WO1990007252A1

WO1990007252A1 - Stereo sound system

Info

Publication number: WO1990007252A1
Application number: PCT/US1989/005843
Authority: WO
Inventors: Raymond C. Cannavo; Cletha J. Cannavo
Original assignee: Cannavo Raymond C; Cannavo Cletha J
Priority date: 1988-12-20
Filing date: 1989-12-20
Publication date: 1990-06-28
Also published as: AU4834090A

Abstract

An improved sound output system includes a primary amplifier (12) having an audio output (14), main speaker (18) connected to the audio output, an attenuator (26) connected to the main speaker for producing a low-level attenuator output, an auxiliary amplifier (32) operatively connected to the attenuator output, and an auxiliary speaker (38) operatively connected to the auxiliary amplifier (32). The connection of the attenuator input directly to the main speaker input provides a particularly useful combination whereby the audio output of a primary amplifier that is designed for driving a speaker is used for that purpose, yet greatly enhanced output is available from the auxilairy amplifier and speaker, without introducing significant distortion. The attenuator input can be provided with a frequency-responsive filter for operating the auxiliary amplifier and speaker within a desired frequency range. The system can have a crossover network for separating frequency components of the primary amplifier, main speakers of appropriate frequency response being connected to different frequency response outputs of the network, the attenuator input being directly connected to one of the main speakers for feeding a desired composent of the amplifier output to the auxiliary amplifier. Low, mid, and high frequency enhancement is provided by separate auxiliary attenuator, amplifier and speaker components. A slight delay between the primary amplifier and the output of the auxiliary amplifier permits high levels of sound output but with reduced potential for listener discomfort.

Description

STEREO SOUND SYSTEM

BACKGROUND

The present invention relates to sound output systems, and more particularly to an improved stereo system that combines low-cost components for exceptional fidelity at high output levels in mobile and stationary applications.

A sound system generally includes an audio signal source such as a radio or television tuner, a tape or disc record player or the like, an amplifier circuit, and one or more speakers, typically in a dual-channel stereo configuration. Many existing systems combine a tuner, record player and amplifier in a single unit that drives separate speakers. In order to faithfully reproduce the audio spectrum, a crossover network is additionally connected in each channel between the amplifier and the speakers, the network having a plurality of frequency range outputs that drive separate speakers for each frequency range. In all such systems, there is a compromise between output power, frequency response, distortion, cost and physical space requirements. Typically, the cost for a complete high- quality, high-output system is many times that for a low- power system of ordinary quality, because of the interrelationships between such performance parameters as frequency response, harmonic and inter odulation distortion, noise, and output power._. Thus it is difficult to provide enhanced performance in one aspect without sacrificing in other areas. Further, it is often desirable to upgrade an existing system without necessarily replacing all of its components. The existing system might have only a stereo tape player/receiver driving a pair of speakers that are mounted, for example, in doors of an automobile, or it might include an auxiliary power amplifier that drives pairs of tweeters, mid-range speakers and woofers through a pair of three-way equalizers.

In many high level and upgraded sound systems, a separate high-power amplifier is connected between a tuner/player unit and the speakers, the amplifier having high-level outputs at from several to tens of volts for driving equalizers or speakers directly, and inputs that are designed for low-level signals on the order of one volt in magnitude. Attenuator circuits, also known as line-level converters and power couplers, are available for driving the low-level amplifier inputs from the high-level outputs of the tuner/player unit. Also, some amplifiers are equipped with both high level and low level inputs for avoiding the need for separate attenuator circuits when the amplifier is driven from a high-level output device; however, the high-level inputs are not generally provided with volume and/or other controls, at least to the extent that they are present for the low-level inputs.

Another problem with high-power amplifiers is that when they are used in high level and upgraded systems, undesirable levels of signal distortion are often introduced, particularly when the amplifiers are driven from high-level outputs originally intended for driving speakers directly. A further problem is that sound systems must usually be tailored to accommodate widely differing preferences of users as well as divergent space and cost restrictions, with a result that production and stocking of the needed components is particularly costly because of the large numbers of different component types that might be needed for particular applications.

Yet another problem is that with many high-power audio systems, a listener experiences irritation and even pain during high-volume operation, although the system fails to accurately simulate either a live performance or a theatre-like reproduction.

Thus there is a need for an improved sound system that is easily configured using existing and readily available components, that is capable of high levels of output power with a full range of frequency response and low distortion for simulating a live performance or theatre environment, but with a low potential for inducing irritation or pain, and that is compatible with a variety of space restrictions as well as being inexpensive to produce.

SUMMARY

The present invention meets this need by providing an improved sound output system having an attenuator for driving an amplifier and speaker directly from an input of a different speaker. In one aspect of the invention, the system includes a primary amplifier means having an audio output, main speaker means connected to the audio output, attenuator means connected to a main speaker input of the main speaker means, auxiliary amplifier means operatively connected to an attenuator output of the attenuator means, and auxiliary speaker means operatively connected to the auxiliary amplifier means. The connection of the attenuator means input directly to the main speaker input provides a particularly useful combination whereby the attenuator circuit and the auxiliary amplifier together introduce a delay between the output of the primary amplifier means and the output of the auxiliary amplifier means, permitting greatly enhanced output without introducing significant distortion, and with a reduced likelihood of listener discomfort. The system preferably includes a frequency-responsive filter for operating the auxiliary amplifier and auxiliary speaker means within a desired frequency range. The input filter advantageously protects the auxiliary components from possibly damaging frequency components while avoiding intermodulation distortion.

The primary amplifier means can include crossover means for producing a plurality of frequency range outputs for separating frequency components of the audio output, and the corresponding main speaker means can include a plurality of frequency range speaker inputs operatively connected to a corresponding frequency range output. Crossover means can be connected instead between the audio output and the main speaker means, including a plurality of frequency range outputs for separating frequency components of the audio output, the main speaker means including a plurality of frequency range speaker inputs operatively connected each to a corresponding frequency range output, the attenuator being connected to one of the frequency range speaker inputs.

