DIY OB build retrospective

I have had a bit of a plan for a while now to build some three or four way active speakers either horns or open baffle using Minidsp or similar. Previous speakers were Mauhorn V with Lowther DX4 (built from 30mm Baltic Birch Ply and weighing about 80kg each!!) which integrated in the room with a Rel S3 sub pretty well. I didn’t have, or notice, the problems others had experienced with this kind of setup although, luckily, I think my room seems to be particularly well behaved. The rest of the system was an SJS Arcadia 1.5, 300B power amp and AN Dac 2.1X Sig.
What I did notice with the Lowthers was the usual break up and distortion at about 4kHz to 5kHz that rises from there. Dynamic but edgy probably the best description with nothing above 10kHz and below 50Hz hence the sub.
The decision to go OB was made at Scalford 16 really as Ritchie’s big horn system was wonderful but illustrated the issue of integration and where the best sound was near the back of the room about 6M (?) from the speakers. My room is 5M long and I have the sofa approx. 2M from the wall behind it so working with 3M in front.
The other speakers I liked at Scalford 16 were Ed’s JBL copies and Steve67’s (?) OBs upstairs in the furthest room from Ritchie’s. I also corresponded with Adam via PM regarding his Lampizator P17d build and found a couple of threads on the similar build another Steve did with walnut kitchen worktops as the baffles.
So……the decision was made and the pre and dac were sold (still trying to sell the power and the speakers) and some drivers bought. Bass is two Fane Colossus 18XB that I had heard in Steve67’s room. I had also heard the Beyma TPL150H there so got a pair of them off Ebay for a good price. These are air motion transformers with a horn or wave guide. To go between them I bought a pair of Beyma 12P80Nd drivers which are popular on DiyAudio to pair with the TPL150. Beyma have also started producing cabinets for their drivers, mainly for pro use, and they pair the TPL150 with the 12P80 or one of their other 12” drivers.
The quoted sensitivities of these drivers are all pretty close and pretty high at 99dB for the 18”, 101dB for the 12” and 102dB for the TPL, and this was another aim at the start of this project in that I wanted to get a speaker system that was in the upper 90s Db efficiency. Not as efficient as some/most horn systems but efficient nonetheless. As an aside, before I went down this route I was pretty much decided to go with the SJS/AN Dac/300B etc and add efficient speakers such as AN Es or Js or the Devore O93 or O96. With the chosen drivers I get to beat their efficiency and also the satisfaction of building something myself (as long as it all goes to plan!!!).
I bought a sheet of 24mm Baltic Birch Ply to make the sides, top and bottom of a U-frame for the 18” drivers so a similar bass arrangement to the one Pete used on the Landfill Olympians. For the front baffles I bought 3M of 40mm Oak worktop from Worktop Express as I was under instruction that they had to look nice when done!!
So all parts assembled by the mid to end of March 2016 and work started. And then, due to training and racing commitments, knocking a wall out and refitting/redecorating a kitchen, and in the best traditions of such projects, progressed at a pace akin to the movements of tectonic plates!
I shaped the baffles using a circular saw to rough –in the shape and then used a router to trim and add a round-over. The circular holes for the drivers were routed with the 12” driver hole also being rebated. The u-frame boxes were cut, glued and screwed together and similarly fitted to the back of the baffles which had been cut into two parts by then. Another reason it took me so long to do these was I was, whilst I had the overall design decided, I was doing the detail design and working out how to do things as I went. The original plan to have a single piece of 40mm oak as each baffle changed into having two pieces of oak for each baffle in an attempt to get some isolation between the 18” and the 12” and TPL. The baffle holding the 12” and TPL still stands on the top of the U-frame behind the 18” via a timber frame that stands on sorbothane pads but there is no direct connection through the oak baffles. The next logical step is to suspend the upper baffle from the ceiling in place above the lower baffle so that there is no connection at all, but that is for the future.
So by the final Saturday before Xmas I finally had them completed, sanded, 5 coats of Danish Oil, in the room and connected up to my amps. I had a Crown Xli1500 on the 18”, another on the 12” and a Leben CS300Sx on the TPL. Crossover was a Najda that Speedy(now Steady)steve had built for me with boards that Pete had left over from a cancelled commission. I set the crossover points at 400 Hz from 18” to 12” and then 1400 Hz from the 12” to the TPL and had a bit of a listen. Immediately they were better than the Mauhorns, more extended and not as edgy or grainy.
I noticed, however, that they sounded a bit “off” tonally on certain music, strummed acoustic guitar could sound a bit flat. I put this down to brand new pro drivers with stiff suspensions needing to loosen up.
I let the speakers play whenever I was in the house and so built up 40 to 50 hours over the Xmas holidays and they did, indeed, loosen up and things started to sound really very nice. I also noticed that as they loosened up they became more efficient as, for the same volume in room, the volume setting on the Najda was at -24 to -26 instead of the -14 to -16 required when they were first completed.
On the Thursday between Xmas and New Year Guy visited with my new power amp for the 12” drivers, an Hiraga Le Monstre which replace one of the Crown pro amps. These are bridgeable mono to provide 900wpc and will be used as such on the 18”s where the extra power should come in handy for any dsp. I listened with Guy for a good few hours and took a few measurements which showed a need for a bit of dsp below 30 Hz and a peak that needed addressing at about 50 Hz. I left that for a later date and just amended the respective levels of the drivers to get a more even sound and changed the 400 Hz lower crossover to 200 Hz. All crossovers were LR4. We listened some more and it is fair to say I am well chuffed with the results.
The Hiraga on the 12” drivers took care of a hardness and graininess that was apparent with the Crown amp, which alternatively is very happy doing bass only duties. A few weeks on from Guy’s visit and the drivers have settled even more and I think the best way to describe the sound is big, effortless, incisive and with no cabinet sound at all. Now they have settled in I intend to make some more measurements and do some dsp below 300 Hz only. The response plots appear a bit lumpy but I can’t hear when listening so I will leave well alone above 300 Hz, at least for the foreseeable future.

More photos to follow shortly.


Drivers assembled ready for when the baffles are complete. The 18" is a bit of a surprise when first opening the box, LP for size comparison, normally see CD cases used for that purpose:sunglasses:


Baffles with the round drivers fitted, 12" rebated into the wood. Baffles did change a bit from here, as in they were cut in half!
The thoroughly professional looking Najda also shown, cheers Steve and Pete.


Excellent,do enjoy reading/seeing DIY builds.

I don’t seem to have much in the way of photos of the journey, we now jump to the finished job:wink:


I recognize that crossover. :smile:

They actually look quite attractive, well done!

And there’s something about 18" drivers… :heart_eyes:

I recognise that amplifier! These did sound extremely good and I understand they are still improving as the drivers run in. That Beyma AMT is a nice item. First time I’ve had a proper listen to one. The rest of Keith’s system is pretty tidy too with a heavyweight NA deck, Groovemaster banana arm, Miyajima Shilabe & Paradise phono stage. All good stuff.

Lovely stuff I have a single 18" driver at home Planning to us it in an OB at some point

me too! :grinning:

The 18s are something else, so effortless, especially with 900wpc up’em:wink:. Feel like I asked lots of questions of Adam, Pete, Steve and Guy and then went a bit underground really while I built them. Not very good at documenting things as I go along really. Sorted in the end though.
Will put some more pics up of the rest of the system later.