ACOUSTIC ENGINEERS SCS70 Pro High-Performance Active Subwoofer User Manual

ACOUSTIC ENGINEERS SCS70 Pro High-Performance Active Subwoofer

Introduction

Welcome. In selecting ATC you have chosen an example of the finest audio engineering available. ATC was founded on a principle of engineering excellence, and that principle still defines our products today. Given the right opportunities, ATC products will deliver exceptional audio performance, but the opportunities will only arise from careful and thoughtful installation and use. Please read the following manual fully. It will help you understand the product and to realize its full potential. We are happy to answer questions and offer advice on any issues that arise through the installation or use of ATC products. Contact details can be found at the back of this manual. ATC was founded in London in 1974 by Australian emigre Billy Woodman, who still heads the company today. An enthusiastic pianist and engineer he was naturally drawn to loudspeaker design and after a period working at Goodmans, where many of the names that went on to found British loudspeaker companies began their careers, he struck out on his own. The premise on which ATC began is a simple one, and one that in many respects is still true today: hi-fi loudspeakers tend to be detailed and accurate but of limited dynamic range, while professional monitor speakers tend to express the opposite character.

ATC products were designed from the outset to offer the best of both. It’s an easy concept to describe, but surprisingly difficult to engineer. The difficulty inherent in designing such loudspeakers is one of scale. Hi-fi levels of accuracy and detail call for lightweight moving parts and delicate engineering. Professional monitor levels of performance however demand far more robust components engineered to survive the rigors of high-level use for extended periods. The only way to combine the two is through precision engineering of a class and scale more often associated with aerospace or motorsport. But the results are worth the effort and the cost. ATC loudspeakers, with their unique in-house designed drivers, combine the best of hi-fi and professionalism to devastating effect. ATC has become synonymous with active systems. Choosing to offer active loudspeakers (where the passive crossover network is replaced by active filters and multiple power amplifiers) is simply a result of the uncompromising attitude to loudspeaker design. While passive systems still have their place, and ATC engineering skills can still bring remarkable results from them, “active” is a fundamentally better solution to the problems posed by accurate, high-level music reproduction. The ATC instinct is always for a better solution. Not cheaper, not quicker, but better. It was the development of active loudspeakers that first brought ATC into electronics design and engineering. Active speakers demand multiple power amplifiers so ATC from the mid-1980s became not just a loudspeaker manufacturing company but an electronics manufacturer too. The further step from electronics for active speakers to a range of stand-alone amplifier products was natural and now means that ATC engineering is available from the recording desk or CD player output to the ears. From modest beginnings, ATC has grown to become one of the very few manufacturers successful across both domestic and professional audio. By selecting ATC you join a group of music lovers, professional audio engineers, studios and musicians across the World that understand and value the engineering that goes into an ATC product – and the sound that comes out.

Product Description

• The ATC SCS70 Pro is a high-performance 12”/300mm active subwoofer, designed from the ground up to deliver the exceptional levels of performance required to partner ATC’s active monitors. Its performance and features make it ideally suited to use within stereo, multi-channel surround and immersive audio systems.
• The sub features a sealed-box (infinite baffle) design, chosen for its balance of sub-bass extension and driver control. The cabinet is heavy and inert to minimize cabinet coloration. For situations requiring flush mounted/in-wall subwoofers, an in-wall variant, the SCS70iW Pro is available which features a shallower cabinet and a 7U/19” rack mounted remote amplifier. The subwoofer cabinet features a panel mounted in its front face with two LEDs to indicate ‘on’/’limit’ and ‘mute’.
• The SS75-314SC driver employed in the SCS70 Pro has been meticulously optimized to reproduce the lowest 3 octaves of the audio band within the design of the SCS70 subwoofer system. It employs a short-coil operating in an exceptionally long magnetic gap to deliver high sound pressure levels with very low levels of distortion.
• The SCS70s convection-cooled amplifier is mounted in the rear of the SCS70 Pro cabinet. Two balanced inputs enable connection to mono or stereo sources. A pair of buffered, un-filtered balanced outputs are provided for connection to partnering active monitor loudspeakers or to ‘daisy-chain’ multiple subs. 21dB range of gain control, three low pass frequency settings, a polarity switch and a 180-degree continuously variable phase setting allow the user to optimize the subwoofer for use with a very wide range of partnering loudspeakers. The low pass filter can also be set to ‘Off’ (320Hz) should the user wish to use the SCS70 Pro with external processing. The amplifier features fault monitoring of amp panel temperature and power amplifier D.C offset either fault condition is indicated via illumination of a single red LED mounted on the amp panel.
• When in use, the subwoofer output can be muted using a single latching footswitch connected via a ¼”/6.35mm jack. The mute function does not affect the outputs to the primary monitor loudspeakers, only the output from the sub itself. Additional subs cab be muted using the same single footswitch via connection to the mute ‘Thru’ jack.
• The in-wall SCS70iW Pro features a remote-mounted amplifier. This is housed within a 7U/19” rack mount chassis. The audio connection between the remote-mounted amp and subwoofer is via speaker cable terminated with Neutrik NL4 connectors. Connection to power & mute indication LEDs is via a 4-core control cable terminated with 5-pin male XLR connectors. Other features of the remote-mounted amp are identical to the amp mounted ‘on-board’.

