SABINE FBX2420 Spécifications télécharger pdf (Page 9)

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Of course, many savvy sound engineers, realizing the limitations of

graphic equalizers in removing problem feedback, prefer to use a

different type of equalizer, called a parametric EQ, for such applica-

tions. If you’re one such audio engineer, you’ll be comforted to know

that FBX lters share much in common with parametrics.

Compared to graphic lters, parametrics allow more precise adjust-

ments — specically, control of lter width, the amount of boost or

cut, and the mid-band frequency of the lter. This greater precision,

however, comes at a price, as parametric lters are not nearly as

intuitive or simple to use as graphic equalizers.

Nothing, however, is easier to use than an FBX lter, which enjoys

the precision of a parametric lter, yet deploys instantly and auto-

matically whenever feedback is detected. Effectively, an FBX lter is

a parametric lter set to a tenth-octave width, restricted to cut-only

activity, and automatic in its choice of frequency band.

7.3.1. Dynamic FBX Filters

Dynamic FBX lters also set automatically, but can change frequency, on a rotating basis,

as the need arises. To help distinguish dynamic from xed lters, consider the example

of a speaker using a wireless lavalier microphone, who walks under a ceiling speaker for

the rst time. In so doing, he enters a location-specic feedback zone, where it’s possible

that a problem frequency may have escaped detection and notching by a xed lter. If

all xed lters have been deployed, a dynamic lter will be set automatically as soon as

feedback appears, solving the problem. Great! But what happens when the speaker then

moves away from the ceiling speaker, and close to a oor monitor? Feedback from the

ceiling speaker is no longer a problem, but a new frequency starts to squeal. If all xed

and dynamic FBX lters are already set, a dynamic lter will change, to adjust to the new

location. An FBX dynamic lter thus stands guard if new problem feedback arises after

all available lters have been set, providing a deeper and more exible level of protection

against the dreaded surprise of feedback. Other than the ability to change frequency, a

dynamic lter is equivalent to a xed lter.

7.3.2. Balancing Fixed & Dynamic Filters

Your FBX1220, and each channel of your FBX2420, offer a total of 12 FBX lters (com-

bined xed and dynamic), which can be used as needed to exterminate feedback. After

years of experience and experimentation, Sabine has settled upon a default balance of

9 xed and 3 dynamic lters, set at the factory. This default condition can be changed to

any combination you require.

If you follow setup instructions for setting FBX lters, your FBX1220/FBX2420 will automati-

cally exit SETUP mode (enter READY status) after all xed lters and the rst dynamic

lter are set. In the default condition, this means you will have set ten lters (nine xed

and one dynamic), with two dynamic lters not set and ready to catch new feedback. If

you wish to set fewer lters, press the READY button before SETUP automatically exits,

after you have set enough lters to safely achieve your desired gain level. In that case, in

the factory default condition, you will have three dynamic lters plus the remaining unused

(and unlocked) xed lters available to catch new feedback.

7.3.3. FBX Filter Width

Sabine’s experience and testing with lters and sound quality led us to decide upon a

default FBX lter width of .10 (one-tenth) octave as the optimal notch width. This elimi-

nates feedback very well without affecting music programs. If, with all lters properly set,

feedback is still a problem, FBX lters may be set to .20 (one-fth) octave width. This

wider lter setting will potentially control more feedback frequencies, especially when they

are clustered, but this wider lter may also affect music programs slightly. For this reason

the wider setting is generally considered to be appropriate where speech (less demanding

than music) is the primary application. You can change FBX lter widths by pressing the

FIFTH OCTAVE button on the front panel. Note that the width of any lter will always be

determined by the position of the switch at the time the lter is created.

7.4. Who Beneﬁts from FBX?

Virtually every sound system will be improved with the Sabine feedback control. Singers

and presenters who do not have sound technicians can now increase their monitor or house

system volume so they can hear themselves clearly and with full delity, without worrying if

their microphones will suddenly squeal if they move to the wrong place.

Auditoriums and churches of all sizes will enjoy reliable feedback control. Hotels and confer-

ence centers around the world can offer meeting rooms with microphones that won’t howl

during programs. Sabine FBX systems can be installed in theaters, schools, sports arenas,

courtrooms, teleconferencing rooms, intercoms or interactive remote classrooms — anywhere

one or multiple microphones are used.

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