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In the Forum: Horn-Loaded Speakers
In the Thread: Midbass Horns and Real Estate.

Post Subject: It is not difficultPosted by anthony on: 10/19/2015

xandcg wrote:
Many thanks!

How do I calculate horn mouth, cycles and length?

The required full-mouth radius of a circular horn is given when the circumference of the mouth equals the full wavelength of the frequency in question. So given that 40Hz has a wavelength of 860cm, the Radius = 860/pi/2 = 136.9cm. Calculate the area of a circle (Area = pi.rad.rad) and then you have the full mouth area (in this case 58855cm2). From there you can divide that area any way you like (within reason) to get the square or rectangular or other dimensions of a full mouth horn.

To horn load you need a horn with a length that is at least as long as a quarter of a wavelength of the lowest frequency you want to load. So, 40Hz = 860cm wavelength, so the horn needs to be at least 215cm (860/4) long. From the perspective of sensitivity gain a longer horn is better and maximum efficiency is gained when the horn is one wavelength long.

Regarding full-mouth vs half-mouth vs quarter-mouth horns, they can all be used in different circumstances. Full-mouth when radiating into open space; half mouth when radiating into 2pi space (i.e. along a ceiling or a floor); quarter-mouth when radiating into 1pi space (i.e. when radiating along two surfaces such as a wall and a floor).

Hope this makes sense.

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