Multichannel loudspeaker enclosure

The multichannel loudspeaker enclosure of the invention comprises an inner part which is realized taking into account only the mechanical and electroacoustical performance of the sound reproduction elements and which consists of a metal framework defining one cell per channel, with a single module being arranged in each cell an being elastically attached to said framework, each module being suspended in its cell by means of two cables in such manner that said module can move like a pendulum in the direction of the axis of the loudspeaker contained in said module.

This invention relates to a multichannel loudspeaker enclosure. It applies 
to all sound reproduction systems, more particularly to high-fidelity 
units. 
In high-fidelity units now commercially available, the reading 
devices--such as turntables with a tangential pick-up arm, magnetic-tape 
readers and, since recently, laser reproduction turntables--and the 
amplification and correction devices have reached a quality standard that 
is quite satisfactory. This is not always true as regards the terminal 
stage constituted by the loudspeaker enclosures. 
The walls of loudspeaker enclosures are practically always liable to 
vibrations that distort the reproduction of sound performed by the 
loudspeakers included in the enclosures. This defect is known as 
coloration. 
These wall resonances are induced by vibration forces having two main 
sources. 
First, the motive force that controls the diaphragm vibrations of each 
loudspeaker in order to produce sound is transmitted, by reaction, to the 
body of the loudspeaker and to its points of attachment to the enclosure. 
The force spreads to all the enclosure walls by the effect of 
conductivity. 
Further, the air pressure fluctuations occurring within an enclosure as a 
result of the rear sound wave produced by each loudspeaker generate 
distributed forces that act directly on all the walls. 
Because of the large area of the enclosure walls compared with the small 
area of the loudspeaker diaphragms, even vibrations of very small 
amplitude alter considerably the characteristics of the reproduced sound. 
The resulting quality degradation in the reproduction of sound is further 
increased by the trailing effect of the vibrations, that is, the time of 
their persistence--which varies with the damping coefficient of the 
materials involved--after the excitation that generated them has 
disappeared. Thus, in music passages where sounds vary quickly in pitch 
and intensity, some sounds, hence some notes, are masked by trailing 
interfering vibrations that were generated during the reproduction of the 
preceding sounds. This results in a woolly-effect in the reproduction of 
sound, with poor fidelity of the quality of the instrument tones and poor 
stereophonic location. 
In addition to such undesired vibrations of the enclosure walls, the 
loudspeakers themselves behave unsatisfactorily, vibrating along with the 
walls and acting the ones on the others. Then, the body of each 
loudspeaker no longer represents the fixed reference with respect to which 
the diaphragm has theoretically to move. This causes detrimental effects 
including a reduction of dynamics, the occurrence of crossmodulation and 
the creation of diaphragm resonances in frequency ranges where the 
diaphragm is not supposed to be operated. 
It is therefore desirable to design a loudspeaker enclosure that will avoid 
the generation of spurious vibrations therein or, at least, that will 
substantially limit the amplitude of such vibrations. as is well known, 
said amplitude depends mainly on the mass, the stiffness and the damping 
coefficient of the materials employed. Ideally, loudspeaker en closures 
should therefore be constructed with very heavy and perfectly stiff 
materials with additionally a high damping coefficient. This, however, is 
hardly compatible with the requirements of easy manufacture and transport, 
not forgetting the aesthetics of the final product. 
The purpose of the invention is therefore to provide a loudspeaker 
enclosure that will avoid the above-mentioned disadvantages. 
One particular feature of the loudspeaker enclosure according to the 
invention is that the inner part of the enclosure comprises one distinct 
module for each loudspeaker, each module being flexibly connected to a 
supporting framework laid on the floor. The aesthetic outline of the 
enclosure is obtained in an absolutely independent manner owing to an 
external housing.