Preferably, the auxiliary speaker means, the attenuator means, and the auxiliary amplifier means each have separate corresponding frequency range counterparts, the respective counterparts being operatively connected for separately enhancing each of the frequency responses of the system. The crossover means can have low, mid, and high frequency range outputs, the main speaker means having low, mid and high frequency main speakers, the attenuator means, the auxiliary amplifier means, and auxiliary speaker means each having corresponding low, mid, and high frequency range counterparts. The system can also include a sealed first enclosure for the low frequency auxiliary speaker with top, back, and orthogonally connected side panels and sloping front panel, a sealed second enclosure for the low frequency speaker with front and back panels, a sealed third enclosure for the mid-range speaker with front and back panels, and means for removably connecting the enclosures, whereby the front panel of each enclosure is coplanar, the back panels of each enclosure is coplanar, the third enclosure being located above the second enclosure.

The primary amplifier means can include a plurality of primary signal channels and associated primary output channels connected to a corresponding plurality of main speaker channel inputs, the system preferably including a plurality of attenuator channels of the attenuator means and corresponding pluralities of auxiliary amplifier channels of the auxiliary amplifier means and auxiliary speaker inputs of the auxiliary amplifier means, the respective auxiliary counterparts being responsively connected to the attenuator outputs. In this configuration, the system is capable of producing high fidelity stereo output at reduced cost as compared with conventional audio systems having comparable output power and frequency response.

Preferably, the main speaker means in the multiple channel configuration includes a pair of main low frequency speakers connected to corresponding low frequency outputs of the crossover means, and a pair of main mid-range speakers operatively connected to corresponding mid-range frequency outputs of the crossover means, and the auxiliary speaker means includes a low frequency auxiliary speaker, the system further including an enclosure unit having a sealed first enclosure for the low frequency auxiliary speaker having a top, back, and orthogonally connected side panels and a sloping front panel, a pair of sealed second enclosures each having front and back panels for respective ones of the main low frequency speakers, a pair of sealed third enclosures having front and back panels for the main mid- range speakers, means for removably connecting the enclosures, whereby the front panels of each of the enclosures are coplanar, the back panels of each of the enclosures also being coplanar, with the third enclosures being located above the second enclosures. The first enclosure can further include a vent having an area of about 0.0001 to about 0.001 times an effective area of the low frequency auxiliary speaker.

The main speakers can also include a pair of main high frequency speakers connected to corresponding high frequency outputs of the crossover means, and the auxiliary speaker means can include a pair of auxiliary high frequency speakers. The delay between the output of the primary amplifier means and the output of the auxiliary amplifier means is preferably from about 5 μs to about 0.5 ms for simulating live or theatre audio without significantly perceptible echo. More preferably, the delay is between about 10 μs and about 200 μs . Another aspect of the present invention provides a kit for improving a sound output system having a pair of high-level stereo output channels for driving a pair of main speakers, each main speaker having a main speaker input, the kit including the attenuator circuit having a pair of attenuator channels for generating low-level attenuator output signals from respective main speaker inputs, the auxiliary speaker means having a pair of auxiliary speaker inputs, and the auxiliary amplifier having a pair of auxiliary amplifier channels for connection to respective attenuator outputs of the attenuator circuit, each auxiliary amplifier channel having an auxiliary amplifier output for driving one of the auxiliary speaker inputs with a slightly delayed counterpart of the primary amplifier output. Preferably the auxiliary speaker means includes an auxiliary woofer, the kit further including crossover means for providing a plurality of crossover outputs responsive to each of two crossover inputs, a plurality of main speakers for connection to respective ones of the crossover outputs, and means for connecting the auxiliary amplifier between respective low frequency inputs of the main speakers and corresponding inputs of the auxiliary woofer. More preferably, the kit also includes a pair of auxiliary tweeters, the main speaker means including a pair of high frequency range speaker inputs driven by corresponding frequency range outputs, another pair of the attenuator channels being connected to the high frequency range speaker inputs and driving an additional pair of the auxiliary amplifier channels for driving the auxiliary tweeters so as to enhance a highest frequency response of the system. The kit includes removably connected sealed enclosures for the auxiliary woofer and for low and medium frequency main speakers, sloping front panels of the enclosures being coplanar, rear panels of the enclosures also being coplanar, the enclosures for the medium frequency speakers being positioned above the others for effective sound projection from behind a seat of the listener.

DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings where:

Figure 1 is a schematic diagram of a sound output system according to the present invention;

Figure 2 is a schematic diagram showing an alternative configuration of the system of Fig. 1 within region 2 of Fig 1;

Figure 3 is a schematic diagram showing an alternative configuration of the system of Fig. 1 within region 3 of Fig 1;

Figure 4 is a schematic diagram showing an alternative configuration of the system of Fig. 1;

Figure 5 is an oblique elevational perspective view showing the sound output system of Fig. 4 installed within a vehicle;

Figure 6 is a sectional elevational view of the system of Fig. 4 on line 6-6 of Fig. 4.

Figure 7 is a schematic diagram showing an alternative configuration of the system of Fig. 1 within region 7 of Fig 1;

Figure 8 is a schematic diagram as in Fig. 3, showing another configuration of the system of Fig. 1;

Figure 9 is a schematic diagram showing another configuration of the system of Fig. 4;

Figure 10 is an oblique elevational perspective view as in Fig. 5, showing the sound output system of Fig. 9 installed within a vehicle; and

Figure 11 is a schematic diagram showing an alternative configuration of the system of Fig. 9 within region 11 thereof. DESCRIPTION

The present invention is directed to a sound output system having one or more auxiliary amplifiers and speakers that are driven from attenuator circuitry that is connected directly to one or more inputs of other speakers of the system. With reference to the drawings, and particularly Fig. 1, a sound system 10 includes a primary amplifier 12 having a primary output 14, the primary output 14 having a pair of primary output channels 16 (designated primary left channel 16L and primary right channel 16R in Fig. 1) the channels 16L and 16R being connected to respective main speakers 18, correspondingly designated 18L and 18R. Each of the main speakers 18 has a main speaker input 20 which is connected to the primary output 14. As shown in Fig. 1, each signal path is depicted in a general form having an active conductor, designated "+" and a return conductor, designated "-". It is contemplated that some or all of the return conductors can be connected in common, within the scope of the present invention. As also shown in Fig. 1, the primary amplifier 12 is provided with low-level audio inputs in the form of a tape deck 22 and a radio tuner 24. It is to be understood that the primary amplifier 12 may include additional low-level inputs (not shown) from other sources that are either internal or external to the primary amplifier 12.

