JPH04144398A - On-vehicle speaker system - Google Patents

Abstract

PURPOSE:To utilize a door of an automobile effectively and to reproduce an ultralow- pitched sound excellently by providing a speaker to a wall face in the cabin side of the door of the automobile, choking a work use opening hole formed to a wall face of the door at the cabin side with a low-pitched sound diaphragm and acting the diaphragm as an auxiliary low-pitched sound radiator. CONSTITUTION:A low-pitched sound diaphragm 3 is fitted to a wall face 1A while choking one of work use open holes formed to the wall face 1A of a front door shell 1 in the car body side. A sound wave radiating in the inside of a door from a speaker 2 fitted to the front door shell 1 propagates a door inside space 1B to vibrate the low-pitched sound diaphragm 3. In this case, the sound wave radiating from the low- pitched sound diaphragm 3 and the sound radiating directly from the speaker 2 are in opposite phase and cancelled at a very low-pitched and a phase difference is caused as the frequency increases, resulting that the remaining amplitude is gradually increased, and the sound wave radiating from the low-pitched sound diaphragm 3 and the sound wave radiating from the speaker 2 are almost in phase at a resonance frequency depending on the compliance in the inside of the door, an equivalent mass of the low-pitched sound diaphragm 3 and the compliance of the low-pitched sound diaphragm 3 and the sound pressure is added.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an in-vehicle speaker system configured to enjoy audio reproduction from a car stereo or the like in the interior of an automobile.

[Prior Art] Conventionally, a speaker system for reproducing audio from a car stereo or the like inside an automobile has a structure in which a speaker is attached to the front door and the volume inside the door is used to reproduce bass sounds. What has been done is known. Such a speaker system has the advantage of being able to reproduce natural bass sounds that can be heard from the front for the occupants.

However, since the front door has a working hole for repairing and maintaining the mechanical and electrical components inside the door, in the deep bass range, the opposite-phase sound waves radiate to the rear of the speaker. The sound waves leak through the working hole through the space inside the door and work to cancel out the sound waves emitted in front of the speaker, making it impossible to reproduce deep bass sounds well.

In particular, since the above-mentioned working holes are provided near the speakers or in the center of the door with emphasis on workability, there is a strong tendency for sound waves to be canceled out. If the cabinet is closed, the volume inside the door will be small, making it difficult to reproduce deep bass sounds.

[Problem to be solved by the invention] Since the conventional in-vehicle speaker system is configured as described above, it is necessary to block the working opening, and if it is blocked with a steel plate, the volume inside the door becomes small. There were problems such as not being able to get enough deep bass.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an in-vehicle speaker system that can effectively reproduce deep bass sounds by effectively utilizing the door of the vehicle.

[Means for Solving the Problems] An in-vehicle speaker system according to the present invention includes a speaker provided on a wall surface on the inside of a door of an automobile, and
The present invention is characterized in that a diaphragm that vibrates in response to sound pressure inside the door is attached to the wall surface in such a manner that it closes a working opening formed in the wall surface on the vehicle side of the door.

In particular, it is preferable to provide a plurality of diaphragms and set the resonance frequencies of the plurality of diaphragms to be different from each other.

[Function] According to the present invention, the diaphragm vibrates due to sound waves emitted from the back of the speaker to the inside of the door, and this vibration is caused by the air spring inside the door, the equal image mass of the diaphragm, and the compliance of the diaphragm support system. It becomes the largest at the determined resonance frequency, and the sound pressure in the deep bass range is increased.

In particular, by setting the resonant frequencies of the plurality of diaphragms to be different from each other, the back pressure applied to the diaphragms is increased, and the radiation efficiency of deep bass is increased.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings.

Fig. 1 shows an in-vehicle speaker system according to an embodiment of the present invention, and Fig. 2 is an external view of a front door of an automobile, and Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. An example is shown right next to the speaker.

In Figure 1, (1) is the front door body, (2) is the speaker, and (3) is the diaphragm (hereinafter referred to as the bass diaphragm).
Then, the wall surface (IA) on the inside of the vehicle of the front door body (1)
) is cut into the wall surface (IA) in such a manner as to close one of the working openings formed in the hole. In other words, the bass diaphragm (3) is placed in a state that also serves as a closing plate for the working hole.
is installed.

(4) is another working hole that is closed to prevent air leakage.

The bass diaphragm (3) is composed of, for example, a diaphragm and an edge that supports it, and the material for the diaphragm is the same as that used for general speaker diaphragms. A material with little air leakage, such as paper, carbon graphite, or an aluminum membrane with a honeycomb structure, is suitable.The material for the edge is the same material as that for the speaker with little air leakage, such as impregnated with resin. Paper, rubber, etc. are suitable.

