1. The problem statement, all variables and given/known data Q. Expalin why an ambulance siren gets louder as the ambulance approaches you and quieter as it drives away from you. 2. Relevant equations None 3. The attempt at a solution Hi, So, I know it's not the Doppler effect, because this only affects frequency. If the siren is only pointing in one direction, then the answer would be because the sound waves are directed at you when it's approaching and pointing away when it's moving away, yes? However, if the siren is producing sound in all directions, I'm stuck. Is it something to do with the wavelengths being closer together on the approach, so there is more sound? But is this not the Doppler effect ie frequency?