My dedicated audio room build - QuadDiffusor's Big Dig

[QuadDiffuser]

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.

 

[QuadDiffuser]

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.

 

[QuadDiffuser]

The basement's external structural wall is on the L. Visible on the R is the sunken portion of the swimming pool. The audio room, being underground, should benefit from background ambient noise being as close to zero dB as practically possible, and the potential to be free from airborne RF pollution. Ultra-low impedance copper rods will be sunken deeply into the surrounding soil to provide my audio system with true “earth ground” access points.

 

[QuadDiffuser]

Sectional view, showing the audio room's front wall. The distances from floor to ceiling differs slightly, depending on the location of the overhead beams and swimming pool bottom (translates to a minimum height of 5.38m).

 

[QuadDiffuser]

Red is where the overhead canopy will hang - acoustic cabinets/modules will be installed through a grid substructure. Green is where the A/C hardware will be placed, with any remaining space filled with acoustic cabinets/modules. I will consider leveling the entire ceiling’s drop for visual uniformity, or alternatively, a single step height transition.

 

[Ron Resnick]

Those dimensions are absolutely amazing! Congratulations on embarking upon this very exciting project -- and thank you for sharing your journey with us!

 

[HughP3]

Wonderful stuff QuadD! Very exciting!

 

[QuadDiffuser]

Those dimensions are absolutely amazing! Congratulations on embarking upon this very exciting project -- and thank you for sharing your journey with us!

Thanks, Ron! The room’s superstructure wall-dimension ratios may initially appear to be non-optimal according to Bonello guidelines but actually the generous ceiling height allows for installation of ceiling modules of both bass velocity attenuators and air gap voids which when combined, perform even better in reducing standing waves (through room resonance broadening/distribution and the lowering of Q-factors) than a solid slab of ceiling concrete marking a theoretically-more-ideal lower ceiling height. Looking forward to advice from you and others!

 

[QuadDiffuser]

Wonderful stuff QuadD! Very exciting!

Thanks Hugh! Looking forward to visiting you in April. Thank you in advance for your generous hospitality!

 

[cjf]

Sounds like a fun project. Your a brave soul having the listening room below grade from a large body of water above it...unless I misunderstood your description?

 

[QuadDiffuser]

Sounds like a fun project. Your a brave soul having the listening room below grade from a large body of water above it...unless I misunderstood your description?

Well, the swimming pool vessel will be designed NOT to leak. Ever!

 

[QuadDiffuser]

My listening room will require acoustic treatment modules, for attenuation of bass pressure and diffusion of mid/high frequencies. There are two basic technologies for bass energy reduction: velocity attenuators via "lossy" fill materials, or Helmholz/membrane sympathetic resonance dampeners. Fundamentally, they operate very differently.

Velocity attenuators "slow down" pressure waves through molecular friction, its effectiveness magnified through filling material such as activated carbon which have incredibly high surface area relative to size, as molecules bounce and slam around back and forth through air gaps/voids, dissipating energy through interactions with both low mass of the highly porous filling, and the high mass of the cabinetry then mechanically coupled to the surrounding wall. Velocity attenuators can operate even when "suspended" away from wall surfaces and boundaries, because the internal space and the mass of the heavy and stiff cabinets BECOME part of the attenuation system. The key is to allow ample flow of air molecules through multiple materials, so the energy maximizes opportunities to interact.

Helmholtz resonators are "tuned" to a particular resonance frequency with a membrane and/or plate oscillating in response to excitation, its dynamic energy then dissipated through mechanical coupling to elastic/lossy material. These sympathetic resonance dampeners work particularly well at high pressure (zero velocity) zones, ie. wall surfaces, and corners/edges where multiple boundaries meet.