Next, the operation of the above configuration will be explained.

Speaker (2) attached to the front door body (1)
) The sound waves emitted from the speaker (
2) The sound waves are broadly divided into the sound waves radiated behind the diaphragm, that is, inside the door, and both sound waves have opposite phases.

” - The sound waves radiated inside the door are inside the door space (IB
) and reaches the bass diaphragm (3), causing the bass diaphragm (3) to vibrate. At this time, at extremely low frequencies, the sound waves inside the door and the vibration waves from the bass diaphragm (3) are in the same phase, so the sound waves radiated from the bass diaphragm (3) and the vibration waves directly from the speaker (2) are in phase. They are in opposite phase to the sound waves that flow, and they cancel each other out.

However, as the frequency increases, the compliance inside the door causes the sound waves inside the door and the bass diaphragm (3
), the amplitude gradually increases, and reaches its maximum at the resonant frequency determined by the compliance inside the door, the equal image mass of the bass diaphragm (3), and the compliance. At this time, the bass diaphragm (3
) The sound waves emitted from the speaker (2) are almost in phase with the sound waves emitted from the speaker (2), and the sound pressure is added to the sound waves emitted from the speaker (2). In addition, in the band further above the above resonance frequency, the bass diaphragm (3)
The amplitude gradually decreases and no longer contributes to the increase in sound pressure.

Such operation is represented by equivalent circuits shown in FIGS. 3 and 4.

In Figures 3 and 4, mc is the mass of the diaphragm and voice coil, CS is the compliance of the support, rs is the mechanical resistance of the support, ma is the mass of the air load, ra is the mechanical resistance of the air load, and C Compliance inside the door
ml is the equal image mass that is the mass of the bass diaphragm (3) plus the mass of the air load, rp is the mechanical resistance of the support of the bass diaphragm (3), and cp is the compliance of the support of the bass diaphragm (3) , fm is the driving force generated in the voice coil.

In the following explanation, since the mechanical resistance rp of the equivalent circuit in FIG. 3 is small, this mechanical resistance rp is assumed to be zero.

First, the frequency fd at which the sound waves radiated from the bass diaphragm (3) and the sound waves radiated from the speaker (2) cancel each other out and the sound pressure is the lowest is expressed as follows.

Bass diaphragm (3) frequency fp The sound pressure emitted from the teeth.

It is expressed as

Therefore, up to the lower limit frequency fp, the sound waves radiated from the bass diaphragm (3) and the speaker (2
) are added in phase and can be reproduced with a high sound pressure.

Next, parameter determination of the bass diaphragm (3) will be explained using an automobile door as an example.

Generally, in the case of automobile doors, the shape of the door is almost fixed, and the internal volume cannot be selected arbitrarily, so the bass diaphragm (3) that is suitable for the internal volume must be determined. . In the above equation (3), the uniform image mass m1 and the compliance cp are calculated.

Transforming equation (3), we get ...(4) becomes.

On the other hand, if the mass of the bass diaphragm (3) is mp and the radius of a circle equal to the area of the bass diaphragm (3) is b, the equal image mass mi in equation (4) is expressed by the following equation (5). Ru.

mi = mp + (16/3) po b
-(5) where ρ0 is the air density.

The uniform image mass mi in the above equation (4) is mainly determined by the constant of the speaker (2), the internal volume of the door, and the lower limit frequency to be set.

Rewriting equation (4) using speaker constants, mo: isometric mass of the speaker, fo: lowest resonant frequency of the speaker, So: stiffness of the speaker support system, a: radius of the diaphragm of the speaker, Sv: door volume Stiffness of V c, Sp: Stiffness of bass diaphragm support system, C: Speed of sound, ρ0 - Air density, [] A speaker with a diameter of 16 cm is shown as an example. The speaker constant is expressed by the following equation (9).

Effective vibration radius a=6. '5cm equivalent mass
mo=7.0g Minimum resonance frequency fo=70Hz...(9)
If Q of the vibration system Qo=0.7 and door volume Vc=54, then from equation (7), 5v=
460.1 (s/m) ... (10) If a support material with the same stiffness of the low-damping diaphragm (3) as the speaker support system is used, and the lower limit frequency fp is 50Hz, then m+=O, Ol 84 ( Kg) −(11
) If the area of the bass diaphragm (3) is the same as the working opening 30cm x I5cm in Figure 1, the radius b of the same area is
12 cm, and from equation (5) m + 2 mp + 0
, 0112 (kg) - (12).

