My dedicated audio room build - QuadDiffusor's Big Dig

[QuadDiffuser]

Here's a rendering of the ceiling for determining the positions of the air conditioning outlets, showing extensive usage of quadratic diffusers; P23s x 8 on the front wall, P17s x 20 on the sidewalls, and P11s x 49 on the ceiling canopy, all constructed out of SOLID tropical hardwood sourced from Indonesia (not veneered plywood) with the voids inside chambers filled with dense, waterproofing-sprayed (to mitigate moisture driven deterioration) activated carbon pellets to dampen bass pressure waves.

Wood choices are ebony, sungkai, or teak; now evaluating pros/cons/costs.

Advantages of solid wood include:
- aesthetics and beauty, with contiguous grain structure in 3D throughout
- warping resistance of the thin dividing "fins"
- no VOC off-gassing
- higher density/mass, leading to less absorption of acoustic energy
- uniformity in color, post-varnishing

Disadvantages include:
- high cost

Trying really hard to make my room sound "world class" great!

 

[MarkusBarkus]

...nice! I searched around for sourcing on the carbon pellets, and man are they expensive. Primarily, shipping as I recall from a few years back. But I do like the concept, as you have described, although I don't recall the "waterproofing" step in my potential plan. Perhaps a good idea, relative to local environment. Very nice Q.

 

[pjwd]

Here's a rendering of the ceiling for determining the positions of the air conditioning outlets, showing extensive usage of quadratic diffusers; P23s x 8 on the front wall, P17s x 20 on the sidewalls, and P11s x 49 on the ceiling canopy, all constructed out of SOLID tropical hardwood sourced from Indonesia (not veneered plywood) with the voids inside chambers filled with dense, waterproofing-sprayed (to mitigate moisture driven deterioration) activated carbon pellets to dampen bass pressure waves.

Wood choices are ebony, sungkai, or teak; now evaluating pros/cons/costs.

Advantages of solid wood include:
- aesthetics and beauty, with contiguous grain structure in 3D throughout
- warping resistance of the thin dividing "fins"
- no VOC off-gassing
- higher density/mass, leading to less absorption of acoustic energy
- uniformity in color, post-varnishing

Disadvantages include:
- high cost

Trying really hard to make my room sound "world class" great!

View attachment 144195

I am continually impressed by your dedication to excelence.. this is epic! However ss you would have noticed I am not a big fan of QRD .. so this looks like a nightmare to me
- you will get a very diffuse soundfield but it will not be correlated at all with the direct sound
- with all those timber blades I am guessing you will get an unpredictable bass absorbtion through vibration.. the common dimensions will means it's a specific fr
- the repeat of similar patterns will creating lobing in the reflected sound not unlike mtm speakers you don't care for
- it's very expensive and perhaps not visually conducive to a relaxing space.. I always feel a good acoustic design works well visually

I don't doubt that it will work ( and possibly pretty well) but the question is it the best approach and can the result be predicted .. I am not trying to be argumentative here but responding to your question for excellence.

I believe you really need to focus on the median plane .. say 400 mm above floor to say 1800 .. where the ear resides .. reflections out of that zone can be specular and correlated and retain life in the room.. general absorbtion can be added to these space to calm the room if needed
Similar with ceiling .. just the area of influence

You want the space to be calm but not lifeless
This would be a much cheaper path
My 2 bobs worth

 

[QuadDiffuser]

Hi pjwd, your observations and opinions are very valuable, as you're helping me think through the issues from multiple angles. Pease continue to engage me!

