Zynsonix Link

January 8, 2015

GR Research LGK 1.0 Full Range Speaker

Every now and again I take a break from building cables and amps to build a speaker. Your better half will typically notice a speaker sneaking into the house a little more reliably than an amp or cable, so be forewarned ;)

Since I don't own a table saw or have anywhere to even put one, I enjoy building speaker kits where the MDF/pine or other wood is pre-cut by CNC machine. The industry nomenclature for pre-cut wood for speakers is a "flat pack". You still get to treat the cabinet interior, fit the crossover, and glue everything together, so you don't miss out on all that fun.

The last flat pack speaker I built was the Frugel Horn from Planet 10 Hifi, which was a simple to assemble back-loaded horn which could house a Planet 10 treated driver, or a stock driver from Fostex or MarkAudio. The speaker build this post will be covering is the GR Research LGK 1.0 Full Range Speaker kit.

The LGK 1.0 uses a 3" driver made by GR Research. Yes you read that correctly... 3 INCHES! Many may think three inches is inadequate, but it's all about how you use it (a-ha). This particular LGK driver is happily seated in a very solid 8"x 4.5" x 12"cabinet that's cut by Subassemble.

LGK Flatpacks made by Subassemble

The rest of the parts for the LGK can be procured from Danny at GR Research. The kit from Danny includes a number of nice quality parts, including Sonicaps, Mills resistors, Erse Air core inductors, Electra tube connectors (which serve as the speaker connectors), No Rez, and other minutia including ports, screws, wire, solder, and heat shrink.

The first part of the process is to cut up the No Rez, which is a thick damping material specially designed for loudspeakers which adds mass and reduces resonance and internal waves. The thicker, bottom portion of the No Rez closest to the adhesive takes a little bit of elbow grease to cut with a razor blade. Remember to change out the blade before you start grumbling under your breath.

Mapping out the cuts of the No Rez

Once the cuts have been made, the CNC cut wood pieces are laid out and the No Rez applied after to ensure it won't bump into anything during final assembly.

No Rez lined up on the side panel

I added a bit of sealing caulk around the edges to prevent air from escaping anywhere but the port. The No Rez needs to be trimmed a little bit to allow clearance for the speaker, port and crossover.

Caulking the edges for a good seal

The next task was to assemble the very simple crossover, which acts as a baffle compensator to help boost the bass. The three parts are soldered in parallel. The part values are proprietary per GR Research so I can't share them unfortunately.  

Crossover parts

I cut two pieces of FRP material and mounted some turrets so the parts could be mounted cleanly, with zip ties holding down the inductor. The board is then mounted to the top wood panel with caulk.

FRB Boards fashioned for the crossover

Once everything is in its proper place and you've tested to ensure everything is working, the speaker is then sealed up with your favorite wood glue and clamped from every angle. Excess glue is removed with a damp paper towel. Don't soak it or the MDF will expand, and no one likes wet, expanded MDF.

Speaker clamped down to dry

Here's the speaker cabinets after drying, right before getting a sand with 60 grit sandpaper. A basic electric sander is pretty affordable and save a lot of effort at this step (if you don't already have one).

Unsanded Cabinets

Below is the difference between sanded and unsanded cabinets. Any gaps in the wood should be filled with wood putty, or if you are going to be painting the cabinets with Duratex, you should use drywall spackle per the directions for better adherance. For the corners, I sanded them lightly with 3-4 quick passes, some people like to round them a bit more, or route them.

Unsanded vs. sanded

The next step is to finish the cabinets. You can stain the cabinets, metal leaf them, paint them, veneer them, the sky is the limit! I chose an interesting finish (which GR Research carries) called Duratex. Duratex, which could be the name of a manufacturer in the family planning aisle, is a lot like a truck bed liner paint, it's durable and creates a very dimensional texture. This is especially great if you screwed up somewhere along the way and need to hide your mistakes or you're a sanding slacker ;) 

Duratex, check out that texture!

Duratex requires two coats, you can vary the texture with the included roller a little bit for either a smoother or rougher texture. When the solution is rolled on, it creates bubbles which pop, adding to the unique finish. 

Next the ports should be installed, there is a small ring around the cork cap which is recessed to allow you to put some caulk down to seal it in.

Sealing up the ports on the back

Now the cool little Electra Tube connectors can be soldered on. These are pretty unique connectors; they have a patent pending from what I understand. They are low mass, so they only use the amount of metal necessary, and allow the internal wire to be very close in proximity to the wire within their proprietary banana connector. The nice thing is that I've found they work with standard banana connectors as well, so they shouldn't affect your speaker resale value much if someone is married to their particular Kimber/Nordost/etc. speaker cable. One of the nicest things about these connectors is you just hammer them in with a rubber mallet. The installation couldn't be simpler. 

Electra Tube Connectors soldered in place

Soldering the driver in is a simple affair. Just two wires to worry about. Note the bottom of the driver cutout has clearance for the solder posts. 

LGK driver before installation

You may have to do a bit of Dremel sanding if the driver doesn't fit perfectly due to paint getting in the routed area. Once in place, you can drill a set of pilot holes, then screw in the four screws. All done!

So if you have three Benjamins, don't have a lot of space to spare, and are looking for a pretty resolving desktop speaker, the LGKs are a great bet. You'll note some very impressive bass response and nicely resolving treble. I have a slightly larger full range speaker with a Fostex driver and baffle compensation "crossover" and I like each of these for different reasons. The bass response and treble energy on the LGK is better, and the Fostex offers slightly better presence and midrange.

Overall a great project and a great speaker. Looking forward to see how Danny incorporates these drivers into other designs.

Need some speaker cables for your LGKs or other speakers? Contact Zynsonix Audio for some great sounding options.

The Fine Print:
The above steps detailing the building of a speaker are for entertainment purposes only, and are not intended to be used as instructions. Zynsonix Audio LLC and DIYAudioBlog do not have any affiliation with SubAssemble or GR Research. The owner of this blog and all associated parties can not / will not be held responsible if you attempt the process posted and cause physical harm to yourself, your surroundings or your property. Please keep this in mind.


  1. How long did the build take?

  2. What are the dimensions of the cabinets and port size??

  3. You'd have to check with GR Research: https://gr-research.com/lgk-series/