[原创]耳机设计中，不同换能器的组合设计 - 耳机设计与测试评价室 - 声学楼论坛

从耳机的发展上来看，不同换能器之间的组合，以相互取长补短，优势互补势在必行！比如静电型换能器，由于其振动膜片极其轻薄，故高音之通透，音质之柔和堪称Number one，但低音下潜和力度却是短板。如能和动圈配合，可谓相得益彰！
任何换能器的组合，首要的便是：1.不同的换能器，其音色要相近或相似，以做到音色上的无缝衔接；2.能够做到相互取长补短，优势互补；比如膜振动（如静电换能器、等电动换能器、铝带式换能器等等）换能器具有优秀的超高频特性以及极佳的瞬态特性，但要做到深度的低频下潜要付出很大的代价；而动圈换能器要做到低音下潜相对要容易，但音色的通透性就永远不如膜振动换能器。所以不同换能器之间的优势互补必将是耳机发展的重要方向之一。当然，大前提是，必须有核心技术作支撑！
笔者以为，2015年耳机展少有的亮点之一，便是台湾某公司的AMT（Air Motion Transformer空气振动变换器，德国专利）高音单元+动圈低音单元组合的耳机，音质不俗（尚有改进空间），只是售价奇贵！

挡不住的世界顶级高音，藏不住的震撼!香港嘉圣德最近推出了其最新出品的黑金系列气动式（海尔式）Air Motion Transformer汽车高音头，纯手工打造做工精致的气动式高音头可以适合任何车系加装或改装，一点也不影响原车风格，更让人震撼的是放出的高音效果恰似在现场享受高保真音乐。气动式汽车高音头设计难度大，高音最大直径仅40mm，高频延伸到惊人的40KHz，绝非一般球顶高音可比，嘉圣德在声音领域和汽车音响领域的这一创造性突破，用专业发烧友的耳朵来打造全球首款气动式高音头，将给汽车音响带来全新的体检。嘉圣德用专业发烧友的耳朵来为普通大众打造恰似专业电影院的高音效果，高频表现上具有更加清晰的解析力，让声音原始、深厚、纯净，欣赏音乐效果显著，美国汽车音响著名评测师Darek Spring博士评测到 “这款气动式高音头能听出小提琴的松香味。”目前，这一汽车高音头正在申请多项国家专利。

自1973年美国的海尔博士（Oscar Heil）发明了一种非常特殊的扬声器声波辐射方式---AMT(Air Motion Transformer)气动式换能器，即气动式扬声器后，嘉圣德公司已经成为高音单元制造领域的先驱者之一。德国留学归国后的Theme博士对嘉圣德公司的指导原则不是以技术第一位，而是更注重能使客户受益的技术以及提供更高的声音品质，以确保放音质量尽可能的真实准确。

海尔扬声器制作工艺复杂，价格高昂，难以普及，只在国外少数著名的大品牌公司的高端产品中看到，如德国ELAC(意力）的Jet气动式高音，香港AudioPur(嘉圣德)，ADAM(亚当）的ART气动式高音，Burmester(柏林之声)，丹麦GRYPHONG(贵丰），美国Mark Daniel(马克丹尼)。

气动式式的高音振膜位于均匀的磁场当中，它的振膜受力远比球顶振膜均匀，不会产生分割振动，在高频表现上具有更加清晰的解析力。

气动式高音比传统顶级金属球顶高音反应速度快，能够反应出音乐中丰富的细节.特别打击乐中的金属声，它没有金属球顶高频的刺耳声，清脆而不干涩。

The Air Motion Transformer (AMT) is a type of electroacoustic transducer or loudspeaker, also called Air Velocity Transformer (AVT) or JET transducer. Invented by Dr. Oskar Heil, it operates on a different transduction principle than other loudspeaker designs, such as moving coil, planar magnetic or electrostatically driven loudspeakers, and should not be confused with planar or true ribbon loudspeakers. In contrast to a planar ribbon loudspeaker the diaphragm of the AMT is of pleated shape similar to a bellows. The AMT moves air in an augmented, semi-perpendicular motion using a folded sheet (made of polyethylene, polyester or polyimide), structured around a series of aluminum struts positioned in a high-intensity magnetic field.

The diaphragm pushes back and forward from itself in a physical motion similar to that observed when an accordion is pushed in and pulled out to pump air though the reed chambers, albeit over an exceedingly smaller motion range.

The result is a dipole driver with an extraordinarily rapid response rate, enabled by the extremely low mass of the polyester driver and the far smaller distance it travels on each “swing” compared to a dynamic driver. In this technical respect, it shares characteristics with the electrostatic driver.

