THAM 12 Subwoofer Build

Toward the end of 2013 I was getting the itch to build something & I decided upon a THAM 12 tapped horn PA subwoofer, a design from Martinsson.

I ordered the wood as a flat pack from Tim Malone on the Speakerplans forums, who runs speaker-cabinets.co.uk dealing in CNC loudspeaker cabinets (both flat pack & assembled/finished).

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I opted to load it with a Precision Devices PD.12SB30, mainly due to price but also due to British loyalty~

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I had to buy a decent drill/screwdriver, decided to do it properly & buy a DeWalt. The screw-&-glue construction method with rebates throughout made assembly so much easier than trying to clamp butt joints without them slipping. Driver attaches to the baffle with M6 T-nuts.

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Tapped horns certainly lead to an interesting internal layout!

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Test fitting the driver before the final panel goes on. Turns out the PD.12SB30 is ever so slightly too wide so I had to slightly extend the rebate on the final panel to let it slide in.

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It’s a pretty small cabinet – here it is compared to the little 8″ reflex sub I built a few years ago for my bedroom system.

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Wiring up STX series Neutrik connectors on the CNC cut aluminium connector plate Tim made up for me. Nyloc nuts so they won’t vibrate loose.

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These connectors are gorgeous.

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First low power test before I even had a spare crossover to use!

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I picked up a pair of Brooke INH-8 8″ + 1″ cabs for a great price from a Speakerplans member local to Fife, a DCX2496 for processing & one of Thomann’s 4-channel switch mode amps – channels 1 & 2 for the midtops, channels 3 & 4 bridged for the sub, stuck in a rusty old flightcase.

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One thing the THAM 12 design doesn’t have is any provision for a grill, so I added a pair of hardwood battens recessed back 4-5mm along the edges of the horn mouth.

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I couldn’t be bothered to remove all the screws, fill them, then buy a router to roundover the edges properly, so I just sanded them down a bit so they don’t suffer quite as badly from abuse.

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I wanted to keep the wood visible, so I opted to cover it in Rustins Plastic Coating – a clear drying urea formaldehyde thermosetting resin that I was told is tougher than regular varnish. I had to do it over about 4 consecutive weekends, because after 12-24 hours you can’t apply any new coats until it has completely cured (which takes 3-4 days). It also smelled dreadful & had to be done indoors to keep it above 18c to cure properly…

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Finally enough coats went on & I could reassemble it with the powder coated grill from Markie on Speakerplans.

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And finally some glamour shots~

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All together it makes for a pretty compact system!!

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2 thoughts on “THAM 12 Subwoofer Build”

  1. Very nice!

    I’ve got one too from Tim (but which he assembled… I was too lazy to do it myself) with a B&C 12PL32 in it. Works OK although the Xmax is a bit on the low side – but I’m using this at home only so SPL is plenty enough anyway.

    1. Xmax on the PD is not ideal either, especially as they don’t give an xlim rating so I don’t want to risk going over too much. It’s rated 1.6kW peak (6dB crest) but by 400W (its AES rating) it’s already at ~8.7mm vs its 7mm xmax.

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