I wanted to make a pair of speakers based on the highly-acclaimed LX Mini Speaker by Linkwitz Labs. These speakers have been called some of the best ever made and I really liked the DIY concept. These speakers possess some of the most natural transparent sound I've ever heard. Since they have no "box" they have no "boxy sound" - just a clean (nearly) omnidirectional sound that makes me think of using a bare flash on a camera vs an aimed flash unit. Simply amazing.
They are a rather unusual monopole design that uses 4" plastic pipe for the bass enclosure with a upward facing 6.5" woofer, and a forward-facing full range speaker. The tube essentially becomes an omnidirectional 'bass radiator' rather than the typical woofer-in-box. The system uses a bi-amplified design with a 2x4 digital crossover to split the channels up and two T-class amps to power the drivers. The original design uses rather ugly rubber pipe junctions and metal clamps along with some other wooden parts to hold everything together.
I thought this was screaming to be 3D printed.....
Here I present my design that uses 3D printed parts to house the drivers and make a more aesthetically-pleasing speaker. Also I wanted to use less-expensive drivers so that I could make the overall project cheaper. For comparison, the original design calls for drivers that cost over $400 alone (and upwards of $700+ once you add in the amps and crossover) - I wanted to create a kit that would cost only $400 total. For this money you will be listening to some of the finest quality loudspeakers available - that look super cool - and that you MADE YOURSELF.
What you will find about these speakers is that they present a very clean, uncolored audio field. Room placement is not as critical with these as with many other loudspeakers. They are especially good for listening to jazz and classical music, but all types of music sounds great on them. Google them to learn more and read reviews.
I hope you enjoy building them and listening to them for years to come.
(A disclaimer - I have no affiliation with Linkwitz Labs. This design is based on the LX Mini, however it is not taken directly from their plans. I have never seen the original plans nor even another LX Mini speaker in person. I have simply used the photos I've seen and designed something similar using my own drivers and components. What I have posted here works well with the drivers I have used. To use your own drivers or those specified by the original LX Mini plans, you will need to alter the dimensions of the 3D printed parts.)
YOU MUST HAVE A FAIRLY LARGE PRINT PLATFORM TO MAKE THE LARGE TOP PIECE. YOUR PRINTER SHOULD BE ABLE TO DO 200MM X 250MM X 200MM MINIMUM.
Here's the parts list that I used:
2x MCM 55-1862 - 6 1/2'' High Excursion Aluminum Cone Woofer
$24 each from MCM
2x Markaudio CHR-70A Champagne Cone 4" Full Range - $36 each from Madisonsound
1x miniDSP 2x4 Digital Signal Processor - $115 from Madisonsound
AMPS for the Bi-Amp
2x Tripath T2021 based 25w stereo T-amps from eBay etc. These are from brands like MUSE and others, that use a very nice T-class amp to deliver nice, low distortion sound. These run $40-$70 each depending on what you want. (update: the only caveat about using these 25W amps is they can't drive the speakers super loud. At full gain they are only the equal to maybe a 60% on a normal amp. If you like your music loud, I'd get 50W @ 8 ohm per channel amps).
PIPE AND OTHER HARDWARE
2x 4" black ABS pipe in lengths from 24" to 36" (depending on the exact size you want and also based to some degree on the formula to calculate the bass enclosure volume for your speaker). I used 24" because it fit well with the guideline for bass enclosure size.
2x 4" pipe end caps
2x 10" x 10" mounting base boards (optional)
2 lb Polyfill to fill the bass tubes and reduce harmonics.
speaker wire (get something 14 gauge at least).
silicone caulk to glue everything up
4x 2 1/2" 10-24 bolts, washers and locknuts.
Nice speaker terminals
Paint for the tubes
You must print the BOTTOMSTAND piece at 121% to get it to fit the 4" NIBCO ABS endcap!<<
You might want to print the TOPBLOCK at 101% to make sure it friction fits properly - on my printer at 100% the small irregularities caused by the seams and the supports made it necessary to trim the PLA to make it fit<<
Print all 4 pieces at 20-40% infill.