After much deliberation, my verdict is to continue favoring P17 QRDs on the sidewalls instead of hemispherical diffusers due to the following desirables:

- attenuation of direct sound striking at a 45 degree of incidence by ~20dB (see chart below), more than sufficient to make the reflected sound inaudible, according to the principles of the precedence effect

- consistent response over a wide bandwidth of 250Hz - 3.5kHz, resulting in a spectrally neutral sound through the midrange and lower treble

- decorrelation of direct sound through comb filtering to increase perceived differences between direct and indirect sound

- avoiding the perception of lobing and out-of-phase reflections, by locating the listening position beyond the minimum distance, typically defined by 1.5-2.0 the wavelength of the lowest bandwidth of the QRD (250Hz wavelength of 7 feet x 2 = 14 feet minimum)

- the math: the sidewalls will be ~2.0m away laterally from the loudspeakers; laterally-projected soundwaves will travel diagonally over longer distances before striking the QRD P17s, then double that distance as travel diagonally towards the listening position, and in total travel more than 6.0m or 20ft

What might the alternatives be?
- absorption (frequency-specific, thus selective and non-linear absorption, most in the highs)
- scattering (typically, small geometries address only the high frequencies, leaving mids and lows untouched)
- untreated first reflections (high-energy phantom reflections)
- redirected first reflections (mid-energy phantom reflections)

All of the above alternatives seem to me to have their own idiosyncratic sonic signatures, departing from the ideals of consistency, neutrality, and predictability offered by the P17 QRDs.

Also, I believe that phase-correct reflections resemble mirror images in a "house of mirrors", creating undesirable duplicates which make it less easy to differentiate between the direct sound and indirect sounds through interference, particularly if the reflections are not attenuated sufficiently. Attenuation will also make the room will sound more "dead", especially if the levels and rates of absorption is not uniform across the frequency spectrum.

Phase-scrambled reflections, on the other hand, increases the contrast between the direct and indirect sounds without deadening the room, enhancing articulation and development of discrete 3D images in the soundstage. It's well documented and universally accepted that the "sound" of large and deep QRDs is extremely neutral, uncolored, and impart a very desirable characteristic of pushing the perceptible boundaries of a room far away, expanding the soundstage while enhancing the articulation and location of the instruments within. I hear this in abundance in my own listening room which is extensively treated with QRDs.

Admittedly, anchoring 10 large pieces of P17 QRDs on each sidewall is a very expensive proposition, but I don't believe it is misguided or risky because there is plenty of psychoacoustical science and rationale for this. Perhaps because of the expense and space required, exactly zero other audiophiles have even attempted doing this, and therefore none have ever heard its qualities to comment objectively?

Aesthetics wise, they will be off to the sides beyond the boundaries of peripheral vision, colored in a dark stain, and unlike horizontal stripes, its vertical slats will not trigger strange flickering neural-visual sensations originating in the retina. The listening environment will be zen-like in its quietness (I expect the ambient noise be sub-30dBA), and very much "alive" with its wonderfully exceptional acoustics.

Would appreciate any information on why phase-correlated sidewall reflections might be a definitively better solution!

 

[MarkusBarkus]

...FWIW I sit theoretically "too close" to a pair of quad diffusors behind my chair, and have never noticed any "lobing" effect. Ditto from hifi friends seated in the G-spot. Following in awe, awaiting the next chapter, QD.

 

[gleeds]

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:

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Cellciburn, I used an extensive suite of Delta Z acoustic panels in our high-end audio showroom in 2016. I was curious about Hansen's technology, but we loved how they looked. In my experience, the product has not caught on in the high-end community for a few reasons) high relative cost, and b) the diffusers are made of CNC MDF and have fragile corners that break off when you look at them. Cecillburn, our panel's combined diffusers/absorbers, worked well for that purpose.

As far as taming bass modes are concerned, we did not find them helpful. Traditional bass traps work well, e.g., ASC, which we use; however, they provide nowhere near the effectiveness and tunability of Shockwave room correction woofers. Per my disclosure below, I am self-interested; however, I make it a point never to comment on something we do not have considerable direct experience with.

 

[pjwd]

Hi pjwd, your observations and opinions are very valuable, as you're helping me think through the issues from multiple angles. Pease continue to engage me!

