WO2012145828A1

WO2012145828A1 - Stereo loudspeaker system with asymmetric speaker enclosures

Info

Publication number: WO2012145828A1
Application number: PCT/CA2012/000392
Authority: WO
Inventors: Stephane Dedieu; Horia ZAGURA
Original assignee: Novero Canada Inc.
Priority date: 2011-04-28
Filing date: 2012-04-27
Publication date: 2012-11-01

Abstract

A loudspeaker system is provided, comprising asymmetric speaker enclosures having different characteristics and housing respective speaker drivers of different sizes, and an audio architecture for separating and driving medium and high frequency signals to respective ones of the drivers within the enclosures which driving the driver in the first enclosure with low frequency signals of both stereo channels, for matching the phase and magnitude of both speakers in the acoustic domain to provide accurate stereo image reproduction.

Description

STEREO LOUDSPEAKER SYSTEM

WITH ASYMMETRIC SPEAKER ENCLOSURES

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention is directed to loudspeakers and more particularly to an ultraportable wired or wireless loudspeaker accessory for music players, tablet computers, netbook computers and smartphones, characterized by maximized bass and loudness.

2. Description of the Related Art

[0002] The most common type of sound system with bass extension (or enhanced bass) for use in homes is known as a "2.1" sound system consisting of a sub-woofer for bass effect and two speakers to produce a stereo sound. Left and right audio signals are high-pass filtered, amplified and output from the left and right speakers while both the left and right audio signals are low-pass filtered, mixed and amplified for output from a single sub-woofer. Such traditional sound systems are too large and cumbersome to be portable.

[0003] Ultraportable and small portable loudspeakers are known, but generally exhibit one or more of poor bass or enhanced bass with poor sound quality (high distortion). Such speakers are either too quiet or sufficiently loud but with high distortion levels.

[0004] One of the more popular types of ultraportable loudspeakers conforms to a "candy bar" form factor, so named because of the resemblance to a candy bar in size and shape. An example of such a loudspeaker is set forth in U.S. Patent Publication US 20080292117. Examples are the Jambox™ loudspeaker by Aliph/Jawbone, and the foxLv2 loudspeaker by SoundMatters International, Inc. In this type of speaker, low frequency range reproduction is enhanced using a passive radiator. At listening volumes close to maximum, the sound reproduction becomes highly distorted since the linear excursion of the cone of the small (e.g. 38 mm) speaker drivers and the passive radiator is limited. As the user increases the volume to produce louder sound, the excursion of all transducers becomes non linear, resulting in distortion. Moreover this type of "candy bar" speaker is characterized by poor stereo separation.

[0005] An example of an arrangement of speaker drivers in asymmetric enclosures is described in U.S. Patent No. 6,278,789, in which a large enclosure in the form of a waveguide, and a sealed smaller enclosure, are provided. In U.S. Patent No. 5,483,689, an audio architecture is described which mixes the low frequency of both channels and plays the resulting signal over one channel (i.e. to one speaker driver). Speaker drivers for both channels play the signals above a certain frequency. However, the above-mentioned systems can suffer from poor stereo picture reproduction.

[0006] Accordingly, there is a need for ultraportable loudspeakers with enhanced bass, clear sound, strong loudness and real stereo.

SUMMARY OF THE INVENTION

[0007] It is an aspect of the present invention to provide an ultraportable stereo loudspeaker system having enhanced bass reproduction and loudness, but in a small form factor. According to an embodiment, asymmetric enclosures of different sizes (e.g. one larger and one smaller) are used in combination with a novel audio architecture for reproducing stereophony signals. The two loudspeakers built with these asymmetric enclosures can be detachable from one another. The audio architecture mixes the low frequency signals of both audio channels under a frequency fc and plays the signals with the speaker driver in the large enclosure. Speaker drivers in both enclosures play audio signals above the frequency fc. The audio architecture allows the matching of phase and magnitude of both speakers in the acoustic domain above the frequency fc for an accurate reproduction of the stereo image, even when both speakers are different in size and specifications.

[0008] These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 shows a loudspeaker system in accordance with an embodiment of the invention.

[0010] Figure 2 shows a rear view of the loudspeaker system of Figure 1 in partial section.

[0011] Figure 3 is a block diagram of an audio processing architecture for the system of Figures 1 and 2.

[0012] Figure 4, comprising Figures 4A - 4D, shows loudspeaker enclosures according to various different embodiments.

