Krix MX-20, MX-30 & MX-40 Installation Manual

Introduction

Krix has been a provider of audio solutions for commercial cinemas for over 35 years, with loudspeakers installed in over 3,000 cinemas across more than 30 countries. A key factor in Krix's success in the commercial cinema market is the development of the infinite baffle wall concept. This concept provides a solid wall or half-space continuous with the front of the loudspeakers, preventing sound leakage into the space behind the screen, which can degrade sound clarity by mixing reflected sound with direct sound.

Krix has also conducted extensive research and development into horn and waveguide loudspeakers, leading to improvements in efficiency, directivity, and distortion characteristics. Krix holds several patents in the area of constant directivity horns, positioning the company at the forefront of technology and design in commercial cinema.

The infinite baffle wall and horn design technologies have been successfully combined in the Series MX range of dedicated home cinema loudspeaker systems. The MX loudspeakers are designed for flush mounting into a false wall, with an acoustically transparent screen placed over the front, replicating the proven commercial cinema concept. The Series MX modular systems feature left, centre, and right screen loudspeaker modules, along with two passive subwoofer modules, all sharing the same height and depth. This modular approach simplifies the design and construction of the false wall at the front of the home cinema and minimizes the required depth. The front of each speaker is covered with acoustic absorbent material to minimize screen reflections and aid in acoustic room treatment for improved intelligibility and overall sound performance. The Series MX range delivers the visual experience and dynamic impact of a true cinema at home.

Image Description: A photograph of a commercial cinema installation featuring a 'Baffle Wall', Krix commercial 4-Way loudspeakers, and dual 18" subwoofers.

Room Suitability

The Series MX systems are designed for media rooms and dedicated home cinemas, capable of delivering high sound pressure levels (SPL). They are best installed in enclosed rooms to avoid disturbing other occupants. Ambient light levels should be fully controlled for optimal image contrast, as the MX loudspeakers are intended for use with projectors and acoustically transparent screens. Enclosed spaces with no windows or openings to other living areas are ideal.

Room ratios are important; a rectangular room is generally most suitable, with main speakers firing down the length of the room. The shallow design of the Series MX main speaker and subwoofer modules minimizes the space required behind the screen and maximizes available space within the home cinema room.

Due to the high SPL capabilities of the Series MX loudspeakers, it is recommended that allowances are made in room design and construction for soundproofing or isolation. Sound isolation is necessary to reduce or eliminate extraneous noises (e.g., traffic, plumbing) from entering the cinema and excessive noise (especially low frequencies) from emanating from the cinema and disturbing others. Soundproofing is best achieved during construction but can be retrofitted. Attention should be paid to the thickness and density of building materials for walls, ceiling, and floor. Reducing air leakage through door seals, windows, vents, and cable ducts can significantly improve isolation.

For sound isolation concerns, consulting an acoustic consultant is highly recommended.

Acoustic Considerations

Room acoustics significantly influence the performance of any audio system in a home cinema. Reflections, slap echo, and uncontrollable bass can detract from clarity and intelligibility. Rooms with predominantly hard surfaces and glass can sound "lively" with excessive reverberation, making dialogue and soundtracks lack definition. Conversely, rooms with excessive acoustic treatment can sound flat and dead.

The ideal scenario involves balancing absorption and diffusion. Sufficient soft material should be added to reduce reverberation time, and strategically placed diffusion can maintain a natural sound and create a sense of spaciousness. Untreated hard surfaces adjacent to loudspeakers are not ideal.

For optimal performance, consult an acoustic engineer for room treatment. Some acoustic treatment suppliers offer design services. A detailed room plan with dimensions, seating layout, and speaker positions is typically required.

Note: Soundproofing (isolation) is distinct from acoustic treatment. It's a common error to focus solely on isolation without considering acoustics.

Room Size

The Krix engineering team's extensive experience in commercial cinema audio system design indicates that room size and listening distance are significant factors in determining the ideal speaker system. Commercial cinemas are typically designed and calibrated to achieve "reference level" (ideal SPL for dynamic range, impact, and realism) at the central seating area. In dedicated home cinemas with larger screens and multiple seating rows, viewers are often further from the speakers. Therefore, speaker sensitivity and amplifier power output must be carefully considered to achieve Dolby® reference levels.

The Series MX loudspeaker systems are designed for various room sizes to deliver a true cinematic experience. The table below illustrates the ideal room size range for each Series MX screen speaker system, considering average seating capacity.

