Protection by the Decibel
Parents are unsuspecting of the effects of noise on their child’s brain development during pregnancy and thereafter, but new research has shown that noise exposure is something not to be toyed with.
Human Hearing is a Work in Progress
In the fetal stages of development, the brain grows amazingly fast with nerve cells created at the rate of 250,000 a minute. By the 24th week of development, the hearing system is already working and by the 35th week the fetus can discriminate the differences in speech sounds such as “E” and “O”. Amazingly, within a couple of days after birth the infant can pick out the mother’s voice from others because of hearing and learning during its development in the womb, while dad’s voice will take a while.
Using microphones in the womb, scientist has shown that the fetus hears normal low tone sounds because of transmission through the fluids of the amniotic sac, in the same way whales hear across great distances in the ocean. Fetal hearing development is a gradual process that makes connections in the brain that suit the low tone rich uterine environment and the mother’s voice. After birth, sound experiences help the brain to add more environmental tones to the infant’s memory libraries, along with speech and language. Ultimately, a network of connections to vision and the other senses link the newborn to the world. This development is responsible for normal brain function (neuroplasticity) over a lifetime and protecting the system from excessive noise is paramount in the early stages of life and thereafter.
The Noise Problem
The fetal and infant ear can hear normal sounds and also be over exposed to noise. Understanding how to separate out normal sound from noise exposure is accomplished using a few simple rules. Normal conversational speech between adults is at 62 dB and the mother’s voice in the womb to the fetus is delivered at 80 dB. To fetal development the loudness of the mother’s voice is necessary to train the brain, calibrate loudness, and grow those important nerve connections. The occasional high noise spike, in-utero MRI, or the acoustic stimulation test and normal daily noise have no effect. However, levels above this that are either chronic or repetitive, steady or impulsive at high levels cause the fetus to startle, change heart rhythms, increase blood pressure, create abnormal physiological changes, and if chronic, develop hearing loss, birth defects, premature birth, and abnormal social behavior after birth. The effects are not limited to just direct contact with the fetus, but if the mother is over exposed to loud noise, similar changes in physiology can occur as a result of noise induced stress. After birth, the newborn is also susceptible to the same noise induced hearing loss as adults and special care should be taken to protect them.
Measuring Acceptable Sound Levels by the dB
Monitoring noise is a simple task that can be accomplished with an app on a cell phone. Acquire the $0.99 Sound Level Meter App from
Faber Acoustical, LLC. It allows measurement of the sound level and peak loudness using a reasonable factory calibration. Measure sound at an arm’s length on the Lp (peak power), dBA (hearing frequencies), and the Slow settings for no more than 10 seconds. Prolonged measurements above 80 dBA or repeat ongoing peaks at 100 dBA or above would suggest that the environment is too loud. For pregnant soldiers, the military allows brief exposure levels up to 104 dBA, but does not recommend prolonged exposure above 84 dBA. A typical busy restaurant would fall at approximately this range, but a rock band, race car track, NFL, NBA, or other events, such as a concert, or other loud equipment noise would be unacceptable. In most cases for infants, ear muffs if fitted properly (-12 dB real world) are not enough in high noise. The simplest way to judge if noise is too loud is when at an arm’s length you need to raise your voice to a shout (80-85 dBA) to be heard.