Browse Category: Appliance

Simplicity LTH lawn tractor

The first step was to identify a half-dozen changes that would put Simplicity ahead of its competition. When Simplicity Manufacturing, Inc., set out to design a better version of its 5200 Series lawn tractor, Simplicity’s strategy was simple: talk, listen, and cut.

“We started out with a seed project,” says John Brackin, vice president of engineering for the Port Washington, Wis.based company. “We spent much time talking with, and listening to, our dealers discuss ways they thought the tractor could be improved.”

During this time, Simplicity was also busy conducting mowing tests with competitors’ products.

After several months of investigating the strengths and weaknesses of its product and competitors’ products, Simplicity developed a “hit list” of changes it wanted to incorporate to achieve a new standard of quality.

* Height adjustment mechanism for selecting any cutting height from 1 in. to 3 1/2, in. to match cutting heights of walk behind mowers.

* Wider, deeper decks for better cutting and discharge.

* Mounting system that permits easy removal of the deck and changing of attachments without tools.

* Automatic transmission instead of mechanical clutching system in answer to changing demographics (more women and teenagers are using lawn tractors).

* Tighter turning radius to cut trimming time and eliminate the need for a walk-behind mower.

* Larger fuel tank (twice the size) positioned in rear of tractor to eliminate the spilling of gas on the hood.

* Ergonomic design to accomodate people ranging from the 5th percentile woman 5’2″, 100 lbs.) to the 95th percentile man 6’2″, 220 lbs.).

* Streamlined shape and form that make it stand out in dealer showrooms.

* Paint finish that shows well under fluorescent lights as well as natural light in dealer showrooms.

Team E – U – C – L – I – D

Everything about Simplicity’s redesign effort was given careful considerationeven the naming of the project.

“Something that will be burned in my mind forever was this product’s code name: EUCLID,” says Mic Schemelin, senior project engineer.

Schemelin says the name reflected what the project team set out to accomplish.

‘E’ was for easy-to-build; U’ for unique features; C’ for capital costs, because we wanted to control tooling costs; L’ for limits placed on product specification costs; I’ for in time for fall of 1989; and D’ for dealer input.”

At the onset of the project, June 1987, Schemelin says Simplicity engineers concentrated on analyzing the functions of component parts and assembly methods.

“We spent a considerable amount of time looking at manuals, taking the product apart, looking at how it was put together, determining parts that could be multifunctional, and deciding where fasteners could be eliminated.” Achieving the look

While Simplicity engineers investigated ways to design a better lawn tractor, Simplicity also involved Renquist/ Associates, a Racine, Wis.-based industrial design firm.

“We provided a framework with motor, tires and a steering wheel to Bruce Renquist,” says Schemelin. “This was used as a styling model.

“Then we had a series of meetings to discuss where Renquist/Associates was going with the look and how our engineers were going to achieve it.”

“This team involvement was marvelous,” says Bruce Renquist, president of the design firm. “It gave us the ability to generate superior product in a shorter time.

“Instead of a linear process in which specs are developed by marketing, then handed over to engineering to interpret, then turned over to manufacturing, we were getting that input throughout the process,” says Renquist.

“When we would make a design change, manufacturing was involved because they needed to evaluate the tooling implication.

“For example, when we were investigating whether or not to tool a new throttle lever, we went through the process of mocking up the old throttle and the new throttle. Ultimately, the decision was to tool up because of the apparent value of the new throttle design.”

Marketing was there offering its input, too, says Jim Myers, Simplicity’s vice president of international marketing and OEM sales.

“As our marketing arm, I would get together with the project team when it reached a checkpoint to help decide matters affecting styling and serviceability.

“When it came to deciding how to enclose the engine compartment, marketing’s concern was to make sure it was done in a way that a dealer wouldn’t spend a lot of time getting at it.”

This cooperative spirit is something Simplicity will strive to duplicate in future redesign efforts, says John Brackin, the firm’s vice president of engineering.

“The chemistry between members of the project team was so favorable, they were high on themselves as well as the product.

“As we launch other DFM efforts our chinning bar will keep moving up in terms of expectations.

Industry pulls together to kick the CFC habit

ARI launches Technology Institute. AHAM’s CFC Consortium is moving on two fronts.

If the amount of energy spent is any measure of success, then the appliance industry should have the CFC issue beat in no time. That may be somewhat simplistic. But, the fact is, the industry gets kudos for tackling the chlorofluorocarbon (CFC) crisis head-on.

