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Standard Audio / Video System Structure
By Dave Hosbach

There are any number of possibilities "on the table" when we go about the work of designing a sound system. The first thing we must do is understand that there is a basic structure to every system - common types of components necessary for the ultimate success of the overall system.

Input devices - microphones (wired and wireless), musical instruments (acoustic and electronic), playback devices (cassette tape, CD, audio from video sources). These are the "ingredients" that carry an audio signal into the sound system.

Mixers - come in many formats and sizes. They take the "ingredients" and "mix" them, or put them together into one balanced signal that, if combined properly, will be pleasing to listen to once it is projected from loudspeakers.

The mixer is also the "command and control center", giving us the ability to route the signals from the various input devices to the electronics that govern "subsystems" like the main loudspeakers, music monitor speakers, assistive listening devices, auxiliary speakers for such areas as narthex and nursery, and recording devices.

In many cases you will see a "console" with a lot of knobs, dials and sliding fader controls. With the advent of computer control, most all of the functions of the mixer can now be controlled via computer, in what we call a "virtual mixer" format. You will have the option to use either method, or a hybrid of both analog console and computer-driven "virtual mixer".

Signal processors - nowadays mostly digital; the "brains" of the system. These pieces provide equalization for the loudspeakers, helping us to shape the sound so that it sounds natural and full, and to provide protection against "feedback", or the howl or squeal that occurs when sound reflects back into a microphone from a loudspeaker.

Signal processors also provide other "fine tuning" functions that allow us to synchronize the sound from the loudspeakers, limit the loudness of the sound where necessary, switch speakers on and off, and generally maximize the simplicity of operation, flexibility and sonic quality of the entire sound system.

Power amplifiers - the "muscle factories" - boost the strength of the signal they receive from the signal processors to a level that can effectively be produced by the loudspeakers. The amount of boost required is determined by worship setting requirements and by the type of loudspeaker that will receive the boosted signal. Depending on the size/complexity of the overall sound system and the type of loudspeaker, just one power amplifier may be adequate, or many power amplifiers will be required to properly "drive" the system's loudspeakers.

Loudspeakers - the "voice" of the sound system. There are too many types and sizes to describe them all here. In basic terms, the job of the loudspeaker is to convert the electronic signal it receives into acoustic energy that our ears will hear. Some loudspeakers perform this conversion more accurately than others. Some loudspeakers are larger than others and as a result will produce more bass sound than others. Most professional loudspeakers use horn-type devices at least in part. The purpose is to aid in projecting the sound toward the listeners' ears while keeping the sound from reflecting off walls and ceilings.

Line array devices are also now in vogue. Some are designed as tall towers of 8-10 feet or more comprised of elements capable of producing a wide range of volume levels with excellent clarity and musical quality. Some line arrays are designed as "digitally steerable" arrays, which means that many small (4-or 6-inch) speakers are vertically oriented in an enclosure that may reach as high as 16 feet.

These arrays can work well under tight aesthetic and physical space conditions. However, these arrays are not as musical sounding as traditional speaker systems, and can be more expensive than creative full-range horn-loaded speaker designs.

General Comment Regarding Loudspeakers & Signal Processing

The loudspeaker system is typically the most expensive portion of the audio system due to equipment and labor requirements associated with "getting it right." However, the loudspeakers are considered the most critical portion of the audio system for a couple of reasons. First, the loudspeaker system must meet coverage needs as well as needs for sound quality and clarity for speech and music reinforcement. Secondly, the loudspeakers are usually in place for 15 years or more and are attached to a wall or suspended from the roof/ceiling structure, and so become a fixture in the space.

Consequently, the thought process that goes into determining the type(s), quantities and locations of the loudspeakers is long and difficult, especially in "classic traditional" church spaces. Experience in similar projects and computer-aided design tools are used in the loudspeaker system design process. Much consideration is also given to the acoustical properties as well as the aesthetic beauty and sight lines within the worship space.

The object of the loudspeaker system is to provide clear sound across the speech and/or music ranges of the sound spectrum, and to direct the sound into the seats while keeping as much of the sound as possible away from the walls and ceiling. Ultimately, the loudspeaker system design will fall into one of several type categories:

Traditional Speaker Arrays. This type of design uses either single or multiple loudspeaker devices either in tight "clusters" or distributed across the space. Usually suspended from the ceiling, the layout of a traditional array is determined by the area needed to be covered, the coverage angle necessary to provide even coverage, and the locations required to keep as much sound as possible from reflecting off walls and ceiling.

Coverage is provided by devices (horns and bass speakers) that are rated to deliver varying degrees of vertical and horizontal coverage. For instance, one loudspeaker may be rated to deliver 90° of horizontal coverage and 40° of vertical coverage. Another device designed to target an area further away might be rated at 40° horizontal and 20° vertical. Used in varying combinations and in strategic locations, very even coverage can be achieved with very high levels of intelligibility (clarity).

