吸(xi)(xi)聲(sheng)(sheng)(sheng)是聲(sheng)(sheng)(sheng)波(bo)撞擊(ji)到材料表(biao)面后(hou)能(neng)(neng)量(liang)損失的(de)現象，吸(xi)(xi)聲(sheng)(sheng)(sheng)可(ke)(ke)以(yi)降低室內聲(sheng)(sheng)(sheng)壓級。描述吸(xi)(xi)聲(sheng)(sheng)(sheng)的(de)指標是吸(xi)(xi)聲(sheng)(sheng)(sheng)系(xi)數a，代表(biao)被(bei)材料吸(xi)(xi)收的(de)聲(sheng)(sheng)(sheng)能(neng)(neng)與入射(she)聲(sheng)(sheng)(sheng)能(neng)(neng)的(de)比值。理論上，如(ru)(ru)果某種材料完全(quan)反射(she)聲(sheng)(sheng)(sheng)音，那(nei)么(me)(me)它(ta)的(de)a=0;如(ru)(ru)果某種材料將入射(she)聲(sheng)(sheng)(sheng)能(neng)(neng)全(quan)部吸(xi)(xi)收，那(nei)么(me)(me)它(ta)的(de)a=1。事實上，所有材料的(de)a介于0和1之間，也就是不(bu)可(ke)(ke)能(neng)(neng)全(quan)部反射(she)，也不(bu)可(ke)(ke)能(neng)(neng)全(quan)部吸(xi)(xi)收。

不同頻(pin)率(lv)上(shang)會有不同的(de)吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)系數(shu)(shu)(shu)(shu)(shu)。人們使(shi)用吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)系數(shu)(shu)(shu)(shu)(shu)頻(pin)率(lv)特(te)性曲(qu)線描(miao)述材(cai)(cai)料(liao)(liao)在(zai)不同頻(pin)率(lv)上(shang)的(de)吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)性能。按照ISO標(biao)準(zhun)和國家標(biao)準(zhun)，吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)測試報告中吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)系數(shu)(shu)(shu)(shu)(shu)的(de)頻(pin)率(lv)范圍是100-5KHz。將100-5KHz的(de)吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)系數(shu)(shu)(shu)(shu)(shu)取平(ping)均得到的(de)數(shu)(shu)(shu)(shu)(shu)值是平(ping)均吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)系數(shu)(shu)(shu)(shu)(shu)，平(ping)均吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)系數(shu)(shu)(shu)(shu)(shu)反(fan)(fan)映了材(cai)(cai)料(liao)(liao)總體的(de)吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)性能。在(zai)工程(cheng)中常使(shi)用降噪系數(shu)(shu)(shu)(shu)(shu)NRC粗略(lve)地評價在(zai)語言頻(pin)率(lv)范圍內(nei)的(de)吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)性能，這一數(shu)(shu)(shu)(shu)(shu)值是材(cai)(cai)料(liao)(liao)在(zai)250、500、1K、2K四個頻(pin)率(lv)的(de)吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)系數(shu)(shu)(shu)(shu)(shu)的(de)算術(shu)平(ping)均值，四舍(she)五入取整到0.05。一般認(ren)為NRC小于0.2的(de)材(cai)(cai)料(liao)(liao)是反(fan)(fan)射材(cai)(cai)料(liao)(liao)，NRC大(da)于等(deng)0.2的(de)材(cai)(cai)料(liao)(liao)才被認(ren)為是吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)材(cai)(cai)料(liao)(liao)。當(dang)需要吸(xi)(xi)(xi)收大(da)量聲(sheng)(sheng)(sheng)能降低室內(nei)混響及噪聲(sheng)(sheng)(sheng)時，常常需要使(shi)用高(gao)吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)系數(shu)(shu)(shu)(shu)(shu)的(de)材(cai)(cai)料(liao)(liao)。如離心(xin)玻(bo)璃(li)棉、巖棉等(deng)屬(shu)于高(gao)NRC吸(xi)(xi)(xi)聲(sheng)(sheng)(sheng)材(cai)(cai)料(liao)(liao)，5cm厚(hou)的(de)24kg/m3的(de)離心(xin)玻(bo)璃(li)棉的(de)NRC可達到0.95。