Room Interaction

The room in which a loudspeaker is placed can be thought of as a filter, altering the acoustic response at the listening position from that of the loudspeaker. The position of the loudspeaker in a room will influence how it interacts with the space and therefore is often critical to achieving the best performance at the listening position. Positioning is particularly relevant to subwoofers because at low frequencies the room will have a strong influence due to room modes/resonances. Room modes manifest themselves in an uneven distribution of acoustic energy within the room, which can lead to either too much or too little bass at the listening position. A room with a well- controlled low-frequency response (reverb time) will have a far smaller influence on the performance of the subwoofer and will be less sensitive to subwoofer positioning. Typically, a combination of resonant membrane traps and porous absorbers are needed to control the low frequency. The resonant membrane traps are effective at treating the low bass, typically below 80Hz and the porous absorbers’ frequencies above this. Porous absorbers such as those made from foams, fiberglass or rock wool are not effective at absorbing low bass energy without a very large air space between them and the wall behind. For this reason, they are a poor choice of absorber for the subwoofer bandwidth. To minimize problems a free-standing subwoofer should be kept away from corners where possible. Avoid placing the subwoofer mid-way between any two parallel walls. Where the subwoofer is to be installed directly into a hard wall, as would be the case with the SCS70iW Pro, an increase in LF efficiency and LF extension should be expected. In-wall loudspeakers are in the optimum position for exiting room modes between the mounting wall and the opposite wall. The requirement for adequate bass trapping in the rear wall in this instance can be even more critical.

Subwoofer Placement

Start with the subwoofer positioned next to one of the stereo monitors and at the same distance from the listening position. When installing two subwoofers, start with one by each of the stereo monitors. In most cases these guidelines will give the best results, however, all rooms vary, and it is a good idea to experiment with both listening and speaker positions until a good compromise is reached. When working on optimizing the positioning, only change one variable at a time. Positioning the subwoofer in the center of the room, equidistant from the two side walls and between the left and right stereo pair must be avoided. In the majority of cases, this position will result in large irregularities in the frequency response. Multiple subs will excite the room from multiple locations and will often give a more even in-room response. Also, a pair of subs can be placed with the same physical relationship to the pair of main speakers and the listener. Please see section 5 for recommendations on how to set the amplifier filters and level. For professional installations, the requirements are often very specific. Please consult with an experienced professional acoustician if necessary.

SCS70iw Pro & RI-300 Remote Amplifier Installation

The SCS70iW Pro cabinet features a rear-mounted recessed input panel containing a NL4 High Level Audio Input Socket and a 5-pin XLR socket for connection to the front panel LED’s. The sockets are to be wired back to the R1-300 Rack Mount Amplifier using the cables supplied by ATC, but not included with the subwoofer. The SCS70iW Pro does not require ventilation behind the cabinet and can be installed directly into a wall. The front face of the baffle should sit flush with the face of the wall.

