KR940010236B1 - Speaker system of tv - Google Patents

Abstract

The system of an MLR (Mass Loaded Reflex) speaker downs low frequency band width applying the theory of Bass Reflex Speaker System implementing to cover quite a low bandwidth as a TV speaker. The system comprises; a resonance unit (13) reaching radiating sound to air elasticity, wave guides (11,12) formed on both sides of the resonance unit, a speaker (9) lying on one side of the wave guide to lessen the limitation of low bandwidth replay by attaching the air mass of the backward wave guide to the speaker vibrator equivalently.

Description

TV speaker system

1 is a perspective view of a speaker box according to the present invention.

2 is a side cross-sectional view of FIG.

3 is a basic structural diagram of an MLR speaker system for explaining the present invention

4 is an acoustic equivalent circuit diagram of an MLR speaker system of the present invention.

5a, 5b or graph of frequency transfer function through computer simulation.

6 is a graph showing the electrical input impedance state of the present invention MLR speaker system.

7 is a system diagram used for measuring frequency characteristics of the present invention MLR speaker system.

8 is a graph of frequency characteristics of the present invention MLR speaker system.

9 is a graph of frequency characteristics of an MLR speaker system using the sound absorbing material of the present invention.

10 is a frequency characteristic graph (MLR) of the present invention.

11 and 12 are conventional frequency characteristic graphs.

* Explanation of symbols for main parts of the drawings

1: speaker box 2: cavity

3: curved portion 4,5,6: waveguide

7,8: Sound output port 9: Speaker

10: reinforcement column

The present invention relates to a Mass Loaded Reflex (MLR) speaker system of a TV, and in particular, a speaker system using the principle of the Bass Reflex Speaker System can be easily installed and configured on an existing TV to significantly lower the bass reproduction frequency band. As a TV speaker, it relates to a speaker system capable of playing down to a fairly low band.

In general, the bass reflex speaker system which is mostly used in the speaker system for audio, the sound wave from the front of the diaphragm of the speaker is directly radiated to the outside space and the sound wave from the rear part is radiated into the box so that the air medium particles resonate in phase By being in phase with the front surface of the speaker, it can be seen that it is a known technique to lower the low range enhancement or bass reproduction limit.

However, when the bass reflex speaker system having the above characteristics is applied to a video sound device, especially a TV, many difficulties are encountered.

Depending on the characteristics required for the design of the speaker system, this is based on the resonant frequency (fb) of the port, the resonant frequency (fs) of the speaker unit, the compliance (Cas) of the speaker unit, and the compliance of the enclosure (Enclosure). Cab), Q (Qe) of electrical resonance, Q (Qm) of mechanical resonance,

h = fb / fs

= Cas / Cab

Q ^-1 = Qe ^-1 + Qm ^-1

This is not an easy problem because the bass reflex speaker system must be designed by adjusting the three parameters of. The determination of the port size of the enclosure also presents a significant difficulty.

Enclosure port dimensions are as follows.

It is determined by, where lp: the length of the pot, Sp: the area of the pot, Vb: the volume of the enclosure.

Thus, the length of the pot is roughly inversely proportional to the volume of the enclosure.

In other words, when the area of the port is constant, the smaller the volume of the enclosure, the longer the port length, and since the loss of the port is nonlinear, reducing the area of the port causes a large loss and adversely affects the frequency characteristics according to the change of the sound output level. to be.

In response to the trend toward the TV monitor type, when the speaker is mounted close to the front of the cabinet, it is easy to design the enclosure as the bass reflex basic type by interfering with internal components such as the CRT and the board. There is a problem that cannot be done.

In the present invention, as a mass-loaded reflex (MLR) speaker system in which only a narrow duct is installed at the rear of the speaker, the sound is radiated from the rear of the speaker diaphragm to the enclosure having a large volume, and air according to the volume of the enclosure is provided. In contrast to the principle that the elasticity and the air mass of the port resonate to lower the low range, the MLR speaker system of the present invention has a relatively narrow duct installed at the rear of the diaphragm, and after the sound passes through the duct, as in the case of bass reflex, It is an object of the present invention to provide a TV speaker system that meets the elasticity of the air, thereby lowering the resonant frequency of the unit itself due to the mass imposed on the diaphragm, and also greatly lowering the low pass reproduction limit.

Hereinafter, the detailed design method and embodiment of the MLR speaker system to be applied to the TV of the present invention and the performance test therefrom will be described in detail.

First, FIG. 1 is a perspective view of the speaker box of the present invention, and FIG. 2 is a side cross-sectional view of FIG.

To design such a speaker box, an MLR speaker system as shown in FIG. 3 was designed based on the principle of a bass reflex speaker system.

It is formed by the resonance means 13 and the waveguides 11 and 12 on both sides of the resonance means 13 so that the radiated sound meets the elasticity of air. The air mass of the rear waveguide of the speaker is mounted by mounting the speaker 9 on one side of the waveguide. It is added equivalently to the speaker vibrator to lower the low pass limit.

This is also shown as the fourth diagram by the acoustic equivalent circuit including the speaker unit.

