soundfield st250 user guide

ST250Stereo Microphone

User Guide 527 - 026

The SoundField ST250 Issue 1.5 User Guide

Contents

Introduction 1

Using the ST250 2

Quick Start 3

Operation 5

Width and Pattern Controls 5

M/S Switch 6

Microphone Positioning 7

END Switch 7

INVERT Switch 7

B Switch 8

ATTEN Switch 8

BATTERY Switch 8

BASS Switch 8

Headphone Monitoring 8

Powering the ST250 9

Specifications 10

Warranty 11

Quality 13

Appendix A - Theory of Operation 14

Appendix B - Converting Between M/S and L/R 16

Appendix C - Shockmount Details 17


1

ST250 Stereo Microphone and Control Unit

Introduction

The ST250 is the most advanced stereo microphone in the world.It produces an accurate stereoimage which, because of its phase coherence, readily sums to a mono signal without comb filtereffects. It incorporates �state of the art� surface mount technology for high reliability and ishand-assembled and individually calibrated. The ST250 offers several unique and practicalfeatures which have previously only been possible with the SoundField MkIV/V microphonesystems.

The flexibility of the ST250 is unique. Its ability to switch remotely from M/S to L/R stereooutputs and from vertical to end-fire with total remote control of the M pattern and the width orS magnitude, allows this microphone to be used in almost any application for stereo or monorecording and with complete compatability.

The option for self-powering allows unrestricted outdoor use for ENG and OB type applications.

All controls for the ST250 microphone are situated on the Control Unit, allowing completecontrol of the stereo image. We recommend that you read through this guide before recordingwith the ST250 as a variable pattern M-S microphone is unique and leads to certain unusualproperties.

Contact your nearest SoundField distributor for full range of accessories.

WARNING: The ST250 microphone is NOT interchangeable with the SoundField MkIV/V. It is imperative that you do not connect the ST250 to the SoundField MkIV/V control unit or the SoundField MkIV/V microphone to the ST250 control unit. SoundField Research Ltd. will not accept any claims for resulting damage if this has been attempted.


2

Using the ST250M-S recording, although known for many decades, has in practise been a minority pursuit.Suitable equipment has not been readily available and whereas most recording engineers couldeasily find a reasonably matched pair of cardioids suitable for X-Y recordings, high qualityfigure of eight microphones (essential for the S signal) were not so common. M-S and X-Yrecordings are exactly the same fundamentally. The mathematical relationship between the twois that of a linear transformation. So why M-S? We believe that M-S is a more natural way tocontrol a recording. Adjust the M pattern to control signals from the rear of the microphone.Wherever the M pattern control is set the gain for something in front of the microphone is heldconstant. The stereo width can then be set using the width control.

These parameters can be clearly heard and with use will become very familiar. The adjustmentof either will not be affected by the other. Contrast this with X-Y recordings where the pattern oftwo microphones and the angle in between are set. The acoustic results here are not at allobvious and, for example, increasing the rear rejection and at the same time maintaining stereowidth is not easy.

NoiseThe self noise of the microphone will differ according to the pattern and width settings. Ingeneral the lowest noise performance is achieved by setting M pattern as close to omni aspossible and having as little width as possible.The microphone, practically, has very low noise.It takes a few minutes for the polarising circuit to charge up the capsules, perhaps 5 minutes ifthe microphone hasn�t been used for several weeks. Otherwise possibly a few seconds if themicrophone ìhas been used within a day. During this time gain will be low, noise will be highand patterns will be peculiar.

CondensationCondensation problems occur when moist warm air comes into contact with the capsules.Typical situations would be when the microphone is brought into a warm studio from outdoorsor when a microphone is used on close vocals. Symptoms are high noise typically with a hissing/rumbling effect. The cure is to leave it to come to equilibrium with its enviroment. This maytake up to half an hour. When powered from 110/240V a capsule heater is in circuit and themicrophone should not suffer from this. Mains/line powering is always the preferred mode. Onclose vocals an anti-pop screen should be set at about 20cm or 8 inches from the microphone. Ithas no acoustic function other than keeping the vocalist at a fixed distance from the microphone(see page 10).

