JP2024059052A - megaphone - Google Patents

Abstract

[Problem] In a conventional electric megaphone, sound waves from a diaphragm 53 and vibrations transmitted from the diaphragm 53 through a peripheral support 60 and a horn driver cover 66 cause a horn 54 to resonate, and a horn vibration sound 58 and a horn vibration 63 are transmitted to a microphone 51. This creates a loop, causing howling. To provide a megaphone horn that can reduce the horn vibration sound 58 and the horn vibration 63 and can also be made lightweight in order to reduce howling. [Solution] In a conventional type, the horn 54 is hard, so that the horn vibration sound 58 and the horn vibration 63 are generated in response to impacts and sound waves, which cause deterioration of sound quality and howling. By replacing the hard material of the horn with a flexible material that has the property of attenuating sound waves and vibrations, the horn vibration sound 58 and the horn vibration 63 are reduced. [Selected Figure] Figure 7

Description

The present invention relates to improving the materials used in megaphone horns to reduce noise and weight.

Conventionally, the horns 1, 11, 12, 13, 21, and 54 of the trumpet-shaped megaphones shown in Figures 1, 2, 3, and 6 have been made of hard materials such as hard plastic, cardboard, wood, and metal.

Patent No. 4262291 Patent No. 6734600

The role of the megaphone horn is to take advantage of its shape to prevent the sound coming from the diaphragm 14, 53 from diffusing, to make the sound directional, and to make the sound louder and audible from far away.

However, in the case of a portable megaphone, the horn is made of a hard material and is thin, so that the vibration of the diaphragm 14, 53 is transmitted to the horn through the peripheral support 17, 60 and the horn driver cover 18, 66, and the sound from the diaphragm 14, 53 and the sound 55 emitted from the mouth easily resonates and vibrates. As a result, the horn itself becomes a diaphragm, and a horn vibration sound (horn whine) 58 that can be heard as noise is generated. If the horn is made of paper, the horn vibration sound 58 sounds like a paper tube, and if the horn is made of hard plastic, it sounds like a hard plastic pipe, and the sound that is generated depends on the characteristics of the material. Therefore, although the sound coming out of the horn is loud, there is a lot of noise, and the sound becomes more or less different from the original voice sound.

Furthermore, in the case of the electric megaphone with attached microphone shown in Figure 1, there is a problem in that howling can easily occur when the volume is turned up.

People with sensitive hearing and young children dislike the sound of megaphones and want to cover their ears. This is because the sound is noisy and unnatural. It is common to see what is commonly referred to as "distorted sound." Although the sound is loud, there is a lot of noise and it is difficult to understand what is being said. If you watch sports events or election speeches, it is common to see children covering their ears in disgust at the distorted sound of megaphones. There is a demand for loudspeakers that are small and lightweight, yet clear and produce sound close to the original sound.

To suppress feedback, it is necessary to suppress the vibration noise of the horn 58. For that reason, in conventional types, the horn is made hard and sturdy to suppress the vibration 63 of the horn, which is the cause of feedback, so the better the sound quality, the heavier it becomes, making it inconvenient to carry around.

In order to solve the above problems, the present invention has manufactured the horn from a flexible material that has properties of attenuating sound waves and vibrations. As a result, a flexible and soft horn 68 has been created. The horn of a conventional portable megaphone is made of a thin and hard material (hard horn 67), so when it vibrates, the vibration sound of the horn easily resonates, and when it is subjected to an impact, it produces a hard and noticeable "clacking" sound, but when a similar impact is applied to a soft horn, it only produces a quiet and dull sound. The soft horn 68 produces a very small vibration sound of the horn.

And the conventional hard horn 67 is made thick and strong to prevent the components from vibrating in order to suppress the horn vibration noise 58, which increases its weight, but the soft horn 68 can be made lighter and easier to carry because the vibration noise of the horn can be reduced by making it thinner.

According to the present invention, the vibration noise of the horn is suppressed, the harsh noise and noise peculiar to megaphones is reduced, and the sound is soft and clear.

In the portable electric megaphone of the present invention, the vibration 63 of the horn and the vibration sound 58 of the horn are suppressed, so that howling is less likely to occur and the noise is less than that of portable electric megaphones of the same class with hard horns. Therefore, it is possible to produce a loud sound without worrying too much about howling.

The horn is significantly lighter than conventional rigid horns, making the overall weight lighter and easier to carry.

