well firstly, i doubt the sub has loose bass, its probably another issue caused by standing waves the 50hz dip on the mirage could be a number of things, placing the close to the side walls could cause cancellation because most walls resonate at 50-60hz alot, try placing the speakers closer to the middle point of the wall behind them then measure again, considering the dip only happens in the center of the room im willing to bet its a cancellation caused by the standing wave coming off of the back wall colliding with the 50-60hz wave of the speaker, as i said before you may be able to solve this issue by placing corner foam bass traps across the back walls corners and ceiling conjunctures. in the meantime what you could do is move your listening position a couple feet closer to the speakers because this will get you out of the cancellation zone. and keep your speakers AWAY from the side walls, every room i have ever been in putting speakers near the side walls has always caused bass issues since bass tends to spread out all over the place and not be directional like mids and treble. apparently you have a way to measure frequency levels, my advice to you is that you track down the problem and eliminate it with bas traps, heres what you should do, play a 55hz sine wave and measure it directly in the center of the room, now measure it a few feet from the back wall, now measure it 1m from your speakers, if it is a cancellation issue you will notice how the level of the 55hz wave goes HIGHER towards the back of the room because the back wall will be a natural source of amplification. what are the dimensions of the room and could you post a pic of it?
