125hz-134hz Null - Help please!

Hey everyone, It's been awhile since I've posted in here, but I moved into a new place and am looking for some guidance on room treatment and/or speaker placement. Room Dimensions: L: 17' / 518.2cm W: 13.75' / 419.1cm H: 8' / 243.8cm amroc: https://amcoustics.com/tools/amroc?l=51 ... .8&r60=0.2 Treatment: I have yet to fully build out the front and back wall, I'd like to figure out a plan of action so I don't build something that's useless or makes things worse. Front: 24" superchunks of RW safe n sound in corners, 9" RW safe n sound 4'x8' with 1/8' hardboard facing listening position. Sides: 6" OC703 2'x8', QRD-11 diffuser, 4" OC703 2'x8' Back: 12" deep membranes in corners (2" OC703 > 2"RW60 > 1.5" Air > 4" OC703 > 2.5" Air > Rigid Back. Sealed.), QRD-11 diffuser, 12" deep membrane (0.5lb MLV > 4" Air > 4" RW60 > 4" Air > Rigid Back. Sealed.) Ceiling: 6" OC703 4'x8' cloud between speakers and listening position, 6" OC703 2'x6' 3/4 from front wall. Speaker Placement: Speakers are Barefoot MM27 with -2db on the subs. I've tried a few placements #1. Speakers against the front wall - 40hz and below spikes, 125hz null still exists #2. Speakers 30" from front wall - 40hz and below is more balanced, 125hz null still exists #3. Speakers 48" from front wall - all bass is a mess, tons of nulls, 125 null still exists #4. Speakers 16" from front wall - 40hz and below is balanced, 125hz null improved about 5db. I tried lowering speaker height from 48" to 45" to see if it was ceiling/floor bounce. I also tried putting treatment in between the listening position and the speaker to see if it was floor bounce, it improved the null by about 3db. I ran a 125hz sine wave and went around the room with an SPL meter, there are no reasonable listening areas where it's improved, only spikes in the modal areas such as side walls and 2-side corners. Questions: - Is it a collection of room modes causing my issue? - What treatment will fix the 125hz null? - Any other general recommendations on improving my room? Budget & Goal Everything I've built thus far is extremely modular, I'm open to moving anything around, adding/changing/removing treatment I've already built. I'm open to building hangers, membranes, slat resonators, VPRs, and more permanent structures as well. Budget $2-$3k. Goal: +/- 5db Link to .mdat file: https://www.dropbox.com/s/5mch5gutii5t2 ... .mdat?dl=0 Let me know what you guys think and what questions you have. Thank you!

Carl Tatz discusses 125 nulls on a podcast or youtube video. Says that ALL speakers "on stands" have this. I believe he was blaming stands. I believe he uses 2 front corner subs timed to remove this. I apologize I do not have the details.

maybe Carl is assuming that everyone has 125hz nulls because all stands and rooms have the same dimensions and positioning? i think we're way past that in terms of knowledge. of course rooms can have similar issues - many rooms are a "standard" height (96" in US, 2400mm elsewhere) and most (fixed) stands likely place the speaker at a "standard" height, etc. but then speaker positions, SBIR, subwoofer placement, listening position, room mode excitation levels, tangential and oblique modes creeping in, and more etc all determine the response. as a note: i've not seen where adding more corner traps (even the cheap ones) has done anything other than improve a room, if someone has seen a room with corner absorption causing a problem, it would be interesting to study. simply adding a pair of subwoofers is not always a proper answer - so best to work within the room you are working in...

Yes, not really looking for active solutions. I'm not sure what the AVAA's could do for me, but not prepared to spend $5k+. I'm wondering if slot resonators on the front and side walls with alternating slot widths to be effective between 100-200hz could be a good option?

the resonators could do the job, however, for 100-200 plain old absorption (POA) should work, and then adding some scattering/diffusing/etc on top of the absorbers to balance HF reflections can be aesthetically correct.

9" RW safe n sound 4'x8' with 1/8' hardboard facing listening position.