The R1-300 Rack Mount Amplifier is to be mounted in a 19” equipment rack. The heatsink must not be covered and should have adequate ventilation. The amplifier can also be mounted in the control room wall, close to the subwoofer if required. Always try to minimize the lengths of speaker cables between power amps and loudspeakers/subwoofers. Cable lengths under 5m are preferable and lengths over 10m should be avoided where possible.

Connection

Either two or three cable connections are required for each subwoofer: one for mains power and one or two for the audio signal. The mains cable is specifically supplied to comply with local statutory safety approvals and alternatives should not be substituted. If you intend to use your subwoofer in an alternative territory, please contact ATC for advice. The main connection must always be earthed.
The signal cable(s) and plug(s) should be of good quality and XLR terminated. Poor cable and plug quality will compromise the performance of your subwoofer. The signal input pin configuration is illustrated in Diagram 2. If two signal connections are made to the subwoofer (i.e. a stereo pair) the left and right signals will be summed by the amplifier, increasing the effective input level to the amplifier stage by 6dB.

Signal Cable Options

A balanced cable configuration is the preferred option, however, an unbalanced connection is possible. Diagrams 3 and 4 illustrate the signal cable connections required for each option. Balanced (XLR to XLR) connection offers lower noise and better immunity to “hum” pick-up. Unbalanced (XLR to Phono or Two Pole Jack) connection carries the risk of hum caused by multiple signal piles of earth. Hum problems resulting from unbalanced connection may be reduced by making one of the following modifications to the signal cable connections: If the driving preamplifier (or desk) is “double insulated” (i.e. has no mains earth), disconnect the signal cable screen at the RCA Phono plug end. Alternatively, disconnect the signal cable screen at the XLR end. This second option will make the source the reference signal earth.

The subwoofer amplifier control and connection panel, shown in Diagram 5, provides a range of functions to assist with system integration. These are explained below.

Power on/off

Powers the subwoofer on or off. When the button is in the inward position, the loudspeaker is powered on. When button is in the outward position, the subwoofer is powered off.

Level and Gain

Sets the overall sensitivity of the subwoofer. Initially, the Level control should be set towards the centre of its range and only adjusted once the Frequency has been set. If one input is connected, start with the Gain switch set at +6dB. If both inputs are connected, start with the Gain switch set at 0dB.
A +10dB setting is also included. This can be used when working with surround/immersive audio formats that require the LFE channel calibrated at a 10dB higher SPL than the LCR channels.
Please refer to Section 9 – Product Specifications for information on system sensitivity.

Polarity and Phase

Sets the overall polarity of the subwoofer and offers an adjustment of the input/output phase. When set to + and 0° the subwoofer will radiate a positive acoustic pressure for a positive electrical signal at the input. When set to – and 0° the subwoofer will radiate in the opposite polarity to the input. The Phase control allows for fine adjustment of the phase relationship between subwoofer and satellite speakers. This can be thought of as a delay, allowing for time alignment with other system elements and is useful when physical adjustment of loudspeaker/sub position is limited.

Frequency

Varies the low pass crossover frequency as indicated on the control panel. This is the fundamental parameter that defines the integration of the subwoofer with the satellites. The Frequency control should be set at, or slightly above the specified low-frequency cut-off of the satellite speakers.
The “open” setting applies a low pass filter at 320Hz. Select this setting if you will apply the sub low pass crossover filter via an external processor.
All filters are of the type 4th order Linkwitz Riley.

Outputs

Provides separately buffered and fully balanced outputs with a signal identical to that at the corresponding input terminals. The output is unfiltered and unaltered in any way, and therefore it is possible to drive a stereo pair of active loudspeakers from these terminals. Likewise, it is also possible to drive a second Studio Control Subwoofer from these outputs. This function allows for an unlimited number of Studio Control Subwoofers to be “Daisy Chained” together, one driving the next.

Footswitch – Input and Thru

Facilitates remote muting of the subwoofer with the addition of a standard latching footswitch (not supplied, see specification). The Mute light on the front of the subwoofer will illuminate blue when the Mute function is enabled. If the system includes more than one Studio Control Subwoofer, a second subwoofer can be controlled from the Thru output socket. This allows for all subwoofers in a system to be controlled simultaneously from one footswitch. The signal at the Output sockets is not affected.