4 shows an equivalent circuit at low frequencies near the unit resonant frequency.

, Where

B: Magnetic flux density of speaker unit

ℓ: winding length of speaker coil

v g: Output voltage of amplifier

S: area of diaphragm

Rg: Output resistance of the amplifier

Re: DC resistance of speaker coil

Rms: Internal loss of diaphragm support

m _s : Sum of the total mass of the speaker moving parts and the mass of air due to the radial reactance

Cms: flexibility of speaker support

Sb: Cross section of diaphragm rear port

l '' b: Effective port length behind the diaphragm

Sp: Cross section of outlet port

ℓ'p: Effective length of exit port

ρ: Volume of speaker rear cavity

p : density of air

C: Sound speed

As shown in FIG. 4, the MLR speaker system has an effect of increasing the equivalent mass of the speaker vibrator by adding a mass due to the speaker rear port, compared to a bass reflex type that is generally used.

Therefore, the resonant frequency of the speaker unit is also lowered. If the unit resonant frequency in free space is fo, the resonant frequency fo 'for MLR speaker system is

Where m _{b is the} mass of air in the rear duct of the speaker, m _b = ρℓ ' _b ' S _b , and mr is the mass of air by radiative reactance, m _r = (8/3) ρ (Sh / ) ^3/2 .

For example, if you use a 4-inch woofer with m _s = 4 g, if you design l '' _{b '} = 20 cm and Sb = 80 cm2, fo' (4 / 6.32) ^1/2 fo = 0.80 fo and fo = 80 At ㎐, the resonant frequency drops to 64 으로 due to air mass.

At this time, the Q of the speaker unit is increased compared to the free space.

The frequency characteristic G (jω / ωo) of the sound output from the MLR speaker system has the characteristics of the high-pass filter of the 4th order as shown in the following equation, and therefore has a slope of 24dB / oct in the low range.

In the above, h: Tuning Ratio, fb (resonance frequency due to reflex port and cavity) divided by fo (unit resonant frequency).

Q _t : Total Q of the speaker unit

: The flexibility ratio of the speaker unit divided by the equivalent flexibility Cac of the cavity as the compliance ratio.

That is, h = f _b / fo

= Cas / Cac

Where Cac has the value of V / ρ c ² when the cavity volume is V.

As mentioned above, in a 4 inch woofer with 4 g of vibration part mass and 80 Hz resonance frequency,

If the volume of the cavity for the reflex is 5 | , the flexibility Cac by the cavity

Is determined to be 1.7, h must change Q _t to find a state in which the frequency transfer function has the most desirable shape.

Graphs of rectified frequency transfer functions under various conditions are shown in FIGS. 5a and b through computer simulations.

(a) When Q = 1.7 and h = 0.8, Q _t was changed from 0.3 to 0.7. (B) is the case where h = 0.9, and the other conditions are the same as those of (a).

Determine the dimensions of the port with h = 0.8.

ℓ'p ': The length of the port with end correction

Assuming one side is a flange and the other is a non-flange,

= ℓp + 0.82 Becomes and substitutes this in Equation (1),

If Lp = 20 cm in this formula, Sp = 16.3 cm 2.

An embodiment of a low-pitched MLR speaker system designed based on the calculated dimensions as described above is the same as the first diagram.

The cavity 2 of the upper and lower light having an inner space is formed, and the upper portion of the cavity 2 is rounded with the curved portion 3 and is enlarged while being inclined downward from the curved portion 3 toward the front. And the waveguides (4) (5) and the waveguide (6) connected to the left and right sides of the cavity (2), respectively. The waveguides (5) and (6) respectively connect the sound output ports (7) and (8). The speaker 9 is interposed between the waveguides 4 and 5, and the speaker 9 is positioned such that the diaphragm front part faces the internal space of the wave guide 4, and the rear part is a wave guide 5. The speaker box 1 is formed by installing the plurality of reinforcement pillars 10 in the inner space of the cavity 2 after placing the inner space toward the inner space of the cavity 2.

The cavity 2 of the speaker box 1 thus obtained was installed in the rear space of the CRT inside the TV cabinet.

The above cautions when manufacturing the speaker box should take into account that a large area should not be resonated by the sound pressure generated from the speaker.

This is because when the enclosure resonates and vibrates greatly, the frequency characteristic of the sound pressure generated is undulated, resulting in a tone with coloration.

To reproduce sound without coloration, the lowest resonant frequency of the enclosure must be made at least in the range of 400 kHz, the highest frequency of the speaker system.

The resonant frequency of the enclosure increases as the thickness of the component plate gets thicker and the area becomes narrower. Therefore, the plate should be as thick as possible.

In the present invention, as the area of the plate and the area of the waveguides 4, 5 and 6 are narrowed, the area of the cavity 3 is inevitably formed relatively.

The problem of this area is to increase the resonance frequency by equivalently narrowing the area of the waveguides 4, 5, 6, or by modifying or reinforcing the inside of the cavity 3 to form a rigid structure.

When reinforcing the wall surface of the cavity 3, that is, by installing the reinforcement pillar 10 inside the cavity 3, the thickness can be equivalently thickened, and the area is narrowed equivalently and the resonance frequency of the structure is reduced. Will be higher.

