My dedicated audio room build - QuadDiffusor's Big Dig

[pjwd]

Recently, I discovered that the suspended floor (in the rear 2/3 of the room) is NOT for isolating ground-borne vibrations from the loudspeaker cabinets, but rather for controlling and suppressing room nodes.

Well, gosh, darn it, am I being bamboozled?

Who here on WBF has ever heard of a 1/4 ton slab (estimated weight) "screed and steel mesh bass absorber", floating on the ground under the listening sofa? What sort of air pressure can possibly resonate this slab, and what might its resonance frequency be?

My guess is that something so massive cannot possibly be energized even the slightest bit by room node air pressure generated by a pair of loudspeakers playing at even insane volumes, as its resonance frequency must be in the single-digit range.

Thoughts?

Quoting a section of my post #74 (above):
[THE FLOOR
Four meters will be allocated to the speaker area, equal to ~38% of the room length, and the remaining six meters will be allocated to the listening area. The two sections of the floor will be physically separated - constrained-layer dampened, decoupled, floated, and grounded - sandwiching dissimilar energy-absorbing materials.

The speaker-area floor will be constructed with the following, starting from the RC structural floor substrate:
- 4mm+ high-density recycled rubber granule underlayment for under-screed/floating floor constructions
- 90mm+ high-density screed, with BRC mesh in the center for mechanical integrity/strength
- high-durability leveling compound
- perimeter decoupled from adjacent structures via sponge rubber strips + caulking

The listening-area floor will be constructed with the following, starting from the RC structural floor substrate:
- high density foam isolation strips (tall, providing vertical clearance), covered with steel C-channel support
- 50% of the space will be filled with 100kg/m3 Rockwool insulation, 50% of the space left as an air gap
- structural steel decking (thin)
- 45mm+ high-density screed, with BRC mesh in the center
- high-durability leveling compound
- perimeter decoupled from adjacent structures via sponge rubber strips + caulking

The loudspeakers (and subwoofers) will have a more solid/stiffer floor foundation from which they will launch their acoustic energy, but energy propagating through the floor will decay rapidly before it reaches the listening area.]

QD I have only ever used such systems to prevent structure borne sound entering from outside or being transmitted to adjacent spaces.
I dont doubt that is possible to excite the floating slab with soundwaves as I have heard a band playing at about 90db through a 200mm concrete filled block wall .. the only way that is possible is by exciting the wall.. but if course that is a membrane supported around perimeter only .. not laying on a "spring" .
Having said that I dont think it is a very efficient way to absorb sound plus I expect it would be narrow band. Steel sheet fixed to springy foam would give a better result I would think. In your size room if you deal with reverb time are room modes a real problem.
At the risk of stating the obvious, you may want to preserve this system for under your speakers to limit structure borne sound entering your equipment ... obviously racks and footers are usually what perform this task
Did you ever nominate rhe membrane your were proposing under the slab

Phil

 

[QuadDiffuser]

@QuadDiffuser I do recall seeing plans/documentation regarding the isolation of a huge and elaborately engineered slab such as you describe. It was for a custom build. My take was it was to isolate and prevent outside vibration from entering the internal audio environment. I suppose it would impact vibrations generated by the audio system as well, but it does seem complicated. I am traveling, but will search my notes for the reference I noted above as post as possible. Cheers.

I'm inclined to believe that the heroically (over-) engineered floor isolation design currently proposed by my Acoustics Consultant will NOT be necessary in my basement listening room.