Reference Level 105dB

Note: The Series MX system should be chosen based on room size, not budget. Selecting an MX-20 for a 14-meter room, for instance, could result in a suboptimal experience for rear-row listeners due to lower SPL, diminishing clarity and impact.

Achieving Dolby® reference sound pressure levels (SPL) in a home cinema requires three critical design elements: room size, speaker sensitivity, and amplifier power output. The Series MX speakers and subwoofers offer higher sensitivity than typical hi-fi speakers, reducing amplifier power requirements even in larger rooms.

For rooms of recommended size, MX-20 Main speakers can be powered by a mid- to top-tier AV receiver. The MX-30 system is best suited for larger home cinemas, requiring separate processors and power amplifiers for optimal performance. Separate power amplifiers deliver more current, producing the desired dynamics and impact for a cinematic experience.

The MX-40 LCR modules necessitate an active crossover and bi-amplification, a configuration used in commercial cinemas for optimal low and high-frequency drive. Recommended active crossover settings are on page 14. Never connect MX-40 LCR loudspeakers without an active crossover to avoid potential damage to the high-frequency element. It is recommended to use the same amplifier model for both low and high frequency elements of each speaker to ensure identical gain. If different amplifiers are used, refer to the note on page 14.

As the Series MX subwoofers are passive, an independent power amplifier connected to the LFE channel(s) of the AV receiver or processor is required. For best results, a professional-style power amplifier with selectable output limiter and high-pass filtering options is strongly suggested. Refer to the Equalisation section (Page 14) for configuration details.

The graphs illustrate recommended amplifier power for each Series MX model relative to room size. The minimum power line indicates the amplifier power needed for Dolby ATMOS® reference levels (105dB mains, 115dB LFE). Higher power provides additional headroom.

Image Description: Two graphs showing recommended amplifier power for MX Main Speakers and MX Subwoofers in relation to room depth in meters. The graphs plot Amplifier Power (Watts) per Channel/Subwoofer against Room Depth (meters), indicating minimum recommended power for 105dB and 115dB reference levels, and power handling limits for different models (MX20, MX30 & MX40).

System Dimensions

MX systems are designed to fit into a niche or cavity in the front wall, located directly behind the screen.

Image Description: Figure 1 shows a diagram illustrating the placement of the MX system within a screen wall cavity, behind the screen. It depicts the screen, the screen wall, and the cavity for the MX system, showing the arrangement of MAIN and SUB speaker modules.

Overall Dimensions

The choice of MX system should consider the screen size. Spacer modules are available to increase the distance between left and right modules for wider screen formats and improved channel separation.

Figures 2 and 4 provide overall dimensions and recommended cavity sizes for each MX system, serving as a guide for matching screen sizes.

MX SYSTEM, Without Spacers

Image Description: Figure 2 shows the layout and dimensions of the MX SYSTEM without spacers. It details the System Width, System Height, System Depth, Cavity Width, Cavity Height, Cavity Depth, and Minimum Screen Size for 16:9 and 21:9 aspect ratios for MX20, MX30, and MX40 systems.

MX SYSTEM, With Spacers

Image Description: Figure 4 shows the layout and dimensions of the MX SYSTEM with spacers. It details the System Width, System Height, System Depth, Cavity Width, Cavity Height, Cavity Depth, and Minimum Screen Size for 16:9 and 21:9 aspect ratios for MX20, MX30, and MX40 systems, including the additional spacer width.

System Positioning

Image Description: Figure 3 illustrates the correct system positioning for optimal listening. It shows the Listening Axis at a 10-degree angle to the listener's ear level from 750mm height, with a 20-degree angle for secondary rows.

Vertical Positioning

When planning a home cinema, prioritize seating locations, then screen size and position. Consider the listening axis of the speakers (MX20 and MX30: 500mm from the base of the speaker module; MX40: 750mm). Position the speaker cavity behind the screen so the listening axis is within 10 degrees of the listener's seated ear level. For secondary viewing rows, keep this angle within 20 degrees.

Ensure the first row of viewers does not obstruct the sound path for those behind. Raising the platform height for subsequent rows can help mitigate this.

Screen Wall Construction

Constructing the false screen wall for the MX system is straightforward. Consider sound isolation into adjoining rooms. If the wall adjoins a utility space, sound leakage might be less critical. If it adjoins a living space, reducing sound transmission is beneficial.