According to the present invention, the system 10 includes a pair of attenuator circuits 26, each attenuator circuit 26 being connected to a respective primary output channel 16 in parallel with the corresponding main speaker input 20 and having a low-level attenuator output 28 for driving a corresponding low-level auxiliary channel 30 of an auxiliary amplifier 32, respective auxiliary outputs 34 of the auxiliary amplifier 32 being connected to corresponding auxiliary speaker inputs 36 of an auxiliary speaker means 38. The connections from the attenuator outputs 28 to the auxiliary input channels 30 are made using shielded cable and conventional RCA pin plugs, the cable shielding providing a return path as indicated here and elsewhere in the drawings where low-level signals are being transmitted. Conventional connections to one or more sources of electrical power (not shown) are further provided for the primary amplifier 12, the auxiliary amplifier means 32, and elsewhere herein as appropriate.

Preferably the auxiliary amplifier 32 is provided with at least one tone control 40 whereby a desired frequency component of the signals from the attenuator 28 is amplified with greater gain than other frequency components. According to the present invention, the auxiliary speaker means 38 is utilized primarily for emphasizing a lowest, and/or a highest frequency response of the system. Thus the tone control 40 can be advantageously implemented as conventional bass and treble controls, which are commonly provided in readily available medium and low cost audio amplifier modules. If the auxiliary speaker means 38 is selected for enhancing or extending a lowest frequency response of the system, the tone control 40 would normally be set with the bass turned to at or near its maximum setting and the treble turned to its minimum setting. On the other hand, if the auxiliary speaker means 38 is selected for extending a highest frequency response of the system, the bass would be turned to its minimum setting and the treble would be turned to at or near its maximum setting. Similar results are obtained if the tone control 40 is configured as a set of equalizer controls (not shown) . Further, the auxiliary speaker means 38 can be selected for enhancing an intermediate frequency response of the system, the equalizer controls being set with lowest and highest control components moved to minimum settings and with intermediate control components at elevated settings. As shown in Fig. 1, the auxiliary speaker means 38 is depicted as having a single large bass speaker or sub- woofer 42 having a pair of isolated voice coils, each voice coil having two terminals of one auxiliary speaker input 36. The sub-woofer 42 produces sound in response to an additive combination of the left and right auxiliary outputs 34, advantageously conserving space requirements for the system 10, yet not unduly compromising performance because the stereo perception of the lowest frequencies of sound is considered a minor factor in the overall performance of the system. A dual-input sub-woofer suitable for use in the present invention is available as Pyramid Model PW 157 Dual- Channel Sub-Woofer from Sound 1984, of New York, NY. Also, an amplifier suitable for use as the auxiliary amplifier 32 is available as Model XA-625 from HiTech Mobil Sound Corp. , of Vancouver, WA. Alternatively, an amplifier suitable for use in a low-cost implementation of the sound system 10 of Fig. 1 for home use is available as Technics Model SA-929; the primary amplifier 12 can be a Model RS-T22 tape/SA-929 receiver; and speakers suitable for use as the main speakers 18 are available as Model SB-K14 speakers, each from Technics Panasonic of Osaka, Japan, and from Panasonic Company, Division of Matsushita Electric Corporation of America, Sercaucus, NT.

The attenuator circuits 26 are independent, each having separate positive and negative inputs as shown in Fig.

1 for use with fully isolated primary output channels 16L and 16R. An attenuator suitable for use as a pair of the attenuators 26 of Fig. 1 is available as PowerLink Model PL-2 from AudioLink of Huntington Beach, CA. Alternatively, a single, dual-channel implementation of the attenuator circuit

26 can be used. As shown in Fig. 2, the attenuator circuit

26 is depicted as having a pair of the attenuator outputs 28, each being responsive to a separate active conductor (+) , the positive conductors being referenced to a single return conductor (-) . A suitable attenuator circuit 26 having such a configuration, suitable for use in the present invention, is available as Model PC-1 power adapter from SoundCraftsmen of Santa Ana, CA. This configuration is appropriate when the return conductors of the respective primary output channels 16L and 16R are directly connected within the primary amplifier 12, or when the return conductors closely track each other.

The sound system 10 can be configured according to the present invention for enhancing or extending both lowest and highest frequency responses of the system. As shown in Fig. 3, attenuator means 44 having a pair of the attenuator circuits 26 as depicted in Fig. 2 is connected to the respective primary output channels 16L and 16R for driving auxiliary amplifier means 46 that includes a counterpart of the auxiliary amplifier 32 and a treble amplifier 48. As also shown in Fig. 3, the auxiliary speaker means 38 includes a counterpart of the sub-woofer 42, connected to the auxiliary amplifier 32, and a pair of auxiliary tweeters 50, each auxiliary tweeter 50 being connected to a corresponding treble output 51 of the treble amplifier 48 through a series-connected blocking capacitor 52. The blocking capacitor 52 protects the auxiliary tweeter 50 from unwanted low-frequency components of the treble output 51. A tweeter suitable for use as the auxiliary tweeter 50 is available as Model UT-R 3510P from Ultimate Sound of City of Industry, CA; and an amplifier suitable for use as the treble amplifier 48 is available as Hi-Comp Model HCB 818 from Audiovox Corp. of Hauppauge, NY. Typically, a capacitor suitable for use as the blocking capacitor 52 is supplied with commercially available tweeters.

