JP3957201B2 - Acoustic board design equipment - Google Patents

Description

【００３６】
ここで、Δ＝ｍλ／２，ｍ＝１，２，３，…と表現すれば、点Ｐからの反射波の位相の正負が表現できる。ここでλは対象とする音の波長である。すなわち行路差から考えると、ｍが奇数のとき反射音は正の位相で反射し、偶数のとき負の位相で反射することが理解される。
【００３７】
そこでまず、図２の条件のもとに、反射波の行路差Δが一定となる点(x,y,z)の満たす式は、次の偏長楕円体の式で表すことができる。
【００３８】
【数２】

【００３９】
但し、定数ａ、ｂは次式で定義する。また、図２より２ｆはＳＲ間の距離（音源−受音点間の距離）に等しいものとする。
【００４０】
【数３】

【００４１】
上記（２）式で定まる偏長楕円体がｘｙ平面と交差する領域は、次の（３）式，（４）式で表すことができる。
【００４２】
【数４】

【００４３】
上記の式で求まる領域は楕円となる。この楕円の形状を明確にするために変形すると、次数ｍに対する楕円の中心ｙ_0mは、次の（５）式になる。
【００４４】
【数５】

【００４５】
また、楕円の短軸と長軸の長さｘ_m、ｙ_mは次の（６）式で表すことができる。
【００４６】
【数６】

【００４７】
但し、Ｄは次の（７）式から求まる値である。なお、次数ｍは定数ａに含まれている。
【００４８】
【数７】

【００４９】
・第２条件（ｂ）：（鏡像音源Ｓ'からの反射音の寄与）：
第２条件では、図３に示すように、各点の座標とパラメータを定める。Ｓ'はｘｙ平面に対する音源Ｓの鏡像であり、鏡像音源Ｓ'と受音点Ｒを結ぶ直線とｙ軸の交点を座標原点に定める。このとき、鏡像音源Ｓ'からの鏡像反射波に対して点Ｐからの反射波の行路差Δは次の（８）で表すことができる。この第２条件は幾何学的な鏡面反射波と同位相の反射領域を考慮するためのものであり、一般の反射面について（面が充分に大きい場合に）反射波として実効的に寄与する領域の影響を扱う場合などに有効である。
【００５０】
【数８】

【００５１】
ここで、Δ＝ｍλ/２，ｍ＝１，２，３…と表現すれば、Ｐからの反射波の位相の正負が表現できる。ここでλは対象とする音の波長である。すなわち行路差から考えると、ｍが奇数のとき反射音は正の位相で反射し、偶数のとき負の位相で反射することが理解される。
【００５２】
そこでまず、図３の条件のもとに、反射波の行路差Δが一定となる点(x,y,z)の満たす式は、次の偏長楕円体の（９）式で表すことができる。
【００５３】
【数９】

【００５４】
ただし、定数ａ、ｂは次式で定義する。また、図３よリ２ｆはＳ'Ｒ間の距離に等しい。
【００５５】
【数１０】

【００５６】
この偏長楕円体がｘｙ平面と交差する領域は、次の（１０）式，（１１）式で表すことができる。
【００５７】
【数１１】

【００５８】
上記の式で求まる領域は楕円となる。この楕円の形状を明確にするために変形すると、次数ｍに対する楕円の中心ｙ_0mは、次の（１２）式になる。
【００５９】
【数１２】

【００６０】
また、楕円の短軸と長軸の長さｘ_m、ｙ_mは次の（１３）式で表すことができる。
【００６１】
【数１３】

【００６２】
但し、Ｄは次の（１４）式から求まる値である。なお、次数ｍは定数ａに含まれている。
【００６３】
【数１４】

【００６４】
以上の結果から、音源Ｓと受音点Ｒの位置が与えられ、設置する反射面を含む平面を直交座標系のｘｙ平面上にとれば、上記の二つの第１条件（ａ）と第２条件（ｂ）に対して、正の位相で作用する領域（ｍが奇数の条件を満たす領域）、または、負の位相で作用する領域（ｍが偶数の条件を満たす領域）が定められる。このとき、図４に示すように、それらの領域は、音源Ｓと受音点Ｒの座標、および次数ｍを与えれば、第１条件（ａ）については（５）式と（６）式、第２条件（ｂ）については（１２）式と（１３）式によって、一意に決定できる。
【００６５】
図４にはフレネル楕円帯の計算例を示したが、一般に、入射角が擦過入射に近づくほど、または高周波になるほど楕円は非常に縦長となる。また、フレネル次数ｍの増加とともに楕円短軸が単調に増加していく傾向がある。
【００６６】
〔反射面の大きさ決定の原理〕
次に、反射面の大きさの求めることについて説明する。
【００６７】
上述のようにして、反射面（吸収面）の位置を求めることができるが、反射面には音源から発生した音波は一般に斜めに入射するので、垂直入射の場合とは異なる。このため、ある次数ｍの値に対して生成される楕円から反射する音波の振幅は楕円上の位置により異なることが予想される。
【００６８】
そこで、ヘルムホルツ積分の振幅項を考慮すれば、楕円上の位置の寄与を評価することができる。ヘルムホルツ積分は、次の（１５）式で表すことができ、その振幅項は、次の（１６）式で表すことができる。
【００６９】
【数１５】

