mount flush and never extend past the front face -- critical for hiding the speaker behind fabric.
I then cut the pine board into two 7.5" long pieces and one 16" long piece. I then bore a hole in each of the side pieces in order to mount the 4" ports. I used a drill press and forstner bit for these as well. I also created a shallow 1/2" rabbet on both the front and rear edges of the pine boards. This will not only help me line everything up when gluing but also increase gluing surface area, which in turn yields a stronger bond!
Step 3: Building the Enclosure - Part 2
In order to have true stereo reproduction, I chose to separate each speaker in each own enclosure. Not sure if this will have a significant effect for such small drivers but it was easy enough to do so I did! To do this, I created a 1/4" channel down the middle of the inside front and rear MDF baffle. I then slipped in a 1/4" thick piece of MDF down the middle.
I also created a 1/2" wide channel on the rear which I will use to mount the LEDs, switch, and DC jack. Additionally, I created pocket-holes using a jig on each side piece that I will use to fasten the top piece. Once everything lined up, I glued all joints, and clamped it overnight.
Once the glue was dry, I used a 3/4" roundover bit to round the edges. This will create a sleek and seamless look when wrapping the fabric.
Step 4: Building the Enclosure - Step 3
The only two pieces remaining on the enclosure are the top and the bottom! I created a rabbet around the perimeter of each so that I could easily mount them. I then clamped the two pieces together and used a scrap piece of MDF as a slide for my router table. I am using the roundover bit again but this time the boards are in the vertical position, making it an awkward and unstable working position. Although my simple slide is by no means safe, it's certainly an upgrade to attempting to run the pieces unsupported against the router table fence.
I then sanded everything with 220 grit sandpaper and wiped off all excess dust. I applied 2 thick coats of shellac to the exterior of main body. MDF does not do well with moisture and shellac will help seal the exterior and provide some protection. Since everything will be hidden, I was pretty sloppy with my application...in this case, thicker coats are better!
The bottom pine piece, I spray painted white. The top piece, which is a nice looking (to me) piece of walnut, I chose to finish with Howard's Restor-A-Finish and some Feed-n-wax. I like the natural look and feel of walnut so I chose not to apply a super protective finish.
Step 5: Testing and Mounting Electronics
The electronics kit I used, comes with everything you will need, including instructions. It's a pretty straightforward process and everything just plugs in. Some soldering is required at the speaker leads. The kit comes with a protection circuit for the batteries which avoids the inherent dangers of working with li-ion batteries -- making this a great kit for those who are electrically inept (me)!
Another nice feature of this kit is that it includes an aluminum L-bracket and PCB stand-offs which can be used to mount the boards in a stacked arrangement in just about any enclosure! I drilled some counter sunk holes in the speaker enclosure to mount the bracket inside the box. I also drilled the LED and DC jack holes in a small strip of walnut which I will use to fill in the channel that I previously created in the rear baffle.
We now have a fully working speaker...all that is left are the finishing touches!
Step 6: Finishing Touches
With everything mounted in place, I measured and cut the fabric. I stretched the fabric around the speaker and stapled it in place. This was honestly one of the most difficult tasks since I have never worked with fabric before and it was quite difficult to keep the fabric stretched and aligned while trying to staple it. If anyone has tips on this feel free to post in the comments section!!
After stapling the fabric, I mounted the LED strip in the rear. I used caulking to seal the top piece and then used pocket hole screws to fasten it to the enclosure. I pre-drilled 4 holes to the bottom piece and used wood screws to fasten it to the enclosure. I covered the screws with some rubberized feet.
That's it! When the DC jack is unplugged, the speaker is powered via the batteries. When the DC power supply is plugged in, the batteries are charged and playback is unaffected!
Hope you enjoyed this Instructable and stay tuned for my next build which will be a boomier, higher-end, version of this speaker + a digital sound processor (DSP) board!