My dedicated audio room build - QuadDiffusor's Big Dig

QuadDiffuser

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There is of course another room acoustical technology that provides a third approach to dealing with low frequencies. Developed for and in use by well known film/recording/mixing studios (links to examples below), it is based on very high numbers per sf of non-parallel surfaces (DHDI ZR Acoustics). Since the secret appears to be a geometry that "deconstructs" the air the sound is riding on, panel thickness is not a key element as it is with conventional room treatments. Unfortunately data/measurements are only available to clients of the architectural firm that developed/designs with/deploys it (after signing an NDA), which (along with dislike of the marketing) is I assume why so few people posting on this forum have been willing to try it. As I've posted extensively, I found the "Sample Rate" and "Hybrid" panels to be superior to conventional room treatments, and deployed them in my listening room to the extent resources permitted. Whether or not one accepts the technical/marketing explanation, I remain puzzled given the blue chip client list that even audiophiles with deep pockets have not been willing to experiment with them - if only for spot applications as part of a larger conventional installation. The space savings alone compared with foot thick bass traps should make such experimentatin attractive. I highlighted the word "experiment" because I don't expect people to be able to "get their heads around" the concept, but hearing is believing. I found them to surpass conventional absorbers in dealing with reflections for example without deadening the room, and remain thrilled with the overall results in my purpose built dedicated basement listening room.

FYI:

https://deltahdesign.com/portfolio/


Hi Cellcbern:

Thank you for recommending the DHDI/ZR Acoustics products for treating low frequency issues in my future dedicated listening room! Navigating through their website was quite a challenge - it took me nearly ten minutes to find a description of their core technology asserting to repeal the laws of acoustics and physics.

Quote: [[ZR’s core principle is simple: Phase Coherency creates Life-Like Imaging and an audible sense of Expansiveness. In the eyes of Quantum Physics, it is now understood that Electrons and Air molecules behave in the same Quantum fashion. Using this core principle, ZR Acoustics® eradicates the most egregious acoustical issues, including low intelligibility, resonant frequencies, excessive reverberation, standing waves, variable frequency response with amplitude, and bass buildup in corners. The root of these issues begins with reflections off hard surfaces. ZR creates the proper environment in which reflections are quantized. Quantized Air at hard reflective surfaces equals no wave action. No wave action means no sound reflections, and no sound reflections means only crisp, clear, Direct sound with high Phase Coherency, resulting in Life-Like Imaging and a true sense of spaciousness.

Quantum Physics and wave particle duality were proven to be a reality In the early 1900’s. It is the basis for the entire Era of Electronics. The concept is that until they are observed, electrons can behave as waves, as individual particles or as both at the same time. ZR Acoustics® creates the proper environment to quantize the behavior of Air molecules from wave fashion to individual particle fashion. When Air molecules behave as individual particles (i.e. no wave behavior), sound energy has no medium to ride upon. Like a radio signal without a carrier wave, the sound simply ceases to exist. In conjunction with precise, artistic design, this effect dramatically increases Phase Coherence, and consequently imaging and spaciousness.

The ZR Acoustics® paradigm is based in science and designed for creativity, like a finely tuned instrument. Designs are handcrafted and embedded with higher order mathematics, complex topologies, and Extreme Acoustic Resolution.]]

With a thickness of just 0.75", those sleek and slender panels with 0.50" deep wells will help diffuse frequencies of 6,780Hz and above, so it will indeed be a Quantum Physics miracle for the panels to eradicate standing waves and bass buildup (wavelengths of 11.3ft for 100Hz, 22.6ft for 50Hz, and 37.7ft for 30Hz) or lower!

While I'm really intrigued by the mind-blowing potential of this out-of-this-world technology, unfortunately the concentric-circle aesthetics clash with my taste violently; in fact just glancing at thumbnail photos of them on my computer screen using only my peripheral vision triggers a headache. I simply cannot imagine life-sized ZR Acoustics panels covering the coveted front wall of my listening room... I think I would be instantly debilitated with severe nausea and vertigo. I think I've discovered that I'm suffering a rare variety of a trypophobia, triggered not by irregular bumps and holes, but by concentric circles.

But in all seriousness, I really appreciate you taking the time to recommend the ZR Acoustics products to me. It's good to keep an open mind to trying new things, even if it means discovering what I don't like. ;-)
 
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Cellcbern

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Hi Cellcbern:

Thank you for recommending the DHDI/ZR Acoustics products for treating low frequency issues in my future dedicated listening room! Navigating through their website was quite a challenge - it took me nearly ten minutes to find a description of their core technology asserting to repeal the laws of acoustics and physics.

Quote: [[ZR’s core principle is simple: Phase Coherency creates Life-Like Imaging and an audible sense of Expansiveness. In the eyes of Quantum Physics, it is now understood that Electrons and Air molecules behave in the same Quantum fashion. Using this core principle, ZR Acoustics® eradicates the most egregious acoustical issues, including low intelligibility, resonant frequencies, excessive reverberation, standing waves, variable frequency response with amplitude, and bass buildup in corners. The root of these issues begins with reflections off hard surfaces. ZR creates the proper environment in which reflections are quantized. Quantized Air at hard reflective surfaces equals no wave action. No wave action means no sound reflections, and no sound reflections means only crisp, clear, Direct sound with high Phase Coherency, resulting in Life-Like Imaging and a true sense of spaciousness.

Quantum Physics and wave particle duality were proven to be a reality In the early 1900’s. It is the basis for the entire Era of Electronics. The concept is that until they are observed, electrons can behave as waves, as individual particles or as both at the same time. ZR Acoustics® creates the proper environment to quantize the behavior of Air molecules from wave fashion to individual particle fashion. When Air molecules behave as individual particles (i.e. no wave behavior), sound energy has no medium to ride upon. Like a radio signal without a carrier wave, the sound simply ceases to exist. In conjunction with precise, artistic design, this effect dramatically increases Phase Coherence, and consequently imaging and spaciousness.

The ZR Acoustics® paradigm is based in science and designed for creativity, like a finely tuned instrument. Designs are handcrafted and embedded with higher order mathematics, complex topologies, and Extreme Acoustic Resolution.]]

