Hi, i am building an outdoor shooting range on my property but i don't want to get complaints from my neighbors and my biggest problem regarding noise is the bullet breaking the sound barrier and the closest shooting range to me has mounds of dirt (15ft high) surrounding the shooter and and those act like sound barriers and they do a really good job of keeping the sound down so is there a certain way i need to make my sound barriers to make them effective? And thanks for any help and advice you can give me!