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Original Message
RE: When does tweeter "waveguide" become horn bandpass device?
Posted by Bill Fitzmaurice on June 3, 2020 at 12:09:43:
Any time you have a chamber between the diaphragm and horn throat that chamber is a low pass filter, making the horn a bandpass. One of the functions of horn phase plugs is to minimize the size of the throat chamber, which minimizes the bandpass effect. If you imagine the amount of space between a driver cone and the horn throat you can understand why the bandpass effect is so much greater with a cone driver versus compression driver. I use phase plugs in my cone woofer loaded midbass straight horns to reduce the throat chamber volume and improve high frequency response.
With a typical wave guide used with a dome tweeter or midrange the throat is at least as large as the dome, so there's no throat chamber and therefore no bandpass effect per se. However, when the throat is a wavelength or more in dimension there's no horn loading of the driver, it acts like a direct radiator above that frequency. That results in the lower end of the pass band having gain, while the upper end does not, so here again you'll get the best results with a tweeter that's not flat to begin with.