Setup is generally simple with a traditional array. Traditional analog or newer digital electronics can be used, though digital is more accurate and now less expensive than analog. We can accomplish very rich full-range sound with great articulation, and give the congregation the ability to turn speaker zones on and off with system presets.

In terms of component cost, the traditional array is typically the least expensive but can be labor-intensive when installing, especially when dealing with expanded arrays distributed across the ceiling. However, the traditional array can be the most flexible in terms of configuring the system for the application (presets) and delivering the sound exactly to the desired locations.

Bethlehem Lutheran Northshore Congregational

Vertical Arrays. This design uses multiple relatively compact speaker enclosures in a vertical configuration. Each loudspeaker enclosure is rated for very narrow vertical coverage (about 3-5°) while the horizontal coverage angle is wide (about 150°). The enclosures contain traditional speaker devices - horns and midrange and bass drivers - arranged in creative ways to deliver the coverage and save space.

The vertical array is suspended from the ceiling at the front of the space. By stacking enclosures in a very tight array and with help from very sophisticated digital electronics, the enclosures combine to provide even coverage to a wide seating area but keeps almost all of the sound off the ceiling and stage.

A Typical Vertical Line Array

The idea is to provide sound coverage to both the far and near field from one point, thus saving labor. However, in order to provide effective coverage with adequate clarity, the vertical array will normally be as high as 10 feet - sometimes more, up to 15 feet.

Sound quality is usually never an issue for the vertical array. Rich, full-range sound is accomplished with all of the drivers tuned and working together. However, the end result depends on the ability of the technician to deal with all of the digital tools in the right way.

When accounting for all of the additional signal processing and amplification required to drive the vertical array, the cost becomes very high. Combining that with the physical height of the typical array, use of the vertical array is usually limited to arena-size concert touring, and concert/production driven evangelical churches where aesthetics are less of a priority.

Digitally Steerable Vertical (DSV) Array. This is the newest player in the loudspeaker design arena. Quite simply it is the marriage of the old column speaker (once seen on the front/side walls in many churches) with complex digital control systems normally found in use with the vertical array. The DSV array has become popular because of its ability to blend into its surroundings.

The DSV array speaker is available from several mainline manufacturers, and ranges in vertical height from about four feet to almost 17 feet. The horizontal dimension and depth are usually about the same at approximately five inches, making this type of speaker especially intriguing to congregations with classic traditional worship spaces (the vertical dimension is not a big concern when the width is so slight - it is easy for this speaker to "hide" on a wall at the side of the chancel).

Cathedral of St John the Evangelist

The DSV array speaker uses a number of four- or five-inch speakers in the vertical column. In the small columns there can be as few as four speakers; the tall columns can contain as many as 32 devices. The idea is the same as with the vertical array: to narrow the vertical coverage and keep the sound off the ceiling and chancel/stage as much as possible. The difference, as stated above, is that the DSV array speaker mounts directly to the front wall as opposed to being suspended from the ceiling.

Since the DSV array is mounted to the front wall, it will project the sound straight out from the speaker. Without any aid in aiming the sound, the sound from the column would pass directly over the worshipers heads and reflect off the rear wall. This is a major reason why the old column speakers typically did not work well. However, in the DSV array each speaker is controlled by a portion of the digital processing electronics. Complex mathematical algorithms are used to adjust volume, delay and equalization for each individual speaker device so that the sound can be aimed toward the seats from the system's vertical position. Hence the term "digitally steerable array".

The DSV array has worked well for speech purposes, but is never promoted by the manufacturers as being particularly musical in nature. Due to the small speaker devices and the lack of enclosure volume, the bass sound is very thin and the treble sound can be somewhat unnatural. For that reason, we are careful about where we install them, typically using them where the application is determined to be speech-only or speech with very limited acoustical music reinforcement. Subwoofers can be added, but only at the location of the DSV array speaker due to the relatively high frequencies that the subwoofer is required to produce along with the deep bass sound.

As is the case with the vertical array described earlier, the cost factor for the DSV array system is high. Labor savings are accomplished due to the ability to mount the system to a structurally-sound wall. However, it is still more expensive than the traditional speaker array, and it is a bit more difficult to provide even coverage to all seating areas.

Distributed Delay Speaker System. The distributed speaker system is very commonly used in shopping malls, office corridors, airports, and other areas where typically the ceiling is low and there is a lot of space to cover with sound. Many small speaker enclosures are utilized and are located either in the ceiling tile or mounted to walls and columns. Implemented properly using the correct type and quantity of loudspeaker, the voice message is clearly distributed through the space very effectively.

