what makes a quality loudspeaker

What Makes A Quality Loudspeaker?A thorough look at the parts that make up a loudspeaker in order to get a better understandingof why some are more expensive than others

November 29, 2011, by Pat Brown

The device commonly referred to as a “speaker” is morecorrectly referred to as a loudspeaker system. It is comprised ofsome transducers, a crossover network, an enclosure, and a fewadditional parts.

Loudspeaker system designers must be familiar with thecomplicated interactions of the components that form thesystem.

An assemblage of good parts does not guarantee a good system.(Note: For the remainder of this article I will refer to a loudspeaker system as simply a “loudspeaker.”)

If I had to pick one word to describe the loudspeaker design process it would be compromise. Everyfacet of a loudspeaker’s performance and ultimate cost is a result of trade-offs.

This is why it is very difficult to compare loudspeakers from different manufacturers. One may appearto be better by focusing on a single specification (such as its power rating), yet it may be inferior as asystem when the performance of the whole is considered.

Let’s look at the parts that make up a loudspeaker in order to get a better understanding of why someare more expensive than others.

The Lowdown on TransducersThe heart of a loudspeaker is its transducers. These are the devices that actually convert electricalenergy into acoustical energy. Most sound reinforcement transducers are pistons.

Today’s designs have changed little in operating principle from those produced by research done earlyin the last century. Technological advancements have produced better materials, lighter weight, andlower cost, but loudspeakers still basically produce sound by vibrating the air molecules around themthrough movement.

No single transducer can reproduce full-range sound at the levels required for auditorium use. For thisreason most loudspeakers are two-way or three-way designs, with dedicated transducers for thelow-frequency (LF), mid-frequency (MF), and/or high-frequency (HF) parts of the spectrum.

Three-way designs have more transducers, so they typically cost more than two-way designs.

All-Important Frame Design ComponentsOne factor that makes a big difference in the price of low-frequency transducers is the frame design.Stamped frame loudspeakers are lower cost due to their ease of fabrication and lower raw material cost.

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Cast frame loudspeakers have less of a tendency to flex as the cone moves in and out.

They also tend to have higher mass and weight than stamped-frame models, as well as higher cost.Since transducers waste much of the applied electrical power, performance improvements can berealized by improving heat dissipation.

The cone material must compromise mass, strength, and cost. While some esoteric materials have beendeveloped for loudspeaker cones, paper remains the most common material because it represents agood compromise between the required attributes. LF transducers range in cost from tens of dollars tohundreds of dollars.

The system designer’s motivation will determine which is used. If they are designing to meet a pricepoint, they will use a cheaper unit. If they are designing for the highest quality performance, a priciermodel may be selected.

The MF and HF components in sound reinforcement loudspeakers are usually horn-loaded designs.Horn loading produces high sound-pressure levels as well as control over the sound radiation pattern.Horns are constructed from a variety of materials, including wood, metal, fiberglass, and plastic.

ABS plastic horns are very popular due to their low cost, light weight, and ease of fabrication.Fiberglass horns are much stronger but they are also more difficult to fabricate, which increases theircost. Low-frequency horns are often made of wood since they can be very large.

The horn driver (a transducer) plays a major role in the performance of a loudspeaker system. Theyrange from relatively low-cost, piezo-electric devices to compression drivers. Cone-type loudspeakerscan also serve as horn drivers.

The compression driver is the optimal way to produce a lot of mid- and high-frequency sound. It ispreferred over lower cost piezo-electric drivers for its high efficiency and fidelity.

Transducer magnet structure is a major cost factor. Large magnets produce higher field density (whichgenerally equates to higher efficiency), accompanied by increased weight. This may necessitate a castframe for support. Rare earth elements, such as Neodymium, produce stronger magnetic fields thanconventional magnet types at a fraction of their weight. Neodymium is also the most expensivemagnetic material commonly in use.

Some loudspeaker companies manufacture their transducers. This gives them full control over thesupply chain and the ability to optimize a component’s performance for a given loudspeaker system.

Most loudspeaker manufacturers use Original Equipment Manufacturer (OEM) suppliers for theirtransducers. OEMs can be very efficient in the manufacturing process because it is all that they do.Most OEMs build a generic line of transducers that are sold to the public along with proprietary designsthat are built to a loudspeaker manufacturer’s specifications.

Crucial Crossover NetworkThough it is unheralded in its role, the crossover network is arguably the most difficult part of aloudspeaker to design. The crossover’s job is to band limit the signal to each transducer so that it onlydelivers frequency content that it can convert into sound. In principle, it is like the transmission of anautomobile.

A good transmission will allow the wheels to spin faster and faster (increasing frequency) as yousteadily increase the vehicle’s speed from zero to 60 mph. The gear changes should be smooth and freeof glitches. A good crossover design does the same thing. It provides a smooth transition between theLF, MF, and HF transducers.

Passive crossovers, on the other hand, are filter networks of passive electrical parts — resistors,capacitors, and inductors. Mass-produced generic prefabricated designs are available; but ultimately thecrossover network must be optimized for the specific transducers that it is driving. This is a task best


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left to a design engineer.

Some crossovers are mounted to printed circuit boards (PCB). These have a nice, clean look and areeasy to mass produce, thereby reducing cost. This can work well for low-power applications, but thecircuit boards can be damaged by heat if driven too hard.

They can also warp and crack from the stress caused by large inductors. This is why manymanufacturers still hard wire their crossovers. This must be done by hand, and the result isn’t verypretty. But, the end result is more robust (and more expensive) than the PCB crossover.

Some loudspeaker systems have no internal crossover network. They are driven by dedicated electricalprocessors that perform the necessary signal processing before the signal is applied to the poweramplifiers — an active loudspeaker system.

