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Painting Pictures With Sounds

By November 1, 2012No Comments

Auralization

Auralization refers to the process of interjecting sound energy into a room and then taking the measurements of that sound’s behavior in the room. We can use this measured behavior to predict how energy will sound like when we play it in the room without any equipment or room treatment placed in the room. We can find the sweet spot and we can actually define the physical dimensions of it. If we change room surface treatments, we can “hear” their impact on the total room sound.

Middle and High Frequencies

Auralization works well for frequencies above 125 Hz. and is also best in large room configurations. I have never been able to find the real definition of what constitutes a large room. For that matter, I do not think I have seen a definition of a small room either. One can use it on smaller rooms and it will assist one with about three different variables that relate directly to our sound presentation.

Direct Vs. Reflected Sound

The first variable we will look at is the ratio of early to late arriving sound. Direct sound is the sound that leaves our speakers and travels the straightest and most direct path to our ears. It is non reflected sound, so it has not struck any room surface and thus finds itself now contaminated by the room. Direct sound is the most wanted. Reflected energy from our room boundary surfaces contains room sound. Measuring the delay from the reflected to the direct, can tell us many things.

D50 – Speech Intelligibility

There is a term called D50. This is the definition and measurement when it comes to speech intelligibility. In order for speech to be heard within a room, we must have a scale or ratio of direct to reflected energy to assist us with defining speech intelligibility. D50 represents all delayed sound arriving within 50 ms of the direct sound. This is our window and reference for speech clarity.

C80 – Music clarity

C80 is defined as the music clarity index and includes all reflected and delayed energy arriving within 80 seconds of the direct. LFC refers to the lateral energy fractions or the impression of spaciousness or “air” in our sonic presentations. This LFC measurement is based on the ratio of laterally arriving reflections between 5 and 80 ms.

T Time – Not Golf Game

The center of gravity or T time is an interesting measurement. This the physical field in which the sound energy is concentrated within. The echogram will show us a low value if the arriving sound is concentrated in the early part of the echogram and a high value if the reflections are less strong and the decay of these is slower.

G10 – Pressure Number

G10 is the pressure measurement. G10 is the measured sound pressure with the room as it is compared to the direct energy from our loudspeakers. We measure for G10 by using 10 feet from a omni directional source. This will give us an idea of how loud the sound will be. This is mainly a large room measurement.

Listening Position

Auralization takes all of these parameters and focuses this data on the listening position. We can now look at the listening position and see the ratio of direct to reflected energy. We can also see the speech intelligibility index along with music clarity, T times and pressure plots. All of these variables can go along way to telling us how the room will sound before the building is even built.

Speaker Locations

We can look at speaker placement and room surface treatments. For example, if we are using speakers that are different in configuration, we can map their spread and look at their impact on the listening position. If we are using dipoles, we can visualize their spread pattern and see where the direct and diffused sound fields are with respect to the listening position. We can map the behavior of different set ups.

Reflection Minimized Area

We can actually listen to all of these variables in real time. We can see how the variables change over time. We can see how the energy from the speakers combines with the given dimensions of the room to pressurize the room. For example, our goal at the listening position is to create a reflection minimized area (RMA) around the listening position. We will be able to see that area by observing the sound pressure levels around the listening position.

Binaural Hearing

Since our hearing is binaural, we can take the binaural impulse responses of the left and right ear and combine them with music in real time, we can measure the difference and be able to hear more accurately the ambiance of the space. If we compare an anechoic music sample which is a music sample that does not contain any room sound with the actual binaural room response, we can hear the impact of the room and the coloration the room produces.

Low Frequency Auralization

Auralization can assist us in predicting room coloration and how to deal with them. It is a process that works well above 125 Hz. but not so well below. Once again, low frequency energy has escaped the predictability that modern technology has given us. We now need auralization for low frequencies. What good is a reflection minimized area if it is smothered by room resonances created by low frequency energy.

Auralization software can help us in determining how our room will sound at the listening position by analyzing the direct vs. reflected energy. It can also tell us pressure levels and the impact of certain acoustical treatments. It is effective from 125 cycles and up and is used mainly in larger room configurations.

MikeSorensen

Author MikeSorensen

I am a structural engineer as well as a master furniture maker. I design cabinets for low frequency, activated carbon absorbers. Connect with me on Google+

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