Acoustical Design of Gymnasium in Harbin Normal University Sports Center

Gymnasium in Harbin Normal University Sports Center is a large-scale gymnasium. This paper analyzes unfavorable factors in its acoustics and illustrates different kinds of intention of the design. At the same time, the questions about the project operation and technique are pondered one by one, it is expected that these thinking can provide some experience to the similar project.     

The Theory and Practice of Acoustic Design in Churches

In this paper, the author used the principle of sound reflection and concept of effective reverberation presented by A.N.Kacherovich to analyze the actual sound field in a church and found out the essential elements which affect the sound energy decay to settle the problem of the reverberation of speech and music by an effective arrangement of some absorbent materials.     

RELEVANCE OF SONOGRAPHIC ARTIFACTS OBSERVED DURING IN VITRO CHARACTERIZATION OF UROCYSTOLITH MINERAL COMPOSITION

Nine pure mineral type canine uroliths (bladder or urethral origin only) were imaged ultrasonographically using 3.5 MHz, 5.0 MHz, and 7.5 MHz fixed focus, mechanical sector transducers in a urinary bladder phantom. The uroliths studied were those composed of 100% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, and calcium hydrogen phosphate dihydrate (brushite), ammonium acid urate, sodium acid urate, cystine, and silica. The occurrence of both reverberation/streak and acoustic shadowing artifacts were compared to urocystolith mineral type (classified by effective atomic number), urocystolith width, urocystolith height (thickness), and ultrasonographic imaging frequency. No predictable relationship was found between either of the artifacts seen beyond the urocystolith (reverberation/streak or the acoustic shadowing) and urocystolith mineral type. There was no statistical relationship between the occurrence of reverberation/streak artifact and the size (width or height) of the urocystolith or the ultrasonographic frequency. There was, however, a statistically relevant relationship between ultrasonographic imaging frequency and the occurrence of acoustic shadowing and between urocystolith height (thickness) and the occurrence of acoustic shadowing. However, regardless of ultrasound frequency, acoustic shadowing was observed less than 35% of the time in any of the urocystolith mineral types examined. Based on the imaging of the bladder phantom supporting apparatus (7.0 mm bolts covered by plastic), the accurate characterization of a curved object surface directly facing the transducer was found to be directly related to the frequency of sound used for imaging and at best predictably limited to curved vs flat. Accurate measurement of the maximum transverse dimension of an echogenic curved object or accurate characterization of the lateral borders of such an object was considered unlikely with general ultrasonographic equipment of the frequencies studied. Therefore, detailed architectural characterization of urocystoliths suitable for mineral composition prediction is considered highly unlikely with general pulse-echo ultrasonographic techniques.     

木质阻尼复合结构中填充多孔材料的隔声性能分析

【目的】利用吸声材料的吸声降噪机制、隔声材料的隔声降噪机制和阻尼材料的阻尼降噪机制,将3种降噪材料以一定形式复合,获得一种兼具吸声、隔声和阻尼性能的新型木质阻尼复合隔声材料,以改善木质材料隔声性能,拓宽木质材料和阻尼材料的应用范围。【方法】先将中密度纤维板(MDF)与橡胶材料在压板温度100 ℃、单位压力3 MPa、加压时间10 min、涂胶量64 g ·m^-2 的工艺条件下进行复合,再利用白乳胶将获得的木质阻尼复合材料与吸声材料粘接,采用小混响室-消声箱法测试复合结构隔声性能,探讨中密度纤维板(MDF)厚度、多孔材料厚度、填充方式、多孔材料种类和阻尼结构等因素对隔声性能的影响。【结果】木质阻尼复合结构中填充聚酯纤维、玻璃纤维和三聚氰胺吸声棉3种不同多孔吸声材料时,在整个频率段,3条隔声性能曲线趋于一致,区别不明显,从减轻复合结构质量及环保角度出发,选择三聚氰胺吸声棉作为填充多孔材料。多孔材料填充方式(BB:利用白乳胶将多孔材料直接粘贴在上下表板上,不含空气层;UU:多孔材料与上下表板不粘接,通过一定厚度空气层分离;BU:多孔材料一侧粘贴在上表板上,另一侧与下表板通过空气层分隔)对复合结构隔声性能具有较大影响,其中BU结构的隔声性能较优。吸声材料与空气层相配合,在不增加复合结构厚度和质量的前提下,可有效提高复合结构的隔声性能,当吸声材料填满空腔时,反而不利于复合结构隔声性能的提高。多孔材料与空气层阻抗不匹配,会增加声波传播途径,声能被损耗。在最佳填充结构的基础上,随着多孔材料厚度从5 mm增加到15 mm,复合结构的隔声性能增加。在低频,共振频率处的隔声性能增加;在临界频率处,多孔材料厚度增加,抑制复合材料的吻合效应,吻合谷变浅,隔声性能增加。MDF厚度增加,复合结构的面密度和刚度增大,可增加复合结构中低频的隔声性能。阻尼结构设计对复合结构隔声性能具有很大影响,自由阻尼结构的耗散能量较小,特别是低频减振效果较差;约束阻尼结构受到振动时,约束层的伸长远远小于黏弹性阻尼层,约束层会阻碍阻尼层的伸长运动;当阻尼层受到压缩时,约束层又会阻碍阻尼层的压缩变形。在阻尼层内除产生拉压变形外,还会产生剪切变形,从而起到比自由阻尼处理更大的耗散振动能作用,阻尼降噪能力更强,可更有效抑制复合结构的共振频率及吻合效应。【结论】表板厚度为6 mm,约束阻尼结构,多孔材料的填充形式为BU结构,填充10 mm三聚氰胺吸声棉和 5 mm 空气层,复合结构的隔声性能较优。