With a thickness of just 0.75", those sleek and slender panels with 0.50" deep wells will help diffuse frequencies of 6,780Hz and above, so it will indeed be a Quantum Physics miracle for the panels to eradicate standing waves and bass buildup (wavelengths of 11.3ft for 100Hz, 22.6ft for 50Hz, and 37.7ft for 30Hz) or lower!

While I'm really intrigued by the mind-blowing potential of this out-of-this-world technology, unfortunately the concentric-circle aesthetics clash with my taste violently; in fact just glancing at thumbnail photos of them on my computer screen using only my peripheral vision triggers a headache. I simply cannot imagine life-sized ZR Acoustics panels covering the coveted front wall of my listening room... I think I would be instantly debilitated with severe nausea and vertigo. I think I've discovered that I'm suffering a rare variety of a trypophobia, triggered not by irregular bumps and holes, but by concentric circles.

But in all seriousness, I really appreciate you taking the time to recommend the ZR Acoustics products to me. It's good to keep an open mind to trying new things, even if it means discovering what I don't like. ;-)
Glad you clarified these room acoustics basics for me. I guess the studios of Universal Music/Mastering, Grammy winners Alan Meyerson and Rafa Sardinia, McGill University, and all of the others are crippled by bass anomalies/room modes and they don't even know it. By the way, even if the ZR panels didn't handle the low frequencies the improvement in midrange and treble clarity when I put them on my walls was unprecedented, which gets back to my point about experimentation. When it comes to aesthetics I guess there is no accounting for taste. The "Hybrid" panels of course are fabric covered. A number of people (my wife included) upon seeing them before I mounted them on the wall thought the "Sample Rate" panels were wall art. I've only received positive comments on their appearance. Fascinating.
 

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QuadDiffuser

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On the subject of acoustical ceiling treatments for my future dedicated basement listening room, I found a product called Silk Metal offered by the company Acoustical Surfaces.

Unlike typical open-celled acoustical foam whose absorptive characteristics below 500Hz dive down a cliff, Silk Metal panels have excellent absorption across a VERY broad range of frequencies from 100Hz to 5kHz when an air gap of 400mm (or more) is incorporated. At less than US$40 for a 600mm x 600mm tile (approximately 2ft x 2ft), they are also extremely cost-effective.

URL hotlink:
Screenshot 2022-01-10 011422.png
When used as drop-grid ceiling panels in combination with an air gap of 400mm, particularly notable is the combo's ability to massively absorb frequencies below 400Hz, as well as its unbelievable absorption linearity from 630Hz to 5kHz. Compared to the one above, the graph below is a sight to behold - I have never seen a Sound Absorption Coefficient graph as ideal as this one for high-end audio applications! The entire basement listening room ceiling canopy can become a very decent bass trap to dampen room nodes, as well as reduce slap echo / reverberation without favoring any particular frequency in the critical mid-range to high frequency spectrum. The woven metal materials of these panels are essentially micro-perforations with variable porosities which results in a consistent barrier to sound energy across a range of frequencies without any significant "cold" or "hot" spots. The full technical test results from Riverbank Acoustical Laboratories for the Silk Metal panels are in the attached PDF (click the icon at the very bottom of this page).
Screenshot 2023-04-03 000230.png My concern is that while treating the entire ceiling surface area will surely remove undesirable slap echo reverberation, it may potentially "deaden" the room to such an extent that the ephemeral and fragile "liveliness" which contributes to ambience cues and overhead spaciousness may be completely and undesirably extinguished. But then again, the round-trip distance of 10+ meters between loudspeaker, ceiling, and listening position will naturally attenuate the higher frequencies anyway, so that the introduction of absorptive ceiling panels may not affect the perception of space at all. Also, loudspeakers typically project very little high frequency information in the vertical axis, so the relative loudness between ceiling reflections and direct projections of sound from the tweeter may make the former completely inaudible.

In fact, during my recent trip to Western Australia's Margaret River region, I visited several underground caves containing massive calcite caverns with ceiling heights ranging from 5m to 30m, no ambience whatsoever was heard from the ceilings when I introduced sounds including hand claps, whistles, and "hellooo"s... they were all fully dampened into oblivion. Yet, not that there was music playing in the caves, but I didn't feel that anything was amiss acoustically. Pretty much the same result for banquet halls and conference rooms with very tall ceilings ranging from 4 to 6 meters - hand claps, whistles, and helloos did not elicit any noticeable overhead ambience which was audible.

Given the horizontal orientation of our outer ears, perhaps we're just not that sensitive to "overhead" sound? Or that results simply matched expectations, so that there was no psychoacoustical cognitive dissonance?

Has anyone listened to music on their audio system on top of a tall ladder at ceiling level, and if so, what does music sound like "up there"? Having done just that in my apartment listening room with a 10-foot ceiling, I noted that bass resonances pretty much dominated at ceiling and wall boundary locations. In fact, the combination of bass traps and quadratic diffusors are highly desirable for low-ish ceilings such as mine, to reduce bass resonance as well as broadly diffuse sound to make the ceiling to seem audibly higher than it really is. "Before and after" photos of my heroically engineered ceiling canopy in my apartment listening room, and it has been very effective in achieving the twin goals!

12080234_10206415911850970_1484178527711899996_o.jpg

ceiling canopy.jpg

But when one already has a ceiling which is ~21 feet high as in my basement dedicated listening room, I'm hoping that there will be no acoustic negatives in installing a linearly mid-high frequency absorptive "bass trap" ceiling canopy at ~16 feet above the floor. Specifically, that the generous absorptive/dampening of frequencies below 400Hz will more than offset the potential (?) subtraction of frequencies between 500Hz to 5kHz. And that any potential resonances/rattling of the relatively lightweight Silk Metal panels at high SPLs can be effectively dampened with a simple application of visco-elastic material (silicon glue?) on the contact points between the suspension grid rails and the panels themselves.

WBF members who have experience with listening rooms with very tall ceilings, do you think that the installation of moderately absorptive (~75% absorption above 630Hz) ceiling panels would be a mistake?
 