Two industry groups, the Air-Conditioning and Refrigeration Institute (ARI) and Association of Home Appliance Manufacturers (AHAM), are rallying their members in an effort that perhaps hasn’t been duplicated since the energy crisis.

Through a task force, each group is pursuing CFC solutions.

In mid-November, ARI launched the not-for-profit Air-Conditioning Technology Institute (ACTI) “to manage and conduct scientific research in the public interest.” The quotes are those of Arnold Braswell, president, ARI.

In September, AHAM organized the Appliance Industry-Government CFC Replacement Consortium, Inc., as a wholly owned subsidiary.

“Through this united research effort, our industry will be able to accelerate the pace and maximize the efficiency of its search for workable CFC alternatives,” explains Tom Young, Consortium vice president for administration.

Here is an update on the CFC-replacement action by ARI and AHAM.

ARI seeks funds

ARI brought members up-to-date at its 37th annual meeting in mid-November in Boca Raton, Fla.

To manage a program of materials compatibility and lubricant research (MCLR) for alternative refrigerants, ARI is seeking funding by the Department of Energy. The program’s objective is to assist industry in phasing out controlled CFC refrigerants.

MCLR activities call for property and compatibility measurements for CFC substitutes. Refrigerant-lubricant mixture properties and their effect on materials and performance will be addressed.

MCLR also covers methods development to predict or accelerate measurement of key properties and compatibility concerns.

Existing and future MCLR data from industry and public-sector tests are being compiled in a refrigerant database. Progress in ARI’s MCLR efforts will be summarized at the July 1990 ASHRAE/Purdue CFC Conference.

Legislative review ARI updated members on legislation.

Congress has considered proposals to accelerate the CFC phaseout beyond the Montreal Protocol and to severely limit the future growth of HCFC-22 and other substitute refrigerants.

Meanwhile, a provision containing extensive CFC regulations and controlling the future growth of R-22 and other HCFCs was removed from the Senate Budget Reconciliation Bill. However, other attempts by Congress to control CFCs and HCFCs are likely.

ARI’s Arnold Braswell contends that legislation is not necessary and “the EPA agrees. With modifications to the Montreal Protocol, there is no need for domestic legislation.”

Although the regulatory provisions were removed from the Budget Reconciliation Bill, the bill contains an excise tax on CFCs covered by the Montreal Protocol. The tax will begin at $1.10 per lb. in 1990 and escalate to $3.10 per lb. in 1993.

State legislatures, too, are involved in CFC regulations and are expected to gear up their activity during 1990 sessions.

To avoid duplicate and different CFC recovery and recycling regulations in the 50 states, the Alliance for Responsible CFC Policy petitioned the EPA in September, requesting promulgation of regulations pertaining to the use, discharge and recycling of fully halogenated CFCs in air conditioners, refrigerators, freezers and other similar cooling devices.

The petition calls for preemption of state and local requirements. EPA indicated it would issue proposed regulations for review and comment by the end of 1989 or early this year.

AHAM Consortium in full throttle

AHAM’s CFC Consortium is pulling member companies together and pursuing its goals at a reasonably good pace, according to Tom Young, the vice president for administration.

The consortium’s major goal is to identify safe, reliable and energy-efficient replacement candidates in two years to three years, so that refrigerator manufacturers can stop using CFCs in production as soon as possible.

The research partnership, as the consortium is called, comprises seven companies: Admiral Appliance Co., Amana Refrigeration, Inc., GE Appliances, Sub-Zero Freezer Co., W.C. Wood Co., Ltd., Whirlpool Corp., and White Consolidated Industries. Other participants include DOE, EPA, as well as compresser, insulation and refrigerant suppliers.

Young describes the consortium’s program as “a highly disciplined and coordinated one designed to create as fast as possible a database adequate for each manufacturer to determine the best CFC substitutes for its products.”

Pinpointing alternatives

Through two technical committees–one for CFC 11 (insulation) and the other for CFC 12 (refrigerant)–work is progressing to narrow down alternatives. These will be evaluated in detail.

For CFC 11, the committee is developing the research protocol for:

  • Water mixtures with two isocyanates–MDI and TDI.
  • Optimization of water blends.
  • HCFC 123.
  • HCFC 123/14lb.
  • Flammability of HCFC 141lb.

Criteria to evaluate CFC 11 replacements include heat-transfer characteristics, density, demoulding time, dimensional stability regarding packing and bowing, flammability, toxicity, reliability and longevity.

For CFC 12, companies are conducting round-robin compressor calorimeter tests to establish a baseline.

