Simulation results

When the loudspeaker is placed in the closed box, the stiffness of the closed-box system will increase. And the first resonance frequency of the closed-box system will rise to the high frequency. Fig. 40. is the frequency response comparison of the infinite baffle and closed-box. From the Fig. 40., the performance of the closed-box system in low frequency is bad than the infinite baffle for a small volume of box.

Figure 41 is a simple simulation of the impedance response of the vented-box system. The null in the impedance plot is at the Helmholtz resonance frequency that is caused by the acoustic compliance of the volume of air and the acoustic mass of the vent. Fig 42 is the simulation of the frequency response of the vented-box. The volume velocity emitted by the diaphragm exhibits a null at the Helmholtz frequency and the volume velocity emitted by port is maximum. The total volume velocity is the sum of the volume velocity emitted by the diaphragm and the port.

Figure 43 is the frequency response comparison of infinite baffle and the vented-box system. The bass response of the vented-box is great than that of infinite baffle.

Figure 44 is the simulation frequency response of the passive radiator system.

The notch at the total frequency response is the resonant frequency of the passive diaphragm. The notch frequency should be below the cut-off frequency for the passive radiator design. From Fig 44, the notch frequency is below the cut-off frequency, so it is a well design.

passive-radiator system. The bass response of the passive radiator is great than that of infinite baffle.

The alignments are not adopted to design the passive radiator and the vented-box system. Because the miniature speaker has higher Q than the _TS conventional loudspeaker, the miniature speaker is not suitable to design according to the alignments of the vented-box and the passive-radiator.

From the discussion above, the simple models of the vented-box and the passive radiator have been constructed. Next, the miniature speaker will be taken to design the sample of the vented-box and the passive radiator, and the design of the sample can be used to realize in mobile phone.

Figure 46 is the 3-D diagram of the vented-box design. The parameters of the vented-box design are limited to realization in mobile phone. The dimension of the vented-box is the main reason. The simulation results of frequency response for infinite baffle and vented-box design are shown in Fig. 47. From the Fig. 47., the bass response of the vented-box design is great than the infinite baffle. Fig. 48. is the frequency response comparison of vented box for vent open and vent close. The vent close is like the closed-box system. The bass response of the vented-box design is great than the closed-box system.

Figure 49 is the 3-D diagram of the passive radiator design. The parameters of the passive radiator design are limited to realization in mobile phone. But the compliance of the passive diaphragm is not easily determined. The value of the compliance just can be determined by measurement. Fig. 50. is the frequency response comparison for infinite baffle and passive radiator design. The frequency response of the passive radiator performs well as the infinite baffle. Fig. 51. is the frequency response comparison of passive radiator design and the passive radiator without passive diaphragm. The passive radiator design without passive diaphragm

is like the closed-box system. The bass response of the passive radiator design is great than the closed-box system.

For the simulation of vented-box and passive radiator design, there is big peak in 15 kHz. That is caused by the acoustic compliance of the small space in the front of the speaker and the acoustic mass of the port around the small space. By placing the damping material in the export of the port, the amplitude of the peak will decrease.

4. Conclusions

There are many different features between miniature speakers and convention loudspeakers. The analysis of miniature speakers is discussed in this paper. These features that cause effects on the performance of miniature speaker are proven from the experiment results. In connection with different applications, these features can dominate the performance of miniature speakers to arrive the demands of user.

Thiele and Small parameters are important indexes. These parameters can make us to realize the difference between miniature speakers and convention loudspeakers.

The inductance of voice-coil is an example. For convention loudspeakers, the high frequency inductance effect is very great. This phenomenon can not be represented by a linear inductance. However, the inductance of voice-coil for miniature speaker is very small. Thus the high frequency inductance effect can be approximately modeled by a linear inductance. The sensitivity and efficiency for miniature speakers are very smaller than convention loudspeakers. The efficiency and sensitivity can be increased by increasing the Bl , by increasing the diaphragm area, by decreasing the voice-coil resistance, and by decreasing the total moving mass.

However, increasing Bl is the best method for miniature speaker.

The EMA analogous circuit is established to analyze the dynamic response of the loudspeaker. When the loudspeaker is placed in the complex enclosure, we can focus on the acoustical system and use lumped parameter method to model the acoustical impedance of the structure of the enclosure. The acoustical impedance is lumped to the electrical element. The overall dynamic response of the loudspeaker can be easily solved by the circuit analysis.

