10dB resonant peak at 40Hz

Given your significant limitations and the severity of the issue I’d suggest looking into some form of room correction from the likes of DSpeaker, MiniDSP, etc.  Best of luck in taming the beast!

My room is about the same dimensions and my last sub. , a REL was used with a Velodyne SMS 1 .   It pulled down that nasty peak.   The sub that replaced it has built in DSP and it also does a good job of getting rid of the boom

Before you do anything, consider an Auralex SubDude isolation platform.  Cheap and effective at taming resonance. Start there then explore DSP solutions.  

Yes, DSP would do it. I'm not using a sub.

Last speaker was the JBL L82 and even the KEF LS50 Meta (which I did not think even went to 40Hz) does it. If I plug the speaker ports, the resonance goes away but so does too much of the bass.

Well, if you could move the speakers I’d say use the AM Acoustics room mode simulator to try to put your speakers and listening room out of the 40 Hz mode. Otherwise EQ is your only option.  If it makes you feel any better, it's a very good option as well.

@erik_squires you mean THIS?

I’ll try moving them around this weekend. Right now, they are 50" out from front wall and 30" from side walls. I did calculate 15 ft resonance is 37 Hz - sounds about right.

Since plugging the ports worked, sealed box may be another idea but would need a larger cabinet.

OP:

Yes, that’s the one.  As you mention, plugging the ports will work but sometimes at the expense of all lower bass.  A parametric EQ on the other hand can clip these enormous resonances effectively and make it possible to better balance the bass output.  With subs clipping peaks can often help you raise the sub volume very effectively.

At that frequency, a high pass filter at 50 hz might work.

I had a similar issue (12 dB @30 Hz), and was able to work with Music City Accoustics to get some wall-mounted tuned bass traps. I tried to work with GIK on this issue, but I found them to be inflexible and uninterested in addressing this targeted issue, by the way.

I am not sure how constrained you are when you say"minimally intrusive." These take up no living space but they are visually apparent. Corner mounting was not required. I ended up buying 4 of them. They are about 14" square each, and they are mounted in a pattern on the wall. I consider them unintrusive, and my SO had no complaints. You/your SO may disagree.

The effect of adding these was immediate and extremely effective. I wouldn't want to address the problem any other way.

I have a couple of GIK Acoustics corner bass traps that are not very intrusive and I'm not using them.  If you're near SD you're welcome to try them. 

Otherwise, look for some near you.  An easy solution if it works.  

@OP - Can you move the speakers closer to the front wall? Even if you still get a resonance you just don't want it on a root note that bass players land on regularly - but even a relatively small movement might tame it anyway.

Another thought not suggested above -- add a high pass filter to the existing speakers and add a powered sub or two. You can try the sub in different positions to find the best spot to even out the 40 Hz resonance.  Subs can often be easier to move into different spots without bothering the other uses of the room as much.

As an additional observation, I've noticed that sometimes the placement of the main speakers which gives the best imaging and soundstage may not work as well for bass resonances, and vice versa.  Since most of us don't have dedicated sound rooms, this means we have to co-exist with home decor and such.  Using a sub can be a good way to handle things.

Dsp is your best option. 40hz is roughly 27’ long so you could put your speakers in the 40hz null which would be 1/4th of 27’ feet… works out to about 7’. But this is only one boundary and all boundary sum…

bass traps would need to be super thick at 40hz. Like 3-5’ feet (just a guess I have no idea). Off loading to subs and using subs to control the room is another option.

Not enough info on the OP, but, I am guessing you are sitting right up against or close to the back wall?

Peaks are easy to handle with dsp (not the case with nulls). If you don’t have dsp, put one sub on front wall and a 2nd sub on the back wall (hopefully you have subs with variable phase?). It should be gone.

You can "remove" peaks and nulls when you have freedom of placement with subs that come with more user dofs. Subs are not just for adding oomph to the low end. Their primary job is to remove peaks/nulls and throw you in a uniform womb of bass (one key ingredient for audio nirvana).

You could also do other discrete tuned resonators, but, you may need to find some nerd to help you with it.

I just set up a sub with a high pass on my mains. It's an astounding and wonderful difference. Just having the low end coming from the floor instead of 30 inches above eliminated most of my 60hz resonance. 