After much deliberation, my verdict is to continue favoring P17 QRDs on the sidewalls instead of hemispherical diffusers, due to the following desirables:

- attenuation of direct sound striking at 45 degree of incidence by ~20dB (see chart below), more than sufficient to make the reflected sound inaudible, according to the principles of the precedence effect

- consistent response over a wide bandwidth of 250Hz - 3.5kHz, resulting in a spectrally neutral sound

- decorrelation of direct sound through comb filtering, desirable to increase perceived differences between direct and scrambled/indirect

- avoiding the perception of lobing and out-of-phase reflections, by locating the listening position beyond the minimum distance, typically defined by 1.5-2.0 the wavelength of the lowest bandwidth of the QRD (250Hz wavelength of 7 feet x 2 = 14 feet minimum)

- the math: the sidewalls will be ~2.0m away laterally from the loudspeakers; laterally-projected soundwaves will travel diagonally over longer distances before striking the QRD P17s, then double that distance as travel diagonally towards the listening position, and in total travel more than 6.0m or 20ft

What might the alternatives be?
- absorption (frequency-specific, thus selective and non-linear absorption, most in the highs)
- scattering (typically, small geometries address only the high frequencies, leaving mids and lows untouched)
- untreated first reflections (high-energy phantom reflections)
- redirected first reflections (mid-energy phantom reflections)

All of the above alternatives seem to me to have their own idiosyncratic sonic signatures, departing from the ideals of consistency, neutrality, and predictability offered by the P17 QRDs.

Also, I believe that phase-correct reflections resemble mirror images in a "house of mirrors", creating undesirable duplicates which make it less easy to differentiate between the direct sound and indirect sounds through interference, particularly if the reflections are not attenuated sufficiently. But attenuation will make the room will sound more "dead", especially if the levels and rates of absorption is not uniform across the frequency spectrum.

Phase-scrambled reflections, on the other hand, increases the contrast between the direct and indirect sounds without deadening the room, enhancing articulation and development of discrete 3D images in the soundstage. It's well documented and universally accepted that the "sound" of large and deep QRDs is extremely neutral, uncolored, and impart a very desirable characteristic of pushing the perceptible boundaries of a room far away, expanding the soundstage while enhancing the articulation and location of the instruments within. I hear this in abundance in my own listening room which is extensively treated with QRDs.

Admittedly, anchoring 10 large pieces of P17 QRDs on each sidewall is a very expensive proposition, I don't believe it is misguided or risky because there is plenty of psychoacoustical science and rationale for this. Perhaps of the expense and space required, exactly zero other audiophiles have even attempted doing this, and therefore none have ever heard its qualities?

Aesthetics wise, they will be off to the sides beyond the boundaries of peripheral vision, colored in a dark stain, and unlike horizontal stripes, its vertical slats will not trigger strange flickering neural-visual sensations originating in the retina. The listening environment will be zen-like in its quietness (I expect the ambient noise be sub-30dBA), and very much "alive" with its wonderfully exceptional acoustics.

Would appreciate any information on why phase-correlated sidewall reflections might be a definitively better solution!

View attachment 144301

I know I am up against it arguing against qrd with someone whose has that as a handle
My slim knowledge is second hand, having worked with an excellent acoustic engineer on a number of projects. He introduced me to Tapio Lokki who has done some amazing research on concert halls. ( worth reading) The principals don't all transfer to a listening room but I believe most do on a reduced scale. The lateral reflections are very important to the experience of a hall .. they improve many aspects of the experience.. and it is ideal they corelate with direct sound .. in halls you have a genuine reverberent field and it will clash with direct sound if not corelated.
In a listening room you have 2 acoustics .. the recorded room and the listening room. You want a live sound in the room and an alignment of those 2 acoustics just makes sense to me. Having a component of non correlated sound in the chain surely will clash. The idea of a delay in reflections and then a corelated reveberent tail to support the direct sound provides an integrated continuum. In halls a delay of 80ms is considered ideal .. the usual figure for a room is 10ms but longer is better.

