NCP-10
Retrofit Noise Control Package for the
ASR-9 Radar Site

• High Efficiency - Achieved by a 2 Stage Acoustic System
• Easy to Position - Roll Around Cabinets With Handles For Easy Maintenance
• 100% Open From The Inlet Of The Baffle To The Inlet Of The ASR-9 Resulting In A No Head Loss Flow Constriction
• Easy Inspection Of Air Filters Through Side Viewing Holes
• Compatible Fit - Looks Like Original Equipment Sized For Aisle Clearance
• Incorporation Of ASC's Patented Bass Traps For Low Frequency Absorption

NCP-10
NOISE CONTROL FOR ASR-9 RADAR SITES

The noise control package, NCP -10, has been developed for the Northrup Grumman ASR-9 radar system. The Beta test sight was LAX, where two systems remain installed and operational. The NCP-10 meets all expectations in terms of free air flow, sound attenuation, compatible appearance and ease of handling. Since then 75% of all ASR-9 equipped airports have the NCP-10 Noise Baffles.

Each baffle is engineered to fit within the physical constraints for clearance and safety yet provide the appropriate sound attenuation for the opening engaged while maintaining a 100% open air passage through the trap. No single acoustic baffle pattern is used, each sound trap is designed for its specific application. All traps that fit similar openings are identical and interchangeable. There are four types of traps, each so different from the other that there can be no confusion as to which goes where.

The NCP - 10 is a 10 piece noise control package. Each unit is designed and built to engage one or more of the ventilation openings of the ASR-9 Transmitter/Receiver Sets.

The NCP-10 package consists of 10 units:

NCP-10-A 2 Transmitter air inlet roll around cabinets

NCP-10-B 2 Receiver air inlet roll around cabinets

NCP-10-C 2 Transmitter air exhaust baffle boxes

NCP-10-D 4 Receiver air exhaust baffle boxes

There are 4 large roll around baffles that weigh about 190 lbs each and handle the noisiest inlet air. On top of the Northrup Grumman radar cabinets there are 6 smaller units to quiet the less noisy airports. All units have a continuous 100% open area and are intended to be easily and quickly removed or replaced. They are beige in color, similar to the color of the Northrup Grumman radar cabinet.

The roll around cabinets can only fit up to the air inlets one way but the baffle boxes that are set on top of the cabinets can be installed forwards or backwards without impact, as they are symmetrical. A design goal was to facilitate accurate damage-free, fit or no-fit positioning of the sound traps by any personnel who may be unfamiliar with them.

The target sound level reduction with all sound traps in position was to achieve 70-71 dB,A in the open area of the transmitter site. This is a full 10 dB,A reduction from the untreated 82 dB,A sound levels. The current improved version of NCP-10 achieves and surpasses this goal by incorporating Acoustic Sciences Corporation's patented bass traps in the inlet baffles. This enables the absorption of lower frequencies thus increasing the efficiency of the Noise Baffle.

PHYSICAL DESCRIPTION

Each Sound Baffle was designed for its location, clearance fit and required attenuation. The inlet cabinets are similar in design but the exhaust baffles are different in shape, size and internal structure. All baffles do maintain 100% open area, 0% line of sight and no more than 90E turns in the air flow.

NCP-10-A The Transmitter Baffle is a roll around unit that has one air inlet and one air outlet. It uses a two stage acoustic system. Low frequency noise is damped out by our patented bass traps, used here for maximum volumetric efficiency. Two port holes are installed, one for a flashlight, the other for the line of sight to easily inspect the air filters. The air rush noise is attenuated by the section of parallel lined ducts.

Size: 13" x 40" x 60" Weight: 215 lbs

NCP-10-B The Receiving Inlet Baffle is a roll around unit that has one air inlet on top and two outlets low to the floor. It is built like the NCP-10-A except that it has been reconfigured for two outlets. It is a smaller unit because less attenuation is needed and has air filter inspection parts.

Size: 13" x 40" x 48" Weight: 170 lbs

NCP-10-C The Transmitter Exhaust Baffle is shaped to accommodate the microwave beam tube that it sits along side of. The acoustic system uses a staggered baffle to provide appropriate attenuation in the allowed space and geometry. It rests on felt skids.

Size: 14" x 20" x 42" Weight: 45 lbs

NCP-10-D The Receiver Exhaust Baffle is the smallest and most simple sound trap. The sound baffle design consists of a single stage staggered baffle, adequate for the amount of noise emitted from the exhaust part it is paired to. It rests on felt skids.

Size: 14" x 10" x 6" Weight: 6 lbs

NCP-10
ACOUSTICAL DESIGN

Although each unit of the NCP-10 package is designed for the noise source to which it is mated, there are some similarities. The primary sound absorbing element used throughout this system is 2" thick acoustical fiberglass covered by a fine mesh geotextile screen. This combination creates a sound trap that is highly absorptive and mechanically durable. The original production models built between 1991-95 incorporated a metal mesh lined wavy duct pattern instead of the present straight duct.

Lined Duct - This technique is used for high sound attenuation of air rush noise, and 100% open air flow. The absorptive strips are 2" thick and separated by 2" of air space. It allows for minimal air pressure drop or head loss. This produces 3 dB/foot for all sound above 500 Hz.

Bass Traps - ASC's patented bass traps are located in side branch cavities to pull out the otherwise difficult to attenuate low frequency noise. Here, semi-cylindrical units are made out of sound absorptive fiberglass that enclose an air cavity. It is the size of the cavity that determines the low frequency efficiency. The traps used here still have high absorption for sound 55 Hz and above.

Blocked Duct - Air rush noise is also controlled by a sequence of staggered baffles that block the sound but allow air to flow. Here the sound simply meets head on with a series of sound absorbing walls. The air, however, flows around the objects. The line of sight is 100% blocked. Flow of air remains 100% open and the attenuation is about 2dB per stage.