Review of Distributed Mode Loudspeaker Technology and Implementation

Kuonan Li

《中華民國振動與噪音工程學會論文集》 2010 (2010/06) Pp. 353-362

https://doi.org/10.30028/CSSVANNUAL.201006.0353

摘要

近年來，由於平板喇叭的市場需求愈來愈大，於是愈來愈多研究投入在彎曲波喇叭(Bending wave loudspeaker) 與分佈型喇叭(Distributed mode loudspeaker)上，也發展了各種不同的應用。這兩種喇叭同樣使用彎曲波的原理，不同之處在於前者使用無限平板之近似法，而後者使用的是有限的平板之近似法，也就是特徵函數之近似法。本文主要在於探討分佈型喇叭之工作原理以及聲學表現，以及它對於傳統動態式喇叭的優勢與弱勢。在本篇文章以分佈型喇叭的簡介開始，然後接下來是特徵函數之近似法以及利用此近似法來描述有限的振動平面，以及聲音散射之方法。另外，分佈型喇叭之聲學特性也一併在此被討論。一個從NXT 取得的分佈型喇叭(實驗組)以及一個傳統的動圈式喇叭(對照組)被當作樣品，以研究分佈型喇叭與動圈式喇叭之聲學表現差異。實驗項目包括：脈衝響應、頻率響應、方向性、聲功率、效率、感度以及失真度。另外，這兩個喇叭分別被放在在一個具有常見聲學特性的教室中，在於不同的30 個量測點量測聲壓值，以畫出聲壓分佈圖。由測試結果所得，可以歸納以下幾點: 分佈式喇叭比起傳統式動圈喇叭具有較低的感度以及效率。此外，由於分佈式喇叭在低頻時的特徵函數密度較低，所以低頻響應較差；而在高頻的部分，由於在高頻彎曲波逐漸的轉換成縱波，所以高頻響應也較差。另外值得一提的是，在實驗中可以看出分佈式喇叭的方向性並不是完全比傳統動圈式喇叭來的廣，在中頻(4 kHz)時動圈式喇叭甚至擁有較廣的方向性。

關鍵字

彎曲波喇叭 ； 分布式喇叭 ； 動圈式

並列摘要

ecent decades; consequently the Bending WaveLoudspeaker (BWL) and Distributed Mode Loudspeaker(DML) have been of great interests of research forloudspeaker producers and have been developed formany different applications. Both of BWL and DMLapplies the theory of bending waves, thus often beconfused by public. The main difference is that theformer uses infinite plates approach while the latterutilizes finite plates approach, or preferably, the modalapproach, which is exactly why the latter one was namedas Distributed Mode Loudspeaker, which is the mainconcern of this paper.As the beginning of this paper, an introduction to thetechnologies of DML is given, and then following themode theories, which says how one uses modes todescribe the vibration patterns of a limit panel. Afterward,the properties of DML are shown, as well as theapproaches to these properties.In order to evaluate the performance of DML, asample from NXT was used for the measurement, as wellas reference, another conventional electro-dynamicloudspeaker. These two speakers were gone through aseries of measurements, containing the impulse responses- which also imply the frequency responses - , thedirectivities, the sound powers, the efficiencies, thesensitivities, and the distortions. In addition, the soundpressure levels were measured at 30 spots in a regularlistening room for the plotting of distribution contours.In the end of the project, a blind listening test was alsoperformed to investigate the audiences’ responses andacceptance to DML and the preference between DMLand piston radiator.With the result of the experiments mentioned above, itis conclude that DML has lower sensitivity and efficiencythan the electro-dynamic loudspeaker. Also DMLs lackof low frequency due to low modal density and highfrequency because of transition of bending waves totransverse waves at higher frequencies. The directivitiesof DML do not outdo electro-dynamic type from top totoe; it is even weaker in middle frequency.

並列關鍵字

bending wave loudspeaker ； distributed mode loudspeaker ； electro-dynamic ； electromagnetic ； DML ； BWL