Experiences with Horns
|I just thought
I'd relate some experiences I've had during my building of three pairs
of horns. If the reader please refer to THIS
PAGE for reference on the innards of a twin path corner folded
horn. You may have been there already; it has five B&W photos
taken during construction. As can be seen from the photos,
this is no easy task due mainly to the complex angles involved in the
wood cutting. However, if you got this far in the project, half
the battle is over as the drawings for the layout and folds can present
obstacles. The first bends above and below the throat, in the
initial front flares are the easiest; however, the second bends at the
rear can be confusing. Keep in mind that the walls, which form the
outside walls of the horn after the second bend, are mutually
perpendicular and fixed. They, in conjunction with the vertical
sides of the air chamber must maintain an exponential flare consistent
with the cutoff frequency and terminate in a mouth opening whose area is
equal to or larger than 1/8 the required mouth area for the selected fc,
If the size of the horn has to be altered, remember, anything that is changed will have an effect on the entire horn. It's like the domino effect. If the sides of the chamber have to be altered to maintain an exponential flare with the walls, then obviously the chamber volume is changed. If changed to become larger, the chamber can be filled to correct the internal volume; if smaller, you're S.O.L. :) Also, changing the vertical chamber sides will change the flare rate of the of the horn path above and below the air chamber. If Lady Luck is with you, and you have to reduce the chamber volume by moving the vertical chamber sides, you might be able to move the upper and lower chamber sides up and down respectively to increase the volume and be within the limit of maintaining the flare above and below the air chamber. This can be adjusted by redesigning the portions of the mid section of the horn path that are labeled face 12a, 13a & 14a shown on the photos, HERE.
In the photos, you'll notice two trapezoidal openings on each side of the throat and outside the boundaries of the initial flare. These open into the air chamber in which the driver is mounted to add volume, as invariably, the chamber will always come out to be too small by itself. Also, accounting must be made for the volume occupied by the magnet assembly and the frustrum of the cone.
If after much juggling around with the drawings proper flare can't be maintained there are still avenues available off the main road of apparent despair. Usually, as has been my experience, the flare will terminate too soon. By that, I mean that you'll reach the mouth long before you reach the required area for it. Before redesigning the whole horn, there is one thing that should be considered that will usually work, the multiple flare. This requires a chapter unto itself.
Horn Theory - Chapter Index