I always think of the needs of a guest when seating them at a table. You can safely assume that your grandparents and guests of their generation will not want to sit next to the band or DJ speakers, so you can seat them towards the back.
Ask your parents and the groom’s if they have a preference. They may want to sit together at a “family table” or they may wish to sit with close relatives and friends. I would sit your parents’ tables close to the dance floor. If you’re dividing the room between bride’s guests and groom’s guests, the parents’ tables can be at the center of each side of the dance floor so they have a good view of your first dance, toastmakers and other special moments.
The bride and groom, whether they sit by themselves or with others, should be at the center of the room - across from the band/DJ - and clear for all to see. You can sit your bridal party and friends on either side of you.
Flank your parents’ tables with tables made up of their family and their friends -- you and your parents will know the “importance” of which guests should be nearer to your mom and dad and who can be a little further away.
As for a bad seat, near the band or speakers may not be a desired spot but your friends (and their ears) can handle it. Another spot is near the kitchen, so try and get as much space as possible between the table nearest to it and the kitchen door. Or see if your caterer/location can throw up a standing divider, an attractive one, so your guests don’t feel like they’re in the kitchen.
And always remember that you can’t please everyone so just do your best and don’t worry so much.