近期对次声波感兴趣，无奈国内缺少相关文章。所以跳墙去国外网站，因本人英文水平有限，加之文章中有好多专业术语，导致翻译出来的文章中存在晦涩难懂的地方（有的地方直接略过没有翻译）。本人将英文原文附录在帖子上，望有识之士可以对本文添砖加瓦。
曾经去过一个超自然现象出没的区域没？放松。。。其实你不需要去那里。一个简单的次声波发生器电路，可以让你在家就能体验令人不寒而栗的感觉！
介绍：我们知道，声音只不过是在空气中产生的震动。通过建立一个固定的频率，我们可以创造一个可以听到的噪音。对于不同的生物，所听到的声音频率是不同的。例如，人类可以舒适的听到的频率在50赫兹和20000千赫之间的声音。一旦离开上述范围，听力将会变得晦涩。然而低于50赫兹以下的频率，尤其是15赫兹的频率被发现是相当独特而有趣的。声音落在这个范围称为次声。令人惊讶的是，人类暴露在这种频率下经常会抱怨莫名其妙的不安和令人心寒的感觉。据说鬼魂经常出没的地区和发生超自然活动的地区，被探测出存在这种次声波。
在另一个经典的例子当中，它见证了丛林食肉动物例如老虎和狮子都会发出次声波。食草动物能感觉到这些信号，尤其是当这些食肉动物太接近他们。所产生的声波振动严重的影响了这些可怜的草食性动物–他们恐惧的不能动弹一步。这像他们看起来像鸭子一样，被凶猛的野兽立刻捕捉。 这篇文章中描述了人为产生次声的一个简单想法。虽然这个项目的应用是微不足道的，你可以在一个密封的空间里创造震动，并邀请你的朋友去那个环境下，看他们毛骨悚然的反映。不过别担心，这不危险。 电路描述： 使用的是低音扬声器，12寸 功率40W，pvc管的直径最好和扬声器统一口径。如果你站在发生器前面，会感到毛骨悚然。 震荡电路： 上面的电阻值可能会调整一下，以获得在输出10至20赫兹之间任何想要的值。
英文原文：Ever been to a paranormal infested area? Relax… you don’t actually need to bethere. The simple infrasound generator circuit explained here should be able togenerate similar spine-chilling effects right in your house!
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Introduction
We know that sound is nothing but oscillations generated in the air. Bycreating disturbance in the air at certain frequencies we are able to create anaudible noise. The frequencies that may be audible to different beings aredifferent. For example humans are able to hear frequencies between 50 Hz and20000 kHz comfortably. Hearing becomes obscure once the frequency shifts awayfrom the above range. However frequencies below 50 Hz especially around 15 Hzare found to be quite unique and intriguing with their features. The soundfalling in this range is termed as infrasound. Amazingly humans subjected tothese frequencies often complain of unexplainable uneasiness and a chillingexperience. Areas infested with ghosts and paranormal activities have been alsoseen to be carrying these infrasound vibrations.In another classic example, it has been witnessed that in jungles,carnivorous beasts like tigers and lions are able to generate sounds atinfrasound levels. Herbivorous animals are able to sense these signalsespecially when these carnivorous animals are too close to them. The generatedinfrasound vibrations produce serious impact over these poor herbivorous animals– they freeze with fear and are just not able to move an inch. This makes themlike sitting ducks and they are instantly grabbed by the deadly beasts.
A simple idea for generating infrasound artificiallyis described in this article. Although the applications of this project arequite insignificant, you may use it to create vibrations in a closed premise,invite your friends there and study their reaction under the generated creepy environment. Don’t worry- it’s not dangerous.
The secret behind generating effective infrasound is creating a sort of“pumping” action over an enclosed volume of air at the specified frequency. Tobe precise the air volume needs to be resonated at the specified frequency. Thisis best done by channelizing the sound waves through pipes or narrow columnsbefore throwing it into the room.The figure alongside shows a circuit basicallycomprised of an amplifier with the required loudspeaker set-up. The chip TDA1521 used here consists of two discrete amplifier modules in one package and isable to produce a good 12-watts of audio power from each channel – quite enoughfor the present application.However the amplifier needs to be fed with a frequency input for it toreproduce them over the attached speakers.Many simple oscillator circuits have already beendiscussed here at Bright Hub, so you may choose any one of them to generate andfeed the specified frequency of around 15 Hz to the above amplifier inputs. Theinformation regarding various oscillator circuits are provided at the end of this article.The speakers used are specifically “woofers” to enable the handling of theproduced low frequencies (infra-level) efficiently. Preferably use 12-inchmodels with 40 watts of power handling capacity. The pipes also need to be ofthe same diameter.The diagram also shows the speakers snugly fitted within hollow, flexible PVCpipes (with corrugated walls).Switching ON the system will instantly start the generation of the vibrationsat infrasound levels and if the volumes are kept sufficiently high, you willfind the nearby objects also vibrating and falling down of the shelf quiteweirdly - the vibrations being totally “invisible.”If you position yourself in front of the speakers of this infrasoundgenerator, the impact will be immediately felt – uneasiness and an inexplicable“chill in the spine.”
The above shown simple oscillator circuit can be built for feeding the infrasound amplifier circuit. It utilizes the famous IC 555 in its most common mode,i.e. in the astable multivibrator mode. The upper resistor value may be tweakeda bit to get any desired value between 10 to 20 Hz at the output, so that mostsuitable infra sound effect becomes obtainable at the speaker channels.
