Introduction: Isobaric Loaded Jar Speaker
Hi everyone, this was something I've wanted to try for a while...
I wanted to see what the results would be to make a isobaric loaded full range speaker on a small scale.
The mason jar worked perfectly for the enclosure as it is the size I had in mind and fit my driver choice just about perfectly.
The results well... take a little journey with me
Step 1: Let's Get Going
A common problem with small bluetooth speakers is the noticeable lack of bass output due to the small size of the speaker drivers. There are a few ways to improve this like using a ported enclosure or adding passive radiators, these methods work but I wanted to try something else...
"The Isobaric loudspeaker configuration was first introduced by Harry F. Olson in the early 1950s, and refers to systems in which two or more identical woofers (bass drivers) operate simultaneously, with a common body of enclosed air adjoining one side of each diaphragm. In practical applications, they are most often used to improve low-end frequency response without increasing cabinet size, though at the expense of cost and weight.
The name is derived from the term Isobar ("equal pressure"), which comes from the Greek word "isobares", meaning "of equal weight". As the word implies, the enclosed air does indeed experience roughly equal pressures from each diaphragm it contacts, but those forces are actually parallel, rather than opposing, so the air is forced to move."
Step 2: Get Printing
The majority of parts needed for this build was 3D printed but it would be possible to make this without a printer using either wood or plastic sheets.
The parts of this build was created in Tinkercad and is available for download on Thingiverse: Mason Jar Speaker
The parts were printed with a 0.6mm nozzle in ABS as there are no intricate details that are difficult to print.
The entire project is about a 5 hour print using conservative speeds.
You might need to modify the two parts that holds the speaker drivers if you are using different drivers.
Step 3: The Jar
The only thing that will need to be done to the jar to use it in this build is to make a small hole in the back that your USB cable will go through to power the speaker.
To do this I used a Dremel with a diamond abrasive ball point bit to slowly grind away at the glass until a hole large enough is formed.
The most important tips for drilling glass is to keep it cooled with a constant stream of water while drilling and to take it slow, I apply almost no pressure..just let the bit do it's thing.
Always wear eye protection when drilling glass as it can shatter if something goes wrong.
At this point I also took the time to cut off the 4 "ears" on the speaker driver otherwise they don't fit in the jar.
Step 4: Electronics
To get the beats pumping we need a amplifier. For this build I used a M38 board, this is a fantastic single board solution for all your portable audio needs. It has bluetooth v5.0, two 5W amplifiers and a built in DAC all powered by a 5V USB or even a 3.7v lithium battery if you want to make it completely portable.
Connecting everything is very simple, you only need to solder the positive and ground wires from your USB to the positions marked on the board +5V and GND. I also added a capacitor on the board to the supply but this is not needed.
Do not solder on the USB plug now as you will need to feed the cable through the hole in the jar first.
Next you need to solder your speaker wires onto the board, I used some ribbon cable that I had lying around to make the exposed cabling a little neater.
After all the wires are soldered you can slide it into the printed box, feed the wires through and seal it up. Pay careful attention to the polarity of your speakers as this is very important for the isobaric loading to work correctly.
That's it we can now start assembly...
Step 5: Assembly
To assemble the speaker I'll be using 2 part CA glue (glue + accelerator).
First we want to glue the amplifier box into the back portion of the jar, feed the power cable through the hole in the bottom of the jar and solder on your USB plug.
The wires going to the speaker drivers need to be cut just long enough that you can still solder on the drivers outside of the jar.
Next we need to add a bead of glue around the round 3D printed mounts for the speaker to ensure the drivers seal against the mount with no air leakage. Solder the wires to the rear mounted driver first and then push it into the jar as pictured.
You want to make sure there will be enough space for the cone to move without hitting the magnet of the driver that will be in front of it.
Glue it in place making sure to it's sealed all around.
Now we can solder the wires to the front speaker making sure the speaker polarity is correct and then glue it in place.
Screw on the jars ring and you're almost done!
I decided to print a handle for the jar as it angles the speaker towards the listener and makes it easier to carry.
The handle simply slides onto the jar, no gluing required...
Step 6: Time to Fire It Up!
Plug your new creation in, sit back and enjoy...
I was pleasantly surprised by the added bass output, I previously had these drivers in a 6L sealed enclosure and I have to say the bass is better now than in the large cabinets.
The only thing I would change in the future is to incorporate a tweeter in the design just to pick up the higher frequencies, other than that i'm very happy with how these turned out.
I hope you guys will share some of your creations here as I'd love to see how the turn out.
First Prize in the
Mason Jar Speed Challenge