In addition, companies are screening potential candidates in CFC 12 compressors and comparing results with the baseline. Each company is assigned a candidate to screen.

All of these calorimeter tests are conducted simultaneously by companies, and the results will be shared.

Criteria to evaluate CFC 12 replacements include thermodynamic and physical properties, material compatibility, oil solubility, flammability, toxicity, impact on energy efficiency, and reliability.

For the work of both technical committees, energy is the real hang-up. “As energy-efficiency requirements become increasingly stringent, our situation becomes more murky,” says Tom Young.

CFC Recovery Process

Whirlpool Corp., Benton Harbor, Mich., has developed a process to recover CFCs during refrigerator and freezer repair.

The process uses a specially designed seven-layer plastic bag that catches and holds refrigerants released during servicing. The old refrigerant is then taken to a recovery center, where it is transferred from the plastic bag to a pressurized tank and held for recycling.

Walter J. Coleman, vice president for consumer services, said the company believes it is the first major U.S. appliance maker to successfully develop a relatively simple process to capture used refrigerant at the time of refrigerator or freezer repair in the home.

“We see this process as a small but important step toward eventual elimination of all CFC use in appliance manufacture.” 1. Used CFC-12 refrigerant removed from a Whirlpool refrigerator or freezer during in-home sealed system repair is captured in a specially designed recovery bag. This bag is made of a multi-layer, puncture-resistant material that prevents the escape of CFCs. 2. The bag containing the used CFCs is taken to a CFC Recovery Center. 3. At the CFC Recovery Center, the used refrigerant is transferred to a storage container, where it is held for recycling.

Vending machine maker’s change to powder puts more change in pockets

Conversion from liquid to powder yields longer finish life and substantial time and material savings. Vending machines take a beating–not only from an occasional disgruntled customer, but also from the environments in which they’re placed. The finish quality on these machines is a key element in their longevity.

That’s why Rowe International, a Whippany, N.J.-based vending machine manufacturer, switched from liquid paint to powder in its coating process.

Another reason was New Jersey’s demand that Rowe comply with the state’s strict emission standards. The liquid paints it was using didn’t cut the mustard in this regard, either.

In addition to helping Rowe meet these stringent quality and environmental standards, powder proved to be effective in coating the many odd component sizes and shapes designed into a vending machine. One machine can have as many as 350 coatable components.

All these factors came together to give Rowe some substantial time and money savings.

Finish quality

Rowe puts its products through periodic salt-spray tests to gauge finish quality. According to Ed Brookman, manager of industrial engineering, Rowe found that components with a high-solid paint finish lasted through 160 hours of salt-spray exposure. The powder-coated components Rowe tested withstood 800 hours.

In addition to needing protection from external elements, vending machines must also be protected from themselves. The extremes in heat and cold these machines generate to meet the needs of the products they dispense threaten the finish of internal and external components.

“If you have a refrigerated machine, humidity builds up on the inside,” Brookman explains. “We found epoxy-based powders to be more durable than liquids under these conditions.”

Team work

In late 1988, as part of its new JIT-based manufacturing-system redesign, Rowe replaced liquid with powder. The new system was designed and supplied by the Nordson Corp., Coatings Division, Amherst, Ohio.

In addition to its environmental concerns, one of Rowe’s key requirements was total product coverage.

The deep dimensions of Rowe’s cabinets, their numerous weldments and the hundreds of discrete components that go into them presented many challenges, both to Nordson and to the powder suppliers, Morton Powder Coatings, Reading, Pa., and H.B. Fuller, Wilmington, Mass.

Morton formulated coatings for the cabinets and doors, while Fuller’s coatings are used for internal components.

The vendor team was charged with developing a coating system that would give Rowe’s machines a durable, textured exterior finish, and provide adequate coverage for interior components.

“Rowe’s old dipping system gave them virtually 100 percent part-encapsulation,” explains Bill Morris, Nordson’s area manager on the project. “Powder had to have the same capability.”

One thing stood in the way: The Faraday Effect.

“We had to develop a textured material to overcome this phenomenon,” explains Walter Lindner, Morton’s Eastern regional sales manager. “Rowe’s products have a number of welded shelves and recessed units on the interiors. We had to develop a coating that could coat those surfaces on a largely automatic basis. We also built in the chemical resistance they needed for the coating to withstand the humidity that builds up inside Rowe’s cabinets.”

In electrostatic powder coating, particles are given a like charge. The problem occurs in corners. Just as positively charged metal particles repel each other, these like-charged powder particles create a force field that inhibits uniform coating.

