Acoustic Rear Radiation Absorption for Loudspeaker Systems

The present invention relates to loudspeaker systems, and more particularly, to an improvement which allows a loudspeaker system to more accurately reproduce the recording site ambience inherent in a recording and which also allows more accurate and natural imaging, i.e., more exact localization of voice and instrumental placement within the soundfield of a pair of stereo loudspeakers.

One of the desirable characteristics of a modern state of the art stereo system is the ability to create a sense of the listener being at the actual musical performance. A major factor in this is the degree to which the amience, i.e., the natural reverberation or echos of the recording hall where the music was played and recorded, can be heard. It is obvious that it would be desirable to eliminate the reflections produced within the listener's room, as such reflections mix with and confuse those in the recording. These listening room reflections reach the listener from a different direction than the direct sound from a loudspeaker, and thus, they also confuse the image placement in the soundfield. Many listeners, and advanced hi fi buffs in particular, have installed sound absorptive damping foam, made specifically for this purpose, on their listening room walls to eliminate reflections and achieve more natural sound. As is discussed in more detail below, the present invention uses foam or other acoustic absorptive material directly as an integral part of the loudspeaker system to acieve this purpose even more effectively.

It is important to distinguish the present invention from prior art loudspeaker systems wherein sound damping foam or the like is located within the speaker housing. Examples of such systems are disclosed, for instance in U.S. Pat. Nos. 4,161,995 (Pohlmann et al); 4,881,850 (Bonn); 3,512,605 (McCorkel); 3,720,285 (Russell et al) 4,286,688 (O'Malley); 3,944,020 (Brown); 3,982,607 (Evans); and 4,051,689 (Stallings, Jr.). Systems of this type are designed to absorb sound produced within the loudspeaker housing and obviously do not have any effect on sound coming from the front of the speaker, and clearly do not provide the advantages of the present invention discussed above, and below.

Because, as discussed above, the greatest problems occurs from the sound reflecting off the wall behind the loudspeaker, the present invention is concerned with preventing any significant amount of sound from radiating to the rear of the loudspeaker in the first place. In this regard, tests have shown that stoping the problem at the source, rather than trying to prevent the reflections after the sound hits the wall is much more effective and requires much less absorptive material.

Generally speaking, the invention involves mounting or supporting sound absorptive damping material directly on the loudspeaker housing or cabinet so as to absorb the rearwardly directed sound waves. In a specific preferred embodiment, sound absorbent foam material is mounted on both sides of the loudspeaker housing. This sound absorbing material serves to absorb the sound radiating in the rear 180 degrees of the loudspeaker radiating angle, i.e., the rear half, so that this sound never reaches the rear wall, and the rear wall reflection problem is effectively eliminated. It is important to note that the purpose of this foam absorptive material is to eliminate the above noted problems and not to prevent loudspeaker cabinet reflections themselves, which can be eliminated with thin foam covering on the front of the loudspeaker cabinet.

Other features and advantages of the invention are set forth in or will be apparent from the description of a preferred embodiment below.

The single FIGURE in the drawing is a schematic plan view of a loudspeaker system incorporating sound absorptive foam material, in accordance with the present invention.

Referring to the drawing, a conventional loudspeaker system is indicated at 10 which basically comprises a loudspeaker 12 and a cabinet or housing 14. As indicated, sound radiates 360 degrees from central loudspeaker 12 and to absorb rearward sound, i.e., sound transmitted to the rear 180.degree., the loudspeaker system 10 is flanked by sound absorptive foam material blocks 16 and 18 located on both sides thereof. In an exemplary embodiment, the size of each foam block 16 and 18 is 48" tall, 10" thick, and 12" wide. As illustrated in the drawings, the size of each foam block is shown to be on the order of the size of the housing 14. The blocks 16, 18 are attached to the sides of the cabinet loudspeaker 14, and a top and bottom extend to the edge of the foam. For the sake of appearance, the entire assembly is covered with an acoustically transparent grill cloth 20.

As can be seen from the plan view shown in the drawings, the sound radiating to the rear is absorbed in the foam 16, 18 thus preventing reflection from the wall behind the loudspeaker system 10. This eliminates to a large extent, the listening room reflections, and allows the listener to better hear the natural recording site reflections and ambience inherent in the music, thereby resulting in more natural music reproduction. Further, as stated, the elimination of such reflections improves image location and resolution of the musical detail.

Although the invention has been described relative to an exemplary embodiment thereof, it will be understood that variations and modifications can be effected in this exemplary embodiment without departing from the scope and spirit of the invention.