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The QSC AD-S28Tw is a surface-mount loudspeaker, specifically a bandpass subwoofer, designed to deliver excellent acoustic performance in an easy-to-install and aesthetically pleasing enclosure. This device is suitable for a variety of installation scenarios, including floor-standing, shelf-mounted, yoke-mounted, and suspended applications.
The AD-S28Tw features dual 8-inch (200 mm) low-frequency (LF) drivers housed within a ported bandpass enclosure. This design allows the subwoofer to produce deep, resonant bass frequencies. A key characteristic of its bandpass design is that all sonic energy exits the cabinet through the port, which must remain unobstructed to ensure optimal performance. The subwoofer is equipped with an audio transformer, making it compatible with both 70V and 100V distributed audio systems. For low impedance applications, a tap-selector switch allows the transformer to be bypassed, enabling 8-ohm operation. Additionally, the AD-S28Tw includes a bypassable 120Hz low-pass filter, offering flexibility in system integration and signal processing.
The AD-S28Tw offers versatile installation options. For floor or shelf standing applications, rubber feet can be attached to the bottom of the enclosure. These feet are secured by screwing them into designated M6 attachment points. It is crucial to only remove the four screws intended for the feet and avoid using tools, as excessive force can damage the rubber. Hand-tightening is sufficient to ensure a proper seal and secure fit.
For suspended installations, the subwoofer can be mounted using either the included yoke bracket or eyebolts and shear plates. The yoke bracket allows for attachment to a vertical surface (like a wall) or an overhead surface (like a ceiling or ceiling beams). The yoke attaches to two sides of the cabinet, and its slotted design provides flexibility for maximum rotation or minimum separation from the mounting surface. It is recommended to attach the yoke to the mounting surface first, then to the subwoofer. When attaching the subwoofer to the yoke, adhesive rubber pads should be placed between the cabinet and the yoke to prevent air leaks and ensure proper performance. The hex-head/Phillips-head M6 bolts should be tightened just enough to hold the subwoofer in place while allowing for alignment adjustments, then fully tightened to prevent rotation.
When suspending with eyebolts and shear plates, there are three possible orientations: port facing laterally in a "wide" orientation, port facing laterally in a "narrow" orientation, or port facing down. Specific attachment points are designated for each orientation. It is important to note that if an attachment point is not on a cabinet side facing up, a shear plate must be used instead of an eyebolt, as an eyebolt in such a position would be significantly derated due to shear forces. Similar to attaching the feet, only the screws for the eyebolts or shear plates should be removed to prevent air leaks. Eyebolts should be screwed in until the shoulder makes contact with the cabinet, then tightened further with a tool if necessary to achieve desired alignment, but without excessive force that could damage the wood. Shear plates should be aligned perpendicularly to the cabinet and tightened securely.
The QSC logo on the grille is rotatable, allowing for proper orientation regardless of the subwoofer's mounting position. If rotation is difficult, a small flat-head screwdriver can be gently used to assist, taking care not to scratch the grille.
Wiring the AD-S28Tw involves accessing the input terminal located on the rear of the subwoofer, covered by a hinged door. The terminal features four sets of screw terminals arranged in positive/negative pairs for parallel wiring: one pair for input and another for output to daisy-chain to other devices. The terminals accept wiring between 18 AWG and 12 AWG. Wires should be stripped approximately 3/4 inch (20 mm) and secured under the screw-down plate with a #2 Phillips-head screwdriver. The output terminals pass the exact signal presented at the input, whether it's low impedance full-range audio, high impedance 70V/100V signal, or low-passed audio from an external filter.
For distributed audio systems using 70V or 100V drive, the internal transformer must be engaged. This is achieved by rotating the tap selector switch to one of the transformer tap settings (200W, 100W, 50W, 25W for 70V; 200W, 100W, 50W for 100V). The tap setting determines the power draw from the amplifier and influences the subwoofer's output. It is recommended to select an amplifier with a channel power rating that is at least 20% greater than the sum of all connected tap settings to provide adequate headroom. To prevent transformer saturation with low-frequency energy, especially below the AD-S28Tw's functional range, engaging a -6 dB, 30 Hz high-pass filter is recommended.
The AD-S28Tw is constructed with marine-grade plywood and features a textured black paint finish that is paintable, allowing for customization to match the installation environment. The grille is made of zinc-plated steel with a black paint coating and black ABS end caps, providing durability and protection. The enclosure is rated IEC 60529 IP-x4 against dust and water incursion, making it suitable for environments where some moisture exposure might occur, though it is not recommended for outdoor installation without adequate cover.
Regular inspection of all hardware, suspension components, cabinets, transducers, brackets, and associated equipment is crucial before placing, installing, rigging, or suspending the subwoofer. Any missing, corroded, deformed, or non-load rated components should be immediately corrected, as they can significantly compromise the strength and safety of the installation. Only hardware rated for the specific loading conditions and potential short-term overloading should be used. Consulting a licensed, professional engineer is advised for any doubts or questions regarding physical equipment installation.
For cleaning, only a dry cloth should be used. All servicing should be referred to qualified personnel, especially if the apparatus has been damaged in any way. The product includes important safety symbols: a lightning flash symbol warns of uninsulated "dangerous" voltage, and an exclamation point symbol indicates important operating and maintenance instructions in the manual. Any unused attachment point can serve as a safety/seismic secondary attachment, provided an eyebolt is attached and connected to a load-rated structure with less than 12 inches (300 mm) of slack in the secondary attachment cable.
General| Type | Subwoofer |
|---|---|
| Nominal Impedance | 8 ohms |
| Enclosure Material | Painted Birch Plywood |
| Driver Size | 8 inch |
| Grille | Powder-coated steel |
| LF Transducer | 2 x 8" |
| Frequency Response (-6 dB) | 45 Hz - 150 Hz |
| Frequency Response | 45 Hz - 150 Hz |
| Operating Temperature Range | -20°C to 50°C |
| Net Weight | 21 kg |
| Weight | 21 kg |
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