For mobile phone, ear-coupling condition is an important index. The low-leak and high-leak conditions are simulated to analyze the dynamic response of mobile

phone in different ear-coupled conditions.

For enhancing the bass response of miniature speakers placed in mobile phone, the concept of the vented-box and passive radiator methods is reviewed in this paper.

From the theory analysis and simulation results, the vented-box and passive radiator methods can efficiently improve the bass response of the loudspeaker. However, the dimension of the mobile phone is limited. Thus the best performance of the bass response for the vented-box and passive radiator design can not be developed well.

However, the bass response is still enhanced. For the passive radiator design, one thing must be noticed is that the passive diaphragm can be choosing to reach the best performance of the bass response

The vented-box and passive radiator design for the mobile phone conferred above is just in the process of simulation. In the future, we will realize this concept to develop a real enclosure and prove that the vented-box and passive radiator design can really enhance the bass response of the loudspeaker from the experiment results.

References

[1] J. Eargle and M. Gander, 〝Historical Perspectives and Technology overview of Loudspeakers for Sound Reinforcement, 〞 Journal of the Audio Engineering

Society, Vol. 52, No. 4, April 2004.

[2] Ingyu Chun, P. A. Nelson and Jun-Tai Kim, 〝Numerical models of miniature loudspeakers, 〞 The 32nd International Congress and Exposition on Noise Control Engineering, Jeju International Convention Center, Seogwipo, Korea, August 25-28, 2003.

[3] Sei-Jin Oh, Han-Ryang Lee, Suk Wang Yoon and Jin-Soo Park, 〝Study of the Acoustical Properties as a Function of Back Cavity for Loudspeaker,〞 The 32nd International Congress and Exposition on Noise Control Engineering, Jeju International Convention Center, Seogwipo, Korea, August 25-28, 2003.

[4] Chang-Hwan Choi, Hee-Soo Yoon, 〝Acoustic and Vibration Characteristics of a Micro Speaker through the Electro-Magnetic field Analysis, 〞 The 32nd International Congress and Exposition on Noise Control Engineering, Jeju International Convention Center, Seogwipo, Korea, August 25-28, 2003.

[5] Sang-Hee Lee, Jung-Ho Kim, Jun-Tai Kim, Oh-Soo Kwon and Chang-Hwan Choi, 〝Development of the simulation program to analyze acoustic characteristics of a miniature type loudspeaker, 〞The 32nd International Congress and Exposition on Noise Control Engineering, Jeju International Convention Center, Seogwipo, Korea, August 25-28, 2003.

[6] W. M. Leach, Jr., 〝Loudspeaker Voice-Coil Inductance Losses: Circuit Models, Parameter Estimation, and Effect on Frequency Response, 〞 Journal of The Audio Engineering Society, vol. 50, no. 6, pp. 442-450, June 2002.

[7] L. L. Beranek, Acoustics, Acoustical Society of America, Woodbury, NY. 1996.

[8] David K. Cheng, Field and Wave Electromagnetics, Second Edition, pp.437-470, 1989.

[9] Desoer, C. A. and Kuh, E. S., Basic Circuit Theory, McGraw-Hill, New York, pp.711-751, 1969.

[10] R. H. Small, 〝Vented-Box Loudspeaker Systems, Parts Ⅰ-Ⅳ, 〞 Journal of The Audio Engineering Society, vol. 21, pp. 363-372. June 1973, pp. 438-444,

July/Aug. 1973; pp. 549-554, Sept. 1973; pp. 635-639, Oct. 1973

[11] R. H. Small, 〝Passive Radiator Loudspeaker Systems, Parts Ⅰ-Ⅱ, 〞 J.

Audio Eng. Soc., vol. 22, pp. 596-601. Oct 1974, pp. 683-689, Nov. 1974 [12] W. M. Leach, Jr., Introduction to Electroacoustics and Audio Amplifier Design, Second Edition

[13] 白明憲, 1999, 聲學理論與應用, 全華書局.

[14] Borwick, J., ed., Loudspeaker and Headphone Handbook, third ed., Focal Press, Oxford, UK, 2001.

