AcAna_paramethers to take in account

The software we are using is able to determinate a wide range of paramethers for each analisys. At first, it is necessary to understand "what we are looking for".

All the following paramethers are funcion of the sound energy: which means that they are function of i.the source (position, directivity and power) ii.the whole ambient (whose implulse response can determine different situations) iii.position (of the "listentner").

It is possible to stimate these paramethers both for each range of frequancy and in a weighted average.

 All the paramethers i'm about to describe have a range of value which is best to listen the music (not speech,the values just change )

1_Levels of Sound Pressure

Sound_Energy= Direct_E+FirstReflections_E+SoundTail_E

In the fifties Haas for first mantained that the contribute of the first (3 orders of) reflections cannot be perceived as distinct from the direct one [1]. For that, if a reflected (non-direct) sound arrives to the listener with less than 0.02 s delay, it is perceived as un-distinct: its contribute just strenghten the sound. It is possible to simulate the impulse response in the case of first reflections only: we obviously want to sort out a result not far from this case, when we'll be considering the reverberation Effects (sound Tail).

0.02 s means that the different in the sound paths (direct-reflected) has to be less than 17m: pratically everywhere within my component. To stimate this, we expect to find an higher Equivalent Level of Sound Pressure  (L eq) within the chair, rather than in an other point whose distance is the same from the direct sound source (that's the image in the last post).

The software is able as well to evaluate the sound pressure level of the Direct sound and of the Reverberated sound. At now, G.Bianchi mantains that the L eq index is more important to evaluate.

2_Early decay time

Relating to the importance of the first reflections, it is possible to stimate the Early Decay Time, also evaluated with the T10 (time of the first 10 dBs decay): Spagnolo [1] considers them the same thing, for a concert all the acceptable range of values is (1.8s , 2.6s).

3_Fundamental Subjective Paramethers

Since the sound is a subjective fenomenon, we need to individuate certain paramethers to stimate our individual perception. According to Spagnolo [1], these are i. G (Strenght and Extension of the source_ more than 28 dB) ii. Ts (Intellegibility related to position-baricentrical time of the energy_less than 0.014s) iii. EDT trend in the range 125 to 2000 Hz band (opinion of the sound_ negative or void trend).

 4_Quality of first Reflections

Two paramethers sums up the quality of the first reflections: Clarity (in the first 0.005s or 0.008s, depending on what we are evaluating, speech or music) and Defintion (percentage of the enery within the first 0.005s). Always according to Spagnolo, in a good concert hall C80 within (-4dB , 2dB) and D50 (less than 50%). We want a component configuration which can give us these values.

5_Spatial Impression

It is important as well for a good listening to determine where the sound comes from. It would be even better to evaluate what difference in sound is perceived between the left and the right ear (Aurality), but the software does not allow this. To obtian a good soun impression it is necessary that a certain amount of energy comes from orizontal reflections: it is possible to determine for that the Lateral Efficiency (Le, amount of energy on the orizontal plane due to wall reflections) and the Lateral Fraction (Lf, amount of energy on the orizontal plane due to the sum of reflections from generic reflector ). Me and G.Bianchi discussed a lot on how to estimate these paramethers: since we need reflections coming from the shelter (which diffuses the sound) but not from the walls. We actually do not exactly know how to evaluate this, we will see trough the reserch.

[1] R.Spagnolo, Manuale di acustica applicata