WO2000041435A1

WO2000041435A1 - Speaker system

Info

Publication number: WO2000041435A1
Application number: PCT/KR1999/000846
Authority: WO
Inventors: Joo-Young Kim
Original assignee: Kim Joo Young
Priority date: 1998-12-31
Filing date: 1999-12-30
Publication date: 2000-07-13
Also published as: KR20000047010A; KR20010101331A; AU1895900A

Abstract

A speaker system (10) includes a speaker unit (14) and a horn (12) having an end portion to which the speaker unit (14) is attached. A first membrane (24) is attached to an end portion of the horn (12) to block the end portion. A second membrane (26) is installed to the other end portion of the horn (12). A closed room (30) is provided by way of the first membrane (24) and second membrane (26). The room (30) is filled with a gas which is heavier than air.

Description

SPEAKER SYSTEM

Field of the Invention

This invention relates to a system which delivers and induces sound and improves low-tone sound in the sound system, especially, to a system having an airtight space filled with heavy gas (heavier than the air), whereby the system can be of high efficiency and produce low-tone sound, and the volume of the system can be reduced.

Background of the Invention

The biggest problem with conventional speaker systems is their low efficiency. To deliver low-tone sound properly, they required large volume of enclosure. The horn speaker system is the solution for this problem. By controlling the speaker unit's diaphragm and the air impedance of the horn, the speaker system can produce significantly improved efficiency compared to the conventional speaker and thus it can produce significanth' improved low-tone sound with lower amplifier input. Horn speaker systems producing middle and high-tone sound have already been put to practical use in the market. However, speaker systems that handle low-tone sound are used in very limited number because of the huge size of the systems. Below qualification should be met to produce 20 Hz (20 Hz is the lowest sound level that human can hear) sound: 2 _π Sm > λ (1)

wherein,

*Sm = size of the horn's mouth, and λ = wavelength = speed of sound/frequency.

If horn's cross-section is circle and its radius is r, the r can be calculated as:

2 v x π r ² > λ

In other words,

2 π r > λ (2)

The wavelength of 20 Hz sound can be calculated as:

Wavelength = Speed of sound/frequency = 340/20 = 17

If we apply this to above equation, we realize that we need a horn with

5.4-meter radius. Likewise, large horn is needed to produce low-tone sound for musical system or instrument. That is why a tube or speaker system which can produce and deliver low-tone sound efficiently as well as of which the size is small has long been demanded.

Summary of Invention

Accordingly, one object of the invention is to produce a small size sound system with high efficiency that can drive significantly improved deliverance of low-tone sound.

Another object of the invention is to provide a speaker system with an airtight space filled with heavy gas in at least part of said system. Another object of the invention is to provide a sound-resonant tube, which is used in musical instruments or speaker systems, with an airtight space filled with heavy gas (heavier than the air) in at least part of said tube.

According to the invention, a system, which is particularly a tube, for the use of delivering and inducing low-tone sound, is blocked at both ends to provide an airtight space between the two ends and then the airtight space is filled with heavy gas. Sound travels slower in the space with heavier gas (than the air).

According to one aspect of the invention, a speaker system comprises a speaker unit and a sound-impedance matching device having an end portion to which said speaker unit is attached. The above system is characterized by a first blocking member that is installed to block one end portion of said sound-impedance matching device in longitudinal direction; and a second blocking member that is installed to block the other end portion of said sound-impedance matching device in longitudinal direction, whereby an airtight space is provided between the two block members, wherein the airtight space is filled with gas heavier than the air.

According to another aspect of the invention, a sound resonant tube that is used in speaker system or musical instrument is characterized by a first blocking member that is installed at one end portion of said resonant tube in longitudinal direction; and a second blocking member that is installed at the other end portion of said resonant tube in longitudinal direction, whereby an airtight space is formed between the two blocking members, wherein the airtight space is filled with gas which is heavier than the air.

Brief Description of the Drawings

The purposes, advantages, and features of the invention will become clearer with the preferable embodiments of the invention that will be explained in detail referring to the drawings annexed to the specification and described briefly as follows:

Figure 1 is the cross sectional view of the horn speaker system according to one aspect of the invention;

Figure 2 is the cross sectional view of the transmission line speaker system according to another aspect of the invention;

Figure 3 is the cross sectional view of the transmission line speaker system according to still another aspect of the invention;

Figure 4 is the cross sectional view of the Pipe Organ according to still another aspect of the invention.