[15] Colloms, M., High performance Loudspeakers, fifth ed., John Wiley & Sons, New York, 1997.

[16] B&K, Product Data, Wideband Ear Simulator for Telephonometry-Type 4195.

[17] Bension, J. E. 〝Theory and Design of Loudspeaker Enclosures, 〞 Amalgamated Wirless Australia Technical Review (1968, 1971, 1972).

Appendix

In this section, Pspice is used to simulate the impedance of the entrance of duct by the transmission line and two-port model. A simple diagram of the duct and testing circuit is show below

R

In_In

^l R

_Out

R ^l R

_Out

A1. A simple diagram of the duct

A2. A testing circuit of the duct

And the impedance is

For the duct whose exit is open, the is small. We will simulate the impedance of the entrance of duct by using two models.

Ex. For a tube that has length 1cm and radius 3.1mm

From Eqs. 68 and 69, then L and C can be computed. In Pspice, there is a component that can model the transmission line. You just indicate the value of L, C and Length. This component is called T2Coupled.

V

Another model is two-port model. This equivalent circuit is complex and needs an analogous dynamic component called ELaplace. It can perform the Laplace transform. A complete circuit is shown below:

A3. A realistic circuit of two-port model

The architecture of the equivalent circuit is to realize the equivalent circuit of two-port model that is shown in Fig 14.

The impedance response comparison of two models is shown below:

A4. The impedance response comparison of transmission line and

For length of duct is 1cm, it resonant frequency is 17150Hz. From A4, the impedance has minimum at 17k Hz. Because the impedance has minimum, the

volume velocity in this frequency will have maximum. A4. shows that the two models can fit approximately.

A5 is the impedance response simulation of duct that has 2cm length.

A5. The impedance response comparison of transmission line and two-port model (length: 2 cm)

For length of duct is 12cm, it resonant frequency is 8575Hz and 17150Hz.

From A5, the impedance has minimum at 8k and 17k Hz and the two models can fit approximately.

If you want to model the impedance response of duct that export is closed. The must be set greatly to infinity.

R

Out

Fig. 1. Electro-mechano-acoustical analogous circuit of loudspeaker.

Fig. 2. The mechanical system of loudspeaker. (M is diaphragm and voice coil mass, k is stiffness of suspension, C is damping factor)

u

Fig. 3. (a) An acoustic resistance consisting of a fine mesh screen (b) Analogous circuit of acoustic resistance

Fig. 4. (a) Closed volume of air that acts as an acoustic compliance

Fig. 5. (a) Cylindrical tube of air that behaves as an acoustic mass.

(b) Analogous circuit of acoustic mass

Fig. 6. Analogous circuit for the radiation impedance on one side of a circular piston in an infinite baffle

p1 p₂

Fig. 7. Geometry of the circular piston vibrating in a tube

Fig. 8. Perforated sheet of thickness

t

having holes

a

of radius spaced a distance

b

on centers.

Piston

Tube

Fig. 9. Geometry of the narrow slit

Fig. 10. Geometry of the duct (left side is entrance; right side is exit).

U

1

p

2

p

1

U

2

l

Piston

t

l

w

Fig. 11. The curves of the

tan(kl)

and the lumped method. (Solid line is

tan(kl)

; Dash line is lumped method)

ω0

Im (Z_A)

1

A

A

M C

ω ⁻ ω

ω

Fig. 12. Analogous circuit of lumped parameter oscillator model of a duct.

1

2

1

2 CA1

0

n= n=1

0

MA M_A1

Fig. 13. Equivalent circuit of a differential length

∆x

of a two-conductor transmission line.

( , )

i x t _{R x ∆}

( , ) V x t

( , )

i x + ∆ x t

L x ∆

C x ∆

G x∆

∆ x

( , )

V x +∆ x t

Fig. 14. Equivalent analog circuit of a two-port model

p

1

Z U

21 1

U

1

12 2

Z U p

²

z 22

U

2

z 11

Fig. 15. Impedance response comparison of simulation and experiment

results for miniature speakers.

Fig. 16. The simple diagram of miniature speaker.

Fig. 17. The real example of miniature speaker.

Fig. 18. The back side of miniature speaker.

Fig. 19. The front side of miniature speaker.

Port

Fig. 20. The impedance response comparison of the three cases (Case 1: original speaker; Case 2: speaker without the damping material; Case 3: speaker without the damping material and the

frame).

