JPH036718B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a speaker system.

Background Art Speaker systems are designed to provide smooth characteristics in a sound field without reflections such as an anechoic chamber, but in an actual sound field, the speaker system is designed to provide smooth characteristics in a sound field without reflections, such as in an anechoic chamber. installed directly on or
Alternatively, it is generally installed on the floor via a stand.

In this kind of speaker setting,
Sound reflection from surfaces such as floors, ceilings, and walls becomes a problem. In particular, when the speaker system is installed on the floor, reflections from the floor cannot be ignored. Figure 1 is a diagram for explaining the reflection of sound by the floor surface. The reflected sound from surface 1 (indicated by the dashed line) reaches the listening point LP. This reflected sound is
Imaginary sound image 3 located symmetrically with respect to the floor
(hereinafter referred to as a virtual speaker). If the path lengths from the loudspeaker 2 and the virtual image loudspeaker 3 to the listening point LP are _l1 and _l2 , respectively, a path difference _l2 - _l1 exists between them. If this path difference is equal to 1/2 of the wavelength of a certain frequency, that is, if the wavelength at frequency a is λa (a = c/λa, c is the speed of sound), then l ₂ - l ₁ = λa/2, At frequency a, a dip in sound pressure level occurs at listening point LP.

Further, when the path difference is equal to one wavelength λb of a certain frequency b, that is, when l ₂ −l ₁ =λb, a peak of the sound pressure level occurs at the listening point LP at the frequency b. After that, dips and peaks will be repeated at 3λc/2, 2λd, etc. However, as the frequency increases, the influence of reflected sound also decreases, making it possible to ignore dips and peaks in the sound pressure level. FIG. 2 shows the frequency characteristics of the sound pressure level, with a dip occurring at frequency a and a peak occurring at frequency b. especially,
The dip in the sound pressure level at frequency a is large and has a large effect on sound quality.

In order to prevent such dips from occurring, it is difficult to make the floor a perfect sound-absorbing surface to eliminate reflected waves, and such a method is at least not suitable for ordinary homes.

Summary of the invention The purpose of the present invention is to
It is an object of the present invention to provide a speaker system that does not cause dips in the sound pressure level at a listening point and can therefore obtain smooth sound pressure characteristics.

According to the speaker system of the present invention, in addition to the main speaker for the bass range which causes reflected sound generation, a sub speaker for the bass range is provided, and at the listening point, the reflected sound from the main speaker at frequency a and the direct sound from the sub speaker are provided. The reflected sound and the direct sound are set to be in opposite phase with each other, so that the reflected sound and the direct sound are canceled out at the listening point.

Embodiment FIG. 3 shows an embodiment of the speaker system of the present invention. This speaker system includes two bass range speakers, namely a main speaker 4 and a sub speaker 5, one medium and high range speaker 6, and networks 7, 8, and 9 connected to these speakers, respectively. We are prepared. It is assumed that this speaker system is installed on the floor surface 10. The three speakers are arranged in a speaker box along a straight line perpendicular to the floor surface in the order of the main speaker 4 for low frequency range, the speaker 6 for medium and high frequency range, and the sub speaker 5 for low frequency range from a position closer to the floor surface 10. It is located within 11.

Assume that there is a listening point LP at a position parallel to the floor surface 10 from the mid-high range speaker 6, and the angle of depression from this listening point to the bass main speaker 4 is θ ₁ , from the listening point to the speaker 4. The distance of l ₃
shall be. The virtual image speaker of the bass range main speaker 4 with respect to the floor surface 10 is indicated by 12, the depression angle when viewing the virtual image speaker 12 from the listening point LP is θ ₂ , and the distance from the listening point to the virtual image speaker 12 is l ₄ .

When only the low frequency speaker 4 is supplied with a signal and driven, the direct sound from the speaker 4 and the reflected sound reflected by the floor surface 10 reach the listening point LP. Therefore, as explained in FIG. 1, a dip in the sound pressure level occurs at the listening point LP at a frequency a such that l ₄ -l ₃ =λa/2.

In order to prevent the occurrence of dips, the following measures are adopted in this embodiment. First, the bass sub-speaker 5 is arranged so that the angle of elevation seen from the listening point LP is the same as the angle of depression θ ₂ toward the virtual image speaker 12. That is, the bass sub-speaker 5 and the virtual image speaker 12 are positioned symmetrically with respect to the line connecting the mid-high frequency range speaker 6 and the listening point LP. In this case, it can be seen that the distance from the listening point LP to the sub speaker 5 is the same as the distance l ₄ to the virtual image speaker 45.

