400Hz-20KHz horn for BMS 4595

Ive had the intention of building a 60x30 horn for my BMS coax drivers for a while and got round to doing some calculations and drawing today, i intend to build it from 22 layers of MDF machined by CNC, then lots of sanding and painting.


Its looking like it will be a little less than 60x30 degrees as i dont have quite enough space to fit them in the cases, more like 55x25 now, not the end of the world but i dont really want them any narrower.  I went for a linear expansion with 1KHz 1/4 wave mouth termination as i am limited by what i can fit.  Path length is 215Hz and im aiming to run them from about 400Hz ish.  

James

Im not a big fan of working with fibreglass, MDF horns tend to be dead and very non resonant, and even if i did make them from fibreglass i would have to make the 1st mold from MDF.  400Hz is fine for the BMS.

ArthurG wrote: Timebomb wrote: Im not a big fan of working with fibreglass, MDF horns tend to be dead and very non resonant, and even if i did make them from fibreglass i would have to make the 1st mold from MDF.  400Hz is fine for the BMS. at HiFi levels yes sure.... but for PA it rips your head off

Cheers guys, Ive made some basic 60x40 horns with the same depth and ran them with 400Hz high pass and they sound very clean to me, distortion increases with power but the integrity of the dynamics holds together very well, better than anything else ive heard i think.  They can be a bit aggressive but thats mainly the really fast dynamics, your getting more information than with other systems.  Ive taken them as loud as i could stand but i haven't given them full power yet, i haven't needed too.  I think there may be excursion issues with a 400Hz highpass and full power so i may have to limit them but i doubt this will be an issue there plenty loud enough. 

Thanks Steve, Yep 22 sheets of 18mm, though when i glue them together it will probably end up slightly deeper, yeah i meant the axial path length is equivalent to 215Hz.  The round over terminates to a flat baffle, It dos not fold back on it self it just looks a bit like it does on that picture, its going into a box anyway so much more practical to end on a flat baffle, and i haven't got the space for a full roundover.

Where the flare intersects with the round over i made it correct for the horizontal axis, so its not quite smooth in the vertical axis, i couldn't think of a better way to do it, its not miles off i may just sand it smooth, any ideas?

Yeah i new a wide mouth woul cause lobeing, its a problem with wide bandwidth horns, it dos not seem too bad with the horns ive done, i might do some off axis measurements later on, as its a nice day outside, the round over version should help a bit with this i think.

Below these i am running a 2x12" horn , currently lowpass at 370Hz and high pass at 400Hz to the BMS, its sounds very good, nice and clear, it can seem a little thin but i think that because im used to cone drivers in the mids.  370Hz lowpass is about the limit of the 2x12" horns, above this i get a resonance creeping in.   Cheers for the tip Steve i didnt think about using polystyrene to make a quick round over, ive done the twisted towel thing and it made a difference, not as much as when i tried it on a small conical 2KHz horn though.

I know Tannoy use these BMS drivers with a 450Hz high pass, and i think one of there horns says 400Hz on it, im quite happy running them down this low.

Cheers for the input guys.

James


 

The above horn, blue is unprocessed, green is with EQ.

Not too sure, i was expecting it to go a bit lower, i cant remember where i set the highpass when i took those measurements but i assume it was well below the cutoff, its quite a fast expansion being 60x40 so that could explain some of it.