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QuadDiffuser

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I obtained and examined 30cm x 30cm samples of the Silk Metal micro-perforated plates in both black and white colors, and determined that they were totally unsuitable as a broadband absorption panels inserted into a drop-ceiling grid; hundreds/thousands of mechanical connection points between the Silk Metal plates and the drop-in grid frames will for sure be the source of countless unacceptable pinging and rattling mechanical noises which cannot be suppressed in any reliable way, short of perhaps applying gobs of viscous silicon glue into every single point of contact. Very unfortunate, but perhaps it was a classic case of "too good to be true"... their sound absorption coefficient graphs were likely buttered flat using very large wide-octave smoothing values, masking multiple high-amplitude high frequency resonances resembling the crinkling snap/pop of acoustically and physically energizing a micro-perforated thin aluminum panel.
 
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Believe High Fidelity

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Very excited for you. I am interested to see your experience with the various products available to treat your room. I ended up going the Acoustic Fields route with 16 ACDA's, 6 CPA's and two of his QDA's diffusers.

I have been looking for years and have found the advertised specifications somehow rarely turn out to be accurate to published specs or in your case the omission of design flaws like the many mechanical connection points that are not included in the measurements given. So I have come full circle back to Acoustic Fields.
 
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QuadDiffuser

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Subsequent to the main contractor tendering process which completed in April, I discovered to my great disappointment that the actual cost for building my "dream" basement was in the stratosphere, far beyond my budget, in a different orbit from what my architect initially advised/forecasted. Many months of wasted time and opportunity cost has gone under the bridge. Going back to the drawing board, the entire basement has now been reduced in height from 6.2m to 4.0m, and the dedicated listening room has been reoriented 90-degrees into a different location inside the basement.

At 4.0m(H) x 6.5m(W) x 10.0m(L) the revised basement listening room will still be quite generous in volume; compared to the previous design, its "width x height" dimensional ratio will be less squarish (closer to the ideal). The swimming pool will now vertically drop merely 0.7m along the back wall ceiling from L to R symmetrically, and horizontally protrude 2.25m out into the listening room. My home office desk will likely be placed along the back wall under the pool protrusion.

A very preliminary sketch (likely not 100% accurate) of the repositioned basement listening room:

WhatsApp Image 2023-05-18 at 11.33.50.jpg
 
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QuadDiffuser

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REVISED ROOM DIMENSIONS

The latest revisions, assuming 6.0m excavation depth (to stay within budget):

4.20m height between floor slab and ceiling slab, the shortest dimension of the listening room
0.65m protrusion (0.85m less 0.2m ceiling slab thickness) by the largest beam, directly over the separating wall, 10+ meters lengthwise
3.55m floor slab to false ceiling clearance, with the 0.65m air gap above used for air-con ducts and acoustic modules
1.50m vertical protrusion of the swimming pool structure, and horizontal ingress of 2.25m (6.50m in width) in the back wall study area
2.70m height between floor slab and swimming pool structure will likely grow to 3.00m (through pool depth reduction from 1.50m to 1.20m)

The access door has been moved from the middle of the listening room to the back wall corner, where the venting of triple-boundary corner bass pressure buildup is optimal but not perfect, as it lacks L/R symmetry from the perspective of the listening seat.

Thankfully, the listening room will still be generously-sized:
4.20m(H) or 13.8ft = 40.9Hz 1st order resonance frequency
6.50m(W) or 21.3ft = 26.5Hz 1st order resonance frequency
10.45m(L) or 34.3ft = 17.2Hz 1st order resonance frequency

Surface area (floor):
67.9 square meters, or 730.6 square feet

Volume:
285.3 cubic meters, or 10,082 cubic feet

Its dimensional ratios of 1.00 x 1.55 x 2.49 will be just inside the (theoretically) optimal Bolt-Area graph, with a good distribution of room nodes.

iteration 2023_05_20.jpg Screenshot 2023-05-21 103442.png
 
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QuadDiffuser

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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, objectively measured (PROVEN) wide off-axis polar response, combining point-source approximation to create a deep/wide soundstage, dynamically scalable (from tiny, small, medium, large to off-to-the-side, depending on what the source) pin-point 3D imaging by WORKING with room acoustics (for the mid/highs) and floor/wall boundaries (for natural augmentation of sub-200Hz long bass wavelengths).

My preference is for vertically aligned dynamic drivers on an appropriately contoured and minimized baffle surface area, with tweeter(s) on top, ideally at ear-height or slightly higher to project a slightly elevated soundscape, and the midrange placed below at very close proximity to the tweeter, ideally within 1/2 the crossover frequency wavelength to minimize deleterious interactions.

I'm not a fan of M-T-M D'Appolito arrays, as I can easily hear driver nulls which among other undesirable polar inconsistencies, separate music into vertical layers of horizontalized donut "rings". I also don't care about "time alignment" through second-order crossovers or voice-coil alignment into a common horizontal plane and vertical line. Anyone who can read a step-response curve knows that propagated sound arrives at different times THROUGHOUT the frequency range, and that achieving perfect time alignment at the listening position is but a misguided dream, and more importantly, our listening ear/brain mechanism is not particularly sensitive to group delay.

Dipoles, and monopoles will not be on my list either, as I have found them to not localize sonic events sufficiently solidly in 3D, especially in the front-to-back Z axis.

Nope to line arrays too, as their hyper-tall cylindrical propagation pattern warp both micro and macro sonic events inside the soundstage in ambiguous and strange ways, including instances where instruments and voices become stretched vertically into the full floor-to-ceiling length of the line-arrayed drivers, morphing into wildly different heights depending on the listening height (between sitting straight-up and slumping down), reminding me of a scene in the movie "The Thing" where the dysmorphic monster towers up/down on its long neck, except that sonically, the ENTIRE neck becomes a vertically-stretched vocal source. I know... pretty bizarre and scary, right?

I prefer my vocals to be right-sized, but also able to size dynamically depending on the gender/vocalist, most of all emanating from a real-sized head as I move around up/down/L/R around the proverbial sweet spot.

MacReady-and-The-Thing.jpg

Applying DSP correction to "time align" arrivals isn't my taste either, as it introduces off-axis anomalies which suck the life out of music, according to my experience experimenting with the one of the most sophisticated room correction equipment featuring a mic array with four microphone capsules (to capture vertical azimuth data).

As far as I know (and heard/seen), only offerings from Von Schweikert Audio provides the adjustability and flexibility to optimize its acoustic output to optimize various loudspeaker placement locations, and room size/volume - attributes which are unique in the marketplace... I'm a HUGE fan of VSA!

