{"id":1581,"date":"2011-08-30T15:19:40","date_gmt":"2011-08-30T05:19:40","guid":{"rendered":"http:\/\/www.bssound.com.au\/wordpress\/?page_id=298"},"modified":"2011-08-30T15:19:40","modified_gmt":"2011-08-30T05:19:40","slug":"passive-and-active","status":"publish","type":"page","link":"https:\/\/bssound.com.au\/?page_id=1581","title":{"rendered":"Passive and Active"},"content":{"rendered":"

PASSIVE & ACTIVE<\/strong><\/p>\n

These words are commonly used to describe D.I Boxes, Crossovers
\nand Speaker Boxes.<\/p>\n

Passive means that no power supply (240 volt, battery or plug
\npack) is required. The audio signal is all that is required
\nfor the device to operate.
\nActive means that the device requires electric power in addition
\nto the audio signal. (any amplifier is an Active device but the
\nword Active is never used as there is no such thing as a Passive
\namplifier!)<\/p>\n

D. I. BOXES<\/p>\n

Passive D.I. (Direct Input\/Injection) Boxes usually consist of a
\ntransformer where the primary coil is high-impedance (between
\n1000-5000 ohms) connected across the sheild & signal connectors
\nof the instrument socket. A second socket is also connected so
\nthat the same instrument can still be connected to an amplifier.
\nIt does not matter which socket is used for instrument or
\namplifier as they are connected together in parallel.
\nThe secondary coil is low impedance (200-500 ohms) (similar to
\na microphone coil) connected across pins 2 & 3 of a cannon\/XLR
\nsocket. Pin 1 (the earth\/sheild) is connected to the case of
\nthe D. I. Box. This secondary\/output of the D. I. Box is a
\nbalanced signal, allowing it to run long distances (40 meters
\nof multi-core) with minimal interferance. There will be a drop
\nin signal level of the audio passing through the transformer
\nbut most mixing desks have enough gain on their microphone
\ninput channels to cope with this. A good quality transformer
\nshould have no significant degradation of dynamics or tonality.<\/p>\n

Active D. I. Boxes are wired in exactly the same way except the
\ntransformer is replaced by a pre-amp with an un-balanced input
\nand a balanced (pins 2 & 3) output. The pre-amp is powered by a
\nbattery or (now things get confusing) by phantom power, supplied
\nby the mixing desk, travelling (backwards) back up the multicore
\n& microphone lead into the D.I. via its output socket.<\/p>\n

Phantom Power; At the mic input of the mixing desk, 48 volts DC
\npositive is applied to both pins 2 & 3, negative is applied to
\npin 1 (sheild). The impact of this voltage on the audio signal
\nis cancelled out as it is a balanced line (pins 2 & 3 are “hot”
\n& “cold”, opposite to each other, and any current or
\ninterferance which is the same will cancel out) The Active
\ndevice (our D. I. Box, condensor mic or shot-gun mic) will tap
\nthe power it requires to run its pre-amp from its output socket.
\nPhantom Power is called that as it is effectivly invisible and
\nworks like magic!<\/p>\n

Personally I prefer to use passive D.I. Boxes as there are no
\nbatteries to go flat and phantom power can create extremely
\nloud noises when D. I. Boxes are connected or disconnected or
\nif the mic leads are faulty.<\/p>\n

Earth Lift switches on D.I.Boxes allow you to break the earth
\nconnection between the earth used by the instrument amplifier
\non stage and the earth used by the mixing desk. This is an
\nadvantage as an earth loop, causing hum, can be created when
\ntwo devices (instrument\/amp & mixer) are connected together
\nbut draw electic power (with earth) from seperate power outlets.<\/p>\n

CROSSOVERS<\/p>\n

Passive Crossovers are usually built into Passive speaker boxes.
\nTheir purpose is to split the full range signal from a single
\namplifier into treble for the horn (or tweeter) and bass for
\nthe low speaker (or woofer). This is what normally exixts
\ninside your home HiFi speakers or in a full-range PA speaker
\nbox.
\nThey consist of an RLC network (resistor, inductor, capacitor)
\nPassive components which divide the frequency spectrum as
\ninductors (coils) prefer to pass low frequencies but choke high
\nfrequencies & capacitors prefer to pass high frequencies &
\nresist low frquencies. No additional power is required, just
\nthe amplified signal as it reaches the speaker box.<\/p>\n

Active Crossovers are connected before the (multiple)
\namplifiers. You would require seperate amps for each of your
\nhorns, mids & low speakers. Active cossovers split the audio
\ninto (usually) Hi, Mid & Low at line level after the output
\nof the mixing desk, and before the inputs of your power amps.
\nThey are defined as an active device since they require
\nelectric power to run their internal pre-amps & tone filters.
\nThe main advantages of an active system is more power amps
\nfor a larger speaker system and more accurate frequency
\ndivision.<\/p>\n","protected":false},"excerpt":{"rendered":"

PASSIVE & ACTIVE These words are commonly used to describe D.I Boxes, Crossovers and Speaker Boxes. Passive means that no power supply (240 volt, battery or plug pack) is required. The audio signal is all that is required for the device to operate. Active means that the device requires electric power in addition to the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1576,"menu_order":5,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1581","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/bssound.com.au\/index.php?rest_route=\/wp\/v2\/pages\/1581","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bssound.com.au\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/bssound.com.au\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/bssound.com.au\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bssound.com.au\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1581"}],"version-history":[{"count":0,"href":"https:\/\/bssound.com.au\/index.php?rest_route=\/wp\/v2\/pages\/1581\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/bssound.com.au\/index.php?rest_route=\/wp\/v2\/pages\/1576"}],"wp:attachment":[{"href":"https:\/\/bssound.com.au\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1581"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}