Building a High End Listening Room 1: Goals

We are about to have a new listening room! On our hands, there is a space a construction of which we will be able to alter in order to reach ideal room proportions and gain the best possible listening space. The articles will be written continuously documenting the birth of the room. Ample acoustic and electrical measurements included.

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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 listening spot
  • 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, standalone circuits for each audio system, lighting, ventilation system.
  • Acoustic treatment:
    • Ceiling Hybrid Diffuser QRD 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 standalone grounding point.
    • Shielding under each system + preparation for the measuring of electrical quantities
  • 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, he sits in the axis of the room and he will be moving from a non-ideal position in the direction of the back wall.

RDacoustic Listening Room REW Measurements

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.

RDacoustic Listening Room REW Measurements

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

RDacoustic Listening Room REW Measurements
RDacoustic Listening Room REW Measurements

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

RDacoustic Listening Room REW Measurements

Out of interest, 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.

RDacoustic Listening Room REW Measurements

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.

RDacoustic Listening Room REW Measurements

We move back 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. Its attenuation coefficient is higher at low frequencies, that is why in reality the reflection from the front wall will not be as prominent in the overall acoustic pressure in the listening spot.

RDacoustic Listening Room REW Measurements

If three people sit in the distance of 3.6 m next to each other with 60 cm 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.

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