My dedicated audio room build - QuadDiffusor's Big Dig

[QuadDiffuser]

I will need to re-examine the propagation of excitation/vibrational energy from the front plate to better understand how it dissipates maximally, and iterate/improve the design accordingly. Ideally, the front plate needs to be able to reach maximum excitation without any hinderance, and all of the energy to dissipate through the glued foam backing.

Yet, the whole apparatus (30-40kg in weight) needs to somehow be mounted sturdily without the risk of collapse. I don't think it would be viable to just glue the foam to the gypsum wall, as the load will rip the foam into pieces in two seconds flat.

Should I minimize the mass/length of the horizontal section by cutting out everything except two small tabs which connect the resilient mounting brackets to the plate? The front metal plate would become "free" and unhindered to resonate more freely, unimpeded by the curved horizontal section which runs through the entire length/width to stiffen the front plate?

Yes, they will be tested progressively as they're added to the room's walls.

BTW, I don't think it's possible to over-absorb bass energy, because even this sort of heroic treatment will only selectively reduce the bass frequencies/pressure very slightly, perhaps just 3-5dB. The demons and gorillas we call room nodes will need to be tamed through other additional means through active bass cancellation devices such as room-node-cancellation subwoofers and PSI Audio AVAAs.

 

[pjwd]

Yes, I need to re-examine the propagation of excitation/vibrational energy from the front plate, and how it dissipates. Ideally, the front plate needs to be able to reach maximum excitation without any hinderance, and all of the energy to dissipate through the glued foam backing.

Yet, the whole apparatus (30-40kg in weight) needs to somehow be mounted sturdily without the risk of collapse.

Should I minimize the mass/length of the horizontal section by cutting out everything except two small tabs which connect the resilient mounting brackets to the plate? The front metal plate would become "free" and unhindered to resonate more freely, unimpeded by the curved horizontal section which runs through the entire length/width to stiffen the front plate?

That would make the plate less stiff but it is pretty thick by the look of it .. obviously targeting low fr .. so my guess us it would not engage with foam "spring" as much as you might want .. ideally you would have a secondary frame.
If you could do a hanger behind panel with a bracket top and bottom to make a U bracket and notch out the bottom flange so the foam is supporting it .. might need to be wide depending on strength of foam ..that would decouple it
Just a thought
I agree you generally can't have too much bass trap in such a solid room but these are beasts

 

[Kingrex]

I find it interesting you say you can't have too much bass absorption. You go on to mention modes in the room. I was arguing with somebody on another thread that I didn't hear modes in my space. Yet a few days later, I was playing the stereo, quite loud and sure enough, I heard the modes.

I use a very different subwoofer than most everybody. Mine is a horn sub that is intentionally placed in the corner and uses the room as part of the the speaker. I am thinking of getting a second one. If only to control reflected bass in the room. I have 3 other corners to try it in.

But anyway, my point or question, is a concern over too much damping. I've always feared the idea of building in absorption traps that would be difficult to remove. What if they did suck something out at a frequency I didn't want them at. Do you have any concerns as such?

 

[QuadDiffuser]

Hi Kingrex,

As you know well already, the physics of mid/high frequencies differs significantly from bass frequencies, which in a typical listening room are shaped through very large boundaries such as floors, ceilings, and walls, and tamed through equally deep, heavy and large acoustic treatment devices. Hence horn subs in your case to leverage room corners to launch bass waves which have a better chance of amplitude and phase linearity without being repeatedly flipped 180* out of phase at each encounter with a parallel boundary surface works well, given room constraints.

Dennis Foley of Acoustic Fields emphasizes that bass frequencies require a vastly different treatment than mids/highs, citing the threshold frequency of ~120Hz, where wavelengths are 10ft and lengthen progressively below this to ~30 feet at 40Hz.

The following YouTube video explains how every dip and peak in room nodes are mutually reinforcing, hence flattening the peaks will help "fill the voids" in room node cancellations.

My belief is that room mode cancellations are impossible to linearize, and that flattening the peaks will only help to reduce the magnitude and standard deviation of the deltas between the peaks and troughs. However, when viewed in 3D, this benefit is profound, as smoothing out peaks and dips in all locations in the room is the Holy Grail to achieving great overall bass reproduction.

 

[Kingrex]

I think I get what hes saying. Not sure I totally agree. Its complex.

 

[pjwd]

I think I get what hes saying. Not sure I totally agree. Its complex.