測(ce)量(liang)(liang)(liang)(liang)材料(liao)(liao)吸聲(sheng)系(xi)(xi)(xi)(xi)數的(de)(de)(de)方法(fa)(fa)有兩(liang)種，一種是(shi)(shi)混響室(shi)法(fa)(fa)，一種是(shi)(shi)駐波管法(fa)(fa)。混響室(shi)法(fa)(fa)測(ce)量(liang)(liang)(liang)(liang)聲(sheng)音無(wu)規(gui)入(ru)射時的(de)(de)(de)吸聲(sheng)系(xi)(xi)(xi)(xi)數，即聲(sheng)音由四面(mian)八方射入(ru)材料(liao)(liao)時能(neng)量(liang)(liang)(liang)(liang)損失的(de)(de)(de)比例，而駐波管法(fa)(fa)測(ce)量(liang)(liang)(liang)(liang)聲(sheng)音正入(ru)射時的(de)(de)(de)吸聲(sheng)系(xi)(xi)(xi)(xi)數，聲(sheng)音入(ru)射角度僅為(wei)90度。兩(liang)種方法(fa)(fa)測(ce)量(liang)(liang)(liang)(liang)的(de)(de)(de)吸聲(sheng)系(xi)(xi)(xi)(xi)數是(shi)(shi)不同的(de)(de)(de)，工程(cheng)上(shang)最常使用的(de)(de)(de)是(shi)(shi)混響室(shi)法(fa)(fa)測(ce)量(liang)(liang)(liang)(liang)的(de)(de)(de)吸聲(sheng)系(xi)(xi)(xi)(xi)數，因為(wei)建筑實(shi)際(ji)應(ying)用中聲(sheng)音入(ru)射都是(shi)(shi)無(wu)規(gui)的(de)(de)(de)。在某些測(ce)量(liang)(liang)(liang)(liang)報告中會出(chu)現吸聲(sheng)系(xi)(xi)(xi)(xi)數大(da)于(yu)1的(de)(de)(de)情況，這(zhe)是(shi)(shi)由于(yu)測(ce)量(liang)(liang)(liang)(liang)的(de)(de)(de)實(shi)驗(yan)室(shi)條(tiao)件等(deng)造成的(de)(de)(de)，理論(lun)上(shang)任(ren)(ren)何材料(liao)(liao)吸收的(de)(de)(de)聲(sheng)能(neng)不可(ke)能(neng)大(da)于(yu)入(ru)射聲(sheng)能(neng)，吸聲(sheng)系(xi)(xi)(xi)(xi)數永遠小于(yu)1。任(ren)(ren)何大(da)于(yu)1的(de)(de)(de)測(ce)量(liang)(liang)(liang)(liang)吸聲(sheng)系(xi)(xi)(xi)(xi)數值在實(shi)際(ji)聲(sheng)學工程(cheng)計算(suan)中都不能(neng)按(an)大(da)于(yu)1使用，最多按(an)1進(jin)行計算(suan)。

在(zai)(zai)房間(jian)(jian)(jian)中，聲(sheng)(sheng)音會很快充滿各個角(jiao)落，因此，將吸(xi)(xi)聲(sheng)(sheng)材料放(fang)置在(zai)(zai)房間(jian)(jian)(jian)任何表面(mian)都(dou)有吸(xi)(xi)聲(sheng)(sheng)效果(guo)。吸(xi)(xi)聲(sheng)(sheng)材料吸(xi)(xi)聲(sheng)(sheng)系(xi)數越大(da)，吸(xi)(xi)聲(sheng)(sheng)面(mian)積越多，吸(xi)(xi)聲(sheng)(sheng)效果(guo)越明顯。可(ke)以利用吸(xi)(xi)聲(sheng)(sheng)天花、吸(xi)(xi)聲(sheng)(sheng)墻板(ban)、空間(jian)(jian)(jian)吸(xi)(xi)聲(sheng)(sheng)體等進(jin)行吸(xi)(xi)聲(sheng)(sheng)降噪。

