Design, fabrication and evaluation of a two-way omnidirectional loudspeaker system Thesis defense presentation for the Masters Degree of Acoustic Engineering

Octavio Lora Aranda

OMNIDIRECTIONAL SOUND

• Point spherical source (monopole) radiating into 4π space

• Limit for omnidirectivity for a single driver is ka < 1 and the upper limit for omnidirectivity, with narrowing coverage without generating radiation pattern side lobes is approximately ka < 3

Driver Radius for Omnidirectional radiationHz Ka = 1 Ka = 3

1000 50 mm 160 mm2000 25 mm 80 mm4000 12.5 mm 41 mm8000 6.25 mm 20 mm

SOLUTION

• High order regular polyhedrons

• Minimize volume and using the maximum surface for the drivers

• Two-way system (Two channels)

Crossover between woofers and tweeters

High pass filter

• EQ independently for each channel

DETERMINING THE DRIVER

Model Weight Sensitivity Power Handling Fs

Faital Pro 3FE22 0.23 Kg 91 dB 20 W 110 Hz

Faital Pro 4FE32 0.26 Kg 91 dB 30 W 100 Hz

Tymphany NE123W-8 0.4 Kg 87 dB 45 W 61 Hz

Galaxy S5N-8 0.4 Kg 91 dB 100 W 140 Hz

FABRICATION TESTING BOXES

• Qtc = 0.707Max Flat Response atLow frequencies

• Boxes for singledrivers

• Boxes for multipledrivers

TESTING THE DRIVERSGround Plane Measurements

• Faital 4FE32 : Higher SPL than the Tymphany NE123W

• Galaxy S5N-8 : Power handling of 100 W

FREQUENCY RESPONSE4FE32 and S5N-8

• Below 200 Hz the Faital 4FE32 has more output.

dB

Hz

MIV TEST FAITAL 4FE32

• The frequency response change with increasing input level is very even with the mid-band undergoing compression.

• At the frequency extremes, particularly below 100 Hz, There is muchless change.

dB

Hz

MIV TEST GALAXY S5N-8

• Output of the Galaxy increases at its resonance frequency (about 200 Hz)

• Above 300 Hz the change in the frequency response is erratic

PEAK SPL

• From 80 Hz to 400 Hz the Faital driver has about 3 dB more peak output capability than the Galaxy driver.

Faital 4FE32 Galaxy S5N-8continuous, broad band

output 98 dB 102 dB

MIV 22 dBV 12.6 V 19.2

W24

dBV 15.8 V 31.4W

broad band compression -2.3 dB -1.2

• lack of low frequency extension in the Galaxy driver and erratic frequency response changes seen in the MIV testing.

Our choice:

Faital 4FE32

CONCLUSIONS

TWEETER

Model Weight Sensitivity AES Power handling Fs

Seas Prestige

27TFFNC/G H1396

0.1 Kg 91 dB 80 W 1170 Hz

BUILDING THE PROTOTYPES

Icosidodecahedron:

Regular polyhedron with 32 faces (12 pentagons and 20 triangles) • Volume:

Qtc = 0.98

V = 15.91 l

• Dimensions:

Ri = 14.42 cm

Ro= 16.95 cm

Dodecahedron:

Regular polyhedron with 12 faces (12 pentagons) • Volume:

Qtc = 1.19

V = 8.91 l

• Dimensions:

Ri = 11.67 cm

Ro= 14.68 cm

Electrical Configuration

Icosidodecahedron:series-parallel configuration with an

equivalent impedance of 6 ohms for the woofer’s channel and 5 ohms for the tweeter’s channel.Dodecahedron:

series-parallel configuration with an equivalent impedance of 6 ohms.

Final Prototypes

DIRECTIVITY MEASUREMENTS

Filter Applied

• Linkwitz-Riley 4th Order (24 dB/octave)

1000 Hz

ICOSIDODECAHEDRONPOLAR RESPONSE

ICOSIDODECAHEDRON Vs. DODECAHEDRON

ICO Ri = 14.42 cm

Dodec Ri = 11.67

ICOSIDODECAHEDRON Vs. DODI

Icosidodecahedron Ri = 14.42 cm

Dodi Ri = 15.6 cm

ICOSIDODECAHEDRON ISO 140-4 and ISO 3382-1

ICOSIDODECAHEDRON Vs. DODIISO 140-4 and ISO 3382-1

CONCLUSSIONS

• Both loudspeakers have 12 main radiation lobes

• From 1000 to 4000 Hz the dodecahedron has better omnidirectivity than the prototype

Above 4000 Hz the prototype has better omnidirectivity than the dodecahedron

• The prototype has, marginally, better omnidirectivity than the Dodi

• The prototype satisfies the omnidirectivity defined in ISO 3382-1 and the ISO 140-4

• The prototype has 6 to 8 dB greater acoustic output between 2000 and 8000 Hz that overcomes the low- and high-frequency imbalance occurring in the dodecahedron

FUTURE WORK

• Measure each channel independently

Set of filters

Delay times

EQ

THANK YOU FOR YOUR ATTENTION