The main benifit of bass absorbtion in a listening room is reducing reverberation time and in a room like QD's that is very solid construction the bass energy hangs around for a long time and the problem is absorbing that energy .. you want to hear the reverbarent space of the recording .. not your room. Whereas a concert hall might be 1.5 to 2 seconds you only want 0.4 seconds or so .. that takes a lot of absorbtion which is why it almost impossible to overdamp a room below say 125hz
A room of standard sheet rock construction with glass windows etc will be very lossy in the bass so less bass absorbtion may be needed .
As QD says the room modes are always there you just have to locate speakers and chair in the least worst spots
Bass absorbtion will reduce the magnitude of nulls and peaks
The principals are not complex but the many possible solutions and the tradeoffs involved are!

 

[QuadDiffuser]

That would make the plate less stiff but it is pretty thick by the look of it .. obviously targeting low fr .. so my guess us it would not engage with foam "spring" as much as you might want .. ideally you would have a secondary frame.
If you could do a hanger behind panel with a bracket top and bottom to make a U bracket and notch out the bottom flange so the foam is supporting it .. might need to be wide depending on strength of foam ..that would decouple it
Just a thought
I agree you generally can't have too much bass trap in such a solid room but these are beastsView attachment 156204

After further examinations and deliberations, these two prototype 1.5mm and 3.0mm steel plates will be modified in the following manner:

1) steel on the horizontal sections (both top and bottom) - keeping only what's essential for the resilient mounting brackets (about 20%), and removing the rest (about 80%) for freer vibrational movement
2) mounting bracket - to be shortened, eliminating the air gap
3) abundant application of 3M spray glue, to bond Basotech foam directly to the underside of the steel plates
4) direct contact between the Basotech foam and the gypsum wall
5) for vertically mounted units, potentially use only one mounting bracket on top (instead of two) to maximize vibrational freedom

 

[QuadDiffuser]

Self-leveling screeding has been applied to the entire floor (to both front and back sections of the independently dampened and isolated floating floors).

 

[MarkusBarkus]

...I'm not sure I exactly understood pjwd's sketch, so you may be past this thinking already: it is possible to mount the steel using a grommet concept, which would allow the plates to float to a greater extent than a rigid attachment.

The floating aspect of the plates/mounts is difficult, isn't it? I did a mass loaded vinyl "super-chunk" in a corner here to experiment.

I stacked several layers of two-inch rigid fiberglass, glued together with that 3M spray-glue, all cut into an equilateral triangle, to fit into the corner.

I attached the heavy vinyl to a piece of wood trim to hang in front of the vertical face of the stacked fiberglass "board." In this way, the MLV moves freely in the plane most of the wave energy reaches it.

I really like the steel version of this concept, QD, but it was too complicated to integrate into my existing room. Yours looks very "trick."

Not everyone agrees, but in my research, and thinking about things, I thought I could use as much bass "trapping" as I could muster. It doesn't deaden the room at all.

Aside from the obvious panels one can see, I have stuff hidden all over. Behind the bar. Inside a platform that supports TV gear. Behind the sofa. And inside the walls.

Thanks, as ever, for posting and sharing your project!

 

[Kingrex]

The main benifit of bass absorbtion in a listening room is reducing reverberation time and in a room like QD's that is very solid construction the bass energy hangs around for a long time and the problem is absorbing that energy .. you want to hear the reverbarent space of the recording .. not your room. Whereas a concert hall might be 1.5 to 2 seconds you only want 0.4 seconds or so .. that takes a lot of absorbtion which is why it almost impossible to overdamp a room below say 125hz
A room of standard sheet rock construction with glass windows etc will be very lossy in the bass so less bass absorbtion may be needed .
As QD says the room modes are always there you just have to locate speakers and chair in the least worst spots
Bass absorbtion will reduce the magnitude of nulls and peaks
The principals are not complex but the many possible solutions and the tradeoffs involved are!

I get that. I don't get how to target 125 hertz and down. Without affecting higher frequency. And is there a way to do it where your considering the gain. I just added a sub to fill in energy from 45 to 90 hertz. Not take it away. Although when I play the music very loud, I do then hear a bass mode. If my traps ate all the 125 and below when playing at say 80 db and below, my stereo would sound very thin. When say 61 hertz jumps up and reverberates back at my chair at 85db, how do you only address that frequency at that volume? That is my concern.

 

[Kingrex]

After further examinations and deliberations, these two prototype 1.5mm and 3.0mm steel plates will be modified in the following manner:

1) steel on the horizontal sections (both top and bottom) - keeping only what's essential for the resilient mounting brackets (about 20%), and removing the rest (about 80%) for freer vibrational movement
2) mounting bracket - to be shortened, eliminating the air gap
3) abundant application of 3M spray glue, to bond Basotech foam directly to the underside of the steel plates
4) direct contact between the Basotech foam and the gypsum wall
5) for vertically mounted units, potentially use only one mounting bracket on top (instead of two) to maximize vibrational freedom

Are you desiging bass traps that are free floating, so to speak. As in you could remove them or add more or move them around as needed? That is an excellent design in my perception.