But I'm casting a wide net out of an abundance of curiosity, and earmarking flagship models from multiple manufacturers (listed below in alphabetical order) for auditioning in an optimized-room-acoustics listening room to properly showcase the capabilities of the loudspeaker. Given the excitement and media coverage at High End Munich 2023, some European brands which I have not auditioned extensively have been added below.

Have I missed any others, which broadly deliver on the performance characteristics I'm looking for?

* * * * *

Magico (upcoming M7/M8 incorporating trickle-down technologies from the M9)
Marten (audition pending)
Rockport (Lyra - audition pending)
Von Schweikert Audio (Ultra 7 or 9 + pair of high-level input bass-management subwoofers)
TAD (co-axial drivers, ie. Reference 1-TX)
Vimberg/TIDAL (auditions pending)
Vivid (upcoming flagship model, one slot above the Giya G1 Spirit)
Zellaton (audition pending)
 
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pjwd

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The latest revisions, assuming 6.0m excavation depth (to stay within budget):

4.20m height between floor slab and ceiling slab, the shortest dimension of the listening room
0.65m protrusion (0.85m less 0.2m ceiling slab thickness) by the largest beam, directly over the separating wall, 10+ meters lengthwise
3.55m floor slab to false ceiling clearance, with the 0.65m air gap above used for air-con ducts and acoustic modules
1.50m vertical protrusion of the swimming pool structure, and horizontal ingress of 2.25m (6.50m in width) in the back wall study area
2.70m height between floor slab and swimming pool structure will likely grow to 3.00m (through pool depth reduction from 1.50m to 1.20m)

The access door has been moved from the middle of the listening room to the back wall corner, where the venting of triple-boundary corner bass pressure buildup is optimal but not perfect, as it lacks L/R symmetry from the perspective of the listening seat.

Thankfully, the listening room will still be generously-sized:
4.20m(H) or 13.8ft - 40.9Hz 1st order resonance frequency
6.50m(W) or 21.3ft - 26.5Hz 1st order resonance frequency
10.45m(L) or 34.3ft - 17.2Hz 1st order resonance frequency

Surface area (floor):
67.9 square meters, or 730.6 square feet

Volume:
285.3 cubic meters, or 10,082 cubic feet

Its dimensional ratios of 1.00 x 1.55 x 2.49 will be just inside the (theoretically) optimal Bolt-Area graph, with a good distribution of room nodes.

View attachment 109800 View attachment 110009
Bummer about the budget constraints but...thats still a pretty good size room !
The only challenge is height under pool ... sorry if missed this but are speakers on long or short wall ( I am a fan of the long wall)
I wouldn't sweat the room proportions when your getting to this size

Phil
 

QuadDiffuser

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Bummer about the budget constraints but...thats still a pretty good size room !
The only challenge is height under pool ... sorry if missed this but are speakers on long or short wall ( I am a fan of the long wall)
I wouldn't sweat the room proportions when your getting to this size

Phil
LONG or SHORT WALL?

Phil, I'll likely have 3.0m of height under the swimming pool protrusion, so I think that'll be quite manageable, given its L/R symmetry at the back of the room with the space filled with bass pressure management modules and covered with broadband quadratic diffusers.

Agree that once the minimum room dimensions and cubic volume grow past a certain dimension, say 6.0m height x 7.0m width (previous design), even a squarish height-to-width ratio shouldn't be a huge issue because there will be very little energy at say 25-30Hz to excite those particular fundamental room nodes. But there's still a real concern that the reduction of 40% in the current design resulting in a higher fundamental room node bass frequency of 40.9Hz may become an issue.

The room-in-a-room design (using sheetrock dampened with MLV and viscoelastic dampening, together with thin 100mm wall-mounted Helmholtz bass absorbers tuned to multiple low bass frequency peaks) will reduce the width of the room by a minimum of 800mm, from 6.5m to "just" 5.7m. The construction of the walls will follow the principles described in the following article to reduce "wall shudder", an undesirable resonance mode (crudely resembling a drum skin) which then dissipates its stored energy tortuously slowly into a long decay-time trailing tail of incoherent and phantom bass not present in the original music.


Quoting a key short passage from the article above, which summarizes the objectives, with a tweak:
* * *
"The resulting wall structure—viscoelastic damping sandwiched between two drywall layers—forms a classic constrained-layer damping system. Constrained-layer damping is widely used in many industries and is a science unto itself. When the wall is flexed by the acoustic pressure of low-frequency sound inside the room, sheer (sic) forces in the viscoelastic layer dissipate that energy as a minute amount of heat in the viscoelastic material. Remember that the resilient channel allows the interior surfaces of the listening room to bend but not vibrate, which is a key element in a constrained-layer damping system. The walls and ceiling are turned into giant diaphragmatic bass absorbers. Moreover, the energy dissipated in the viscoelastic damping is energy that’s not putting the walls into structural resonance. The framed structure is rendered quiet and inert. A small tweak is to specify different densities of drywall for the two layers. One layer of standard drywall and one layer of moisture-resistant drywall will do the trick. The idea is that the different wallboard densities will exhibit different resonant characteristics, and thus distribute the resonant energy that remains over a wider band but at a lower amplitude."
* * *

Assuming that the speakers will be placed at 1/4 of the room length on the 25% or 2.5m away from the front wall, spread apart by 3.1m (10.2 ft), that leaves just 2.6m/2 = 1.3m (4.26 ft.) of sidewall clearance for each speaker. Though the sidewalls will be lined with P17 quadratic diffusers to decorrelate the amplitude spectrally and temporally, would this 1.3m clearance be enough? Alternatively, if the longer dimension of the room was used as the front wall, effectively there will be NO sidewalls, and the depth between front and back wall will be reduced to 5.7m, BOTH which I think will be sub-optimal.

Any suggestions or thoughts are welcome!

I intend to use the shorter width of the room as the front wall, so that there is a better chance of perceived "envelopment" of the musical soundstage, as part of the listening room optimization process, in the realm of psychoacoustic enhancement. Diagram (b) below, extracted from Floyd E. Toole's book, "Sound Reproduction, Third Edition", provides empirical data on the optimal angles (for the launching of primary and secondary sound sources in a multi-channel system) to achieve the most desirable soundstaging results. I believe that this effect can be synthetically replicated through the deliberate and thoughtful leveraging of sidewall diffusion.

