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In Reply to: Eizik's Church Of Olsonology Part 0.9? - Weems "Mello Monster" posted by freddyi on February 10, 2007 at 14:46:22:
Hey FreddyiThe design originated, as far as I know, from the Oct. 1962 issue of Popular Electronics magazine. A smaller cabinet for an 8" driver was featured, and plans were offered (by mail) for a larger cab for a 12" driver which is pictured in your post. The author was Roald E. Dybvig of Minnesota. As far as I can tell, the 12" version was never copyrighted (unless the mice ate the "C"). I've never seen the Weems version, but both seem to owe a lot to Harry F. Olson. The length dimensions of the baffle boards in the top manifold are not shown in the top view because a full scale top-down drawing was included with the plans. These dimensions can be easily extrapolated from the drawing however. It's a fairly easy cab to build, just a big box with a shelf in the middle, and a number of baffle boards. The only tricky part is the top manifold section, in that these boards can't be too tall (or short) so they can closely mate with the top when it is installed. I built a box extension on the front so that I could mount an EVM 15B. Using the original configuration with this 15"er ( constricted throat back horn with direct radiator front), this horn will go down to about 80 HZ. It fairly begs to be hot rodded though, and mine are barely recognizeable from the originals at 6 ft tall, and 250+ Lbs. being bi-polar with 6 drivers per side. Warning: big horns tend to get away from you!
Follow Ups:
A friend of my father's built the 8" version, in our basement when I was in high school. Ran it with an 8" EV Wolverine fullrange. When he upgraded to stereo (Dynakits as I recall) I inherited the mono speaker (too much work to clone it for stereo I guess!). I already had a Heathkit FM tuner someone else gave me because they could not make it work (I fixed the cold solder joint and it worked great for years). That inspired my first single-ended design, an ultralinear 6BQ5 amp with transistor RIAA preamp - a cheap Garrard 'table and I had hifi in my bedroom!Went to the library to get records; that's when I discovered Mahler. The combination of late Romantics with high-school angst was pure magic! Been a hifi nut ever since ... :^)
PaulMy Dad built the 8" versions for himself in the early 60's, and 2 pairs of the 12" versions for guys in his hi-fi club, and I got a left over pair of the 12"ers. Those were heady days indeed! Most people had console boom boxes back then, and our family was decidedly behind even this curve with our tiny Webcor Midgey. The rig my Dad assembled was utterly mind blowing to most people: Knight 708 woofs on the BLH, EV 828 mids and T35 tweets. Horns were considered a bonifide Hi-fi alternative back then. I somehow missed the anti-horn movement which seemed to later come mainly from the (then) underground Stereophile and Absolute Sound mags. The mainstream Stereo Review largely ignored horns. It sounds like our formative years were similar.
Dear Reverend Paul ----maybe Weems speaker wasn't a 1937 Olson type? - I built a one and half fold t-line by Weems which must had been larger than this horn and Mellow may had been something different yet - perhaps a concentric labyrinth?
by 80Hz - what does this imply for visceral power with an 8.75 cubic foot BLH vs a big tubby reflex and what parameters/ or characteristics in a twelve might this horn like?
Brother FreddyHorns and T-lines have many similarities and can both get rather large. As to viceral power, the back loaded MM's (with horn mids and tweets) made one outing as a sound system for a rock band at a block party back in the 80's. They had no trouble keeping up with the band, powered by my 300 Watt bridged Hafler and home made 16 X 4 mixer. When the band took a break, a couple of girls and me made an inpromptu reggae jam band. Because there was no bass player, I cranked up the kick drum mic, and it was pretty viceral. The girl on the drum kit had to get used to having that much horse pressure at the end of her foot. A classic M.I. big magnet/low Q driver would work great with this horn. My Dad built the smaller 8" version, and even with a cheapo driver, it could rattle the windows with his 120 W. Citation back in the late 60's. With a larger horn mouth (achieveable by adding a superstructure to the front of the cab) the MM's can go down to the driver Fs, about 40-45 Hz in the case of the EVM15B.
your drawings for 15" BLMM look ~25 cubic foot - that oughta get it into monster power - maybe a door for dual-use as confession booth at the plywood chapel?btw- would you have dimensions for the baffle spacing on version 1&2 or would the baffles be made movable for adjustments?
FreddyCoincidentaly, one of the next experiments will be to open up a trap door on the back of the cab so it can exhaust rearward into a corner, as well as frontwards. Actually, the whole rear panel at the last bend could be eliminated if this is successful. The Rev could place his head there, the confessor could place their's in the front horn mouth and proceed with various audio related confessions. Audio confessions only please! Organized religion can handle the other stuff, and this religion is anything but organized.
It's a good idea to allow for some baffle adjustment, especially at the back horn throat. When I added a front horn on the 15" EV, I opened the throat of the MM back horn up to the max, not that easy a job with a sawzall, and it would have been really tedious by hand. We originally asssembled the cab (douglas fir) with glue and 8 penny coated "sinkers", so modifications usually require a sawzall. Following recent discussions here, I would also allow for adjustment of the holes linking the top manifold section to the lower "S" bend. I can barely get my hand up in there, but I want to test the effect of restrictimng these holes. I suspect it would just lower the level of the back horn, but one never knows, do one? (as Fats Waller was fond of saying).
wonder how close RCA-Fan can sim Olson's BLHs to real reault and how dependent these designs were on certain parameters and low mass to play smooth?Freddy waiting for the holy Olson's return (via affordable books, and cabinet-plans/kits)
FreddyWell, to sim this puppy with any accuracy you'd have to: start with the back horn front chamber (a factor even in McBean's program); factor in the acoustic capacitance and inductance of the chamber following this; factor in the acoustic capacitance and inductance of both of the following "W" sections and their termination in acoustic abOhms; factor in the final "S" bend (which is probably the easy part, as I have found that alterations there don't have much of an effect) ; factor in the final mouth size termination. You'd have to build at least one model and measure it to establish these perameters. Following this, you could describe how this one example works, but if you begin changing the perameters around to a great degree, the tolerance of the sim will start to get fuzzy. Now you could spend your time fine tuning this and writing lots of code, or just making some sawdust and building another mate speaker. At a certain point, you have to wind up at the sawdust stage anyway. Maybe sometime in the future the speakers will be reviewed by the high-end magazines as computer simulations before they are even ever constructed and listened to. Time is money. "Hard times here, everywhere you go...": Skip James.
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