Fault

Indicates a temporary or permanent amplifier fault. The Fault LED will illuminate if there is a DC fault on the amplifier or if the thermal limit of the heatsink is reached. In the rare case that the Fault LED illuminates, the subwoofer should be switched off. Ensure the subwoofer heatsink has adequate ventilation and after 45 minutes switch it back on. If the Fault LED remains illuminated the amplifier is registering a fault that should be investigated by an approved technician. Please contact your ATC dealer or distributor, details can be found at www.atc.audio. If the Fault LED is no longer illuminated, the amplifier shut down safely due to reaching high temperatures. Please reduce the system listening level, and subwoofer Level or improve amplifier ventilation and continue to use the subwoofer.

Front Panel Display

Indicates operational state. The Studio Control Subwoofer has two LED’s mounted in the front-facing badge (Diagram 6). The LED to the left is a Bi- Colour Green/Red LED. When Green the subwoofer is powered ON, when Red, the subwoofer amplifier is limited, please reduce the listening level. Persistent and/or continuous illumination of the Red LED can result in damage to the amplifier or driver. The LED to the right is not lit when the subwoofer is operational and will illuminate Blue when the subwoofer is Muted via an external footswitch, see Section 5.6

Typical System Configurations and Recommendations

It is likely that a subwoofer will be used in one of two different scenarios: either as Bass Reinforcement/Extension in a Stereo System or as a discrete channel in a Multichannel Surround/Immersive Audio system.

Bass Reinforcement/Bass Extension of a Stereo System

Typically, a full-range stereo signal is driven into both Left and Right subwoofer Inputs. The subwoofer Outputs connect to and drive the main monitors. Alternatively, the Studio Control Subwoofer and main monitors can be driven independently from a suitable monitor controller. Example systems are shown in Diagrams 7, 8 and 9. All subwoofers can be controlled using the method described in section 5. All panel settings should be set independently for each subwoofer. All ATC loudspeakers deliver significant low-frequency output, more so with the larger monitors in the range, therefore there will always be some degree of acoustic overlap between the subwoofer and stereo loudspeaker in this configuration. Applying a high pass filter to the main monitors will introduce phase shift in the main monitors and should be avoided where possible. Good results can be achieved through experimentation with the subwoofer Level, Frequency and Phase adjustment.

Diagram 7 – Typical Configuration – Stereo playback (Mono Sub). A monitor controller or preamplifier output is connected to the L and R Inputs of the subwoofer. The subwoofer L and R Outputs are connected to the Input of the L and R main monitors. In this configuration the Gain switch is normally set to 0dB.

Diagram 8 – Typical Configuration – Stereo playback (Stereo Subs). A monitor controller or preamplifier output is connected to a single Input on each subwoofer. The corresponding Output of each subwoofer is connected to the Input of the main monitor on that channel. In this configuration, the Gain switch is normally set to 0dB. Note that it is also possible to connect the monitor controller output to both Left and Right channel Inputs on the subwoofer using a Y-Splitter cable. If connected in this way the “spare” output can be used to connect further subwoofers.

Diagram 9 – 2.1 Configuration – The subwoofer is driven by a monitor controller with a dedicated subwoofer output. Additional subwoofers may be daisy chained where more than one is required.

The recommended initial settings are shown in Diagram 10.

The recommended number of subwoofers required in each system is shown in Diagram 11.

Multichannel Surround/Immersive Audio

A single subwoofer is driven from the 0.1/Lfe channel output of a multichannel processor/monitor controller. For increased dynamic range and headroom, multiple subwoofers can be connected in series as described in Section 5.5 and 5.6. All panel settings must be set independently for each subwoofer. The choice of loudspeaker model and the number of subwoofers required in any system is dependent on room size, mix format and target calibration level at the listening position. Diagram 12 can be used as a guide to determine suitable partnering system elements from the ATC Professional product range. Please refer to the format developer guidelines when specifying hardware for Immersive Audio and Surround systems.

Diagram 13 – Typical Multichannel System wiring. Depending on the Monitor Controller output level and number of subwoofers, the Gain switches may need to be set to 6dB. Further subwoofers can be added to the system using the same “Daisy Chain” method shown. The system shown is an example and other configurations are available. Recommended initial settings for the Studio Control Subwoofer when used in a multichannel system are shown in Diagram 14.

