If you plan in building this MTM floorstanding speaker from scratch or already made it and plan for an incremental upgrade, keep reading. I didn’t delete or overwrite the first article and YouTube video about these speakers. Consider the plans for these speakers in 2 parts or whatever. Here are the links:

For construction tips, please watch both videos, even if you building from scratch.

The box

Let’s go directly to the numbers. I’m using MDF for constructing the box. But, you can use plywood if that’s what you wish, or have it readily available. I’m recommending MDF though. I’m going to give you 2 sets of dimensions : 18mm and 19mm. Why? Because 18mm is standard in Europe and 19mm is standard in US. As a result, regardless where are you from, you can build this speaker box without making tedious extra calculations.

The picture just above, gives you an idea how the speaker box should look like, how the braces position inside the box. Also, you’re not seeing double. The front baffle is made out of 2 panels.

18 mm thickness (Europe standard)

Panel dimensions:

  • Front and back : 1012 x 242 mm (6 pieces)
  • Top and bottom : 242 x 239 mm (4 pieces)
  • Sides : 976 x 239 mm (4 pieces)
  • Brace : 239 x 206 (8 pieces)

Make the braces as a frame, or window frame. Round the interior edges if you feel especially sassy.

Nothing to describe here. Just a sketch of the front panel and where the speakers and braces will go. The panel which will go on the front needs to be rounded. Use a decent size round-over bit on your router, or the largest one you have available.

19 mm thickness (US standard)

Panel dimensions:

  • Front and back : 1031 x 242 mm (6 pieces)
  • Top and bottom : 242 x 237 mm (4 pieces)
  • Sides : 993 x 237 mm (4 pieces)
  • Brace : 237 x 204 (8 pieces)

19 mm front panel

Regardless of what type of thickness you choose for this MTM floorstanding speaker, the cutouts for the speakers and the ports are the same. Here are the dimensions:

  • Seas CA18RNX – 7″ for step and 5″ + 13/16″ hole
  • Morel CAT 408 –  2″+14/16″ for step and I used a 48 mm drill bit for the hole
  • Precision port 4″ – 7″+5/16″ for step and 6″+5/16″ for hole

I’m giving you the dimensions in inches because I’m assuming you are going to use the Jasper circle jig for making the cutouts. Putting your hands on a metric circle jig is quite rare, so assuming you have an imperial one is legit thinking. Please note that the tweeter is offset (not centered). This means that you will offset to the right for one speaker and offset to the left for the other speaker. Offsetting in the same direction for both speakers will look awkward and you will regret your decision / forgetfulness.

For the back panel you just have to make the holes for the binding posts. The position ain’t important as long as it’s in the lower chamber. As a result, grab your 9 mm drill bit and drill where you find it most pleasing the 2 holes.

Parts list

The following links are affiliate paid links:

Item Qty Europe US
Seas CA18RNX 4 pcs Sound Imports Madisound
Morel CAT408 2 pcs Sound Imports Parts Express
Precision port 2 pcs Sound Imports Parts Express
Binding posts 2 pcs Sound Imports Parts Express
Stuffing 1 pcs Sound Imports Parts Express
Sound damping 3 pcs Sound Imports Parts Express
Vibration damping 6/1 pcs Sound Imports Parts Express
Crossover
8.2 uF cap 2 pcs Sound Imports Parts Express
0.56 uF cap 2 pcs Sound Imports Parts Express
5.6 uF cap 4 pcs Sound Imports Parts Express
0.27 mH Inductor 2 pcs Sound Imports Parts Express
1 mH inductor 2 pcs Sound Imports Parts Express
Crossover Hi-end
8.2 uF cap 2 pcs Sound Imports Parts Express
0.56 uF cap 2 pcs Sound Imports Parts Express
5.6 uF cap 4 pcs Sound Imports Parts Express
0.27 mH Inductor 2 pcs Sound Imports Parts Express
1 mH inductor 2 pcs Sound Imports Parts Express

Damping material

There are 3 types of damping material used for this box. First, you are going to use the sound absorbent pads and line the walls in the following positions: on the top panel and on the panels behind the bass speakers. After that, use the vibration reduction pads to line the whole box. If you have left-overs, do a double layer just on the bottom chamber (under the port). Next, return to the sound absorbent pads and line the whole bottom chamber. Finally, use the stuffing in the bottom chamber. The quantity you will use is 315-320 grams.

Crossover

Follow this schematic and make an OCD approved circuit board, which will go inside the box to never be seen again.

crossover design

Final thoughts

Let’s take a look at the frequency response:

MTM floorstanding speaker frequency response

As you can see, this MTM floorstanding speaker has a nice flat frequency response. These speakers are very revealing and micro-details in music are easily identified. However, these are not your typical bass-head speakers. If you are that types of person, look elsewhere or pair them with a subwoofer. Good luck with your build or your upgrade!