The final type of sound system is a standard car stereo amplifer with two external outdoor type speakers. The speakers have two heavy duty magnets attached so that they can be placed on the hood of my Jeep. This type of sound system is very good for putting out extremely loud calls. Best suited for the mountains when the distance that you are trying to reach is far away.
I have not used this system a lot, preferring the smaller portable units.
In summary – their are dozens of different setups and many variations of sound blasters. Most researchers have their favorite ways of doing things.
As far as responses, I have been very successful using sounds. A vocal response is not necessarily the criteria to judge how successful you are. When nighttime visitors come through your camp rattling door handles, slapping the tops of cars or checking things out that may have been a response to earlier sound blasting.
We are dealing with an animal of very high intelligence and it is always a guessing game as to what will interest them.