My current listening room uses both technologies, activated-carbon filled cabinets from Acoustic Fields which are essentially "passive" velocity attenuators, as well as "active" Helmholtz/membrane anti-noise generators from Switzerland's PSI Audio called AVAAs. They are complimentary, as the ACDA cabinets inserted on the wall and hung on the ceiling are "fixed" in position as well as bass frequency effectiveness but can attenuate vast amounts of bass energy in a brute-force fashion, whereas the AVAAs are positionally mobile and respond dynamically, generating "anti-waves" in real-time responding to what its microphone hears in its immediate vicinity - nimble, but very likely limited in its ability to cancel voluminous bass energy due to its membrane's small surface area and limited displacement distance.

Data on RPG Acoustical Systems' Modex family of products suggests that they outperform both the ACDA-10 and ACDA-12 modules from Acoustic Fields and the active bass absorber AVAA from PSI Audio.

 

[QuadDiffuser]

Firstly, data on Acoustic Fields' bass velocity attenuators, extracted from their website. The ACDA-10 addresses a broader band of bass frequencies from 30Hz to 100Hz , while the ACDA-12 is tuned to the lower frequencies from 30Hz upwards, reaching peak absorption at 50Hz. These modules are expensive, heavy, and massive, requiring deep pockets to purchase (and ship internationally) in sufficient amounts to treat large surface areas. If they're suspended from the ceiling, heroic engineering and hardware is required to install (as I have done in my listening room).

In the chart below, note the specific absorption coefficient corresponding to the respective bass frequencies. 1.00 (and above) denotes complete absorption, with lower coefficients denoting proportionally lower absorption.

The page with superimposed blue (ACDA-10) and red (ACDA-12) lines shows the respective products' absorptive abilities graphically. The highest peak with the red dot normalizes the ACDA-12's absorption coefficient at 50Hz of 1.08, to 100%.

 

[Ron Resnick]

as well as active bass absorbers from Switzerland's PSI Audio called AVAAs. Data on RPG Acoustics's Modex family of products suggests that they outperform both the ACDA-10 and ACDA-12 modules from Acoustic Fields and the active bass absorber AVAA from PSI Audio.

Very interesting. I am presently awaiting a demo of AVAAs in my listening room.

Given that they are promoted primarily to the pro audio market, rather than to the audiophile market, I have to believe that AVAAs actually do what they purport to do.

Was your strategy to have the RPGs focus on certain frequencies and the AVAAs focus on other frequencies? Or was using both products and techniques an additive, "boot and suspenders" concept?

 

[QuadDiffuser]

Next, data from two Modex products offered by RPG Acoustical Systems.

The Modex Plate shows very admirable absorption coefficients across a broader frequency range, in a much smaller space, volume-wise.

 

[QuadDiffuser]

The Modex Corner incorporates membrane absorption tuned to selectively target a particular bass peak; the magnitude of their absorption coefficients as well as the breadth of coverage are impressive. In my very large listening room where longer wavelength room resonances will dominate, I will most likely be using the 40Hz version.

 

[QuadDiffuser]

Very interesting. I am presently awaiting a demo of AVAAs in my listening room.

Given that they are promoted primarily to the pro audio market, rather than to the audiophile market, I have to believe that AVAAs actually do what they purport to do.

Was your strategy to have the RPGs focus on certain frequencies and the AVAAs focus on other frequencies? Or was using both products and techniques an additive, "boot and suspenders" concept?

Hi Ron, the Acoustic Fields' ACDAs and PSI Audio's AVAAs are complementary. Please see the additional comments I've added into my previous post, as well as this thread:

PSI Audio AVAA C20 Active Bass Absorber

Has anyone had experience with this product, an active bass standing wave cancellation device? http://www.psiaudio.swiss/avaa-c20-active-bass-trap/ Reviews/forum discussions: https://www.stereophile.com/content/psi-audio-avaa-c20-electronic-bass-trap...

www.whatsbestforum.com

 

[spiritofmusic]

21' is a Hell of a height. Our main living space here at the chapel is just short of that at 35x30x20...I always wonder how those dims would have worked out.