While this should reduce the cost of the loudspeaker system itself (less parts), loudspeakers of this typeultimately cost more to implement due to the required external processor and possibly extra amplifi erchannels. Active designs can yield higher fidelity and higher sound pressure level (SPL) than passiveloudspeakers.

Even so, a good passive design can provide excellent performance at a lower overall cost, plus it isusually easier to implement than an active loudspeaker system.

The CabinetThe cabinet and its construction are a major factor regarding the price of a loudspeaker. Cabinets mustbe strong and stiff. If the cabinet vibrates it becomes a transducer itself, which will interact with theother transducers and degrade the overall system performance. A stiff cabinet requires a lot of mass, alot of bracing, or both. The trade-off is the weight of the box.

Concrete is an excellent cabinet material, but is impractical for all but custom subwoofer systems.Medium density fiberboard (MDF) is also a good material. It is very dense and low cast, but it is alsovery heavy and is subject to warping if it gets wet.

Particle board cabinets are cheap, but should be avoided. Plywood is lighter and stronger than MDF, butit can have voids between the layers. Baltic birch plywood is best (11+ layers and free of voids), but itis also the most expensive wood for loudspeaker building.

Composite materials can be very strong and very light, but are also very expensive. Fiberglass is strongand weather-resistant, yet it is difficult to fabricate and therefore much more expensive than wood orplastic.

Molded-plastic loudspeaker cabinets have become common in recent years. They are lightweight andcan be made weather-resistant. The initial high tooling costs incurred by the manufacturer are recoveredthrough mass production over many years. This type of cabinet construction is practical for small-dimensioned enclosures, but more rigid materials are required for large boxes.

Loudspeakers that will be flown over an audience must have special rigging hardware (fly-points).They must also be pulltested to ensure cabinet and hardware integrity.

Fly-able loudspeakers don’t look a lot different than ground-stack or pole-mount loudspeakers, but willgenerally cost a good deal more due to the required cabinet construction, integral fly-points, and testing.

Self-Powered LoudspeakersI have shown that the loudspeaker is a system of inter-dependent parts. This can be expanded to includethe power amplifier. Amplifier selection can be complicated, and the ramifications for choosing thewrong one can be disastrous.

This has prompted some manufacturers to incorporate the amplifier and signal processing right into theloudspeaker. These are commonly called self-powered loudspeakers. This was not a practical approachwith older amplifier topologies, but modern Class-D amplifiers are relatively small and lightweight, and


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they are also very efficient. They can be incorporated into the loudspeaker cabinet without undueincreases in size or weight.

The result is a plug-and-play loudspeaker that needs only an electrical outlet and a signal from a mixer.Of course, self-powered loudspeakers will be comparatively more expensive than passive models. Theycan also be more difficult to install since they require AC power.

Both passive and self-powered loudspeakers can provide equivalent levels of performance. The prosand cons of each must be considered in light of the application.

Loudspeaker SpecificationsLoudspeakers should be tested by the manufacturer and supplied with performance data. Some keyspecifications include sensitivity, power handling, coverage angles, and impedance. These specs areuseful for providing a general idea of a loudspeaker’s performance (and hence its suitability for aproject), yet they shouldn’t.

not be used for comparison shopping between brands. This is especially true for power ratings, whichare seldom understood and usually wildly exaggerated. One big difference between loudspeaker brandsis the availability of engineering data for use in computer modeling programs. This data goes farbeyond the spec sheet that almost all loudspeakers have.

A popular program among sound system designers is the Enhanced Acoustic Simulator for Engineers(EASE). Another is CATT-Acoustic. One data type is proprietary to the EASE program, and others (i.e.,the Common Loudspeaker File Format or CLF) are generic.

A very quick way to narrow the field when selecting loudspeakers is to only consider models that areaccompanied by EASE or CLF data. The testing required to produce this data is extensive, so itsavailability is usually limited to professional models.

Consistent QualitySince the loudspeaker is a system of interdependent parts, the selected transducers must be of similarquality and have a similar level of performance. A better MF driver must be accompanied by better LFand HF drivers for the benefits to be realized.

The same is true for the enclosure and crossover network. It makes no sense to combine high-qualitycomponents with a cheap enclosure. This is like building a house, where it is sensible to be consistentwith the quality of materials. You don’t mount solid gold faucets onto a cheap sink.

But as with a house, if each part selected is a little better, then the cost of the whole will be muchgreater.

ConclusionRemember to compare apples with apples when evaluating loudspeakers. Consider a loudspeaker withthe following attributes:

Cast-frame LF transducer Fiberglass MF horn with compression driver ABS plastic HF horn withcompression driver Baltic birch cabinet rated for overhead use Integral fly-points Robust internalcrossover network (if applicable) EASE and CLF performance and design data Technical supportdepartment and available parts

The cost of a loudspeaker is affected by all of these factors and others. Even in a competitivemarketplace, a loudspeaker with these attributes will not be cheap. If one brand is half the price of allthe others, then “buyer beware.”

With loudspeakers, you get what you pay for and you can expect to pay for what you get. Aloudspeaker represents a set of compromises and trade-offs.

A competent sound system designer can weigh these out to select an appropriate make and model for


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your specific application.

Pat Brown teaches the Syn-Aud-Con seminars and workshops. Synergetic Audio Concepts(Syn-Aud-Con) has been a leader in audio education since 1973. With nearly 15,000 “graduates”worldwide, Syn-Aud-Con is dedicated to teaching the basics of audio and acoustics. For moreinformation visit their website at www.synaudcon.com.

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what makes a quality loudspeaker

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