1) vibrations from outside (with no major roads in the vicinity) will be negligible as tons of compacted earth will surrounding three of the four walls (creates a tomb-like chamber which can't/won't be disturbed from the outside)
2) the basement floor slab will be buried ~4.5m below the ground
3) speaker cabinet vibrations will be isolated locally at the source, via decoupling bearings/dampening
4) airborne vibrations generated by the speaker into the room will be dissipated through wall treatments
5) airborne vibrations will be too feeble to excite a "floating" multi-ton slab of screed + metal mesh under the listening sofa

 

[pjwd]

I'm inclined to believe that heroically engineered floor isolation design currently proposed by my Acoustics Consultant won't be necessary in my basement listening room, as:

1) vibrations from outside will be negligible (tomb-like) as tons of compacted earth will surrounding three of the four walls
2) the basement floor slab will be buried ~4.5m below the ground
3) speaker cabinet vibrations will be isolated locally at the source, via decoupling bearings/dampening
4) airborne vibrations generated by the speaker into the room will be dissipated through wall treatments
5) airborne vibrations will be too feeble to excite a "floating" multi-ton slab of screed + metal mesh under the listening sofa

Agree
As I said above this would normally only be used for vibration control in or out of the space.
I presume you dont have a heavy trafficked road or subway nearby
Phil

 

[MarkusBarkus]

...and man, I looked everywhere I thought I had traversed in the past few years for that article, and zilch.

And I agree re: slab. If you aren't over Penn Station, probably overkill, or something that could be mitigated with some active vibration control on a piece-by-piece basis.

Seisemon seems to target these very low frequencies:

Seismion – Vibration Technology

seismion.com

Very cool project, @QuadDiffuser Hoping you will post some pics as time allows.

 

[QuadDiffuser]

Sharing some very basic screen-capture pics from a 3D rendering video of my elevator-equipped, and solar panel roofed, five-level future home. The 50+ year-old structure was demolished a few months ago, with ongoing sheet piling and column piling. Excavation will take place in coming months, and completion in 1Q-2025. Fingers crossed!

Basement:
1) dedicated two-channel audio room, and a home office/study under the (rear wall) pool protrusion
2) living room, with a LCD TV, generic home-theater audio system + storage
3) home office/study for my wife + storage

Ground floor:
1) dining room + breakfast bar/island
2) dry kitchen
3) helper's quarters + outdoor wet kitchen
*) lap pool + IR sauna + shower + powder room
*) parking for two cars + EV chargers

Mezzanine floor:
1) guest living room

Second floor:
1) guest bedroom #1 w/shower + washroom
2) guest bedroom #2 w/shower + washroom
3) activity room / gym

Top floor:
1) master bedroom, w/closets, washroom, and amenities

 

[MarkusBarkus]

...so glad my wife doesn't read WBF. Terrific concept. Nice of you to post, @QuadDiffuser Cheers...

 

[HughP3]

Sharing some very basic screen-capture pics from a 3D rendering video of my elevator-equipped, and solar panel roofed, five-level future home. The old structure was demolished a few months ago, with ongoing sheet piling and column piling. Excavation will take place in coming months, and completion in 1Q-2025. Fingers crossed!

Basement:
1) dedicated two-channel audio room, and a home office/study under the (rear wall) pool protrusion
2) living room, with a LCD TV, generic home-theater audio system + storage
3) home office/study for my wife + storage

Ground floor:
1) dining room
2) dry kitchen
3) helper's quarters + wet kitchen
*) lap pool
*) parking for two cars + EV chargers

Mezzanine floor:
1) guest living room

Second floor:
1) guest bedroom #1
2) guest bedroom #2
3) activity room / gym

Top floor:
1) master bedroom

View attachment 119018 View attachment 119019 View attachment 119020 View attachment 119021

Wow. Best wishes for the build…

 

[pjwd]

Sharing some very basic screen-capture pics from a 3D rendering video of my elevator-equipped, and solar panel roofed, five-level future home. The old structure was demolished a few months ago, with ongoing sheet piling and column piling. Excavation will take place in coming months, and completion in 1Q-2025. Fingers crossed!

