4Hz to 28Hz vertical, horizontal, 3C geophone. CDJ middle & high frequency geophones, 4,10,15,28,30,40,60,80 or 100Hz, are widely used to seismic prospecting of petroleum, coal, metallurgy, national defense, engineering and etc.SPECIFICATIONS CDJ-Z/P4CDJ-Z/P4.5CDJ-Z/P10CDJ-Z/P15CDJ-Z/P28 Vertical/HorizontalVerti/HoriVerti/HoriVerti/HoriVerti/HoriNature Frequency Fn (Hz)4±10%4.5±10%10±5%15±5%28±5% ...