The Decibel (db)   
Can a sound kill you?

The decibel (abbreviated to dB) this is a unit that is used in the measurement of sound. They are much like a percentage in that they are dimensionless.

How dangerous some of the sounds in our every day lives are?

A shocking possibility is the creation of “acoustic weapons” these weapons would attack the enemy with a sound wave of the same equivalent as a 5.0 Richter earth quake at over 200 decibels.


Here is a list of basic sounds and the sound's decibel level produced.

Basic Sound levels

Normal conversation – 70dB

Telephone dial tone – 80dB

City Traffic (inside car) – 85dB

Level at which sustained exposure may result in hearing loss

Howler Monkey Screams – 88 dB

Subway train travelling at 200 MPH – 95dB

Fire Alarm – 95dB

Motorcycle – 100dB

Lawn mower – 107dB

Power saw – 110dB

Car horn – 110dB

Loud Rock Concert – 115dB

The Cicada – 120dB

Ear pain begins!

Pneumatic riveter – 125dB

Vuvuzela horn – 127 dB (against your ear)

iphone, ipod & other MP3’s – 80dB and 130dB

Short term exposure causes permanent damage – recommended exposure WITH hearing protection.

Jet Engine – 140dB

Gun Blast – 140 dB

Fireworks – 145dB

NHRA Dragsters – 155dB

Eardrum rupture is now a real possibility.

Space Shuttle Launch – 170dB

Death of hearing tissue starts to occur.

Volcano – Krakatoa – 180 dB

The Blue Whale – 188 dB (underwater).

Lung rupture and presumably embolism due to air blast occur at 200 decibels.

1-Ton TNT Bomb – 210 dB

5.0 Richter Earth Quake – 235dB

Tunguska Meteor – 315dB

Sound used as a weapon

Long Range Acoustic Device (LRAD)
 
The LRAD is the round black device that has been mounted on the tops of the New York City police Hummer squads.The Long Range Acoustic Device (LRAD) is a crowd control and hailing device developed by LRAD Corporation.

According to the manufacturer's specifications, the equipment weighs 45 pounds (20 kg) and can emit sound in a 30 beam (only at high frequency, 2.5 kHz) from a device 83 centimetres (33 in) in diameter. At maximum level, it can emit a warning tone that is 146 dBSPL (1,000 W/m2) at 1 metre. The maximum usable design range extends to 300 metres. At 300 metres, the warning tone (measured) is less than 90 dB.

How the LRAD Functions


The parameter "ka", which is the wave number multiplied by the speaker radius, is often used to characterize sound source directivity. For this source, ka=19 at 2.5 kHz, and according to the LRAD data sheet, the beam angle of about 30 degrees total is precisely what is predicted for a regular loudspeaker. The device does not use ultrasound, nor is it a phased array; it uses an array of conventional acoustic tweeters, the same as those used in professional audio applications, all driven together in parallel.

Whitnesses have said that being within 90 metres (98 yd) of the device is extremely painful, but its use should be limited to 270 metres (300 yd) to be effectively used. He concedes that the device is powerful enough to cause permanent auditory damage, but that it is only meant to be used for a few seconds at a time.

Small spherical "point-source" acoustic devices follow the known inverse square law, which predicts the loss of 6 dB per doubling of distance from the source. Large speakers (or large arrays), such as these mentioned above or those commonly used in concert halls, etc., produce less loss with distance in the nearfield, typically 3–4 dB per doubling of distance from the source. The larger the speaker, and the higher the frequency, the longer the effective nearfield is. Devices like this generally have nearfields of only a few meters.

The device was originally intended to be used by American warships to warn incoming vessels approaching without permission, and some reports claim that this is now a "non-lethal weapon". Its output up to 155 db, focused at a distance, is sufficient to produce permanent ear damage and temporarily disrupt vision.

So the LRAD is a device that can produce a sound and direct it to a point in the distance, like throwing ones voice or ventriloquism.

Magnetic Audio Device (MAD)

The Magnetic Audio Device (MAD) is a revolution in acoustic transmission and safety technology, providing unrivalled clarity and range. This product range provides directional, high quality verbal challenges and warning tones at distances previously thought impossible.
Using patented technology the MAD product range can be used as part of an escalated response and challenge procedure, using clear, totally intelligible verbal communication or warning tones to determine intent and for hailing/warning. It is also a versatile safety tool, which can be used to communicate in man overboard situations, assist in collision avoidance, crowd direction and control. The option of an MP3 player, pre-loaded with challenges and a range of tones and warnings, and a real time translation device, which allows for communication worldwide, is also supported. The system has been fully environmentally tested and with the maritime environment in mind, powder coating is available in a range of custom colours, built to an exceptionally high specification from the highest quality components, they are robust, durable and easy to operate.


Some common bio-effects of electromagnetic or other non-lethal weapons include effects to the human central nervous system resulting in physical pain, difficulty breathing, vertigo, nausea, disorientation, or other systemic discomfort. Interference with breathing poses the most significant, potentially lethal results. Light and repetitive visual signals can induce epileptic seizures (see Bucha effect). Vection and motion sickness can also occur. Cavitation, which affects gas nuclei in human tissue, and heating can result from exposure to ultrasound and can cause damage to tissue and organs.

Studies have found that exposure to high intensity ultrasound at frequencies from 700 kHz to 3.6 MHz can cause lung and intestinal damage in mice. Heart rate patterns following vibroacoustic stimulation has resulted in serious negative consequences such as atrial flutter and bradycardia.


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