【００７０】
【数１６】

【００７１】
この評価は、上記ヘルムホルツ積分の振幅項を包落線と見なすことで、その寄与を評価することができる。その一例のプロットを図５に示すが、場所により非常に振幅項が異なることが理解できる。すなわち、このように振幅項の（１６）式を数値計算し、その値が大きい領域にのみ反射面を設置すれば、上記の楕円全部の領域に反射面を設置しなくとも、充分な効果を得ることが可能となる。
【００７２】
なお、本条件の特別の場合として、音源と受音点が面に立てた同一の法線上に存在する場合、つまり、垂直入射の条件に一致するときには、任意の次数ｍに対応する定式で定義される楕円は同心円（所謂フレネル輪環帯）となる。すなわち、任意の次数ｍに対応する同位相の面は同心円であるドーナツ状の領域となるが、このときには、この領域の面要素からの寄与は回転対象であり、場所による違いは生じない。従って、上述の方法のように、反射に有効に寄与する特定の領域を決めることはできない。
【００７３】
図５では、特に、ｈ₁＝ｈ₂かつｈ<<ｒの場合には、音源と受音点の近傍の点で振幅は極大となり、幾何学的な反射点(ｒ/２，０）で鞍部点を有する（ｈ₁≠ ｈ₂では両者は一致しない）。
【００７５】
以上より、擦過入射に近づくほど、フレネル帯内でもその寄与は場所により大きく変化するという知見を得て、この知見では重要な寄与は音源と受信点の近傍の範囲から生じることが理解できる。特に重要な寄与が音源と受信点の近傍の範囲から生じることは、幾何光学的反射点が主たる寄与をするという考えと異なるものである。また、音源と受音点近傍の吸音が効果的であるという騒音対策の経験則に沿う結果が得られた。
【００７６】
〔反射面設計装置〕
次に、上記原理に基づく反射面設計装置について説明する。
【００７７】
図６に示すように、反射面設計装置１０は、ＣＰＵ１２，ＲＯＭ１４，ＲＡＭ１６が入出力ポート（以下、Ｉ／Ｏという）１８に接続され、コマンドやデータが授受可能なコンピュータ構成とされている。このＩ／Ｏ１８には、各種データやプログラムが格納されたメモリ２０が接続されている。また、Ｉ／Ｏ１８には、コマンドやデータ入力のためのキーボードなどの入力装置２２、及びコマンドやデータを表示するための表示装置２４が接続されている。
【００７８】
なお、メモリ２０には、上述の偏長楕円体の数式データや係数、ヘルムホルツ積分の振幅項の数式データや係数、以下に説明する処理プログラムが記憶されている。
【００７９】
反射面設計装置１０では、図７に示す処理ルーチンが実行される。まず、ステップ１００では、音源Ｓ及び受音点Ｒの座標入力値を読み取る。次のステップ１０２では、オペーレータの入力による選択値を判別することによって、上述の第１条件による反射面の計算を実行するか否かを判断する。肯定されると、ステップ１０４へ進み、否定されると、ステップ１１６へ進む。
【００８０】
ステップ１０４では、第１条件による直接音を考慮する偏長楕円式を設定する。ここでは、上記（２）式が設定される。次のステップ１０６では、設定した偏長楕円式を用いて偏長楕円体がｘｙ平面と交差する領域すなわち楕円領域を導出する。ここでは、上記（３）式及び（４）式が求まる。なお、これらの式は、上述のように、上記（５）式及び（６）式によることで楕円形状を明確に規定することができる。
【００８１】
次に、ステップ１０８において楕円領域の積分項を導出し（上記（１６）式参照）、次のステップ１１０で評価する。この評価は、振幅項の（１６）式による数値計算の値が大きい領域を求める。数値計算の値が大きい領域とは、数値計算の最大値になる領域、最大値から所定数の領域、所定値を超える値の領域などがある。
【００８２】
次のステップ１１２では、上記ステップ１１０の評価により求めた領域に対して反射面を設置するための位置及び大きさを求める。この位置及び大きさは、上記ステップ１１０の評価により求めた領域に見合うものであればよい。このステップ１１２で求めた位置及び大きさの反射面の計算値を、次のステップ１１４で表示装置２４へ出力する。
【００８３】
一方、ステップ１０２で否定されたときは、ステップ１１６において、第２条件による直接音を考慮する偏長楕円式を設定する。ここでは、上記（９）式が設定される。次のステップ１１８では、設定した偏長楕円式を用いて偏長楕円体がｘｙ平面と交差する領域すなわち楕円領域を導出する。ここでは、上記（１０）式及び（１１）式が求まる。なお、これらの式は、上述のように、上記（１２）式及び（１３）式によることで楕円形状を明確に規定することができる。
【００８４】
そして、楕円領域の積分項を導出して評価する（ステップ１０８、１１０）。この評価により求めた領域に対して反射面を設置するための位置及び大きさを求め（ステップ１１２）、表示装置２４へ出力する（ステップ１１４）。
【００８５】
これによって、反射面の位置及び大きさを得ることができる。すなわち、（１６）式による振幅項の大きな領域が最も効率的に音源からの音を反射または減衰できるので、この位置及び大きさにのみ反射面を設置すれば、上記の楕円全部の領域に反射面を設置しなくとも、充分な効果を得ることが可能となる。
【００８６】
このように、本実施の形態では、反射面を設けるのみの簡単な構成で、電源供給が必要な装置を用いることなく、効率的に音源からの音を増強したり減衰したりすることができる。また、目的に応じて反射と吸音のいずれかについて、シンプルな部材（プラスターボードや合板）だけで構成することができる。さらに、反射・吸音パネルの位置にはある程度の任意性を有することができ、実用上、設置可能な位置に設けることができる。従って、音源からの音を増強したり減衰したりするにあたって、ランニングコスト、材工費の削減が図れる。また、設計の自由度が大きいので、従来、対策が困難と考えられた場合にも対応が期待できる。
【００８７】
本方法（本実施の形態の反射面設計装置１０）による計算結果は、次の音響環境に用いることが好適である。
【００８８】
図８には、騒音源の発生音の低減に用いた適用例を示した。
【００８９】
騒音源からの直接音を低減するため、反射性のパネルを第１条件（ａ）の方法に沿って設計できる。このとき次数ｍが偶数となる領域が対象域となり、必要なパネルの寸法は上記（１６）式を計算して決定できる。そして、設置時の施工条件などを同時に考慮して適正なパネルの位置と寸法を決定すれば、騒音低減の効果が得られるパネルが設計できる。
【００９０】
図９には、騒音対策のための吸音処理のエリアの決定に用いた適用例を示した。
【００９１】
騒音源からの放射音を低減するため、例えば、音響反射に寄与すると予想される壁面に吸音処理を行う場合がある。これは、例えば天井や床面である。この場合、従来は、対象とする壁面に施工する吸音材料のどの部分が有効に作用するかを判定できなかったため、壁面の全面積に施工することが行われている。そこで、この場合、第２条件（ｂ）を想定し、正の位相（ｍは奇数）の領域でかつ、上記（１６）式によって、振幅の大きい領域に限定して吸音材を施工すればよい。
【００９２】
図１０には、コンサートホールの音響反射板への適用例を示した。
【００９３】
コンサートホールの舞台では、演奏者が自分の音を聞いたり、演奏者同士のアンサンブルを取るために、舞台周辺には反射面（通常、音響反射板と呼ばれる）が設置される。これにより、有効な反射音がこれから演奏者に返ることが必要である。この場合、第２条件（ｂ）に該当し、有効な反射音を得るため次数ｍが奇数となる領域かつ上記（１６）式の振幅項が大きくなる場所に、反射面を設置する設計が可能となる。
【００９４】
図１１には、ホールや講堂などの有害エコー除去への適用例を示した。
【００９５】
ホールや講堂などでは、舞台上の演奏者や拡声用スピーカから遠方の特定の壁面から、直接音から遅れて受音点に到達して、スピーチや音楽の品質を阻害するエコーが発生する場合がある。これを消去するため、コンピュータシミュレーションなどでエコーを発生する壁面を同定することは現状の技術で可能である。ただし、その面を吸音してエコーを消去する場合、その壁面が大きい場合には全面に吸音処理を行うことは部屋の残響時間を低下させて好ましくない影響を生じる場合がある。この場合にも、第２条件（ｂ）の次数ｍが奇数の条件を満たし、かつ、上記（１６）式を計算して必要最小限の領域面積を決定して、この部分に吸音処理を行う設計が可能となる。
【００９６】
【発明の効果】
以上説明したように本発明によれば、入力設定された音源、受音点、及び特定面の位置による、音源からの直接音に対する特定面の反射音による位相が所定関係を有する特定面上の位相領域の振幅に基づいて、反射領域を設定するので、音源からの音を打ち消したり補強したりする領域を容易に設定することができる、という効果がある。
【図面の簡単な説明】
【図１】 本発明の実施の形態にかかる音源と受音点の位置関係の説明図である。
【図２】 第１条件による位置関係を示す線図である。
【図３】 第２条件による位置関係を示す線図である。
【図４】 音源と受音点の位置関係及び楕円領域の位置関係の説明図である。
【図５】 ヘルムホルツ積分の振幅項による寄与の度合いの説明図である。
【図６】 本発明が適用された反射面設計装置の概略構成を示すブロック図である。
【図７】 本発明が適用された反射面設計装置の処理の流れを示すフローチャートである。
【図８】 本発明を、騒音源の発生音の低減に適用する場合の説明図である。
【図９】 本発明を、騒音対策のための吸音処理のエリアの決定に適用する場合の説明図である。
【図１０】 本発明を、コンサートホールの音響反射板に適用する場合の説明図である。
【図１１】 本発明をホールや講堂などの有害エコー除去、に適用する場合の説明図である。
【符号の説明】
Ｐ…点
Ｒ…受音点
Ｓ’…鏡像音源
Ｓ…音源
Δ…反射波の行路差
１０…反射面設計装置
２０…メモリ
２４…表示装置[0001]
BACKGROUND OF THE INVENTION
  The present invention is an acoustic board.Design equipmentIn particular, an acoustic board that sets the acoustic board in the space to increase or decrease the sound emitted from the sound source in the three-dimensional space at the receiving pointDesign equipmentAbout.
[0002]
[Prior art]
At present, there is no clear quantitative guideline for the design problem of the reflective surface in the acoustic design of the hall and the method for evaluating the position and size of the acoustically significant (reflective) surface in the CAD simulation shape input.
[0003]
For example, when the position of the sound source and the sound receiving point is set at an arbitrary position in the space, and the intensity of the sound generated from the sound source itself cannot be controlled, the magnitude of the direct sound that reaches the sound receiving point is controlled. As a method, the following three methods exist in principle. Note that here, as a sound source to be controlled, a loudspeaker such as a speaker that can actively control the intensity of sound is excluded.
[0004]
As a first method, an acoustic reflecting surface (or sound absorbing surface) is installed, and a sound having the same phase as that of the direct sound reaching the sound receiving point from the sound source (or a sound having an opposite phase) is generated by the surface. .
[0005]
As a second method, an obstacle such as a barrier is installed between the sound source and the sound receiving point to inhibit direct sound propagation.
[0006]
