Multi-Blaster, is a 4 way (360 degree) speaker. It is run by 2 sound generators, thereby putting out 2 different sounds in a 360 degree circle.
The Multi-Blaster can use any two ot the many Bird Gard sound units. For example if your problem was crows and starlings - you might use the Electronic Scarecrow(ESC) which works well on crows and the Bird Bat Control(BBC) which works particularly well on starlings. The combination of both these sounds will effectively repel both species at the same time as well as all the the others that are repelled by these sounds.
A multiblaster will protect a large area in a circle around it. The area of this circle depends on the crop type and bird pressure but is usually about