Bluetooth Speaker - Quarter Wave Transmission Line

thingiverse

After seeing a post on the CR10 Facebook group by Jason Bach, I decided to design my own 'quarter wave transmission line' Bluetooth Speaker - inspired by his work. This thing is incredibly loud for it's size and the audio appears to be very nicely balanced considering this is made of plastic. It doesnt rattle or vibrate in any unwanted ways. See video: https://youtu.be/yui068SL0e0 I had originally planned to sand and finish this, but the print came out so good, I just left it as it is. This project requires 2x 3" speakers and a Bluetooth dual channel 50w Amp - Total cost about £30. All of the parts mentioned in this project can be bought from ebay. Full Bill of Materials below. Firstly, I am not an audiophile. Nor do I know a huge amount about speakers and sound systems. I used some basic math to work out the required dimensions for the enclosure and the transmission line. The math revealed I needed a transmission line (or port/resonator) length of approx 777mm and its dimensions needed to be approx 90mmx33mm. It's important to use the same speaker drivers as me (listed below), as the enclosure was designed specifically for their respective 'free air resonant frequency' and 'effective cone area'. You can find out more about 'Quarter Wave Transmission Line' speakers and the math involved in a video link I posted in the comments section of this thing. It's similar to the wave technology Bose use. From watching the video, you could design your own enclosure for your own specific speakers. Be advised - This is a large print! It takes approx 90 hours to print in total, and requires a build area of around 300x300x200 - so the CR10 is perfect for this project. The side cover attaches with 6mm x 3mm magnets. 32 pairs of them. I glued them into position, triple checking the polarity of them each time. The side cover also has two little 'locator notches' to ensure it snaps on in the correct position easily. I am thinking about adding a self adhesive sheet of felt to the side cover, as it 'snaps' on quite violently with the pull of the magnets. I added some self adhesive foam sheet inside the transmission line because something about absorbing unwanted resonant frequencies. I also added polyester pillow filling (polyfil) to the majority of the transmission line, which improved the bass sound so much. I might even experiment by adding more. There are 4 recesses on the base of the speaker to allow you to fit 4x 1" self adhesive furniture felt feet so the speaker doesn't vibrate when placed on hard surfaces.. There are 2 holes on the back to allow fitment of a 20mm round on/off toggle switch and wireable 2.1 DC jack input. There is an additional version with no holes on the back too, if you want to incorporate your own ideas. You could easily run this off of some batteries for full portability. I might even add batteries to this myself. Pro's & Cons of this project: Pros: - Awesome looking little speaker and project. - Surprising loud for its small size. Like really loud in the mids and highs. - Relatively Cheap to make (~£30 + filament). Cons: - There is a slight background hiss coming from the cheap bluetooth amp, noticeable at lower volume parts of audio tracks. Apparently this is normal for these to do this. - The bluetooth amp makes this horrible sounding chime when powered up. - Lacks bass in my opinion, but I do like listening to music with a bass heavy sound and with a sub normally. - The 20mm Switch I had in my 'bits box' appears to be a reversed switch, so it illuminates when up not pressed down (on). - Gluing the magnets into place was way more fiddly and messy than I had anticipated!! Bill of Materials: Approx 1.5kg Filament - 1 x Bluetooth 4.0 50W+50W Amplifier Board Audio Receiver TDA7492P - 2 x Faital Pro 3FE25 3" Speaker Driver 20W (40W max) 8 Ohm - Some 0.75mm copper cable - 12vdc AC adapter with a 2.1 plug (I had a spare 5A one lying around - I think 2A should work fine too, but not tested yet). - 64x 6mm round x 3mm deep neodymium magnets. - 8x M4x20mm screws - Super Glue or resin Optional parts: - 20mm round toggle/rocker switch - 1 x male rewireable 2.1 plug - 1 x female rewireable 2.1 socket - 4 x 1" round felt feet - A4 Sheets of self adhesive foam - A4 Sheets of self adhesive felt - 12v LED strip lights to make the port illuminated - Polyester Pillow stuffing (polyfil). I would love to see someone print this in a wood filament!!