Suckout at 40 hertz...less pricey solutions?

Are the woofers side firing (side mounted)? If they are, try switching them with each other so the woofers will be on the opposite side.If they are, this might fix the problem.

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.

Marty

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.

Good Luck

Marty

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.