LevelsIf it is anticipated that the level of sound may exceed 115dB SPL peak then the attenuator shouldbe engaged. In practice the microphone is not much noisier in this mode. We have been caughtunawares by the levels of sound generated by some instruments (eg a trumpet playing jazzpeaking at 133dB SPL at half a meter). The power indicator LED serves as a crude levelindicator it will blink on peak levels about 10dB below clipping level.

HeadphonesThe headphone output is only for use as a quick check; it is not intended for serious monitoring.Phones used should be high impedance (400 ohms minimum), highsensitivity (100dB SPL per mW minimum) and closed.On phantom or battery power the phones should not be used during a recording.The reason for this is that the power available is restricted and headroom may suffer if power isdiverted to the headphones.


3

End Out Inv Out

End Out Inv In

End In Inv Out

End In Inv In

Right

Left

SOURCE

Right

Left

SOURCE

Right

Left

SOURCE

Right

End Fire Mic

InvertedEnd Fire Mic

InvertedSide Fire Mic

Side Fire Mic

Left

SOURCE

Quick Start

Getting StartedThe ST250 microphone head is powered from the control box which is powered in one of threeways - mains, phantom or battery. With mains and phantom, the unit is active as soon as poweris supplied, but with battery the BATTERY button needs to be depressed. When the control boxis powered up the red LED on its front panel illuminates. Before powering up ensure that themulticore cable is firmly connected to both the microphone head and the control unit. The twoscrew connectors ensure that the cable cannot come free. Next connect the control unit to yourdesk/recorder by means of the two XLR sockets on the back. The output levels of the controlunit are such that you can connect to either hi-mic or line level inputs. However, whenconnected to a microphone input ensure that your input gain controls are turned right down.Connect power to the control box and switch on (red LED lights up). The unit will take up toone minute to polarise the capsules, but may take up to 5 minutes to stabilise depending onconditions. Your ST250 is now ready for action.

Initial SettingsThe default setting for the ST250 is achieved with all of the six buttons at the bottom left of thecontrol unit out (a button�s function is active when the button is in). In the default condition youhave a side fire microphone with flat response, a peak signal level of 115dB and Left/Rightoutputs from the controller.The effective operational position of the ST250 is determined by the settings of the END andINV buttons. Use the label on the front of the microphone as a reference point.

Microphone Orientation


44

Other Functions

Buttons

BASSwhen in, a bass roll off filter (120Hz, 2 pole) is added as the microphone signal enters thecontrol box.

ATTNwhen in, puts a 20dB pad on the microphone, allowing a peak signal of 135 SPL.

M/Swhen in, gives the separate M and S components at the outputs of the control box.

Bwhen in, gives the four B-format signals at the outputs of the control box. Refer to page 8 andAppendix A for more detail on B-format.

BATTERYwhen batteries are fitted, acts as an ON/OFF switch to conserve battery power. ON when pressedin.

Miscellaneous

OVERLOADthe POWER LED will flicker when overload is approached.

PHONESStandard Stereo 6.3mm (1/4") jack output. Volume control located above socket. Monitors theXY output at all times regardless of any other setting.

Width and Pattern Controls

It must be realised that the ST250 operates as a M/S microphone whether it is outputting M/S orLeft/Right. If you are not familiar with the concept of M/S, refer to the next section.

WIDTHThis controls the gain of the sideways facing (S) figure of eight component. The scaling of thecontrol is 0-10 (0-100%). When this control is fully rotated (100%) the S gain is equal to that ofthe M gain.

