This article is an excerpt from our Sefer
Buy me here or on Amazon.com
11. If many people are blowing at the same time:
If there are many people blowing simultaneously, one fulfills his obligation so long as he intends to listen to the blowing of a single blower and that blower is sounding all the sounds.
 Now although we generally rule that if there are two sounds being heard at the same time one is unable to fulfill his obligation with either sound [as ruled in 141:2], nevertheless Shofar is an exception to this rule as since its Mitzvah is only once a year the listener gives it special appreciation and pays close attention and is thus able to hear the sound of the Shofar even amongst other sounds. Thus even if other people were playing a trumpet during the Shofar blowing one fulfills his obligation. It is however invalid to simultaneously hear a Tekiah, Teruah and Tekiah from three different people as in such a case one does not have a Tekiah precede and follow the Teruah as the sounds are all being heard at the same time. [ibid]