The analogy of mirrors is exactly how I think of the space but your ears are not everywhere, they are in one location and it's the "mirrors" to that spot that will influence the sound. By angling panels or just masking reflections you can have a calm zone in the listening spot while the rest of the space is quite live... It's sometimes called a reflection free zone but its more a reflection delay zone

Now having said that, as you note you have a large room with quite long reflection paths ... also qrd will drop the level quite a lot so non correlation may not be an issue and the room will sound great. But is it the optimum.

I have never been in an anechoic chamber but have been in recording sound stages that are heavily damped.. they are unervingly dead.
I would be concerned that the extensive use of qrd will drop the reflected sound levels in a similar way. The other thing about acoustics is that when you put in a lot of stuff there are unintended consequences. I suspect that you will get some strong suckouts at unpredictable frequencies from many similar size parts vibrating. In projects we sometimes found ourselves pulling stuff out because of this.
As your qrd are bespoke I guess you can't stage the manufacture ?
Enough waffle from me.. I normally wouldn't bat on like this but you did ask for engagement

Regardless it's going to be an awesome room
Cheers
Phil

 

[dcathro]

Hi pjwd, your observations and opinions are very valuable, as you're helping me think through the issues from multiple angles. Pease continue to engage me!

After much deliberation, my verdict is to continue favoring P17 QRDs on the sidewalls instead of hemispherical diffusers due to the following desirables:

- attenuation of direct sound striking at a 45 degree of incidence by ~20dB (see chart below), more than sufficient to make the reflected sound inaudible, according to the principles of the precedence effect

- consistent response over a wide bandwidth of 250Hz - 3.5kHz, resulting in a spectrally neutral sound through the midrange and lower treble

- decorrelation of direct sound through comb filtering to increase perceived differences between direct and indirect sound

- avoiding the perception of lobing and out-of-phase reflections, by locating the listening position beyond the minimum distance, typically defined by 1.5-2.0 the wavelength of the lowest bandwidth of the QRD (250Hz wavelength of 7 feet x 2 = 14 feet minimum)

- the math: the sidewalls will be ~2.0m away laterally from the loudspeakers; laterally-projected soundwaves will travel diagonally over longer distances before striking the QRD P17s, then double that distance as travel diagonally towards the listening position, and in total travel more than 6.0m or 20ft

What might the alternatives be?
- absorption (frequency-specific, thus selective and non-linear absorption, most in the highs)
- scattering (typically, small geometries address only the high frequencies, leaving mids and lows untouched)
- untreated first reflections (high-energy phantom reflections)
- redirected first reflections (mid-energy phantom reflections)

All of the above alternatives seem to me to have their own idiosyncratic sonic signatures, departing from the ideals of consistency, neutrality, and predictability offered by the P17 QRDs.

Also, I believe that phase-correct reflections resemble mirror images in a "house of mirrors", creating undesirable duplicates which make it less easy to differentiate between the direct sound and indirect sounds through interference, particularly if the reflections are not attenuated sufficiently. Attenuation will also make the room will sound more "dead", especially if the levels and rates of absorption is not uniform across the frequency spectrum.

Phase-scrambled reflections, on the other hand, increases the contrast between the direct and indirect sounds without deadening the room, enhancing articulation and development of discrete 3D images in the soundstage. It's well documented and universally accepted that the "sound" of large and deep QRDs is extremely neutral, uncolored, and impart a very desirable characteristic of pushing the perceptible boundaries of a room far away, expanding the soundstage while enhancing the articulation and location of the instruments within. I hear this in abundance in my own listening room which is extensively treated with QRDs.

Admittedly, anchoring 10 large pieces of P17 QRDs on each sidewall is a very expensive proposition, but I don't believe it is misguided or risky because there is plenty of psychoacoustical science and rationale for this. Perhaps because of the expense and space required, exactly zero other audiophiles have even attempted doing this, and therefore none have ever heard its qualities to comment objectively?

