Speed of Sound   

The speed of sound varies depending on the type of elastic medium it is propogated in.  

The speed of sound in dry air at a temperature of 0 degree C is approximately 344 m/sec (1130 ft/sec). 

Medium Speed (ft/sec) (meters/sec)
air 1130 344
water (salt) 4900 1500
wood (fir) 12500 3800
steel 16600 5050
gypsum board 22300 6800
This difference in speed explains why (for example) one may hear a train coming through the steel rails long before you hear the train via air-conduction.