As a third method, a signal that reinforces direct sound is generated using an electroacoustic device (speaker, amplifier, and electrical control system) (so-called loudspeaker). In order to weaken the sound, this electroacoustic device is used to generate a sound having a phase opposite to that of the direct sound (active noise control technology). As an example, a sound field reproduction device that can realize a wide listening range with a plurality of speakers is known (see, for example, Patent Document 1).
[0007]
When taking acoustic countermeasures for an arbitrary sound source, it is impractical to use the second method or the third method because of the economics, effects of the method, or restrictions on the shape and arrangement conditions of the surroundings. Absent.
[0008]
Therefore, the first method is appropriate in view of simplicity.
[0009]
First, a flat or gently curved reflecting surface or sound absorbing surface is installed at a position where a reflected wave can be generated from the sound source to the sound receiving point. In this case, the determination of the position and size of the reflecting surface or the sound absorbing surface is arbitrary. The determination method includes an intuitive determination method such as an operator and a determination method based on a simple approximate calculation.
[0010]
Since the above intuitive determination method relies on empirical things such as an operator, a stable effect cannot be obtained. Therefore, assuming a quantitative method by simple approximation calculation, as an approximation theory, a method of evaluating Fresnel integration (for example, see Non-Patent Document 1) or a method using the concept of Fresnel band for normal incidence (for example, It has been generally based on Non-Patent Document 2). By installing an acoustic reflecting surface (or sound absorbing surface) by these techniques, it was possible to generate a sound having the same phase (or opposite phase) as the direct sound from the sound source.
[0011]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-48008
[Non-Patent Document 1]
I.G.Leizer "APPLICABILITY OF THEMETHODS OF GEOMETRIC ACOUSTICS FOR THE CALCULATION OF SOUND REFLECTION FROM PLANE SURFACES" (SOVIET PHYSICS-ACOUSTICS VOL.12, NO.2 OCTDEC, 1966, P180-184)
[Non-Patent Document 2]
L. Cremer "Fresnels Methoden zur berechnung von Beugungsfeldern" (ACUSTICA vol.72,1990)
[0012]
[Problems to be solved by the invention]
However, in the Leizer paper, a limited approximation formula is used for evaluation by Fresnel integration. That is, since Fresnel integration itself is an approximate expression and is established only under limited conditions, it includes an error, cannot be calculated with high accuracy, and cannot be used for general conditions. In other words, the technology according to the Leizer paper can be applied only when both the sound source and the sound receiving point are sufficiently far from the reflecting surface, and the frequency of sound such as a target ultrasonic wave is high.
[0013]
The Cremer paper only considers the assumption of normal incidence. In other words, in order to adopt the technology based on the Cremer paper, both the sound source and the sound receiving point must be on one normal line from the reflecting surface. However, the situation in which normal incidence can be assumed is very limited, and sound is normally incident obliquely on the surface, so application of this method is difficult.
[0014]
Therefore, in other words, the position of the reflecting surface for reaching the sound receiving point from a sound source at an arbitrary position in the space must be relied upon empirically, and it is difficult to set it simply and easily. It was.
[0015]
  In consideration of the above facts, the present invention is an acoustic board that can easily and easily enhance or weaken the sound from the sound source to the receiving point.Design equipmentThe purpose is to provide.
[0016]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention provides an acoustic board design apparatus for setting an acoustic board in a space in order to increase or decrease the sound emitted from a sound source at the sound receiving point. An input means for inputting a position;A predetermined plane in a three-dimensional space including the position of the sound source and the sound receiving point,Specific plane in the spaceAsFrom the surface setting means to set and the sound sourceAt the receiving pointDirect sound that reaches directlyAnd a difference in path between the reflected sound wave reflected from the sound source by the minute reflector in the three-dimensional space and reaching the sound receiving point is an integral multiple of a half wavelength of the sound emitted from the sound source, and the sound source And by obtaining a region of the Fresnel elliptical band formed by intersecting each of the ellipsoids having the focus at the position of the sound receiving point and the specific surface,By the reflected sound on the specific surfaceSaidOn the specific plane having a predetermined phase that acts to strengthen or weaken the sound that reaches the receiving pointIs the region of the Fresnel elliptical zoneA region calculation means for obtaining a phase region;By obtaining the amplitude term of the Helmholtz integral for the reflected wave in each region of the Fresnel elliptical zone,Amplitude calculation means for obtaining the amplitude of the sound reflected in the phase region on the specific surface, based on the obtained amplitude and the phase region, The region in the phase region in which the obtained amplitude value exceeds a predetermined value,A region in the phase region where the sound reaching the sound receiving point becomes stronger or weakerAsAnd an area setting means for setting a reflection area on the specific surface using the obtained area as a reflection area.
[0017]