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.

Envelopment.jpg
 
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pjwd

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Phil, I'll likely have 3.0m of height under the swimming pool protrusion, so I think that'll be quite manageable, especially if that space on the rear wall will be treated liberally with bass pressure management modules, as well as broadband quadratic diffusers.

Agree that once the minimum room dimensions and cubic volume grows past a certain dimension, say 6.0m height x 7.0m width in my previous design, even a squarish ratio won't be a huge issue because there's very little energy at say 30Hz or 25Hz to excite room nodes excessively. But it is definitely still a real concern in my current listening room design, which only has 60% or so of the former design.

My intended room-in-a-room design for the room, which will crimp all three dimensions by a minimum of 800mm. But I intend to use the shorter width of the room as the front wall, so that there is a better chance of perceived "envelopment" of the musical soundstage, as part of the listening room optimization process, in the realm of psychoacoustic enhancement. If I were to use the longer dimension as my front wall, effectively there will be NO sidewalls, which I don't think will be optimal. Diagram (b) below, extracted from Floyd E. Toole's book, "Sound Reproduction, Third Edition", provides empirical data on the optimal angles (for the launching of primary and secondary sound sources in a multi-channel system) to achieve the most desirable soundstaging results. I believe that this effect can be synthetically replicated through the thoughtful usage of sidewall reflections.

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 liberal and strategic placement of broadband quadratic diffusers on both the front wall and the sidewalls, providing the amplitude-weakened, 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.

View attachment 110222
I admit to not having read this work .. and I am too lazy to start :) I wonder what convolutions they applied to simulate reflections
I come at it more from acoustic research in concert halls etc where the aim is to get a good delay between first reflections and direct sound and then have a nice reverbarent decay that is as highly correlated with direct sound as possible. No easy feat in a hall or a listening room.
In this world the long wall is your friend .. as you say side walls virtually disappear... but front and rear walls come into play.. tradeoffs as always.

I think the best stereo image is created by the direct sound and then supported by the delayed reverbarent field ... I have tried both long and short walls in a modest 7.2x4.4x3m room and preferred the long wall ( with some treatments on front wall) and I have a second room that is 9x6x3.4m with speakers on long wall .. it sounds excellent .. this room is also soundproofed (ambient about 25db) and that is a big step up in itself
The interesting thing about listening room acoustics is recordings already have a real or manipulated acoustic embedded and the extent to which the room overides or supports that is probably going to vary quite a bit.

You have obviously had quite a bit of experience and have applied deep thought to the subject so it is quite interesting to see your approach.. with the pool intrusion its a lot easier to get symmetry using short walls
Are you building a room within a room to get sound isolation .. it seems as though you would have quite sound proof walls
 
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QuadDiffuser

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ROOM ACOUSTICS - TREATMENT

Phil, my understanding is that the acoustics in concert halls could not be more different than in a (relatively) much smaller dedicated listening rooms like mine.

In large "rooms" typical of performance venues, reverberation time (RT60) is so long that instrumental/voice incoherence and unintelligibility results from undirected, unfettered propagation of sound as they travel over long distances in multiple vectors and reflect back, in a phenomenon called reverberation. Paradoxically, higher frequency energy diminishes rapidly over long distances so it is as precious as saffron or pixel dust; in controlling/reducing reverberation, the venue must not be overdamped. The challenge is, therefore, how to deliberately shape large boundaries and surfaces which assist in consistently and predictably redirecting the sound from the source/stage into the audience/venue, in both amplitude (directivity/spread) and time domain (consistent decay, post initial arrival).

De-correlating the reflections is actually extremely critical and desirable for articulation and intelligibility of the original signal. Practically, this is impossible to do over long distances, as the benefits of de-correlated sound (for example, through the installation of deep, wide bandwidth QRDs) are extinguished over very long distances, as other highly-correlated reflections drown it out.

Reflections which are correlated with the actual signal are actually detrimental, especially those inside of 20ms, as well as those outside of 100ms - that’s why I don’t like hemispheric “diffusers”. The relatively shorter distances between the boundaries in typical audiophile listening rooms benefit from consistent and uniform decay of acoustic energy in a much shorter time frame, far below the reverberation time window typical of churches, concert halls, etc.

These are major topic all by themselves, so I’ll leave them for another time to discuss. Suffice it to drop a hint here that the key to understanding the psychoacoustic “illusion” of stereo is actually through understanding the reproduction of mono music through a pair of stereo speakers, and then flipping the phase on just one channel, then listening again.

Onto the physics of sound waves.

For frequencies above 200Hz, the strategic placement of quadratic diffusers to deliberately introduce comb filtering effects which randomize (and shift) amplitude, spectral distribution, and time arrivals of the primary sound will result in a pleasant ambient environment through the redirection and shaping of secondary (redirected/reflected) sound, generally perceived as the expansion of the listening room boundaries and volume. In my basement listening room, the entire front wall (behind the speakers), as well as the sidewalls (behind the speakers) will be covered with broadband P23 quadratic diffusors. And on the ceiling, a shallower quadratic diffuser will cover most of the central area.

Frequencies below 200Hz are long tsunami "pressure waves" which persistently want to force itself into and over everything, stopping at nothing. The objective in an audiophile listening room is to essentially find methods to make the pressure waves dissipate/disappear. This is done in three ways. We’ll, four ways if we include simply opening the door to the and venting the pressure buildup to the infinite outside, but achieving symmetry to the midline of the listening axis would be difficult.

Velocity attenuators typically use materials which introduce friction, turning air molecule movement into heat, but heroic amounts of mass (hundreds, if not thousands of kilograms of dense material) is required to do this job. No amount of building insulation or acoustic foam will do anything to attenuate deep bass, but large, robust cabinets with progressively resistant compartments filled with activated carbon (having prodigious amounts of surface area through their astonishing porosity) can work in various degrees. Diaphragmatic bass absorbers are a hybrid solution, combining the bass attenuation attributes of heavy thick-walled cabinet boxes (via the quarter wavelength rule), together with internal partitions filled with activated carbon pellets which pound-for-pound are highly efficient in accelerating the attenuation of bass by raising the acoustic impedance as bass energy dissipates between the innards of the boxes.