Basement:
1) dedicated two-channel audio room, and a home office/study under the (rear wall) pool protrusion
2) living room, with a LCD TV, generic home-theater audio system + storage
3) home office/study for my wife + storage

Ground floor:
1) dining room
2) dry kitchen
3) helper's quarters + wet kitchen
*) lap pool
*) parking for two cars + EV chargers

Mezzanine floor:
1) guest living room

Second floor:
1) guest bedroom #1
2) guest bedroom #2
3) activity room / gym

Top floor:
1) master bedroom

View attachment 119018 View attachment 119019 View attachment 119020 View attachment 119021

That is one serious project .. if your into the excavation your 90% complete
Best of luck

 

[QuadDiffuser]

MID-to-HIGH Frequencies: front wall, sidewalls, and ceiling

The front wall will be covered with P23 QRDs, which will randomize and horizontally diffuse/disperse frequencies between 185 Hz - 3,400Hz.

The ceiling will have a sub-structure built as a canopy, in which diffusers can be inserted in a grid-like fashion. I'm considering these 2D diffusers from RPG. Any suggestions from WBF members who are familiar with ceiling treatments, and these products?

Some bass absorption, with decent diffusion and scattering in the mid/upper frequencies:

https://www.rpgacoustic.com/wp-content/uploads/2022/07/Harmonix-T-Data-Sheet.pdf

More overall diffusion and scattering in the mid/upper frequencies:

https://www.rpgacoustic.com/wp-content/uploads/2022/06/Omniffusor-W84-Data-Sheet.pdf

Even more diffusion and scattering in the mid/upper frequencies, due to its deeper cavities:

https://www.rpgacoustic.com/wp-content/uploads/2023/10/Omniffusor-W76-Data-Sheet.pdf

The two side walls will be covered with P17 QRDs right up to (but short of) the first reflection point, randomizing and horizontally diffusing frequencies between 225Hz - 3,400Hz. Four 0.94m wide units placed side-by-side equates to 3.76m in total, and this width inside a 9.8m long room seems about right. But if for whatever reason P-17 QRDs covering 100% of the sidewalls are undesirable, I'll be happy to reduce coverage, or even remove them altogether.
[ The drawing below shows six units (in blue), but their dimensions are likely incorrect, and will need to be rectified. ]

I mentioned in post #30 that I'd like to achieve not just a generally diffuse and uncorrelated reflective soundfield in the front hemisphere, but ideally to also have a high percentage of diffusion from the outer perimeter of a virtual 120* arc to best simulate a natural sense of soundstage envelopment. The placement (and quantities) of the sidewall P17 QRDs will likely determine how well this goal can be achieved. In any case, to preserve flexibility in placement (as well as quantity), the sidewall QRDs will not be permanently fixed, but rather be slid along a supporting structure on the sidewalls.

[ https://www.whatsbestforum.com/thre...uaddiffusors-big-dig.36359/page-2#post-879611 ]
[ The near-equilateral triangle placement (60-degree spread) of the L/R speakers will provide the primary +/- 30* soundfield. The diffused sidewall reflections (120-degree spread) will be delivered through the strategic placement of broadband quadratic diffusers on both the front wall and the sidewalls, providing the amplitude-weakened (-6dB?), frequency comb-filtered, and temporally/time de-correlated soundfield of +/- 60* which will enhance the perception of soundstage ambience height/depth/width, a very desirable and natural psychoacoustical embellishment. ]

I'm unsure how best to treat the first reflection points on the two sidewalls, but will likely apply absorption, to decrease the chance that the ear/brain will perceive the two symmetrical high-energy direct reflections as discrete sonic events, confusing them with the primary signals launched by the L and R speakers.

Any suggestions, WBF members?

 

[MarkusBarkus]

...regarding first reflection points and the use of the QRDs, I puzzle over this myself. I have two light-weight "skylines" on the ceiling first reflection points.

But in either your case or mine I wonder: isn't a lot of the incoming wave actually hitting the sides of the diffusors? It seems like an uncertain or partial effect of diffusion.

I pose this as a question as well as a statement. I have kept my skylines in place, to no detriment, but I wonder what positive effect they have other than a general mix.

Maybe an curved reflector is really the best application there?

