The secret behind generating effective infrasound is creating a sort of “pumping" action over an enclosed volume of air at the specified frequency. To be precise the air volume needs to be resonated at the specified frequency. This is best done by channelizing the sound waves through pipes or narrow columns before throwing it into the room.
The figure alongside shows a circuit basically comprised of an amplifier with the required loudspeaker set-up. The chip TDA 1521 used here consists of two discrete amplifier modules in one package and is able to produce a good 12-watts of audio power from each channel – quite enough for the present application.
However the amplifier needs to be fed with a frequency input for it to reproduce them over the attached speakers.
Many simple oscillator circuits have already been discussed here at Bright Hub, so you may choose any one of them to generate and feed the specified frequency of around 15 Hz to the above amplifier inputs. The information regarding various oscillator circuits are provided at the end of this article.
The speakers used are specifically “woofers" to enable the handling of the produced low frequencies (infra-level) efficiently. Preferably use 12-inch models with 40 watts of power handling capacity. The pipes also need to be of the same diameter.
The diagram also shows the speakers snugly fitted within hollow, flexible PVC pipes (with corrugated walls).
Switching ON the system will instantly start the generation of the vibrations at infrasound levels and if the volumes are kept sufficiently high, you will find the nearby objects also vibrating and falling down of the shelf quite weirdly - the vibrations being totally “invisible."
If you position yourself in front of the speakers of this infrasound generator, the impact will be immediately felt – uneasiness and an inexplicable “chill in the spine."