Weird problem with faces, black lines I'm making a studio monitor and i'm having trouble with the face selection, vertex. I'm pretty new to blender and 3d, so i think this must be a pretty common error.

Here is the mesh, i want to select the faces were are triangles so i can make them quads


But this happens every time i try to select the face, it select the hole section. 


And this is how it looks out of edit mode, full of black lines


This i what happens when i try selecting the vertex of the triangle and using subdivide
Instead of creating triangles and trying to fix them later, keep your topology using quads all the time. 

It is a common misconception that the topology of an object comes at the end of the process. The topology of the object should always be worked out from the beginning.

A simplified way to do a speaker:

Start with a cube, scale it on the $Z$ axis, and make a loop cut in the middle.





Position the cut to divide the two main sections of the speaker.

Create some vertical loop cuts And subdivide each of the sections with an equal amount of cuts.



select the edges that will become the round part and press &#8679; Shift+&#9095; Alt+S (to sphere) and move the mouse to create a circular shape.



Do the same for the top part.



Select the central faces to extrude.



If you select the loop ring in the front you should be able to bevel the holes.