Fig. 21. The frequency response comparison of the three cases (Case 1: original speaker; Case 2: speaker without the damping material; Case 3: speaker without the damping material and the

frame).

Fig. 22. The impedance response comparison of speaker and speaker with

closed-port (closed-port means rear-side ventilation of speak is close).

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Fig. 23. The directivity of the Merry speaker (a) 500 Hz (b) 1k Hz (c) 2k

Hz (d) 5k Hz (e) 7k Hz (f) 9k Hz (g) 10k Hz (h) 11k Hz.

Fig 25. The cavity of the mobile phone

Fig. 24. The different views of enclosure for mobile phone.

(b)

Fig. 25.The analogous circuit of miniature speaker in mobile phone.

Cavity Duct Po P o rt r t

(a)

(b)

Fig. 26 (a) The structure of the front side of speaker (b) The analogous circuit of acoustic impedance

Z_AF

.

Duct Cavity

Frame Port

(a)

(b)

Fig. 27 (a) The structure of the rear of the speaker (b) The analogous circuit of acoustic impedance

Z_AB

.

PoPorrtt PPoortrt

CCaavvitityy

MBP2

1 2

MBP1

1 2

CBB2 RBP1

CBB1

RBP2

Fig. 28. The impedance response comparison of speaker and speaker in mobile phone.

Fig. 29. The frequency response comparison of speaker and speaker in

mobile phone.

Fig. 30. The impedance response comparison of experiment and simulation results.

Fig. 31. The frequency response comparison of experiment and

simulation results.

Fig. 32. Electrical equivalent circuit diagram of low-leak of high-leak pinna simulator and IEC 711 Coupler. (Solid line: low-leak of high-leak

pinna simulator; Dash line: 711 Coupler)

Fig. 33. Simulation acoustic impedance for type 4195 Low-leak ear

simulator compared to High-leak ear simulator.

Fig. 34. Simulation pressure frequency response for mobile phone

coupled with low-leak and high leak Pinna.

Fig. 35. The simple diagram of the vented-box design.

M

AP

V

AB

Speaker

Tube

Fig. 36. Low-frequency Model: EMA analogous circuit of vented-box system.

M

MD

R

E

e

C

MS

S p

D

B i l B u l

1

M

A

M

AB

S U

D

U

M

AP

i u

R

AL

C

_AB

R

MS

Fig. 37. Low-frequency model: Acoustical analogous circuit of the vented-box system.

R

AL

M

_AP

U R

_AS

M

_AC

C

AS

S e

D

Bl R

^AE

C

^AB

Fig. 38. The simple diagram of the passive radiator design.

S

Sp p ea

e

ak k er

e

r

Pa

P

as ss si iv v e

e

d d ia

i

ap p hr

h

ra ag g m

m

C

AP

M

AP

R

AP

V

AB

Fig. 39. Low-frequency model: Acoustical analogous circuit of the passive radiator system.

R

AL

C

AS

S e

D

Bl

^AB

C

U

R

AE

R

AS

M

AC

M

AP

R

AP

C

AP

Fig. 40. The frequency response comparison of Infinite Baffle and Closed-Box.

Fig. 41. The simulation of impedance response of speaker and vented-box

system.

Fig. 42. The simulation of the frequency response of vented-box system.

Fig. 43. The frequency response comparison of Infinite Baffle and

vented-box system.

Fig. 44. The simulation of the frequency response of Passive radiator system.

Fig. 45. The frequency response comparison of Infinite Baffle and

passive radiator system.

Fig. 46. The3-D diagram of the vented-box design for mobile phone.

Tube

Fig. 47. The frequency response comparison of Infinite Baffle and Vented-Box design.

Fig. 48. The frequency response comparison of Vented-Box: Vent open

and Vent close.

Fig. 49. The 3-D diagram of the passive radiator design for the mobile phone.

Passive diaphragm

Fig. 50. The frequency response comparison of Infinite Baffle and Passive Radiator design.

Fig. 51. The frequency response comparison of Closed-Box and Passive Radiator design (Closed-Box means that passive diaphragm

of passive radiator design is replaced and closed).

在文檔中 微型喇叭運用於行動電話之分析與設計 (頁 48-96)