吸聲原理

纖維多孔(kong)(kong)吸(xi)(xi)(xi)聲材(cai)(cai)(cai)料(liao)，如(ru)離心(xin)玻璃棉、巖棉、礦棉、植物(wu)纖維噴涂等，吸(xi)(xi)(xi)聲機(ji)理是(shi)材(cai)(cai)(cai)料(liao)內部(bu)(bu)有(you)大(da)量(liang)微(wei)小的(de)(de)連(lian)通(tong)(tong)的(de)(de)孔(kong)(kong)隙，聲波沿著(zhu)(zhu)這(zhe)些孔(kong)(kong)隙可以(yi)深入(ru)材(cai)(cai)(cai)料(liao)內部(bu)(bu)，與(yu)材(cai)(cai)(cai)料(liao)發生(sheng)摩(mo)擦作用(yong)將聲能(neng)轉化為(wei)熱能(neng)。多孔(kong)(kong)吸(xi)(xi)(xi)聲材(cai)(cai)(cai)料(liao)的(de)(de)吸(xi)(xi)(xi)聲特性是(shi)隨著(zhu)(zhu)頻率的(de)(de)增高吸(xi)(xi)(xi)聲系數逐漸增大(da)，這(zhe)意味(wei)著(zhu)(zhu)低頻吸(xi)(xi)(xi)收沒(mei)有(you)高頻吸(xi)(xi)(xi)收好。多孔(kong)(kong)材(cai)(cai)(cai)料(liao)吸(xi)(xi)(xi)聲的(de)(de)必(bi)要條件是(shi)：材(cai)(cai)(cai)料(liao)有(you)大(da)量(liang)空隙，空隙之間互相連(lian)通(tong)(tong)，孔(kong)(kong)隙深入(ru)材(cai)(cai)(cai)料(liao)內部(bu)(bu)。錯誤(wu)認(ren)識(shi)之一是(shi)認(ren)為(wei)表面粗糙的(de)(de)材(cai)(cai)(cai)料(liao)具(ju)有(you)吸(xi)(xi)(xi)聲性能(neng)，其實(shi)不(bu)然(ran)，例(li)如(ru)拉毛(mao)水泥、表面凸凹的(de)(de)石才基本(ben)不(bu)具(ju)有(you)吸(xi)(xi)(xi)聲能(neng)力。錯誤(wu)認(ren)識(shi)之二是(shi)認(ren)為(wei)材(cai)(cai)(cai)料(liao)內部(bu)(bu)具(ju)有(you)大(da)量(liang)孔(kong)(kong)洞的(de)(de)材(cai)(cai)(cai)料(liao)，如(ru)聚苯(ben)、聚乙(yi)烯、閉孔(kong)(kong)聚氨脂等，具(ju)有(you)良好的(de)(de)吸(xi)(xi)(xi)聲性能(neng)，事實(shi)上，這(zhe)些材(cai)(cai)(cai)料(liao)由于內部(bu)(bu)孔(kong)(kong)洞沒(mei)有(you)連(lian)通(tong)(tong)性，聲波不(bu)能(neng)深入(ru)材(cai)(cai)(cai)料(liao)內部(bu)(bu)振(zhen)動摩(mo)擦，因(yin)此(ci)吸(xi)(xi)(xi)聲系數很小。

與墻面(mian)或(huo)天花存在(zai)(zai)空(kong)氣(qi)層的(de)穿(chuan)孔板，即使材料本身吸(xi)聲性能(neng)(neng)很差(cha)，這種結構也具有吸(xi)聲性能(neng)(neng)，如穿(chuan)孔的(de)石膏板、木板、金屬板、甚(shen)至是狹縫(feng)吸(xi)聲磚等。這類吸(xi)聲被(bei)稱為(wei)亥姆霍(huo)茲(zi)共(gong)(gong)振(zhen)吸(xi)聲，吸(xi)聲原(yuan)理類似(si)于(yu)暖(nuan)水瓶(ping)的(de)聲共(gong)(gong)振(zhen)，材料外部(bu)(bu)空(kong)間與內(nei)部(bu)(bu)腔體(ti)通過窄的(de)瓶(ping)頸連接(jie)，聲波入射時，在(zai)(zai)共(gong)(gong)振(zhen)頻率上，頸部(bu)(bu)的(de)空(kong)氣(qi)和內(nei)部(bu)(bu)空(kong)間之間產生(sheng)劇(ju)烈的(de)共(gong)(gong)振(zhen)作用(yong)損耗了聲能(neng)(neng)。亥姆霍(huo)茲(zi)共(gong)(gong)振(zhen)吸(xi)收的(de)特點是只有在(zai)(zai)共(gong)(gong)振(zhen)頻率上具有較大的(de)吸(xi)聲系(xi)數(shu)。

薄(bo)膜或薄(bo)板(ban)與墻體(ti)或頂棚存在空腔時也能吸聲，如木板(ban)、金屬板(ban)做成(cheng)的天花板(ban)或墻板(ban)等，這種結構的吸聲機理是薄(bo)板(ban)共(gong)(gong)振吸聲。在共(gong)(gong)振頻率上(shang)，由于(yu)薄(bo)板(ban)劇烈振動而大(da)量吸收聲能。薄(bo)板(ban)共(gong)(gong)振吸收大(da)多在低頻具有較好的吸聲性(xing)能。

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