HK1036727A - Telephone with means for enhancing the low-frequency response - Google Patents

Description

Telephone set with device for enhancing low frequency response

The present invention relates to telephones with means for enhancing low frequency response and, more particularly, to such telephones of the type having a speaker mounted behind the earpiece portion of the housing and having at least one sound opening in the central region of the earpiece portion from which sound generated by the speaker emanates.

In the above-mentioned technical field, the sound quality of a telephone set is not always perfect, which is well known. The main reason for this is the limited frequency response of the telephone set (between about 300 and 3400 hz). The limitations on frequency response are prescribed in various officially approved regulations, which are mostly based on a draft laid down by the no longer existing CCITT (International telegraph telephone council, formerly known as the ITU (International telecommunication Union) Committee, itself a United nations negotiation (unity) organization.

According to a generally accepted test method, the frequency response of a loudspeaker in a telephone is measured with a test microphone, which is coupled directly to the loudspeaker by means of a gastight seal. The test microphone is typically mounted centrally in the handset portion of the telephone housing, i.e., immediately above the speaker located behind the handset portion. The prior art telephone manufacturing techniques are fully capable of making the frequency response sufficiently flat and well within prescribed limits during testing by means of the hermetic seal between the loudspeaker and the microphone described above, so that the telephone can pass the test.

However, since the test specifies a hermetic seal as described above, even a small gap between the speaker and the microphone results in a less than satisfactory frequency response of the speaker. In real life there is little perfect seal between the speaker and the user's ear. In contrast, telephones are typically held at a small distance from the human ear. This is especially true for mobile phones where the reception loudness is high and the noise level may be quite large, the user is likely to keep some distance between his ear and the phone speaker. The result is that the lower frequency regions of the sound received through the speaker will not exhibit the perfect loudness exhibited during the speaker qualification test; but the sound amplitude of low frequencies is much lower than in the ideal case of a flat frequency response.

Previously known methods for solving the above problems involve boosting the low frequency region of the sound emitted from the speaker, wherein difficulties arise in maintaining the overall frequency response of the telephone at a sufficiently flat level. In addition, one obvious approach is to utilize quality acoustic, electrical or electronic components to reduce noise overall. However, this approach means an increase in the manufacturing cost of the telephone set.

An object of the present invention is to solve the above problems. In essence, the low frequency response of the telephone can be improved by the implementation method of the invention: the low frequency loss can be corrected by a means which amplifies the low frequency region of the sound and causes the sound to emanate from a location spaced from the center of the handset, the speaker sound is typically emanated from the center of the handset, and the test microphone is hermetically sealed coupled to the center of the handset during the qualification test. In other words, in accordance with the present invention, the frequency response obtained in the center of the handset during testing is maintained at a flat level sufficient to pass the test, while at the same time the low frequencies of the sound (i.e., bass) are amplified and emitted from the non-central portion of the handset or telephone housing. Thanks to the invention, the telephone will still be able to pass authentication tests, while at the same time the user will enjoy an improved bass tone quality in normal use, with a certain distance between the human ear and the loudspeaker of the telephone.

Thus, the object of the invention is achieved for a telephone set: the telephone includes a speaker mounted behind a handset portion of the housing, a central region of the handset portion having at least one acoustic opening through which sound generated by the speaker is emitted, at least one bass opening being provided in the housing remote from the central acoustic opening; and means are provided for producing sound with enhanced low frequency characteristics through the bass sound openings.

Other objects, features and advantages of the present invention will be described in the following detailed disclosure, drawings and appended claims.

Preferred embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a portion of a telephone in accordance with one embodiment of the present invention;

FIG. 2 is a schematic circuit diagram of the embodiment of FIG. 1;

FIG. 3 is another schematic circuit diagram of the embodiment of FIG. 1;

FIGS. 4 and 5 are graphs illustrating the frequency response of the embodiment of FIGS. 1-3;

FIG. 6 is a schematic cross-sectional view of a second embodiment of the present invention; and

fig. 7 is a graph illustrating the frequency response of the embodiment shown in fig. 6.