 

[QuadDiffuser]

I think the angle of incidence matters a lot, as the amplitude of the diffused reflection will be impacted greatly. While the decorrelated (scrambled) nature of the sound should confuse the ear/brain into being unable to localize these diffused reflections (a GOOD thing to have), being seated inside of the minimum distance (generally, 2-3x the lowest bandwidth) raises the risk of hearing undesirable comb-filtering " unnatural zippiness" artifacts of the QRDs. Even with my 7.2m wide sidewalls, by the time all of the wall surface treatments are installed, the room will be narrower by 1.0m, leaving less space in the clearance between the L and R speakers and the sidewalls. I'm therefore inclined to think that extinguishing the audio signal at the first-reflection point is likely far better than diffusion.

Curved reflectors largely retain the phase information of the original sound, and hence are even more likely to be mistaken for being part of the original sound signal, especially at first-reflection points where high-amplitude signals strike them. They're also visually incongruent with the modules and panels in my listening room, so I will NOT use them, period.

With such a large surface area, the ceiling will be the ideal place to build bass trapping, since it's "out of the way" - I've already designed that into my room. The ceiling will also likely be receiving very little direct acoustic energy from the loudspeakers, as most dynamic driver designs have progressively narrower dispersion in both the horizontal and vertical axis, especially above 2kHz, receiving only a moderate amount of mid/high reverberant acoustic energy which has already diminished in amplitude after traversing multiple boundary surfaces. A ceiling canopy which has decent 2D diffusion will be adequate to preserve natural ambience, by not being overly absorbent and sounding over-dampened in the mids/highs.

 

[MarkusBarkus]

...yes, I do understand your points re: SQ and especially aesthetics. I was poking for your opinion on the "impact" angle. Thanks much Quad.

 

[QuadDiffuser]

The deeper the wells, the deeper the low frequency bandwidth (desirable) of QRDs, but the tradeoff is that more distance needs to be maintained between the listener and the diffusor.

P13s

My dedicated audio room build - QuadDiffusor's Big Dig

SPEAKER CHOICES Perhaps it's not too early to start daydreaming about component choices for my future basement listening room scheduled for completion in 24 months' time. I'm a huge fan of linear, predictable, and objectively measured (PROVEN) wide off-axis polar response, combining...

www.whatsbestforum.com

P17s

My dedicated audio room build - QuadDiffusor's Big Dig

SPEAKER CHOICES Perhaps it's not too early to start daydreaming about component choices for my future basement listening room scheduled for completion in 24 months' time. I'm a huge fan of linear, predictable, and objectively measured (PROVEN) wide off-axis polar response, combining...

www.whatsbestforum.com

P23s

My dedicated audio room build - QuadDiffusor's Big Dig

SPEAKER CHOICES Perhaps it's not too early to start daydreaming about component choices for my future basement listening room scheduled for completion in 24 months' time. I'm a huge fan of linear, predictable, and objectively measured (PROVEN) wide off-axis polar response, combining...

www.whatsbestforum.com

 

[Lee]

Sharing some very basic screen-capture pics from a 3D rendering video of my elevator-equipped, and solar panel roofed, five-level future home. The 50+ year-old structure was demolished a few months ago, with ongoing sheet piling and column piling. Excavation will take place in coming months, and completion in 1Q-2025. Fingers crossed!

Basement:
1) dedicated two-channel audio room, and a home office/study under the (rear wall) pool protrusion
2) living room, with a LCD TV, generic home-theater audio system + storage
3) home office/study for my wife + storage

Ground floor:
1) dining room + breakfast bar/island
2) dry kitchen
3) helper's quarters + outdoor wet kitchen
*) lap pool + IR sauna + shower + powder room
*) parking for two cars + EV chargers

Mezzanine floor:
1) guest living room

Second floor:
1) guest bedroom #1 w/shower + washroom
2) guest bedroom #2 w/shower + washroom
3) activity room / gym

Top floor:
1) master bedroom, w/closets, washroom, and amenities

View attachment 119018 View attachment 119019 View attachment 119020 View attachment 119021

That's beautiful!

