關於雙混響室測隔聲材料?
用兩個相鄰混響室測隔聲材料,隔牆開窗(以便放待測材料),由一個混響室內的聲源發聲,測兩個混響室中的聲壓差。但是發現第一間聲場中沿聲源到隔牆窗方向有隨距離2dB的衰減,不是完全混響,這是為什麼呢?在測量中需要注意些什麼呢
感謝邀請,拋磚引玉。
混響室測隔聲是基於兩個房間都是擴散場的假設。擴散場意味著各點能量密度相同,不相干聲波來自所有方向。混響室的低吸聲和不規則牆體使它接近擴散場,但不可能成為理想擴散場,至少在靠近聲源(來自聲源的直達聲太強)或牆(反射波干涉)的地方。
題主的問題可能是由於聲源離測試材料太近或者麥克風離聲源太近造成的。麥克風需要多選幾個位置, ISO 140里有推薦一些聲源和麥克風的設置,我複製粘貼幾段:
- Place the loudspeaker enclosure so as to give a sound field as diffuse as possible and at such a distance from the separating element and the flanking elements influencing the sound transmission that the direct radiation upon them is not dominant.
- Microphone positions:The following are minimum separating distances:
- 0,7 m between microphone positions;
- 0,5 m between any microphone position and room boundaries or diffusers;
- 1,0 m between any microphone position and the sound source.
- NOTE Greater separating distances should be used wherever possible.
- Ensure that the microphone positions are outside the direct sound field of the source. Each fixed microphone position shall lie outside the region in which levels decrease significantly with distance from the source.
- Guidance on the selection of optimum source positions
- The suitability of source positions also depends on the radiation characteristic of the loudspeaker as well as on the microphone positions (or the microphone path in the case of a moving microphone).
- The distance between different loudspeaker positions shall be not less than 0,7 m.
- At least two positions shall be not less than 1,4 m apart.
- The distance between the room boundaries and the source center shall be not less than 0,5 m.
- Different loudspeaker positions shall not be located within the same planes parallel to the room boundaries.
- Deviating from the above-mentioned requirements concerning the distance between the room boundaries and the source, especially in small rooms it is often of advantage for the practical execution of the measurements to use loudspeaker positions in the corners of the source room. Take special care with regard to possible influence on the flanking transmission and with regard to unwanted increase of level fluctuations in the source room.
@吐槽無力不耐乳糖
兩個混響室測隔聲基於 ISO 140 - Part 3: Laboratory measurement of airborne sound insulation of
building elements. 我們需要測量的是傳入receiving room的聲功率,如果receiving room是假設擴散場的混響室,我們可以測量平均聲壓和吸聲面積,通過入射和吸收的聲能量平衡來計算入射功率。我想receiving room用消聲室也可以。但需要聲強計在包圍隔聲材料的表面做積分,比較麻煩不如用混響室。不知你們是不是這樣測的?我覺得只用一個mic不能測量聲功率,除非是點聲源,但隔聲材料肯定不是點聲源。手頭只有ISO 140 part 4,沒有part 3,不知裡面有沒有消聲室的內容,歡迎交流!雙混響室測隔聲是大部分建築隔聲材料測量採用的方法。是建立在兩個房間都滿足擴散聲場的前提下分別測量聲壓級表徵聲功率,由於實際與理想的差距,復現性差一點。
一個混響室和一個消聲室組成的隔聲測試套間,混響室這一邊仍然是建立在擴散聲場的前提下測聲壓級聲功率。消聲室這一邊測聲強級然後積分表徵聲功率,復現性比較好,但設備貴一點,測量麻煩一點。其實接收室這一邊不一定需要消聲室。
回到題主問題:你說的其實可能是可以接受,建議認真看看gbt 19889.1和19889.3兩部分標準,再重新做一下實驗。
你的聲源室聲源沒有完全混響這個應該是合理的,因為聲源發出雜訊有直達聲和反射聲,直達聲是由設備發出向外擴散的聲源,混響是經過反射的了,直達聲是有距離衰減規律的,在聲源太近的位置沒有達到混響,直達聲佔主流,這個應該是正常的,ISO140或者GB/T19889規定了你在聲源室布置測點要離開聲源一定距離的,你只要在這個控制的範圍外取點,應該是可以的,至於你說的衰減問題,你評價是否可行的辦法是標準里,GB/T19889.1等對於聲壓級聲場均勻度的標準來去考核,因為你提到的這個我不清楚你具體布點,如果你有個點離聲源太近,那出現這個現象是正常的,你不應該取聲源過近的點。
兩個混響室測隔聲?你們用的哪個標準?我們從來都是聲源混響 Mic放消聲室啊
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