echo

echo, reflection of a sound wave back to its source in sufficient strength and with a sufficient time lag to be separately distinguished. If a sound wave returns within 1/10 sec, the human ear is incapable of distinguishing it from the orginal one. Thus, since the velocity of sound is c.344 m (1,130 ft) per sec at a normal room temperature of about 20°C; (68°F;), a reflecting wall must be more than 16.2 m (561/2 ft) from the sound source at this temperature for an echo to be heard by a person at the source. In this case the sound requires 1/20 sec to reach the reflecting surface and the same time to return. Bats navigate by listening for the echo of their high-frequency cry. Sonar and depth sounders work by analyzing electronically the echo time lag of sound waves, generally between 10 and 50 kilohertz, produced by underwater transducers. Radar sets broadcast radio waves, usually between 100 and 10,000 megahertz, pick up the portion reflected back by objects, and electronically determine the distance and direction of the objects. A sound echo that is reflected again and again from different surfaces, as by parallel walls in a tunnel, is called reverberation. When a surface reflects sound it partially absorbs and partially reflects the energy. As the process is repeated the sound becomes weaker and weaker and eventually ceases.

Echo is a city in Yellow Medicine County, Minnesota, United States. The population was 278 at the 2000 census.

Geography

According to the United States Census Bureau, the city has a total area of 1.0 square miles (2.6 km²), all of it land.

Demographics

As of the census of 2000, there were 278 people, 119 households, and 69 families residing in the city. The population density was 273.1 people per square mile (105.2/km²). There were 136 housing units at an average density of 133.6/sq mi (51.5/km²). The racial makeup of the city was 97.48% White, 1.08% Native American, and 1.44% from two or more races. Hispanic or Latino of any race were 1.08% of the population.

There were 119 households out of which 28.6% had children under the age of 18 living with them, 49.6% were married couples living together, 4.2% had a female householder with no husband present, and 41.2% were non-families. 37.8% of all households were made up of individuals and 26.1% had someone living alone who was 65 years of age or older. The average household size was 2.34 and the average family size was 3.16.

In the city the population was spread out with 27.0% under the age of 18, 6.5% from 18 to 24, 24.1% from 25 to 44, 19.8% from 45 to 64, and 22.7% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 91.7 males. For every 100 females age 18 and over, there were 95.2 males.

The median income for a household in the city was $27,656, and the median income for a family was $35,500. Males had a median income of $25,714 versus $20,385 for females. The per capita income for the city was $15,275. About 6.3% of families and 10.6% of the population were below the poverty line, including 13.2% of those under the age of eighteen and 5.6% of those sixty five or over.

References