 

[QuadDiffuser]

Photo below - an example of a listening room with a ceiling canopy filled with 2D diffusers, something I'd like to do, using modules which are deeper (than the standard designs), which have deeper bandwidth.

The D'Appolito driver array on the L/R loudspeakers guarantee zero vertical dispersion of high frequencies, so none of it will ever be launched directly into the ceiling. However, the longer wavelengths of the mid frequencies will diffuse and reflect around and find its way to the ceiling, where additional 2D diffusion can be desirable to deliver the perception of an even higher ceiling height, instead of absorption which will likely excessively "deaden" the room.

There's probably perspective distortion from this wide-angle photo, but at the listening chair, the ratio of direct and indirect sound looks like 20/80, given the abundance of in-phase reflective surfaces (floor, window, narrow-bandwidth sidewall diffusors, etc.), an outcome which I'd like to avoid.

Specifically, the sidewall diffusors of this example appear much too shallow to have much lower frequency bandwidth, and therefore selectively diffusing only the higher frequencies where the ear has the greatest sensitivity, potentially causing localization incongruence as the brain struggles to localize the origin of the direct signals.

If given the same space in the example below, my preference would be to cover the entire front wall with extremely deep broadband 1D diffusers such as the P-23s to decorrelate/scramble the majority of the acoustic energy, so that the front wave launch will predominantly be the L and R channel audio signals which will be heard as being distinct from the diffused sound.

And to treat the sidewalls with mostly broadband absorption, mixed with broadband diffusion, to keep the direct signals from the L/R as intact as possible as they arrive at the listening position. The ratio of direct/indirect sound may be 50/50, but the key is that the indirect sound being uncorrelated to the direct signal will diminish its power to confuse the ear/brain, so that subjectively the ratio will sound like it's 80/20 without the room sounding unnaturally over-dampened.

 

[pjwd]

Photo below - an example of a listening room with a ceiling canopy filled with 2D diffusers, something I'd like to do, using diffusors which are deeper, which therefore will have deeper bandwidth.

The D'Appolito driver array on the L/R loudspeakers guarantee zero vertical dispersion of high frequencies, so none of the energy will ever be directly launched into the ceiling. The longer wavelengths will diffuse and reflect around and find its way to the ceiling, where additional 2D diffusion can be desirable to deliver the perception of an even higher ceiling height, instead of absorption which will likely excessively "deaden" the room.

There's probably perspective distortion from this wide-angle photo, but at the listening chair, the ratio of direct and indirect sound looks like 20/80, given the abundance of in-phase reflective surfaces (floor, window, narrow-bandwidth sidewall diffusors, etc.), an outcome which I'd like to avoid.

Specifically, the sidewall diffusors appear much too shallow to have much lower frequency bandwidth, and therefore selectively diffusing only the higher frequencies where the ear has the greatest sensitivity, potentially causing localization incongruence as the brain struggles to localize the origin of the direct signals.

Given the space in the example below, my preference would be to cover the entire front wall with extremely deep broadband 1D diffusers such as the P-23s to decorrelate/scramble the majority of the acoustic energy, so that the front wave launch will predominantly be the L and R channel audio signals which will be heard as being distinct from the diffused sound.

And to treat the sidewalls with mostly broadband absorption, mixed with broadband diffusion, to keep the direct signals from the L/R as intact as possible as they arrive at the listening position. The ratio of direct/indirect sound may be 50/50, but the key is that the indirect sound being uncorrelated to the direct signal will diminish its power to confuse the ear/brain, so that subjectively the ratio will sound like it's 80/20 without the room sounding unnaturally over-dampened.

View attachment 119094

QD
For an alternative take on side first reflections .. I worked with an acoustic engineer on these studios and to avoid the non correlated reflections from diffusers we worked out sloping reflector absorbers that bent at ear level .. this ensured sound was reflected away from listener and reflections were specular.. for ceiling we did baffles to stop reflections as much as possible

All this only works down to a certain frequency of course but it worked quite well .. you could keep qrd's if you desired and slope them similarly.