FIG. 1 is a perspective view showing a typical folded horn type electric megaphone. FIG. 2 is a cross-sectional view showing the diaphragm and horn of a folded horn type electric megaphone according to one embodiment of the present invention. FIG. 1 is a perspective view of a non-electrical handheld megaphone according to one embodiment of the present invention. This is the frequency response when a conventional rigid horn is subjected to an impact. 4 shows the frequency characteristics when an impact is applied to a soft horn according to one embodiment of the present invention. 1 is a diagram showing a cross section of a horn and sound and vibration. This is a diagram showing how feedback occurs, showing the difference in the amount of horn vibration and vibration sound transmitted to the microphone between a hard horn 67 and a soft horn 68. 1A and 1B are a perspective view and a cross-sectional view of a horn speaker using a foamed polyethylene material according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A megaphone according to an embodiment of the present invention will be described
Fig. 1 is a perspective view of a typical folded horn type electric megaphone. There is almost no difference in appearance between the one using the soft horn material of the embodiment of the present invention and the conventional hard horn. The difference is in the hardness and weight of the horn, so the difference can be felt by touching them.
Fig. 2 is a cross-sectional view of a folded horn type electric megaphone according to one embodiment of the present invention. The main body case, amplifier, microphone, power supply, and other parts that are not related to the invention are omitted. In this case, the cross-sectional view is the same, except for whether the horn is made of a hard material or a soft material.

The device actually used was a small electric megaphone, ER-1106 (output 6 W, mass 660 g (excluding batteries)) manufactured by TOA Corporation. The hard plastic folded horn of this electric megaphone was removed and replaced with a horn of the same shape that was 3D printed out with a thermoplastic polyurethane (TPU) filament. The external dimensions are almost the same, but the thickness of the horn corresponding to the third horn 13 is 1 mm instead of the original 3 mm. It was made thinner in order to reduce weight and to make it more flexible, which reduces the vibration noise of the horn.

Figure 4 shows the frequency characteristics (amplitude spectrum) measured using an FFT analyzer application (Spectroid) when a hard plastic horn (weight approximately 200g) from a TOA ER-1106, which was removed for the experiment, was struck with the second joint on the back side of the middle finger. It is possible to know the strength of each frequency. The upper jagged line 31 is the peak value when tapped three times with a finger. Line 32 is the instantaneous value of the background noise when no tapping is being performed.

Figure 5 shows the same impact on a soft horn (weight approx. 100g) 3D printed using thermoplastic polyurethane (TPU) filament. As the measurement results clearly show, a plastic horn makes a loud noise when struck, while a soft horn is relatively quiet. Anyone can tell that. If you have a desk, try tapping the center of the desk with your finger. Then try tapping your thigh or any other part of your body with the same strength. A softer object will be quieter even when subjected to the same impact.

We measured the impulse response using a TSP signal (a sound in which the frequency of a sine wave is continuously swept from high to low values in a short period of time) to see how long it took for the horn vibration sound to converge on the time axis, and confirmed that the softer sound calmed down in a shorter period of time.

Due to this characteristic, the vibration noise 58 of the horn is less likely to be included in the megaphone sound 57. Therefore, there is less noise and the soft horn sounds closer to the sound of the voice 55 speaking into the microphone.

An experiment was carried out to see how much difference this would make to the actual hearing sensation. First, a non-electrical hard hand megaphone made of ABS material and 3D printed in the shape shown in Figure 3, and a soft hand megaphone made of TPU material were used. The megaphone in Figure 3 does not have a built-in horn driver or microphone. The experiment was carried out in a suburban park about 30m away, and although the hard megaphone only seemed a little harder to hear, there was no obvious difference in sound. The soft megaphone is good in that it is lightweight and can be bent, making it easy to store.

However, in another outdoor experiment using a small electric megaphone made by TOA Corporation, the ER-1106 (a folded horn type portable electric megaphone), there was a big difference. With the unmodified hard plastic horn, the sound had a lot of mid-to-high frequency noise, and when the dial-type volume was turned up, feedback was noticeable. When the volume was turned up to maximum, a "beep" feedback noise was heard even when no one was speaking into the microphone. If that happened, it would no longer be useful as a loudspeaker, and there was a risk of damaging the electric megaphone.

The ER-1106 electric megaphone shown in Figure 5 uses a soft horn made of thermoplastic polyurethane (TPU) that is quiet even when struck, and produces low noise and clarity. The sound is soft and not sharp. This is the sound quality that is closest to the real voice.

