Personal Stereophonic Speaker System

Abstract

A self-standing personal stereophonic speaker system which employs a near field effect and includes in a preferred embodiment a rigid curved baffle frame supporting two opposed speakers each disposed in a plane of the frame, which planes intersect at an included angle measuring between 90.degree. and 120.degree. so that each speaker is in spaced relationship for receiving a listener's head therebetween within about two inches of the listener's ears so as to optimize the system for sound reproduction and excellent bass performance is disclosed.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a loudspeaker apparatus and more particularly to a personal stereophonic loudspeaker system.

2. Prior Art

Headrests which include loudspeakers are well known in the art and generally are shown as attachments for chairs for use in home enjoyment or in aircraft flight. Examples of such headrests are set forth in the following U.S. Pat. Nos.; 3,512,605; 3,384,719; 3,303,279; 3,290,450; 2,908,766; 2,501,993. There are a number of difficulties with such prior headrests, including the fact that they must be affixed to a chair, require mechanical contact between the listener's head and the headrest, include acoustic enclosures which create undesirable resonances, are often uncomfortable and do not provide high quality sound reproduction. Accordingly, there is a pressing need for an improved personal stereophonic loudspeaker system which is freestanding, thus allowing it to be used with any chair or sofa without mechanical attachment, which is comfortable to the listener, and which is free of enclosure resonances to provide the highest quality sound reproduction.

It is an object of the present invention to provide an improved personal stereophonic loudspeaker system having an improved bass performance.

A further object of the invention is to provide a loudspeaker system which is particularly comfortable for a listener, and which does not require mechanical contact with the listener's head for proper sound reproduction and utilizing a near field effect.

A still further object of the invention is to provide a loudspeaker system which does not have to be attached to a chair and which system is self-standing or freestanding.

SUMMARY OF THE INVENTION

In accordance with a disclosed preferred embodiment of the invention, a personal stereophonic loudspeaker system includes a rigid baffle frame and a pair of opposed loudspeakers mounted on the frame such that the front surface of each speaker defines a plane, which planes intersect at an angle from between about 90.degree. to 120.degree.. It is a feature of the invention that the loudspeakers are disposed on the rigid baffle frame such that a typical listener's ears will be about two inches from the front surface of the speakers. It has been found that by maintaining these two parameters the quality of sound can be greatly improved over the prior art, since the listener is now able to register or detect and receive a "near field effect" sound which greatly improves the listener's enjoyment and bass performance of the system.

There are many advantages of this invention which are set forth in a portion of the description of the preferred embodiment entitled "Advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the attached drawings wherein:

FIG. 1 is a side elevational view of a personal stereophonic loudspeaker system freestanding in accordance with the invention;

FIG. 1A is a perspective view of the personal stereophonic loudspeaker system of FIG. 1.

FIG. 2 is a top view of the personal stereophonic loudspeaker system showing a listener's head disposed within a curved baffle frame on which loudspeakers are mounted.

FIG. 3 is an exploded perspective fragmentary view of the personal stereophonic loudspeaker system showing a sound-absorbant disk which is mounted on an axis of each of the loudspeakers shown in FIG. 2; and

FIG. 4 is a circuit diagram of a portion of the equalizer network for each of the loudspeakers of the personal stereophonic loudspeaker system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Inasmuch as the present invention may be employed with a number of loudspeakers or speakers and associated audio-electronic equipment, the description of the present invention will be directed in particular to elements forming part of or to elements cooperating more directly with a personal stereophonic loudspeaker system in accordance with the invention. It should be understood that parts not specifically shown or described are selectable from those known in the art.

Referring now to FIGS. 1 and 1A, there is shown a personal stereophonic loudspeaker system 10 which is freestanding and includes a rigid curved baffle frame 1, a vertical support 2 which may be solid or laminated for resiliency and is fastened at one end to the baffle frame 1, and fixed to a block member 3 by means of bolts 4. The block member 3 is in turn fixedly secured to a base plate 5 which is flat and sufficiently narrow to fit between the back legs of a chair. The vertical support 2 includes adjustment holes 52 which may be used for adjusting the height of the baffle frame 1 relative to the base plate 5. Wires 6 are shown running along the vertical support 2 up to first and second loudspeakers 12 and 13 and are shown in more detail in FIGS. 2 and 3. The wires 6 are also connected to an equalizing network circuit 29 as shown in FIG. 4.