As shown in Fig. 7, one or more of the attenuator circuits 26 can be provided with filter means 53 for limiting its response to a desired frequency range component, thereby protecting the auxiliary amplifier means 46 and the auxiliary speakers means 38 from high levels of unwanted frequency range components. The filter means 53 provides the further advantages of reducing intermodulation distortion and reducing component and system power requirements for a given output sound level. The filter means 53 is implemented as a choke coil 54 connected in series between the primary output channel 16 (and the parallel-connected main speaker input 20 of the main speaker 18L) and the input of the attenuator circuit 26 that is connected to the auxiliary input channel 30 of the auxiliary amplifier 32 for driving the sub-woofer 42. The coil 54 effectively blocks high frequency components of the main primary output channel 16 and the input of the attenuator circuit 26 that is connected to the input of the treble amplifier 48 for driving the auxiliary tweeter 50. It will be understood that counterparts of the filter means 53 would normally be used in each channel of the system 10 to which the auxiliary amplifier means 46 and the auxiliary speaker means 38 is applied, that is, between both of the main speakers 18 and 18R and the corresponding attenuator circuits 26. It should further be understood that the filter means 53 can be included as a part of the associated attenuator circuit 26. Accordingly, the "direct connection" of the attenuator circuit 26 to the main speaker input 20 as used herein includes the series connection of the filter means 53 between the speaker input 20 and the attenuator circuit 26. The present invention advantageously permits low-power components to be used for the coil 54 and the series capacitor 55, because the attenuator circuit 26 can have a high input impedance. A coil suitable for use as the coil 54 in the present invention is available as an iron core choke made from 18 gauge wire and having an inductance of 12.0 mH for passing pure bass, Model ACL-10 which is available from David Levy Co. Inc. of Paramount, CA. This component is capable of transmitting high power levels to a bass speaker. It is anticipated that similar results would be obtained with a readily available low-power choke having the same inductance. A capacitor suitable for use as the series capacitor 55 is also available from David Levy Co. as a 50V non-polarized "crossover-capacitor" CC-X, where X is an integer from 1 to 10 that designates a desired capacitance of from 2.2 μF to 100 μF.

In applications where it is desired to provide enhanced sound output in remote locations, one or more secondary attenuators 27 can be driven from the auxiliary speaker inputs 36 as shown in Fig. 8. The secondary attenuators 27 can be conveniently located proximate the sub- woofer 42 and/or the auxiliary amplifier 32 for driving a remotely located secondary auxiliary amplifier 32a and a secondary sub-woofer 42a. This configuration advantageously reduces the power output requirements of the auxiliary amplifier 32 and the sub-woofer 42. More importantly, transmission of the attenuator output 28 of the secondary attenuator 27 to the secondary auxiliary amplifier 32a is facilitated by the low-level, low power characteristics of the attenuator output 28, such that heavy wiring that might otherwise be required for avoiding transmission losses is not needed. Further, the low-level wiring is easily shielded for avoiding interference, whereas high power speaker wiring is generally not shielded because of the transmission losses that would otherwise result.

With reference to Figs. 4-6, another and preferred configuration of the sound system 10 includes a player/tuner or other low-level source 56 of stereo audio input, the source 56 being operatively connected to a primary amplifier 58 having a counterpart of the primary output 14. The primary output channels 16L and 16R of the primary output

14 are each operatively connected to a three-way crossover network 60, designated 60L and 60R in Fig. 4, for separating frequency components of the audio output from the primary amplifier 58, each crossover network 60 having a high frequency output H, a medium frequency output M, and a low frequency output L. The H, M, and L frequency outputs of each crossover network 60 are connected, respectively, to counterparts of the main speaker input 20 of a main tweeter 62, a main mid-range speaker 64, and a main woofer 66, each main tweeter 62 being connected in series through an adjustable rheostat 68.

According to the present invention, a first attenuator circuit 70, having a pair of the attenuator outputs 28, is operatively connected to the low frequency outputs L of the crossover networks 60, in parallel with the respective main speaker inputs 20 of the main woofers 66 for driving counterparts of the auxiliary amplifier 32 and the sub-woofer 42 as described above. In this configuration of the sound system 10, the treble adjustment of the tone control 40 of the auxiliary amplifier 32 serves mostly for attenuating noise that might otherwise be generated by the attenuator circuit 70 and/or the auxiliary amplifier 32, the function of separating the frequency components of the primary output 14 being performed mainly by the crossover network 60. A crossover network suitable for use in the present invention is available as Model C- 103 from Jet Sound Electronics, Inc. of Long Beach, CA; an amplifier suitable for use as the primary amplifier 58 is available as Model JSE-1010 A, also from Jet Sound; the source 56 can be a Kraco KF-1190 Stereo AM FM Tape Player from Kraco Enterprises,

Inc. , of Compton, CA. Speakers suitable for use as the main tweeter 62 are available as Dyna-Flite HCT-100P Honeycomb Tweeters from Ultimate Sound, above; the mid-range speakers 64 can be Model SP-44 speakers from Rockford Corp. of Tempe, AZ; and speakers suitable for use as the main woofers 66 are available as Model S-4040 from Jet Sound, above.

