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Machined Free Standing Baltic Birch Horn for 1.4" Drivers

Dave A

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Finished a long term project today and it is a stacked BB  horn lens with removable clamp plate for 4" center line diameter  four bolt drivers. The block is 13.5" x 9" x 6.875" deep. Mouth is 11.5" x 7". Stacked and machined with no steps and very little hand sanding. These had a pair of N314X drivers on there and they sound very good. No testing done just listening. I have been kicking around the idea of making something like the Elliptracs which are no longer available and this is the first version. Meant to be free standing and might add a bracket to tilt and swivel in time. For now I am just sticking them on top of a speaker I have sitting around and enjoying them. 




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OK Here is a larger one and the last for this week. Of the three larger wood horns I have cut this one is by far the best and I may be done tinkering for a free standing horn. The one above is stacked on the new one for reference. The larger one is a 6.75 deep, 16" long and 9" tall and the mouth is 14" x 7". I am impatiently waiting for the second one to finish cutting so I can hear a pair in service.




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4 hours ago, Panelhead said:

  I asked Dave about an Eliptrac 400 a few months ago and he had at least one pair. Could not bring myself to butcher the La Scala top hat to mount.

  DaveA, what is the machine time running on these masterpieces?

Of course there is more than just machine time to these but here is the machining side of things. There are two steps to cutting the clamp plate top and bottom. There are two cuts for the main block. The first cut roughs 4" of the stack out and provides the side finish surfaces and cuts the cavity for the clamp plate to fit in. Then the second cut trims the rest of the rough block sides out and also cuts the cavity. All told the machine time is just over 2.25 hours each with all the cuts and part indexing and then I route the top and bottom corners with a router while on the mill. Step over per pass is .015" and that is a linear dimension and not just a vertical down dimension which keeps the surface finish uniform no matter the slope. This yields a finish I find good enough to just oil it and go after a bit of scrubbing with some 7446 scotch brite pads. The plys of course do cut a little differently and are not homogenous so you can see the lines but it is smooth to the touch. A perfectionist would probably want to use a wood pore filler and sand for a total glass smooth surface. I however like the wood look and would oil it or spray it with satin polyurethane.


  I am still tossing around the idea of a direct K-400 drop in but I am not sure that is the right way to go. Fiddling around with these horns and just like the K-402's discovering that relative to the bass bin or speaker cabinet these horns are best when free standing so you can rotate and tilt to get your best sound. I am coming to the conclusion that all your drivers mounted in one board makes perfect sense for a factory who wants to keep things simple and to satisfy most customers who also want plug and play and don't have any desire to tinker except for toe in. But for those who want the best out of their components I think the horn has to be movable. The KPT-456's, KPT-904's, K-402's, and KP-450's I have had all benefit from being able to move the HF around.


   B&C has a new 1.4" coaxial driver out I am going to try later this year on a wood horn. It might not be these as a bigger horn might be required to make those coaxials sound their best so first these and then bigger if required. Chris A talks about coherent sound from those German drivers and I figure the B&C ones are good too. Then you could aim both mid range and HF and have better time and sound alignment. There is just no way a K-400 or similar with separate tweeters will work as well as the coaxials is what I figure. Right now I am using a set of Eminence N314X drivers on the horns and they sound very nice as a two way setup. I will be trying a set of B&C DE-1090's soon also. I really like the Eminence drivers but with songs I am familiar with on the S-MWM's  I can tell some of the music is missing. You would never know this though unless you had a very good benchmark system to compare it with.

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