Interference between ultrasonic range sensors

I am building a device to measure the velocity of a tennis ball being shot through a box. Currently I am using two ultrasonic range sensors to pick up the position and time of the ball passing and then calculating the velocity from this. However it appears that upon the ball passing the first sensor, the reflected waves interfere with or are intercepted by the second sensor and trigger it prematurely. Is there some way to make the second sensor not pick up the interference from the first? Is there a better solution to my problem, keeping in mind they have to be close together (6 inches), and the ball is not being shot straight so I need vertical and horizontal values? Thanks.

You need to separate the operation of the sensors in time or space, there is only one air for sound waves to travel through! Being in a box will increase the crosstalk a lot by the way. Can the sensos be fired out of sync with each other?

Utrasound beams are very directional so you may be able to introduce a baffle between the receivers to separate the beams in space. Don't place in a box if you can help and there will only be the reflection from the ball to worry about. If you have to have a box try lining with acoustic wadding?

They do it with laser trip wires or infrared photo gates. Don’t use sonic ranger for this project. Two reflective photo gates will tell you speed.

So what I found now that works is having the first one trigger the second, so only one sensor is receiving at a time. However the delay has to be set to 50ms it seems to let the waves dampen and fade. Do you know any way around this? My only idea is to line the area around with sound absorbing materials which hopefully will allow me to reduce the delay?

The issue with using photo gates is we need to track x and y movement.

coju93: So what I found now that works is having the first one trigger the second, so only one sensor is receiving at a time. However the delay has to be set to 50ms it seems to let the waves dampen and fade. Do you know any way around this? My only idea is to line the area around with sound absorbing materials which hopefully will allow me to reduce the delay?

The issue with using photo gates is we need to track x and y movement.

Neither photo gates nor sonic rangers can track 2-D. What exactly is happening inside the box? You need to paint a complete picture what you are doing here. I prefer some description and a diagram telling why 2-D measurement is needed.