This is the spectrogram of a boat at a range of approximately 200 metres (650 feet). The skipper is rev’ing the engine while warming it up. Listen carefully to the sound sample and you can hear the pistons operate! As the engine rev's you can see a very clear 'whine' centered around 640 hz. You can also hear 'snapping shrimp' in the background. (mostly showing as a light 'blue' color)
Sounds are clearly picked up all the way down to 1-2 Hz, showing the quality of the DolphnEAR hydrophone! Human hearing has a lower limit of about 18-20 Hz, so using DolphnEAR with the Spectrogram Program lets you 'see' sounds you normally cannot hear. This is a useful feature if you go hunting for long range (up to 100-150 Kilometres) whale vocalizations.
This sample was made using an inexpensive cassette recorder ($40). DolphnEAR was connected to the MIC INPUT jack.