Bass cancellation around 42-44 Hz

[pickindoug]

Hoping to get feedback from the voices of experience in the group. Room dimensions are attached. It is a basement room with vinyl over concrete. There is a 9' high drop ceiling with good quality 2 x 2 acoustic tiles, a sofa at the X listening position, a love seat along the wall with the dog leg, and the gap marked open does not have a closeable door. There are 6 other doorways throughout the room, but all have doors, so these measurements were taken doors closed. Attached are REW averages taken with both speakers in various positions, all somewhat along golden triangle dimensions, using two different speaker systems. The common denominator of cancellation in the low-mid 40 Hz range suggests a room mode, and wavelength math seems to . Due to doorways and general layout needs, the system is where is needs to be, and from a subjective perspective, sounds very good with excellent imaging and soundstage. If this were your room, how would you treat it?

 

[Sonnie]

Is this for movies, music, both... and will you do serious music listening? If serious music listening... forgo the various positions and stick with the main listening position and focus solely on those measurements. If it were my room, that's what I'd do.

This really just looks like lack of sub-bass, which is common for main speakers that typically have to be pulled out from the wall a bit to get the best sound stage, imaging and even more so depth acuity. I would pull the speakers out farther from the front wall... and add a couple of subs. If it were my room, that's what I'd do.

Unfortunately there are any acoustic panels that will do much for your bass below 100Hz... but some good 2ft x 4ft x 4in panels can get rid of slap echo, etc. Pulling those speakers out will help eliminate some of the need for treating wall reflections.

 

[Sonnie]

Another idea is use the 20ft as width, 22ft as depth and wall off that dog leg area, put your equipment wall there with access to it from behind. Not what I'd do, but an idea.

 

[pickindoug]

Sonnie, I appreciate your input. All measurements were taken at the listening position. The equipment wall is one of the "monuments" that can't be changed, nor can I block off the smaller portion of the room in an effective way. There is a TV in the middle of the wall over the equipment rack that is used occasionally, but it's not intended to be an AV setup. I moved the speakers quite a bit to arrive at the averages shown, generally within Golden Ratio dimensions, as much as 3' off the back wall and 6' off the side walls. The Thiels respond down to the mid 20s, and the Maggies probably check out down to the mode near 40. What I can do with the room is use furniture, i.e. tall shelving units, as a way to break up the mode a bit, if that's even possible. Wall mount acoustic panels might work as well. Using the adjacent rooms as Helmholtz resonators crossed my mind, but I didn't get much change to the response curves with doors open or closed. As of interest, this is a much better room than I had in my last house, where merely standing up changed the perceived level of bass in the room.

 

[Mike-48]

A couple of things. First, the bass. I had a similar problem in my listening room -- similar in frequency, but worse in amplitude and width. A pair of subs, properly placed, now fill in the 40 Hz area nicely. I had to try many spots for them to find the one that did the job.

I looked into tuned absorption traps, but in my much smaller room, I would have needed too many to do that job, and at 40Hz, they are almost a foot thick -- rather ungainly. As to acoustics in general, one can hardly have too much bass trapping, and a combination of diffusion and absorption sufficient to kill all slap echo will work wonders for general clarity.

You didn't ask, but I'd like to mention the midrange. The top graph shows a depression of ~6 dB between about 600 Hz and 2500 Hz. That might be perceived as a lack of body or presence. I wonder if you are thinking of filling that in a little with DSP, or perhaps adjusting the toe-in of the speakers to see if you can flatten that area out a bit?

 

[pickindoug]

Mike-48, appreciate your thoughts. I don't have issues with slap echo thanks to the area rug and the acoustic ceiling tiles. I have played bass guitar for many years, and am typically critical of systems that don't provide well defined bass. Oddly enough, with 42-43Hz falling in the lower end of the bass guitar range, I'm surprised I don't notice this absence as much as the charts indicate. Please note that the graphs were an average of several positions along the Golden Ratio path to ferret out what would be room issues vs speaker issues. The depressed mids on one set of speakers indicates that some crossover tweaks may need to be done, since the mids aren't original. On the other hand, those speakers go lower than the 1.6QR, thus the reason for having them in the measurements. The problem with using subs is that I rotate speaker systems frequently, plus have two different preamps, four amps, etc, that would make the changeover more tedious than a simple banana plug swap. I will try moving some of the larger pieces of furniture around to see if placement can help break up the mode.

 

[Mike-48]

Doug-

Because of the usual smoothing, it's hard to tell from your graphs if the dip about 42-43 Hz is a narrow or a wide one. I've been surprised by how relatively inconspicuous narrow dips can be. That seems to be the case in your situation, and it's a good thing for sure.

The problem with using subs is that I rotate speaker systems frequently, plus have two different preamps, four amps, etc, that would make the changeover more tedious than a simple banana plug swap.

I definitely get that! I tried to compare two power amps recently, and because I use subs, and the power amps' gains weren't the same, it became a logistical nightmare. Finally I gave up on any kind of formal comparison and just picked the one I thought was a little cleaner sounding. It was a nice dilemma to have, choosing between two really good amps.

If you find a way of killing the 42 Hz null, do let us know.

 

[pickindoug]

Mike-48,

Thanks for the thoughts. The null valley spans about 10 Hz peak to peak, which is a lot to lose in that Hz range. I'm really surprised I don't hear it with as much absence as the graph indicates. Probably should try the same mic / interface setup in another room to ensure it's not measurement system error. It's a Dayton mic with calibration chart loaded.

D

 

[Mike-48]

Doug, If the dip is less than about 1/3 octave, the ear is much less sensitive to it. It's surprising, but my experience has been, it's true (and a good thing for audiophiles).

 

[pickindoug]

Mike, that is good to know. Until I started measuring, I was convinced this was the best listening room I've ever had. And it still is, but it is amazing what small moves in speaker placement can do. Unfortunately, the null has so far been immune from placement.