Originally Posted by UncleBob
In my difficult corners, couldn't i just put a bass trap vertically at the top, then another horizontally, tucked into corner created by the cut into the wall underneath?
The quick answer, yes you can!
There are two ways to approach this:
1. The right way ie measure the room with an analysis package like Room EQ Wizard (free from hometheatreshack). Then treat the space accordingly by identifying the problem walls and, importantly, the correct areas of walls/ceiling to treat.
2. The "sling it up in the corner and hope" approach.
I fully accept both that you are in rented accomodation and are a musician, so you just
want a good sounding room without a Masters in acoustics right? But, use this as an opportunity to learn
Take a look at this hunecke.de | Room Eigenmodes Calculator
it is very good for visualising the issues. Insert your room dimensions. The dark areas are pressure maxima (white areas by inference minima) of standing waves (room modes, eigenmodes) in your room. Modal issues are, I believe, why you are experiencing a boomy bottom end!?. Normally one would expect to treat these modes with pressure
based absorbers, these are tuned, panel type absorbers. If you look at the first three modes on the above mode calculator these are the fundamental axial
modes, arguably the strongest modes and in your case 69, 75, and 82Hz, right in the crucial bass drum/ bass guitar part of the spectrum. You are going to get ringing (longer decay time) around
that area. Importantly notice that the pressure maxima of those primary modes are across the whole
area of their associated wall, not just at the corners!
The "bass" traps you have bought are really glorified "velocity" based absorbers, ie they are porous foam (of some sort). You will notice from the above mode calculator that all modes to a greater or lesser extent have pressure maxima in the tri-corners. This is the reason that they are sold/marketed on the basis of corner placement for max effect, despite the fact that technically they are not pressure absorbers. By tri-corner placement you are "bracketing" the number of modal pressure maxima the treatment is in contact with, all be it with velocity based absorbers. They will have some effect of course (not at very low frequency) however in a room such as yours if you are just going to have corner placement then be aware that you are going to need a lot of them and they will have minimal effect on the axial modes.
When you have put up all the treatment you can afford/justify (in a rented room) experiment with listener/loudspeaker relative placement. You are not going to have much of a tolerance for moving about but you should be able to find an optimum seating position with respect to loudspeakers to minimise modal issues. If I were you I would start with seating in the centre of the room and experiment with small adjustments from there. When you are as happy as you can be with relative listener/loudspeaker location, think about some free standing absorbers (DIY on legs?) to cover first reflection points on the side walls? Good luck