[0013] Figure 5 shows a measurement set-up for matching gain and phase of the loudspeaker system of Figure 1 , according to a further aspect of the invention.

[0014] Figure 6 shows an embodiment wherein two loudspeakers are docked.

[0015] Figure 7 shows an embodiment wherein two loudspeakers are incorporated into the same housing.

[0016] Figure 8 shows an illustration of the acoustic transfer function as measured with the set-up shown in Figure 5, and the effect of the correction filter for matching the magnitude and phase of both speakers above the crossover frequency fc = 400 Hz.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The sound pressure level generated by a loudspeaker depends on the speaker driver diaphragm (or cone) volume velocity: S x icoX (i.e. the volume of air moved by the diaphragm or cone), where S is the speaker diaphragm (efficient) surface area, X is the speaker diaphragm normal displacement, and ω = 2ττί, which is the circular frequency (f being the frequency in Hz).

[0018] Under the speaker 1st resonance frequency fO (piston mode) the velocity is low, resulting in poor or overly quiet sound reproduction.

[0019] Small speaker drivers generally have a high fO and small surface area S, which are the two major reasons why such speakers are unable to reproduce low frequencies at a satisfying level.

[0020] Moreover, coupling the speaker driver to an enclosure only shifts fO upward, and the smaller the enclosure volume is, the higher the first resonance frequency will be. Better bass reproduction requires a large enclosure volume.

[0021] According to the present invention, the bass reproduction and the loudness of an ultraportable stereo loudspeaker system are improved by using asymmetric enclosures, as shown in Figures 1 and 2, in combination with an audio-processing method for reproducing stereophonic signals, as illustrated in Figure 3. [0022] The stereo loudspeaker system of Figures 1 and 2 includes at least two full range speaker drivers in two separate enclosures of different sizes. The speaker drivers in both enclosures can be identical or different. The large enclosure speaker system allows a better reproduction in the low frequency range, as discussed in greater detail below.

[0023] More particularly, the asymmetric enclosures of Figures 1 and 2 comprise a large enclosure 10 connected via a wire 12 to a small enclosure 14. Enclosure 10 includes a large speaker driver 16, while enclosure 14 includes a small speaker driver 18. As shown in Figure 2, the large enclosure 10 also includes a battery 20 and circuit board 22 containing the audio processing architecture of Figure 3, along with buttons, connectors, etc. (not shown). In the illustrated embodiment, the larger speaker enclosure 10 is shown on the left. However, it will be understood that the larger enclosure 10 can be on the right.

[0024] The audio processing architecture illustrated in Figure 3 re-establishes stereo image for the different loudspeakers 10 and 14, each of which has different acoustic characteristics, while taking advantage of the full frequency range capabilities of the speaker drivers 16 and 18, even if these speaker drivers are different in size and/or have different characteristics.

[0025] As in prior art "2.1" sound systems, extended bass is achieved by driving both left and right channel low frequency audio signals to the larger enclosure loudspeaker driver 16.

[0026] Left and right audio inputs are provided to the circuit (e.g. via an audio jack connector or a special connector like the Apple iPod/iPhone docking connector). The right channel audio signal is low-pass filtered via filter 30 at a defined crossover frequency fc and mixed with the left channel via mixer 34. The right channel audio signal is also high-pass filtered at the crossover frequency fc via high pass filter 35. The left channel audio signal is phase corrected via a circuit 32 prior to being mixed with the output of low-pass filter 30 from the right channel. Circuit 32 can be, for example, an all-pass filter selected to match the phase of low- pass filter 30. In general, circuit 32 compensates for the delay introduced by low-pass filter 30, in order to match the phases of the inputs to mixer 34.

[0027] The left channel is further processed via block 36 for matching the gain and the phase of both loudspeakers in the acoustic domain. This requires an acoustics measurement procedure for determining the phase and gain correction required, as discussed in greater detail below with reference to Figure 5. In other embodiments, a block similar to block 36 could be provided on the right channel, at the output of high-pass filter 35, in addition to, or instead of, block 36. [0028] The asymmetric enclosures of Figures 1 and 2 permit better distribution of the available enclosure volume and optimization of the bass response by (1) reducing the first resonance frequency of the speaker driver 16 coupled to the large enclosure 10 and (2) allowing the implementation of a larger speaker driver (or several speaker drivers) in the large enclosure 10 for better bass reproduction and greater loudness at lower distortion levels.