Another more targeted and space-efficient method is through Helmholtz resonators which are tuned to a particular bass frequency, exhibiting high/narrow specificity to a narrow bass frequency. Models can predict the fundamental bass resonance frequencies, but then there are plenty of other frequencies which arise from secondary and tertiary boundaries and reflections. Therefore, a variety of bass frequencies, as well as surface area leveraging air gaps are typically required to ensure complete eradication. I will be using hundreds of such dampened metal-plate Helmholtz resonators in my basement listening room, mounted directly on the structural walls at the zero-velocity high pressure zones, where they will be most effective.

Lastly, subwoofers are extremely effective at generating "anti-waves" which moderate the severity of bass peaks and nodes. However, it is tricky to figure out the placement of subwoofers, as well as shaping their output relative to the music. I will be using two subwoofers in my basement listening room as bass management devices.

Ironically, a solid concrete room buried twenty feet below the ground is a perfect place to trap the wild bass beast, hell-bent on destroying/fighting/struggling as it has nowhere to escape to. The audiophile adage, "the best room is no room" holds especially true for low bass energy!

The reason for building a "gypsum board room within a concrete basement room" is not for sound isolation per se, but as one of the three methods to quickly (and hopefully quietly) slay the proverbial bass beast.

BTW, I will try to expand the room width from 6.5m to 7.0m, as more space is required between the loudspeakers and the side wall. By doing so, instead of 1.3m, this distance will hopefully be able to expand to 1.55m (5.09ft).
 
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sbnx

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Mar 28, 2017
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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 point-source approximation to create a deep/wide soundstage, dynamically scalable pin-point 3D imaging by WORKING with room acoustics (for the mid/highs) and floor/wall boundaries (for natural augmentation of sub-200Hz long bass wavelengths).

My preference is for vertically aligned dynamic drivers on an appropriately contoured and minimized baffle surface area, with tweeter(s) on top, ideally at ear-height or slightly higher to project a slightly elevated soundscape, and the midrange placed below at very close proximity to the tweeter, ideally within 1/2 the crossover frequency wavelength to minimize deleterious interactions.

I'm not a fan of M-T-M D'Appolito arrays, as I can easily hear driver nulls which among other undesirable polar inconsistencies, separate music into vertical layers of horizontalized donut "rings". I also don't care about "time alignment" through second-order crossovers or voice-coil alignment into a common vertical line. Anyone who can read a step-response curve knows that propagated sound arrives at different times THROUGHOUT the frequency range, and that achieving perfect time alignment at the listening position is but a misguided dream, and more importantly, our listening ear/brain mechanism is not particularly sensitive to group delay.

Applying DSP correction to "time align" arrivals isn't my taste either, as that introduces off-axis anomalies which suck the life out of music, according to my experience experimenting with the one of the most sophisticated room correction equipment featuring a mic array with four microphone capsules (to capture vertical azimuth data).

As far as I know (and heard/seen), only offerings from Von Schweikert Audio provides the adjustability and flexibility to optimize its acoustic output to optimize various loudspeaker placement locations, and room size/volume - attributes which are unique in the marketplace... I'm a HUGE fan of VSA!

But I'm casting a wide net out of an abundance of curiosity, and earmarking flagship models from multiple manufacturers (listed below in alphabetical order) for auditioning in an optimized-room-acoustics listening room to properly showcase the capabilities of the loudspeaker. Given the excitement and media coverage at High End Munich 2023, some European brands which I have not auditioned extensively have been added below.

Have I missed any others, which broadly deliver on the performance characteristics I'm looking for?

* * * * *

Magico (upcoming M7/M8 incorporating trickle-down technologies from the M9)
Marten (audition pending)
Rockport (Lyra - audition pending)
Von Schweikert Audio (Ultra 7 or 9 + pair of high-level input bass-management subwoofers)
TAD (co-axial drivers, ie. Reference 1-TX)
Vimberg/TIDAL (auditions pending)
Vivid (upcoming flagship model, one slot above the Giya G1 Spirit)
Zellaton (audition pending)
You have some very nice choices in your list. The speakers in your list have a wide range of tonality. Having a speaker that offers some adjustability is a huge thing in getting it to work in a room. The only speaker in your list that has adjustability it the VSA. Another speaker similar is the Sonus Faber Aida. It offers a good amount of adjustability and something to consider.
 

pjwd

Well-Known Member
Jun 22, 2015
504
339
298
Brisbane
ROOM ACOUSTICS - TREATMENT

Phil, my understanding is that the acoustics in concert halls could not be more different than in a (relatively) much smaller dedicated listening rooms like mine.

In large "rooms" typical of performance venues, reverberation time (RT60) is so long that instrumental/voice incoherence and unintelligibility results from undirected, unfettered propagation of sound as they travel over long distances in multiple vectors and bounce around into a phenomenon called reverberation. Paradoxically, higher frequency energy diminishes rapidly over long distances so it is as precious as saffron or pixel dust; in controlling/reducing reverberation, the venue must not be overdamped. The challenge is, therefore, how to deliberately shape large boundaries and surfaces which assist in consistently and predictably redirecting the sound from the source/stage into the audience/venue, in both amplitude (directivity/spread) and time domain (consistent decay, post initial arrival).

The relatively shorter distances between the boundaries in basement listening room also requires consistent and uniform decay of acoustic energy leaving no lingering (spurious) acoustic energy, but in a much shorter time frame, outside of the reverberation time window.

It's essential to understand the physics of sound, how 200Hz+ frequencies interact and behave very differently from sub-200Hz bass energy.

For frequencies above 200Hz, the strategic placement of quadratic diffusers to deliberately introduce comb filtering effects which randomize (and shift) amplitude, spectral distribution, and time arrivals of the primary sound will result in a pleasant ambient environment through the redirection and shaping of secondary (redirected/reflected) sound, generally perceived as the expansion of the listening room boundaries and volume. In my basement listening room, the entire front wall (behind the speakers), as well as the sidewalls (behind the speakers) will be covered with broadband P23 quadratic diffusors. And on the ceiling, a shallower quadratic diffuser will cover most of the central area.

