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7.4. Horn Loudspeaker Systems(Compound Horn Loudspeaker;Multiple-Horn, Single-Channel System)【基本概念】1 复合号筒扬声器(compound horn loundspeaker)(电声词典):由复合号筒与策动单元组成的扬声器。在振膜的一边安装低频用的长号筒,另一边安装高频用的短扬声器,用以展宽重放频带。2 声容(acoustic capacitance)(电声词典)对声学系统中远小于波长的空腔加压使其压缩时,表现其弹性效果的常数,相当于机械系统的柔顺性。若空腔的体积为V0(m3),媒质中声速为C(m/s),媒质密度为ρ0(kg/m3),则声容CA=V0/C2ρ0(S2m4/kg)=V0/C2ρ0(m5/N)。3 声顺(acoustic compliance)(电声词典)抵抗所加压力变化的声元件。它的倒数亦称“声劲”。它用下式定义:P=x/CA。其中,CA是声顺;P是声压;x是体积位移。一个具有刚性壁的空腔,体积为V,如其尺度比波长小的多,则腔内空气压缩与膨胀近似同相位,这样的空腔可以认为是声顺元件,其值为CA=V/ρ0C2(m5/N)。式中,C是声速,ρ0是空气密度。【备注】(AI)声容(acoustic capacitance)指的是声学系统中的“容纳”能力,类似于电气系统中的电容。它是指在声学系统中,在给定的压力下,系统中气体的体积变化与所施加的压力之间的关系。它可以用来描述声学系统中气体的弹性和变形特性,通常以体积与压力的比值来表示;而声顺(acoustic compliance)则指的是声学系统中的“顺从性”或者“柔软度”,即系统对体积变化的响应程度。它描述了系统中气体对外界压力变化的敏感程度,可以理解为系统的柔软度或者弹性。它通常以单位压力变化引起的体积变化来表示。这两个参数之间的联系在于它们都描述了声学系统中气体体积与压力之间的关系,只不过侧重点不同。声容描述了压力变化引起的体积变化,而声顺描述了体积变化对压力的响应。在声学系统的分析中,声容和声顺通常是一起考虑的,因为它们共同决定了系统的振动特性和响应特性。4 电抗(reactance)(电声词典)在具有电感和电容的电路里,对交流电所引起的阻碍作用。电抗是复数阻抗的虚数部分,常用符号X表示,电抗为感抗与容抗二者之代数和。由于电压在线圈及电容器上有相反的相位移,故电抗为X=XL-XC=ωL-1/ωC,式中XL为感抗,XC为容抗。电抗与电路的能量消耗无关,电动势在1/4周期内使电容器和线圈获得电能和磁能而储存起来,在下一个1/4周期内,电容器和线圈又把全部储有的能量送回。单位为欧[姆]。5 声学电抗(acoustic reactance)(AI)它描述了介质对声波振荡产生的惯性响应,类似于电路中的电抗。它表示介质对声波振荡的阻力,与声波在介质中传播时的惯性响应有关。6 电感(inductance)(电声词典)也称自感系数或自感。它是表示导体回路产生自感应能力的一个物理量。当导体回路中不存在铁磁介质时,通过导体回路的磁通量与回路中的电流成正比,它们的比值就称为回路的自感系数或电感。它由回路的几何形状及周围介质的磁导率所决定。常用L来表示,单位为亨[利]。7 声学电感(acoustic inductance)(AI)它是描述声学系统惯性的量度,类似于电路中的电感。它表示声学系统在振动过程中对于体积流动的惯性响应,描述了声学系统中贮存和释放能量的能力。【正文】7.4. Horn Loudspeaker Systems(未完待续)(三)复合号筒扬声器(Compound Horn Loudspeaker) The compound horn loudspeaker consists of a single diaphragm mechanism with one side of the diaphragm coupled to a straight axis horn and the other side coupled to a long folded hom, Fig. 7.22. The equivalent of the system is shown in Fig. 7.22. The functional acoustical network of the vibrating system is also shown in Fig. 7.22.
在低频时,声容的声抗较大,它对低频声音的传播起主导作用。即声容的声学电抗CA2相对于低频号筒的喉部声阻抗ZA2来说很大,声音从低频号筒发出。而在高频时,声容的声学电抗相对较小,即声容CA2的声学电抗相对于声阻抗ZAl和ZA2来说很小,因此屏蔽了低频号筒,声音从高频号筒发出。在中频范围内,声音同时从两个号筒发出。At the low frequencies the acoustical reactance of the acoustical capacitance, CA2, is large compared to the throat acoustical impedance, ZA2, of the low-frequency horn and sound radiation issues from the lowfrequency horn. At the high frequencies the acoustical reactance of the acoustical capacitance, CA2, is small compared to the acoustical impedances, ZAl and ZA2, and, therefore, shuts out the low-frequency horn and radiation issues from the high-frequency horn. In the mid-range, radiation issues from both horns. The response frequency characteristic, Fig. 7.22, shows the response range of the two horns. The throats of the two horns may be chosen so that the efficiency characteristic of this loudspeaker will be the same as that of the two-channel system discussed in the preceding section. However, the power handling capacity is somewhat smaller because the size of the diaphragm must be a compromise between high-and low-frequency requirements.(四)多号筒-单通路系统(Multiple-Horn, Single-Channel System) 多号筒-单通路系统消除了多通路系统的许多不利因素:两个声道之间路径长度的差异而产生的相位差;滤波器和分频网络中的相位差和功率损失等。The multiple-horn, singlechannel system consists of a large number of multiple flare horns, each driven by a diaphragm, Fig. 7.23.
A comparison of the efficiency characteristics of a multiflare horn loudspeaker, Fig. 7.23, with a multichannel system, Fig. 7.23, shows that the efficiencies are of the same order. The multiple-horn, single-channel system eliminates many of the following disadvantages of the multichannel system: the phase difference due to the difference in path length between the two channels, the phase difference and power loss in the filters and dividing network, the nonuniform directional characteristics due to the small size of the high-frequency unit, and the distortion in the relatively small throat of the high-frequency horn. The space required for the single-channel system is greater than that for the multichannel system. However, from a technical standpoint the single-channel system is far superior to the multiple-channel system.
A multiple-horn, single-channel system loudspeaker suitable for high-power announce systems is shown in Fig. 7.24. This loudspeaker performs the same function as the system shown in Fig. 7.15. The stresses in the diaphragm and the voice coil system are reduced by the use of a number of smaller units as contrasted to a single large unit. 使用多个较小单元相比于单个大型单元可以减少振膜和音圈系统中的应力,主要有以下几个原因: (1)分担负荷:通过使用多个较小的单元,可以将扬声器所需的总功率分担到多个单元上。这样每个单元需要处理的功率就会降低,减少了单个单元承受的压力。 (2)散热效果:多个较小单元相比单个大型单元在工作时产生的热量更为分散。这有利于散热,可以减少因过热而导致的应力集中问题。 (3)抗失效性:当使用多个较小单元时,如果其中一个单元发生故障,系统仍然可以继续运行,而不会完全失效。这种冗余设计可以减轻整体系统的压力。[color=rgba(0, 0, 0, 0.9)]
 The possibility of failure of the system is reduced by the use of a multi-unit driving system. The use of a multiple-horn system makes it possible to obtain a greater variety of directional patterns than is possible in the single-horn system of Fig. 7.15.【Reference】Acoustical Engineering, by Harry F. Olson, copyright 1940, 1947 by D. Van Nostrand Company, Inc.《电声词典》第二版
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