1000-hours/sounds-of-american-english/3.1.7-aɪ.md
亚洲语系基本上都没有和英文一样长度的双元音。韩文日文的母音和中文的韵母虽然都有少数由两个基础音素构成的组合音，但，它们和英文的双元音不同的地方在于，它们都是和其它韵母或者母音等长的，而不是像英文双元音的长度那样几乎是短元音的两倍。
比如，当中国人说 “太累了”<span class="speak-word-inline" data-audio-other="/audios/太累了-zh-cn-male.mp3"></span> 的时候，“太” <span class="pho">[tài]</span> 这个字的 “韵母” 就很接近英文的双元音 <span class="pho">aɪ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_eye_2023feb.mp3"></span>；“累” <span class="pho">[lèi]</span> 这个字的韵母就很接近英文的双元音 <span class="pho">eɪ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_day_2023feb_002.mp3"></span>…… 但，它们的长度就是不一样，英文的双元音总是相对更长。
英文的双元音，都是两个元音的组合。它们都是从第一个元音滑向第二个元音，所以，它们从长度上来看，相当于是长元音；节奏在感觉上大抵是乐谱里的 “一拍里均放着三个等长音符的三连音”，前一个音素更长一些，后一个音素相对较短。
读 <span class="pho">aɪ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_eye_2023feb.mp3"></span>, <span class="pho">eɪ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_day_2023feb_002.mp3"></span>, <span class="pho">ɔɪ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_boy_2023feb.mp3"></span> 的时候，唇形分别从 <span class="pho">ɑ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_father_2023feb.mp3"></span> <span class="pho">e</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_head_2023feb.mp3"></span>, <span class="pho">ɔ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_horse_2023feb.mp3"></span> 开始，唇形保持不变，用喉咙完成从起始元音到 <span class="pho">ɪ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_ship_2023feb.mp3"></span> 的过度。
读 <span class="pho">aʊ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_mouth_2023feb.mp3"></span> 和 <span class="pho">oʊ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_nose_2023feb.mp3"></span> 的时候，唇形有变化，要分别从 <span class="pho">ɑ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_father_2023feb.mp3"></span> 和 <span class="pho">ə</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_above_2023feb.mp3"></span> 开始，而后过度到 <span class="pho">ʊ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_foot_2023feb.mp3"></span>。
同样的道理，读之前讲过的儿化音 <span class="pho">er</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_hair_2023feb.mp3"></span>、<span class="pho">ɪr</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_ear_2023feb.mp3"></span>、<span class="pho">ʊr</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_pure_2023feb.mp3"></span> 的时候也一样，唇形分别从 <span class="pho">e</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_head_2023feb.mp3"></span>、<span class="pho">i</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_sheep_2023feb.mp3"></span>（注意不是 <span class="pho">ɪ</span>）、<span class="pho">ʊ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_foot_2023feb.mp3"></span> 开始，而后唇形保持不变，接着用喉咙完成从起始元音到 <span class="pho">ə</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_above_2023feb.mp3"></span> 的过度 —— 而它的儿化音 <span class="pho">ɚ</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_mother_2023feb.mp3"></span> 则使用舌背后缩的方式。所以它们相当于是 <span class="pho">eɚ, ɪɚ, ʊɚ</span>，进而干脆写成了 <span class="pho">er, ɪr, ʊr</span>。
在读它们的时候，最重要的是，要把它们读得足够长 —— 几乎要占用两个元音的发声时长，并且足够饱满。
除了双元音之外，还有另外两个三元音：<span class="pho">aɪr</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_fire_2023feb.mp3"></span> 和 <span class="pho">aʊr</span><span class="speak-word-inline" data-audio-us-male="/audios/us_phonetics_sound_hour_2023feb.mp3"></span> —— 同样要刻意拉长。