Introduction: "Hydra" a MONSTER Bluetooth Speaker!

About: An engineer who likes to tinker with electronics and make stuff!

Wow - this is one monstrous sounding and great looking speaker - even if I do say so myself!

This is basically a 2.1 (stereo + sub woofer) system made with 3D plastic parts. Both the full range and sub woofer speakers are based on closed (sealed) cabinet design principles. There are 6 full range speakers (2/channel) and the sub woofer also employs a passive radiator to enhance its low frequency response.

If you are wondering why I named this speaker 'Hydra" it's after the Greek mythological creature which was a many headed serpent. Alternatively if you remember your biology then perhaps its the simple freshwater animal belonging to the phylum Cnidaria (ok, I looked up that last part on Wikipedia)!

Hopefully I've given you a good set of instructions to make your own - let me know if you need some more details....other than that ....Enjoy!

Step 1: Tools and Skills

Unfortunately this build does require you to have one special tool, namely a 3D printer. I took the plunge a few months ago and purchased a Lulzbot Mini since then I've made a few projects and have had heaps off fun getting to grips with this technology.

I have to say its been pretty painless and most, if not all of the mistakes have been of my own making so I think I can recommend this as a good option for 3d printer noobs such as myself. NB: This instructable is not sponsored by Lulzbot and this is not an advert just an honest opinion of my 1st hand experience.

Other than that the tools and skills are:

1) Drilling

2) Cutting

3) Gluing

4) Painting

5) Soldering (very small amount)

Overall I'd rate the project as requiring moderate skills.

Step 2: Parts Required

Apart from the 3D printed parts - (which is the major effort required in this project - detailed in the next step), there are a number of purchased parts you will require and the links to where I purchased them from.

1) Bluetooth amplifier - I have used this amplifier before as it has a great sounding (for the price). Its based upon the super efficient and popular TPA3116D2 chip. - data file for the TPA3116D2 attached.

If you want more information on why I used this particular board then see my other instructable for the reasons behind this choice (see step 2 of the following link).

...alternatively here is a direct link to the one I purchased

2) Sub woofer - Tang band 3" Sub W3-1876S - specification file attached

3) Passive Radiator - Peerless 830878 3 1/2"


4) Full Range Driver - 14Ohm full range speakers - possibly used in Panasonic branded speakers?

5) Gooseneck (flexible) conduit (200mm Black)

6 "M2" self tapping screws (for full range drivers)

7) 24V DC Power Supply - I purchased a Meanwell power supply (GST60A24-PJ1) from a local source in Australia (1st link). But if you want to take a chance I've also used this Chinese supplied one (2nd link)

8) 100mm DWV PVC pipe. Being in a metric country (Australia) I have used DN100 pipe which has an OD of 110mm and an ID of 104mm - typically used in drain waste and vent uses around the home (hence DWV). If you are in the good 'ol USA then you'll need the nearest inch equivalent which is 4" sched 40. As the ID of the inch size is larger (by about 4mm/0.157") then the 3D printed parts need adjusting.... no fear I've done this for you in the next step!

Link to the metric pipe that I bought:

Step 3: 3D Printed Parts

There are 6 different 3D printed parts to make.

NB: note there are inch AND mm versions of 2 parts. The mm version is suitable for DMV DN100 metric pipe and the inch version is for 4" (4.5" OD x 0.237" wall thickness (sched 40). The inch version has a thicker wall than the metric and will be good for this design. There are very thin 4" tubes available in the US but at 0.075" wall thickness its probably too flexible for a speaker housing.

1) 1 off Passive Radiator Mount -this has 4 legs attached to it and attaches to the base of the pipe body.

(Either print the mm or inch version depending on your needs).

2) 4 off Hydra Legs - these 4 legs assemble to part 1 above

3) 6 off Goosneck supports - these allow the full range speakers to mount to the pipe body

4) 1 off Sub-woofer Mount - this is facing upwards at the top of the pipe body and holds the sub-woofer in position.

(Either print the mm or inch version depending on your needs).

5) 6 off Full range speaker housing back.