Referring now to FIG. 2, the rigid curved baffle frame 1 is shown to include two identical speakers or loudspeakers 12, 13 which are fixedly mounted on baffle frame portions 15 and 17 respectively of the baffle frame 1. Frame portions 15, 17 are formed in a V-shape so that the front surfaces of the loudspeakers 12, 13 and their respective frame portions 15, 17 intersect at an angle .theta.. It has been determined that optimum sound quality with excellent bass performance is obtained when the angle .theta. is within the range of approximately 90.degree. to 120.degree.. At the apex of the angle, .theta., a radius of curvature is formed by the frame portions 15, 17 at curved portion 9. The curved portion 9 of the frame 1 is slightly greater than the radius of the back of the average human skull or listener's head 8 so that the listener's head 8 is supported comfortably and may be at rest against the baffle frame 1, even though the frame 1 is rigid and may be made of a non-resilient material such as plastic or wood. The listener may of course choose not to rest his head 8 continuously against the frame 1, but in accordance with the invention, the sound produced will be of high quality in either case, whether or not the listener chooses to maintain mechanical contact with the frame 1 in a manner to be described hereinafter. The curvature of the frame 1 and the arrangement of the frame portions 15, 17 are such as to guide the listener's head 8 between the frame portions 15, 17 to a position substantially equidistant or midway between the two speakers 12, 13 to insure balanced sound reproduction and to utilize a near field effect, also to be described hereinafter.

Each of the speakers 12, 13 generate audio back waves and audio front waves in response to signals from an equalizer network circuit 29. Because of the shape of the baffle frame 1 and in accordance with an aspect of this invention, the ears 11 of the listener should be typically two or three inches from the speakers 12, 13, as shown by the dimension "d " to be in registry with the near field effect to be described hereinafter. Consequently, the front waves from each of the speakers 12, 13 are substantially stronger in the immediate vicinity of the listener's ears 11 than the back waves evan at low frequencies. Although the back waves are out of phase with the front waves at these lower frequencies and tend to cancel the front waves, the close proximity of the listener's ears 11 to the front of each speaker 12, 13 combined with the baffle effect of the curved plate frame 1 insure that the front waves are substantially stronger than the back waves in the immediate vicinity of the listener's ears 11. This phenomenon is called a "near field" effect and can be demonstrated conclusively if the listener moves his head 8 forward by more than a few inches; the low frequency response of this system 10 begins to drop off dramatically in this case. By using the near field effect in this manner, the several disadvantages of an enclosure as in the prior art to entrap the back waves (enclosure resonances, cost and the tendency of an enclosure to raise the resonant frequency of the speaker, thus limiting its bass response) are completely avoided.

It has been found that the self canceling effect of the front and back waves at a distance of approximately 2 or 3 feet from the system 10 provides an advantage since the speakers 12, 13 can produce sound within the system 10 without interference with other sound producing devices in the same room or area. In fact, persons electing not to use the personal stereophonic loudspeaker system 10 will not be annoyed by the system 10 since they would hear substantially no sound produced by the speakers 12, 13 even though they are in the same room with the system 10.

Referring now to FIG. 3, one of the speakers, namely, loudspeaker 13 is shown in some detail comprising a cone 18, a disk 22, a grill 23 and decorative cloth grill 24. The speakers 12, 13 are similar speakers. The cone 18 is a relatively small cone, approximately four inches in diameter. However, the invention is not restricted to this size of speaker and other size speakers may be used. Since cost and weight may be a factor in the preferred embodiment, the smaller speaker 13 is selected. The speaker 13 has some tendency at high frequencies (above 10,000 hertz) to emanate in a relatively narrow beam along the cone axis 26 of the speaker 13. This can be annoying to the listener if he turns his head 8 in such a way as to move in and out of these high frequency beams. To eliminate this problem, a disk 22 of acoustically absorbant material, for example, heavy felt, is mounted on the grill 23 along the cone axis 26 of the speaker 13 and far enough forward that it will not be struck by the cone 18 at its maximum excursion in accordance with the invention. The grill 23 may be either a plastic or metal mesh and also serves to protect the speaker 13 from accidental damage. The decorative cloth grill 24 has good acoustical transparency and is placed between the grill 23 and the frame portion 17. These three elements 22, 23 and 24 are held together by adhesive and the entire assembly is then joined by bolts 50 to the frame 17. In the preferred embodiment, a fairly open weave of rayon backed black velvet was used as the cloth grill 24 with good acoustical and esthetic results.

