User:Robert.Harker/Sound reinforcement speaker

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Sound reinforcement speakers are loudspeakers designed to project sound over a large area at reasonable levels. They range from small speakers with a single full-range loudspeaker driver to amplify the spoken voice in a modest sized room to hundreds of speakers each using multiple drivers and driver types driven by sophisticated signal processing equipment to drive amplifiers for each type of driver to cover large arenas or outdoor areas with high levels of sound.

History[edit]

The 1960s[edit]

In the 1960s SR speakers were almost always "columns" of multiple drivers mounted in a vertical line in a tall enclosure or horn loaded theater loudspeakers. Examples of the horn loaded speakers included the Altec "Voice of the theater" or JBL cinema speakers.[1]

The 1970s[edit]

1970s and early 1980s was a period of innovation in loudspeaker design with most sound companies designing their own speakers. The basic designs were based on well known designs and the speaker components were commercial speakers made by JBL, Altec Lansing, Electro-Voice and others. The areas of innovation were in cabinet design, durability, ease of packing and transport and ease of setup. SR Speaker designs during this time evolved into 4 basic designs:

  • One-box Modular Full Range system: bass, low-mid, mid-range and high frequency drivers in one box
  • Modular with sub woofer: A three way One-box modular system with a sub-woofer
  • Two-box Modular: One box with low-mid, mid-range and high frequency driver, a second box with bass speakers
  • Stacked Component System

One-box modular system:

Two box modular system:

Two box modular system with sub woofer:

Stacked Component System:

This period also saw the start of hanging or "flying" the main loudspeakers at large concerts.

The 1980s[edit]

During the 1980s the large speaker manufactures started producing standard products using the innovations of the 1970s. These were mostly smaller two way systems with 12", 15" or double 15" woofers and a high frequency driver attached to a high frequency horn. One of the first of these products were the Altec Stanley Screamers introduced in 1979. They included full range speakers using Altec 604 co-axial speakers and direct and horn loaded bass bins.[3] They were designed by Stan Miller.[4] The 1980s also saw the start of loudspeaker companies focused on the sound reinforcement market such as Meyer Sound and Eastern Acoustic Works.

The 1990s[edit]

The 1990s saw the introduction of hanging Line array speakers where long vertical arrays of speakers are used to increase efficiency and provide even dispersion and coverage. The 1990s also saw the introduction of inexpensive molded plastic speaker enclosures on tripod stands. Many have built-in power amplifiers which made them practical for non-technical operators to hook-up and use them successfully. The sound quality available from these simple 'powered speakers' varied widely depending on implementation.

Sound reinforcement loudspeaker[edit]

Sound reinforcement loudspeakers may range from a small loudspeaker with a single full-range driver to more elaborate loudspeakers incorporating different drivers to provide low-, middle- and high frequency sounds with crossover networks to route the different frequencies to the appropriate divers.

Most loudspeakers used in sound reinforcement use two types of loudspeaker components, cone speakers and compression drivers attached to high frequency horn Cone speakers are used as woofers and sub-woofers for low frequencies(20-1,000Hz) and mid-range speakers for the lower middle frequencies (200-2,000Hz). Compression drivers are used for the upper mid-range (800-5000Hz) and the upper range (2,000-20,000Hz). Note the overlap between different frequency bands. Different loudspeaker designs will use different components to cover the entire frequency range. In order to fill large areas with sound or to create high volume levels sound reinforcement loudspeakers must be able to handle high levels of power. Full range speakers should be able to handle 200-400 watts of continuous power. Other important features are rugged construction, durable finish, heavy duty speaker grills, and sturdy handles. While 1/4 inch jacks are still common, the sound reinforcement industry now considers Neutrik Speakon speaker connectors as the preferred standard. An important issue with speaker placement is to the the mid and high frequency speakers above the heads of the audience.

Small sound reinforcement loudspeakers[edit]

The simplest SR speaker is a compact 2-way speaker mounted on a tripod stand. This is sometimes called "a speaker on a stick". The enclosure may be made of plywood or be an injection molded plastic enclosure. It may be a passive speaker with a passive crossoverers or may be an active speaker with a built-in active crossover with built-in power amplifiers for the low and high frequency drivers. 2-way speakers work well for speech, quiet live or background music. For live or pre-recorded music the 2-way speakers may be augmented with large sub-woofers. Many sub-woofers are equipped with a pole socket and pole so they can replace the tripod stand. The sub-woofer will typically use and active crossover and separate power amplifier.[5]

Large sound reinforcement loudspeakers[edit]

Large sound reinforcement loudspeakers are typically 2-way with double 15 inch woofers or 3-way speakers placed on top of sub-woofers. An active crossover is used to split the sub, low, mid and high frequencies to different power amplifiers to drive the different speaker components. If a large area needs to be filled with sound or high sound levels are needed then multiple sets of speakers are used typically stacked horizontally on the sub-woofers. The speakers typically have a trapezoidal shape so they can be splayed for wider more even coverage.