6) 6 off Full range speaker housing front.

Due to the duplication of the 6 'heads' of the hydra all this printing takes quite a few days!

NB: Note the special requirements for part 3 in the next step!

Step 4: Print Out the Goosneck Supports (with Nut Insert)

Here you can see I'm printing out 3 of the 6 gooseneck supports required for the full range drivers. I got the 3D printer to pause at a z height of 7mm at which point I pressed the hexagon nuts into place. The 3D printer then resumed it's print run and the nuts are fully encapsulated within the PLA part.

Step 5: Preassemble the Base and Legs

The base (mount for the passive radiator speaker) and the 4 legs can be assembled 1st. You may want to prepare your model for painting (sanding) before you assemble the legs but I managed to do it after. I definitely think its better to paint after pre-assembly then the joints will look good! I did not take any pictures of this but here is a 3D render of what you are creating!

Each leg has 2 prongs/studs which mount into holes in the base. I recommend gluing with Loctite gel and also using a self tapping screw in the lower peg for mechanical strength. The screws are hidden from view underneath the base.

Step 6: Prepare the Body of the Hydra

The body of the hydra is made from PVC pipe purchased from the local hardware outlet. I used a metric version which is commonly available for home use (drains etc), however you may use the inch version, you just need to use the appropriate inch version 3D parts noted in step 3.

1) The pipe can 1st be cut to length (210mm or 8.25"). It can be a bit longer if you wish but no shorter as we have a lot to fit inside!

2) Drill the 4 holes are to correspond to the 4 potentiometers on the amplifier. I used a 13mm (1/2") spade bit. The spade bit results in a flat(ish) countersunk hole which is needed for the potentiometer nut to fasten against.

3) Drill 6off 10mm holes equally around he circumference of the pipe body (30mm down from what will be the top of the speaker body). I used a centre finder to help with this task but accuracy is not paramount here. I also drilled a smaller 3mm hole 10mm above the 10mm hole to take the self tapping screw. I offset the holes so the potentiometer knobs sit in-between.

4) Drill 2 holes for the stereo jack and the 24V DC jack. I used a 13mm
(1/2") spade bit which puts a nice flat on the curved outer surface of the pipe to ensure a good airtight seal.

Step 7: Fit the Amplifier

Wire up a generous length of speaker wire to the 3 pairs of outputs and also a length of wire for the 24V DC before installing the amplifier to the pipe body. These will be trimmed to a suitable length at a later stage. To get the amplifier into the tube the body has to be squeezed (to an oval). I did this in a vice although with a friend holding the pipe you should be able to do it manually. Once the pipe is squeezed to a slight oval the amplifier can be slid into place and the 4 potentiometers can now be placed through the prepared holes and fixed in position. As with all joints on this speaker body, please use a smear of silicone to ensure an airtight seal.

Step 8: Fit the 6 Goosneck Supports

To ensure the mount stays in position there are 3 methods employed to spread the load.

1) There is a raised web which fits into the drilled hole to locate the 3d printed part.

2) I used Loctite gel to glue the parts together and there is a good surface area between the pipe body and the part.

3) A small self tapping screw is the belt and braces to ensure this does not come adrift!

Step 9: Prep, Undercoat and Top Coat

The finish is up to you but I spent quite a lot of time preparing the surface of the PLA before spray painting. I started by rubbing down with 60 grit wet and dry then worked up through 80, 120 and then 180 grit. The surfaces where then undercoated with a filler primer. I got my filler primer from an automotive shop - its great for filling in any dings or ridges left after the sanding down. In hindsight, I could probably have done less sanding.....Note for future!

Here are links to 2 brands - I couldn't get the Rustoleum here in Australia but the Septone version from Supercheap auto was perfect.

The top coats were then applied (2-3 coats) I chose gloss black and a gloss green for a contrast.

Step 10: Assemble the Gooseneck to the Driver Housing

Firstly the nut supplied with the gooseneck has to placed in position inside the driver housing. This is easily achieved by pushing it into place using the gooseneck itself - in reverse if you see what I mean! Once in position its a simple matter of attaching the gooseneck, this time from the outside.

