Overnight Sensation MTM Speakers
The Overnight Sensation MTM is a speaker designed by Paul Carmody. It is the larger version of the Overnight Sensation and is very popular in the DIY audio community.
I haven’t had much experience with wood working before, so this project is going to be a fun challenge.
Day 0: Ordering Parts
It is possible to order a full kit that includes the cabinet pre-cut, and only requires gluing together. This saves a lot of time and effort.
However, I live in New Zealand, and shipping costs a lot. Especially when it’s large and heavy (like a flat-pack kit of 3⁄8” MDF board).
So, I decided to build the kit myself. At the time of writing this, I’ve spent more on tools then it would have cost me to just order the pre-cut boards, but I feel like I’ve learnt more. Also, if I ever decide to make another speaker in the future, I’ll only need to purchase the wood.
I ordered most of the parts from Parts Express. However, they didn’t have the model of tweeter I needed in stock, so I ordered that from The Loudspeaker Kit. They also didn’t have any 10uF non-polarised electrolytic capacitors in stock, so I picked those up from my local Jaycar.
- 2x Hivi B4N Midbass Drivers
- 2x Dayton ND20FA-6 Tweeters
- 2x 1.5 Ohm 10W Resistors
- 2x 10 Ohm 10W Resistors
- 2x 0.15mH 18 AWG Inductors
- 2x 0.90mH 20 AWG Inductors
- 2x 10uF 100V Non-Polarized Capacitors
- 2x 0.22uF 250V Polypropylene Capacitors
- 4x 0.47uF 250V Polypropylene Capacitors
- 4x 1-3⁄8” Adjustable Port Tube
- 2x Speaker Terminal Binding Posts
Day 1: Planning
There are cabinet design plans for 1⁄2” and 3⁄4” MDF. However, I only have access to 18mm MDF, which is a just a millimetre thinner than 3⁄4”. In order to maintain the same internal volume, I calculated my own sizes.
- 368mm high
- 114mm wide
- 216mm deep
External dimensions (with 18mm MDF):
- 404mm high
- 150mm wide
- 252mm deep
I used the 2D cutting optimizer at optimalon.com to plan out what size MDF boards I would need to purchase. I ended choosing 2x 1800x300x18 boards.
I wanted to rebate the edges of the boards so they join together nicely. I did plenty of sketches to figure out what cuts I needed to make.
I used SketchUp to double check that I had all the dimensions correct and that my rebate joins were the right size.
Day 2: Cutting
I started by roughly cutting the boards in half using a circular saw.
I, with help from Dad, used a radial-arm saw to cut the boards into the correct dimensions. We made sure the saw was cutting at 90˚ by doing a few cuts on a bit of scrap.
It took a while to make all the cuts. The front, back, and sides, which were just a little bit longer than what the saw could reach, needed to be spun around to finish off the cut.
Day 3: The Router
I spent the morning shopping for a Router and the necessary cutting bits.
I needed a router to cut the holes for midwoofer and tweeter, as well as to rebate the edges.
I ended purchasing the Black & Decker KW900EKA Plunge Router, as well as an 18mm straight cutter, a flush trim cutter, and a 10mm rebate cutter.
I used the flush trim cutter to clean up any inconsistances between the tops, bottoms, sides and backs.
The 10mm rebate cutter was also used to cut a 10x8mm rebate on the side boards. I also needed to cut an 8x8mm rebate, but at that time I hadn’t figured out how I was going to do that.
Day 4: More Routing
I needed to cut an 8mm rebate with only a 10mm rebate cutter, so I made a simple jig for the router to slide across, at the just the right distance. It was a bit slow to setup, but it worked ok.
I then needed to cut a channel in the side and back panels to hold the brace. I used the included fence attachment to cut a parallel 18mm groove.
All the panels laid out:
I fitted all the panels together (without glue), just to check that I hadn’t made any mistakes with the measurements. Overall I was quite impressed, though it was wider by about 1.5mm than I had planned for, so I’m going to measure everything and find out what I need to trim down.
Day 5: DIY Router Table
It rained nearly all day today, so I didn’t have much of a chance to finish off the routing.
I took a trip down to Bunnings and picked up six cheap quick-release clamps, which I’ll need when I glue the cabinets together. I also bought some quality PVA glue, a couple dust masks, and some vernier calipers for precision measuring.
I used the calipers to check how accurate I was with my routing, and found that I was short a millimetre in some places. I needed a more accurate way to rebate the panels, so I decided I was going to turn my plunge router into a router table.
I wanted something cheap, simple and portable. I found this wood working article with plans for building exactly what I wanted.
I started by finding four bolts that would fit into the bottom of my router, as the ones it comes with aren’t long enough to go through a thick piece of wood.