Next, the characteristics of networks 7, 8, and 9, especially network 8, are selected as follows. The main speaker 4 for low range and the speaker 6 for medium and high range are for crossover, and if the crossover frequency is x, the network 4 connected to the speaker 4 functions as a low pass filter with a cutoff frequency of x. A network 9 connected to the speaker 6 is configured as a high pass filter with a cutoff frequency of x. The parts consisting of the speakers 4 and 6 and the filters 7 and 9 are the same as a normal speaker system.

On the other hand, the network 8 connected to the bass sub-speaker 5 is constituted by a low-pass filter whose cut-off frequency is a frequency a smaller than the crossover frequency x and whose attenuation characteristic is -36 dB/octave.
This low-pass filter 8 has a function of shifting the phase of the input signal to the filter by 180 degrees at the frequency a, that is, shifting the phase by 180 degrees. These low pass filters 7, 8 and high pass filter 9 are connected in parallel to the signal input terminal 13.

Next, the operation of this embodiment will be explained. frequency a
In the smaller bass range, there is almost no phase difference between the signals supplied to the main speaker 4 and the sub-speaker 5 via the low-pass filters 7 and 8, and these speakers for the bass range operate in complete parallel connection. Also, in the frequency range smaller than a,
There is no dip in the sound pressure level due to the influence of sound reflected by the floor surface 10 from the bass main speaker 4, and the sound quality is stable.

When the frequency increases to a, the signal supplied to the low-pass filter 8 is output after being phase-shifted by 180 degrees, and has a phase opposite to that of the signal output from the low-pass filter 7. Therefore, the low frequency range generated from the main speaker 4 and the sub speaker 5 will be out of phase by 180 degrees. The low-frequency sound from the main speaker 4 that is reflected by the floor surface 10 and reaches the listening point LP can be considered as the low-frequency sound generated by the virtual image speaker 12.

As mentioned above, the bass sub-speaker 5 is
Distance to the virtual image speaker 12 from the listening point LP l ₄
Because they are placed at the same distance from each other, there is no phase shift due to path differences, and the direct sound from speaker 5 and the reflected sound from speaker 4 can be heard at listening point LP.
reach. These direct sounds and reflected sounds are out of phase.
Since they are shifted by 180 degrees, that is, they are in an anti-phase relationship, they cancel each other out at the listening point LP. Therefore, it is the same as if the reflected sound did not reach the listening point LP, and no dip in the sound pressure level at frequency a occurs.

When the frequency becomes greater than a, the low-pass filter 8 attenuates the signal to the sub-speaker 5 and only the main speaker 4 operates, but since the influence of reflected sound is small, no dip in sound pressure level occurs.

In FIG. 4, the frequency characteristic of the sound pressure level at the listening point LP in this embodiment is shown by a solid line. For comparison, the frequency characteristic when a dip occurs at frequency a is shown by a broken line. As described above, according to this embodiment, smooth sound pressure characteristics can be obtained.

Next, another embodiment of the present invention will be described based on FIG. This example is based on the third example except for the following points.
The embodiment is substantially similar to the embodiment described in the figures, and the same elements as those in FIG. 3 are designated by the same numbers.

In this embodiment, the virtual image speaker 12 and the listening point LP
sub speaker 5 and the listening point for the distance l ₄ between
Set the distance _{l 5} between the LP and the subwoofer so that it is larger than the distance _{l 4} within a range that can be ignored compared to the wavelength of the bass range, and at the same time, at frequency a, Place the speaker 5. By doing this, the phase of the direct sound from the sub-speaker 5 is delayed by 90 degrees with respect to the reflected sound from the main speaker 4 around the frequency a.

On the other hand, the low-pass filter 8 has a cut-off frequency of
It is made to have a gentle attenuation characteristic of -12 dB/oct at a, and a phase shift of 90° is caused at frequency a.

In the speaker system configured as above, when the frequency increases to a, the output signal of the low-pass filter 8 is delayed by 90 degrees in phase with respect to the output signal of the low-pass filter 7, and as a result, the direct signal from the sub-speaker 5 is The phase of the sound will be delayed by 90° compared to the sound reflected from the main speaker 4.