[0029] Figures 4A-4D shows implementations of enclosure 10, according to various embodiments. As seen in Figure 4A, large enclosure 10 can be sealed. As seen in Figure 4B, large enclosure 10 is ported for enhancing the bass below fO; this arrangement is also known as a "bass reflex" enclosure. Figure 4C shows an embodiment in which large enclosure 10 includes a passive radiator in addition to driver 16, for enhancing the bass below fO. Further, Figure 4D shows an embodiment in which large enclosure 10 can be configured as a waveguide- transmission line speaker (similar to that used in the Bose Wave® system by Bose Corporation).

[0030] The use of large driver 16 in the larger enclosure 10 provides a larger efficient sound radiating surface area than the smaller driver 18 for higher excursion with lower distortion, while keeping the first resonance frequency of the system sufficiently low (i.e. approximately the same value as provided by the smaller driver 18 in smaller enclosure 14), thereby providing more volume velocity around and under the large speaker's first resonance fO for reproducing low frequencies. An additional advantage is that the large driver 16 generally has a higher sensitivity and higher input nominal power, which makes it possible to further extend the low frequency range of the large speaker (driver 16 and enclosure 10) by equalizing the input signals, using filtering techniques such as the Linkwitz transform.

[0031] A test set-up system for measuring phase and gain correction is illustrated in Figure 5. The methodology for performing phase and gain correction comprises (1) driving the two speakers 10 and 14 with an appropriate test sound signal generated by a sound source 50; (2) simultaneously capturing the sound from both speakers at the same distance d using a pair of matched measurement microphones 52a and 52b, (3) maintaining the distance between speakers D as large as possible for minimizing the cross channel interference. The methodology then comprises (4) measuring the transfer function [left microphone output/right microphone output] TF_LR(co), or in other words, the quotient of one microphone's output and the other microphone's output in the frequency domain, within an analyzer 54. The methodology then comprises, in response to the transfer function measurement, (5) determining and implementing correction filter 36 for maintaining both the gain of TF_LR(oo) as close as possible to 0 dB and the phase of TF_LR(w) as close as a possible to 0 deg, in the full frequency range of interest above the crossover frequency, fc. The correction filtering provides an accurate stereophonic picture reproduction above the crossover frequency fc.

[0032] An example of the correction of TF_LR(OO) is illustrated in Figure 8. The example system used in the generation of the data shown in Figure 8 has two asymmetric enclosures, the larger enclosure 10 having a volume of 200 cc, and the smaller enclosure 14 having a volume of 30 cc, with drivers 16 and 18 being, respectively, 50 mm and 38 mm speaker drivers. By acoustic design their frequency response varies in a 5 dB tolerance between fc=400 Hz and 16 kHz. The magnitude and phase of TF_LR(w) is maintained as close as possible to 0 for matching the acoustic frequency response of both loudspeakers and ensuring accurate stereo image reproduction.

[0033] Both left and right channels are amplified by audio amplifiers 38 and 39, respectively. The amplifier outputs drive the two loudspeakers 16 and 18 and may include additional filtering for preventing noise or EMI.

[0034] The audio processing architecture illustrated in Figure 3 is implemented in the analog domain. However, a person of skill in the art will understand that the process of low pass filtering a first channel and mixing it with the second audio channel, high pass-filtering the first channel and dealing with the two resulting channels, as described above and shown in Figure 3 can be implemented in the digital domain via appropriate digital circuitry such as a CPU, DSP, CODEC, or equivalent (FPGA design), or in an audio amplifier having audio enhancements and filtering capabilities.

[0035] It is known from psychoacoustic theory that it is difficult for the human ear to localize low frequency sounds, generally under 150Hz. Accordingly, stereophonic separation is provided by the left and right speakers in the illustrated embodiments at frequencies above the crossover frequency maintained as low as possible via full-range speaker drivers in the left and right enclosures, and proper equalization and phase correction via the audio circuitry of Figure 3.

[0036] For small system where the crossover frequency is significantly higher than 150 Hz, stereo separation may be somewhat compromised, with unbalanced sound at low frequency.

[0037] A person of skill in the art will appreciate that the loudspeaker system of the present invention can be wireless, for example using Bluetooth. Moreover, the system can be operated in either wired or wireless modes, with a switch to toggle between the wireless and wired input options. [0038] It is contemplated that the loudspeaker system of the present invention can be implemented in laptops, netbooks, tablets, docking loudspeakers and any other loudspeaker device where space is limited, and where the method can provide significant bass enhancement.