From the viewpoint that the sound phase calculation alone is insufficient to control the intensity of the sound, the present inventor calculated the Fresnel reflection band for the oblique incidence of the sound wave and the intensity distribution of the reflected sound from the reflector. It was found that the position and size of the reflecting surface can be easily derived by obtaining the value by Kirchhoff-Helmholtz integration. The calculation of the Fresnel reflection band is to evaluate the phase of the reflected sound, and the calculation of the intensity distribution is to evaluate the amplitude of the reflected sound. For example, when the phase is positive, the reflected sound has the same phase as the target noise or the sound generated in the hall, and acts to reinforce this. On the other hand, when the phase is negative, the reflected sound has an opposite phase and acts to cancel the target sound wave. However, the phase information alone is not sufficient, and it is necessary that the reflected sound has sufficient amplitude (intensity). If this is obtained by integral evaluation, the position of the effective reflecting surface (having sufficient amplitude) Can be decided.
[0018]
Therefore, in the present invention, the position of the sound source and the sound receiving point is input, and a specific plane is set in the space. Then, a phase region on the specific surface in which the phase of the sound reaching the sound receiving point by a reflected sound on the specific surface has a predetermined relationship with respect to the direct sound directly reaching from the sound source is obtained. This phase region has a certain relationship between the sound from the sound source at the sound receiving point and the phase relationship from the specific surface, and is a region to be canceled or reinforced. By obtaining the amplitude of the phase region on this specific surface, it is possible to actually evaluate the sound state at the sound receiving point. Therefore, by setting the reflection region to the phase region having a predetermined amplitude from the phase region of the amplitude obtained on the specific surface, it is possible to set a region for canceling or reinforcing the sound from the sound source.
[0019]
  The phase of the predetermined relationship that acts to strengthen or weaken the sound that reaches the sound receiving point isIt is an odd multiple of a half wavelengthPositive phase orAn even multiple of half a wavelengthNegative phase can be employed.
[0020]
As described above, when the phase is positive, the reflected sound is in phase with the sound from the sound source and acts to reinforce the sound source, and when the phase is negative, the reflected sound becomes the opposite phase and cancels the sound from the sound source. Acts as follows. Therefore, by adopting at least one of the positive phase and the negative phase, it is possible to easily set a region where the sound from the sound source is canceled or reinforced.
[0022]
  In addition,In order to cancel or reinforce the sound from the sound source, it is preferable to set a reflector, and by adopting a reflective curved surface for the reflector, the sound from the sound source can be effectively canceled or reinforced. Can be.
[0023]
  As the sound source, a mirror image sound source which is a virtual sound source in which the sound source is symmetric with respect to a predetermined curved surfaceIt can be. That is, an acoustic board design apparatus for setting an acoustic board in a space in order to increase or decrease the sound emitted from a sound source at a sound receiving point, the input means for inputting the position of the sound source and the sound receiving point, and the sound source And a predetermined plane in the three-dimensional space including the position of the sound receiving point is set as a specific plane in the space, and a position symmetrical to the specific plane is determined as a virtual mirror image source for the sound source. A setting means, a sound that is assumed to directly reach the sound receiving point from the mirror image sound source, and a reflected wave that is reflected from the mirror image sound source by a minute reflector in the three-dimensional space and reaches the sound receiving point. A path difference is an integral multiple of a half wavelength of the sound emitted from the mirror image sound source, and each of the ellipsoids having the focal point at the position of the mirror image sound source and the sound receiving point intersects the specific plane. Frene formed by By determining the area of the elliptical band, the frequency of the Fresnel elliptical band on the specific surface having a predetermined phase that acts to strengthen or weaken the sound reaching the sound receiving point due to the reflected sound on the specific surface. Amplitude calculation for obtaining the amplitude of the sound reflected in the phase area on the specific plane by obtaining an amplitude term of the Helmholtz integral for the reflected wave of the Fresnel elliptical band area, and an area calculation means for obtaining a phase area that is an area A region in the phase region in which the value of the determined amplitude exceeds a predetermined value based on the means, the determined amplitude and the phase region, and a region in the phase region where the sound reaching the sound receiving point is strengthened or weakened And an area setting means for setting a reflection area on the specific surface with the obtained area as a reflection area.
The phase of the predetermined relationship that acts to strengthen or weaken the sound that reaches this receiving point is a positive phase that is an odd multiple of a half wavelength or a negative phase that is an even multiple of a half wavelength with respect to the direct sound. Can be adopted.
[0024]