Here, if the mass mp of the bass diaphragm (3) is selected to be approximately 7.2 g, the equal image quality Ff< m of equations (11) and (12)
i becomes equal, and the door volume and the low 7r and diaphragm (3) suitable for the speaker (2) can be determined.

In this case, the diaphragm material may be a slightly lighter cone paper, styrofoam, etc., and the diaphragm can be adjusted by attaching a weight to it.

FIGS. 5 and 6 show another embodiment of the invention.
Figure 5 is an external view of a Freon I. The difference from the embodiment shown in Figure 2 is that 2 is used as the bass diaphragm.
Two bass diaphragms (3a).

(3b) is the wall surface (I) on the inside of the car of the front door body (1).
The point is that the working openings formed in A) are drilled into the wall surface (IA) in a state where they are respectively closed, and the other configuration is the same as the above example, so the same part is used in the corresponding part. , and their explanation will be omitted.

”-Paper sound diaphragms (3a) and (3b) remove magnetic circuits such as voice coils and magnets from car speakers and have only a diaphragm and a diaphragm support system, and are therefore newly designed for work use. There is no need to develop a bass diaphragm with a shape that matches the opening, and it can be constructed at low cost.

Furthermore, both bass diaphragms (3a) and (3b) have the same image mass and compliance, and are mounted close to each other. In the bass range where these bass diaphragms (3a) and (3b) work effectively, one wavelength is 3 meters or more, which is three times the door size. At this time, a sound pressure difference is generated between the left and right ends, the top and bottom ends, and the diagonal ends of the front door body (1) due to the sound waves radiated into the door. On the other hand, the difference in sound pressure is small between close positions in the center of the door, and the diameter is 10c.
Bass diaphragm (3a), (3b) of m ~ 30cm
If you can pick it up close, the center distance is 5cm to 4cm.
The bass diaphragm (3a) is small and close to each other, approximately 0 cm above one wavelength.

(3b) operates in the same way as a single bass diaphragm, and provides the same effects as in the above embodiment.

FIGS. 7 and 8 show an in-vehicle speaker system according to another embodiment of the present invention, in which FIG. 7 is an external view of a front door of an automobile, and FIG. It is. In this embodiment, like the embodiments shown in FIGS. 5 and 6, a plurality of bass diaphragms (3A),
(3B), and each diaphragm (3A), (3
The resonance frequency of B) is changed depending on their installation position, and in this example, the bass diaphragm (3A)
, (3B) are installed right next to and directly behind the speaker (2), respectively.

The operation in this embodiment is represented by equivalent circuits shown in FIGS. 9 and 10.

In the same figure, mea and mab are each bass diaphragm (3A)
, (3B) and the air load mass, rpa is the mechanical resistance of the support of the bass diaphragm (3A), c
pa, c pb are bass diaphragms (3A), (3B
), me is the mass of the diaphragm and voice coil, CS is the compliance of the support, rs
is the mechanical resistance of the support, ma is the mass of the air load, ra is the mechanical resistance of the air load, cv is the compliance inside the door, and fm is the driving force generated in the voice coil.

In this way, the bass diaphragm (3A) with different resonance frequencies,
When both (3B) exist, the sound diaphragms on both sides correspond to parallel connection, and the equal image mass is m ia @ m ib/(
mia+m1b), compliance is (cpa+c
pb), each bass diaphragm (3A), (3B)
Frequency fpa, f at which the sound pressure radiated from
pb is expressed as...(13)...(14), and its composite frequency fp is expressed as follows. Therefore, −1− the lower limit frequency f
Each bass diaphragm (3A), (3B
) and the sound waves emitted from the speaker (2) are added in phase and can be reproduced with a high sound pressure.

Note that the three scenes can also be considered to be connected in parallel.

When formula (15) is squared and set as (16), the frequency fp is expressed as fp-, calendar ζ1 f2 (17). Therefore, the resonance frequencies of the bass diaphragms (3A) and (3B) are fa = (1/2πcpa mia) fb =
(1/2πE-1-1)...(18) Therefore, fp can be obtained from equations (16) to (18).

Next, an example of the resonance frequencies fa and fb will be explained based on the sound pressure characteristics of a door in an automobile.

FIG. 11 is a sound pressure characteristic graph obtained by numerically analyzing the sound pressure inside the front door of a 2000cc class automobile using the boundary element method.

In the figure, the vertical axis indicates the sound pressure at the working hole surface before the bass diaphragm is attached.

