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Building a High End Listening Room Part 1: Goals, Construction Works, Diffusers

RDacoustic

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This is an account of the process and the steps we took when building our listening room last year. This part deals with preparations, plans and the construction, while the second part will deal with acoustic tuning and include more theory+advice+measurements. The goal: the best possible listening space.

RDacoustic_Listening_Room-scaled.jpg


Our Goals
  • Optimising the ratio of the listening space walls—optimising modal resonance frequencies in a closed space (applicable to up to cca. 200 Hz)
  • Optimising reverberation times on low frequencies
  • Ideal ratio of acoustically absorbing and diffusing elements
  • Ideally positioned speakers and the listening spot
  • A standalone grounding point and power source completely galvanically separated from the power grid
  • Electromagnetic shielding underneath the audio system (larger signal/noise distance)
  • Video projection
  • Two listening systems
The Plan
  • The listening space is in a quiet location, aside from the main road, yet accessible with its own parking lot. The ratio of wall sizes in the room is not ideal though, so construction works are ahead of us. We are going to enlarge the current space, brick up niches between the supporting pillars of the building and acoustically seal up the windows. Further, we are going to lay down our own wiring to our switchboard, with standalone circuits for each audio system, lighting and the ventilation system.
  • Acoustic treatment:
    • Ceiling QRD Hybrid Diffuser 6.7*4.5 m, 25 cm in depth
    • Acoustically absorptive carpet
    • System 1
      • Hybrid Diffuser 5.45*2.6 m, 20 cm depth
      • Left Hybrid Diffuser 2*2 m (circle pattern)
      • Right inverse Hybrid Diffuser 2*2 m (circle pattern)
      • Other acoustic treatment is going to be decided upon on the basis of measurements and subjective tests.
    • System 2
      • Inverse Hybrid diffuser 5.45*2.6 m, 20 cm depth
      • Left Hybrid Diffuser 2*2 m (circle pattern)
      • Right inverse Hybrid Diffuser 2*2 m (circle pattern)
      • Other acoustic treatment is going to be decided upon on the basis of measurements and subjective tests.
  • Audio system power supply
    • Each system will have its own power circuit, complete galvanic separation and a standalone grounding point.
    • Shielding under each system + preparation for taking electrical measurements
  • Preliminary simulation of modal frequencies
Simulation of Modal Frequencies In the Listening Space

Using a handy program called REW, the influence of resonance frequencies in a closed acoustic space can be simulated.

I put in the inner dimensions of the room: 5.45*8.7*2.5 m. A large part of the ceiling will be occupied by a quadratic acoustic diffuser with the max. depth of 25 cm (12.5 cm on average). Converted to the entire ceiling area, it is 8 cm. That is why I intentionally put in the ceiling height lower by 8 cm. For the initial simulation, we will place the speakers 1 m from the back wall and 1 m from the side walls.

The entire area of the front and back walls is going to be covered by the hybrid diffuser, reflectivity/absorption of which changes in relation to the direction in which acoustic energy reaches it. The same goes for the ceiling and large diffusion areas on the walls. That is why I choose medium reflectivity.

Ears of the listener are in 1.2 m, they sit in the axis of the room and they will be moving from a non-ideal position in the direction of the back wall.


s1.jpg



The listener is 2.6 m far from the front wall, we can see a fall on 77 Hz that is starting to fade away in the distance of 3 m.


s2.jpg



On 103 Hz, however, another resonance fall becomes apparent. In the distance of 3.6 m from the front wall, the resonance falls equalize.


s3.jpg
s4.jpg



We approximately got to the generally recommended equilateral triangle. Moving the listener to 4 m is not ideal anymore; another fall becomes apparent at 166 Hz.


s5.jpg



Here, I highlight the reflections from side walls (turquoise and green) which are most prominent in this position. The two 2*2 m hybrid diffusers placed exactly in the middle of the distance between the speakers and the listener will help with their elimination.


s6.jpg



If I highlight other reflections (the front wall is blue, the back purple, ceiling pink, floor grey), we can see that the aforementioned fall at 166 Hz is mostly caused by the side walls.


s7.jpg



We move again to the most homogenous level of acoustic pressure in the distance of 3.6 m. Highlighting reflections from all walls, we see a fall at 109 Hz (blue) caused by a reflection from the front wall. The whole front wall will be covered by a hybrid acoustic diffuser which is most absorptive in the corners where acoustic energy of low frequencies primarily accumulates. Also, its attenuation coefficient is higher at low frequencies, which is why in reality, the reflection from the front wall will not be as prominent a part of the overall acoustic pressure in the listening spot.


s8.jpg



If three people sit in the distance of 3.6 m next to each other with 60cm gaps between them, the listeners on the left and right will hear a fall at 118 Hz (turquoise and green), while the listener in the middle (black) will not hear it.