In the configuration shown in Fig. 4, the sound system 10 further includes a second attenuator circuit 72 for driving counterparts of the treble amplifier 48 and the auxiliary tweeters 50 as described above in connection with the circuit of Fig. 3. As shown in Fig. 4, the auxiliary tweeters 50 are connected in parallel with an additional pair of auxiliary tweeters, designated auxiliary tweeters 74 in the drawings. A speaker suitable for use as the auxiliary tweeter 74 is available as Mini-Dome Model KD2215H from Pyle Industries, Inc. of Huntington, IN, this device having a swivel mount for providing a directional adjustment which is often needed in vehicle applications. The second attenuator circuit 72 is responsive to the high frequency outputs H of the respective crossover networks 60L and 60R, the inputs of the second attenuator circuit 72 being connected in parallel with the main speaker inputs 20 of the main tweeters 62, downstream from the respective rheostats 68 for amplitude control thereby. By connecting the second attenuator circuit 72, as well as the main tweeters 62, downstream of the rheostats 68, the rheostats 68 are particularly effective in removing "hiss" that might be present in the H frequency outputs of the crossover networks 60. The removal of "hiss" in this manner is so effective that the overall response has been observed to be superior to the alternative of including a Dolby^® noise reduction filter at the source 56. A dual rheostat suitable for use as a pair of the rheostats 68 in the present invention is available as Archer Catalog No. 271- 261 Balance Control from Radio Shack of Fort Worth, TX.

As further shown in Figs. 5 and 6, the sub-woofer

42, the main mid-range speakers 64, and the main woofers 66 are located in an enclosure unit 80 that can be conveniently mounted within the passenger compartment of a vehicle 82. The enclosure unit 80 has separable modules, including a sub- woofer module 84 for enclosing the sub-woofer 42, a pair of woofer modules 86 for enclosing the main woofers 66, and a pair of mid-range modules 88 for enclosing the mid-range speakers 64. As shown in the drawings, the enclosure unit 80 is wedge-shaped in side elevation, having a base length B and a top length T, a base portion formed by the sub-woofer module 84 and the woofer modules 86 extending upwardly a distance D_τ from the base B, each woofer module 86 having a lateral width W and the centrally located sub-woofer module 84 having a lateral width S. The mid-range modules 88, extending upwardly a distance D₂ from the sub-woofer module 84 and the woofer modules 86, each have a lateral width C. In an exemplary and preferred configuration of the enclosure unit 80, the base B is approximately 11 inches, the top length T is approximately 2 inches, the width S of the sub- woofer module 84 approximately 34 inches, the width W of each woofer module 86 is approximately 15 inches, the distance D₁ is approximately 19 inches, the distance D₂ is approximately 7 inches, and the width C of the mid-range module 88 is approximately 23.5 inches. Each of the modules 84, 86, and 88 is fabricated from sheets of particle board having a thickness of about 0.75 inch. The sheets form, for each of the modules 84, 86, and 88, a top panel 90, a bottom panel 91, a rear panel 92, side panels 93 orthogonally connected to the top, bottom, and rear panels 90-92, and a sloping front panel 94, the panels being joined by screw fasteners, with a sealant 95 being applied continuously along each joint for air-tight construction. The air-tight construction produces an "air-suspension" of the sub-woofer 42, the main mid-range speaker 64, and the main woofer 66 that advantageously avoids resonance at particular frequencies. Also, a liner 95 of an insulating material is applied to the inside of the sub- woofer module 84 and the woofer module 86, but not the mid- range module 88, for preventing resonance of the modules 84 and 86. As shown in Fig. 5, the modules 84, 86, and 88, are removably joined by a plurality of connecting straps 96 and angle brackets 97 that are attached by appropriate screw fasteners 98 to the particle board panels of the modules. Also, one or more of the brackets 97 connects the combination of the modules to the vehicle 82. The modules 84, 86, and 88, thus joined, have the front panels 94 and the rear panels each in a common plane for facilitating use of the sound system 10 in locations having minimal space availability, as in the vehicle 82. The sloping front panels 94 of the enclosure unit 80 advantageously orient the speakers thereon for directing the sound over and around vehicle seats behind which the enclosure unit 80 is located. The backs of such seats are normally backward-sloping, which the rear of the available space within the vehicle 82 is typically oriented vertically. Consequently, the coplanar configuration of the front panels 94 and of the rear panels 92 contribute to advantageous use of the available space. Also, the sub- woofer module 84 and the woofer modules 86 are advantageously located at the bottom of the unit 80 where the increased longitudinal spacing between the rear panels 92 and the front panels 94 contributes to high internal volumes of the modules 84 and 86 for matching the low frequency characteristics of the sub-woofer 42 and the main woofers 66. The low frequency sound from the modules 84 and 86 is not seriously blocked by vehicle seats because low frequency sounds are less directionally sensitive than higher frequency sounds such as are reproduced by the mid-range modules 88. Conversely, the mid-range modules 88 are located above the modules 84 and 86 for more direct transmission of the sounds therefrom to listeners ahead of the vehicle seats, the lesser internal volumes needed for the modules 88 being available within reduced spacing between the upper portions of the seats and the rear of the interior of the vehicle 82. The removable connection of the modules 84, 86 and 88 advantageously facilitates installation of the enclosure unit 88 into the vehicle 82 through restrictive door openings thereof; also, the quality of the sound is improved by avoiding mechanical resonance between the modules.

As shown in Fig. 5, the sub-woofer module 84 is provided with a vent 100 for reducing distortion during high volume operation of the sound system 10. It has been discovered that the vent 100 is effective in reducing distortion at high power when it is configured as an opening of approximately 0.25 inch in diameter, in conjunction with the sub-woofer 42 having an active diameter of about 15 inches. In this configuration, the opening has an area of approximately 1/3600 of the active area of the sub-woofer 42. It is expected that the vent 100 will be effective as described when it has an area of from about 0.0001 to about 0.001 times the effective area of the sub woofer 42. When very high power operation of the sub-woofer module is not contemplated, the vent 100 can be plugged or omitted altogether.

A prototype of the system 10 has been fabricated as shown in Figs. 4-6, the system 10 being installed in the cab of a pick-up truck. It has been discovered that the system 10, so configured, provides unexpectedly high performance and fidelity, in view of the low-cost components which were used in the prototype system 10. During confidential evaluations of the prototype system 10 by leading manufacturers of vehicle stereo systems, the performance and fidelity were viewed as being significantly higher than that which would ordinarily be provided by the same amplifiers and speakers. In fact, the representatives of the manufacturers, who were not informed how the circuits were connected, indicated that they would not have believed such performance was possible from those amplifiers and speakers. One of the representatives said that it is technically impossible to have this amount of sound magnitude in such a small volume of air space.

