Kissing the Frog V2.0 - Back Horn Bluetooth Speaker Fully Printable
Introduction: Kissing the Frog V2.0 - Back Horn Bluetooth Speaker Fully Printable
Introduction
Let me start with a little background. So what is a back loaded horn speaker? Think of it as a reversed megaphone or gramophone. A megaphone (basically a front horn loudspeaker) uses an acoustic horn to increase the overall efficiency of the driving element (i.e. the sound coming out at the front). A back loaded horn speaker does pretty much the same thing. However, here the horn is mounted to the back of the speaker. So you get the direct output from the front of the driver PLUS the one from the horn at the back. Which frequencies are amplified and how well depends on the air chamber, throat (the narrow part), and on the length, design, and diameter of the horn. Particularly with small (and cheap) drivers this can very much improve the sound quality.
I would call this concept "Kissing the frog". You take that little tweeter and hope it turns into a prince. And yes, it actually does. It is amazing how much sound you can get out of a $10 3.3" driver.
You will find loads of books, papers, and online references for how to design an optimal horn speaker. The problem is that your calculated optimal horn will likely end up taking up most of your living room. However, I found these tools incredibly helpful to better understand the dynamics (i.e. what happens when I change the diameter, length, design of the horn?). Ultimately, the design of a (back) horn speaker (definitely a 3D printed one) will largely be guided by the available space while trying to get as much sound out of a relatively small enclosure / driver.
For this design you will need to have access to a 3D printer. I am using a $ 200 Creality Ender 3 3D printer, which can do prints up to 220x220x250 mm (and does a great job at that). The body is designed to fit a standard 200x200 mm build plate, so most (even budget) printers should be capable of printing this. 729
If you want to use it as a Bluetooth speaker you will need basic electronic and soldering skills. Make sure that you know what you are doing (particularly dealing with high voltage! So take care, all at your own risk and no warranty whatsoever). However, remember, you can always use the enclosure as a passive speaker, which omits all the soldering.
Step 1: Electronic Supplies
Basically this is a super cheap project. All electronic supplies you need for the Bluetooth version should cost around $20.
- First of all you will need an MP3 Bluetooth Decoder Board (approx. $ 1) (the same on Amazon). You could in theory use an amplifier with integrated BT board. The problem is that this way you will inevitably end up with a stereo speaker signal - good if you want to connect 2 speakers (the 2nd speaker being connected to the first by wire), bad if you want a single (mono) speaker as you cannot pool output signals from both amplifier channels. The separate BT board allows for pooling the line out signal before feeding it into the amplifier.
- The amplifier is a TPA3116 D2 Dual Channel 50Wx2 Amplifier Module (approx. $ 3.5) (the same on Amazon)- this one is stereo (which seems like a waste, however, stereo amplifiers are nowadays easier to find than mono and considering the cost of 3.5 $... and may come handy in case you want to connect 2 speakers). For mono you will need to bridge L and R channels coming from the BT board (see the wiring section).
- Pretty much any 12V/1A+ (the more the better) power supply (approx. $ 1.7) (the same once again on Amazon) will do. E.g. an old 12V laptop power adapter would be great. I use a small 10x15 mm rocker switch as power switch (which is optional as the amplifier has a switch built into the volume control - which, however only switches the amplifier).
- A small LM1117 Step Down converter (approx. $ 0.2) (the same on Amazon). This will convert the 12V from the power adapter to 5V needed for the BT board.
- The driver I use is a Visaton FRS 8 M - 8 Ohm 8 cm (3.3") full-range speaker (around $ 10). The exact same driver may be difficult to find in the US but here a few options on Amazon.
However, basically any combination will do (as long as the driver is 3.3" or smaller so it fits the enclosure - if you use a different driver you may have to slightly adapt the mounting holes). 485