Is it possible to register the effects of sound interference in everyday settings? For example, sound interference could lead to a loud room feeling louder simply because of sound waves colliding. Or an orchestra which is perfectly synchronized could create loud and quiet spots in the concert hall. Are there any everyday situations where some kind of sound waves interference could be demonstrated?
 A: To avoid a "big list", I'll try to describe a general case.
The phenomenon of sound interference is clearly demonstated in most (acoustic) musical instruments. In general, what you need is some enclosed space with reflective borders or surfaces, where sound waves can bounce around and by interference form standing waves. Depending on wavelength, resonance occurs.
A bathroom usually has the right properties: hard reflective parallel walls. If the sound from the fan happens to be a distinct hum, the loudness will vary with the location of your ears. Or do the humming yourself, while moving around. Whistling works even better, because it contains only one frequency, hence one wavelength.
Note that an ideal studio for recording musical instruments has the exact opposite properties: sound absorbing non-parallel walls.
Okay, one more example: A fast moving car with a partly opened window may work like a very low-tuned flute. When you are a passenger, move your head around and notice that in some spots the sound is clearly heavier than in others.
PS: In fact all wave phenomena involve interference in some sense. I just picked a dramatic case.
A: Because different frequencies will have different attenuations for the same paths taken, it's often the case that sounds with only a single frequency will show the effect.  This could be an intentional tone (such as a repeating phone beep) or something like a particularly narrow "squeak" sound from a motor.
In those cases you may notice that small movements of your ears will result in large changes in the volume of the sound.  If the sound were more complex and had many different frequencies, only a few would have the same degree of attenuation and the effect would probably not be noticable.