Referring now to FIG. 4, the personal stereophonic loudspeaker system 10 includes an equalizing network circuit 29, connected to the speakers 12, 13. The circuit 29 as shown includes two channels A and B. Since these channels are identical, only channel A has been shown in detail. The channels A and B of the circuit 29 are connected to the speakers 12, 13 by the lead wire 6. The channels A and B of the circuit 29 include volume control switches 30 which are coupled to work in unison to control the same volume in speakers 12, 13 respectively. The switches 30 are three-position switches which set the sensitivity of the speakers 12, 13 to a "normal" level, a "background" level at approximately 10 db below the normal level and a third "off" position. In the normal position, the switch 30 is electrically connected to resistor 31, and in a background position, it is connected to a resistor 32. The resistance parameter of the resistor 32 is selected to be greater than the resistance parameter of the resistor 31.

A capacitor Cl is connected in parallel with each speaker to control its high frequency response. The relative effectiveness of this capacitor Cl and hence the high frequency response of each speaker 12, 13 is determined by the resistance parameters of the resistors 41, 42, 43. The resistance parameters are selected such that the resistor 41 is greater than the resistor 42, which is greater than the resister 43. A three-position switch 40 removes both resistor 42 and resistor 43 from the circuit when placed in the "maximum" position. In this case, only resistor 41 is in series with capacitor Cl, the high frequency shunting effect of this network is minimized and the high frequency response of the speaker is at its maximum setting. Switch 40 may be used to place either resistor 42 or 43 in parallel with 41, thereby increasing the high frequency shunting effect of capacitor Cl and progressively reducing the high frequency output of the speakers 12, 13. The effectiveness of the high frequency response switch 40 is such that when the switch 40 is at the "max" setting, a response at 5,000 hertz is raised approximately 4 db. At the "min" position, it is reduced 5db from normal at this frequency. This high frequency response switch 40 duplicate the function of the tweeter level control found on most expensive high fidelity speakers, and does so simply and inexpensively.

The switches 30 are usually set at the normal position, however, since it may be desirable to reduce the sensitivity of the speakers 12, 13, particularly when loudness compensation is being used in the amplifier 27 in order to advance the amplifier volume control to a higher position and thus decrease the amount of compensation, the switches 30 may be switched to the "background" position. The sensitivity of the speakers 12, 13 may be decreased particularly when they are being used in conjunction with other conventional front speakers (not shown) to produce quadriphonic effects.

The high frequency response switch 40 may be adjusted to compensate for various amounts of high frequency content in the audio program material, or to set the high frequency response in accordance with the individual preferences of various listeners; some listeners prefer definition at even the highest frequencies while other listeners prefer a more mellow sound. Also when using the personal stereophonic loudspeaker system 10 as the rear speakers 12, 13 in a quadriphonic arrangement, it is sometimes desirable to reduce the high frequency response of the rear speakers 12, 13 relative to the front speakers (not shown) so that the sound sources appear to be in front of the listener while the ambience sound which typically has less high frequency content because it has been reflected from the interior surfaces of the concert hall comes from behind.

An additional advantage of this circuit 29 is that it raises the impedence of each of the channels A and B to approximately 40 ohms, so that as many as ten such systems can be connected in parallel across the output terminals 28, 29 of the amplifier 27 designed to drive speakers not lower than 4 ohms. Futhermore, the relatively high impedence of this circuit 29 allows these speakers 12, 13 to be used in parallel with conventional low impedence speakers for quadriphonic effects, without significantly increasing the loading on the amplifier 27.

The circuit 29 shown in FIG. 4 accomplishes the volume and high frequency adjustments by means of double-pole, double-throw toggle switches 30, 40, with center-off positions. Such switches 30, 40 are commercially available at inexpensive prices. Since both the volume switch 30 and the high frequency response switch 40 operate both channels A and B simultaneously, there is no danger of having the two channels A and B mismatched inadvertently because of improper settings.