Aesthetics wise, they will be off to the sides beyond the boundaries of peripheral vision, colored in a dark stain, and unlike horizontal stripes, its vertical slats will not trigger strange flickering neural-visual sensations originating in the retina. The listening environment will be zen-like in its quietness (I expect the ambient noise be sub-30dBA), and very much "alive" with its wonderfully exceptional acoustics.

Would appreciate any information on why phase-correlated sidewall reflections might be a definitively better solution!

View attachment 144301

Hi ,

Do you have an acoustic engineer specifying your project, or are you specifying this yourself based on theory?

I think pjwd has a lot of valid points.

My own experience with acoustics is that too much can be as bad (or worse) as too little. I have also found a blend of absorption and diffusion to be better than diffusion alone. Finally, it is critical to only have treatment in the spots that you need them.

I always hesitate to give advice, as we all need to tread our own path, and I wish you the best with your project!

Cheers

David

 

[QuadDiffuser]

Hi ,

Do you have an acoustic engineer specifying your project, or are you specifying this yourself based on theory?

I think pjwd has a lot of valid points.

My own experience with acoustics is that too much can be as bad (or worse) as too little. I have also found a blend of absorption and diffusion to be better than diffusion alone. Finally, it is critical to only have treatment in the spots that you need them.

I always hesitate to give advice, as we all need to tread our own path, and I wish you the best with your project!

Cheers

David

David,

All of the above, and much more!

I have:

1) already designed and built the best sounding audio room I've heard anywhere in my 40+ years as an audiophile
Every time I sit in the listening seat, I feel so grateful and fortunate to be able to enjoy a 3D panoramic soundscape, replete with authentic depth, width, and height - marveling at the musicality of it all, never having to worry about audiophilia upgrade-itis

2) digested many complex books on the subjects of acoustics, diffusers, psychoacoustics (see my Kindle folder below)
Unlike "opinions" which are so abundant (and redundant) on the Internet, there's plenty of objective data and science inside these books, written by seasoned acoustic engineers

3) deeply researched all available sources of information on the Internet - forums, websites, YouTube, etc.
Not surprisingly, this task never ends, but I'm "getting there"; armed with increasing knowledge, I'm better able to distinguish fact from fiction, and separate the wheat from the chaff.

4) hired the best professional acoustician in town, to assist me in designing and building my new basement audio room
Hey, how else am I able to show everyone the construction drawings and model the predicted acoustic performance of the modules, plates, and diffusers?

5) been auditioning the "sound" of variable diagonal, and off-axis 1D quadratic diffusion (simulation of my sidewall QRD diffuser design for my future audio room), by alternatively turning off one of the L or R channel monoblock amplifiers and doing a "walk around" diagonally to experience what can be heard from the 16 inch deep wall mounted P17 QRDs. So far, so good! Nothing offensive or deleterious of the cohesiveness to either speaker's direct sound.

 

[QuadDiffuser]

Quadratic diffusers vs Polycylindrical diffusers

Here's an old, but great video on the subject.

As polycylindrical diffusers ("polys") focus sound into certain directions at certain frequencies (their diameter determines bandwidth), I'm inclined to think that horizontal arrays of polys on walls may cause unpleasant repetitive grating effects, especially when placed in an orderly, repeating fashion. Theoretically, units should therefore have different radii of curvature, be placed at different positions (or even randomly) in the room. However, doing so will violate the rules of consistency, predictability and L/R symmetry in a stereo setup - hence they will not be optimal when used on sidewalls.

 

[Zuman]

Please forgive this very pedestrian question, but are rooms with such extensive treatments unusually difficult to clean, with thousands of little dust-traps, including in hard-to-reach places? Do you take any special measures outside the room to mitigate dust accumulation inside? Thanks!

 

[pjwd]

David,

All of the above, and much more!