Fig. 1 illustrates a first embodiment of a telephone with a low frequency response boosting device according to the present invention. The telephone includes a device housing 30 with an earpiece portion 20 provided with an acoustic opening 40. The first speaker 10 is mounted in a conventional manner within the device housing 30 behind the earpiece portion 20, in alignment with the acoustic opening 40. The first loudspeaker 10 is designed to have a flat frequency response which meets the above-mentioned approved specifications, where the frequency response is measured with a test microphone mounted on the earpiece portion 20 by means of a hermetic seal. In addition, the telephone is provided with a second speaker 70, which is mounted inside the device housing 30, behind the first speaker 10. As will be described later, the second speaker 70 is arranged to produce sound enhanced in low frequency characteristics through the bass opening 60 in the apparatus casing 30.

As seen in fig. 1, the bass vents 60 are located away from the central acoustic vent 40 at the center of the earpiece portion 20. In addition, the first loudspeaker 10 is provided with a first sound chamber 12 formed by a wall 14, while the second loudspeaker 70 has a second sound chamber 62 formed by a wall 64. The sound chambers 12 and 62 are acoustically isolated from each other.

The first loudspeaker 10, hereinafter called flat-response loudspeaker, and the second loudspeaker, hereinafter called woofer, are both connected to a common amplifier 72. The flat response loudspeaker 10 is connected directly to this amplifier 72 to provide the flat frequency response shown in figure 4, while the woofer 70 is connected to the amplifier 72 through an intermediate low pass filter 74 that attenuates the higher frequencies of the drive signal provided to the woofer 70 and provides a frequency response primarily in the low frequency region, as illustrated in figure 4. As illustrated in fig. 2, the low pass filter 74 includes a 10nH (millihenry) coil 76 in series with a 10 uf capacitor 78. Low-pass filters of this type are well known in the art and will not be described in more detail below.

Thus, the woofer 70 is arranged to emit sound with enhanced bass or low frequency characteristics through the non-central bass sound opening 60. The bass sound openings 60 are located sufficiently far from the central sound opening 40 so as not to affect the measurement results of the above-mentioned qualification tests performed in the central area of the earpiece portion 20. On the other hand, in normal use, as illustrated in fig. 5, providing enhanced bass sound through the bass vents 60 will improve the sound quality provided to the user.

The lowest curve of fig. 5 represents the sound quality obtained with a microphone held at a distance of 2cm from the end of the telephone including the earpiece portion, when only the flat response speaker 10 is used (i.e., equivalent to a prior art telephone using only one speaker). The upper curve in fig. 5 represents the sound quality measured with the same microphone located at the same distance from the telephone using the two-speaker arrangement according to the above-described embodiment of the invention. As is clear from fig. 5, the sound quality in the low frequency region is significantly improved due to the present invention.

As illustrated in fig. 3, instead of sharing one amplifier 72 for both speakers 10 and 70 in fig. 2, the flat response speaker 10 and the woofer 70 may be driven by respective amplifiers 80 and 82. A low pass filter 84 is connected before the second amplifier 82 so that only low frequencies are amplified in the drive signal supplied to the woofer 70. As will be appreciated by those skilled in the art, the low pass filter 84 may be implemented with conventional passive components such as resistors and capacitors. Alternatively, the low pass filtering may be implemented with a Digital Signal Processor (DSP).

A second embodiment of the present invention will now be described with reference to fig. 6 and 7. The second embodiment provides a more compact solution than the first embodiment because it does not require the use of an additional woofer 70. A schematic diagram of a second embodiment is given in fig. 6. The telephone includes a device housing 30 with an earpiece portion 20 provided with a central sound opening 40. The speaker 10 is mounted inside the device housing 30, behind the earpiece portion 20. In addition, the device housing 30 is provided with a bass sound opening 60 at a distance from the central area of the earpiece portion 20 and the central sound opening 40. The elements described so far are the same as or similar to the corresponding elements in the first embodiment described in fig. 1.