Frequencies below 200Hz are long tsunami "pressure waves" which are forceful and persistently want to dominate over everything, stopping at nothing. The objective in an audiophile listening room is to essentially find methods to make the pressure waves dissipate/disappear. This is done in three ways.

Velocity attenuators typically uses materials which introduce friction, turning air molecule movement into heat, but heroic amounts of mass (hundreds, if not thousands of kilograms of lossy material) is required to do this job. No amount of building insulation or acoustic foam will do anything to attenuate deep bass, but deep, large, robust cabinets with compartments filled with activated carbon (having prodigious amounts of surface area through their astonishing porosity) will be useful.

Another more targeted and space-efficient method is through Helmholtz resonators which are tuned to a particular bass frequency, exhibiting high/narrow specificity to a narrow bass frequency. Models can predict the fundamental bass resonance frequencies, but then there are plenty of other frequencies which arise from secondary and tertiary boundaries and reflections. Therefore, a variety of bass frequencies, as well as surface area leveraging air gaps are typically required to ensure complete eradication. I will be using hundreds of such dampened metal-plate Helmholtz resonators in my basement listening room, mounted directly on the structural walls at the zero-velocity high pressure zones, where they will be most effective.

Lastly, subwoofers are extremely effective at generating "anti-waves" which moderate the severity of bass peaks and nodes. However, it is tricky to figure out the placement of subwoofers, as well as shaping their output relative to the music. I will be using two subwoofers in my basement listening room as bass management devices.

Ironically, a solid concrete room buried twenty feet below the ground is a perfect place to trap the wild bass beast, he’ll-bent on destroying/fighting/struggling as it has nowhere to escape to. The audiophile adage, "the best room is no room" holds especially true for low bass energy!

The reason for building a "gypsum board room within a concrete basement room" is not for sound isolation per se, but as one of the three methods to quickly (and hopefully quietly) slay the proverbial bass beast.

BTW, I will try to expand the room width from 6.5m to 7.0m, as more space is required between the loudspeakers and the side wall. By doing so, instead of 1.3m, this distance will hopefully be able to expand to 1.55m (5.09ft).
I pretty much agree with all you say excepting for the treatment of reflections .. the repeated use of qrd ( no disrespect to your avatar :)) creates both phase change and comb filtering as you note which then does not correlate with direct sound . This is not as pleasing in my view as a delayed and correlated reflection. Clearly you have experienced it and favour that approach .. so it goes. They must be quite deep to work at those fr
I also wonder about the double wall absorber system .. how accurately can you predict the result and is it worth the loss of space.
Bass traps acting below 125hz in all 4 wall corners and all 4 ceiling corners can do a pretty good job on cleaning up bass reverb
Good move on widening room ... if you could remove dual wall in that zone to get the maximum width that also may help.

Overall I guess I favour a more minimalist approach.

It is intersting that the "great" halls of the world have a reverb time of 2s or so but when research has been done on users it was found that the preference split was about 50/50 between long and short reverb times .... I think this plays very much into the different kind of sound we like in our rooms .. a lot shorter reverb if course! Also the roll of of high frequency in halls correlates to varied toe in preference and the downward slope of preferred fr curves. After all it just music in a room in all cases

It would be more pleasant discussing this over a glass !

I am looking forward to seeing the design develop
Phil
 
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Retearl

New Member
Mar 26, 2022
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Colorado Springs
View attachment 104522
A mole's eye view of one corner of the basement, containing the audio room, whose dimensions will be 6.4m(H) x 7.0m(W) x 10.0m(L). That's 21ft(H) x 23ft(W) x 33ft(L). Apologies - I'll stick with the metric system, as that is the standard used in the plans. Conversion from meters to feet: 1.0m = 3.28ft. The rectangular structure on the bottom R is a portion of the swimming pool to be built above.
Well done! Normally the most prevalent barrier for a great listening room in a home is size. To design on a completely blank slate is such a treat! Congratulations! For listening rooms bigger is better!!!
 
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Retearl

New Member
Mar 26, 2022
3
1
3
66
Colorado Springs
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 point-source approximation to create a deep/wide soundstage, dynamically scalable pin-point 3D imaging by WORKING with room acoustics (for the mid/highs) and floor/wall boundaries (for natural augmentation of sub-200Hz long bass wavelengths).

My preference is for vertically aligned dynamic drivers on an appropriately contoured and minimized baffle surface area, with tweeter(s) on top, ideally at ear-height or slightly higher to project a slightly elevated soundscape, and the midrange placed below at very close proximity to the tweeter, ideally within 1/2 the crossover frequency wavelength to minimize deleterious interactions.

I'm not a fan of M-T-M D'Appolito arrays, as I can easily hear driver nulls which among other undesirable polar inconsistencies, separate music into vertical layers of horizontalized donut "rings". I also don't care about "time alignment" through second-order crossovers or voice-coil alignment into a common vertical line. Anyone who can read a step-response curve knows that propagated sound arrives at different times THROUGHOUT the frequency range, and that achieving perfect time alignment at the listening position is but a misguided dream, and more importantly, our listening ear/brain mechanism is not particularly sensitive to group delay.

Applying DSP correction to "time align" arrivals isn't my taste either, as that introduces off-axis anomalies which suck the life out of music, according to my experience experimenting with the one of the most sophisticated room correction equipment featuring a mic array with four microphone capsules (to capture vertical azimuth data).

As far as I know (and heard/seen), only offerings from Von Schweikert Audio provides the adjustability and flexibility to optimize its acoustic output to optimize various loudspeaker placement locations, and room size/volume - attributes which are unique in the marketplace... I'm a HUGE fan of VSA!

But I'm casting a wide net out of an abundance of curiosity, and earmarking flagship models from multiple manufacturers (listed below in alphabetical order) for auditioning in an optimized-room-acoustics listening room to properly showcase the capabilities of the loudspeaker. Given the excitement and media coverage at High End Munich 2023, some European brands which I have not auditioned extensively have been added below.

Have I missed any others, which broadly deliver on the performance characteristics I'm looking for?