PATTERNThis controls the polar response of the mid facing (M) component. It is continuously variablefrom omni to figure-of-eight.The relation between M/S and LEFT/RIGHT can be summed up as follows:

LEFT = M + SRIGHT = M - S

Refer to the graph in the Appendix B for quick conversion between the M/S settings and theirLEFT/RIGHT equivalents.


5

Operation

IntroductionThe ST250 is an M-S microphone and the two controls on the front panel allow independentcontrol of the middle and side signals. The pattern control will vary the M polar pattern of themicrophone from omni-directional through various sub-cardioids to cardioid and then throughthe hyper-cardioids to figure-of-eight. No matter which pattern is selected the signal level for asource at the front of the microphone is constant.This is the essential point of the design.

Width and Pattern ControlsThe width control varies the level of the sideways figure of eight; at maximum the sensitivity isthe same as that of the M signal for a source to the front of the microphone. A given controlconfiguration implies a corresponding equivalent crossed pair of microphones.By definition

Left = M + Sand Right = M - S.

The effective width of the stereo image can be adjusted from mono at one extreme to a verywide stereo image equivalent to the image produced by two back-to-back cardioids with anangle of 180 degrees between them when the width control is set to 10 and the pattern is set toomni. The graph in Appendix B allows conversion between the M-S settings of the ST250 andan equivalent crossed pair. The graph is given to allow comparisons only, in practice people willuse their ears. Adjust rear rejection with the pattern control. Adjust stereo image width with thewidth control. The two are independent.

M/S STEREOM

S

L/R STEREO

RIGHTLEFT

0 10

2.5 7.5

5

Stereo Contro lU n i t

Battery Power Phones

PatternWidth

Bass Atten End Inv M/S B

SOUNDFIELD RESEARCH

50-60Hz 1A B=ZYB=WX ST250 Mic

(M)Left Right

(S)

240V

Made in England

W

Z

Y

X

SOUNDFIELD

ST 250

66

M

-+

M / S

L R L R

L R L R

M

S+

S+- -

M

M

-+

FIGURE 3

M/S Switch

In its normal position L/R signals are sent from the L and R output sockets. Pushing the M/Sbutton will send M to the L connector and S to the R connector. Note that the microphone isalways an M-S microphone whatever this setting.

Figure 4 shows the equivalent L/R patterns when the M/S patterns are as indicated in Figure 3above.

L / R

L R L R

L R L R

Pattern set at 40% rotationwidth at 4

Pattern at cardioidwidth at 5

Pattern at omniwidth at 10

Pattern at figure of eightwidth at 10

2 Cardioids at 900 2 Hypercardioids at 900

2 Figure of Eights at 900 2 Cardioids at 1800

Figure 4



7

Microphone Positioning

As this microphone can be switched from vertical to end-fire and also inverted, it is importantfor the user to identify the positioning of the microphone relative to the stereo image. TheSoundField logo has been placed on the microphone to identify the front in the vertical mode.When used in the vertical or inverted position, the logo should be directed towards the soundsource. When used in the end-fire position the logo indicates the underside of the microphone.Obviously, if the microphone is physically inverted and the INVert button is depressed, theidentifying mark will then represent the top of the microphone.

END Switch

By depressing the END button the ST250 can be switched from use in the vertical or uprightposition to the end-fire position. In the end-fire mode the angle and polar pattern controlsoperate in the same way as for the vertical mode. See Figure 5.

INVERT Switch

If the microphone itself must be physically positioned upside down, left and right outputs areeffectively reversed. The INVert switch on the ST250 Control Unit allows the user to maintain atrue configuration of the L - R channels by reversing the L - R channel outputs if depressed. SeeFigure 6.