As described above, the present invention has a structure in which the cavity 3 is less likely to vibrate by providing four reinforcement columns 10 between the cavity 3 inner wall surfaces.

On the other hand, the electrical impedance was measured for the performance test of the MLR speaker system fabricated as shown in FIG.

The input impedance of the speaker was measured from 20 kHz to 300 kHz. For comparison, the input impedance was measured again with the reflex port, that is, the acoustic output port (7) (8), closed and closed.

6 is a graph showing the measured electrical input impedance of the MLR speaker system, with the solid line showing the case of the present invention MLR speaker system and the dotted line showing the state when the present invention is sealed.

In the closed case, there is only one peak value, whereas in the case of MLR, it has two peak values.

This shows the typical shape of the input impedance of the base reflex. The first peak is smaller than the second peak due to the internal loss and tightness of the enclosure.

In the case of the MLR of the present invention, it has a minimum value at about 50 kHz, which is the resonance frequency of the enclosure, which has a minimum of the active impedance, in which the displacement of the speaker diaphragm is minimized while the maximum of the enclosure port is maximum. Sound output is emitted.

The small peak in the vicinity of 250 Hz is due to the fact that the shape of the enclosure is a cuboid and can be interpreted as a result of the generation of the resonance mode by the opposing faces.

In order to measure the frequency, a measurement system such as the seventh degree was constructed in the anechoic chamber and the frequency characteristics of the manufactured MLR speaker system were measured.

The measurement results are as shown in FIG. 8 and are measured at a distance of 1 m from the speaker system when 1 watt of power is applied to the speaker.

The vertical axis of FIG. 8 shows a small division of 1 dB in increments of 50 dB.

As an example, 150 dB in FIG. 8 is 80 dB / w / m.

The woofer used in the MLR loudspeaker system is a unit with 83 kHz resonant frequency.

The measurement result shows that -3dB frequency is 65kHz, -10dB frequency is 45kHz, and it is a speaker system that reproduces to a very low band as a TV speaker by far lowering the bass reproduction frequency band from the resonant frequency of the unit. It can be seen that the purpose is achieved.

Dip at only about 250 mmW is a problem, but this is improved if the shape of the cavity is not made of a cuboid, as mentioned above, i.e., as in FIGS.

The peak and the dip above about 500㎐ are formed because the plate in front of the unit is in parallel with the unit and the resonance mode occurs on the front of the unit.

In order to improve the frequency characteristics of FIG. 8, sound absorbents were installed inside the enclosure and sound output ports of the MLR speaker system and measured again.

The sound absorbing material used was glass fiber with a density of 64㎏ / ㎥ and a sound absorbing material was installed on the inner wall surface of the sound output port to block standing waves in the enclosure.

9 shows the results of the measurement after the sound absorbing material is installed, showing a remarkably improved performance.

It can be seen that the valley was filled in the vicinity of 250㎐ due to the wall sound absorbing inside the enclosure, and the acid and valleys generated at 500㎐ or more were removed by absorbing the wall of the sound output port.

The results show that the proper use of sound absorbing materials greatly improves the acoustic properties.

Meanwhile, the frequency characteristics of the present invention MLR speaker system and the existing speaker system (Panasonic TH-29TS1, Daewoo 29-inch C-280) were compared and measured.

For comparison of low frequency regeneration capability, only frequency band of 400 kHz or less was used for comparison.

FIG. 10 is a frequency characteristic graph of the present invention MLR speaker system, and FIG. 11 and FIG. 12 are frequency characteristic graphs of Daewoo C-280 and Panasonic TH-29TS1, respectively, and -3dB frequency based on the level indicated by the dotted line. The MLR is 70Hz, the Daewoo C-280 is 130Hz, and the Panasonic TH-29TS1 is 95dB, demonstrating that the MLR loudspeaker system of the present invention has excellent low-frequency reproduction capability.

Claims (8)

Resonance means 13 so that sound meets the elasticity of the air, and waveguides 11 and 12 are formed on both side surfaces of the resonance means 13, and a speaker 9 is mounted on one side of the waveguide, A speaker system of a TV, characterized in that the air mass is added to the speaker vibrating portion equivalently to lower the low pass reproduction limit. 2. A speaker system according to claim 1, wherein the resonance means (13) has a structure of reciprocal light. The speaker system of claim 2, wherein a plurality of reinforcement columns are provided in the internal space of the resonance means. 2. A speaker system according to claim 1, wherein waveguides (4) (6) are connected to both waveguides (11) (12) of the resonance means (13). 5. A speaker system according to claim 4, characterized in that the waveguide (5) is attached to the waveguide (4) or the end of the waveguide (6). 6. A speaker system according to claim 5, wherein a speaker (9) is provided between the waveguide (4) (5) or the waveguide (6) (5). 2. The speaker system according to claim 1, wherein a sound absorbing material is attached to the inside of the resonance means (13) and the port wall of the waveguide (11) (12). 8. The speaker system of claim 7, wherein the sound absorbing material is made of glass fiber.