Unlike the first embodiment, the telephone of fig. 6 has no additional woofer. Instead, bass chambers 92 are arranged on both sides of the central sound chamber 12. The bass chambers 92 are formed by walls 96 and are connected to the respective bass sound openings 60. In addition, each bass chamber 92 is connected to the central sound chamber 12 by an aperture 90 in a wall 96. In addition, each bass chamber 92 contains an acoustically attenuating material 94 arranged to filter out high frequency components of the sound leaking from the central acoustic chamber 12 through the openings 90 into the respective bass chamber 92.

The single speaker 10 is driven by amplification means such as an amplifier and a filter, so that a low frequency region of sound emitted from the speaker 10 is amplified. This boost in the low frequency region appears to conflict with the acoustic flat response requirement detected with the test microphone through the central acoustic opening 40. However, a certain amount of sound generated by the loudspeaker 10 in the central sound cavity 12 leaks through the opening 90 to the bass cavity 92. The higher frequency regions of the sound are attenuated by the attenuating material 94 and the openings 90 themselves, but a certain number of the lower frequency components will emanate through the bass sound openings 60, thereby enhancing the bass portion of the overall volume received by the human ear at some distance from the earpiece portion 20.

To obtain both a sufficiently flat frequency response when measured directly on the central sound opening 40 by means of a hermetic seal, and the desired bass enhancement when the phone is listened to in normal use, the central sound chamber 12 as well as the bass chambers 92, openings 90 and 60, and acoustic attenuation material 94 all need to be carefully designed and adjusted during real life and laboratory testing. Given the basic guidelines set forth above, it is well within the ability of one skilled in the art to make such adjustments.

The frequency response of the second embodiment measured with the test microphone held tightly against the earpiece portion 20 is shown in fig. 7. The lowest curve represents the frequency response of loudspeaker 10 without amplification or compensation for low frequency loss. The uppermost curve represents the frequency response of the amplifier used to improve the bass sound characteristics. As can be seen in fig. 7, the amplifier is arranged to provide high level amplification up to frequencies of around 300 hz, with linearly decreasing amplification to frequencies of around 300 hz to 900 hz. For frequencies above 900 hz, the amplifier provides low level amplification. The resulting synthesized frequency response of the loudspeaker 10 is illustrated by the middle curve, which shows that the overall sound quality obtained with the second embodiment of the invention exhibits a sufficiently flat frequency response characteristic.

The resulting frequency characteristic obtained in normal use corresponds substantially to the frequency response of the first embodiment shown in fig. 5.

The present invention has been described above with reference to the first and second embodiments. However, various embodiments other than the ones explicitly disclosed herein are possible within the scope of the invention, as defined by the appended independent claims. For example, with the first embodiment, two speakers may also be placed beside each other instead of behind each other. In addition, all amplification and filtering functions may be performed by means other than those disclosed herein. Furthermore, the central sound openings and the further bass sound openings may be arranged differently, and may be more or less numerous than those shown in the figures and described above. With the second embodiment (fig. 6), the use of acoustic attenuation material 94 can be avoided by careful design of the acoustic properties of the bass chamber 92 and the openings 90 and 60.

Claims (6)

1. A telephone comprising a loudspeaker (10) mounted behind an earpiece portion (20) of a housing (30), a central region of the earpiece portion having at least one sound opening (40) through which sound generated by the loudspeaker is emitted, characterized in that:

at least one bass vent (60) located in the enclosure (30) away from the at least one central acoustic vent (40), and

means (70, 72, 74; 70, 82, 84; 10, 92, 94) for generating sound with enhanced low frequency characteristics through the at least one low sound opening (60).

2. A telephone according to claim 1, wherein: the means for generating sound with enhanced low frequency characteristics comprises an additional loudspeaker (70).

3. A telephone according to claim 2, wherein: the additional speaker (70) is acoustically isolated from a speaker (10) mounted behind the earpiece portion (20).

4. A telephone according to any of claims 1-3, wherein: the means for generating sound with enhanced low frequency characteristics includes an amplifier (72; 82) and a low pass filter (74; 84).

5. A telephone according to claim 1, wherein: the means for generating sound with enhanced low frequency characteristics comprises a cavity (92) for directing sound generated by the loudspeaker (10) to the at least one bass sound opening (60).

6. The telephone set according to claim 5, wherein: the cavity (92) includes an acoustically attenuating material (94).