End Out Inv Out

End In Inv OutRight

Left

SOURCE

Right

Left

SOURCE

End Fire Mic

Side Fire Mic

End Out Inv Out

End Out Inv InRight

Left

SOURCE

Right

Left

SOURCE

InvertedSide Fire Mic

Side Fire Mic


888

B SwitchThis switch allows the user to record �B-format� four channel sound via the special STCB cable.These signals facilitate the complete post production of the sound (with control over bothresponse and position) after the recording has been made with a suitable B-format processor (ega SoundField control box). B-format can also be used to generate a surround sound recording.The B-format [X W Y Z] signals are unbalanced and exit the control unit via pin 2 and 3 of eachthree pin XLR output. The output impedance of each of these signals is 750R, thus a short cableshould be used.

Note also that to maintain compatibility with the MkIV and MkV SoundField microphone the Wor pressure signal is decreased by 3dB and these outputs are all in antiphase to the acousticsignal.

ATTEN SwitchThe attenuation switch is for use when recording very high signal levels. The button pads theinput of the microphone by 20dB to avoid distortion.The microphone will handle sound levels ofup to 115 SPL before the attenuator needs to be engaged.

BATTERY SwitchThe above switches the batteries in circuit (housed in the control unit) for self-powering. Usingstandard alkaline C cells, the expected operational life for the batteries is a minimum of 5 hours.

BASS SwitchThis switch rolls off the bass response of the microphone from 120Hz (3dB down) to reducewind noise or unwanted low frequency ambient signals.The bass roll off switch affects the bass frequencies of both the "M" and the "S" signals. It isprobably most needed when the microphone is used on close voice when a very directionalpattern is chosen.

Headphone MonitoringWhether in L/R or M/S mode you can monitor the output signal from the control unit in L/Rformat. This is intended as a checking device to ensure the system is working correctly and forbalancing the stereo image. It is not intended as a permanent monitoring facility, nor should it beused as an output as the signal from the monitor has not been processed to the same specifica-tions as the main outputs.Continuous monitoring when battery or phantom powered will affect the performance of theST250 and, if using battery power, will reduce battery life and lower the headroom.

0 10

2.5 7.5

5

Stereo Contro lU n i t

Battery Power Phones

PatternWidth

Bass Atten End Inv M/S B

SOUNDFIELD RESEARCH

50-60Hz 1A B=ZYB=WX ST250 Mic

(M)Left Right

(S)

240V

Made in England

W

Z

Y

X

SOUNDFIELD

ST 250


9

++

++

FRONT

Top View

Powering the ST250Powering is from either 100v, 110v, 240v mains, 48v phantom power or batteries.

Mains PowerThe microphone is supplied set to operate at the voltage of your local mains supply. Should youwish to use the ST250 in a country where there is a different mains voltage, we recommend thatbattery power is used. If this is not possible please contact your SoundField representative whowill explain how to change the operating voltage.

Phantom PowerThe ST250 is designed to run on 48v +/- 5v phantom power systems.However, 20mA of current is required and most boards will not supply this without a minormodification. Phantom power is taken from both XLR connectors and 10mA per connector isrequired. 25 volts is required to operate the unit. This implies that the phantom resistors must beless than 3K9 per side (potential drop 5mA x 3900 = 20v) and to avoid an excessive load on thesignal these resistors should be greater than 3K3. The standard phantom power resistor of 6K8will cause misoperation with typical symptoms being high noise and peculiar stereo imaging.The unit is safe to operate on transformer phantom power supplies.

NOTE - problems may also arise if standard phantom power is fed to an ST250 as it is being powered from the mains or battery. Once again, high noise and peculiar imaging can result. We recommend either switching off the phantom power or connecting the unit to a LINE level input. If this is not practical, a small modification of the control box removes the phantom power circuit and the mic is powered from the mains or battery. Contact your SoundField representative for further details.

Battery Power and ReplacementThe battery power supply is housed in the control unit. Unscrew the chrome knurled nut abovethe battery switch and pull out the front panel to reveal access for 2 x "C" size battery cells. It isrecommended that alkaline (Duracell) type batteries are used. Be careful to ensure that thebatteries are placed with the positive end pointing towards the front panel. See Figure 8. Replacethe front panel and ensure the knurled screw is tight.


