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Is a horn with a length of less than 1.67 meters a bandpass enclosure or a horn?

A horn with a path less than 1.67 meters works as both a horn with a high cutoff point and as a bandpass type enclosure. The driver has a rear chamber, a front expansion chamber and a horn, all these functions are those of a 4th order bandpass enclosure as well, the horn acting as a tapered port in this case. The enclosure can be designed as a horn with the wl fo point well above the desired fo, or as a bandpass enclosure using a tapered port. Both routes will yield results that are very similar and altering the operating conditions in one enclosure type will show very similar changes to the response in the other enclosure type. Any reflex port can be tapered just as long as its overall length is not changed and the internal volume remains the same. Below are some observations about tapered ports and there use
1) A tapered reflex port may be viewed as two back-to-back horns operated well below their [fo]. Here, phase velocity is infinite and the air inside the horns moves back and forth as a unit. In this setting, it is treated as an acoustic mass [kg/m^4].

2) The effective volume of air extends beyond the ends of a port. If the ends are flared, the end corrections will be larger as they are determined by aperture area and the absence/presence of an adjoining surface.

3) If the volume of air is surrounded by a minimal surface, that by definition is required to be smooth, then airflow resistance will also be at a minimum and radiating efficiency (from both port apertures) will be maximized. Bottom line is that the port should be circular in section and flared at both ends in a manner as smooth as possible. The geometric object that accomplishes this is a full catenoid, i.e. two horns (cantenoidal) joined at the throat.

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