I traced around the bottom of the router, and setup a temporary jig about 6mm from the edge. Why 6mm? Because I was going to use the included router guide bush with the jig, and it happens to be 6mm from the edge of the collet to the edge of the cutter.
I cut about 9mm into the board, so that I would have about 21mm left. Doing this gives me a bit more height on the cutter bit, and also so I don’t have to find some longer bolts.
While trying to cut out middle of the hole, the router accidentally slipped off the jig and gouged the bottom of the board. Next time, I just do as much as I can, and then finish with a chisel.
I marked screw holes, and drilled them out. So far, so good.
I flipped the board over, and counter sunk the holes, just enough so that the bolts wouldn’t stick out.
I used a hole saw and a rasp to cut out the hole for cutter. I then flipped the board over again, and attached the router.
I flipped the board back over, so that the router was on the bottom. That’s the hard part done.
I found a piece of wood to use as the fence, and drilled a hole through one side, large enough for a bolt. Then I marked out where wood hits the cutter, and cut out hole large enough for the cutter to sit.
I gave it a quick test, and found that it worked pretty well. All that I need to do now is use some tape to keep the power button on the router pressed, so I don’t have to keep one my hand on it all the time.
The great thing about this setup is that I can simply unclamp it from the table, and move it around, or bring it inside for storage.
Day 6: Routing & Glueing
To finish off the router table, I needed an easy way to be able to switch the router on and off. I used several rubber bands to keep the router button depressed, and a power strip to turn the router on.
I clamped the board to the table with a wooden stake so I the clamps wouldn’t get in the way. I clamped the vacuum right next to the router to minimize the amount of dust.
In case the board wasn’t strong enough to hold the router, I stacked up some scrap wood underneath it. This was also useful when I needed to adjust the plunge depth, as I could use the wood to hold the router in place while I tweaked the depth.
I ended up needing to cut another hole in my fence, as the first one I made was too wide, and it made cutting smaller pieces difficult.
Later on in the day I started to glue the cabinet together. I did a test fit before to make sure all the panels fit together properly.
I prepared by putting plenty of newspaper down, and getting a damp cloth ready to wipe off excess glue.
I started with one corner, clamping it for half an hour, and then doing another corner. I left the cabinet clamped overnight, for maximum strength.
Day 7: Glueing & Bracing
The first cabinet I glued was finished, and I was quite impressed by how strong it feels.
I glued the second cabinet, this time doing two corners at a time to speed up the process.
I’ll need to do a bit of sanding, but overall I think the glueing went pretty well. The brace and back panel are not glued in yet.
The Dayton tweeters arrived. They were a bit smaller than I expected, probably because I was assuming that would be similar to the HiVi T-20 that meniscus.com offers.
The diameter of hole needed to mount the tweeter is 33mm. The flange around it has a diameter of 45mm and is 2.25mm thick.
Time to cut the brace supports with a jigsaw.
My jigsawing skills aren’t the greatest, but it doesn’t too much, as you will not be able to see the brace once it’s installed.
I gave the edges a quick sand to smooth them a bit. Not at all necessary, but it might make installing the midwoofer and tweeter a bit nicer.
Here is how the braces look installed in the cabinets. I haven’t glued them in yet. I think I’ll wait until the rest of the parts arrive.
Day 8: DIY Circle Jig
It rained again today. The parts are still in transit, so there wasn’t much to do except build the circle jig so I can cut cicles with the router.
I went with a design I saw on Richard Morley’s YouTube Channel where the center point is fixed and the router slides back and forth on rails.
I started by marking out what I needed on some spare hardboard. I then cut out the pieces using a jigsaw.
To make the jig a bit stronger, and because the only thick washer I could find was thicker than a single piece of board, I decided to glue two pieces together.
I then drilled a hole for the washer.
The washer is used to protect the wood from being eroded when it rotates around the center bolt.
I then used the radial-arm saw to square up the edges.
I gave the edges a quick sanding to make them a bit smoother.
To make the rails for the router, I first drilled holes at one end, then used my table router to cut a straight line.
I then used a larger cutter to cut out channels a couple millimeters deep so that a washer could fit in there.
I found a couple old washers that were the right size.
Unfortunately I didn’t cut the channels deep enough to cover for the washer and the head of the bolt. By this time I had already disassembled my table router, so I’ll probably fix this tomorrow.
I attached the router to the circle jig, and cut the center rail for the cutter bit to go through.
It was getting quite dark, so I decided to give it quick test before packing up. I found a bit of scrap MDF and drilled a hole so I could fit a bolt through it.
I then fit the router with the circle jig attached over the bolt. Tomorrow, I might cut the bolt down a bit, as I’ll need to cut circles where the bolt will be under the router.
The result was pretty decent.
The finished circle jig. Just need to make the channels a little deeper.