Listening

The ear and brain tend to interpret distorted sound as loudness and thus underestimate the actual level of undistorted sound. ATC subwoofers, like all ATC products, demonstrate very much lower levels of distortion than conventional systems of a similar size and it is, therefore, advisable to begin listening at an artificially low level and carefully increase the volume. It is also possible for the ATC systems to produce sufficient sound pressure levels for your ears themselves to become a source of distortion and make the sound appear harsh. Any audible distortion indicates that either the system or your ears are being overloaded and that the volume level should be reduced. When a subwoofer is successfully integrated into a system it should become impossible to discern from the main monitors. If the subwoofer is audible as a separate element, then it is likely the level is too high, the filter settings require adjustment or the positioning can be improved. Please refer to Section 5 of this manual.

Care and Maintenance

High-technology material finishes are used in this product. The surfaces are durable and with a little care can be kept as good as new even under conditions of heavy use. Normally, a dry duster will be all that is required to keep the finishes clean. Heavy soiling can be cleaned using a cloth slightly moistened with a non-abrasive household cleaner. There are no components within the speakers that can be considered expendable, or that would benefit from regular maintenance. There is no requirement for any kind of routine service work and there is no schedule for preventative maintenance. There are no user-replaceable parts within the speaker, and in the unfortunate event of any malfunction, repair should be referred to either the supplying dealer or consultant, the relevant importer, or ATC. ATC has every confidence in the quality of each product that it manufactures.

Acoustic specification

• Low-Frequency Cut-off: 22Hz (-6dB, half space, low pass filter set at 80Hz).
• Low Pass Filters: 50Hz, 65Hz, 80Hz, 320Hz. (-6dB, 4th order Linkwitz Riley).
• MaxSPL: 110dB continuous, 116dB peak (IEC Weighted Pink Noise, measured at 1m, half space, low pass filter set at 80Hz). Sensitivity: +4dBu ref 88dBC (single channel driven, Gain +6dB, Level
• 0dB, pink noise, low pass filter set at 80Hz).

Electronic specification

• Amplifier type: Grounded Source MOSFET based Class A-B, convection cooled.
• Output Power: 300W in to 8Ω.
• THD+N: <0.003%/-90dB, at 100Hz, 300W into 8Ω over 90kHz bandwidth.
• Input CMRR: 90dB at 200Hz.
• Input Impedance: Approx. 20kΩΩ(differential).
• Output Impedance: Approx. 100ΩΩ(differential).
• Frequency Response: <2Hz (-3dB) – 320Hz (-6dB, set by panel-controlled LP filter).
• Low Pass Filters: 4th Order Linkwitz Riley
• Gain Control: 0, +6dB, +10dB.
• Level Control: 0dB -11dB in 1dB steps. Total range 21dB with use of Gain switch.
• Phase Control: 0-180° ref. Input.
• Polarity Control: In-phase/Out-of-phase ref. Input.
• Limiter: ATC Active FET Momentary Gain Reduction, active limiter indicated on front panel.
• Sensitivity: 1.55Vrms for full power (single channel driven, Gain 0dB, Level 0dB).
• Power Consumption:
• Idle 8W / 14VA,
• 1/8th Power 170W / 230VA,
• Full Power 500W / 600VA.
• Mains Input: 220-230V, 115V – Factory set. Please observe panel markings and labels.

Physical specification

Warranty

All ATC products are guaranteed against any defect in materials or workmanship for a period of two years from the date of purchase. Within this period, we will supply replacement parts free of charge provided that the failure was not caused by misuse, accident or negligence. Purchasers who complete the Product Registration process, either by returning a completed Warranty Card to ATC or by registering the product at www.atc.audio, will have their warranty period extended up to a period of six years from the date of purchase. This guarantee does not limit statutory rights.

Contact

Loudspeaker Technology Ltd Gypsy Lane, Aston Down Stroud, Gloucestershire GL6 8HR

United Kingdom
Telephone +44 (0)1285 760561
Email: info@atc.audio
Website: www.atc.audio
Acoustic Transducer Company is the trading name and ATC is the registered trade mark of Loudspeaker Technology Ltd.

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