D'Appolito arrangement

The D'Appolito arrangement describes various rules for the construction of loudspeakers , which affect both the arrangement and the control of the individual loudspeaker chassis.

Loudspeakers in D'Appolito arrangement

history

Since the late 1960s, loudspeaker configurations based on the "(low) midrange-high frequency (low) mid-range" pattern (in English 'midwoofer-tweeter-midwoofer' or 'MTM' for short) have been known. The spatial deviation of the radiation from the midrange and tweeter from one another was difficult to handle .

The radiation pattern can be imagined as a "radiation lobe" (referred to in English as 'acoustisc lobe'), it varies at certain frequencies and is directed past the listening position (with several loudspeaker chassis) when the loudspeaker is viewed from the side. The directional characteristic of a combination of two or more chassis is above and below the listening position in a "standing" arrangement (vertical), and in a "lying" arrangement (horizontally) past the side. This “tilting away” of the radiation from the center occurs even with normal two-way speakers in a “(low) mid-range-high frequency” configuration (“Midwoofer-Tweeter”, “MT”), and leads to a distortion of the radiation at a certain level Crossover frequency between the loudspeaker chassis. This can be counteracted by spatial arrangement of the chassis on the front of the housing (e.g. relocation) and time alignment with one another (see also loudspeaker box # types of loudspeaker fronts ).

The D'Appolito arrangement was developed by the American Joseph D'Appolito . He dealt with how the maximum sound pressure (efficiency) of the satellite system according to Siegfried Linkwitz could be increased without having to accept any loss of quality. D'Appolito presented his findings in 1983 at a conference of the Audio Engineering Society in New York.

Conventional MTM construction

Many loudspeakers that look like 2-way D'Appolito loudspeakers because of the same size chassis above and below the tweeter are actually ordinary 2½-way loudspeakers . Instead of two woofers, they have one woofer and one woofer. In the midrange, only one chassis is active, which means that the bundling proposed by D'Appolito is not given. Also supposed "D'Appolito-Center" (loudspeakers for the center channel in a surround sound multi-channel arrangement, like in the home theater) are often normal 2½-way loudspeakers without a pronounced bundling effect.

D'Appolito construction

In the case of loudspeakers based on a D'Appolito arrangement, two woofers and midrange drivers are arranged symmetrically above and below the tweeter and are operated in parallel . So both radiate the frequency range up to the frequency of the tweeter. This minimizes the sound components radiated upwards and downwards due to phase shifts and the associated interference effects. The reduction of sound reflections on the ceiling and floor should lead to a significantly better spatial resolution. There is a vertical bundling effect (similar to a “point radiator”), which is more directed towards the listening position. Floor-standing speakers with a D'Appolito arrangement (typically with 'THX' certification) are found in home cinema systems in particular, as the broad horizontal radiation makes sense for several listeners.

In a “real” D'Appolito arrangement, the distance between the two membrane centers of the midrange drivers must not be greater than two thirds of the wavelength of the crossover frequency between the midrange and tweeter. According to D'Appolito, this achieves the optimum in the radiation ratio. In the area of the crossover frequency, a single main beam is formed, which allows the listeners to change their listening position over the entire horizontal area without having to fear loss of sound. Another criterion for the D'Appolito arrangement is a loudspeaker crossover with an odd order. Normally, 3rd order acoustic high and low pass filters are used to achieve an 18 dB separation.

Horizontal arrangement

An interpretation of this concept that does not correspond to the purpose is "lying" D'Appolito centers, as they are very often found in prefabricated loudspeakers. These bundle horizontally strongly and unevenly. Due to the radiation characterized by interference, such a construct mainly covers the listener sitting in the middle as well as the ceiling and the floor. The rest of the audience has to be content with quiet, bass and treble-heavy sound and the resulting poor speech intelligibility. The advantage of this type of loudspeaker is that it can be placed on or under a television to save space while preserving acoustic symmetry. Furthermore, the horizontally symmetrical arrangement of the chassis corresponds to aesthetic considerations.

Sample calculation

Wavelength:

${\ displaystyle \ lambda = {\ frac {c} {f}}}$

( is the wavelength, the speed of sound in air (approx. 340 m / s), the frequency .) ${\ displaystyle \ lambda}$ ${\ displaystyle c}$ ${\ displaystyle f}$

The formula would then be converted to the principle of D'Appolito

${\ displaystyle f \ leq {\ frac {2 \, c} {3 \, d}} \ ;,}$

where the distance between the centers is the midrange. ${\ displaystyle d}$

If the distance (d) between the centers of the two mid-range speakers is 21.5 cm (0.215 m, which roughly corresponds to the resulting distance when using two 4-inch chassis and a tweeter with a 9 cm front panel), one would calculate :

${\ displaystyle f \ leq {\ frac {2 \ cdot 340} {3 \ cdot 0 {,} 215}} = 1054}$ (rounded).

The crossover frequency between midrange and tweeter would be around 1054 Hz, which is difficult to achieve in practice, as only a few tweeters can be separated so deeply. Crossover frequencies above 2000 Hz are more realistic.

As a rule, a real D'Appolito arrangement is very difficult to adhere to, as the tweeter is usually much too big and the distance between the two mid-range speakers is therefore further apart than the formula allows. Although many speaker manufacturers boast of developing D'Appolito loudspeakers, there are very few “real” speakers in this arrangement. Failure to adhere to the principle leads to interference in the midrange due to the further spacing of the chassis centers and thus to uneven radiation behavior in the vertical direction.

literature

Joseph D'Appolito: Testing Loudspeakers. Audio Amateur Press Peterborough, NH 1998, ISBN 978-1-882580-17-0 .

Web links

Joseph A. D'Appolito: Geometric Approach to Eliminating Lobing Error in Multiway Loudspeakers . 74th AES Convention, New York 1983 ( AES E-Library)
A Presentation by Joseph D'Appolito at Audio Video Design (English)

Individual evidence

↑ aes.org
^ ^A ^b Douglas Self: Design of Active Crossovers. 2nd ed., Taylor & Francis 2018, ISBN 978-1-351-74146-0 , p. 33 f. (English, restricted view: books.google.com ).
^ Thomas Görne: Sound engineering. 4th edition, Hanser Verlag 2014, ISBN 978-3-446-44149-1 , p. 293 (restricted view: books.google.com ).
↑ Thom Holmes: Routledge Guide to Music Technology. Routledge 2013, ISBN 978-1-135-47780-6 , p. 67, (English, restricted view: books.google.com ).
↑ Why recumbent D'Appolito centers don't work - Donhighend Audio.

[1] s.org

[SelfCrossovers-2] A ^b Douglas Self: Design of Active Crossovers. 2nd ed., Taylor & Francis 2018, ISBN 978-1-351-74146-0 , p. 33 f. (English, restricted view: books.google.com ).

[GörneTontechnik-3] Thomas Görne: Sound engineering. 4th edition, Hanser Verlag 2014, ISBN 978-3-446-44149-1 , p. 293 (restricted view: books.google.com ).

[RoutledgeGuide-4] Thom Holmes: Routledge Guide to Music Technology. Routledge 2013, ISBN 978-1-135-47780-6 , p. 67, (English, restricted view: books.google.com ).

[HeimkinoCenter-5] Why recumbent D'Appolito centers don't work - Donhighend Audio.