ADVANTAGES

The described system 10 has been designed to produce very high quality sound for the individual listener.

Because the listener's ear is typically within 2 or 3 inches of the speakers 12, 13, the system 10 is able to take advantage of the "near field" effect. No enclosure is needed to trap the back waves. This feature avoids the resonances usually associated with enclosures, avoids raising the resonant frequency of the speakers 12, 13 as is typical with most enclosures, and thus gives a very smooth bass response down to the lower limits of audibility.

Since there is no enclosure, the "boxy" sound caused by enclosure resonances in the lower mid range is completely avoided, giving a very natural quality to the sound.

By operating in the "near field" of the speakers 12, 13, only modest power handling capability of the speakers 12, 13 is required. This permits the use of a single, small, wide-range cone speaker for each of the channels A and B, thus avoiding the need for separate woofers and tweeters to reproduce the entire frequency range. In addition to reducing the cost and complexity of the system, it also avoids cross-over interference which is typical of two-way speaker systems and which can cause uneven frequency response in the mild range.

Since the speakers 12, 13 are in close proximity to the listener's ears 11, the sound is not effected by the acoustics of the listening room or area. The uneven bass response of conventional speaker systems caused by standing waves in the listening room is completely avoided. The system has the additional practical advantage that it provides excellent sound quality even used out of doors, whereas conventional speaker systems are heavily dependent on listening room acoustics to provide full-bodied sound.

Since the listener is very close to the speakers 12, 13, they are typically operated at only a small percent of their rated power and thus are virtually distortion free.

The system 10 is inherently very efficient and requires only modest power from the amplifier 27. Measurements showed that concert hall levels (90 db) were produced in the vicinity of the listener's ear 11 with approximately 1 volt across the voice coil of each speaker 12, 13. Since these speakers 12, 13 have an eight ohm impedence, this measurement showed that concert hall levels were being produced with only one-fourth of a watt of electrical power into the speakers. The practical advantage is that this system 10 is capable of providing good sound levels with inexpensive, low-powered amplifiers.

An outgrowth of the inherent high efficiency of this system 10 is the fact that it can produce very high sound levels, approaching the threshold of pain if desired, with only modest amplifier power, and it does so with very little distortion.

The system 10 provides very little disturbance to others, even when the listener is experiencing high sound levels. Measurements show that at a distance of only 4 feet from the speaker system, the sound level is down 30 db. Thus, the listener can enjoy "concert hall levels" and yet the sound will be barely audible across the room.

Because of the V-shape of the baffle frame, the listener's head 8 is guided to the properly centered position midway between the two speakers 12, 13 for perfect stereo balance.

The radius of the curved portion 9 of the rigid baffle frame 1 supporting the speakers 12, 13 is such that the head 8 may be rested against the curved portion 9 and frame portions 15, 17 in complete comfort. Resiliency is provided by the "give" of the vertical support 2.

It is not necessary that the listener actually be in contact with the baffle frame 1 for good sound quality.

For stereophonic listening, nothing is required in front of the listener. This provides great freedom to the interior decorator and permits a listener's chair to be faced toward an adjacent window or in other orientations where there is little or no room for conventional speakers in front of the listener.

Since the speakers 12, 13 are outside of the listener's peripheral vision, he is not consciously aware of the presence of the speakers 12, 13 and is free to enjoy the music without a constant reminder that it is being mechanically reporduced.

Tests have shown that the speakers 12, 13 provide excellent performance as rear channel speakers in a quadriphonic arrangement. The decorating problem of trying to position four conventional speakers around a listener in an ordinary room is enormous; the use of the described system 10 along with another pair of conventional speakers (not shown) to handle the front channels greatly simplifies the problem.

Although the system 10 provides many of the advantages of high quality stereophonic headphones, it avoids the many disadvantages of headphones. There is no weight, heat or pressure on the listener's head. There is no wire connecting him with the amplifier 27. The described speaker system 10 does not completely block out other sounds within the room, and experience has shown that the listener can respond to conversation in the room by merely moving his head forward a few inches; it is not necessary to touch the volume control switch 30. Further, as noted above, the system 10 can be used as part of a quadriphonic arrangement, unlike conventional stereophonic headphones.

Since the sound drops off so rapidly with distance from the system 10, it is practical to have two or more systems in the same room reporducing entirely different program material without interference.