* * * * *

Magico (upcoming M7/M8 incorporating trickle-down technologies from the M9)
Marten (audition pending)
Rockport (Lyra - audition pending)
Von Schweikert Audio (Ultra 7 or 9 + pair of high-level input bass-management subwoofers)
TAD (co-axial drivers, ie. Reference 1-TX)
Vimberg/TIDAL (auditions pending)
Vivid (upcoming flagship model, one slot above the Giya G1 Spirit)
Zellaton (audition pending)
One speaker you may want to start with, for a room that size is a vintage speaker, but what that owners would say has not been bested; the Dunlavy SC-VI. It has been around since the 90s, very flat & very efficient, giving you a wide choice for other components. Also, a near-perfect pair can offen be had for $10k or less, a small fraction of what that level of performance/perfection would cost new today. They’re the size & weight of a refrigerator, but most who own them are the original owners, as they claim to have never heard better. Then, if you really want to go over the top, not to be bested by any, find a pair of matching bass towers that are VERY rare! It is said the John Dunlavy took extra care with his flagship model & most left the factory better that +/- .5 dB. It’s not a speaker for the masses, but it is THE massive speaker for the select few…
 

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Retearl

New Member
Mar 26, 2022
3
1
3
66
Colorado Springs
Us audiophiles are a special breed, persistently pursuing perfection despite diminishing returns, to reach the asymptotic limits of whatever constraints life imposes on us. Rarely do we have the chance to bust through and quantum-leap into a higher orbit, as we typically run out of energy, resources, and especially, time. During the past 40+ years as an audiophile, this hobby has brought me immense enjoyment and knowledge, always returning far more than the cost... few pursuits are as compelling as this one!

During my search for a new home to move into, the ideal space for a dedicated listening room was a Top Three on my criteria list. When the occasion would present itself, my wife will reveal to our friends the reason our search had dragged on for over a year - my obsession with finding the space for the audio room. How amusing it was when the occasional audiophile acquaintance we'd meet would be in rabid agreement with me.

The long search finally concluded last fall, when we found our dream “home“, a piece of land on which a very old 50+ house stood. Yay, an opportunity to design and rebuild a new home, which of course, must have a dedicated listening room!

I'd like to share my home-building, or more accurately, my dedicated audio room build, with my fellow WBF denizens. The "Big Dig" alludes to the basement in which the audio room will be built, and to fellow-WBF member Hugh, who started a forum thread describing his journey of digging deeply to build his very own dedicated listening room in a ground-breaking and heroic way. Collectively the experience and knowledge of everyone on WBF far exceeds whatever I've had the luck to acquire. Together, I'm hoping that this project will be a satisfying and worthy accomplishment on par with successfully reaching a magnificently higher orbit.
This video is worth watching! https://forums.stevehoffman.tv/thre...ritz-the-worlds-finest-stereo-system.1137797/
 

QuadDiffuser

VIP/Donor
Apr 2, 2017
372
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Hong Kong
One speaker you may want to start with, for a room that size is a vintage speaker, but what that owners would say has not been bested; the Dunlavy SC-VI. It has been around since the 90s, very flat & very efficient, giving you a wide choice for other components. Also, a near-perfect pair can offen be had for $10k or less, a small fraction of what that level of performance/perfection would cost new today. They’re the size & weight of a refrigerator, but most who own them are the original owners, as they claim to have never heard better. Then, if you really want to go over the top, not to be bested by any, find a pair of matching bass towers that are VERY rare! It is said the John Dunlavy took extra care with his flagship model & most left the factory better that +/- .5 dB. It’s not a speaker for the masses, but it is THE massive speaker for the select few…
Retearl, thank you for the suggestion for the Dunlavy. As I have mentioned, regret that I'm not a fan of MTM D'Appolito configurations, second-order crossover networks, nor discontinuous baffles which are a source of coherence-destructive diffraction.
 
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QuadDiffuser

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Apr 2, 2017
372
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Hong Kong

stephen_volker

Well-Known Member
Nov 2, 2015
172
8
248
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 point-source approximation to create a deep/wide soundstage, dynamically scalable pin-point 3D imaging by WORKING with room acoustics (for the mid/highs) and floor/wall boundaries (for natural augmentation of sub-200Hz long bass wavelengths).

My preference is for vertically aligned dynamic drivers on an appropriately contoured and minimized baffle surface area, with tweeter(s) on top, ideally at ear-height or slightly higher to project a slightly elevated soundscape, and the midrange placed below at very close proximity to the tweeter, ideally within 1/2 the crossover frequency wavelength to minimize deleterious interactions.

I'm not a fan of M-T-M D'Appolito arrays, as I can easily hear driver nulls which among other undesirable polar inconsistencies, separate music into vertical layers of horizontalized donut "rings". I also don't care about "time alignment" through second-order crossovers or voice-coil alignment into a common horizontal plane and vertical line. Anyone who can read a step-response curve knows that propagated sound arrives at different times THROUGHOUT the frequency range, and that achieving perfect time alignment at the listening position is but a misguided dream, and more importantly, our listening ear/brain mechanism is not particularly sensitive to group delay.

Applying DSP correction to "time align" arrivals isn't my taste either, as that introduces off-axis anomalies which suck the life out of music, according to my experience experimenting with the one of the most sophisticated room correction equipment featuring a mic array with four microphone capsules (to capture vertical azimuth data).

As far as I know (and heard/seen), only offerings from Von Schweikert Audio provides the adjustability and flexibility to optimize its acoustic output to optimize various loudspeaker placement locations, and room size/volume - attributes which are unique in the marketplace... I'm a HUGE fan of VSA!

But I'm casting a wide net out of an abundance of curiosity, and earmarking flagship models from multiple manufacturers (listed below in alphabetical order) for auditioning in an optimized-room-acoustics listening room to properly showcase the capabilities of the loudspeaker. Given the excitement and media coverage at High End Munich 2023, some European brands which I have not auditioned extensively have been added below.

Have I missed any others, which broadly deliver on the performance characteristics I'm looking for?

* * * * *

Magico (upcoming M7/M8 incorporating trickle-down technologies from the M9)
Marten (audition pending)
Rockport (Lyra - audition pending)
Von Schweikert Audio (Ultra 7 or 9 + pair of high-level input bass-management subwoofers)
TAD (co-axial drivers, ie. Reference 1-TX)
Vimberg/TIDAL (auditions pending)
Vivid (upcoming flagship model, one slot above the Giya G1 Spirit)
Zellaton (audition pending)
You might also consider use Nearfield Acoustic Pipedream speakers.
 

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