【英语时差8,16】扩音器（下）

This is because whenever a sound wave moves suddenly from a narrow space to a more open one, some of the sound is reflected backward. This is exactly what happens when the sound of your voice moves from the narrow confines of your mouth into the wide, open air. The abrupt¹ change bounces some of the sound energy backward, where it’s absorbed by your mouth, reducing the overall volume. A cone-shaped megaphone creates a more gradual transition from your mouth to the open air. By reducing the amount of sound that bounces back into your mouth, this allows more volume to come out. For full effect, a megaphone should be at least as long as the wavelength² of the sound it’s amplifying³. Human voices have wavelengths⁴ up to several feet long, so a professional megaphone, like a cheerleader might use, is also several feet long.

1 abrupt   

adj.突然的，意外的；唐突的，鲁莽的

参考例句：

• The river takes an abrupt bend to the west.这河突然向西转弯。
• His abrupt reply hurt our feelings.他粗鲁的回答伤了我们的感情。

2 wavelength   

n.波长

参考例句：

• The authorities were unable to jam this wavelength.当局无法干扰这一波长。
• Radio One has broadcast on this wavelength for years.广播1台已经用这个波长广播多年了。

3 amplifying   

放大，扩大( amplify的现在分词 )； 增强； 详述

参考例句：

• Often they use borrowed funds, amplifying their gains and losses. 他们通常会用借贷的资金交易，从而放大收益或损失。
• An amplifying type (or analog) device, as opposed to digital device. 放大器类（或模拟）器件，相对于数字器件而言的。

4 wavelengths   

n.波长( wavelength的名词复数 )；具有相同的/不同的思路；合拍；不合拍

参考例句：

• I find him difficult to talk to—we're on completely different wavelengths. 我没法和他谈话，因为我们俩完全不对路。 来自《简明英汉词典》
• Sunlight consists of different wavelengths of radiation. 阳光由几种不同波长的射线组成。 来自辞典例句