The volume is louder with a hard horn at the same volume position. However, the hard horn megaphone has a lot of noise, and although the sound is loud, it is sharp, noisy, and tiring. This is probably due to the vibration noise of the horn. If you turn up the volume, the noise gets louder and you can't hear what's being said.

However, even though the soft horn has a lower volume, it has a clearer, softer, less tiring sound. It is easy to turn up the volume to the same volume as the hard horn, and even at maximum volume there is no feedback, and although the noise increases, it is not too loud. It was confirmed that the practical maximum volume of a portable electric megaphone is louder with a soft horn than with a hard horn.

The weight of the unmodified electric megaphone ER-1106, including the battery, was 813g in total, but the weight of the one with the horn of the present invention was 718g. That's a weight reduction of 95g. It's noticeably lighter.

Why does feedback occur so easily? Before explaining this, let's talk about resonance, which is the cause of feedback. For the experiment, prepare two 440Hz tuning forks with resonating boxes and one 442Hz tuning fork with a resonating box. This means preparing two identical tuning forks and one tuning fork with a different frequency. First, set up two 440Hz tuning forks and ring one. Then, the tuning fork next to it, which is not touching, will also ring. Sounds of the same frequency will vibrate. This is resonance. Next, place 440Hz and 442Hz tuning forks side by side and ring 440Hz. This time, the 442Hz one will not ring. It will not resonate because it is a different frequency. You can see how this experiment works by searching the Internet for a video called "Tuning Fork Resonance Experiment."

Alternatively, there are "experiments on breaking a glass with sound" on television and the Internet. To break a glass, first gently tap the glass or rub the edge of the glass with wet hands to make a sound. This sound is the sound of the glass vibrating. If you make a loud sound with the same frequency as the sound of the glass vibrating with your mouth or a speaker, the glass will resonate and break even though you are not touching it.

In these experiments, the tuning fork or glass is used, but in the case of the megaphone, the horn is used. If you record the vibration sound of the horn when it is lightly impacted and play that sound back to the horn, it will resonate and produce the vibration sound of the horn, just like in the tuning fork and glass experiments.

Fig. 6 is a cross-section of an electric megaphone. Fig. 7 shows the mechanism that causes feedback. The voice 55 spoken into the microphone 51 becomes an electric signal, which is amplified by the amplifier 52. The amplified electric signal vibrates the diaphragm 53, and becomes the sound 57 coming out of the horn.

At this time, the vibrations generated by the operation of diaphragm 53 are transmitted to horn 54 through peripheral support 60 and horn driver cover 60, causing horn 54 to vibrate. In addition to this vibration, sound 57 emitted from diaphragm 53 causes horn 54 to resonate. This causes horn 54 to vibrate, generating horn vibration 63 and horn vibration sound 58. Sound 59, a mixture of horn vibration sound 58 and sound 57 emitted from the horn, is directed toward microphone 51.

Another cause of noise is horn vibration 63. Horn vibration 63 is also transmitted to microphone 51 through the megaphone's body 3. Most small portable electric megaphones have a microphone built into the megaphone body. In such a structure, when vibrations are applied to the horn, the vibrations are transmitted to the microphone, which also becomes a source of howling. If the microphone is not built into the megaphone body, but is an external microphone with a soft cable, or a wireless microphone, horn vibration 63 is almost never transmitted.

As a result, the horn vibration sound 58 is amplified, causing the horn 54 to resonate, increasing the vibration of the horn 54, further amplifying the horn vibration sound 58 and the horn vibration 63. The microphone 51 picks up this sound and amplifies it again, repeating the process. Even if you stop speaking 55, the horn vibration does not stop, so the howling continues until you turn off the switch, turn down the volume, or it breaks.

If the horn vibration noise 58 and horn vibration 63 were reduced, this problem would be less likely to occur. Conventional techniques have attempted to solve this problem by increasing the thickness of the horn, adding reinforcing materials, or using stronger materials to prevent vibration. However, this increases the weight and makes the device unsuitable for portability. There are methods to electronically eliminate the horn vibration noise 58, to make the microphone 51 high quality and highly directional so as to pick up as little sound 59 as possible, or to attach the microphone externally as mentioned above, but these methods have problems such as increased costs and the need to be careful about how the microphone 51 is held.