An ellipsoid can be uniquely defined based on the sound source and the sound receiving point. Moreover, an ellipsoid can be uniquely defined based on a mirror image sound source and a sound receiving point which are virtual sound sources that are symmetrical with respect to a predetermined curved surface. Therefore, the specific surface employs a curved surface formed by intersecting an ellipsoid defined based on a sound source or a mirror image sound source and a sound receiving point and an arbitrary plane that can intersect the ellipsoid. Thereby, the curved surface which considered the phase and the amplitude can be set. As an example, when a reflective surface is provided, there are a case where an object of a certain size is positively installed, and a case where it is further provided on an existing surface (for example, the ground surface) such as soundproofing. Therefore, by adopting a curved surface that intersects the plane including the sound source and the sound receiving point as the specific surface, a reflecting surface can be positively provided, and a curved surface substantially parallel to the plane including the sound source and the sound receiving point. By adopting, it is possible to provide a reflecting surface in consideration of the existing environment such as the ground.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
[0026]
First, when reinforcing or attenuating the target sound with respect to the sound generated by the sound source, there is a noise countermeasure as the one to attenuate. For example, if there is a device that generates noise outdoors and a target area for noise reduction is given, in principle, if a sound wave having a phase opposite to that of the sound source is generated and returned to the sound receiving area, the noise is reduced. However, an electrical system including a microphone, a phase converter, a speaker, and the like is necessary and is substantially difficult. In addition, when the noise level increased due to reflections from the surrounding earth and buildings, it was difficult to determine which area affected the noise, so the total reflection surface was subjected to sound absorption processing. .
[0027]
Moreover, there exists room sound as what reinforces a sound. For example, in halls and other places, acoustic reflectors are installed above and around the stage to help players perform ensembles. However, the position, size and shape of the player and reflector should be specified. The reflector was set based on an empirical rule. Furthermore, in a hall or the like, a sound absorbing process is applied to a wall or the like in order to eliminate unnecessary reflected sounds such as echoes, but it is also set based on empirical rules.
[0028]
Therefore, in the present embodiment, when the positional relationship between the sound source and the sound receiving point is given, the phase of the sound wave reflected from a minute reflector placed at an arbitrary point in the space is determined. Thereby, it is possible to determine whether a reflection surface having the same phase or opposite phase can be obtained by arranging a reflection surface of any size at which position. Therefore, the position and size of the panel (for anti-phase) that should be arranged to reduce the direct sound from the noise source is determined, and similarly the position of the panel that returns the reflected sound useful for the player (for in-phase) And the size is decided. In addition, if the panel to be used is reflective, the material is arbitrary and plywood, acrylic, glass, etc. can be used. In addition, the position, size, and shape of the panel are not uniquely determined, but can be selected from a certain degree of freedom, so that a degree of freedom in design is ensured.
[0029]
Next, in the field of noise control / architectural acoustics, reinforcing and attenuating the target sound wave with respect to the sound wave generated by the sound source will be described.
[0030]
[Principle of position determination of reflective surface]
First, obtaining the position of the reflecting surface (absorbing surface) will be described.
[0031]
Given the position of the sound source and the receiving point, considering the plane placed at any point in space, the phase relationship of the reflected sound generated from it with respect to the direct sound is positive (0 to 180 degrees) Or a negative phase (from 0 degrees to -180 degrees). That is, if the phase is positive, the reflected sound acts to enhance the direct sound, and if the phase is negative, the reflected sound acts to directly cancel the sound. In the following description, all surfaces are acoustically reflective surfaces (plywood, boards, glass, metal panels, etc.).
[0032]
Therefore, if the surface can be designed to generate only positive phase reflected sound (or only negative phase reflected sound), the panel can be installed without using an electrical method for direct sound volume control. Only possible.
[0033]
As shown in FIG. 1, when a sound source S and a sound receiving point R are set in a three-dimensional xyz space, it is assumed that the reflecting surface exists on a plane formed by the xy axes, and a point P is assumed on the xy plane. At this time, it is necessary to divide the control to be the target of the sound behavior into two conditions. The first condition is a case where the contribution (phase) of the reflected sound from the point P is controlled with respect to the direct sound reaching the sound receiving point R from the sound source S, and the second condition is reflective on the xy plane. When controlling the contribution (phase) of the point P to the so-called geometrically reflected sound generated from the mirror image sound source S ′ with respect to the original sound source S and reaching the sound receiving point R generated by installing the surface It is.
[0034]
First condition (a): (contribution of reflected sound to direct sound):
In the first condition, as shown in FIG. 2, the coordinates and parameters of each point are determined. At this time, the path difference Δ of the reflected wave from the point P with respect to the direct wave from the sound source S can be expressed by the following equation. This first condition is for considering the existence area of the reflecting surface that is in phase with the direct wave (within a phase difference of λ / 2). For example, the effect of the reflecting surface around the stage (around the sound source) is handled. It is effective in some cases.
[0035]
[Expression 1]