The discernible motion of each diaphragm flexure is very small, but because of the folded structure, more air is moved than would be by a conventional cone or electrostatic driver of the same plotted surface area. As a matter of surface comparison, a standard 1-inch-wide (25 mm) AMT strip has a functional driver area comparable to an 8-inch-diameter (200 mm) circular dynamic cone. The folded driver design, combined with the small motion range, means the AMT acts like a point source version of a larger driver, inherently resulting in lower sound reproduction distortion. As a result of its motion pattern, the AMT "spits" the air out in a way similar to the action of shooting a watermelon seed from your hand by squeezing it between thumb and forefinger. The speed of the air as it leaves the diaphragm is approximately five times faster than the speed of the actual driver structure, hence the name, Air Motion Transformer.

Although it is possible to operate the diaphragm without the magnetic field, using piezoelectric technology, this method has been used only by TakeT for their headphone and tweeter products.

There are a couple of companies producing Heil AMTs:
Dayton Audio (USA)
EmotivaPro (USA) under the name Airmotiv
MartinLogan (USA) under the name Folded Motion Tweeter^[3]
Precide (Switzerland) who calls their version the AVT (Air Velocity Transformer). Precide uses an AMT driver for their top of the line headphones.
ELAC (Germany) who calls their version of the transducer JET
ADAM (Germany), under the name Accelerating Ribbon Technology^[4]
ETON (Germany)
Beyma (Spain)
Furuyama Audio Labs - FAL (Japan)
SoundTouch (China)国内有厂在做（嘉兴的）

美国有专利：

Heil's "Air Motion Transformer" US patents[edit]

US#3,636,278 issued Jan 18, 1972.

(Describes the Heil AMT variations, some of which resemble the ELAC JET transducer) [1]

US#3,832,499 issued Aug. 2, 1974.

(Describes the Heil AMT embodiment used in the ESS AMT series) [2]

US#4,056,697 issued Nov 1, 1977.

Movable diaphragm connector method flexible hinge diaphragm surround and... [3]
US#4,039,044 issued Aug 2, 1977.

(Low-frequency AMT. The patent also describes the principle used by Tymphany for their LAT transducer including the embodiment type) [4]

US#4,107,479 Aug 15, 1978.

(Further refinements of the low-frequency AMT) [5]

US#4,160,883 Jul 10, 1979.

Acoustic transducer and method of making same [6]

点评振膜型换能器
众所周知动圈型换能器的特点是集中驱动，这样振盆必须有很高的强度，否则会产生强烈的众多模式的分割振动，随之而来的是谐波失真以及分谐波失真。于是，振盆材料成了动圈换能器的核心之核心！理想的振盆材料要满足两个完全相反的要求：既要强度大的同时，又要内耗大！然而几乎是一切材料，要么是强度大，内耗小（如金刚石，碳纤维，凯夫拉纤维，铍，陶瓷等等）；要么是强度低，内耗大（锰铜合金，橡胶，木头，聚丙烯等等），所以振盆材料的选取往往顾此失彼，一直纠结至今，仍是‘进行时’！
振膜型换能器实际上是换位思考的结果，如果将驱动力均匀施加与整个振膜的表面，那么就无需再考虑强度的问题了。所有的振膜型换能器皆是如此。然而，由此又带来新的问题，静电、等电动、AMT、铝带等换能器的效率低下，而且由于最大振幅受限，最大声压级亦受到限制，不适于重放低频。故无论是音箱还是耳机的设计中，振膜型换能器通常担任中音至高音的重放。
衡量一种振膜型换能器优劣的标准：欲使换能器有向超高频延伸的高频频响以及优秀的瞬态特性，显然振膜的质量愈轻愈好，这是因为振膜的质量越轻，则启动速度越快，且空气对振膜的制动能力也越强。以此为标准，显然：
静电换能器的聚合物振膜厚度仅1.2微米，即质量为0.168mg/cm2约相当于1.3mm厚的空气质量（笔者已经做到了0.9微米即0.126mg/cm2，约相当于0.98mm厚的空气质量！）。由于其振膜比鸿毛还要轻，自然高频延伸以及瞬态特性上是一览众山小！
至于平面音圈类（等电动，铝带式，AMT等）的振膜，聚合物的厚度约3微米，铝箔的厚度为5微米，质量为1.77mg/cm2，约是静电换能器的10倍，约相当于13.7mm厚的空气质量。
显然，静电换能器具有最优的高频延伸能力以及瞬态特性！
其它的平面振膜换能器虽然比静电的要差些，但是仍然远胜过动圈换能器，不失为可选择的优质组合！

主题：[原创]耳机设计中，不同换能器的组合设计

Heil's "Air Motion Transformer" US patents[edit]