Midwoofer-tweeter-midwoofer
The D' Appolito configuration describes various rules for the construction of loudspeakers, which concern both the arrangement and the control of the individual speakers.
For speakers that are built on a D' Appolito configuration, two deep middle or midrange are arranged symmetrically above and below the tweeter and operated in parallel. So both emit the frequency range up to the cutoff frequency of the tweeter. Characterized the radiated sound components up and down can be minimized due to phase shifts and related interference effects. The reduction of sound reflections on ceiling and floor should lead to a significantly better spatial resolution. Especially with home theater systems boxes are found with D' Appolito arrangement, since the still wide horizontal dispersion for multiple listeners seems to make sense.
The D' Appolito configuration was developed by the American Joseph D' Appolito as he was concerned with how one could increase the maximum sound pressure level (efficiency ) of the satellite system Linkwitz to have to accept without sacrificing quality. In a "real" D' Appolito arrangement of the distance between the two centers of the midrange diaphragm must not be greater than two -thirds of the wavelength of the crossover frequency of midrange and tweeter. Thus, according to D' Appolito the optimum of the Abstrahlverhältnisses is achieved. It comes in the crossover to form a single main lobe, which allows listeners to change over the entire horizontal area of their listening position, without fear of loss of sound. Another criterion for the D' Appolito arrangement is a crossover separation with odd order. Normally, acoustic high - and low-pass 3rd order are used and thus achieves a 18 -dB isolation.
An unfortunate interpretation of this concept are " lying " D' Appolito Center, as they can be found in manufactured speakers very often. This bundle horizontally strong and uneven. By dominated by interference radiation such a construct sonicated mainly the seated in the middle of the audience as well as the ceiling and the floor. The rest of the audience had to be satisfied with a quiet and bass and höhenlastigem sound and consequent low intelligibility. The advantage of this type of center that they can be a space-saving set at or below a television. Furthermore, corresponding to the horizontally symmetrical arrangement of the chassis aesthetic point of view.
Many speakers that look for the same size chassis above and below the tweeter in such a way as if they were two -way D'Appolito speakers are actually ordinary 2 ½ -way speaker. Instead of two midrange speakers have a woofer and a midrange speaker. The midrange so only one chassis is active, thus the proposed D' Appolito bundling is not given. Also alleged D' Appolito centers are often 2 ½ -way speaker equally bundling effect.
Example calculation
Wavelength:
In meters, c - speed of sound in air 340 m / s, f - frequency in Hertz.
Changed to the principle of D' Appolito the formula would be
Where d = distance between the centers of the midrange.
If, then, the distance ( d) of the centers of the two midrange 21.5 cm ( 0.215 m, which corresponds approximately to the distance resulting from the use of two 4 -inch speaker and one tweeter with 9 cm front panel), one would expect:
( rounded).
The crossover frequency between the midrange and tweeter would be equivalent to about 1054 Hz, which is practically difficult to achieve since there are only few separate tweeters so deep. Are more realistic crossover frequencies above 2000 Hz
In general, a real D' Appolito arrangement is very difficult to maintain, since the tweeter is usually much too large and thus the distance between the two midrange is further apart than allowed by the formula. Although many HiFi speakers boast manufacturer to develop speakers to D' Appolito, there are only very few "real" D' Appolito boxes. Non-compliance with the principle leads to interference in the midrange and thus to an uneven dispersion in the vertical direction due to the widely spaced chassis centers.
D' Appolito itself does not keep strictly to this rule, as can be seen for example in his self-developed reference home theater system.