[0036]
Here, if expressed as Δ = mλ / 2, m = 1, 2, 3,..., The sign of the phase of the reflected wave from the point P can be expressed. Here, λ is the wavelength of the target sound. In other words, considering from the path difference, it is understood that the reflected sound is reflected with a positive phase when m is an odd number and reflected with a negative phase when m is an even number.
[0037]
Therefore, first, the equation satisfied by the point (x, y, z) at which the path difference Δ of the reflected wave is constant under the conditions of FIG. 2 can be expressed by the following ellipsoidal equation.
[0038]
[Expression 2]

[0039]
However, the constants a and b are defined by the following equations. 2f is equal to the distance between SRs (the distance between the sound source and the sound receiving point).
[0040]
[Equation 3]

[0041]
The region where the ellipsoid determined by the above equation (2) intersects the xy plane can be represented by the following equations (3) and (4).
[0042]
[Expression 4]

[0043]
The area obtained by the above formula is an ellipse. When this ellipse is deformed to clarify its shape, the ellipse center y with respect to the order m_0mBecomes the following equation (5).
[0044]
[Equation 5]

[0045]
Also, the short axis and long axis length of the ellipse x_m, Y_mCan be expressed by the following equation (6).
[0046]
[Formula 6]

[0047]
However, D is a value obtained from the following equation (7). Note that the order m is included in the constant a.
[0048]
[Expression 7]

[0049]
Second condition (b): (contribution of reflected sound from mirror image sound source S ′):
In the second condition, as shown in FIG. 3, the coordinates and parameters of each point are determined. S ′ is a mirror image of the sound source S with respect to the xy plane, and an intersection of a straight line connecting the mirror image sound source S ′ and the sound receiving point R and the y axis is defined as a coordinate origin. At this time, the path difference Δ of the reflected wave from the point P with respect to the mirror image reflected wave from the mirror image sound source S ′ can be expressed by the following (8). This second condition is for considering a reflection region having the same phase as that of the geometric specular reflection wave, and is a region that effectively contributes as a reflection wave for a general reflection surface (when the surface is sufficiently large). This is effective when dealing with the effects of
[0050]
[Equation 8]

[0051]
Here, if expressed as Δ = mλ / 2, m = 1, 2, 3,..., The sign of the phase of the reflected wave from P can be expressed. Here, λ is the wavelength of the target sound. In other words, considering from the path difference, it is understood that the reflected sound is reflected with a positive phase when m is an odd number and reflected with a negative phase when m is an even number.
[0052]
Therefore, first, under the conditions shown in FIG. 3, the equation satisfied by the point (x, y, z) where the path difference Δ of the reflected wave is constant can be expressed by the following equation (9) of the ellipsoid: it can.
[0053]
[Equation 9]

[0054]
However, the constants a and b are defined by the following equations. 3f is equal to the distance between S'R.
[0055]
[Expression 10]

[0056]
A region where the ellipsoid intersects with the xy plane can be expressed by the following equations (10) and (11).
[0057]
## EQU11 ##

[0058]
The area obtained by the above formula is an ellipse. When this ellipse is deformed to clarify its shape, the ellipse center y with respect to the order m_0mBecomes the following equation (12).
[0059]
[Expression 12]

[0060]
Also, the short axis and long axis length of the ellipse x_m, Y_mCan be expressed by the following equation (13).
[0061]
[Formula 13]

[0062]
However, D is a value obtained from the following equation (14). Note that the order m is included in the constant a.
[0063]
[Expression 14]

[0064]
From the above results, if the positions of the sound source S and the sound receiving point R are given and the plane including the reflection surface to be installed is on the xy plane of the orthogonal coordinate system, the above two first conditions (a) and second For condition (b), a region that operates in a positive phase (a region that satisfies an odd condition of m) or a region that operates in a negative phase (a region that satisfies the condition that m is an even number) is determined. At this time, as shown in FIG. 4, if the coordinates of the sound source S and the sound receiving point R and the order m are given to those areas, the expressions (5) and (6) for the first condition (a), The second condition (b) can be uniquely determined by the equations (12) and (13).
[0065]
FIG. 4 shows a calculation example of the Fresnel elliptical band. In general, the ellipse becomes very long as the incident angle approaches the fretting incidence or the frequency becomes high. In addition, the minor axis of the ellipse tends to increase monotonically as the Fresnel order m increases.
[0066]
[Principle of determining the size of the reflective surface]
Next, obtaining the size of the reflecting surface will be described.
[0067]
As described above, the position of the reflecting surface (absorbing surface) can be obtained. However, since the sound wave generated from the sound source is generally incident obliquely on the reflecting surface, it is different from the case of vertical incidence. For this reason, it is expected that the amplitude of the sound wave reflected from the ellipse generated for a certain value of order m varies depending on the position on the ellipse.
[0068]
Therefore, if the amplitude term of the Helmholtz integral is taken into consideration, the contribution of the position on the ellipse can be evaluated. The Helmholtz integral can be expressed by the following equation (15), and its amplitude term can be expressed by the following equation (16).
[0069]
[Expression 15]

[0070]
[Expression 16]