Referring now to FIGS. 1 and 2, there is going to be described an example 
of embodiment of the inner part of a three-channel loudspeaker enclosure 
using electro-dynamic loudspeakers and designed according to the 
invention. 
The arrangement shown in FIG. 1 consists of a framework (1), possibly made 
from metal section bars, which delimit three cells (2, 3, 4). Inside each 
one of the three cells there is arranged a module (5, 6, 7), each 
including a single loudspeaker (8, 9, 10). Within its cell, each module is 
suspended by means of two thin cables (11-12, 13-14, 15-16), made 
preferably of steel, in such manner that the module will be able to move 
like a pendulum in the direction of the axis of the corresponding 
loudspeaker, as shown by arrow 17 in FIG. 1. 
This way, no vibration resulting from the axial electro-magnetic force that 
drives the loudspeaker diaphragm can be transmitted to the framework (1), 
hence to the other modules. The vibrations of the walls as a result of air 
pressure fluctuations within the module are symmetrical with respect to 
the other two axes normal to the loudspeaker axis. These vibrations 
counterbalance one another and their resultant effect is nil. 
Each module is made of a specific material or combination of materials, Its 
dimensions are chosen in consideration of its field of application, more 
particularly of the range of frequencies of the sounds the loudspeaker 
contained therein is expected to reproduce. The material is so chosen that 
its mass and stiffness in combination with the dimensions of the module 
will determine the resonance frequencies of the module to lie outside said 
range of frequencies of the sounds to be reproduced. This way, said 
resonance frequencies cannot be excited. 
The module suspension method enables positioning each module optimally in 
relation to the other modules, hence solving the electroacoustic problems 
encountered in loudspeaker enclosures of known types. The suspension 
method makes it possible to adjust the height and orientation of each 
module so as to optimize the acoustic radiation lobes. Each module can 
also be adjusted in depth so as to obtain an aggregate phase coherence 
between the loudspeakers. 
Such position adjustments are critical in high-grade loudspeaker enclosures 
however, they cannot obviously be achieved easily in known-type enclosures 
where the cabinet is used as the loudspeaker supporting structure. 
In the diagram of FIG. 3, there is shown an example of embodiment of an 
attachment and adjustment device for the steel cables designed to suspend 
the modules shown in FIGS. 1 and 2. 
The device of FIG. 3 consists of a metal piece (18) cylindrical in shape, 
with its lower part being extended by another cylindrical, concentrical 
piece (19) of smaller outside diameter, i.e. about half the outside 
diameter of the upper part (18). The aggregate block includes a central 
bore (20). 
The smaller diameter cylindrical part (19) is inserted into a hole provided 
in the relevant cross-piece of the framework (1). The steel cable (12) is 
threaded through the central bore (10) where it is held in correct 
position by means of a radial tightening screw (22). 
The other end of the suspension cable is attached the same way. Once the 
required adjustments have been made, the length of cable that protrudes 
beyond the top of the cylindrical part (18) is cut a few millimeters above 
said part (18). For obvious reasons of reliability, the remaining top 
length of cable is provided with a bulging end of larger diameter than the 
diameter of the bore (20). The bulging end can be obtained, e.g., by means 
of a soldering point (23). 
As can be seen from FIG. 4, the loudspeaker enclosure according to the 
invention also includes an external part or cabinet (24) having its inner 
walls covered with an absorbing material. The purpose of this material, 
which may be felt, is to attenuate any possible residual radiation from 
the inner part walls (FIGS. 1 and 2). 
According to a preferential embodiment of the invention, the cabinet (24) 
is manufactured separately and, once completed, it is slipped over the 
metal framework (1) from the top, in the manner of a hood. 
Owing to this procedure, and quite independently of any technical 
consideration--whether mechanic or electroacoustic--in achieving the inner 
part (FIGS. 1 and 2), the cabinet can be chosen only in terms of its 
aesthetical appearance, thus allowing finally an acoustic baffle that will 
match its environment while offering optimal sound reproduction qualities. 
It is to be understood that the foregoing description has been given only 
as an unrestrictive example and that many other embodiments may be 
considered without departing from the scope of the invention.