In one embodiment of the present invention, the horn 67 made of a hard material was replaced with a horn 68 made of a soft material, reducing the horn vibration noise 58 and horn vibration 63. The horn was made of TPU (thermoplastic polyurethane), a resin also used in smartphone cases. The same effect can also be achieved by using natural rubber, synthetic rubber, thick fabrics (canvas and jeans are typical examples), flexible resins such as thermoplastic polyurethane (TPU), expanded polyethylene (EPE), low density polyethylene (LDPE), and EVA foam. It is important that the horn is quiet even when subjected to impact.

The upper side of Figure 7 shows the horn vibration noise 58 and horn vibration 63 when a conventional horn 67 made of a hard material is used, and the lower side shows the horn vibration noise 58 and horn vibration 63 when a horn 68 made of a soft material is used. A softer horn is quieter and has less vibration.

Materials such as thin cloth, tissue, and sponge that allow sound and air to easily pass through the horn 54 are not suitable because they do not provide the desired effect of the horn, do not amplify the sound, and do not provide directivity. This is because they have little ability to attenuate sound waves and vibrations. For this reason, the minimum thickness is set at 0.5 mm. Other types of paper that appear soft at first glance but are bendable and do not allow air to pass through easily are hard and prone to making noise when struck, making them unsuitable.

The thickness of the horn is also a factor. Even soft resin, leather, rubber, etc. can become hard as the thickness increases. However, the thick horn 71 made of foamed polyethylene (described later in Fig. 7) has a low density, so it is highly flexible even if it is thick, and the horn vibration noise 58 is less likely to be generated. In short, it is sufficient to make the horn softer so that the horn vibration noise 58 is reduced without impairing the directionality of the sound.

This invention can also be applied to a non-electric handheld megaphone as shown in FIG. 3. The material of the horn 21 of the handheld megaphone used therein may be made soft.

The thick horn 71 in Figure 8 is also one of the examples. The cross-sectional view (A-A') is on the right side. The thick horn 71 is made of foamed polyethylene. In conventional technology, this horn is made of metal, hard plastic, wood, ceramics, etc. This shape is very heavy in conventional technology and is not used for portable megaphones, but it is also adopted in high-end speakers that pursue high sound quality and commercial speakers that require high volume. Because it is sufficiently heavy, the vibration sound of the horn is very small.

The foamed polyethylene used in the embodiment of Fig. 7 has a density of about 0.06g per cubic centimeter, which is about one-tenth the density of MDF (medium density fiberboard) used in general speakers, making the horn very light. Because the horn driver 72 is heavy, the weight of the horn can be ignored from the overall weight.

Speakers that utilize the soft characteristic have been patented in the past, namely, Patent No. 4262291 (Speaker Device) and Patent No. 6734600 (Acoustic Cushion Device). These two were invented by the present inventor, but the difference is that both are cone-type speakers, not horn-type. The enclosure of the cone-type speaker is made soft to reduce the generation of standing waves inside the enclosure and the sound generated by the enclosure vibration. Patent No. 4262291 aims to be lightweight, high sound quality, and easy to assemble. Patent No. 6734600 (Acoustic Cushion Device) aims to create a bodily vibration that allows the user to enjoy the vibration on their skin, as the enclosure absorbs the sound from the back of the cone and vibrates. This invention is novel because it is about a horn that has not been used before.

1 Horn 2 Microphone 3 Grip and body 11 First horn of folded horn 12 Second horn of folded horn 13 Third horn of folded horn 14 Diaphragm 15 Magnet 16 Voice coil 17 Peripheral support 18 Horn driver cover 21 Hand megaphone horn 22 Hand megaphone mouthpiece 31 Sound when hitting a hard horn 32 Background noise 41 Sound when hitting a soft horn 42 Background noise 51 Microphone 52 Amplifier 53 Diaphragm 54 Horn 55 Voice speaking into microphone 57 Sound coming from horn 58 Horn vibration sound 59 Mixed sound of horn vibration sound and sound coming from horn 60 Peripheral support 61 Magnet 62 Voice coil 63 Horn vibration 65 Horn driver 66 Horn driver cover 67 Horn made of hard material 68 Horn made of soft material 71 Thick horn 72 Horn driver

Claims (2)

A megaphone or horn speaker characterized in that the megaphone horn has flexible sound wave and vibration damping properties. 2. The speaker device according to claim 1, wherein the horn is made of the following materials: natural rubber, synthetic rubber, fabric, flexible resin, thermoplastic polyurethane (TPU), expanded polyethylene (EPE), low density polyethylene (LDPE), and EVA foam, and the wall of the horn has a thickness of 0.5 mm or more.