Originally Posted by craig john
My friend, these "dips" are true nulls... room mode induced cancellations
. Look closely at the trough of the nulls. One is at 48 Hz, and the other is at exactly double that frequency... 96 Hz. These nulls are caused by the same room dimension(s).
A frequency of 48 Hz has a wavelength of 23.46 ft. The 1/4 wavelength is 5.87 ft.
If you have one or more room boundaries at 5.9 ft from the LP, it is these dimensions that are causing the cancellations. Floor/ceiling, front/back walls, side walls, if they converge at 5.9 ft., they are your problems Your *best* solution is to move your listening position out of these dimensions.My seat to ceiling height is 4.91 ft, The Mic to side wall is 8ft. (but above the ledge 8'10") I also have the alcove area which is being wall off to be symmetric with the upper and lower walls respectively. So currently the alcove area adds 2-3 ft of depth depending on height. The mic to back wall is 5 ft. exactly. The mic to front wall is 10 ft exactly.
It seems I have a few boundaries that are close to the 5.9' problem area, though not exact.
I don't know how much it matters about the side wall having the alcove area. But it's next on my list to fix that area.
More importantly, because these nulls are cancellations, they don't respond to EQ. Adding energy, (boost) to a cancellation just cause more cancellation. EQ can be effectively used to knock down peaks, such as the ones you have at 37, 63 and 78 Hz. But boosting nulls is not an effective use of EQ. In fact, it is detrimental to use EQ to try to boost nulls; it uses amplifier power and driver excursion without having any impact on the problem. It eats up massive amounts of headroom, adds distortion and it will make the sound in other locations REALLY bad.While not what I wanted to hear- I kind of suspected from what others have said that I would have this issue.
The good news is that nulls are not "heard." You "hear" peaks as boominess and smearing of bass notes. But the sound in the null is cancelled, like noise cancelling headphones. So all you might notice is some thinness, especially of the fundamentals of notes in the range of the null. Still, a null over a brad range of frequencies, like the 48 Hz null, which extends from 42 to 58 Hz, will have a significant impact on the
Looking at your pics, that would have been my 2nd option, the first being as far back into that L area as you could get, preferably on the opposite side wall from the sub in the front. Can you try either of those locations?I can go all the way back in the opposite corner of the L area. Will it have an affect if the cabinet is placed on its side vs. standing up? There is a sliding glass door back there so I'd much rather stand it up in the very corner vs. lay it down in front of the glass. However, the front speaker needs to remain on it's side.
Potential problem?? Would there be any affect of standing both speakers upright in the front of the room vs. them laying on their side? Guess I could just try it.
Nonetheless, IMO, the *best* option you have is to move your listening position OUT of the nulls.Below is a graph with a movement of the mic back towards the back wall. I'm not sure how much closer to the back wall I can go because of the massive rear surrounds. I like the idea of putting the one sub in the back corner of the L area and keeping the seating at the 4-5 ft. mark. Currently the two center chairs are at 5'.
PS. It's hard to tell from your pics, but it looks like you're measuring from the point between the 2nd and 3rd seat. No one will ever sit there, (unless you shift the entire row left or right.) Try picking either the 2nd or 3rd seat, make it the primary LP, and then measure from there. You may find that the nulls you're measuring are in a location where no one will ever hear them, and the response at your "new" primary LP is better than at your current measuring location.You are correct. I've moved the mic in between chairs and gotten big differences, but have not focused yet on placing the mic in one chair. I would like to have a nice average between the two center chairs.