The prototype of the system 10 of Figs. 4-6 has been modified to incorporate upgraded components for determining whether substantial further enhancement of the performance would result. The system 10 as modified included for the a dual-input sub-woofer 42 an MTX "Cranker" speaker model RFL-15F1P85F4; for the auxiliary amplifier 32 a Model KAC-1020 power amplifier from Kenwood U.S.A. Corp. of Long Beach, CA. The RFL-15 speaker, available from MTX of Winslow, IL, has a single coil; accordingly, a single channel of the auxiliary amplifier 32 is driven by the output of a conventional "Y" adapter (not shown) from stereo outputs of the first attenuator circuit 70, a bridge switch of the KAC- 1020 amplifier being set for "bridged output". Also, the primary amplifier 58 was changed to a Model KAC-820; the source 56 was changed to a KRC-999 stereo tuner and cassette player, together with a KDC-80 compact disk player; the treble amplifier 48 was changed to a KAC-720; the main tweeters 62 and the auxiliary tweeters 74 were each changed to KFC-T101 tweeters; the mid-range speakers 64 were changed to KFC-M104; and the main woofers 66 were changed to KFC- W108, each from Kenwood. The results of these changes were that a further improvement in sound quality was obtained. However, due to the greater diaphragm stiffness of the substituted main woofers 66 and the sub-woofer 42, it was found necessary to modify the sub-woofer module 84 and the woofer modules 86 to provide increased venting, as further described below in connection with Fig. 10.

The prototype system 10 in the pick-up truck as modified above was also demonstrated to the stereo system manufacturers, but with similar results. The system 10 was found to have performed as well as or better than stationary systems costing several times as much as the total cost of the components that were used in the present invention.

In consequent reflections by the present inventors, it has been suggested that unexpected results are attributable to a slight delay that is introduced by the attenuator and the auxiliary amplifier circuitry. Thus a listener first hears a reproduction of the sound from the main speakers; then, the listener hears an enhanced counterpart of the sound from the auxiliary speakers. Ordinarily the combination of an original sound signal and a delayed counterpart produces an "echo" that is confusing to the listener. The prototype of the system 10 was not heard to produce such an echo, however. After further investigation and testing, the inventors have concluded that a very slight, but beneficial delay is associated with the attenuator and auxiliary amplifier circuitry of the present invention.

A series of tests were conducted for determining the delays associated with the attenuators and auxiliary amplifiers in the sound system 10. In one test, a signal generator was connected for driving the primary amplifier 58 at selected frequencies. Probes of an oscilloscope were connected to both main and auxiliary speaker inputs for measuring a delay associated with the attenuator and auxiliary amplifier components. In one test, the signal generator provided a sine-wave signal, the test results being presented in Table 1, below.

Table 1 Sine-Wave Auxiliary Delay Measurements

The oscilloscope was triggered by the appropriate frequency range signal from the crossover network, and the relative phase delay of the corresponding auxiliary amplifier output was read from the oscilloscope display from the relative positions of the displayed waveforms. Unexpectedly, the HiTech XA-625 amplifier (used for the auxiliary amplifier 32 in the original prototype) was found to provide a "negative delay", suggesting that a "phase-lead" was being generated in that a true negative delay is not known to be physically possible. Accordingly, the signal generator was set for a square wave output in an attempt to measure delay independent of the fundamental frequency of the signal. The results of this test are presented below in Table 2. Due to limitations of the test equipment, it is believed that the accuracy of these results is uncertain.

Table 2 Square-Wave Auxiliary Delay Measurements

As a result of the testing, it is believed that the enhancement of the sound resulting from the delay is not apparent when the delay is less than about 1.0 μs. It is also believed that a distinct perception of echo may result from a delay in excess of about 1.0 ms. Accordingly, it is believed that a preferred enhancement of sound is produced by the system 10 when the delay is between about 5.0 μs and about 0.5 ms and, more preferably, about 100 μs.

With reference to Figs. 9-11, the sound system 10 of the present invention was further modified for providing both main and auxiliary amplifiers and speakers in each of the frequency ranges, thus achieving a corresponding combination of direct and slightly delayed sound output at mid frequencies, as well as at low and high frequencies.

In this most preferred configuration of the present invention, a third attenuator circuit 102 is operatively connected to the mid frequency outputs M of the crossover networks 60, in parallel with the respective main speaker inputs 20 of the main mid-range speakers 64 for driving a mid-range auxiliary amplifier 104, the amplifier 104 being connected for driving a pair of auxiliary mid-range speakers 106. The sensation of listening to a live performance or theatre presentation, discussed above, is further enhanced by the inclusion of the auxiliary mid-range speakers 106 and associated circuitry. Further, a pair of mid-range rheostats 108 are connected in series between the mid frequency outputs M (+) of the crossover networks 60 and the third attenuator circuit 102 (the main mid-range speakers 64 remaining directly connected to the crossover networks 60) for permitting operator adjustment of the sound amplitude from the auxiliary mid-range speakers 106 relative to the main mid-range speakers 64. It has been discovered that this adjustment, lowering the sound amplitude from the auxiliary mid-range speakers 106, permits the system 10 to be operated at a higher level of overall sound power (and higher perceived sound amplitude) without reaching a threshold of pain, or otherwise irritating the listener's ears, than would otherwise be possible. The mid-range rheostats 108 can have the same configuration as the rheostats 68 discussed above, the elements thereof each having a resistance of approximately 1000 ohms. The rheostats 68 and 104 can also be furnished as separate conventionally configured components, rather than the ganged configuration described above.

