As aforementioned in an enclosure system the loudspeakers are arranged in phase or in an acustical alignement allowing a linear transistion among the several frequency ranges.
As a matter of fact such frequency ranges are portions of the audio spectrum covering from: 30 - 100 Hz, 500 - 5000 Hz and 5000 - 20000 Hz, respectively low, mid and high frequency. In order to achieve a controlled transition between the several frequencies ranges an eletrical device called dividing network or crossover network is used.
Most enclosure systems use passive dividing networks which are connected between the amplifier output and the individual loudspeakers.
Active dividing networks are sometimes used for bi-amplification in sound reinforcement or recording studio applications.
Originally the first loudspeakers enclosures systems were develop for cinema or auditorium applications when were established the industrial technical standards. The early cinema system were one-way design consisiting of large exponetial horns which curved back themselves. The frequency response was limited covering no more than 100 to 5000 Hz.
Based on continuous researches the engineers soon developed many important tecnological innovations among them are: the woofers and high frequency drivers had three-inch voice coils. The high frequency drivers coils were made of flat wire and some desing used an annular slit phasing plug. In 1936, ALNICO, a new magnetic material appeared in the market. Due to its high coercitivy soon was employed for the manufacturing of loudspeakers cores. Around 1940 it was launched in the market the first two way coaxial loudspeaker.
In the early fifties with the birth of the stereophonic magnetic recording new types of loudspeaker enclosure were developed for the precise reproduction of the directivity effect created by the this recording technique. One of those types of loudspeaker enclosure was the accustic supsension developed by the american engineer Edgard Villchur.
Folded low frequency horn
Straigh, front-load horn
Folded-corner horn
The horn for the reproduction of the mid and high frequencies comprises an electro dynamic assembling where are located the coils and the magnet. Over the years many types of horns were developed as per shown in the here under mentioned pictures:
Several types of the bass reflex loudspeaker enclosure showing the tuning port.
a- straight horn
b - 45ºx90º radial sectorial horn
c- small exponetial horn
d- 40ºx60º conical horn
e- 30ºx60º multi-cell radial horn
f- bent horn
The first two way coaxial loudspeaker made in the USA by Altec-Lansing circa 1940.
In the left: the infinite baffle loudspeaker enclosure
In the right: the acustic suspension loudspeaker enclosure