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75.109.11.25
In Reply to: RE: Olsen Modified BLH monster posted by Paul Eizik on June 22, 2007 at 10:20:30
hey Paul -- looks like something I'd like
whats your offhand guess of flare type, path length, chamber volume and mouth size? What adjustments to response and to "tone" can be made by adjusting the manifold's panels? --- is that mainly tackling overtones fed into the horn whihc end up suming with the front which ends up as overall sound to the listener?
Fred
Follow Ups:
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
if you throw away the wood, now much air volume would the horn have? - or maybe another way is to ask its external bulk and ~how many 4x8 sheets went into it?how big is the throat area -?
heres a sim Tty One
26Hz is pretty low - horn mass load can shift things- got AJ-Horn for toy but not sure if cna do it right unless the epansion is fits one what it wants
Hi Freddy,
from memory I needed ~4 sheets to make this. I was fortunate enough that the local hardware shop to me was able to cut the MDF to my measurements, and I must say, he did a great job, most being exactly as ordered. To see this big box take shape and fit together was great. I also had spare MDF left over. Now thats for my next project, a dolls house for my little girl. Of cousre to have next to the horn cabinets so as she can listen music too!
best wishes
john
Fred
25 Hz is indeed low, like: "best case scenario"; "down hill with a tail wind"; "give er 5 dB down cause she's a horn" etc. The AJ sim predicts about 45-50 Hz , about what my rig will do, but that's a very big mouth and long horn on John's rig. As a sidebar, I recently wondered why measurments of my rig from the early 90's showed 45 Hz -3dB, while later ones showed more like 50 Hz. After I measured my Ampex 402 pre-amp I stopped wondering (in the early 90's I ran Hafler S.S.). Anyway, 50 Hz of horn bass beats 30 Hz of direct radiator bass, with bass dynamics being the deciding factor.
The throat is about 12" diameter. That's an interesting proposition of considering the mass of air in the horn minus the wood, which would affect the point where reactance with this mass would raise the bass response above what the mouth/horn length would indicate. This however ignores the contribution of the manifold and folds along with the various other tuning variables. John has anounced his intention to obtain some measuring equpt, and it should be interesting to see how the D.U.T. compares with the sim. I assume the sim can't compensate for variations from between the lines of the horn continuum: i.e. specify a mouth area/termination and horn length, and then name that horn expansion. John would have to say how many 4 X 8 sheets (to the wind?) this horn takes.
Paul
Paul
~105dB halfspace for 2.83v/50Hz ain't too shabby and should kick like a mule with drumkit (does it "kick" or just sound clean??)
John should have a real nice horn rig. I'm sorely lacking in that dept. (although have 3-k-horn & 2-Sentry IV carcasses)
re:kickdrum - what do you think's the highest cutoff which will get most of the sound and feel? Karlson in the "middle" of my yard which drops off 8 feet behind the mic is about F8-F10 around 50 - I want to drop the size even more so it can be carried.
I';m not overly fond of reflex and hate to see their cone flap in the wind on hard transients - my K will get pretty lood in a little room with 1/8" peak to peak and ~300W peak
Fred
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