110

10

Specification ST250Output levels are measured with a high impedance load

with 20dB attenuatorFront Sensitivity at 80SPL (fixed) -27dBV -47dBVMaximum variation of M with pattern +/- 1.5dBS sensitivity at 80dB SPL (maximum) -27dBV -47dBVW output 80dB SPL -30dBV -50dBVX,Y,Z output 80dB SPL -27dBV -47dBVFrequency range +/- 2dB 20Hz - 20kHzwith bass cut 120Hz - 20kHzNoise (M cardioid or omni) 17dB SPL A weighted

(anechoic measurement)Maximum sound level 115 dB SPL 135 dB SPL

Powering:a) Mains 240V/110V set by internal link.b) Battery 2 alkaline C cells will power the unit for 5hrsminimum.c) Phantom powering from 48V+/- 5V current drawn 4x5mA Impedance less than 3K9 per line.

Output two 3 pin XLR male connectors. Pin 2 has signal on it and pin 3 provides an equalimpedance connection to ground. It should be connected to a balanced input.Output impedance 220R M/S A/B balanced.B-format 750R unbalanced.

As a policy of continual improvement of products is pursued, specifications are subjectto change without notice.

Humidity and CondensationCondensation which is caused by rapid changes in humidity and cold, damp conditions can be aproblem to ALL polarised capacitor microphones. Moisture from the atmosphere or from thebreath, if used close to the mouth, may condense on the capsules resulting in noise and reducedsignal. The ST250 microphone includes a heater in the capsule cluster to minimise this effectand normal performance is restored when this moisture has completely evaporated. The heater isonly operative when the unit is powered from the mains. It is therefore advisable when themicrophone has been stored in a cold place, such as in a vehicle overnight, to bring themicrophone into a warm dry environment prior to use and full performance will be achievedmore quickly. It is also desirable to fit the foam windshield if the microphone is used at closerange, and to use an anti-pop screen at about 20cm distance.


11

WarrantyLimited LiabilitySOUNDFIELD RESEARCH LTD., HEREIN AFTER KNOWN AS THE MANUFACTURER,GUARANTEES THIS EQUIPMENT FROM DEFECTS IN MATERIAL AND WORKMAN-SHIP UNDER NORMAL USE AND SERVICE FOR A PERIOD OF ONE YEAR. THISGUARANTEE EXTENDS TO THE ORIGINAL PURCHASER ONLY AND DOES NOTAPPLY TO FUSES OR ANY PRODUCT OR PARTS SUBJECTED TO MISUSE, NEGLECT,ACCIDENT OR ABNORMAL CONDITIONS OF OPERATION. THE GUARANTEE BEGINSON THE DATE OF DELIVERY TO THE ACTUAL PURCHASER OR TO HIS AUTHORISEDAGENT OR CARRIER.

IN THE EVENT OF FAILURE OF A PRODUCT COVERED BY THIS GUARANTEE, THEMANUFACTURER OR THEIR CERTIFIED REPRESENTATIVES WILL REPAIR ANDCALIBRATE EQUIPMENT RETURNED PREPAID TO AN AUTHORISED SERVICEFACILITY WITHINìONE YEAR OF THE ORIGINAL PURCHASE AND PROVIDED THATTHE GUARANTORS EXAMINATION DISCLOSES TO ITS SATISFACTION THAT THEPRODUCT WAS DEFECTIVE, EQUIPMENT UNDER THIS GUARANTEE WILL BEREPAIRED OR REPLACED WITHOUT CHARGE. ANY FAULT THAT HAS BEENCAUSED BY MISUSE, NEGLECT, ACCIDENT, ACT OF GOD, WAR OR CIVIL INSUR-RECTION; ALTERATION OR REPAIR BY UNAUTHORISED PERSONAL; OPERATIONFROM AN INCORRECT POWER SOURCE OR ABNORMAL CONDITIONS OF OPERA-TION, WILL NOT FALL UNDER THIS GUARANTEE. HOWEVER, AN ESTIMATE OFTHE COST OF THE REPAIR WORK WILL BE SUBMITTED BEFORE WORK ISSTARTED.