As the coating supplier with responsibility for covering Rowe’s many interior components, Fuller found the Faraday Effect was particularly challenging.

“Rowe has so many different machines that a huge variety of parts come down that production line,” explains Jim Long, Fuller’s eastern regional sales manager. “The coating material we supply has to have enough latitude that it will charge in the Tribomatic booth to coat all of them.”

Nordson, Morton and Fuller worked together in fine-tuning the powder-coating system so that the coating hardware and materials would accommodate each other’s performance requirements.

“The challenge comes because every customer’s parts are different,” says Long. “So the close working relationship between the customer, the equipment vendor and the powder suppliers is necessary not only to design a system with the right number of guns, but to position and move those guns properly within the booth.”

The coating system consists of:

  • Nordson “Tribomatic” spray booth for applying smooth powder to internal components.
  • Manual spray booth for applying off-colors.
  • Texture booth for applying textured powders to cabinets and doors.
  • Overhead, nonsynchronous power-and-free conveyor system from Unibilt Division of Jervis B. Webb., Farmington Hills, Mich.

Why power-and-free?

According to Brent Brosch, national sales manager for Unibilt, power-and-free was the only type of conveyor system that could accommodate Rowe’s limited square footage.

“We packed a great deal of conveyor into their building,” says Brosch. “The finishing area in particular was very small and congested.

“If they had stayed with their original in-line liquid process,” Brosch concludes, “I don’t think they could have continued in the same facility much longer.”

System flow

After surface preparation and oven drying, parts are ready to be coated. The power-and-free conveyor system transports parts between cleaning, painting and curing stations.

Coded carriers pass through readers which automatically identify the part and direct it to the proper spray booth. Carriers can be segregated without segregating colors, saving color change time.

The three paint booths are run by a single-shift crew of five, plus a lead man. The liquid system required the same number of people, but on a shift-and-a-half (14 hour) basis.

The Tribomatic booth is used for coating the discrete components. This is where the Tribo-charging technique combats the Faraday Effect.

The texture booth coats cabinets and doors. Here, high voltage power charges the particles for adequate adhesion.

Clean and economical

The people running the booths are happier with the new system, says Rowe’s Ed Brookman, because they are no longer coated with overspray at the end of the day.

Not only are the people cleaner, adds Brookman, but the equipment is easier to clean and maintain as well.

“High-solid paints are abrasive and cause a lot of wear and tear on equipment,” Brookman says. “Although powders are also abrasive, they are easier to clean off equipment, so we save maintenance, equipment and labor costs.”

Brookman adds that powder yields substantial material savings.

“Powder gives you 95 percent utilization,” he continues. “You get a 60 percent transfer efficiency, but you can collect almost the entire 40 percent overspray. We expect to see a material savings in the neighborhood of $50,000 a year.”

Rowe also saves on waste disposal. Brookman points out that the dearth of landfills on the East Coast translated into “ferociously high” waste transportation and disposal costs.

Nordson’s Bill Morris hopes the success of powder coatings on Rowe’s complex product line convinces skeptics of powder’s competitiveness with liquid for such challenging applications.

Concludes Morris: “This system proves that intricately designed parts can be powder-coated successfully in an automated system.”

Steelmakers step up services

Cost modeling, tear-downs, technical data, and computerized programs aid the OEM in materials selection.

  • At InlandSteel , Chicago, a computerized “metals vs. alternative” materials program simulates the total cost of a design.
  • At U.S. Steel, a division of USX Corp., Pittsburgh, customer technical service people participate in the tearing down ofappliances to determine how materials utilization can be improved.
  • At LTV Steel Co., Cleveland, engineers in the customer technical service center work “elbow to elbow” with appliance customers to measure properties such as formability and paint adhesion.
  • At Bethlehem Steel Corp., Bethlehem, Pa., a computerized program makes it possible to provide wider, heavier coils that require less set-up time.

These are some of the ways steel companies are strengthening their role in the appliance industry.

Understanding trade-offs

“It’s important for us to help our customers understand which material is most cost-effective,” says Tim Treacy, account manager, appliance materials division, Inland Steel Co.

“We are not going to mislead our customers and point them to steel if their performance criteria say otherwise.”

Inland’s newly introduced computer cost-modeling service aids Treacy and Bob Hudson, also an appliance materials account manager, in providing customers with the information necessary for making sound materials-selection decisions.

“Variables such as tooling, capital investment and depreciation are all taken into account,” says Hudson.