I have:

1) already designed and built the best sounding audio room I've heard anywhere in my 40+ years as an audiophile
Every time I sit in the listening seat, I feel so grateful and fortunate to be able to enjoy a 3D panoramic soundscape, replete with authentic depth, width, and height - marveling at the musicality of it all, never having to worry about audiophilia upgrade-itis

2) digested many complex books on the subjects of acoustics, diffusers, psychoacoustics (see my Kindle folder below)
Unlike "opinions" which are so abundant (and redundant) on the Internet, there's plenty of objective data and science inside these books, written by seasoned acoustic engineers

3) deeply researched all available sources of information on the Internet - forums, websites, YouTube, etc.
Not surprisingly, this task never ends, but I'm "getting there"; armed with increasing knowledge, I'm better able to distinguish fact from fiction, and separate the wheat from the chaff.

4) hired the best professional acoustician in town, to assist me in designing and building my new basement audio room
Hey, how else am I able to show everyone the construction drawings and model the predicted acoustic performance of the modules, plates, and diffusers?

5) been auditioning the "sound" of variable diagonal, and off-axis 1D quadratic diffusion (simulation of my sidewall QRD diffuser design for my future audio room), by alternatively turning off one of the L or R channel monoblock amplifiers and doing a "walk around" diagonally to experience what can be heard from the 16-inch deep wall-mounted P17 QRDs. So far, so good! Nothing offensive or deleterious of the cohesiveness to either speaker's direct sound.

View attachment 144753

View attachment 144754

Have you ever looked at smt wing diffusers .. particularly the acrylic models .. I have wondered what the dispersion pattern might be .. they look quite interesting

 

[QuadDiffuser]

Please forgive this very pedestrian question, but are rooms with such extensive treatments unusually difficult to clean, with thousands of little dust-traps, including in hard-to-reach places? Do you take any special measures outside the room to mitigate dust accumulation inside? Thanks!

Zuman,

Nope, nothing special used for keeping the air clean in my audio room over the years. Just the usual air conditioning during the warmer months, having rudimentary air intake filters which were vacuumed once every couple of weeks.

Thanks for reminding me - it's been 7-8 years already since I "cleaned" the QRDs! I used my Dyson V8 Fluffy cordless vacuum (with its thin extension rod + tiny brush attachment) to clean the compartments of my P17 QRDs just now - it took less than 600 seconds (10 minutes) to vacuum (16 wells/unit x 6 units) all 96 wells, or an average of 6.25 seconds/well. Scrutinizing the contents of the vacuum's lint trap, it was mostly just fine dust. Guessing it's mostly dried skin cells (believer it or not, the majority of household dust) and plaster (recent repair of a nearby false ceiling).

Guess I could use a microfiber cloth (then wet wipes) to clean them more thoroughly.
But I think it's good enough for now, less critical than cleaning our ear canals periodically to rid of ear wax, LOL.

 

[dcathro]

David,

All of the above, and much more!

I have:

1) already designed and built the best sounding audio room I've heard anywhere in my 40+ years as an audiophile
Every time I sit in the listening seat, I feel so grateful and fortunate to be able to enjoy a 3D panoramic soundscape, replete with authentic depth, width, and height - marveling at the musicality of it all, never having to worry about audiophilia upgrade-itis

Great,

I am really pleased that you are getting what you want. Knowig what YOU want is half the battle!

2) digested many complex books on the subjects of acoustics, diffusers, psychoacoustics (see my Kindle folder below)
Unlike "opinions" which are so abundant (and redundant) on the Internet, there's plenty of objective data and science inside these books, written by seasoned acoustic engineers


View attachment 144753

Interestingly, I read all the books that I could get my hands on 27 years ago when I was having my studio built in London. I just got confused, as just like in audio, every acoustic engineering expert has a different view on how it should be done.

4) hired the best professional acoustician in town, to assist me in designing and building my new basement audio room
Hey, how else am I able to show everyone the construction drawings and model the predicted acoustic performance of the modules, plates, and diffusers?

That's the ticket! I was put on to Nick Whittaker and Recording Architecture by the late Billy Woodman of ATC.







Although I have better equipment today, I don't have that amazing room.

I do wish you success in your project.

 

[pjwd]

Great,

I am really pleased that you are getting what you want. Knowig what YOU want is half the battle!