Step 11: Assemble the Full Range Drivers

For the best performance its essential you follow these steps paying particular attention to the sealing of the enclosure

1) Pass a generous length of speaker wire through the gooseneck and seal where it enters the back of the speaker housing with silicone sealant. Leave to cure.

2) Terminate the wire to the driver (solder or crimps). Make a note of the wire polarity for later (mark either/both the +ve and -ve lead).

3) Place a small amount of polyester wadding into the back of the housing (to damp reverberations).

4) The driver can then be screwed in place using 4 self tapping screws but as you do this smear some silicone sealant around the driver to ensure that the driver is fully sealed, To fully ensure I had a good seal, after the driver is screwed in place I used some more silicone to seal up any possible leakage paths. Leave to cure..

5) Assemble the front to the driver using 8 of the very small self tapping screws. Essentially the speaker front is cosmetic and won't provide a seal - so its important the sealing was successful in the previous steps! You might want to leave this last step until the very end of the build (after you have heard the speakers performing). If you hear any puffing/chuffing sounds you may have a leaky speaker - I had to go back and redo 2 of the drivers to cure some leaks!

Repeat 6 times!

Step 12: Mount the 6 Full Range Drivers

Thread the speaker wire through the mount and into the pipe body then screw the end of the gooseneck into the nut encapsulated in the joining elbow.

Seal the speaker wire where it comes into the pipe body with the usual silicone sealant.

Repeat 6 times!

Step 13: Wiring Up the Full Range Drivers

The wiring of the full range drivers is done in parallel. For the 2 stereo channels twist all the positives for 3 of the speakers on one side of the body together. Do the same for the 3 negatives. I then joined the +ve and -ve bundle to one of the stereo channels.

Further reading if you are interested!

As the drivers have quite a high Ohm rating (14) they are wired in parallel to lower the overall resistance 'seen' by the amplifier. To add resistances in parallel we use the formula:

1/Rtotal = 1/R+1/R+1/R = 1/14+1/14+1/14 = 3/14 so.....Rtotal = 14/3 = 4.6Ohms - perfect for this amplifier!

Step 14: Connecting the Blue LED

I soldered the 3mm Blue LED to the ends of the wires (supplied in the amplifier kit). The wires connected to the amplifier through a 2 pin JST connector. I installed the LED by pushing it through the previously drilled 3mm hole in the pipe body and using some silicone sealant to seal it in place.

Step 15: Installing the 3.5mm Stereo Input Jack

...sorry this is a bit out of focus but I'm adding a small amount of silicone to the 3.5mm jack before installing it in the pipe body of the speaker

Step 16: Installing the Power Jack

In a similar manner, a small amount of silicone sealant is used before mounting the 24V DC jack in place.

Step 17: Install the Passive Radiator Into the Base.

The passive radiator is assembled to the base with 6 self tapping screws. The passive radiator comes with a sealing medium on the mating surface so no need to add any sealing of our own here.

Step 18: Mount the Sub-Woofer

Mount the sub woofer its mount. I used some foam sealing (closed cell draft excluder) to ensure that the sub woofer has an air tight seal. The sub-woofer is held in place by 6 off, M3 x 25mm socket head screws with shake proof washers and M3 nuts.

Step 19: Assemble the Pipe Body to the Base/legs

Rather than sealing this joint permanently I opted to put a layer of (red) insulation tape around the circumference of the passive radiator mount and simply push the pipe body over this joint. Alternatively you may want to seal this with silicone sealant.

Step 20: Assemble the Subwoofer

After crimping/soldering the sub-woofer speaker wired the sub assembly can be inserted into the pipe body in a similar manner to the previous step, (black insulation tape used this time).

Step 21: Your Finished!

Push on the 4 potentiometer knobs and you are read to go....

Plug the amplifier in to the 24V Power supply, pair your Bluetooth device then sit back and enjoy the music!

Comments and feedback most welcome. And please sub to me here and also my YouTube channel (not all projects get written up but most are videoed)!