The Folded Horn Speaker Enclosure
From ancient times the special properties of the horn as an acoustic amplifier have been appreciated. It has been used widely in musical wind instruments and public address systems. The horn can also be used for some hi-fi reproducers of music.
If the loudspeaker cone is placed at the beginning of a duct that has an increasing area along it’s length, it first moves one small slice of air with a small volume. This moves an adjacent one of slightly larger area, which moves one that that is larger still, and so on. The final slice actuates the free air at the end of the duct, of considerably lager volume than the original driver. The horn also has a better dispersion quality than many normal drivers.
Manufacturers such as JBL have used their knowledge of Public Address systems to utilise flared horns with compression tweeter drivers in hi-fi speakers such as the £850 SVA1600.
However, for domestic bass applications, a full size horn is terribly impractical. To accommodate such a design, the horn must be folded. This way the available space is used effectively. There are numerous methods of folding the horn. These types of enclosure are often termed ‘bass bins’ and are more commonly used in Public Address situations where large amounts of bass are required with huge enclosures without the need for combined higher frequencies.
The waves directly emerging from the front of the driver can also be released to hear mid and higher frequencies. Those without direct radiation would need additional drive units mounted separately to handle frequencies above around 500Hz.
These designs require a lot of complex woodwork and a large amount of material.