This type of loudspeaker layout has been employed in various ways and with varying degrees of success in auditoriums and churches through the years. In almost every case, it has been used as an inexpensive way to reinforce a pastor's voice without suspending loudspeakers from the ceiling. The mistake made in many of these cases is threefold. The first mistake is that the loudspeaker used is "cheap". The sound quality is poor. Secondly, not enough loudspeakers are used. Consequently, the sound coverage is very inadequate, leading people to sit in areas where they can hear well. Thirdly, the speakers are located improperly. The talker seems to be speaking from a side wall or from the rear of the room as opposed to from the front of the room.

With the advent of higher quality compact speaker systems, and with careful creative design and delay techniques employed, a distributed speaker system can be very effective. An example of a successful distributed speaker system in a church is one where the ceiling is very high and the room is very reverberant. By distributing the sound from the columns with good quality loudspeakers, and by using modern digital electronics to synchronize the speakers in time, everyone hears clearly, and the sound will always seem to originate from the front of the church where the talkers are. Depending on the type of music employed, this style of system design might also carry music playback for worship. The photos below show this type of design in a very successful installation which carries liturgy as well as some music.

A good distributed speaker system design is somewhat labor intensive due to the multiple speaker locations and the required cable installation and digital electronics. However, this design almost always costs less to implement than a DSV Array system due to the relatively low cost of the compact speakers used in the distributed system.

St Anthony Catholic Church

When discussing loudspeakers, there is a grouping of components that must be considered as part of the loudspeaker system. It is the processing and amplifying electronics - i.e. the power amplifiers and signal processors/controllers. The loudspeakers, type and quantity, are determined first, with the power amplifiers and signal processors determined by the loudspeaker system layout and the tuning and sound level requirements for the application.

The traditional and vertical arrays require processing and power amplification for proper setup. The DSV array has complex processing built in along with power amplification, however, additional signal processing is still required for setting up gain-before-feedback and balance between it and other supplemental speakers.

When a congregation is considering a loudspeaker design, we always lay out the caution regarding sound quality, flexibility and aesthetics. Keeping in mind that the loudspeaker system should be in place for a minimum of 15 years, the congregation needs to decide where the line is to be drawn between looks (form) and works (function), and then study the budgetary impact of the decision.

We have had good success with utilizing an expanded traditional array system in worship spaces of many varied sizes and applications. In terms of coverage, a digitally steerable vertical array will work as well. In either case, supplemental speaker systems are usually necessary for under and upper balcony areas.

Basic Video Structure

There are two basic components in a video system: the projector and the screen. The basic principles to follow are:

  • Ensure that the projector is bright enough to light the screen in a room with high levels of ambient light from windows and lights. In cases where windows and doors let in a great deal of light, it may become necessary to shade at least some of the windows. Rear projection can be used to ensure the best performance, but this method does not work in many rooms due to space limitations.

  • Ensure that the screen is large enough to allow for clear viewing from the farthest seat. If the farthest seat is about 70 feet away from the screen, then we divide that dimension by 8 to arrive at the proper height of the screen. The screen size can be modified somewhat depending on the visual impact of the screen itself and its housing. However, if the screen is too small, people will not be able to see text clearly.

Everything else in the video system becomes a matter of choice for function and convenience in operation.

Source switching - Two devices should be used to ensure that the video signal is sent to the projector in the proper format from one of a couple locations. First is a small computer selector if more than one computer is to be used from time to time. Second is a video switcher-scaler. The switcher-scaler will allow for direct plug-in of computer, DVD, camera and other video devices as they are added to the system. The unit will automatically put the video signal into the resolution format native to the projector. Switching between sources then will be seamless and very convenient. Any audio signal associated with the video sources will be transported to the sound mixing console.

Control - A third-party system such as those manufactured by Xantech, Crestron and AMX may be used for controlling one or all of the video devices (screen, projector, DVD, computer, camera, etc.) as well as room lighting and some portions of the sound system. Using either a wired or wireless remote control, any authorized user can press buttons to power up the projector, drop the screen, etc. separately, or presets can be established to allow for dimming lights, projector power-up, screen drop, etc. from one button. There are many variables in components and cost.

Camera - Video cameras can be installed at locations such as the side and/or the rear of the worship space. The cameras can either be fixed position units or pan/tilt/zoom units (pan=side-to-side adjust; tilt=up-and-down adjust; zoom=in-out adjust). We recommend the pan/tilt/zoom style because this offers the most flexibility for the future, especially when it comes to recording weddings.

Most often the camera is used for recording purposes. It can also be used to send video signal to other rooms. Both purposes can be accomplished by using video split electronics to send the signal to a device such as a DVD recorder and at the same time to video monitors in other rooms.