Interesting, and something I would sometimes encourage based on a great absorption boost found by a pal Jeff Hedback. His frontage was pegboard, maybe more compliant? But your narrow room is killing you. So I would be very curious to measure the response with these reversed. I am also curious about that alcove. The big area of glass is a kind of resonant panel bass trap. It is also a large aberration in your Front Wall in terms of boosting all LF by 6dB. Perhaps it is a 125Hz 'Hole'

gullfo wrote:

the resonators could do the job, however, for 100-200 plain old absorption (POA) should work, and then adding some scattering/diffusing/etc on top of the absorbers to balance HF reflections can be aesthetically correct.

I tried 4" of 703 and 4" of Isobond 035 covering the entire front window/wall with zero improvement to the null. Not sure if more layers or more absorption on other walls would help? When I had the RW safe n sound with the absorption facing, 200-1khz was about 5db lower than everything else.

DanDan wrote:

9" RW safe n sound 4'x8' with 1/8' hardboard facing listening position.

Interesting, and something I would sometimes encourage based on a great absorption boost found by a pal Jeff Hedback. His frontage was pegboard, maybe more compliant? But your narrow room is killing you. So I would be very curious to measure the response with these reversed. I am also curious about that alcove. The big area of glass is a kind of resonant panel bass trap. It is also a large aberration in your Front Wall in terms of boosting all LF by 6dB. Perhaps it is a 125Hz 'Hole'

At the time, it seemed to balance the midrange out more, but that was with a different speaker placement. I tried removing that treatment from the corners completely and the 125hz null was still apparent, but I should try with the treatment reversed to see what it looks like. I'll run some new tests and post them here. Agreed, maybe that window is really causing all of the issues. Here are the old speaker placement test, speakers up against the front wall, with the treatment reversed RW safe n sound facing: https://www.dropbox.com/s/x4coh8uuhpal6 ... .mdat?dl=0

one thought - the omni mic should be vertical... a "null" cannot be treated. there is nothing there. :-) a simple test would be to turn on the REW generator @ 125 hz and move around the room with the mic (and/or your ears) to fix the exact spot of the null (mark with tape, label altitude of ears/mic) and the spots without the null (mark those with tape and also the altitude notes). if you have the null forward and back of the listening position null, this could be the side walls or ceiling - the constant null along a center line would be indicative of this. changing altitude will determine if its the ceiling or side walls. if it does change then if could be the front or back walls if it's periodic intervals in spacing, or SBIR if its pretty much localized to the listening position.

gullfo wrote:

a "null" cannot be treated. there is nothing there. :-)

That's what I thought! But I wasn't sure. I thought treating the octaves below maybe would help, but even starting the test at 100hz still gets the same results.

gullfo wrote:

one thought - the omni mic should be vertical... a "null" cannot be treated. there is nothing there. :-) a simple test would be to turn on the REW generator @ 125 hz and move around the room with the mic (and/or your ears) to fix the exact spot of the null (mark with tape, label altitude of ears/mic) and the spots without the null (mark those with tape and also the altitude notes). if you have the null forward and back of the listening position null, this could be the side walls or ceiling - the constant null along a center line would be indicative of this. changing altitude will determine if its the ceiling or side walls. if it does change then if could be the front or back walls if it's periodic intervals in spacing, or SBIR if its pretty much localized to the listening position.

Alright, I set the mic vertical. I played 125hz and walked around the room at different heights. It was really hard to pinpoint the exact spot of the null, it sounds like it's 5' all around the listening position in all directions, standing, sitting and in between. The db meter changed only by 5db at most. Here are some tests of many different movements, starting with listening position, moving back, moving forward, then the same at 72" high. Then some tests with the mic near the left and right wall and rear wall: https://www.dropbox.com/s/cekcpn4xbnmvf ... .mdat?dl=0

so, by 5' do you mean the diameter of the circle around the listening position? or 5' in altitude around the room?

gullfo wrote:

so, by 5' do you mean the diameter of the circle around the listening position? or 5' in altitude around the room?

Sorry yes, 5’ diameter around the listening position.

and when you went closer to the back wall? same reading at listening height?

gullfo wrote:

and when you went closer to the back wall? same reading at listening height?

Correct, just slight changes in frequency. In the attached picture it starts with the listening position, test 2 moves back 6", then 12", and finally 18". All at listening height of 46". There's slight improvement in 12" and 18" placement, but then creates spikes around 28hz.

hmmm ok, but if you step outside of the 5' circle, say 2' off the back wall, same?

gullfo wrote:

hmmm ok, but if you step outside of the 5' circle, say 2' off the back wall, same?