Line array loudspeakers[edit]

Line array speakers are long vertical arrays of speakers are used to increase efficiency and provide even dispersion and coverage. The cabinets in a line array are horizontally arranged trapezoidal cabinets so that the array can be curved for better vertical coverage. The theory behind line arrays is that the sound waves propagate more like a cylinder than as a sphere. There are 3 main benefits:

  • Acoustical power loss over distance is half of a traditional speaker
  • Acoustical coverage is more even over the audience because interference is minimized between the different speaker components
  • Narrow vertical coverage minimizes sound projection to unwanted places

The main drawback of a line array is that the low frequency cutoff of the line array effect is four times the wavelength of the frequency. So for a 100 Hz wave with a wavelength of approximately 11.3 feet (3.4 m) you need a line array at least 113 feet (34 m) long.[6]

Powered speakers[edit]

A powered speaker has the speaker management system and amplifiers built into the speaker. The speaker management system is calibrated and preset at the factory is not adjustable by the operator. The power amplifiers are sized appropriately for the individual drivers. Powered speakers eliminate the need for amplifier and speaker signal processing racks. They also simplify setup, no speaker or patch cables. Only a signal and AC power cord needs to be run to the powered speaker.

Speaker management system[edit]

Signal processing equipment is used to "tune" loudspeaker systems for flat frequency response and phase coherence and to protect the speaker drivers from overload. In small SR systems the only signal processing equipment may be a graphic equalizer to adjust the tonal balance and to reduce feedback.[7]

In larger SR systems the various signal processors used to control the speakers may include graphic and parametric equalizers, active crossovers, and compressors and limiters. The collection of these components is called a drive rack. An analog drive rack start with a graphic and/or a parametric equalizer which feeds an active multiband crossover which splits the sound into multiple frequency bands, sub lows, lows, mids and highs typically. Each frequency band then may drive a time delay to make up for alignment differences between different drivers and then a compressor/limiter to protect the driver from overload.[8]

With advances in digital electronics all of these processors have been combined in to a single unit called a Digital speaker management system. Most digital speaker management system units have calibration and testing functions such as a pink noise generator coupled with a real time analyzer to allow automated room equalization.

Systems may include several loudspeakers, each with its output optimized for a specific range of frequencies (i.e. bass, mid-range and treble). bi-, tri- or quad-amping a reinforcement system with a DLMS makes more efficient use of amplifier power by sending each amplifier only frequencies appropriate for its respective loudspeaker.

Bi-amping, tri-amping speakers[edit]

Systems may include several loudspeakers, each with its output optimized for a specific range of frequencies (i.e. bass, mid-range and treble). bi-, tri- or quad-amping a reinforcement system with a DLMS makes more efficient use of amplifier power by sending each amplifier only frequencies appropriate for its respective loudspeaker.

Speaker protection[edit]

Many reinforcement speaker systems incorporated protection circuitry, preventing damage from excessive power or operator error. Positive temperature coefficient resistors, specialized current-limiting light bulbs and circuit-breakers were used alone or in combination to reduce driver failures. During the same period, the sound reinforcement industry standardized on the Neutrik Speakon NL4 and NL8 input connectors, replacing the 1/4" jacks, XLR connectors and Cannon multipin connectors which were limited to a maximum of 15 amps of current.

Designs[edit]

The four different types of transducers (woofers, compression drivers, and tweeters) all use the same components: a voicecoil, magnet, cone or diaphragm and a frame or structure. PA speakers have a power rating (in watts) which indicates their maximum power capacity, to help users avoid overpowering them. Thanks to the efforts of the Audio Engineering Society (AES) and the loudspeaker industry group (ALMA), power-handling specifications became slightly more trustworthy, although adoption of the EIA-426-B standard is far from universal. Starting in the mid 1990s trapezoidal-shaped enclosures became popular as their wedge-like shape allowed them to be arrayed easily in multiples.

Flying the speakers[edit]

Professional sound reinforcement speaker systems often include dedicated hardware for "flying" them above the stage area, to provide more even sound coverage and to maximize sight lines within performance venues. Stanley Screamers were among the first commercially produced SR speakers that were designed to be flyable[9]

References[edit]

  1. ^ Grubsdorf
  2. ^ Building Pro Audio Loudspeaker Enclosures, Jeffery Forsburg, Grubsrof, Inc. 2002
  3. ^ http://www.lansingheritage.org/images/altec/catalogs/1979-screamer/page03.jpg Introducing the Stanley Screamers
  4. ^ http://www.pinkfloyd-co.com/disco/wall/wall_trivia.html The Wall Trivia and Quotes
  5. ^ http://acapella.harmony-central.com/archive/index.php/t-1981519.html The Portable PA & the Solo Performer
  6. ^ http://www.rh.com/loudspeakers/linearrays/LineArrays-White-Paper.pdf Designer’s Note Book: A Fresh Approach to the Line Array
  7. ^ http://www.livesoundint.com/archives/2004/june/audiobasics.pdf Attaining Tonal Balance Getting a handle on EQ essentials
  8. ^ http://www.laservisionworld.com/css/documents/SpeakerProcessor.pdf Using Speaker Processors
  9. ^ http://srforums.prosoundweb.com/index.php/m/0/32019/16/0/ Re: Writing about the history you know