[0071]
In this evaluation, the contribution can be evaluated by regarding the amplitude term of the Helmholtz integral as an envelope. An example of the plot is shown in FIG. 5. It can be understood that the amplitude term varies greatly depending on the location. That is, if the equation (16) of the amplitude term is numerically calculated and the reflecting surface is installed only in the region where the value is large, sufficient effects can be obtained without installing the reflecting surface in the entire region of the ellipse. Can be obtained.
[0072]
As a special case of this condition, when the sound source and the receiving point are on the same normal line upright on the surface, that is, when the condition of normal incidence is met, it is defined by a formula corresponding to an arbitrary order m The ellipse formed is a concentric circle (so-called Fresnel ring zone). That is, the in-phase surface corresponding to an arbitrary order m is a donut-shaped region that is a concentric circle. At this time, the contribution from the surface element of this region is a rotation target, and there is no difference depending on the location. Therefore, it is not possible to determine a specific region that effectively contributes to reflection as in the above-described method.
[0073]
  In FIG. 5, in particular, h₁= H₂And if h << r, the sound source and the vicinity of the receiving pointIn terms ofThe amplitude is maximal and has a saddle point at the geometric reflection point (r / 2, 0) (h₁≠ h₂So they don't match).
[0075]
  From the above, the closer to fretting incidenceTheEven within the Rennel zone, the contribution varies greatly depending on the location.With this knowledge,It can be seen that the important contribution comes from the range near the sound source and the reception point. In particularSignificant contributions originate from the vicinity of the sound source and the receiving pointIs different from the idea that geometrical reflection points make the main contribution. In addition, the results were in line with empirical rules for noise countermeasures that sound absorption near the sound source and the sound receiving point was effective.
[0076]
[Reflective surface design equipment]
Next, a reflection surface design apparatus based on the above principle will be described.
[0077]
As shown in FIG. 6, the reflecting surface design apparatus 10 has a computer configuration in which a CPU 12, a ROM 14, and a RAM 16 are connected to an input / output port (hereinafter referred to as I / O) 18 and commands and data can be exchanged. The I / O 18 is connected to a memory 20 that stores various data and programs. Further, an input device 22 such as a keyboard for inputting commands and data and a display device 24 for displaying commands and data are connected to the I / O 18.
[0078]
The memory 20 stores mathematical data and coefficients of the above-described ellipsoid, mathematical data and coefficients of the amplitude term of Helmholtz integration, and a processing program described below.
[0079]
In the reflecting surface design apparatus 10, the processing routine shown in FIG. 7 is executed. First, in step 100, the coordinate input values of the sound source S and the sound receiving point R are read. In the next step 102, it is determined whether or not to perform the calculation of the reflection surface according to the first condition described above, by determining the selection value by the operator input. If the determination is affirmative, the process proceeds to step 104, and if the determination is negative, the process proceeds to step 116.
[0080]
In step 104, an ellipse formula that takes into account the direct sound according to the first condition is set. Here, the above equation (2) is set. In the next step 106, a region where the ellipsoid intersects with the xy plane, that is, an ellipse region is derived using the set ellipse equation. Here, the above equations (3) and (4) are obtained. In addition, as above-mentioned, these formulas can prescribe | regulate an elliptical shape clearly by the said (5) Formula and (6) Formula.
[0081]
Next, in step 108, an integral term of the elliptic region is derived (see the above equation (16)) and evaluated in the next step 110. In this evaluation, a region where the value of numerical calculation by the equation (16) of the amplitude term is large is obtained. The area where the value of the numerical calculation is large includes an area where the maximum value of the numerical calculation is obtained, a predetermined number of areas from the maximum value, and an area where the value exceeds the predetermined value.
[0082]
In the next step 112, the position and size for installing the reflecting surface are obtained for the region obtained by the evaluation in step 110. This position and size may be any as long as it matches the area obtained by the evaluation in step 110. The calculated value of the reflection surface at the position and size obtained in step 112 is output to the display device 24 in the next step 114.
[0083]
On the other hand, when the result in Step 102 is negative, in Step 116, an ellipse formula that considers the direct sound according to the second condition is set. Here, the above equation (9) is set. In the next step 118, an area where the ellipsoid intersects with the xy plane, that is, an ellipse area is derived using the set ellipsoidal equation. Here, the above equations (10) and (11) are obtained. In addition, as above-mentioned, these formulas can prescribe | regulate an elliptical shape clearly by the said (12) Formula and (13) Formula.
[0084]
Then, an integral term of the elliptic region is derived and evaluated (steps 108 and 110). The position and size for installing the reflecting surface are obtained for the area obtained by this evaluation (step 112) and output to the display device 24 (step 114).
[0085]
Thereby, the position and size of the reflecting surface can be obtained. In other words, the region with a large amplitude term according to Equation (16) can reflect or attenuate the sound from the sound source most efficiently, so if the reflecting surface is installed only at this position and size, the region reflected by the entire ellipse is reflected. Even if a surface is not installed, a sufficient effect can be obtained.
[0086]
As described above, according to the present embodiment, the sound from the sound source can be efficiently enhanced or attenuated without using a device that requires power supply with a simple configuration in which only the reflection surface is provided. . Further, depending on the purpose, either reflection or sound absorption can be configured with only a simple member (plaster board or plywood). Furthermore, the position of the reflection / sound absorption panel can have a certain degree of arbitraryness, and can be provided at a position where it can be practically installed. Therefore, in increasing or attenuating the sound from the sound source, it is possible to reduce running costs and material costs. In addition, since the degree of freedom of design is large, it can be expected that countermeasures are conventionally considered difficult.
[0087]
The calculation result by this method (the reflecting surface design apparatus 10 of the present embodiment) is preferably used for the following acoustic environment.
[0088]
FIG. 8 shows an application example used to reduce noise generated by a noise source.
[0089]
In order to reduce the direct sound from the noise source, the reflective panel can be designed according to the method of the first condition (a). At this time, the region where the order m is an even number is the target region, and the necessary panel dimensions can be determined by calculating the above equation (16). If the appropriate panel position and dimensions are determined in consideration of the installation conditions at the time of installation, a panel capable of reducing noise can be designed.
[0090]
FIG. 9 shows an application example used to determine a sound absorption processing area for noise countermeasures.
[0091]
In order to reduce the radiated sound from the noise source, for example, sound absorption processing may be performed on a wall surface that is expected to contribute to acoustic reflection. This is, for example, a ceiling or a floor surface. In this case, conventionally, since it has not been possible to determine which part of the sound-absorbing material to be applied to the target wall surface is effective, it is applied to the entire area of the wall surface. Therefore, in this case, the second condition (b) is assumed, and the sound absorbing material is limited to a region having a positive phase (m is an odd number) and a region having a large amplitude according to the above equation (16). .
[0092]
FIG. 10 shows an application example to an acoustic reflector in a concert hall.
[0093]
On the stage of the concert hall, a reflective surface (usually called an acoustic reflector) is installed around the stage in order for the performers to hear their own sounds and take ensembles between performers. This requires that an effective reflected sound be returned to the performer. In this case, in order to meet the second condition (b) and to obtain an effective reflected sound, it is possible to design a reflective surface in a region where the order m is an odd number and where the amplitude term of the above equation (16) is large. It becomes.
[0094]
FIG. 11 shows an application example to the removal of harmful echoes such as halls and auditoriums.
[0095]
In halls, auditoriums, etc., echoes that interfere with speech and music quality may occur from a specific wall far from the performers or loudspeakers on the stage, reaching the receiving point with a delay from the direct sound. is there. In order to eliminate this, it is possible to identify a wall surface that generates an echo by computer simulation or the like with the current technology. However, when the sound is absorbed by the surface and the echo is erased, if the wall surface is large, performing the sound absorption process on the entire surface may reduce the reverberation time of the room and may have an undesirable effect. Also in this case, the order m of the second condition (b) satisfies the condition of an odd number, and the above-described equation (16) is calculated to determine the necessary minimum area, and the sound absorbing process is performed on this part. Design becomes possible.
[0096]
【The invention's effect】
As described above, according to the present invention, the phase of the reflected sound of the specific surface with respect to the direct sound from the sound source due to the input sound source, the sound receiving point, and the position of the specific surface is on the specific surface having a predetermined relationship. Since the reflection region is set based on the amplitude of the phase region, there is an effect that the region where the sound from the sound source is canceled or reinforced can be easily set.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a positional relationship between a sound source and a sound receiving point according to an embodiment of the present invention.
FIG. 2 is a diagram showing a positional relationship according to a first condition.
FIG. 3 is a diagram showing a positional relationship according to a second condition.
FIG. 4 is an explanatory diagram of a positional relationship between a sound source and a sound receiving point and an elliptical region.
FIG. 5 is an explanatory diagram of a degree of contribution by an amplitude term of Helmholtz integration.
FIG. 6 is a block diagram showing a schematic configuration of a reflecting surface design apparatus to which the present invention is applied.
FIG. 7 is a flowchart showing a processing flow of the reflecting surface design apparatus to which the present invention is applied.
FIG. 8 is an explanatory diagram in a case where the present invention is applied to reduction of sound generated by a noise source.
FIG. 9 is an explanatory diagram when the present invention is applied to determination of an area of sound absorption processing for noise countermeasures.
FIG. 10 is an explanatory diagram when the present invention is applied to an acoustic reflector in a concert hall.
FIG. 11 is an explanatory diagram when the present invention is applied to the removal of harmful echoes such as halls and auditoriums.
[Explanation of symbols]
P ... dot
R ... Sound receiving point
S '... Mirror image sound source
S ... Sound source
Δ: Path difference of reflected wave
10 ... Reflective surface design device
20 ... Memory
24 ... Display device

