I grafici

paulberry

Posted on 8/12/2007, 12:12 by: paulberry

User deleted

Il precedente post e' stato censurato su TNT:per lui i grafici non contano nulla.

Aggiungo:
A Brief comparison with conventional acoustic instruments.
Below is a table showing informal estimations of the frequency ranges, approximate directivity and sound pressure level of a variety of acoustical instruments vis-à-vis both a typical good loudspeaker and an ideal one.

Instrument Low freq. fundamental High freq. fundamental Overtones to: Low freq. radiation directivity High freq. radiation directivity Min dB SPL (3m) Max dB SPL (3m)
Flute 250 2K 10k omni, transverse forward horizontal 50 90
Clarinet 150 1.2K 5K omni, downward lateral horizontal 50 90
Oboe 250 1.2K 15K weak omni omni 60 85
Bassoon 75 400 15K weak omni omni 50 80
Saxophone, tenor 125 600 15K omni, forward lateral horizontal 55 90
Trumpet 180 1.2K 20K+ forward lateral, vertical 60 100
French Horn 100 800 5K rearward rear, lateral 55 95
Trombone 40 500 20K+ forward lateral, vertical 60 105
Tuba 30 250 8K forward omni 60 90
Violin 200 2K 20K+ weak omni Vertical 45 85
Viola 150 1.5K 20K+ weak omni Vertical 45 80
Cello 60 1K 20K+ forward omni Forward 45 85
Doublebass 40 500 20K+ forward omni Forward 45 80
Snare Drum 200 4K 20K+ vertical, horizontal dipole omni 55 105
Cymbal 500 10K 20K+ vertical, horizontal dipole omni 50 95
Tympani 40 250 1K omni weak omni 40 95
Glockenspiel 250 1K 20K+ omni omni 60 95
Marimba 250 1K 2K omni weak omni 50 80
Xylophone 250 1K 5K omni omni 50 85
Triangle 1K 2K 20K+ none omni 50 90
Bells 200 800 15K omni, downward horizontal plane 50 80
Bass Drum 20 100 2K horizontal, vertical dipole weak omni 40 105
Piano 30 2K 15K omni, vertical, horizontal dipole omni, forward 40 100
Pipe Organ 20 2K 12K omni omni 50 105
Loudspeaker (typical traditional) 50 20K - omni narrow forward 0 dB 99
Loudspeaker (ideal) 20 20K - omni horizontal 0 dB 120

Table 1: Various acoustical instruments vis-à-vis a typical “good” loudspeaker and an “ideal” loudspeaker, showing the range limits of their various fundamental frequencies and informal estimations of the upper limits of their significant harmonics, and their patterns of polar radiation at low and high frequencies, plus estimations of the minimum and maximum Sound Pressure Levels such instruments can obtain as observed at 3 meters in a free field.

This table illuminates several interesting things.

First, all traditional instruments generate complex waveforms with extensive overtone structures. As a general rule, the frequency range for the fundamental frequencies of musical notes spans four octaves, from 65 to 1040 Hz. (low C to high C), while overtones extend up to five octaves above that range. Loudspeakers, on the other hand, do not generate overtones as such, except when driven into distortion.

Second, the directivity of acoustical instruments varies widely at both high and low frequencies. There is no uniformity, and no particular trend. In a collective sense, we can generalize that high frequencies are radiated laterally and upward, occasionally forward, while low frequency radiation tends to be either bidirectional or somewhat directional as a function of horn coupling with free space. It needs also to be noted that the timbral results of such directivity is also affected by the comparatively large size of performance venues – the strident harshness of a violin in a small practice room, with extremely strong high frequency early reflections off a low ceiling is in marked contrast to the warmth of the same instrument in a concert hall, with the attenuated vertical high frequency radiation lending a silky reverberant patina to the sound.

In contrast, traditional loudspeakers have a comparatively distinctive pattern of directivity, as noted above, a pattern generally unlike almost all acoustical instruments. While low and mid frequencies are radiated approximately omnidirectionally, high frequencies are beamed narrowly, so narrowly that for the most part a listener cannot sit more than 15° off-axis and still perceive the spectrum the designer intended. The result of this is a particular interaction with rooms that sounds quite unlike other instruments.

It is therefore quite important to note that no other instrument requires such a precise orientation by the listener as does the loudspeaker, simply in order to take in the spectral range of the loudspeaker. Also, as noted earlier, the volley of early reflections are spectrally deficient vis-à-vis the on-axis radiation. This has led to compensations, in many instances, during the act of recording and production. By tradition, many recordings are overly bright to fill in for this spectral deficiency and to compensate for off-axis listening.

Finally, when we compare the maximum sound pressure levels that can be obtained by loudspeakers vs. acoustical instruments, we see that loudspeakers have a much larger dynamic range and appear to be equivalent or greater in range in almost all regards. However, comparisons here are extremely tricky when we start accounting for variables such as concert hall vs. playback room, listeners’ distance from the source, etc. Further, instruments aggregate into ensembles that may include as many as 250 members (orchestra and chorus). Finally, the subjective perceived loudness from many sources is not easily matched by the phantom images generated by a loudspeaker pair.

At best, loudspeakers can generate sound pressure levels in a small listening room that effectively mimic the subjective quality of loudness obtained by a full orchestra, but it is safe to say that they cannot replicate the amplitude at bandwidth that an orchestra can achieve. Further, the mimicry of a live rock or heavy metal band is always going to be reduced in subjective loudness (and this is probably as it should be).

We can further generalize that the amplifier power available, when coupled with the given sensitivity of most domestic loudspeakers, is usually insufficient to achieve such levels, introducing a further constraint on loudspeaker playback.

By Moulton laboratories Thank you.

Di nuovo: il fuori asse regolare e' fondamentale.

248 replies since 8/11/2007, 17:07 41157 views

e dove va l'hifi