THE MANUFACTURER SHALL NOT BE RESPONSIBLE FOR ANY LOSS OR DAMAGE,DIRECT OR CONSEQUENTIAL, RESULTING FROM MACHINE FAILURE OR THEINABILITY OF THE PRODUCT TO PERFORM.

THE MANUFACTURER SHALL NOT BE RESPONSIBLE FOR ANY DAMAGE OR LOSSDURING SHIPMENT TO AND FROM THE FACTORY OR ITS DESIGNATED SERVICEFACILITY.

THIS GUARANTEE IS IN LIEU OF ALL OTHER GUARANTEES, EXPRESSED ORIMPLIED, AND OF ANY OTHER LIABILITIES ON THE MANUFACTURERS PART.THE MANUFACTURER DOES NOT AUTHORISE ANYONE TO MAKE ANY GUARAN-TEE OR ASSUME ANY LIABILITY NOT STRICTLY IN ACCORDANCE WITH THEABOVE.

THE MANUFACTURER RESERVES THE RIGHT TO MAKE CHANGES OR IMPROVE-MENT IN THE DESIGN AND CONSTRUCTION OF THIS UNIT WITHOUT OBLIGATIONTO MAKE SUCH CHANGES OR IMPROVEMENTS IN THE PURCHASER�S UNIT.

ANY DISPUTE ARISING FROM THIS WARRANTY SHALL BE SUBJECT TO THE LAWSOF ENGLAND.

What to do if a fault is foundIf a fault develops in the unit, notify SoundField Research Ltd. or their nearest service facilitygiving full details of the difficulty. On receipt of this information, service or shipping instruc-tions will be forwarded to you. No equipment should be returned under the warranty withoutprior consent from SoundField Research Ltd or their Authorised Representative.


12

Shipping Information

Authorised returns should be prepaid and must be insured. All SoundField products are packagedin specially designed containers for the best possible protection. If the unit is returned theoriginal container should be used. If this is not possible, a new container can be obtained fromSoundField Research Ltd. please specify the model number when requesting a new container. Ifthe specially designed container is not used ensure that a suitable rigid container of adequate sizeis used, wrap the instrument in paper and surround it with a good thickness of shock absorbingmaterial.

Claim for damage during transit

The instrument should be thoroughly inspected immediately upon delivery to the purchaser. Ifthe instrument is damaged in any way a claim should be filed with the carrier immediately. Aquotation to repair shipment damage can be obtained from SoundField Research Ltd. or theirCertified Representative. Final claims and negotiations with the carrier must be completed bythe customer.

Applications problems

SoundField Research Ltd. will be happy to answer all applications questions to enhance your useof this equipment. Please address all correspondence to:

SoundField Research Ltd.Charlotte Street Business CentreCharlotte StreetWakefieldWest YorkshireWF 1 UHENGLAND

13


Quality Assurance and Service Policy

Over the years SoundField products have gained an enviable reputation for their quality ofdesign, performance and reliability, however, in the unlikely event that problems areencountered with this unit, please contact SoundField Service at the appropriate address belowor alternatively inform one of our world wide network of distributors who will be able ìto assistwith any of your queries.

SoundField Research Ltd.Charlotte Street Business CentreCharlotte StreetWakefieldWest YorkshireWF1 1UHENGLAND

All SoundField products are sold subject to our �General Conditions of Sale� and the purchasershould note �that the equipment is not being sold to him to meet his individual requirements andit is therefore the buyer�s responsibility to ensure that the purposes and functions of theequipment meet his requirements prior to purchase.� However, we would non-the-less be gratefulto receive any constructive criticism or ideas for additional features which you feel mightenhance the usefulness of our product in the studio environment.