The cost-modeling tool is just one aspect of Inland’s commitment to the appliance industry, says Treacy.

“There are companies out there that truly don’t understand the depth of our capabilities,” he says.

Inland, therefore, is striving to initiate a continuous dialogue with its appliance customers. This effort is being facilitated through a recent reorganization.

“We have research staff, manufacturing engineers, technical service people and quality control staff assigned solely to the appliance market,” says Treacy.

The reorganization, he says, has resulted in helping customers achieve overall improved quality, product and cost performance.

Answering needs

LTV encourages appliance customers to take advantage of its newly opened customer technical service center.

“We have a customer technical staff dedicated to responding to appliance customer needs and problems, and to developing products that will answer their needs,” says James Sprong, director, market development division.

Sometimes it’s a matter of working together on testing methods.

“Some of our customers will send manufacturing engineers in here to work `elbow-to-elbow’ with our engineers and technicians on testing specific properties,”

These capabilities have spurred interest in prepainted steel among OEMs in the home-laundry segment, says Sprong.

“Until a couple of months ago the attitude of the OEMs was `When you drive by, toot and say hello, but don’t bother us with your prepaint program.

“Now the OEMs are very interested in prepaint. We’re taking them through a lot of testing to prove that the product is acceptable in terms of standing up to bleaches and detergents.” Sprong says LTV also offers customers seminars in specific problem areas.

“One of our customers expressed concern about its welding operation. It didn’t realize we had such a large staff of welding engineers.”

Sprong says if a customer has the need, LTV will conduct an in-plant seminar on a topic such as welding.

“We’re able to go into the customer’s plant and discuss the vagaries of steel and why their welding sometimes doesn’t come out the way they would like.”

Upside of teardowns

“We’re working closer with appliance customers at a grass-roots level to reduce cost of manufacturing,” says Kevin McCarthy, industry manager, appliances, U.S. Steel.

One method for accomplishing cost reductions is to participate in the teardown of an appliance, he says.

“We will watch a customer take apart a range, for example. The customer defines for us the function of each piece and its specs.

“This practice allows us to recommend areas in which we can reduce the gauge, eliminate parts or go to a lighter coating weight.”

Win-win coils

Bethlehem Steel has introduced a computer program designed to “produce the heaviest and widest coil possible, depending on the customer’s slitting requirements,” says Otto Ehrsam, market development engineer -industry marketing.

“This is a win-win situation. It provides the customer with master coils that require less set-up time. And because we’re able to produce wider, heavier coils, our efficiency is increased.”

Ehrsam says the program takes into account the customer’s slit widths for any given thickness and grade.

“The data are put through the program. Based on the maximum weight the customer can handle and how much edge trim is needed, the size of the coil is determined.”

Ehrsam says the program is a good planning tool for purchasing.

HVAC molded in plastics

Carrier and GE Plastics in joint effort develop components. GE Living Environments house is the showcase. In a three-phase developmental program, Carrier Corp., Syracuse, has joined GE Plastics, Pittsfield, Mass., to determine the extent to which plastics can be used in HVAC applications.

GE’s 3,000-sq.-ft. Living Environments concept house in Pittsfield is the testing ground for the program. (See “Is an All-Plastic House in Your Future?” in December’s Managers Update.)

“Carrier is working with GE Plastics on this project to develop low-cost heating and air-conditioning components that are high in quality and reliability,” says Ian Shapiro, Carrier senior engineer.

Carrier supplied and helped install state-of-the-art equipment in the house.

Phase I of the program embraces applications that are in production or will be within the year.

Applications and material used are:

  • Air-conditioner control boxes–LEXAN [R] resin.
  • Thermostats and controls–CYCOLAC [R] resin.
  • Draft inducers, drain pans and furnace-header boxes–VALOX [R] resin.
  • Flue pipe–ULTEM [R] resin.

Design for Manufacturing

Phase II projects are still in development, with commercialization anywhere from one year to four years away.

The Phase II gas furnace uses engineering thermoplastics for styling, performance, and design-for-manufacturability advantages.

The added efficiency that tomorrow’s furnaces will require is enhanced by the use of corrosion-resistant insulative materials, according to Kevin Quinn, HVAC programs specialist for GE Plastics.

The furnace’s enclosure is of highly styled, impact-resistant structural and insulative panels of LEXAN and XENOY [R] resins. The panels provide thermal and acoustical insulation along with the durability that engineering plastics offer.

Several new applications for the working (internal) components are also under development.