The simulation can differ from reality due to improperly specified absorption of the sides of the simulated block. Hybrid diffusers change both the absorptive and reflective characteristics in relation to frequency, which is why it is very hard to simulate their influence. Their influence is, however, measurable and hearable, so we have to wait for real measurements.

Ideal Ratios

With modal frequencies in the back of our mind, we extended the original 5.5 x 5.6 x 2.6 m space to an ideal 5.45 x 8.7 x 2.6 m, removing the original partition and building a new one.

The building skeleton is reinforced concrete, the ceiling and floor concrete—all ideal. Construction materials that are susceptible to vibrations (such as plasterboard or glass) vibrate on certain frequencies and from the point of view of acoustics, they act similarly—as an unwanted mechanical resonator. Our goal is a clear and sound-wise the best space, which is why we wall up the niches between the supporting pillars and the windows. Ventilation will be provided by an automatic heat recovery ventilation unit.


20200330_181714-scaled.jpg


Separate Wiring

We lay down a new supply leading from the main switchboard using a 5×4 copper conductor. We chose fuses as the securing elements of the individual circuits. We have all three phases coming to our switchboard, so in the future, we are going to be able to choose the one with the least interference to power the audio systems and connect devices with higher electromagnetic emissions, such as LED lighting circuits, to another phase.


20200417_173754-scaled.jpg


Grounding

In order to find out the resistivity of the soil behind the building, we used two earthing rods as probes (1 m in the ground, 9 m apart). The resistance between them is 75 Ω, which translates to a very good soil resistivity of 8.3 Ωm. In order to verify the accuracy of the measurement, we put the probe into the depth of 1.5 m and measured 52 Ω, which confirm the initial result. Behind the building, we put down two separate main grounding points, one for each audio system. According to the calculations, we should reach an outstanding grounding resistivity under one ohm with only eleven grounding rods.


20200322_111036-scaled.jpg


Construction Works Finishing

What comes next is leveling the new floor, plastering, laying down the carpet inside and heavy-use grade linoleum in the hall…

Acoustics

As the construction progresses, we prepare the acoustic elements for the room. The next article is going to focus on those.


20200420_105853-scaled.jpg


We finished a third step towards a perfect listening space. A hybrid acoustic diffuser now covers almost the entire ceiling. We tried to make a photo of it, but even a wide 10mm lens could not capture it in its entirety.


20200426_191820-scaled.jpg



QRD67H – Hybrid acoustic diffuser

This will disperse unwanted acoustic reflection and without absorbing too much acoustic energy inside the space at the same time. There will be more spatiality and perceived openness to the sound. Size: 6.7 x 4.5 m, number of segments: 3015, segment size: 10 x 10 cm.

Along the outline of the ceiling diffuser, there are two separate sections of LED lighting.


IMG_9807-scaled.jpg



On the front walls of the listening studio, there will be placed two hybrid diffusers we are currently preparing in our workshop. A detail is shown below. Segments made from acoustic foam are covered with a thin layer of real oak wood treated with natural oil.


RDacoustic-Acoustic-Hybrid-Diffuser-540x260cm-scaled.jpg

20200502_134641-scaled-e1617867782726.jpg



Taking in mind the acoustic parameters, for the floor, we chose a high quality carpet with high pile (11 mm) made of polypropylene fibres.


IMG_9810-1024x683.jpg



Part 2 of this post is going to bring a look at acoustic measurements following the individual steps of acoustic treatment, including subjective evaluation of the sound.
 

Somafunk

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Stunning, nothing more to be said.
 

Wes

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How would things change if you were doing all new construction, instead of an extensive remodel?

Did you consider making the ceiling slope up and away form the front? (like in a concert hall)
 
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Of related interest. Unfortunately, good comments that Mr. Harley appreciated about the wall construction of his new listening room are no longer online, because The Absolute Sound moved to a new server, and no longer has comments.

Building a Listening Room, by Robert Harley
May 28th, 2019
 

Χ Ξ Σ

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Thanks for the detailed write-up. Can you also talk about how do you soundproof the room? Or was it not a concern once you have all the acoustic treatment installed?
 
OP
RDacoustic

RDacoustic

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How would things change if you were doing all new construction, instead of an extensive remodel?

Did you consider making the ceiling slope up and away form the front? (like in a concert hall)

One would have a free hand at how large does one want the space to be and the wall ratios could be as best as possible vis-a-vis resonance frequencies. Generally, one is limited even when planning a new house entirely. Otherwise, however, the steps would be the same. Ideal room size, ideal speakers/listener position (many people can't afford either of these), symmetry in the space, diffusers between the speakers, ideal ratio of absorptive/diffusive materials.