14

Appendix A

Theory of Operation

The ST250 produces truly coincident stereo signals, it achieves this using the much acclaimedSoundField technology and this next section describes in some detail how this technology hasbeen developed for use in the ST250.

The microphone head contains four sub-cardioid capsules set in a regular tetrahedron. Thecapsule signals are in fact added and/or subtracted to provide a set of four signals known as B-Format, as described below.

Closer examination of the capsule array shows that the Left Front and Right Back capsules areback to back, but tilted symmetrically from the vertical. If the signals from these 2 capsules aresubtracted then the two sub-cardioid capsules produce a horizontal figure-of-eight pattern withits axis along the line left front to right back.

Similarly, Right Front and Left Back are tilted symmetrically downwards and when subtractedproduce a horizontal figure-of-eight pattern with its axis along that line. The two figure-of-eightpatterns are added with Left Front and Right Front in phase to produce a figure-of-eight patternwhose axis lies front/back and this is termed the X component of the �B� Format signal.

Subtraction of the 2 diagonal figure-of-eight patterns produces a figure-of-eight pattern whoseaxis lies along the left/right axis and this is the Y component (positive left).

Further combination of pairs produce 2 figure-of-eight patterns at 45° to a vertical axis resultingin a final Z component whose axis lies along the up/down axis (positive up).

The remaining B-Format component, W, is an omni-directional pattern produced by summingthe four capsule outputs in phase.

Thus the B-Format components are:

W = LF + RB + RF + LBX = LF - RB + RF - LBY = LF - RB - RF + LBZ = LF + RB - RF - LB

The �B� Format signal can therefore represent sound from any point in space by 3 directional co-ordinates X, Y & Z, and the pressure component W.

Note, that each capsule makes an equal contribution to each of the four B-Format signals and itis this factor and the symmetry of the array which causes a certain amount of cancellation ofcapsule errors to produce performance characteristics not possible except with SoundFieldtechnology.

Moreover, compensation is applied to the resulting signals in amplitude and phase, to effectivelybring the four B-Format signals to an origin at the centre of the cluster. This coincidence of thesignal components has remarkable effects on the accuracy of a synthesised stereo microphonewhich can be set up from combinations of the B-

Format signals and contrasts vividly with other approaches where coincidence is often lost atfrequencies as low as 1kHz (if there at all!). How this is done will now be described:

If a microphone is required to be omni-directional then only the W component is used. If aforward facing figure-of-eight is required the X component is used. An end-fire figure-of-eightwould be represented by the Z component.


15

X

X

X Y

Y

2 2

If a cardioid is required facing forward, then the sum of W and X produces this, (although instandard B-Format X, Y & Z are enhanced 3db for similar programme levels to W).

A cardioid is therefore actually W +

If two cardioids facing left-front and right-front are required then the transverse figure-of-eightcomponent Y (like S in M/S format), is introduced, positively for left and negatively for right asfollows:

Left W + +

Right W + -

The further reduction in level of the X signal by 3dB allows for the introduction of the Y signalat a similar level to produce a pressure gradient signal of the same levelto that for mono to produce cardioid patterns.

It becomes obvious at this point how the B-Format components may be combined andmanipulated to achieve desired effects. For example, trading X for Y and vice versa will alter thewidth of the stereo pick-up whilst trading the X-Y combination for W and vice versa will alterthe patterns from omni-directional through all the cardioids to figure-of-eight.

Controls are provided to achieve these variations. Moreover, by simply reversing Y, themicrophone may be suspended upside down, instead of being placed vertically on a stand, andthe signals remain correct. What is more important, is that Z and Y may be used instead of Xand Y, and all the aforementioned features may be achieved with the microphone in an end-firemode.