Five comfort appliances

Phase III projects are conceptual applications in the early research and developmental stage. These projects aren’t targeted for commercialization for four or more years.

The heart of Living Environments is the Total Environmental Control (TEC) system. Five home-comfort appliances combine in this residential heating and cooling unit that uses thermoplastics for light weight, easy installation and service, aesthetics, corrosion resistance, durability, and component integration.

The TEC system performs heating, air conditioning, humidifying, water heating, and air filtering, with add-on capabilities for extra functions such as wasteheat recovery and ventilating.

Modularity allows user flexibility and enhances serviceability, explains Quinn.

A basic heat and hot-water system easily accommodates slide-in components. A malfunctioning component is easily diagnosed with a hand-held monitor and can be replaced immediately without shutting down the entire system. Piping and wiring are easily accessed by pop-off panels.

Snap fits and automatic electric power and control connections ease installation.

  • The TEC system includes:
  • Blow-molded panels made of LEXAN and XENOY resins with foam fill for thermal and sound insulation.
  • Primary blower wheel and housing of NORYL [R] resin.
  • Plate fin heat-exchanger components of either NORYL, ULTEM, or SUPEC [TM] resins, depending on the heat resistance required.

High-strength AZDEL [TM] technopolymer structures are under consideration for structural bases and heat shields.

TEC will operate on different power sources, providing versatility for the different systems it comprises.

GE Plastics and Carrier are designing plastics for HVAC to meet UL 746C guidelines and American National Standard Institute’s proposed Standard Z21.

Loudspeaker loses weight due to polystyrene

Molded-in capability of material enhances acoustics and improves design.

Plastic speakers? Precisely.

JBL, Inc., Northridge, Calif., has developed two professional-quality loudspeakers that offer the acoustic quality and ruggedness of high-density particleboard.

The difference is the enclosure is made of a weather-resistant structural foam polystyrene resin from Mobil Chemical Co., Edison, N.J.

Molded by Xytec, Inc., Tacoma, Wash., the new cabinets are found on JBL’s Control 10 stereo loudspeaker and Control 12 professional stage monitor/loudspeaker. Each weighs 17 lbs.–40 percent less than a conventional particleboard-based cabinet.

The design flexibility of plastic also allowed designers to mold-in specific acoustic features to enhance sound and improve design.

“Structural foam polystyrene reduces cabinet weight significantly while retaining the necessary wall stiffness and load-bearing strength,” says Dan Siefert, senior systems engineer. “We also gain by using a waterproof material that enables the cabinet to withstand the temperature and humidity extremes encountered in indoor and outdoor concerts.”

Another plus is cabinet service life, especially when speakers go “on the road.”

“Particleboard cabinets used in professional concert loudspeakers look old very fast after they go on tour,” says Chuck Willard, director, product planning. “Precolored plastic, coated with a durable, black polyurethane finish, helps hide the dents and scratches without revealing the underlying material. And the high melt viscosity of the resin results in a very smooth, high-quality surface.”

Polystyrene vs. engineering materials

After the initial decision for plastic construction was approved, JBL audio engineers conducted an extensive cost/benefit analysis on a number of materials.

“While ABS and polycarbonate have higher strength ratings, we determined they would have cost 30 percent more without offering any needed properties,” says Willard.

“It wasn’t a contest to build the strongest possible cabinet. For the cabinet to work economically, as well as acoustically, we wanted it to have the best cost/performance profile. We soon realized polystyrene would meet our needs without the expense of engineering materials.”

Wall thicknesses in the trapezoid-shaped cabinet vary from 0.125 in. to 0.025 in. Cabinet dimensions are 24 in. x 17 in. x 12 in.

About 20 ribs, ranging in width from 0.75 in. to 2 in., stiffen the cabinet to limit resonances from sustained low-frequency sounds. Further stiffening is accomplished with a hollow PVC tube as a transverse brace and a lateral brace of hard wood.

A proprietary sodium borosilicate-based coating, Aquaplas [TM], is also applied after molding to dampen high-frequency resonance.

The front panel and enclosure for the L-Pad volume controls are the only parts of the cabinet that require added heat resistance to withstand temperatures of 275 [degrees] F or more. These components are molded from polycarbonate.

Supports molded in the rear of the cabinet accommodate hardware for wall-mounting, and are conservatively rated to handle the 44-lb. weight of the system with a 4:1 safety factor.

Future system enhancements include plans for a rear-mounted integrated amplifier to make the speakers self-powered for simplified use during concerts.

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