If I'm not mistaken, the main reason different venues slope up is that the seats/floor do so as well so that people could see (ceiling copies the floor). Then in general, this is a completely different type of space; it is much larger, so the approach is different. The main thing that comes to mind is that in cinemas/theatres, you need much more wall treatment. Because of sound reflections, one beat of a drum would be heard several times, etc. On the other hand, in your living room, you need some sort of sonority, and it's easier to kill the sound with too much absorption...
 
OP
RDacoustic

RDacoustic

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Thanks for the detailed write-up. Can you also talk about how do you soundproof the room? Or was it not a concern once you have all the acoustic treatment installed?

A detailed description of the treatment is in the Part 2 thread. That said, yes, with approximately what you see on the final picture above, the room becomes ideal. The diffusers (ceiling and front/back) are acoustic foam + a layer of wood, so they are responsible for soundproofing also. On top of that, thanks to their pattern, you get more absorption in the corners (because there the pattern is less dense), so (especially) if you cover the entire wall, you don't need anything else for the corners/standing waves. The floor is carpet, so that's also absorption, then there is a curtain on the door niche, and acoustic canvases on the sides (cute cats + our logo with the notes) that dampens reflections on high frequencies. The armchairs also help, of course. But to answer you question; yes, with this installed, the ratio is perfect. You don't want to overdo it with absorption in rooms this size...
 

DWPress

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Looking forward to part 2. I've been doing some room treatments myself and need to remeasure the space soon.
 

caught gesture

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I’d be interested in the construction details of your ceiling hybrid acoustic diffuser. Materials, how you cut them to size, what you based your design on, etc. The finished product looks spectacular as an installation. I’d love to do something similar in my lounge!
 
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RDacoustic

RDacoustic

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I’d be interested in the construction details of your ceiling hybrid acoustic diffuser. Materials, how you cut them to size, what you based your design on, etc. The finished product looks spectacular as an installation. I’d love to do something similar in my lounge!

The ceiling diffuser is similar to the wall one. Both are acoustic foam plus a layer of wood on top of the segments, and they are based on the same pattern. Going for the quadratic version instead of the smooth lines was (here at least) purely an aesthetic choice. I won't give out the exact formula, but the "drop" pattern is a widely known thing based on the modulo operation and a circle equation, I'm sure you'll figure it out. :) These are part of our standard produce, so we have developed our own software to calculate a blueprint and a model of different variations on the pattern for any size. We use a CNC cutter for the foam and a standard saw for the wood.
 

pseudoid

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If anyone ever asks me what "Passion for Audio" is about; I hope I can remember to direct them to this post for the proper definition.
Wow!
Just the time it took you to share your passion with the rest of us is no 5 minute job... and I cannot possibly imagine how long it must be taking you to fret-out the minutiae (e.g., the measurement and grounding of external rods). Let alone the cost of your BST for this project.
Part2??? Link???
 

Descartes

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Whoa how much did that cost! Also it looks lonely, I would rather have a dedicated home theater to enjoy with family and friends.
 
OP
RDacoustic

RDacoustic

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If anyone ever asks me what "Passion for Audio" is about; I hope I can remember to direct them to this post for the proper definition.
Wow!
Just the time it took you to share your passion with the rest of us is no 5 minute job... and I cannot possibly imagine how long it must be taking you to fret-out the minutiae (e.g., the measurement and grounding of external rods). Let alone the cost of your BST for this project.
Part2??? Link???
To be fair, this is a re-post of one of our blog posts that we do as part of our business activity. You are not far off from the "no five minute job", though, there are still things to react to in another thread I started during summer... And the room took like half a year, even with our background. One way or another, it's good of you to appreciate our passion. :) Part 2 has been posted some time back: https://www.audiosciencereview.com/...-room-part-2-fine-tuning-the-acoustics.23555/
 

5kywalker

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I found this post via google and I have been so inspired that I joined the forum. I am trying to design an acoustic space from zero. Now consuming as much information from this thread and others on this excellent forum.

Once again well done!!
 

pseudoid

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I found this post via google and I have been so inspired that I joined the forum. I am trying to design an acoustic space from zero. Now consuming as much information from this thread and others on this excellent forum.

Once again well done!!
Welcome aboard,
You have not even scratched the surface just yet for knowledge to assist.
Don't forget to go out for some air and exercise... dump the gf (or the bf) << there is much more important things to do, and we will not make fun of you if your drain your bank account.
 
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