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Re: Anyone know dimensions for Olson rear horn rectangular enclosures?

Hi John

Sorry I'm late : ) If you scale the backloaded horn design (from Olson's patent # 2,224,919) up to accomodate your 15" driver, you would wind up with a cabinet about 65" tall. As DJK observes, the original design was for an 8" driver, implying a cabinet about 36" tall. A 65" tall cab would put the center of your driver's coaxial horn at about 55" high. You could easily (?) raise your current OB rig up to this height to see if this will be a problem from your listening position. If not, and you're not put off by a 65" tall box in your listening room, this backloader has some possibilities. Most modern backloaded designs use a narrow profile in the vertical dimension to push the Diffraction Loss/Baffle Step as high as possible, and this design would fly contra to this, with a cab front about 45" wide. The baffle step would in this case be about 100 Hz, where the 15" direct radiator would start to lose it's ability to load the baffle. The design Olson pictured in the 1936 JAES (?) which is the somewhat similar double loader in the patent, had a crossover about 200 HZ or less (where the output of the front and rear of driver crossover into each other). You should be able to adjust this down by modifying the air chamber on the back of the driver (i.e.: making it larger). It's hard to say how much volume you would need here to get it down around 100 Hz, the usual formulas asume a strait horn, and the backloader has several bends which add a muffler effect to the output. Let's say that you find a compromise somewhere you are satisfied with, or just let the crossover fall where it may (probably about 180 Hz), just how low will this beast go? The path of the back horn would be about 150", which should be good for about 45 Hz. The horn mouth would come out to about 202 sq. inches, which should get it down to about 66 Hz. This mouth seems a bit small to me. I would modify the design so that the area below the top manifold, that is to say the final "S" bend, more resembles the double loaded design. So angle the top baffle in the lower end down, and move the last baffle board up at an angle so that you increase the size of the horn mouth as much as you can. To visualize all this, just overlay the bottom part of the double loader onto the top section of the backloader, and adjust the bottom floor up a bit. There is also a possiblilty of opening up a trap door on the back of the cabinet to get more mouth area, which may be useful if there is a corner in the room nearbye for the horn to exhaust into, you can definitely get some more bass extension this way. An interesting project! BTW, I fixed my scanner. The next step is how to attach a scan to an e-mail, which was quite simple when I sent Fred that stuff a few years ago, perhaps less so on OSX. I'll try to get some drawings to you soon.

Good luck in your search!

Paul


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