I used a similar idea in my room and it works quite well compared to qrd's I have had in the past
You end up with minimal targeted treatment and can add diffusion and absorbtion in non critical areas if you need to tame the room more
A thought to add to the mix
Phil

 

[QuadDiffuser]

CEILING diffuser canopy

Looking at the specifications of various 2D diffusers from RPG, it's evident that the deeper the wells, the deeper the bandwidth, and correspondingly the broader the scatter and diffusion properties. Essentially, I'm looking for as broad, flat, and wide a diffusion coefficient (blue line) as possible, together with a broad, flat, and wide scatter coefficient (green line):

Firstly, the 8x8, 4" deep model (standard, and shallow) - see specs below:




Next, the 7x7, 6" deep model (slightly deeper wells) - see specs below:




Lastly, the 5x5, 8" deep model (deepest wells) - see specs below:

 

[QuadDiffuser]

QD
For an alternative take on side first reflections .. I worked with an acoustic engineer on these studios and to avoid the non correlated reflections from diffusers we worked out sloping reflector absorbers that bent at ear level .. this ensured sound was reflected away from listener and reflections were specular.. for ceiling we did baffles to stop reflections as much as possible

All this only works down to a certain frequency of course but it worked quite well .. you could keep qrd's if you desired and slope them similarly.

I used a similar idea in my room and it works quite well compared to qrd's I have had in the past
You end up with minimal targeted treatment and can add diffusion and absorbtion in non critical areas if you need to tame the room more
A thought to add to the mix
Phil
View attachment 119095

Hi Phil,

I also wondered whether applying diffusion on the sidewalls and angling them away would be beneficial, but the bottom line is that in my particular setup, it would be difficult to do this due to its close proximity to the listening position. Therefore, absorption seems to make more sense.

The setup below utilized P23 QRDs which is exactly what I'll be doing. Plus, the outer modules are angled slightly, which directs their output at an angle to the listening position, which adds to the diversity and non-repeating nature of the diffusion. I'll consider incorporating this tweak to my system, too. Possibly with a modification splay out the modules at the perimeter, to widen (instead of narrowing) their directivity to the listening position. Doing so will (very slightly) approximate a curved diffuser panel.

 

[pjwd]

Hi Phil,

I also wondered whether applying diffusion on the sidewalls and angling them away would be beneficial, but the bottom line is that in my particular setup, it would be difficult to not hear the output due to its proximity to the listening position. Therefore, absorption seems to make more sense.

The setup below utilized P23 QRDs which is exactly what I'll be doing. Plus, the outer modules are angled slightly, which directs their output at an angle to the listening position, which adds to the diversity and non-repeating nature of the diffusion. I'll consider incorporating this tweak to my system, too. Possibly with a modification splay out the modules at the perimeter, to widen (instead of narrowing) their directivity to the listening position. Doing so will (very slightly) approximate a curved diffuser panel.

View attachment 119100

Fair enough .. my concern with absorbtion is it is generally non correlated due to a limited fr but as long as you drop the db by quite a bit it's probably fine
You need to make surface has a low flow resistivity to avoid hf reflections .. I assume you are already looking at layered systems

That front wall looks cool .. you could increase the non correlation of diffuser patterns by slightly tilting the centre 2 as well .. angles would have to be optimised
Those angled panels at edges would make a great bass trap if there was a 100mm slot between it and wall

 

[QuadDiffuser]

Bass Traps - many!

Between the reinforced concrete structural wall and the 27.5mm thick gypsum "sandwich" (12.5mm Sheetrock + 2.5mm damping sheet + 12.5mm Sheetrock), the air space/gap distance (partially filled, with 50mm Rockwool, to maximize frictional losses) will be the following:

Front/Back walls: 100mm
Left/Right walls: 50mm
Ceiling: 200mm

These structures will be one of many other ”bass traps", the others being suspended/damped metal plates, and (very likely) the floor slab below the seating area, as well as activated carbon pellets filling the voids inside the P-17 and P-23 QRDs.