Yes, 2' from back wall is where I had the mic for test #12 on the graph attached, the null widens to almost 250hz. Test #14 & 15 are left and right 6' of listening position, showing an improvement in the 125hz range.

the improvement moving to one side or another is likely the side wall mode given no change in response with an altitude change. doesn't mean there is no SBIR (which is proven when you move the monitor positions around, like up again the wall left-right, etc) etc but i'd look into more modal response from the sides. you might not change it for the entire room easily (cheaply?) but at the listening position, you may need some pressure or resonant traps to shift that. one test is if you have 4" (or thicker) absorbers) which you can move out from the wall about 3"-4" (75mm-100mm) and see if you have a shift. it should be minimal but there.

Thanks for your help Glenn. I tried the 4" panels on the sides away from the wall, but couldn't see a change, or hear a change. I'm going to build out some slot resonators for the for the sides and see if there's some improvement. I feel like even after the side treatment, the speakers will need to be pushed to the front wall completely. Then I'll be left with bulking up the low end treatment. Really wish I could just get some different speakers and soffit mount them.. sometime in the future.

Pink Noise PN Spectrum Zoom to the area of interest. You will have to play with it hoping to get a stable image. Move the mic inquisitively. I would start by moving it towards a spot on the floor half way between LP and speaker line. Let's see if the frequency of the null changes.

DanDan wrote:

Pink Noise PN Spectrum Zoom to the area of interest. You will have to play with it hoping to get a stable image. Move the mic inquisitively. I would start by moving it towards a spot on the floor half way between LP and speaker line. Let's see if the frequency of the null changes.

For some reason my Noise test in greyed out in the measure tool on REW. I ran some standard sweeps instead, moving from Listening Position towards speaker in 6" increments: The current speaker position is right up against the front wall. https://www.dropbox.com/s/wtsnn7gds89av ... .mdat?dl=0

hmmmm... 21 126.6 Hz B2 2-2-1 obl 22 127.15 Hz C3 1-3-0 tan 23 128.38 Hz C3 3-1-1 obl 24 128.68 Hz C3 3-2-0 tan there are 4 modes within 2hz. and the bonello distribution is not a good one. i was originally thinking maybe something in the 65-67hz range was actually the main culprit.. 4 66.2 Hz C2 2-0-0 ax but it might be the main one still @ 33hz 1 33.1 Hz C1 1-0-0 ax the Barefoot monitors are pretty good down to that range. if you run the sweep from say 90hz and up are you getting the same result? just trying to determine if this is due to a LF excitation (possibly something resonating) or these modes are truly and fully excited at those frequencies.

gullfo wrote:

hmmmm... 21 126.6 Hz B2 2-2-1 obl 22 127.15 Hz C3 1-3-0 tan 23 128.38 Hz C3 3-1-1 obl 24 128.68 Hz C3 3-2-0 tan there are 4 modes within 2hz. and the bonello distribution is not a good one. i was originally thinking maybe something in the 65-67hz range was actually the main culprit.. 4 66.2 Hz C2 2-0-0 ax but it might be the main one still @ 33hz 1 33.1 Hz C1 1-0-0 ax the Barefoot monitors are pretty good down to that range. if you run the sweep from say 90hz and up are you getting the same result? just trying to determine if this is due to a LF excitation (possibly something resonating) or these modes are truly and fully excited at those frequencies.

I thought the same thing, but I ran some tests previously starting at 100hz and I still have the same null.

just a quick question then - since i must confess to not having read every post on this - are you doing this test with a single speaker at a time? and did you run a full room test - one speaker in lower front corner, omni mic up in far opposite corner, then swap corners?

gullfo wrote:

just a quick question then - since i must confess to not having read every post on this - are you doing this test with a single speaker at a time? and did you run a full room test - one speaker in lower front corner, omni mic up in far opposite corner, then swap corners?

Yes, I'm running a single speaker at a time, both L and R are showing the same nulls. I have not run a full room test as you've mentioned... I'm assuming I would do so in an empty room without treatment?

ideally the full room without treatments but it depends on how hard it would be to move them out for the testing.