Two construction methods are recommended, depending on building constraints and budget:

Fixed Directly to Rear Wall: This simpler method involves fixing the shelf studwork supporting the MX modules securely to the baffle wall and the rear wall of the adjoining room using construction adhesive and screws/nails. This method increases the likelihood of sound transmission.

Isolated from Rear Wall: This method aims to decouple the false wall and speakers from the adjoining room wall. The shelf studwork is fixed to the baffle wall but not directly to the rear wall. Vertical studs at the rear of the support shelf should be secured to the floor, ceiling, and side walls. Additional plasterboard sheets on the inside face of the adjoining wall can reduce sound transmission. Filling the cavity between the false wall and the adjoining room wall with dense bulk-fill insulation is strongly recommended to prevent vibrational energy storage and standing wave buildup.

Image Description: A series of diagrams illustrating screen wall construction. Figure 5 shows the cavity frame. Figure 6 shows the screen wall frame fixed to the floor, ceiling, and walls. Figure 7 shows noggins being fixed between frames and insulation being added. Figure 8 shows the finished wall with plasterboard and a timber cavity floor, including a detail of the cable hole. Figure 9 shows details of corner beads and J-beads. Figure 10 shows the initial setup for the isolated wall construction. Figure 11 shows the screen wall frame for the isolated method. Figure 12 shows noggins and insulation. Figure 13 shows the finished wall with a timber cavity floor. Figure 14 shows details of corner beads and J-beads for the isolated method.

General Construction Notes:

• Ensure fixings are properly anchored and plasterboard is well adhered to studwork to prevent unwanted resonance.
• For the 'Fixed Directly to Rear Wall' method:
1. Fix the cavity frame to the rear wall.
2. Erect a frame for the screen wall and fix it to the floor, ceiling, and adjoining walls.
3. Fix noggins between frames for plasterboard or timber board. Insulate the void around the speaker cavity with bulk insulation for sound absorption.
4. Finish the wall with plasterboard or timber board panels and a timber board cavity floor (minimum 16mm thickness). Place the speaker cabling hole at the front corner of the cavity floor.
• For the 'Isolated from Rear Wall' method:
1. Erect a false wall frame adjacent to the rear wall, fixing it to the floor and ceiling.
2. Erect a frame for the screen wall and fix it to the floor, ceiling, and adjoining walls.
3. Fix noggins between frames for plasterboard or timber board. Insulate the void around the speaker cavity with bulk insulation.
4. Finish the wall with plasterboard or timber board panels and a timber board cavity floor (minimum 16mm thickness). Place the speaker cabling hole at the front corner of the cavity floor.

Subwoofer Setup and Configuration

All Series MX systems feature a dual subwoofer configuration, with subwoofers oriented asymmetrically (up and down) to balance in-room low-frequency response. Subwoofers can be wired in the following ways:

• INDIVIDUAL CHANNEL (Stereo Power Amplifier, 8 Ohm load): Each channel of a stereo power amplifier is connected to each subwoofer separately.
• BRIDGED, PARALLEL (Stereo Power Amplifier, 4 Ohm load): Both subwoofers are wired in parallel across a single pair of output terminals using the amplifier's bridged mono configuration. Check amplifier manual for bridge mode support.
• PARALLEL (Mono Power Amplifier, 4 Ohm load): Both subwoofers are wired in parallel across a single pair of output terminals using a single amplifier channel.

Image Description: Figure 15 illustrates three wiring configurations for the subwoofers: Individual Channel, Bridged Parallel, and Parallel. Each diagram shows the connection from the power amplifier outputs to the subwoofer terminals.

Note: Wiring subwoofers in parallel halves the load impedance to 4 Ohms, requiring double the amplifier output current. Ensure the amplifier specifications support this loading, especially in bridged mono mode.

It is strongly recommended to run separate cabling for all channels in the MX modular loudspeaker system back to the central amplifier rack for future wiring flexibility.

Wiring

The Series MX systems are installer-friendly, with convenient terminal placement for easy wiring installation. MX40 Left, centre, and right main speakers require active crossovers and two amplifiers per channel, necessitating 2 x 2 core or 1 x 4 core cable per module. MX20 and MX30 main speakers require a single length of 2-core speaker cable per speaker.