 

[QuadDiffuser]

The 21' ceiling height in itself should not a problem, because 4 - 7ft. will be subtracted through a "dropped" ceiling; the air gap above the false ceiling canopy will be used to hide and house a wide range of hardware including a swimming pool vessel, air conditioning fans/ducts, structural beams, and most importantly, bass pressure attenuating fill material.

The surface of the ceiling canopy will likely be covered by 2D diffusion modules to mitigate "slap echo" reverberation. There are a number of products on the market which can be installed into a drop-grid, for a visually harmonious and pleasing look. Or perhaps the roundtrip distance of 15' x 2 = 30' will obviate any type of surface treatment (as both high and mid frequencies will naturally decay over its journey)? Good news, as this will save me money. Either way, I suspect that apart from the ceiling canopy being designed as a giant bass trap, the next priority would be for it to be maximally diffusive, so the distance won't inadvertently extinguish the fragile high frequencies so important for creating desirable room ambience.

My greatest challenge will be dealing with similar dimensions for both height and width, which would be the worst ratio room ratio possible, potentially causing MASSIVE coincidental room modes.

Using the simple formula: 1130÷2L [where 2L = room dimension x 2, and 1130 is the speed of sound], the primary room modes are calculated to be 26.9Hz (for the 21' ceiling height) and 24.6Hz (for the 23' room width). Since there's very little musical energy in those frequencies, perhaps I can be spared? Perhaps the solution is to build a "room in a room", deliberately adding isolated Sheet Rock walls having disparate resonance frequencies for dampening overall bass energy. I have retained the services of an acoustician for room optimization suggestions, so I'm curious what they will suggest.

 

[Cellcbern]

My listening room will require acoustic treatment modules, for attenuation of bass pressure and diffusion of mid/high frequencies. There are two basic technologies for bass energy reduction: velocity attenuators via "lossy" fill materials, or Helmholz/membrane sympathetic resonance dampeners. Fundamentally, they operate very differently.

Velocity attenuators "slow down" pressure waves through molecular friction, its effectiveness magnified through filling material such as activated carbon which have incredibly high surface area relative to size, as molecules bounce and slam around back and forth through air gaps/voids, dissipating energy through interactions with both low mass of the highly porous filling, and the high mass of the cabinetry then mechanically coupled to the surrounding wall. Velocity attenuators can operate even when "suspended" away from wall surfaces and boundaries, because the internal space and the mass of the heavy and stiff cabinets BECOME part of the attenuation system. The key is to allow ample flow of air molecules through multiple materials, so the energy maximizes opportunities to interact.

Helmholtz resonators are "tuned" to a particular resonance frequency with a membrane and/or plate oscillating in response to excitation, its dynamic energy then dissipated through mechanical coupling to elastic/lossy material. These sympathetic resonance dampeners work particularly well at high pressure (zero velocity) zones, ie. wall surfaces, and corners/edges where multiple boundaries meet.

My current listening room uses both technologies, activated-carbon filled cabinets from Acoustic Fields which are essentially "passive" velocity attenuators, as well as "active" Helmholtz/membrane anti-noise generators from Switzerland's PSI Audio called AVAAs. They are complimentary, as the ACDA cabinets inserted on the wall and hung on the ceiling are "fixed" in position as well as bass frequency effectiveness but can attenuate vast amounts of bass energy in a brute-force fashion, whereas the AVAAs are positionally mobile and respond dynamically, generating "anti-waves" in real-time responding to what its microphone hears in its immediate vicinity - nimble, but very likely limited in its ability to cancel voluminous bass energy due to its membrane's small surface area and limited displacement distance.

Data on RPG Acoustical Systems' Modex family of products suggests that they outperform both the ACDA-10 and ACDA-12 modules from Acoustic Fields and the active bass absorber AVAA from PSI Audio.

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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