JPS6327517Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automobile audio device having a door-mounted speaker.

In car stereos, the left and right speakers are often installed on the sun deck at the rear of the car, but recently some have been installed on the front dash board or door. In particular, in the 4-speaker system, the front speakers are naturally installed at the front, and a door-mount system is adopted. FIG. 1 is a diagram explaining this, where 10 is the front door of the automobile, 12 is a handle for raising and lowering the window glass attached to the inside of the door, 14 is a lever for opening and closing the door lock, and 16 is the window glass. . The door is usually made of a steel plate, and the inner surface is lined with a plastic sheet 22, etc., and the inner surface 10a of the steel plate covered with the sheet has an opening 1 as shown by a dotted line.
It is normal to have 8.20. As shown in FIG. 1B, the front speaker 24 is mounted using this opening, and since water droplets enter the inside of the door due to water spraying or rain, the door is waterproofed with a plastic film 26. film 26
is originally placed inside the door, and is pressed from the inside of the vehicle and recessed into the shape shown.
If waterproofing is still uncertain, a rain shield 28 is provided as shown by the dotted line.

Since door-mounted speakers have such a structure, parasitic vibrations (chattering) are likely to occur. In other words, as shown in Figure 2, if the output is about 5 [W], no chatter will occur, but if the output is higher than that, chatter will occur when a low frequency signal of 200 Hz or less is input (shown with diagonal lines). The higher the output, the higher the frequency of the low frequency signal that causes chatter. Note that this second
In the figure, the power of the input signal to the speaker was kept at a value of 5W, 10W, etc., and the frequency was varied in the range of about 30 to 30KHz to check whether chatter occurred. When chatter occurs, it becomes difficult to hear, so I have no choice but to lower the amplifier output, and even though I have a high-output amplifier, I am unable to produce its full potential and have to settle for a low output.

There are various places where chatter occurs, such as window glass 16,
A few examples include plastic film 26 and handles. Therefore, the chatter of the plastic film 26 is caused by the vibration between the film 26 and the speaker 2.
This can be considerably improved by filling the space between the speaker and the speaker 4 with foamed urethane, but since there are other causes, it is difficult to create a speaker mounting structure that does not cause vibration even when the power is increased.

Therefore, the present invention attempts to deal with this problem by devising the amplifier side, and the feature is that the preamplifier and the power A filter circuit is provided between the amplifiers to control the level of a low frequency region that causes chatter among signals input from the preamplifier to the power amplifier in accordance with the output of the preamplifier.

FIG. 3 shows the characteristics of the amplifier according to the present invention, in which the low frequency region where chatter occurs is blocked by a filter. The dotted line is the frequency range where this is cut off and removed, and at low output when no chatter occurs, the curve C ₁ is the frequency characteristic of the amplifier itself, while when chatter occurs,
At high output, the curve shows the amplifier frequency characteristics at that output, with the chatter-generating low frequency region shown by the dotted line removed.
Let them be C ₂ and C ₃ . In this way, although some parts are missing in the low frequency range, it is possible to output a high output that is at the full capacity of the amplifier without vibration.

FIG. 4a shows an embodiment of the present invention, in which a preamplifier 30 receives an input from a magnetic head or the like (not shown), amplifies it, and corrects (equalizes) the recording characteristics. A controllable filter 32 is a high-pass filter whose cutoff frequency _c is changed by the output of the level detection circuit 38. 34 is a power amplifier, and 36 is a speaker. In the case of stereo, a plurality of illustrated systems are provided. With this device,
The input level to the speaker 36 is determined by the level detection circuit 3.
8, and when this becomes equal to or higher than the chatter generation output, the level detection circuit 38 sends a signal Sg to increase the cutoff frequency _c of the filter 32 in accordance with the preamplifier output.
is generated and inputted to the filter 32. As a result, for example, the dotted line portion of curve _C2 is removed when the output is 10W, and the dotted line portion of the curve _C3 is removed when the output is 15W, thereby preventing the occurrence of chatter.

This level detector 38 uses a power indicator integrated circuit. Add the output of the power amplifier 34 to the input terminal IN, and operate the variable resistor VR to output terminal 1' to output terminal 1' when the output is 10W, output terminal 2' to output terminal 3' when the output is 20W, and output terminal 3' to output terminal 3'. Adjust so that the output is 30W. FIG. 4b shows the output status of the output terminals 1', 2' and 3'. The filter 32 consists of a capacitor C ₁ , resistors R ₁ , R ₂ , R ₃ , and transistors Tr ₁ , Tr ₂ , Tr ₃ that connect one ends of these resistors to the ground. When an output is generated at terminal 1', transistor Tr ₁ is turned on, and in filter 32, C ₁ and R ₁ are enabled. terminal 2',
When an output is generated at 3', transistors Tr ₂ and Tr ₃ are turned on, and C ₁ and R ₂ and C ₁ and R ₃ are enabled. The time constants are C ₁ R ₁ > C ₁ R ₂ > C ₁ R ₃ .

Instead of using a controllable filter to continuously change _c in accordance with the speaker output, an approximate method can be considered in which the level is adjusted in the entire low frequency region where chatter may occur. Figure 5 shows an example, 40
is a high-pass filter, and 42 is a low-pass filter. The cutoff frequencies _c of these filters are the same and fixed. For example, _c is 300Hz
Choose the degree. 44 is a mixer, and 46 is an electronic attenuator. The level detection circuit 38 detects the output of the low-pass filter 42, and when the output becomes a chatter-generating output, the attenuator 46 is adjusted according to the output, and the attenuated low-pass filter output is applied to the mixer 44. . Preamplifier 3 passed through high pass filter 40
The output of 0 is applied to the mixer 44 without being attenuated, and therefore, according to this circuit, the chatter generation region has a frequency characteristic that is attenuated according to the output, so that no chatter occurs and the frequency is as low as possible. The result is a car audio system with fewer defects.

As explained above, according to the present invention, it is possible to output high output without causing chatter using a door-mounted speaker, and there is an advantage that dropout in the low frequency range can be suppressed as much as possible.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of a door-mounted speaker, where a is a plan view, b is a cross-sectional view, Figures 2 and 3 are frequency characteristic diagrams explaining the occurrence of chatter, and Figures 4 and 5 are implementations of the present invention. FIG. 2 is a block diagram showing an example. In the drawing, 30 is a preamplifier, 34 is a power amplifier, 10 is a door, 24, 36 are speakers, and 32, 38, and 38-46 are filter circuits.

Claims (1)

[Scope of utility model registration request] In an automobile audio device that includes a preamplifier, a power amplifier, and a speaker mounted on the door, the level of the low frequency region that causes chatter among the signals input from the preamplifier to the power amplifier is measured between the preamplifier and the power amplifier. An automobile audio device characterized in that a filter circuit is provided for controlling according to the output of the preamplifier.