[0039] In the embodiment of Figure 6, the small speaker enclosure 14 is docked to the large speaker enclosure 10 in a compact or candy bar mode.

[0040] In the embodiment of Figure 7, the two enclosures are integrated within the same "housing". However, in this embodiment the small enclosure is not detachable and the benefit of real stereo reproduction above fc is lost.

[0041] The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

[0042] For example, the loudspeaker system set forth herein may be used advantageously in ultraportable sound systems having small full-range speaker drivers (that is, speaker drivers able to accurately reproduce sounds from fO to 20 kHz) in small enclosures, although it is not intended to apply to large enclosures with large or very large diameter speaker drivers (e.g. 6", 10" , 20" and the like), which are known to have very poor reproduction capabilities at high frequencies.

Claims

1. A loudspeaker system comprising:

asymmetric first and second speaker enclosures having different dimensions and characteristics, said first enclosure being larger than said second enclosure;

at least one speaker driver within each of said first and second enclosures, wherein said at least one speaker driver within said first enclosure is larger than said at least one speaker driver in said second enclosure; and

an audio architecture for driving medium and high frequency signals of respective stereo channels to respective ones of said speaker drivers while driving said at least one speaker driver in said first enclosure with low frequency signals of both stereo channels, said audio architecture for matching the phase and magnitude of both speakers in the acoustic domain to provide accurate stereo image reproduction.

2. The loudspeaker system of claim 1 , wherein said larger one of said enclosures houses said audio architecture.

3. The loudspeaker system of claim 1 , wherein said audio architecture includes a low pass filter for filtering signals from one of said stereo channels above a crossover frequency, and a mixer for mixing the low pass filtered signals with the signals of the other of said stereo channels for driving said at least one speaker driver within said first enclosure.

4. The loudspeaker system of claim 3, wherein said audio architecture includes a high pass filter for filtering signals from said one of said stereo channels below said crossover frequency for driving said at least one speaker driver within said second enclosure.

5. The loudspeaker system of claim 4, wherein said audio architecture includes phase and gain correction circuitry for matching the gain and the phase of sound from said at least one speaker driver within each of said enclosures in the acoustic domain.

6. The loudspeaker system of claim 5, wherein said audio architecture includes a pair of amplifiers for amplifying signals output from said phase and gain correction circuitry.

7. The loudspeaker of claim 1 , wherein said first enclosure is a sealed enclosure.

8. The loudspeaker of claim 1 , wherein said first enclosure is a bass-reflex enclosure.

9. The loudspeaker of claim 1 , wherein said first enclosure further comprises at least one passive radiator.

10. The loudspeaker of claim 1 , wherein said second enclosure is docked to said first enclosure in a "candy bar" configuration.

11. The loudspeaker of claim 1 , wherein said second enclosure is disposed within said first enclosure in a "candy bar" configuration.

12. The loudspeaker system of claim 1 , wherein said audio architecture comprises one of analog circuitry and digital circuitry.

13. A measurement system for matching gain and phase of the loudspeaker system defined in claim 5, comprising:

a sound source for generating and applying a test sound signal to said at least one speaker driver within each of said first and second enclosures;

a pair of matched microphones for receiving sound from said at least one speaker driver within respective ones of said first and second enclosures; and

an analyzer for performing acoustic analysis of the signals received by said pair of microphones.

14. A method for performing phase and gain correction using the measurement system of claim 13, comprising:

separating said first and second enclosures by a distance D that is sufficiently large as to minimize cross channel interference;

driving said at least one speaker driver within each of said enclosures with said test sound from said sound source;

simultaneously capturing sound from said at least one speaker driver within each of said first and second enclosures via respective ones of said microphones, said microphones being located a distance d from respective ones of said at least one speaker driver within said first and second enclosures; measuring within said analyzer a transfer function TF_LR(U)), being the quotient of an output of one of said microphones and an output of the other of said microphones in the frequency domain, and in response determining and implementing said phase and gain correction circuitry for maintaining the gain of TF_LR(w) as close as possible to 0 dB and the phase of TF_LR(CO) as close as a possible to 0 deg, above a crossover frequency, for ensuring correct stereophonic picture reproduction above the crossover frequency.