I've used these sonic devices for a bunch of different projects. One thing that you have to pay attention to is the mechanical aspect of the transducers. They have to be rigidly fixed to the PCB and enclosure. Hanging off the pins as shown in your picture can cause all kinds of problems.

These things continue to "ring" after they've been pulsed. Many dampening circuits are available for electrically clamping the transducer. At the very least, wrap a small piece of felt around the body of the transducer, with a piece of dense foam around that (the dense weather stripping with an adhesive back is an ok place to start; buy it in a hardware store, something like 20' for $5.00). You can (and probably should) place a small plastic can around the transducer to make it more directional.

Years ago when my kids were younger we built a small robot for the science fair. It tooled around on its own through the crowd not bumping into anyone (people thought it was remote control). Anyway, we put the transducers in small plastic film cans with the pins sticking out the bottom. Line the film can with some thin felt (adhesive back - buy it at the craft store). Then take a piece of dense foam the same width as the transducer cut to length so that it wraps once and push it down around the transducer. We spaced the transducers so that they looked like "eyes". We also stuck some high brightness leds in there... you can experiment with the distance between the two. We used the full length of the film can but you can try cutting them back a little at a time until you get the response you want.

You will be amazed at the difference in performance.