Detailed Description of the Preferred Embodiments

The invention is explained in detailed referring to the drawings annexed to the specification. Referring to Fig. 1, the horn speaker system 10 is composed of a horn 12 and a speaker unit 14 (which is also being referred to as a 'driver.'). The horn consists of throat 16 and mouth 18. The wall of the horn, of which the cross-section is circle, extends from the throat 16 to the mouth 18. The wall becomes wider as it approaches from the throat 16 to the mouth 18. The size of cross-section of the horn increases with certain functional ratio. If this is applied to the exponential function, the horn becomes an exponential function type of horn.

A speaker unit 14 is attached at the horn's 12 throat 16. The speaker unit 14 comprises a diaphragm and a converter that generate sound. Said converter converts electrical signal into mechanical motion. The converter can be made up of either voice coil system or piezoelectric device. The size of the horn's throat 16 and the size of the speaker unit's throat are desirable to be the same, but the former can be smaller than the latter.

A first membrane 24 is installed at the throat 16 of the horn perpendicularly to the longitudinal direction of the horn. The first membrane 24 covers the entire throat 16 area. A second membrane 26 is installed in the mouth 18 of the horn in a similar way to cover the area of the mouth 18. The first and second membranes are made up of either rubber or silicon rubber. An airtight space 30 is formed as first and second membranes 24, 26 and the wall of the horn 19 block the space 30. Then this airtight space 30 is filled with heavy gas (heavier than the air). The larger the molecular weight of said gas, the better. It is also necessary for the gas to be harmless to humans and not to incur any chemical reactions with the membranes. Xenon (Xe) may be a good example.

Heavy gas enables the size of the sound system to be reduced. Shortening the wavelength is one of the best ways to reduce the size of the horn. In other words, slowing the speed of sound in the horn is needed referring to the below equation:

Sm = 4 π

^{λ ~} f

Sm = C -(3)

4 π f

Wherein,

Sm = size of the horn's mouth (18), λ = wavelength,

C = speed of sound, and f = frequency

As is known, speed of sound is inversely proportional to the square root of the molecular weight of the media in which the sound travels.

If an airtight space is filled with Xe (which has the molecular weight of 131), then the speed of sound becomes 160 m/s {with the assumption that sound travels 340 m/s in the air (air has the molecular weight of 29)}. If we apply this to equation (3) (with the assumption that the cross section of the mouth is circle), the radius of the mouth (18) of the horn (12) needs only to be 0.46 times compared to that of the horn in the case where the gas is the air. Flare constant, m, can be calculated as:

The m in the air when the low-tone blocking frequency is set as 60 Hz is:

m_a,r = 4 7T 60/340 = 2.22 (5)

If sound travels 160 m/s in the heavy gas like Xe, m is:

m_Xe = 4 ;r 60/160 = 4.7 (6)

We can compare the size of the horn's mouth by applying each m into equation (3).

In air,

Sm_air = 340² / 4 τr 60² = 2. 56 m² (7)

And in Xe (molecular weight of 131),

Smxe = 160² / 4 τr 60² = 0.57 m² (8)

and the result is just about 2/9 of the air.

Now, we will compare the length. If the horn is exponential type, the length will be Sm = St x e ^mx (9)

Wherein,

Sm = size of the horn's mouth, St = size of the horn's neck, and m = flare constant.

Therefore, the length that is expressed as x is

In Sm x St -(10) m St m

If we assume St as 0.049 m, the length of the horn in the air will be

x_a,r = 1/ 2.22 [ In (2.56 / 0.049) ] = 1.78 m (11)

The length of the horn filled with Xenon (speed of sound in Xe is 160 m/s) will be

xχ_e = 1 / 4.7 [ In (0.57/0.049) ] = 0.52 m (12)

Accordingly, we can recognize that the length of the horn with Xe can be reduced to 1/3.4 of the horn with the air. In this way, it is possible to make a useful horn that efficiently delivers low-tone sound with minimized size and length. Although we have mentioned the tube with circle cross section only, this technique can be applied to the horns with square, rectangle, or eclipse cross section. The exponential function is not the only way to calculate flare ratio, rather, we can also adopt hyperbolic, conical, or parabolic function. The application of this heavy gas concept is not limited to horn speaker systems, but this technique can also be applied to the transmission line speaker system 50 (often referred to as quarter wave loading or sound labyrinth) that is drawn in Fig. 2. The transmission line speaker system 50 is composed of a speaker unit 52 and a sound resonant tube 54 with regular radius. The speaker unit 52 comprises a diaphragm and a converter.