In the configuration shown in Figs. 9 and 10, the auxiliary mid-range speakers 106 are located on opposite side doors 110 of the vehicle 82, in place of the auxiliary tweeters 50 of Figs. 4 and 5. Speakers suitable for use as the auxiliary mid-range speakers 106 are available as model KFC-M104 from Kenwood. More suitable are Pyramid Phase III model TW16 120 Watt dome tweeters, available from Sound 1984, above. Also, the sub-woofer module 84, and the woofer modules 86, are each provided with enlarged vents 112, the vents 112 each having an opening approximately 1.94 inches in diameter for relieving pressure within the respective enclosure cavities when used with speakers having particularly stiff diaphragms as discussed above. The vents 112 are formed from tubular members having a length of approximately 5.0 inches, the members extending into the associated enclosure portion. As further shown in Fig. 10, two of the vents 112 are provided in the sub-woofer module 84.

In the sound system 10 of Figs. 9 and 10, the audio source 56 includes conventional "front" and "rear" low level outputs, and a balance control 114 for adjusting the relative output volumes of each. The system 10 as thus far described makes use of only one set (either the front or rear) of such outputs, the balance control being set fully in favor of the utilized outputs. It will be understood that a full complement of the primary amplifier 58 and its associated downstream components can be connected to each of the front and rear outputs of the source 56, but the advantages of the present invention are normally obtained without resort to such complexity. However, and as shown in Fig. 9, the present invention finds application in situations where both front and rear outputs are active. Accordingly, the primary amplifier 58 is shown as being driven by a pair of low level rear outputs 116 of the source 56, a similar pair of front outputs 118 being connected through a front amplifier 120 to a pair front speakers 122. According to the present invention, it is preferred that the balance control 114 be adjusted in favor of those outputs of the source 56 that are connected to the primary amplifier 58, namely the rear outputs 116 in Fig. 9. Thus that portion of the sound system 10 which includes the attenuators (70, 72 and 102) , the auxiliary amplifiers (32, 48, and 104), and the auxiliary speakers (42, 74, and 106) is driven more strongly for effecting the sound enhancements described herein. In setting up the sound system 10, the input volume trim adjustments of the various amplifiers are set for a slight emphasis of the auxiliary tweeters 74 and auxiliary woofer 42 over main tweeters 62 and the main woofers 66. Conversely, the auxiliary mid-range speakers 106 are preferably slightly de-emphasized relative to the main mid range speakers 64 by means of the mid-range rheostats 108.

As further shown in Fig. 9, the source 56 of the system 10 includes means for playing compact disks. Accordingly, low-level outputs of a disk player 124 are connected for driving external inputs 126 of the source 56.

With further reference to Fig. 11, a pair of auxiliary woofers 128 can be substituted for the sub-woofer 42 in applications having sufficient space, such as in homes, the auxiliary woofers 128 being mounted in separate sub- woofer modules 130 for enhanced coverage of the listening environment.

Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example, the crossover networks 60 can have four or more frequency range outputs, the system 10 including attenuators and associated auxiliary amplifiers and speakers on some, preferably all of them. Therefore, the spirit and scope of the appended claims should not necessarily be limited to the description of the preferred versions contained herein.

Claims

What is claimed is:

1. A sound output system comprising: (a) primary amplifier means having an audio output responsive to a low-level input; (b) main speaker means operatively connected to the output of the primary amplifier means for sound output into a listening environment and having at least one main speaker input;

(c) attenuator means connected to the output of the primary amplifier means and in parallel with the speaker means, the attenuator means having an attenuator output at a level not exceeding approximately 1.0 volt;

(d) auxiliary amplifier means operatively connected to the attenuator output; and (e) auxiliary speaker means operatively connected to the auxiliary amplifier means for enhancing the sound output, whereby the attenuator circuit and the auxiliary amplifier together introduce a delay between the output of the primary amplifier means and the output of the auxiliary amplifier means for permitting high levels of sound output with reduced likelihood of discomfort to listeners.

2. The apparatus of claim 1 further comprising a frequency-responsive filter connected between the main speaker means and the auxiliary amplifier means for operating the auxiliary amplifier means and the auxiliary speaker means within a desired frequency range.

3. The apparatus of claim 1 further comprising:

(a) secondary attenuator means connected to the output of the auxiliary amplifier means and in parallel with the auxiliary speaker means;

(b) secondary amplifier means operatively responsive to the secondary attenuator means and having a secondary amplifier output; and (c) secondary speaker means operatively connected to the secondary amplifier output.

4. The system of claim 1 wherein the primary amplifier means includes crossover means producing a plurality of frequency range outputs for separating frequency components of the audio output, and the corresponding main speaker means includes a plurality of frequency range main speaker inputs, each frequency range main speaker input being operatively connected to a corresponding frequency range output, the attenuator circuit being connected to one of the frequency range speaker inputs.

5. The system of claim 1 further comprising crossover means connected between the audio output and the main speaker means, the crossover means having a plurality of frequency range outputs for separating frequency components of the audio output, and the main speaker means has a plurality of frequency range main speaker inputs, each frequency range main speaker input being operatively connected to a corresponding frequency range output, the attenuator means including an attenuator circuit responsively connected to one of the frequency range speaker inputs.

6. The system of claims 4 or 5 wherein the auxiliary speaker means comprises a plurality of frequency range auxiliary speakers, the attenuator means comprises a corresponding plurality of attenuator circuits respectively connected to the frequency range speaker inputs, and the auxiliary amplifier means provides a corresponding plurality of auxiliary amplifier outputs for respectively driving the frequency range auxiliary speaker for separately enhancing each of the frequency responses of the system.

7. The apparatus of claim 6 wherein the crossover means has low, mid, and high frequency range outputs, the main speaker means including low, mid, and high frequency main speakers, the attenuator means, the auxiliary amplifier means, and the auxiliary speaker means each having corresponding low, mid, and high frequency range counterparts responsively connected to the respective frequency range outputs.