If the church has a cable-TV line running through the building, a modulator can be used to place the sanctuary video signal onto an unused TV channel. The user in each room then simply turns the TV in the room to that channel in order to receive the church service.

Recorder - This is the most common device to use when beginning a video recording ministry. Depending on desires for webcsasting and the like, some congregations will record to hard-drive units and then edit using software-based editing programs.

Application Requirements

Every worship space is unique architecturally and acoustically. Every congregation "gets the message out" in differing ways - contemporary, traditional, visually, musically. In every case, and whether new construction or existing structure, there are application requirements that must be taken into account. These requirements include, but are not limited to:

  • Loudspeaker type and placement - The objective is to provide the coverage needed with as little potential for feedback as possible. Factors that help us determine the type, quantity and locations for main loudspeakers are:
    • The physical size, shape and acoustical properties of the space;
    • The seating arrangement;
    • The chancel layout;
    • Placement of video screens;
    • Placement of items such as lighting fixtures and cross.
  • Number of sound system inputs - In order to answer this we must ask the question - What is your worship setting going to consist of?
    • Wireless microphones - Lapel? Handheld? Low-profile headworn?
    • Contemporary and/or traditional music?
    • CD accompaniment?
    • Musical instruments - piano, digital keyboard, guitar, drum kit (electronic or acoustic)?
    • Vocal ensembles?
    • Choirs? Where will the choir sing from?
    • Will the pastors preach from a pulpit or will they preach free-standing?
    • Video? Will we need to provide audio-for-video functions?
    • Computer? Will we need to provide a feed from a sound card?
  • Number of system outputs - To where will the signal from the mixer be sent?
    • Main sanctuary loudspeakers?
    • Dedicated choir/music loudspeaker systems?
    • Narthex loudspeakers?
    • Monitor loudspeakers for musicians?
    • Audio recording? Tape or CD?
    • Video recording? Analog or digital?
    • Systems for the hearing impaired?
    • Radio or TV broadcast?
    • Personal monitor loudspeakers for the pastors' chairs?
  • Video screen - most importantly the screen size and location.
    • Are we looking to avoid visual conflict with the cross at the chancel? If so, then a single, centrally-located screen may not be a good solution.
    • Where will people be seated in relation to the screen(s)? The maximum viewing angle (side-to-side) is approximately 50 degrees, if a consistent image quality is desired.
    • Will people need to turn their heads to view the screen, or will they be able to view straight-on with no head-turning required?
    • Use the [(8 X vertical dimension in inches) = Maximum Clear Viewing Distance] formula to determine the best screen size.
  • Video Projector - This is as critical as the screen!
    • How bright is the room? Do we need to work with window shades?
    • Is there the ability to turn off lights near the screen to avoid "washing out" the image on the screen?
    • Will the projector(s) be pendant-mounted from the ceiling near the screen(s) or wall-mounted at the rear of the room?
  • Video application in general:
    • Do you desire the capability, now or in the future, to incorporate cameras for service recording or for sending video to other rooms?
    • DVD playback?
    • VCR playback?
    • Computer graphics?
      • Sent from computer at control desk?
      • Sent from computer at lectern in chancel?
    • Recording in analog (VCR)?
    • Digital recording (DVD, hard drive, digital tape recorder)?
    • Wired or wireless remote control?
  • Conduit/wireways
    • What has already been designed into the building?
    • Additional conduit/wireway may be necessary to accommodate master plan items now and for the future;
      • Microphone, video and loudspeaker lines must be run in separate conduit to avoid buzzes, hum, and crosstalk.
      • Conduit size to be determined by number of lines in a single pipe and in the case of loudspeakers, the thickness of the wire.
    • What is the routing scheme for conduit?
      • Under floor?
      • Over ceiling?
      • Through walls?
      • Across basement ceiling?
  • AC Power
    • Power for audio, video and lighting must occupy separate circuits;
    • Audio power must be kept on a single phase of the building's three-phase electrical system
    • Audio power must be kept off the phase that carries lighting
    • Audio and video power systems must carry dedicated, isolated ground to power panel, not just ground to the outlet boxes ("pipe ground").
  • Structure
    • If a traditional speaker array is employed, the building structure must be such that the roof/ceiling can support loads from loudspeakers weighing in a range from 70 - 150 pounds each.
      • Traditional loudspeakers will generally be rigged from three points. The ceiling structure must be reinforced and blocked at the loudspeaker suspension points such that a safety factor of at least 8:1 is achieved for each suspension point.
    • If digital steerable array or distributed speaker systems are employed, there needs to be sufficient structure on building support columns and walls to accommodate up to approximately 35 pounds.

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