In addition, in the same figure, the solid line is the sound pressure on the aperture surface at the bass diaphragm (3B) position, and the chain line with the X mark is the bass diaphragm (3A).
This shows that the sound pressure on the aperture surface at position ) varies greatly depending on the shape of the inside of the door, and also varies greatly depending on the position of the aperture.

The sound pressure at the position of the bass diaphragm (3A) has a dip at 150 Hz, and at 120 Hz, the sound pressure is about 7 dB smaller than the sound pressure at the location of the bass diaphragm (3B). At this time, 120
At Hz, there is a similar difference in the back pressure applied to the sound diaphragms (3A) and (3B) of both papers. When designing the frequency fp at which the sound wave radiation from the bass diaphragm becomes the largest using the above equation (17), both sound diaphragms (3A).

If the resonance frequencies of (3B) are both selected to be 120 Hz, the back pressure applied to the bass diaphragm (3A) will be small and the efficiency of bass radiation will be poor.

However, for example, if the resonance frequency of the bass diaphragm (3A) is set to 20
~ 80 Hz, by selecting the resonance frequency of the bass diaphragm (3B) from a higher range of 90 to 140 Hz and determining the composite frequency fp, the back pressure applied to the bass diaphragm (3A) can be increased. , has good bass radiation efficiency. Furthermore, since both back pressures are approximately equal, the synthesized frequency fp is approximately close to the design value.

For automotive applications, it is difficult to arbitrarily set the resonant frequency of the bass diaphragm, but the above range can be achieved using a speaker diameter that can be mounted on a vehicle and an acoustic material suitable for automotive use, and the selection of the diaphragm is Formulas (1) to (3) and (13) to (
18) It can be done using Eq.

In the interior of a car, a peak dip occurs in the low frequency range due to a resonance phenomenon caused by the size and shape of the cabin itself. in this case,
It is even more effective to match the resonance frequency fp of the bass diaphragm to the frequency at which the dip occurs.

Further, in FIG. 11, the sound pressure characteristics when there is an opening diagonally to the speaker are shown by a dashed line.

This sound pressure characteristic is close to the characteristic of the bass diaphragm (3B), and the position of this hole corresponds to the working hole (4) in FIG. When the working hole (4) is used as the bass diaphragm in FIG. 3, it is understood that the resonance frequency fc may be set to the same value as the bass diaphragm (3B) in the example in FIG. 11.

Therefore, the resonance frequency of each bass diaphragm is fa = 20-80Hz, fb = 90 N1
40Hz.

By selecting fc=90 to 140 Hz, the same effect as described above can be obtained.

[Effects of the Invention] As described above, according to the present invention, the working opening is closed with a low-pitched sound diaphragm and is configured to function as an auxiliary low-pitched sound radiator, so that the door of a car can be effectively used. By using this, deep bass can be reproduced well.

In particular, by using a plurality of diaphragms with different resonant frequencies, the back pressure applied to the diaphragms can be increased, the radiation efficiency of deep bass sounds can be increased, and deep bass sounds can be reproduced with high sound pressure in the negative layer.

[Brief explanation of the drawing]

Fig. 1 is an external view showing an embodiment of the in-vehicle speaker system according to the present invention, Fig. 2 is a sectional view taken along line III in Fig. 1, Fig. 3 is an equivalent circuit diagram, and Fig. 4 is a sectional view thereof. , FIG. 5 shows another embodiment of the present invention, which is an external view when two bass diaphragms are used, and FIG. 6 shows the VI- of FIG.
FIG. 7 is a cross-sectional view taken along the VI line and shows another embodiment of the present invention, and FIG. 8 is an external view when two bass diaphragms with different resonance frequencies are used. 9 is an equivalent circuit diagram of 7, 10 is a sectional view taken along the line ■-■.
The figure is a cross-sectional view, and FIG. 11 is a graph showing sound pressure characteristics. (])...Freon)・Door body, (2)...Speaker, (3), (3A), (3B)...Bass diaphragm,
(4)...Aperture for work. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (2)

[Claims] (1) A speaker is installed on the wall on the inner side of the door of a car, and a diaphragm that vibrates in response to the sound pressure inside the door is used to close the working opening formed on the wall on the inner side of the door. An in-vehicle speaker system characterized in that it is mounted on the above-mentioned wall surface. (2) A speaker and a plurality of diaphragms that vibrate in response to the sound pressure inside the door are provided on the wall surface on the inside of the door of an automobile, and the resonant frequencies of the plurality of diaphragms are set to be different from each other. Features of the car speaker system.