Processors, amplifiers, and other components may be mounted remotely. High-quality, flexible, multi-stranded copper cables of suitable gauge are recommended for optimal performance. For cable runs up to 24m, a minimum 14AWG gauge cable is advised. Thicker cables have lower AWG numbers. For longer runs, use heavier gauge cables. Consult a Krix authorized dealer or system designer if unsure about cable gauge.

MAXIMUM WIRE LENGTHS

Equalisation

Krix constant directivity horns and waveguides in the Series MX systems deliver more direct sound to the listener with less room reflection. The baffle wall design ensures the frequency response is unhindered by acoustic diffraction effects and front wall reflections common in conventional home theatre setups, making the MX systems less susceptible to room acoustics.

Before equalizing, ensure the room's acoustics are adequately addressed. Equalization can only partially compensate for poor room acoustics.

Speaker Size

While the MX-20, MX-30, and MX-40 main speakers are physically large, setting them to 'small' allows lower bass frequencies to be directed to the subwoofers, which are better equipped for low-frequency reproduction.

• MX-20 Main: Recommended 'small' with 60Hz crossover.
• MX-30 Main: Recommended 'small' with 40Hz crossover.
• MX-40 Main: Recommended 'small' with 40Hz crossover.

Speaker Distances and dB Levels

Automated speaker configuration systems excel at setting speaker distances (delays) and dB levels. Verify these settings manually. Increasing the center channel level by 1-3dB can improve dialogue intelligibility. Subwoofer levels often require manual adjustment to listener preference, with boosts or cuts up to 9dB being common.

Subwoofer Power Amp Configuration

• Limiter: Using a power amplifier's soft limiter function on MX subwoofers is strongly recommended. This protects the driver from clipping damage and reduces distortion when the amplifier is overdriven.
• High Pass Filter: A high-pass filter is advisable for MX subwoofers. Filtering out subsonic frequencies improves overall system power handling. Recommended settings: MX20 Sub - 25Hz, MX30 Sub - 20Hz, MX40 Sub - 20Hz, all at 24dB/Octave (Butterworth).

Dynamic Compression / Night Listening

The MX systems reproduce the full dynamic range of movies. Disable dynamic compression or night listening mode settings in AV receivers/processors and Blu-ray players to experience the soundtrack as intended by the director.

Dynamic Equalisation / Loudness Controls

'Loudness' settings adjust equalization by boosting bass and treble due to the human ear's reduced sensitivity at these frequencies at low listening levels. Disable this setting for faithful source material reproduction unless listening at very low volumes.

Room Equalisation

The native response of the MX system is consistent across the frequency range, but room equalization can fine-tune the system's response to the environment. Room equalization involves understanding room acoustics. Consider room characteristics and system equalization separately.

Room Size and 'Liveness' / Reverberation Time: Rooms with many absorbing surfaces (highly treated) are effective at higher frequencies and may benefit from a treble lift to avoid sounding dull. Larger, moderately treated rooms might sound too bright, potentially benefiting from a gentle treble roll-off. The MX systems have a slight treble roll-off, sounding most balanced in larger, moderately treated rooms. Smaller or highly treated rooms may require some treble lift, possibly to compensate for loss through perforated acoustic screens (woven screens are acoustically superior with minimal treble loss).

Standing-Wave Issues: Small to moderate rooms with standard ceilings are prone to standing waves below 500Hz, causing peaks and dips. Automated DSP solutions can help, but results vary. Close proximity of sidewalls and ceiling in small/medium rooms can skew bass and mid-bass response. Applying a cut in the 100-250Hz region can mitigate these issues.

Automated Room Correction and Speaker Equalisation: Many room equalization products aim for a flat frequency response, which can sound bright or harsh in home cinemas. Some automated algorithms excessively cut mid-bass, resulting in a thin sound lacking warmth. Evaluate automated room correction results carefully.

Manual Graphic Equalisation: Manual equalization allows for a gentler curve, preserving the 'cinema sound' of the MX system. The following are suggested equalization settings for manual tuning:

Suggested Equalisation Settings

Highly Treated Room Under 8m Deep

Lightly Treated Room Under 8m Deep

Lightly Treated Room Over 8m Deep

Highly Treated Room Over 8m Deep

MX40 Active Crossover Settings

The MX-40 LCR modules require an active crossover. Use the following settings:

*Gain values assume identical or gain-matched amplifiers for low and high frequency elements. Adjust gain offset if using amplifiers with different gains. Electrical or acoustic measurements may aid in determining the correct gain offset.