Bose 901 Series IV Equalizer Manual

The Bose 901 Series IV Active Equalizer is a critical component designed specifically for use with the Bose 901 Series IV Direct/Reflecting® speaker system. It provides the precise equalization required to achieve the system's intended acoustic performance, compensating for the unique characteristics of the nine full-range drivers in each speaker. This manual covers setup, operation, controls, specifications, and troubleshooting for optimal audio reproduction.

1. Features at a Glance 2. Installation & Connection 3. First-Time Setup 4. Specifications 5. Controls and Functions 6. Connecting to Your System 7. Equalization Theory & Use 8. System Calibration 9. Care & Maintenance 10. Regulatory Information 11. Troubleshooting

Features at a Glance

Key components: Active equalizer unit with slide controls, input/output jacks, power switch, and bypass function.

FeatureDescription
Active EqualizationProvides precise frequency response correction for 901 Series IV speakers
Bypass SwitchAllows comparison of equalized vs. non-equalized sound
Slide ControlsAdjusts equalization curves for optimal room acoustics
Input/Output JacksStandard RCA connectors for system integration
Power Switch & IndicatorControls unit power with visual indicator
Designed for 901 Series IVOptimized specifically for the nine-driver array
Direct/Reflecting® CompensationCorrects for the speaker's unique radiation pattern
System ProtectionHelps prevent amplifier overload
Compact DesignFits standard audio rack spaces
Required ComponentEssential for proper 901 Series IV operation

Installation & Connection

Unpack and inspect contents. Place equalizer near your amplifier/receiver.

  1. Connect source to equalizer: Connect preamp output or tape monitor output to equalizer INPUT.
  2. Connect equalizer to amplifier: Connect equalizer OUTPUT to main amplifier input.
  3. Connect speakers: Ensure 901 Series IV speakers are properly connected to amplifier outputs.
  4. Plug into AC power: Use provided power cord and connect to grounded outlet.

WARNING! Always turn off amplifier power before making connections. Ensure all connections are secure to prevent hum or distortion.

First-Time Setup

Power on system; follow setup procedure for optimal sound.

  1. Initial connection: Verify all cables are connected correctly as per Installation section.
  2. Power sequence: Turn on equalizer first, then amplifier to prevent thumps.
  3. Bypass check: Engage bypass switch to hear unequalized sound as reference.
  4. Slide control adjustment: Begin with all slide controls at center (flat) position.
  5. Room adjustment: Make small adjustments based on room acoustics and listening position.

CAUTION! Do not operate equalizer without connected speakers. Avoid extreme equalizer settings that may cause amplifier clipping.

Specifications

Controls and Functions

Front Panel: POWER switch, Bypass switch, Slide controls for equalization adjustment.

Slide Controls: Adjust specific frequency bands to compensate for room acoustics. Center position is flat response.

Bypass Switch: Engages/disengages equalization for comparison. Power Indicator: Shows when unit is powered. Rear Panel: INPUT jacks (from preamp), OUTPUT jacks (to amplifier), AC power inlet.

Equalization Theory: The equalizer corrects the natural response of the nine-driver array to achieve flat overall response when combined with room acoustics.

Connecting to Your System

Integration with various audio system configurations.

  1. Standard Stereo System: Connect between preamp and power amp sections.
  2. Receiver with Tape Monitor: Use tape monitor loop for equalizer connection.
  3. Integrated Amplifier: Connect between source selector and amplifier stage.
  4. Multiple Source Systems: Equalizer affects all sources when connected in main signal path.

Tip: For best results, use high-quality interconnects and keep cable runs as short as possible.

Equalization Theory & Use

The 901 Series IV requires specific equalization to achieve its designed performance.

  1. Direct/Reflecting® Design: Equalizer compensates for the unique radiation pattern.
  2. Nine-Driver Array: Correction for multiple full-range drivers working together.
  3. Room Interaction: Adjust slide controls to compensate for your room's acoustics.
  4. Listening Position: Optimal equalization may vary with listening position.
  5. Program Material: Different music types may benefit from slight adjustments.
  6. Bypass Comparison: Regularly use bypass to appreciate equalization effect.
  7. Gradual Adjustment: Make small changes and listen for several days before further adjustment.
  8. System Synergy: Equalizer settings interact with amplifier and source components.

WARNING! Extreme equalizer settings can cause amplifier overload and speaker damage. Use moderation.

System Calibration

For optimal performance, calibrate system to your room.

  1. Start with flat: All slide controls at center position.
  2. Play reference music: Use familiar, well-recorded material.
  3. Adjust for balance: Make small adjustments to achieve natural tonal balance.
  4. Check bypass: Compare equalized/unequalized sound regularly.
  5. Finalize settings: Once satisfied, note positions for future reference.

Professional Calibration: For critical applications, consider professional calibration with test equipment.

Care & Maintenance

Unplug before cleaning. Use dry cloth only; no liquids or aerosols.

Control Maintenance: Occasionally exercise slide controls to maintain proper contact. Connection Check: Periodically verify all connections are secure. Ventilation: Ensure adequate ventilation around unit.

CAUTION! Do not spray cleaners directly on unit. Keep away from moisture and extreme temperatures.

Regulatory Information

FCC Compliance: Class B digital device; complies with interference limits for residential use. Copyright © Bose Corporation. Bose and Direct/Reflecting are registered trademarks of Bose Corporation. For support, contact Bose Customer Service or authorized service centers. This equalizer is designed for use exclusively with Bose 901 Series IV speakers.

Troubleshooting

SymptomPossible CauseCorrective Action
No soundIncorrect connections/powerCheck all cables; verify power indicator is on; try bypass mode.
Distorted soundExtreme equalizer settingsReturn slide controls to center; reduce amplifier volume.
Hum or noiseGround loop/poor connectionsEnsure secure connections; try different grounding configuration.
Bypass not workingSwitch issue/internal faultCycle power; contact service if persistent.
Uneven frequency responseIncorrect slide settings/room issuesReadjust slide controls; consider room acoustics treatment.
Intermittent operationLoose connections/component faultCheck all cables and connections; contact service if needed.

Reset: Return all slide controls to center position for flat response.

Service: Contact Bose Corporation or authorized service center. Do not attempt internal repair.

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