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Bass arriving out of phase at the listening position

Axo1989

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The mass-concrete pillar behind the left speaker and the closet beside the right speaker present different geometries and reflectivity. If you can manage it, I suggest rotating the room configuration 180º so your main speakers are against the flat wall (which is the back wall currently).

After that, in my experience those deep FR dips around/below 100 Hz are likely confluence of lateral, tangential and/or oblique room modes at the problem frequencies. Try moving the speakers laterally (from a narrow starting position, then stepping toward the side walls say 200 mm (8") increments or similar, measuring FR at LP after each step to see how those nulls behave. I've been able to significantly mitigate similar issues that way. Your room is small, and you still have the asymmetric entry nook, but hopefully you'll have more scope/consistency doing this against the flat wall than the current front wall which has more asymmetries and obstructions.

Edit: looks like @Chromatischism was on to this already
 
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NTK

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Here are the simulation results with @edechamps' room dimensions.

Room modes.
room_modes.png

In room frequency response. The horizontal plane show the response at the ear height.
30-80_hz.gif82-132_hz.gif134-180_hz.gif
 

Rescue911

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Nearfield monitors are usually located at a distance of up to 1.5 meters from the listener, in ideal conditions it is 70-90 cm. At the same time, they should be turned by the speakers towards the listener and form an equilateral triangle with it.
In addition, the monitors must be on the same plane as the ears.
IMHO, your ears are too far away from the monitors.
Move the table forward.
And, more - be prepared that your huge display will be a problem.
Good luck.
PS Having rear monitors isn't always a good thing.
 

kongwee

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Same, you have to listen to them nears-field. If you can find a smaller desk will help too.
 

Thomas_A

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I would turn the room the other way. Better sound, better feng shui. :)
 

pierre

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I currently use Mathematica, and have a couple of threads on the methods.

Doing it in Mathematica is quite troublesome IMHO. It isn't easy/convenient to define the geometry and to plot the results. I use it more for prototyping and for my own fun and learning purposes. I have been looking into other open source and free tools, and think a combination of OpenSCAD (for building the 3D room model), GMSH (for mesh generation), FEniCS (for the numerical problem solving), and ParaView (for visualization) may do the job. The project will take a fair amount of time and effort, and I am hoping in the end we may be able to come up with a container that is usable by other "enthusiasts".
We should talk (@NTK). I use GMSH and FeniCS/Firedrake/PETSc to solve the Helmotz equation. Example: horn2.py
Original idea was to compute the optimal shape of a waveguide to get smoother directivity. I built the possible shape of the waveguide as a spline with few parameters.
Gradients are computed with JAX or hand made. I have a 2D working version somewhere but stopped before I went 3D. I would need to optimise the Helmotz solver by
doing something similar to what Mathematica does or maybe simply interpolating between frequencies. Clearly GMRES converge much faster for freqency F when the starting point is the previous solution at frequency F2 ~ F.

Project is stalled by lack of time.
 
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edechamps

edechamps

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Here are the simulation results with @edechamps' room dimensions.

Room modes.
View attachment 231881

In room frequency response. The horizontal plane show the response at the ear height.
View attachment 231882View attachment 231883View attachment 231884

Thanks @NTK! I can see that the response becomes a nullfest at the listening position around 80-100 Hz :(

I note that you decided to treat the wardrobe next to the entrance as a wall, instead of a recess. Not sure that makes sense physically. The wardrobe is one of these objects that seem "acoustically suspicious" to me standing in the room. Especially given that if I touch the wardrobe doors while a 86 Hz tone is playing I can feel them vibrating with my bare hands.

I think my next steps will be to dig into the measurements some more (especially things like step response, excess group delay) and try to use @NTK's tools to reproduce his simulation so that I can then play with the simulated space (e.g. rotating the system, adding tuned bass absorbers, adding subs). Having a simulation at hand makes it possible to at least check if a potential solution could possibly work before going through the hassle and expense of actually trying it.
 

hmt

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Maybe you could also measure the response in the recess to see what's going on there. I think the best chance to solve this would be like two small closed Subs and your Mains playing low frequencies, optimized by MSO. So you would have multiple sources of bass in the room.

Edit: Instead of rotating the system you could also try to measure your surrounds L and R. When they show the same issue you don't even have to think about it.

Edit2: I see BL and BR already look good at least on your listening position now. Maybe you can try to measure this at with the mic where you MLP would be when listen rotated.
 
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SoundGuy

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Obviously it is the region your subwoofer and speakers share some output. Subwoofer is out of phase.

Since the subwoofer is about 1.5 meters from your right speaker horizontally and 1.5 meters below your left speaker then the out of phase behaviour alternates between left and right speaker between 60hz (6 meter wavelength) and 120Hz (3 meter), and above that it isn’t present because only speakers are contributing.

Note that I use rounded numbers for wavelength so it is easier for you to understand. Your frequency problems will be related to the phase shift caused by 1.5 meters distance and this will obviously cause cancellation or in phase response at the listening position with either speaker depending on the frequency.

If you switch subwoofer phase then you will still have issues related to the length of about 1.5 meters difference in distance to right speaker. This will cause problems but less so than being completely out of phase with both speakers.

If you wish to keep everything in as much phase as possible then you need to position the subwoofer between the two speakers.

If you want the smoothest in room response then place the subwoofer roughly 1/3 of the distance between your speakers. The idea being to have as much difference as possible in distances to surfaces so boundary reinforcement does not all line up.
 
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JohnPM

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My point was that asymmetric absorbtion coefficient does not affect FR [in this model]. Here is the reference with left 0.00 right 0.90:
I guess I'm not properly understanding your expectations, but probably not a topic for this thread.

1663583262611.png
 
OP
edechamps

edechamps

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Obviously it is the region your subwoofer and speakers share some output. Subwoofer is out of phase.

The subwoofer is not used in any of the measurements I shared in this thread. All measurements are raw main speaker measurements with no bass management nor filtering of any kind.
 

SoundGuy

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The subwoofer is not used in any of the measurements I shared in this thread. All measurements are raw main speaker measurements with no bass management nor filtering of any kind.
In that case the port tube on one speaker is loose/disconnected/blocked. Open up your speakers. A port will operate in this range also.

As general observation - the closet will resonate and your seated position is far to close to a wall. In a room this size you must position diagonally for best sound - so that the listener is not close to a wall.
 
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edechamps

edechamps

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In that case the port tube on one speaker is loose/disconnected/blocked. Open up your speakers. A port will operate in this range also.

The ports aren't blocked. (I think I already tried blocking ports some time ago and concluded it made no difference, but I guess I could check again.)

This is not a speaker defect. I already tried swapping both speakers for another pair and it made exactly zero difference.
 

Thomas_A

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As noted I would swap position. Pad the wall behind the spealers with damping panels and add reflective things on wall behind you. Speaker front/drivers in same line as TV front. Push the llistening position and desk somewhat nearer back wall, avoiding desk reflection to ear level and blocking floor reflection.
 
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