Is you equiptment setup on the 9ft side of the ceiling with the sound going up to the 12ft.which would be the correct direction.You must follow the vault upwards with the sound. Any other direction might cause the suckout.
Hello Radioheadokplayer, What program did you use to measure this? How deep is the null? If there is a null there must be peaks, where and how big are those? Are you using a sub? How low does your sytem go? Can you post the in room freq response plot?
Don't be overly concerned with nulls for two reasons. 1) Nulls are almost impossible to fix. 2) Level out the peaks and you've half fixed the nulls.
Peaks are much easier to handle. EQ is the obvious way, but before sinking money into that you might try speaker position first. A couple of feet this way or that with the speakers and/or your listening position can make a surprising change in bass response.
1. Play with listener/speaker placement since nulls can cover small spaces. I got rid of the one noticeable suck-out in my current room by moving my seat six inches forwards. Try slightly asymmetric setups - sufficient speaker directivity, side-wall spacing, and toe-in can avoid image shift. I've had very good results from two asymmetric rooms with my Linkwitz Orions, and one failure on stand mounted monitors in my home office with book shelves on one wall where I had to use stereo tone controls as a band-aid.
40 Hz is tough. Nothing commercially available would touch that. If they could, it would be too big to be shipped.
You could make an entire wall as a series of 4' X 8' membrane panels. 1/4" panelling or hardboard or even 1/2" drywall could serve as the membrane if its furred out, even just an inch, from the center studs. Screws at the edges only, maybe some Silflex (marine adhesive silicone) to alleviate rattling. Caulk it airtight and lots of rigid fiberglass insulation (not touching the membrane) . Of course, you wouldn't want to hang pictures on that wall.
The good news is that a 40 hz suckout won't to be an audibly meaningful problem with more than 95% of the music program material out there. However, if you want to address that last 5%, good luck, it's a bitch down that low. You could go with DRC (preferably a subwoofer) or you could just ignore it.
I had a similar problem and my room is 14x22x10 ft. I have a 40-50Hz suckout that can be 15db at its worst ( ctr of the room). I got it to 2-5db (depending on smoothing of freq curve). Many reviewers have a similar issue, just take a look at the measured room response on stereophile. John Atkinson constantly mention this when reporting his measurements in his room. I suspected he left the problem there to simulate rooms of most readers.
More info on room size, sitting location and speaker location would help. I'd guess that you are sitting fairly close to the center of the room which has the null. Hopefull, it is a narrowband suckout. I would also guess that you have peaks above and below the suckout.
One way is to sit closer (but not too close) to the wall behind the listening chair. This brings in some boundary bass reinforcement to counteract the suckout. Trade off is comb filtering issues smearing the midrange and treble but this can be reduced with traps/absorbption or diffusion. I'd position mic at different locations of the room and learn the frequency response. Do not forget vary the height of the mic slightly as bass response also change with height.
Another way is to move the chair futher up pass the center of the room and get out of the null. This probably would yield a nearfield listening location with great clarity. Also try using room optimizer software to generate a few sets of theoretical speakers/sitting locations to save time.
Room treatment and attention to acoustics is a must. People talk about how great a seal box design can generate clean/well damped bass but if room has many issues, the advantage would be lost. Conversely, ported design can work well in treated rooms.
I also have a Bagend trap. This only works 20-65Hz and tames peak only. There are just two bands with adjustable Qs. When taming the peaks above and below 40Hz, sometimes it can recover energy at the suckout point. This did not happen in my room. I have a 5db peak at 25Hz which the bagend can reduce it. I usually don't turn it on. On most music, this not too bad. The peak become noticeable on sustained bass notes (organ) and it loads up the room.
I also tried the subwoofer route. If I am at the null point, no sub can generate enough power to overcome the suckout. Outside of that, the sub can indeed compensate for the suckout and get a ruler flat response. There is a need to use some type of notch filtering (high pass filter with adjustable low cutoff). Otherwise it would worsen the peaks around the suckout. For me, it introduce group delay issues in the time domain. I think that if you go the subwoofer route, active crossover would work better. Some parametric equalizer would let you implement crossover and equalize at the same time. Problem is that they do not address reverb issues.
When you are done with freq response, optimizing RT60 would also yield big improvement in sound.
Good luck. I am just learning. Since we have similar problems, I 'd like to share what I went thru. I highly recommend room optimizer software, fuzzmeasure and room treatments. All are cheap comparing to two quality subwoofers or equipment overhaul.