The freestanding arrangement of the baffle frame 1 does not require physical connection to the listener's chair. The baffle frame 1 is adjustable vertically to accommodate chairs of various heights.

The adjustable equalizing network circuit 29 is passive, requiring no power line connection and works in the output leads of an amplifier 27.

By means of the control switches 30, 40 in the equalizing network circuit 29, each listener adjusts the loudness and the high frequency response of the reproduced sound to his taste.

Because the equalizer network circuit 29 raises the impedence of the system 10 to approximately 40 ohms, a number of such systems 10 may be connected in parallel without damaging the amplifier 27. Further, a system may be connected in parallel with conventional low impedence speakers 12, 13 without adding significant loading to the amplifier 27.

By means of the volume switch 30 in the equalizer network circuit 29, the listener can adjust the volume of the system 10 relative to a pair of conventional front speakers so as to produce properly balanced quadriphonic effects.

By means of the high frequency switch 40, the listener can instantly adjust the high frequency content of the reproduced sound to accommodate program material of various quality or to aid in producing more satisfactory quadriphonic effects.

Because the system 10 is inherently very compact, it is particularly useful in close quarters, such as small apartments, mobile homes, boats and campers.

If the amplifiers 27 is located next to the listener's chair, the amount of wiring is greatly reduced, thus simplifying the installation.

The invention has been described in detail with reference to the preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention .

Claims

What is claimed is:

1. A personal loudspeaker system comprising:

a. a baffle frame,

b. near field effect means including first and second spaced opposed loudspeakers mounted on said baffle frame in cooperative relationship for deriving between said first and second loudspeakers, first and second near field effects proximal to said first and second loudspeakers respectively, in response to electrical signals applied to said first and second loudspeakers,

i. said first and second opposed loudspeakers being spaced apart to receive a listener's head therebetween so that the ears of said listener are in registry with said first and second near field effects of said first and second loudspeakers respectively, and

c. said frame having means for guiding and registering said ears of said listener with said first and second near field effects between said first and second loudspeakers.

2. The invention defined in claim 1 wherein said loudspeakers are disposed within approximately 2 inches of the listener's ears when the listener's head is positioned between said loudspeakers.

3. The invention defined in claim 1 wherein said baffle frame is a curved rigid frame.

4. The invention defined in claim 1 wherein said baffle frame includes means for centering said listener's head an equal distance from each of said speakers.

5. The invention defined in claim 1 further including a base means having a resilient support means connected to said baffle frame for resiliently supporting said baffle frame in a freestanding manner.

6. The invention defined in claim 1 further including a pair of acoustical absorbing pads positioned in cooperative relationship with said first and second loudspeakers to attenuate and diffuse high frequency components of said electrical signals when present in said near field effect.

7. The invention as set forth in claim 1 further including an amplifier having an output, circuit means having an adjustable low pass filter means and adjustable volume control means coupled to each of said loudspeakers for deriving said electrical signals,

i. said circuit means and said volume control means being connected between said output of said amplifier and said loudspeakers.

8. The invention as set forth in claim 7 wherein each of said low pass filter means includes a series resistor-capacitor circuit connected in parallel with said loudspeakers.

9. The invention defined in claim 1 wherein said first and second loudspeakers are disposed in a fixed spaced relationship to each other and each of which have front surfaces which define planes that intersect at an angle between 90.degree. and 120.degree..

10. A personal stereophonic loudspeaker system comprising:

a. a baffle frame,

b. resilient support means for resiliently supporting said frame in a freestanding manner,

c. first and second opposed loudspeakers mounted on said frame to receive a listener's head therebetween,

i said first and second opposed loudspeakers being mounted on said frame in cooperative relationship to derive a near field effect between said first and second opposed speakers in response to electrical signals applied thereto,

d. said baffle frame having means for guiding and centering said listener's head in a predetermined position between said loudspeakers, and

e. circuit means connected to said first and second opposed loudspeakers for controlling the intensity of an audio signal produced by said first and second loudspeakers.

11. The invention defined in claim 10 further including an amplifier having an output and wherein said circuit means includes means for adjusting the relative high frequency content of said audio signal produced by said first and second loudspeakers,

i. said circuit means being connected between said output of said amplifer and said first and second opposed loudspeakers.