Furthermore, due to the path difference between the distance _l5 and the distance _l4 , the direct sound from the sub speaker 5 is different from the reflected sound.
Since the phase is delayed by 90 degrees, the direct sound that finally reaches the listening point LP will be delayed in phase by 180 degrees with respect to the reflected sound that reaches the listening point LP. Therefore, as in the embodiment described above, the direct sound from the sub-speaker 5 and the reflected sound from the main speaker 4 are canceled out at the listening point LP, and the reflected sound is eliminated. This makes it possible to prevent dips caused by reflected sound from occurring at frequency a.

In the above two embodiments, the low-pass filters 7 and 8 are connected in parallel, but they can also be connected in series as shown in FIG. The cutoff frequency a of the low-pass filter 8 is the cut-off frequency a of the low-pass filter 7.
Since it is smaller than the cutoff frequency x of
The low-pass filter 8 can output a signal that is out of phase with the output of the low-pass filter 7.

Further, although a low-pass filter is used in the network 8 to shift the phase, it is clear that a phase shifter can also be used.

Furthermore, if level control is performed to match the level of the low-frequency sound from the sub speaker 5 to the level of the reflected sound from the main speaker 4, the reflected sound can be completely eliminated.

The speaker system of the present invention can deal with not only reflections from the floor but also reflections from the ceiling. Furthermore, the speaker system is not limited to being installed on the floor, but can also be installed on the wall.

Effects According to the speaker system of the present invention, a sub-speaker for low frequency range is provided, and the direct sound from the sub-speaker unit is reflected at the listening point LP by making the phase shift of 180 degrees with respect to the reflected sound. Since the sound can be canceled out and eliminated, and the dip at frequency a due to reflected sound can be prevented from occurring, smooth sound pressure characteristics can be obtained.

In addition, in the bass range smaller than frequency a, two bass speaker units operate in parallel in the same phase, so the radiation area is doubled compared to when there is only one bass speaker unit, resulting in lower sensitivity. 3dB
In addition to this, the allowable input also doubles, and the maximum output sound pressure increases to 6dB. This enables rich bass reproduction with excellent linearity.

Furthermore, in a typical parallel-connected double woofer system, the sound image becomes too large in the midrange, and sound pressure synthesis cannot be performed properly due to the phase difference caused by the path difference between distances l ₃ and l ₄ . In contrast, in the speaker system of the present invention, the signal to the bass sub-speaker is attenuated in the middle range above frequency a, so only the main speaker for the bass range operates, which is different from the conventional double woofer system. Since interference can be prevented, the reproducibility of sound images is also improved.

According to the present invention, good sound quality and characteristics can be obtained without requiring a special room or acoustic treatment, so it has great practical value.

Furthermore, since the three speaker units are arranged in a straight line, the space factor of the speaker box is also good.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the reflection of sound by the floor surface, Fig. 2 is a diagram showing the sound pressure characteristics at the listening point in the case of Fig. 1, and Fig. 3 is an example of the present invention. FIG. 4 is a diagram showing the sound pressure characteristics at the listening point in one embodiment of FIG.
FIG. 5 is a diagram showing the configuration of another embodiment of the present invention,
FIG. 6 is a diagram showing another example of network connection. Explanation of symbols of main parts, 4...Main speaker for bass range, 5...Sub speaker for bass range, 6...
Speakers for medium and high frequency range, 7, 8, 9...Network, 10...Floor, 11...Speaker box,
12...Virtual image speaker, 13...Signal input terminal.

Claims (1)

[Scope of Claims] 1. A main speaker and a sub-speaker for bass reproduction, which are sequentially arranged along a straight line perpendicular to the sound-reflecting wall surface, starting from the one closest to the reflecting wall surface; The difference between the distance from the listening point to the virtual image speaker of the main speaker and the distance from the listening point to the main speaker, which are assumed to be in a symmetrical position with respect to the reflecting wall surface, blocks a frequency a corresponding to a half wavelength of sound. and a network that causes a phase shift in the supplied signal so that the signal is out of phase with respect to the signal to the main speaker, and at the frequency a, the sound reflected from the main speaker by the reflecting wall surface and A speaker system characterized in that the phase difference between the direct sound from the sub-speaker and the direct sound is 180° at a listening point. 2. The sub-speaker is arranged so that the distance from the listening point is equal to the distance from the listening point to the virtual image speaker, and the amount of phase shift of the network is
Claim 1 characterized in that the angle is 180°.
The speaker system described in section. 3 The distance of the sub-speaker from the listening point is
than the distance from the listening point to the virtual image speaker,
2. The speaker system according to claim 1, wherein the speaker system is arranged such that the frequency is 1/4 wavelength larger at the frequency a, and the phase shift amount of the network is 90 degrees.