Interestingly, I read all the books that I could get my hands on 27 years ago when I was having my studio built in London. I just got confused, as just like in audio, every acoustic engineering expert has a different view on how it should be done.



That's the ticket! I was put on to Nick Whittaker and Recording Architecture by the late Billy Woodman of ATC.

View attachment 144820

View attachment 144821

View attachment 144822

Although I have better equipment today, I don't have that amazing room.

I do wish you success in your project.

You hung with Billy Woodman ? Very cool..
Nice plush velvet chairs for you clients ... what era was that

 

[dcathro]

You hung with Billy Woodman ? Very cool..
Nice plush velvet chairs for you clients ... what era was that

Billy Woodman was a great and very down to earth guy! I bought quite a few pairs of ATCs ( 20s, 50,s & 100s ) back in the early 90s. Those shots were taken around 98.

 

[QuadDiffuser]

Objective data from tightly twisting the AC line's Live and Neutral conductors together to cancel magnetic induction, resulting in a dramatic reduction of audible noise; simple, but extremely effective!

In this experiment, 12AWG (2mm2) conductors were spiraled at five twists/foot.
From the 2021 AES Convention; by Bill Whitlock, AES Fellow

https://www.jensen-transformers.com/wp-content/uploads/2015/02/AES-Ground-Loops-Rest-of-Story-Whitlock-Fox-Generic-Version.pdf

 

[QuadDiffuser]

Back to the topic of twisting Live + Neutral conductors for the in-wall AC cables, I found this patent application (from 2012) for an even better twist geometry to improve the rejection of EMI/RFI reveals a couple of variations:

https://patentimages.storage.googleapis.com/2e/31/c7/dbf898942be81e/US20120103646A1.pdf

Firstly, the most basic version mirrors what I'll be doing for the "in wall" AC cables in my basement listening room:

 

[QuadDiffuser]

Skipping through a few variations (fig. 5, 6, 7, and 8) to the most elaborate design (fig. 9) submitted for the patent application, purportedly has the best EMI/RFI rejection.

Essentially, it's a four-conductor Star-Quad configuration between the Live and Neutral conductors, with the Ground conductor wrapped in a looser twist. Achieving this twist geometry using DIY methods would be prohibitively difficult due to its complexity.

Perhaps there is a similar design already available today in the marketplace? I'll try looking for it from the usual suspects, ie. Belden.

 

[QuadDiffuser]

To overcome the inevitable challenges of "TLR" (difficulties in digesting very complicated and lengthy text), I harnessed the power of AI. ChatGPT summarized the patent application as follows:

Optimal Power Cable Configuration (Per the Patent)

1. Twisted Pair for Current-Carrying Wires
The live (L) and neutral (N) conductors (or phase conductors in multi-phase systems) should be twisted together.
The twist pitch should be between 2 to 2,000 times the diameter of the conductor. Why? Twisting ensures that the electromagnetic fields created by the conductors cancel each other out over the cable’s length, reducing induced voltages.

2. Untwisted or Loosely Twisted Ground Wire
The ground (G) wire should not be twisted at the same rate as the live/neutral conductors.
Instead, it should run straight along the cable or be helically wrapped at a much lower pitch than the current-carrying wires. Why? Keeping the ground wire separate ensures that any magnetic flux imbalance does not accumulate along the length of the cable, limiting ground-loop voltages.

3. Maintaining a Constant Distance Between Ground and Current-Carrying Wires
The ground wire should be positioned at a fixed distance from the twisted conductors to equalize the average proximity of each conductor to ground. Why? This prevents the ground conductor from being closer to one current-carrying wire than the other, which would otherwise create an imbalance and induce voltages.

4. Optional: Helical Rotation of the Entire Cable
For long cable runs, the entire assembly (twisted pair + ground wire) can be helically rotated at a different pitch.
The ground wire’s pitch should still be lower than the current-carrying wire’s pitch. Why? This helps maintain cable integrity in installations with bends while still preventing voltage buildup.