8. The system of claim 7 further comprising an enclosure unit comprising:

(a) a sealed first enclosure for the low frequency auxiliary speaker, the first enclosure having top, back, and orthogonally connected side panels, and a sloping front panel;

(b) a sealed second enclosure for the low frequency main speaker, the second enclosure having front and back panels; (c) a sealed third enclosure for the mid frequency main speaker, the third enclosure having front and back panels; and

(d) means for removably connecting the enclosures, whereby the front panels of each of the enclosures are coplanar, the back panels of each of the enclosures also being coplanar, with the third enclosure being located above the second enclosure.

9. The system of claim 6 wherein:

(a) the primary amplifier means includes a plurality of primary signal channels and corresponding primary output channels;

(b) the main speaker means includes a plurality of main speaker channels and corresponding main speaker inputs, each main speaker input being connected to a corresponding output channel of the primary amplifier means;

(c) the attenuator means comprises a plurality of attenuator channels and corresponding attenuator outputs;

(d) the auxiliary amplifier means comprises a plurality of auxiliary amplifier channels and corresponding auxiliary amplifier outputs, each auxiliary amplifier channel being responsively connected to a respective attenuator outpu ; and

(e) the auxiliary speaker means comprises a plurality of auxiliary speaker inputs, each auxiliary speaker input being connected to a corresponding auxiliary amplifier output for enhancing the sound output associated with the corresponding primary output channel.

10. The system of claim 9 wherein the main speaker means includes a pair of main low frequency speakers connected to corresponding low frequency outputs of the crossover means, and a pair of main mid-range speakers operatively connected to corresponding mid-range frequency outputs of the crossover means, and the auxiliary speaker means includes a low frequency auxiliary speaker, the system further comprising an enclosure unit comprising:

(a) a sealed first enclosure for the low frequency auxiliary speaker, the first enclosure having a top, back, and orthogonally connected side panels, and a sloping front panel; (b) a pair of sealed second enclosures for respective ones of the main low frequency speakers, the second enclosures each having front and back panels;

(c) a pair of sealed third enclosures for the main mid-range speakers, the third enclosures having front and back panels; and

(d) means for removably connecting the enclosures, whereby the front panels of each of the enclosures are coplanar, the back panels of each of the enclosures also being coplanar, with the third enclosures being located above the second enclosures.

11. The system of claim 10 wherein the first enclosure further comprises a vent having an area of from approximately 0.0001 to approximately 0.001 times an effective area of the low frequency auxiliary speaker.

12. The system of claim 10 wherein the main speaker means further includes a pair of main high frequency speakers connected to corresponding high frequency outputs of the crossover means, and the auxiliary speaker means includes a pair of auxiliary high frequency speakers for enhancing a highest frequency response of the system.

13. The system of claim 1 wherein delay between the output of the primary amplifier means and the output of the auxiliary amplifier means is from about 5 μs to about 0.5 ms.

14. The system of claim 13 wherein the delay is between about 10 μs and about 200 μs.

15. The system of claim 6 wherein the delay is from about 5 μs to about 0.5 ms.

16. The system of claim 15 wherein the delay is between about 10 μs and about 200 μs.

17. A kit for improving a sound output system having a pair of high-level stereo audio output channels for driving a pair of main speakers for sound output into a listening environment, each main speaker having a main speaker input, the kit comprising:

(a) an attenuator circuit having a pair of attenuator channels for connection to respective main speaker inputs of the pair of main speakers, each attenuator channel generating a low-level attenuator output signal at a level not exceeding approximately 1.0 volt in response to the associated main speaker input;

(b) auxiliary speaker means having a pair of auxiliary speaker inputs; and

(c) an auxiliary amplifier having a pair of auxiliary amplifier channels for connection to respective attenuator outputs of the attenuator circuit, each auxiliary amplifier channel having an auxiliary amplifier output for driving one of the auxiliary speaker inputs for enhancing the sound output associated with the corresponding primary output channel, whereby the attenuator circuit and the auxiliary amplifier together introduce a delay between the output of the primary amplifier means and the output of the auxiliary amplifier means.

18. The kit of claim 17 wherein the auxiliary speaker means comprises an auxiliary woofer, the kit further comprising: (a) crossover means having a pair of crossover channels for connection between the audio output channels and the pair of main speakers, each crossover channel having a crossover input for connection to a respective output channel, and a plurality of crossover outputs responsive to each crossover input for separating frequency components of the output channels;

(b) a plurality of main speakers for connection to respective ones of the crossover outputs, a pair of the main speakers each having a low frequency range input; and (c) means for connecting the auxiliary amplifier between the pair of low frequency inputs and the auxiliary woofer for enhancing a lowest frequency response of the system.

19. The kit of claim 18 wherein the auxiliary speaker means further comprises a pair of auxiliary tweeters, the main speaker means including a pair of high frequency range speaker inputs connected to corresponding ones of the frequency range outputs, a further pair of the attenuator channels being connected to the pair of high frequency range speaker inputs, the auxiliary amplifier means having a further pair of the auxiliary amplifier channels connected between the further pair of attenuator channels and respective inputs of the auxiliary tweeters for enhancing a highest frequency response of the system.

20. The kit of claim 18 wherein the main speakers include pairs of low frequency, medium frequency, and high frequency range speakers, the kit further comprising an enclosure unit comprising: (a) a sealed first enclosure for the auxiliary woofer, the first enclosure having top, back, and orthogonally connected side panels, and a sloping front panel;

(b) a sealed second enclosure for the low frequency main speaker, the second enclosure having front and back panels;

(c) a sealed third enclosure for the medium frequency speaker, the third enclosure having front and back panels; and (d) means for removably connecting the enclosures, whereby the front panels of each of the enclosures are coplanar, the back panels of each of the enclosures also being coplanar, with the third enclosure being located above the second enclosure.

21. The kit of claim 17 wherein the delay between the output of the primary amplifier means and the output of the auxiliary amplifier means is from about 5 μs to about 0.5 ms for permitting high levels of the sound output and correspondingly high levels of sound perception while limiting hearing discomfort.