Glai points out that using DRC to address a null can be difficult, but it can be done. For example, several manufacturers produce a 12" sub with 1000 WPC. A pair of such subs (especially those with largeish cabinets) will provide 2 kW of amplifier power (more on peak) into a reasonably sensitive driver/box mechanical system, which will go a long way toward fixing the most stubborn null. This is a blunt force approach, maybe inelegant to some, but it works. As Glai notes, it may also prove expensive.
PS - When I note that your 40hz null will be mostly inaudible, I assume that it's deep and narrow @ 40hz. A broader null (particularly one extending higher in frequency) might certainly pose a more audible problem.
Hi you may want to try to use this program to help you with placement of your speakers. http://www.hunecke.de/en/calculators/loudspeakers.html Cut and paste it to your browser.
I too have a similar problem to yours. My room is 13 x 14 feet with a 14 foot ceiling. The first thing I found was that the speakers have to be on the shortest end of the room. Or the end furthest from the door that enters that room and shortest in width. I tried my speakers on the long wall and I did not have good success. I also found that a room that small is not very good for bass when using some full range speakers that go below 35Hz and that can vary. I spent over 3 years looking for speakers that sound good in my Box Of a Room and I ended up with Spica TC60's and 2-Dali Suite 1.2 Acoustic Suspension Subs. The Spicas are rear ported but you can compensate for that in several ways. The subs were the hardest to place. I first had them between the speakers and the outcome was not consistent. Sometimes boomy, sometimes not much bass and sometimes just right. Mr. Bau told me to move the subs closer to my listening position. This improved things. That helped but I needed them to be even closer. Because I didn't have any wall sockets nearby I could not move the subs closer to me from the front so I moved the subs behind the loveseat. I was instructed to put the phase to "0" and turn the subs half way of what they were when I had them in the opposite end of the room. This amounted to be about a 1/4 turn and my crossover was set to the lowest setting about 40 or 50Hz. I don't know what happened but my system was transformed. The bass tightened up tremendously and even though the subs were behind the loveseat I didn't notice they were there. I used this as a guidline to place my subs: Mr. Bau shared this with me: For inverting subs - place them near the speakers. For non-inverting subs - place them near the listener.
With the phase set to Zero this worked out beautifully. The other thing you can do to control bass is have some filters made to control the bass on your main speakers. The filters makes your speakers roll off where you want them too and then the subs take over and to their thing. Vandersteen sells filters for it's speakers. I also don't know if you can do this for a solid state amp. I have all tube gear and it does work. I had Alon I MKII, VonSchweikert VR3, Living Voices, Athena 2's, Wharfedale, and may other speakers and I could not control the bass or it overwhelmed my room. The Spica TC60 or T50 with The Dali Suite Acoustic suspension 12" Subs worked. This may be more difficult to do if you have an integrated amp. I have tried every trick to control the bass and this worked best for me so far. I also used the speaker placement guide included at the beginning to place my Spica TC 60's which helped allot. If you don't find your speakers on the list try to find a speaker with similar characteristics as your. If you have a floor speaker choose a floor speaker, etc. Place them according to the directions and see if you hear a differnce. Next, I will do the wall treatments. I'm very satisfied with my outcome but remember your small room cannot support a speakers going down low in the bass region. You have to tame it and control it as best you can. I hope this helped you some.
I had a 50Hz suckout (-10dB) I resolved with a pair of bass traps (GIK 244). I have two powered subwoofs and just for the heck of it I took one bass trap off of the wall behind my head and I had one extra just sitting in the closet. I stood them up near each of the two subs in various configurations. After numerous iterations I (luckily) found that by placing them next to one another (for a 4'x4' trap), 6" from one side of one of my subs the null disappeard (mostly, only -3dB now). Bingo! -3dB for a narrow null ain't bad. Problem solved! p.s. During the juggling process I tried one behind the other for a double thick trap and one on top of the other for a tall trap, but standing on the floor side-x-side worked best for me. Try it!
I had a few nasty nulls at low frequencies. Between adding GIK Monster traps and 6 244's, thing improved, but I still had one narrow but deep null at 60hz. Speaker repositioning was the only thing that fixed it. I pulled the speakers a little further into the room, which also added more depth to my soundstage.
A Behringer DEQ2496, which you can get (with mic and cable) for about $350 will show you what your problem is with its spectrum analyser (Real Rime Array, RTA). The RTA will also help you see the effectiveness of various room treatments that you might try. Oh, and by the way, you can also correct the problems using the equalizer function. You will no doubt recieve comments that the equalizer aproach won't work. I say, try it, and decide for yourself.