基於聲音特性之鐵琴片設計分析

Design Analysis of Metallophone Bar Base on Percussion Sound Characteristics

10.6346/NPUST.2009.00201

謝明憲

鐵琴 ； 和弦 ； 自然頻率 ； 振動模態 ； 聲音頻譜 ； metallophone ； chord ； natural frequency ； vibration mode ； sound spectrum

屏東科技大學機械工程系所學位論文

2009年

碩士

王栢村

繁體中文

鐵琴片為常見之打擊樂器，各音階的鐵琴片敲擊後之聲音，具有其主頻率及泛音頻率組成，鐵琴片發聲之頻率與其振動模態特性相關。本文主要探討具有C和弦聲音特性之鐵琴片形狀設計，引用貝茲曲線的特性，利用幾何節點控制產生平滑曲線，以建立鐵琴片的有限元素模型，進行模態分析，求得自然頻率與其對應之模態振型，由模態振型可判斷鐵琴片的發聲機制及效果。本文設計出兩種具有C和弦音組成之鐵琴片形狀，並分別以鋁合金及不銹鋼材質製成實體鐵琴片，進行聲音量測與振動模態之實驗分析，利用麥克風作為感測器，進行C和弦鐵琴片敲擊之聲音量測分析，可量測得鐵琴片之聲音頻譜及峰值頻率，將實測所求得之峰值頻率亦即鐵琴片之自然頻率，作為有限元素模型之修正基準，由模態參數比較均相當吻合，故成功地驗證有限元素模型的正確性。最後再運用有限元素分析方法，將C和弦鐵琴片進行幾何形狀結構之變更，結果顯示鐵琴片厚度變化及形狀比例縮放後的自然頻率，與原尺寸和弦鐵琴片之自然頻率呈現特定的比例倍數關係。本文建立之C和弦鐵琴片形狀設計方法，並經由實體量測分析驗證，將有助於C和弦鐵琴片形狀更精準的設計參考，也可應用於其他和弦組之設計。

The metallophone is one of percussion instruments. The percussion sound of a metalophone consists of the fundamental frequency and overtone frequencies that are related to the vibration modes of the metallophone. This work presents the geometry design of the metallophone with C chord sound characteristics. The Bezier’s curve formulation is adopted to generate smooth curves so as to construct the finite element model of the metallophone. By performing modal analysis the natural frequencies and mode shapes can be obtained. The sound generation mechanism can be interpreted by mode shape patterns. This work designs two types of metallophones that can generate the C chord sound. Both aluminum and stainless steel materials are used to shape the designed metallophones. The microphone is used as the sensor to measure the percussion sound and characterize the modal properties of the metallophones. The sound spectrum can be obtained and identified those peak frequencies that are used to correlate and adjust the finite element model. Results show that the finite element model can be well calibrated. The finite element model is then adopted to carry out geometry design modification. The scaled thickness and geometry shapes can change the modal properties in a scale relation. This work establishes the design method for the C chord metallophone and validates the design by experimental measurements. The developed methodology will be beneficial to the design of specific types of metallophones, in particular for different chord combinations.

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