Partial preview of the text
Download practicing exercise on acoustics engineering and more Exercises Microwave Engineering and Acoustics in PDF only on Docsity!
[ERR RE EE EEE BIEN EE NESS SDT I I I OT ETO ENO EIU EES Wis (Ss ole 1g SP sic wt SOTA YI LG, Ni VERGE OS AU EI care for NTs Gel | | seer reereae coun renee reap eI ES TOI ER SAT EIE Su i 4 | @ ie | a ' Be A o f be + 4 7 4 | a i B : o @ Z | | i i | a | a Name: ME 513 Final Exam — Fall 2013 --- 12/10/2013 Note: To help you complete this exam, you may refer to your class notes, your homework, solutions provided to you and other material distributed as part of the course, and the text (Kinsler, Frey, Coppens and Sanders) or to any other acoustics text e Problem 1: /30 ¢ Problem 2: /20 e Problem 3: /20 © Problem 4: /20 e Problem 5: /20 ¢ Problem 6: /20 Problem 1. (30 points) @ Gi) Gii) Gy) ) (vi) (vii) What is sound? What are the characteristics of a stiffness-like impedance? When a SDOF system is driven at frequencies well below its natural frequency, its response is controlled by How does a pulse propagating along a tensioned string reflect from a rigid termination? upad dgun + baclwarels How does the sound pressure magnitude vary with radius in the farfield of a cylindrical source? The ratio of pressure to particle velocity for a freely propagating plane wave is said to be the At the interface between two ideal fluids, which component of the acoustic particle velocity is continuous across the interface? Why? Problem 5. (20 points) A dipole can be considered to consist of two closely-spaced monopoles of equal strength operating 180 deg. out-of-phase with each other. The sound field radiated by the dipole is zero on the surface defined by @= x/2, where @is the polar angle measured from the dipole axis. However, it may be desirable that the sound field be zero at some other polar angle. So, imagine that the phase, g, of the first of the two monopoles that make up the dipole is adjustable: i.e., the sound field radiated by the first monopole is A o-iin git 4 By following an approach similar to that used to derive the farfield of a dipole, find the value of g that is required to make the sound radiation zero on the surface defined by 9= 1/4. Sketch the directivity of the sound field in this case. uv A a “ikea ans = Ae Me gM sey =i Fhirns) = CAA =Ae Ig > wes Je =10 KS? —_ 2 2 2 CH, CeA ¢ =, Lt . | =< = Ae! pe Pl Se 7 are) t 2 — ( C Y oe J = hake Pc RO EY) oO aU QO = - 5s «2G G= . 4 Problem 1. (i) What is sound? (i) | What are the characteristics of a stiffness-like impedance? (iii) | When a SDOF system is driven by an external force at its natural frequency, it is said to be (iv) | Why was the reference intensity chosen to be 1 x 107!? W/m’? . . ¥. i Win nm sar pote’ aucibl, ley Meet Gd oe pak j SPL’s ant poakue (v) In the development of the wave equation for an ideal fluid, the fluid is assumed to have no and to undergo compression. pe aeflechrine from botlin (vi) | When a plane wave in air hits the surface of a yery deep layer of water at normal incidence, the transmitted pressure magnitude is 2 than that of the incident wave while the transmitted intensity is than that of the incident wave. (vii) (viii) (ix) (x) (xi) (xii) When considering sound transmission through a limp barrier, doubling either the or the causes the transmission loss of the barrier to increase by 6 dB. A “Level” has the units of A small axial fan can be modeled as a When a point monopole is placed at the junction of three rigid, perpendicular surfaces, image sources are required to satisfy the hard wall boundary conditions. Does a point monopole possess a “velocity nearfield”? Ye comeponenh tL c In a public address system, why is it normal to use many high frequency drivers, and a relatively small number of low frequency drivers? Problem 3. A thin limp membrane having mass per unit area ms is positioned a distance Z above a rigid surface as shown in the sketch below. A plane wave strikes the membrane at normal incidence. @ Give the appropriate assumed solutions form for the sound field in the region between the membrane and the rigid backing. ii) By using the linearized Euler equation, derive an expression for the particle velocity in the region between the rigid backing and the membrane. (iii) | Apply the appropriate boundary condition at the rigid backing surface, and give a solution for the sound field between the rigid backing and the membrane in terms of a trigonometric function. alculate the normal specific acoustic impedance, zs, on the positive-z-facing side of the membrane: i.e., at z = -L*. (v) Calculate the total normal specific acoustic impedance, z; of the membrane plus the backing airspace:i.e., find the impedance on the negative-z-facing side of the membrane atz=-L. (vi) For the case AL << 1, find an approximate expression for the resonance frequency of this system. ir Incident plane wave _ . “ft x (iv) © ge (rh apo a + Ae il ef (MACH + DO) 2 kas me Re z| >I 1 ivy ox 40 aed ca = nh fo Bs (th + gail) & eae = tp ( rea gin ky) 2h Siw ley, < 2Acoky a poate OC) gene (£9) (acer ate sta (-e) Ips eA y 22 ww “h me wis mass /wrTarta, SZ fenee) = o>. es , jen, =. feet fn OD was esrtht > (L \ core = L ) Sn. eee neate S egilaest =Ss Name: ME 513 --- Engineering Acoustics Final Exam — Fall 2009 --- 12/16/2009 Note: To help you complete this exam, you may refer to your class notes, your homework, solutions provided to you and other material distributed as part of the course, and the text (Kinsler, Frey, Coppens and Sanders) or to any other acoustics text — Problem 1: 30 Problem 2: /20 Problem 3: /20 Problem 4: /20 Problem 5: /20 Problem 6: /20 Problem 6. A circular rigid piston in a rigid baffle radiates into air at 100 Hz. The radius of the piston is 0.05 m. (i) Calculate the displacement amplitude of the piston required to produce a sound pressure level of 90 dB re 20 :Pa at a distance 2 m in front of the piston. Make use of whatever simplifying assumptions you feel appropriate under these conditions (but justify your assumptions). Comment on why a relatively large displacement amplitude is required in this case. Gi) By using the appropriate form of the radiation impedance, calculate the sound power radiated by the piston. @ at 100 Hy Az dtm — rading of Giler= A> Sy plrasarye Tek ee pith came modildan merogel { a Fi -ikr . GR = 1 Bebe” er Oe ks at LPP 10le4 10 fwS peed do brow) ® R =% te 2m z Pe 2 49 a = Jer al ne = 40 ras > me¥G o - Ack e@ Prme = Grae 10 Prne= |e e— ( ine = ae CH - 19 (gets 1QY = \uls We = 0%, . [Mal © | Bol as 
