Bass trap couch

Can a couch also work effectively as a bass trap? That depends partially on where it is placed. If in the middle of a room, it isn't likely to be very effective. However, if you are in a small room where you are forced to place the couch very close to the rear wall, then it can work quite well as a bass trap. A couch is a fairly large area of a foam near the floor to wall junction. You can make it more effective by putting foam between the couch and the wall, and foam that fills in the space between the couch and the floor. The difference is shown here:

Comparing the two it seems that peaks and dips are changed. Not all the changes are an improvement. The dip just above 100 Hz related to boundary interference is made effectively worse, but this is mainly because it remains while the level comes up on either side. Minor dips are added around 150 Hz, but the peak and dip higher up are both smoothed out. 

Overall I'd call it a slight improvement and some improvement in the decay time is also seen. This is a good result, especially considering that no extra space is taken up in the room. A single foam mattress was placed in between the couch and wall. Most of the improvement is in the lower midrange, above 80 Hz.