Specialist in Acoustic Components

The diaphragm of the speaker 喇叭振膜對聲音的影響

喇叭的振膜對於聲音的表現有相當大的影響, 可以從厚度,花紋,材質三方面來討論

The diaphragm of the speaker affects the sound a lot; let us discuss the affection in the thickness, surface pattern and material.

1. 厚度
額定輸入功率愈高的喇叭,就需要搭配愈厚的膜片,因為大的功率表示膜片的振幅會愈大,承受的力量會更強,若膜片的強度不夠的話,就會有雜音,甚至膜片會被過大的力量拉扯而破裂,相同大小的振膜,厚度愈厚的膜片,低頻響應會較差,故功率較大的喇叭fo通常也較高.
1. Thickness
The speaker with higher input power, needs thicker diaphragm to match, because the higher input power means the higher load and the stronger vibration will be generated. If the diaphragm is not strong enough, the noise will happen, and even the diaphragm will be ripped by the strong power. With the same diameter, the thicker diaphragm has worse frequency response (FO) at the low frequency (LF); therefore the speaker with higher input power will have higher FO.

2. 花紋
Mylar的花紋主要分為同心圓及放射狀 二狀,(如圖1,圖2),不同的表面花紋,所產生的頻率響應特性是不一樣的,如圖3,圖4分別是同心圓及放射狀花紋的曲線,同心圓在5KHz之前有比較高的輸出,但5KHz之後會迅速的往下掉,而放射狀花紋的頻率則會比較平坦,但若在喇叭的其他條件都一樣的情況下,在5KHz之前的音壓會比同心圓的差,故我們需視產品的應用來選擇喇叭的花紋,以獲得最高的音量輸出,主要發出人聲的,可選用同心圓膜片,要播放音樂為主的,就該選擇放射狀花紋的喇叭.
2. Pattern
There are two mainly patterns of Mylar diaphragm: concentric circles and radiate patterns (picture. 1 and picture. 2). The different surface patterns will generate different characteristics of FO. For example, picture 3 and picture 4 show the curves of concentric circles and radiate. The concentric circles speaker has higher output S.P.L. before 5 KHz, but dramatically falsl after 5 KHz; the radiate speaker has more stable output S.P.L., but to compare with concentric circles speaker, the output S.P.L. will be lower before 5 KHz. Therefore, depend on the application, we can choose the suitable patterns of diaphragm, the concentric circles is good for the human voice, and the radiate pattern should be selected for playing the music.

3. 材質
常用於小喇叭,微型喇叭的材質為Mylar, 紙,布三種,成本依序增加,
Mylar有好成型加工,成本低的優點,但不適合做大功率或大尺寸的喇叭
紙質的振膜音質較自然,成本低,但尺寸在30mm以下就不太好加工,不良率會提高,布質的振膜可加入許多不同的纖維,可以改變頻率響應的特性,音質最好,但成本高通常只用在大尺寸的喇叭上.

3. Material
Mylar, paper and clothes are the main material of diaphragm for mini/ micro speakers, the cost increases in order.

Mylar has the advantages of lower cost and easier to shape up, but mylar is not suitable for the high power or large size speaker; the paper diaphragm also have lower cost but more natural sound than Mylar, however if the diameter is smaller than 30mm, it might cause difficulty to manufacture and the defective rate may increase. Clothes diaphragm, which can change the frequency response by adding different kinds of fibers, has the best sound quality. However, clothes diaphragm is usually used in the large size speakers because of the high cost.