The difference in clarity with the mains freed from low end duty is pretty dramatic. Coupled with clean and even low end it's even better than I expected. 

After playing with the parametric eq, I ended up not using it. Playing with the low pass roll off curve was more helpful in blending the low end.. And variable phase surprisingly making a big difference. Still fine tuning but much closer than ever to "the sound". 

@cdc What are you using to verify that it was 40hz? Do you have an HVAC system near the room? As silly it my seems,  I have a 30hz peak in my room and it is similar in size so every time the AC unit is on which is right above the room, presents rumble at that frequency.  I use a RTA to measure room response every now and then when I change out speakers or subs for that matter. 

Another situation is consistent of balance of frequency response of a bass guitar or any matter of instruments that has frequency response that low. 

Yes, DSP would do it. I'm not using a sub.

@cdc You have a standing wave that is causing the peak. If you poke around, I think you'll find you also have some dips caused by the same issue.

The best way to break up standing waves is by using subs placed asymmetrically about the room. They must not be active above about 80Hz else they will attract attention to themselves. Because 80Hz has a 14 foot waveform (so 40Hz is 28 feet) the bass in your room is 100% reverberant before your ears can make out what bass note it being played. For that reason, the subs can be driven with a mono signal. 

Bass traps help, DSP helps (and can be pretty good about peaks but can't do anything about dips since they are due to cancellation) but both techniques together offer about a 5% solution if you have a dip. Subs offer about 95% effectiveness since they can break up the standing waves causing the problem; they work so well you may not need any other help.

This approach to dealing with standing waves is known as a Distributed Bass Array. If your main speakers make decent bass, you really only need two subs to sort things out.

@atmasphere 

My single sub with the HP filter is doing such a nice job, I'm considering adding a second. But I'm concerned that while two may fill the room more evenly, I'm inviting phase issues with two sources. I'm thinking that one reason a single sub sounds so good is the absence of two sources of low end interacting with each other and the room. 

I've already found that adjusting the phase on my SVS SB1000 Pro has a significant effect on the overall balance but with two it could get much more complicated. 

Your thoughts?  

Your thoughts?  

@mashif 'It depends'. If the subs are only active below 80Hz than interactions won't be a problem unless you place them side by side and operate them out of phase.

If you have only one sub (and its only active below 80) then its a matter of placement; you have to move it around bit by bit until you find a spot (which you may already have found) where all frequencies can be heard at the listening position. Two subs makes that go a bit easier; 3 even more so and you really don't need to go past 4.

My room has a pretty bad bass cancellation at the listening position and my speakers are flat to 20Hz. To break up the standing wave causing the problem I added two subs- one to the left of the listening position and the other to the rear and a bit to the right. It was pretty easy dialing them in.

Thanks for all the responses. So there are many options to address this problem.

Walking around the room, the bass is more resonant in the corners and near the back wall. I listen above 3 feet from the back wall and even there is audible.

My personal conclusion: this is a room, not a speaker problem. There is nothing wrong with the speakers per say. Second, I have not had good success with DSP as it changes the FR but also degrades the sound quality. Third reducing sound at 40Hz does not address the problem. Sure the hump is gone but I think I would loose bass quality as what is left is still a resonance and not music.

So looking into it as a room problem, I tried moving the speakers around and nothing helped. If there is some magic spot, I could not find it.

- One foot front the front wall.

- Middle (7 feet out) of the room.

- Speakers 5 feet apart up to 10 feet apart.

If you want to test your system, I play Madonna’s " I don’t search I find". When she drops that depth charge at 0:46 my room goes kaboom.

I heard back from GK Acoustics and they say "you’ll need a decent amount of coverage all over the surfaces of your room" with 10.5-17" thick panels to get any decent attenuation.

So it looks like Atmasphere’s "Distributed Bass Array’ is only viable solution.

Second, I have not had good success with DSP as it changes the FR but also degrades the sound quality.  Third reducing sound at 40Hz does not address the problem. Sure the hump is gone but I think I would loose bass quality as what is left is still a resonance and not music.

What did you use for DSP?

Your concern about hearing resonance rather than music can be addressed by a combination of HP filter and sub. By reducing the energy below 60hz in your mains and REPLACING it with a sub with DSP that you can move around, you would have some control over the low end. The SVS subs have great DSP software that can tailor the FR precisely in the low end without affecting the overall SQ of your mains.