Solution-2021-10-11

	A	B	C	D	E	F	G	H	I	J	K	L	M
1	Solution of in class test - 11/10/2021						Matricola
2							A	B	C	D	E	F
3	Check the sentences you think are always TRUE						1	2	3	4	5	6
4	(multiple answers allowed)
5	¨ The energy density level is always larger than the sound intensity level: LD>LI
6	¨ The values of the levels in dB of sound pressure, particle velocity, sound intensity and sound energy density are always the same: Lp=Lv=LI=LD
7	¨ A value of the ratio I/Dc close to 0 means the sound field is strongly reverberant/reactive
8	¨ A value of the ratio I/Dc close to 1 means the sound field is strongly reverberant/reactive
9	¨ The sound speed in air is invariant (340 m/s)
10	¨ The sound speed in air is variable, being proportional to the temperature
11	¨ The sound speed in air is variable, proportional to the square root of temperature
12
13	The power of a source is quadruplicated. What effect do you expect?
14	(multiple answers allowed)
15	¨ The sound power level of the source increases by 3 dB
16	¨ The sound power level of the source increases by 6 dB
17	¨ The sound power level of the source increases by 10 dB
18	¨ The sound pressure level at the receiver increases by 3 dB
19	¨ The sound pressure level at the receiver increases by 6 dB
20	¨ The sound pressure level at the receiver increases by 10 dB
21
22	What is the bandwidth (fhi-flo) of the octave band filter centered at 4 kHz?
23	(a single answer)
24	¡ 717 Hz
25	¡ 1000 Hz
26	¡ 1414 Hz
27	¡ 2000 Hz
28	¡ 2828 Hz
29	¡ 4000 Hz
30
31	What's the sound pressure corresponding to a SPL = 110+F dB ?
32	(write number and measurement unit)						SPL = 20*lofg10(p/p0) with p0=2E-5 Pa
33	SPL =	116	dB		p=p0*10^(SPL/20) =	12.62	Pa
34
35	What’s the particle velocity level corresponding to v= 0.1+E/10 mm/s?
36	(write number and measurement unit)
37	v =	0.6	mm/s				Lv = 20*log10(v/v0) with v0=50E-9 m/s =	81.6	dB
38
39	Compute the coherent sum of the sound pressure levels
40	of 80+E and 80+D dB produced by two phase-matched sources
41	(write number and measurement unit)
42	Lp1 =	85	dB	Lp2 =	84	dB					Lptot = 20*log10(10^(Lp1/20)+10^(Lp2/20)) =	90.5	dB
43
44	The unweighted octave-band spectrum of a fan is given here below.
45	Compute the SPL in dB(A)
46	(write number and measurement unit)
47	f (Hz)	125 Hz	250 Hz	500 Hz	1000 Hz	2000 Hz	4000 Hz	Total - dB(A)
48	Lp	81	77	76	74	75	76	81.6
49	A-weight	-16.1	-8.6	-3.2	0	1.2	1
50	Lp(A)	64.9	68.4	72.8	74	76.2	77
51	10^(Lp(A)/10)	3090295	6918310	19054607	25118864	41686938	50118723	145987738
52
53	The background noise in a room is 50+F dB(A). A sound source is switched on, and the total SPL increases by 2+E/5 dB(A). Compute the SPL of the second source alone.
54	(write number and measurement unit)
55	Lbackgnd =	56	dB(A)
56	Increase =	3	dB(A)
57	Total SPL =	59	dB(A)
58	Lsource = 10*log10(10^(SPLtot/10)-10^(Lbackgnd/10)) =					56.0	dB(A)
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