Claims (4)

A sound board design device for setting a sound board in a space in order to increase or decrease the sound emitted from a sound source at a sound receiving point,
Input means for inputting the position of the sound source and the receiving point;
A plane setting means for setting a predetermined plane in the three-dimensional space including the position of the sound source and the sound receiving point as a specific plane in the space;
A path difference between a direct sound that directly reaches the sound receiving point from the sound source and a reflected wave that is reflected from the sound source by a minute reflector in the three-dimensional space and reaches the sound receiving point is emitted from the sound source. A region of a Fresnel elliptical band formed by intersecting each of the ellipsoids that are integral multiples of a half wavelength of the sound and that is focused on the position of the sound source and the sound receiving point and the specific plane. by the phase region is a region of the Fresnel ellipse band on the particular surface having a predetermined relationship between the phase which acts to dampen the action or intensify the sound reaching the sound receiving point by reflecting sound in the specific surface Region calculation means to be obtained;
Amplitude calculation means for obtaining the amplitude of the sound reflected in the phase region on the specific surface by obtaining the amplitude term of Helmholtz integral for the reflected wave of each region of the Fresnel elliptical band ;
Based on the amplitude and the phase region was determined, the region of the phase region in which the value of the amplitude determined exceeds a predetermined value, determined as a region in the phase region in which the sound is strengthened or weakened to reach the sound receiving point, An area setting means for setting the reflection area on the specific surface as the obtained area as a reflection area;
A sound board designing apparatus comprising: The phase of the predetermined relationship that acts to strengthen or weaken the sound that reaches the receiving point is a positive phase that is an odd multiple of a half wavelength or a negative phase that is an even multiple of a half wavelength with respect to the direct sound. The acoustic board designing apparatus according to claim 1, wherein the acoustic board designing apparatus is provided. A sound board design device for setting a sound board in a space in order to increase or decrease the sound emitted from a sound source at a sound receiving point,
Input means for inputting the position of the sound source and the receiving point;
A plane predetermined in the three-dimensional space including the sound source and the position of the sound receiving point is set as a specific surface in the space, and a position that is symmetric with respect to the specific surface is set as a virtual mirror image sound source. Setting means defined in
And sound that is supposed to directly reach the sound receiving point from the mirror image sound source path difference between the reflected waves reaching the sound receiving point from the mirror image sound source is reflected by the micro-reflector of the three-dimensional space is Each of the ellipsoids that are integral multiples of a half wavelength of the sound that is supposed to be emitted from the mirror image sound source and that is focused on the position of the mirror image sound source and the sound receiving point intersects with the specific surface. by determining the area of the Fresnel ellipse zone to be Fresnel on the particular surface having a predetermined relationship between the phase acting as the weakened action or as sound reaching the sound receiving point is strengthened by the reflection sound in the specific surface An area calculation means for obtaining a phase area that is an elliptical band area ;
Amplitude calculation means for obtaining the amplitude of sound reflected in the phase region on the specific surface by obtaining the amplitude term of Helmholtz integration for the reflected wave in the Fresnel elliptical region ,
Based on the amplitude and the phase region was determined, the region of the phase region in which the value of the amplitude determined exceeds a predetermined value, determined as a region in the phase region in which the sound is strengthened or weakened to reach the sound receiving point, An area setting means for setting the reflection area on the specific surface as the obtained area as a reflection area;
A sound board designing apparatus comprising:   The phase of the predetermined relationship that acts to strengthen or weaken the sound that reaches the receiving point is a positive phase that is an odd multiple of a half wavelength or a negative phase that is an even multiple of a half wavelength with respect to the direct sound. The acoustic board designing apparatus according to claim 3, wherein the acoustic board designing apparatus is provided.

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