A first membrane 55 is installed at the sound resonant tube 54 near the speaker unit 52. Unlike the embodiment, the diaphragm can replace the first membrane as a blocking member in another embodiment. In the mouth area, a second membrane 56 is installed. Both membranes are made of either thin rubber or silicon rubber. The first and second membranes 55, 56 and the wall 58 of the sound resonant tube 54 secure an air-blocked space 60.

The air-blocked space 60 is filled with a gas heavier than the air. The higher the molecular weight of the gas, the better. It is necessary for the gas to be harmless to humans and not to chemically react with the membranes. For example, Xenon (Xe) gas may be used.

This speaker system uses the principle that resonance occurs when the length of the sound resonant tube (54) is 1/4 of the wavelength of a specific frequency. Wavelength can be calculated as: λ -- C π i^ -

/

wherein, λ : wavelength,

C : speed of sound, and

F : frequency.

If we were to produce a transmission line that can generate up to 60 Hz, the wavelength would be :

λ = 340/60 = 5.67 m (14)

Therefore, the length (L) of the sound resonant tube (54) must be 1.42 m, which accounts for 1/4 of the wavelength. If the airtight space is filled with Xe, speed of sound in this space becomes 160m s and the length of the sound resonant tube 54 becomes 2.67 m. Accordingly, the length of tube filled with Xe can be shorter (0.67 time shorter) compared to the air filled tube to produce same low-tone sound.

Figure 3 provides an alternative embodiment. Referring to Fig. 3, the transmission line speaker system 100 is composed of a speaker unit 102 and a sound resonant tube 104 of which the tube has same diameter from throat to mouth. The speaker unit 102 comprises a diaphragm 106 and a converter 108. The resonant tube 104 is blocked with said diaphragm 106 on one side. Another diaphragm 110 that is not attached to a converter and functions as a passive radiator blocks the other side of the resonant tube 102. Said diaphragm 108 is not attached to the converter. A soft material of supporter member 112 is lied between the rims of the both diaphragms 106, 110 and the sound resonant tube 104 so that the diaphragms can be connected to the sound tube 104 via the supporter member 112. An airtight space 114 is formed as the diaphragms 106, 110 and the wall 105 of the sound resonant tube 104 block the space 114. We could fill heavy gas in this space 114. The higher the molecular weight of the gas, the better. The gas must be harmless to humans and not incur any chemical reactions with the materials of the diaphragms 106, 110 and supporter member 112. Xenon (Xe) suits these needs.

Figure 4 explains the application of this system to the sound resonant tube of the Pipe Organ. To provide airtight space 152, first and second membranes 154, 156 are installed on both sides of the sound resonant tube 150. Then, the heavy gas is filled in the airtight space 152. The sound system according to the embodiments of the invention can be composed of a small size sound resonant tube or horn, yet can deliver quality low-tone sound. Especially, the speaker system according to the invention has enabled the small size sound resonant tube or labyrinth. According to the invention, the size of the sound resonant tube of the musical instruments also can be minimized.

Claims

1. A speaker system comprising a speaker unit and a sound-impedance matching device having an end portion to which said speaker unit is attached, characterized by a first blocking member that blocks one end portion of said sound-impedance matching device in longitudinal direction; and a second blocking member that blocks the other end portion of said sound-impedance matching device in longitudinal direction, whereby an airtight space is provided between the two blocking members, wherein said airtight space is filled with gas heavier than the air.

2. A speaker system according to Claim 1, wherein said impedance-matching device is a horn comprising a neck to which the speaker unit is attached and an open mouth, the first blocking member that is installed near the neck is a diaphragm, and the second blocking member that is installed in the mouth is a passive diaphragm.

3. A sound resonant tube used in a speaker system or musical instrument, which comprises a first blocking member that is installed at one end portion of said resonant tube in longitudinal direction, a second blocking member that is installed at the other end portion of said resonant tube in longitudinal direction, whereby an airtight space is formed between the first and second blocking members, wherein said airtight space is filled with gas heavier than the air.

4. A sound resonant tube according to Claim 3, wherein the tube further comprises a speaker unit at one end portion, said first blocking member is a diaphragm of said speaker unit, and said second blocking member is a passive diaphragm.