The Prophet (SAWS) said in Sahih Muslim 2940: 
عن عبد الله بن عمرو رضي الله عنه قال : قال رسول الله صلى الله عليه وسلم : " .. ثم ينفخ في الصور فلا يسمعه أحد إلا أصغى ليتا ورفع ليتا قال :وأول من يسمعه رجل يلوط حوض إبله قال فيصعق ويصعق الناس ثم يرسل الله أو قال ينزل الله مطرا كأنه الطل أو الظل ( شك الراوي ) فتنبت منه أجساد الناس ثم ينفخ فيه أخرى فإذا هم قيام ينظرون "
It is narrated that ‘Abd-Allaah ibn ‘Amr (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “… then the Trumpet will be blown and no one will hear it but he will bend his neck to one side and raise it from the other side. The first one who will hear it will be a man who is busy in setting right the cistern meant for supplying water to the camels. He will swoon and the other people will also swoon. Then Allah will send or He will send down rain which will be like dew and there will grow out of it the bodies of people. Then the trumpet will be blown again, and they will stand up and begin to look around.”
'The first one who will hear it' suggests that everyone in the world will hear it and they will then swoon. The hearing of the trumpet will make the first one who hears it swoon and thus when it says 'other people will also swoon', it indicates that they will have to have heard it in order to swoon.
What you must understand is that the trumpet won't be like any on Earth. The trumpet may even be bigger than the whole planet, we don't know. It might be very loud and cause us to 'swoon', we do not know. It might be quiet enough to hear. We cannot explain how the trumpet can do this. It's all part of the Unseen. We don't have the capability to understand it.
- Note that the hadith above is only part of a big hadith so it is not the full hadith, only part of it.