This is particularly valuable in TV work on a boom where the microphone can �point� at thesubject. Further examination reveals that since it is becoming extremely popular to work in theM/S format, it is ìprobably better to introduce other controls rather than patterns and stereoangle. There can be a variation of the M pattern by varying the ratio of W and X and the stereowidth by simply varying the amplitude of Y. The combinations are clearly endless and thechoices actually made have been determined after considerable discussions with recordingengineers from many areas of the audio industry.

222

2


16

Figure of 8

Hypercardioid

Cardioid

M Pattern

Omni

S Gain

Width

127˚

53˚ 90˚

c

d

b

a

Sub-cardioid

1

.75

.5

.25

0

0 .25 .5 .75 1

0 45 90 135 180

Appendix BConverting Between M/S and L/R

a locus of cardioidsb locus of 135° hyper cardioidc locus of 120° hyper cardioidd locus of figure of eights

The three other angled lines are loci of the nominated angles between synthesised L/R pairs.

ExampleIf a pair of cardioids with an angle of 90° between them is required, look at the intersection ofthe 90° line and the cardioid locus. This corresponds to an S Gain of about 40% and a pattern atslightly below the cardioid setting.


17

Appendix C

ST250 Microphone Shockmount Assembly Instructions

List of Parts

1 x Geodesic Suspension Cradle2 x Elastic Loops1 x ST250 Microphone Holder1 x Stand Mounting Knuckle Joint - 2 pieces, slotted nut and bolt1 x Allen Screw - 4mm hexagonal head2 x Knurled Head Screw (Fischer Boom)

Stand Mounting

1 Fit the holder into the cradle (Figure 1). The top four hooks on the holdershould clip onto one elastic loop and the bottom four onto the other. SeeFigure 4 for position.

2 Adjust the tension of the elastics so that the holder is held equidistant fromthe sides of the cradle.

3 Undo the slotted nut and bolt holding the knuckle (Figure ì3) together andremove, allowing the two pieces of the knuckle to separate. This will provideaccess to the head of the Allen screw.

4 With a 4mm hexagonal screwdriver, fix knuckle to cradle by screwing Allenscrew into one of the two threaded holes on the cradle.

5 Reassemble the removed section of the knuckle and tighten nut and bolt.

6 Unclip the lugs. Fit the microphone as described below.

Rycote MountingRycote manufacture a special ST250 system for special applications. This has beendesigned to work in conjunction with the ST250 microphone holder (2).

1 Fit the holder into the Rycote suspension. Each elastic loop on the Rycoteshould pass around two adjacent fixing hooks on the holder. For ease of use,put the securing lugs of the holder uppermost.

2 Unclip the lugs. Fit the microphone as described below.

Fixing Microphone in Holder

1 Relax the holder (Figure 2) by compressing the large and small ringsandunclipping the securing lugs.

2 Insert the ST250 microphone and refasten the lugs so that the larger end ofthe microphone clamps just at the base of the windshield. Remember to takeinto account the orientation of the microphone (refer to the ST250 usermanual for details).

3 Screw the microphone cable onto the base of microphone

FIGURE 4 : ASSEMBLED SUSPENSION SYSTEM

18

TOP HOOKS

LUGS

LUGSTHREADED HOLE

ELASTIC

THREADED HOLE

ELASTIC

Fig 1 : Cradle Fig 2 : Holder Fig 3 : Knuckle

BOTTOM HOOKS

SLOTTED NUT AND BOLT



IMPORTANT NOTE:

This is an M-S microphone. PATTERN refers to Mpattern and WIDTH is the S control.

The microphone has been designed to be used withphantom power supplying 10mA down each of two3-pin XLRs. This gives a total of 20mA.

If there is more than 3,900 ohms in each of the phantomsupply lines then the performance of the microphonewill be impaired. This may not be immediately apparent.Please refer to page 8 in the manual.

IMPORTANT NOTE:

RETAIN THIS PACKAGING

If for any reason it becomes necessary to returnthis equipment use this original packaging tominimise the risk of shipment damage.

Failure to do so could invalidate the warranty.

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soundfield st250 user guide

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