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RE: Olson Modified BLH monster

Posted by Paul Eizik (A) on June 22, 2007 at 13:53:44

In Reply to: RE: Olsen Modified BLH monster posted by freddyi on June 22, 2007 at 10:43:49:

Fred

My offhand swag is that this is kinda close to a hyperbolic expansion sorta (mostly). As in most bass horns, it's what fits inside the box and winds up being close to being recognizable to one of the known horn expansions. The mouth size is about 1050 square inches, the path length is about 12.5 ft., and it should be able to go down to about 25 Hz. The Tannoy Gold is a bit of a wild card here (as were some of the BM iterations) in that it has a rather lowish Fs of 26 Hz, unlike the usual suspects/musical instrument drivers usually put to work to drive bass horns. I would expect some ripple at the bottom end as a result, along with some difficulty going up to the mid crossover freq, but measurements will tell if these concerns are valid. Can't find my notes on the front chamber, bit it is about 3" deep, about 19" high and about 33" wide. Subtracting the triangular ends, it comes out to about 1805 cu. in. (not fuguring in the mass the rear of the 15" driver occupies). This was made as large as possible to accomodate tuning the volume. This type of chamber is ususally of concern in where it starts to limit the high freq. output of the driver as Fhc: Fhc=(2Qts)Fs(Vas/Vfc). However, if you make the chamber large enough it can begin to act as a notch filter as Olson has shown in his Dynamical Analogies, as can the area where the horn throat begins. The hole which determines the horn throat is adjustable, and is generally "choked" in a BLH in order that the bass horn does'nt overpower the direct radiator front output. I had originally conceived the coupling holes between the top manifold and "S" section to be merely useful as another adjuster for attenuating to output of the horn, but after some of Steve's comments and looking at the Olson patent again, I think it it's more complex than that. If you make these holes smaller than what would seem optimum for maximum output, the top manifold would begin behaving more like a vented box or a TL. The overtones created by the manifold panels should fall in the 900 Hz region, while the output from the bass horn itself should roll off under 200 Hz, so this is a non-issue due to the muffler effect of the manifold. Quite a few perameters to adjust in this design, but that's the fun of an experimental horn!

Paul

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