Print out 2 copies of all four .stl files. I print these using a bed at 30º C and blue tape. (Heated bed tends to warp such large pieces). Extruder at 215 using PLA. I use Sli3er and it makes good supports which are mainly needed for the TOPBLOCK file.
After all parts are complete - cut the 4" pipe to size. I used 24" length pipes for my build.
Using the black silicone, make a straight bead that is about 20mm down from one end of the ABS pipe. This bead will go straight around the outside circumference and will act as a 'lip' to hold the top piece in place. Let it dry overnight.
After 'lip' has dried overnight, carefully slide the large conical top (LXMINITOP) onto the pipe and fit to the lip. Check the fit and make sure the top sits perpendicular to the pipe. Next drill 4x 2mm holes (or any small size for which you have a bolt) at the each of the 4 sides so that they pass through the wall of the 3D printed top piece and into the ABS pipe (see photo). Into these I placed small brass screws to provide extra support to the top. Then apply silicone sealer on the inside of the pipe to secure it in place. Let dry overnight.
The full range speaker is friction-fit into the TOPBLOCK - just make sure the terminals are down and bent out of the way.
Using the 2 1/2" bolts, secure the TOPBLOCK to the SPACERBLOCK and then to the LXMINITOP as shown in the photo shown. Tighten the lock nut carefully to avoid damaging the 3D printed pieces.
Solder speaker wires to the woofer and the full range speakers. TEST THEM NOW!!
Thread the wires into one pipe and glue the 6.5" woofer in place facing upward. Run the wires out the bottom of the pipe.
Fill the tube with about 12 oz (400 grams) of the polyfill material. It'll really be packed in there pretty tight.
Drill a small hole in the 4" end cap to run the wires out of and fill the hole in the endcap with silicone to keep the enclosure airtight.
Now TEST the speaker before you start gluing everything together for good.
Once you've tested it...
Press-fit the endcap with the completed speaker enclosure into the STAND piece and using wood screws affix this to the mounting board. You may want to glue everything together at this point to get.
Likewise drill a hole in the boards you will use to mount the speakers.
That's one down and one more to go. Repeat for the other speaker.
This is a Bi-Amp design. You can either use one amp for L and one for R channels or use one for WOOFER and one for FULL RANGE. I chose the latter since my amps weren't exactly the same.
Also you'll need to download the App for the Mini DSP - this little gadget can do amazing things! And here's a tip: when you first plug in the speakers and the Mini DSP and try it out, it will sound REALLY bad! Don't be disappointed because until you carefully set the input gain, the crossover points, the type of crossover and the output channels, it will sound awful. Please resist the urge to crank it up until you're 100% certain you've got all the inputs and outputs assigned correctly or you might blow a driver by sending odd frequencies to it.
For this build we only need it to crossover somewhere around 450Hz - sending the low frequencies to one amp and the higher ones to the other. One amazing aspect of these speakers is the ability to have each channel have it's own EQ and crossover point. You could spend hours tweaking the sound to suit your own taste. You can save different EQs for different styles of music for example. I use the -48dB Linkwitz-Riley (L-R) curve as a tip of my hat to the inventor of these amazing speakers. And if you have a decent USB microphone (not a cheap one) you can use it's automated EQ features to make the sound acoustically 'flat' in your listening space. Pretty neat stuff...
So plug in your input to the Mini DSP, take the 4 outputs and send them to the correct inputs of the T-amps, then on to the proper drivers. I use a mini-jack input that connects to the Mini DSP, then route outputs 1 & 3 to the L & R of one amp (the below 450 Hz frequencies) and 2 & 4 to the L & R of the other amp (for above 450 Hz). Use the amp volume controls to get the proper balance between the woofers and the full range speakers. And the 450 Hz rolloff is just a suggestion - see what you like. With only 25W per channel they aren't ear-poppingly loud, but plenty loud enough. And that sound...
Get ready to have your audiophile mind BLOWN!