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Rear loaded horn enclosures are the most common speaker cabinet for the Lowther driver (and maybe for other full range drivers as well). This design allows the mid and high frequencies to be radiated directly from the front of the driver, while the bass gets amplified by a horn whose throat is attached to the rear of the driver. The horn shape is tuned to emphasize bass. Because bass frequencies have a very long wavelength, the size of the horn needs to be large to cover low frequencies. A straight horn would be very
long, so bass horns are usually folded to fit into a smaller space.
The ideal shape for a horn is a round cross section, with a contour of either an exponential or tractrix shape. Round horns are difficult to build with conventional materials, so square or rectangular horns are often constructed. Square horns are actually quite difficult to build and so are usually only used in front loaded (front facing) applications. Rectangular horns are the most common. Most of the Lowther factory speakers are rectangular horns. These speakers have parallel walls, so the width of the rectangle is fixed. The height of the rectangle increases from small to large (from the throat to the mouth). Some people say that the parallel walls produce "colored" sound or ragged frequency response. Also most of these cabinets use flat wood to create the bends (curves) of the folded horn which might also color the sound. Multiple folds might also be a problem, a couple of speakers have only one fold. The Medallion enclosure represent a compact implementation of the rectangular horn design. It's compact size, modest cost and good sound makes it a particularly attractive cabinet for many home environments. Medallion II enclosures work best with the following Lowther or AT drivers: PM2A, PM5A, PM6A or PM7A |