Toa F-121C/M Instructions d'installation et d'utilisation

APPLICATION NOTE ON TOA'S

UNIFORM DIRECTIVITY CEILING

SPEAKER

In open areas with low ceiling heights, dead spots often

occur in areas between speakers mounted in the ceiling.

Often, there is a noticeable difference in the quality of the

sound between the area directly below the speaker, or on

axis, and the area off-axis. Sound engineers and system

designers have known for many years that higher frequency

material is more narrowly dispersed from cone speakers

than lower frequency material. A listener standing on-axis

gets a better, more total sound than one standing off-axis.

The attenuation of higher frequencies is a problem because

of intelligibility loss as well as degradation of quality.

One solution is to decrease the distance between

ceiling speakers, thus putting more of the floor space and

listening area into the on-axis coverage. However, this will

drive up the cost of the system since more speakers, wire,

back boxes and labor will be consumed in the installation,

and more amplifier power will be needed.

A better solution

is to use TOA’s new F121C Uniform Directivity Ceiling

Speaker with the AC-120 Dedicated Equalizer. This speak-

er is equipped with a unique sound diffuser, housed in an

attractive mesh cone. The diffuser helps to smooth out the

dispersion of the higher frequencies, which eliminates the

dead spots even when the speakers are spread out. The

graphics shown on this page and the next dramatically

demonstrate how the frequency and polar response of the

F-121C compares with standard 4”ceiling speakers, and

shows that better sound with less speakers is possible

when the F-121C is used in restaurants, offices, shopping

malls, retail stores, and other space requiring ceiling mount-

ed speakers.

The F-121CM is transformer equipped with multi-

ple line taps for loudness selection.

Polar Response F-121C

•500Hz •1000Hz •2000Hz •4000Hz •8000Hz

Frequency Response of F-121C/F-121CM

0/Degrees

30/Degrees

60/Degrees

90/Degrees

20100

200 lk 2k

10 k

20 k

Frequency Response of 4” Ceiling Speaker

0/Degrees

30/Degrees

60/Degrees

90/Degrees

I

100

200 lk 2k 10k 20k

Polar Response 4”Ceiling Speaker

•500Hz

•1OOOHz

•2000Hz •4000Hz •8000Hz

Sound Level Distribution Patterns TOA F-121C/F-121CM

s 8000Hz t s 4000Hz t s 2000Hz t s 1000Hz t

Sound Level Distribution Patterns 4” Ceiling Speakers

Sibilants (“s”sounds) and plosives (“p”sounds) are fre- The above sound level distribution patterns were obtained

quent in all human speech. Compared to the F-121C from four speakers placed (as marked by the “+”signs) in

Uniform Directivity Ceiling Speakers, standard 4”and espe- an anechoic space measuring 65 ft. (W) X 65 ft. (W) by 6.5

cially 8”co-ax ceiling speakers do not adequately disperse ft. (H). The patterns above show the area represented by

these high frequency sounds.

1 W/m of sound pressure level.

04-97-f121ap

Printed in U.S.A. 4/97 BL

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