 

[Kingrex]

Self-leveling screeding has been applied to the entire floor (to both front and back sections of the independently dampened and isolated floating floors).

View attachment 156349

Nice steel in the ceiling for cloud supports.

 

[pjwd]

I get that. I don't get how to target 125 hertz and down. Without affecting higher frequency. And is there a way to do it where your considering the gain. I just added a sub to fill in energy from 45 to 90 hertz. Not take it away. Although when I play the music very loud, I do then hear a bass mode. If my traps ate all the 125 and below when playing at say 80 db and below, my stereo would sound very thin. When say 61 hertz jumps up and reverberates back at my chair at 85db, how do you only address that frequency at that volume? That is my concern.

I don't believe you can change those modes other than by moving chair and speakers... what bass traps do is reduce the time they bounce around which reinforces peaks and nulls. Bass traps don't reduce spl dramatically so they won't make your sound thin.. unless your room already allows a lot of bass energy to escape via lightweight construction , windows, doors etc.
I know the idea of absorbing bass to improve bass is counter intuitive but it happens
Most traps have good info about the range they cover

 

[MarkusBarkus]

...really no "trapping" those low-low waves, just changing their timing a bit, as you noted @pjwd . I think the name "trap" is misleading to folks. Best...

 

[microstrip]

Hi Kingrex,

As you know well already, the physics of mid/high frequencies differs significantly from bass frequencies, which in a typical listening room are shaped through very large boundaries such as floors, ceilings, and walls, and tamed through equally deep, heavy and large acoustic treatment devices.

Sorry, the "physics" are the same for any frequency. Surely wavelengths are different and boundaries react differently depending on wavelength. The same boundary can absorb some frequencies and absorb others.

(...) My belief is that room mode cancellations are impossible to linearize, and that flattening the peaks will only help to reduce the magnitude and standard deviation of the deltas between the peaks and troughs. However, when viewed in 3D, this benefit is profound, as smoothing out peaks and dips in all locations in the room is the Holy Grail to achieving great overall bass reproduction. (...)

Bass dips are due to reflection the back wave that sums in anti phase at the listening point. If we absorb the backwave and it is not reflected the dip can be cancelled - I managed to do it in my 30 feet long room with giant bass traps tuned to the dip frequency. Extremely rigid walls are more susceptible of creating bass dips. In fact, sometimes absorbing bass increases bass.

 

[pjwd]

Sorry, the "physics" are the same for any frequency. Surely wavelengths are different and boundaries react differently depending on wavelength. The same boundary can absorb some frequencies and absorb others.



Bass dips are due to reflection the back wave that sums in anti phase at the listening point. If we absorb the backwave and it is not reflected the dip can be cancelled - I managed to do it in my 30 feet long room with giant bass traps tuned to the dip frequency. Extremely rigid walls are more susceptible of creating bass dips. In fact, sometimes absorbing bass increases bass.

Bass is omnidirectional so all reflections (ncluding diagonal) can create peaks and dips various locations .. I assume you have identified the primary dip at your listening spot and dealt with it ( presumably quarter wavelength from speaker to wall)
What kind of bass trap have you used to get that precision

 

[microstrip]

Bass is omnidirectional so all reflections (ncluding diagonal) can create peaks and dips various locations .. I assume you have identified the primary dip at your listening spot and dealt with it ( presumably quarter wavelength from speaker to wall)
What kind of bass trap have you used to get that precision

Yes - I measured the room and built four very large membrane bass trap tuned to it. It was easy to confirm dips due to cancellation increasing level during measurements.

It was something similar to what I had built before - see https://www.whatsbestforum.com/threads/diaphragmatic-versus-membrane-bass-traps.7710/post-133862

We must be careful building them - I remember that there is an error in the formula shown in the "Master Handbook of Acoustics" that propagated in the net.

 

[pjwd]

Yes - I measured the room and built four very large membrane bass trap tuned to it. It was easy to confirm dips due to cancellation increasing level during measurements.

It was something similar to what I had built before - see https://www.whatsbestforum.com/threads/diaphragmatic-versus-membrane-bass-traps.7710/post-133862

We must be careful building them - I remember that there is an error in the formula shown in the "Master Handbook of Acoustics" that propagated in the net.

Are your speakers about 2.3m from wall ?

 

[Paul1960]

Self-leveling screeding has been applied to the entire floor (to both front and back sections of the independently dampened and isolated floating floors).

View attachment 156349

How reverberant is your room without anything in it? I visited a dedicated room build today that had just finished the sheetrock and I was surprised at just how much echo there was in the bare room.

 

[microstrip]

Are your speakers about 2.3m from wall ?

It was my previous room - I am not sure of the exact distance, but yes something like 2,2m. I put the speakers at such distance because the room was symmetrically wider at such location.