Ceiling Speaker Calculator Guide

The Speaker Calculator help page provides detailed descriptions of the parameters in the user data fields, the calculation results, and the coverage map. This guide assists in understanding the information necessary to calculate the number of ceiling speakers needed for a room or listening area, and to effectively apply the Speaker Calculator recommendations to a sound reinforcement system design.

A Note on Data Entry

The Speaker Calculator is simple to navigate. Pressing the <tab>key allows you to efficiently progress through the data fields as you enter the parameters. Use <shift tab> to move backwards through previous entries. Once the information has been entered, press the Calculate button to view the speaker quantity recommendation as well as amplifier power requirements. You can revise any of the input parameters and then update the results by pressing the Calculate button.

User Data Fields

Select Unit of Distance Measurement – Allows you to define the unit of measurement in feet or meters, for the user input parameters as well as the calculation results.

Room Length – Approximate length of the coverage area. The coverage area can be a room, or a specific area in the room where listeners will be situated.

Room Width – Approximate width of the coverage area.

Speaker Height – Approximate height at which the speakers will be installed. In most cases, this will be the height of the ceiling. The value entered must be greater than 7 feet (2.13 m).

Listener Height – This is the ear height of a typical listener. Consider whether the typical listener will be seated or standing. The default value is 4 feet (1.22 m), which is typical for seated listeners. For standing listeners, 5.5 feet (1.68 m) is the typical ear height. The maximum value that can be entered is 1 foot (0.3 m) below the speaker height value.

Advanced Options

Hidden from view are five optional parameters that may be left at their default settings for most estimation projects. Designers and engineers may choose to adjust these settings to fine-tune their speaker calculations.

Force Grid Spacing – Allows the user to define a ceiling grid spacing distance, and effectively force the speakers into a pattern that will match ceiling tile spacing. The default value is 0, which provides ideal speaker locations without alignment to any grid pattern. Defining a specific value will constrain speaker spacing to multiples of the grid spacing distance. This may introduce a degree of error in the calculations, resulting in the need for additional speakers to compensate. The greater the grid spacing distance, the greater the chance of error introduced.

Ambient Noise (dB SPL) – This is the amount of background noise within the environment. The default setting is 50 dB SPL and the maximum value that can be entered is 90 dB SPL. The following are common environments and their typical ambient noise levels:

Environment Typical Ambient Noise Level (dB SPL)
Videoconference room 35
Quiet library/residence 40
Quiet office/empty classroom 50
Busy restaurant 60
Noisy office 70
Busy cafeteria 80
Airplane cabin 90

Desired S/N (dB) – The desired sound pressure level (SPL) of the audio system above the specified ambient noise. This signal-to-noise ratio will define the intelligibility of the audio system. The default setting is 25 dB. The user can increase this value to provide additional margin above the ambient noise, and enhance intelligibility.

Minimum Needed Level (dB SPL) – This field displays the sum of the ambient noise and desired S/N, and represents the target sound pressure level for baseline intelligibility. This parameter will be used to calculate the minimum amplifier power necessary to drive the speakers.

Maximum Target Level (dB SPL) – This allows the user to target a specific maximum sound pressure level, to ensure adequate system headroom for the loudest anticipated sounds. Some common audio sources and their typical SPL values are listed in the following table:

Audio Source Typical SPL (dB)
Whisper 20
Soft stereo in a residence 40
Very soft music 50
Conversational speech 60
Soft classical music 65
Vacuum cleaner 70
Soft popular music 75
Alarm clock 80
Moderately loud classical music 85
City traffic 90
Loud classical music 95
Firecrackers, subway train 100

Speaker – Select the speaker you wish to design into your project. The Speaker Calculator includes all current Extron ceiling speaker models, with the exception of the Extron SI 26X ceiling speaker.

CS 1226T Plus Two-Way 70/100 V SpeedMount Ceiling Speaker System
CS 123T Full-Range 70/100 V SpeedMount Ceiling Speaker System
CS 26T Plus Two-Way Open Back Ceiling Speaker with 70/100 V Transformer
CS 3T Full-Range Open Back Ceiling Speakers with 70/100 V Transformer
SF 26X Two-Way SoundField Open Back 8 Ohm Ceiling Speaker
FF 120T Full-Range Flat Field® Speakers with 1' x 2' Low Profile Enclosure and 70/100 V Transformer
FF 220T Full-Range Flat Field® Speakers with 2' x 2' Low Profile Enclosure and 70/100 V Transformer
SF 228T Two-Way SoundField® Ceiling Tile Speakers with 8" Woofer and 70/100 V Transformer
SI 26CT Two-Way Ceiling Speakers with 8" Back Can and 70/100 V Transformer
SI 3C LP Full-Range Ceiling 8 Ohm Speakers with 4" Low Profile Back Can
SI 3CT LP Full-Range Ceiling Speakers with 4" Low Profile Back Can and 70/100 V Transformer

Content – Select the typical content that will be presented in the room, whether paging, speech, program, or music. Each of these content types has an approximate maximum frequency. As the frequency increases, a speaker’s coverage angle generally decreases. This in turn translates to more speakers necessary to achieve the desired room coverage. Therefore, it is important to carefully consider the content that will be presented in the application.

Content Maximum Frequency (Approx.) Selection Criteria
Paging 3 kHz Only basic speech intelligibility is required. Paging generally requires the fewest speakers for coverage.
Speech 7 kHz Full-range voice reproduction
Program 10 kHz Video programming is the primary audio source.
Music 12 kHz Full-range audio is necessary for music reproduction. Music generally requires the most speakers for coverage.

Edge-to-Edge Isobar (Speaker Spacing) – In the general sense, this input describes the amount of SPL variation allowed within the room, commonly referred to as seat-to-seat variation. The specific choices are defined as edge-to-edge isobars, and these define how the coverage angles used by the calculator are chosen. The term Isobar denotes sound pressure measurement. Each isobar defines a different amount of attenuation allowed at the edge of the radius of coverage. The higher the isobar, the more attenuation is allowed, and therefore the larger the coverage area (and corresponding coverage angle). Higher isobars allow more SPL variation, and therefore fewer speakers are required.

The available isobars loosely describe the seat-to-seat and perimeter variation as follows:

3 dB Isobar (0-1 dB seating; 1-4 dB perimeter)
6 dB Isobar (0-2 dB seating; 2-6 dB perimeter)
9 dB Isobar (0-5 dB seating; 5-10 dB perimeter)
12 dB Isobar (0-8 dB seating; 8-14 dB perimeter)

Coverage Pattern – The coverage pattern as defined by the arrangement of the speakers. A square coverage pattern is produced by a uniform layout of speakers in columns and rows, while for a hexagonal coverage pattern, every other row or column is offset. When compared to a hexagonal pattern, a square pattern results in a more consistent coverage throughout a room, but usually requires more speakers. A hex pattern is produced by a staggered arrangement of rows or columns which typically results in fewer speakers. This type of pattern may be ideal for applications in which coverage at the edges of the room is less important than toward the center.

Speaker Operation – The type of wiring used to connect the speakers to the amplifier. The speakers must be set up correctly and connected to the appropriate type of amplifier output. Low Impedance wiring generally requires a direct connection between each speaker and the amplifier, while high impedance 70/100 volt wiring allows an amplifier to be connected to several speakers in sequence. While 70/100 volt wiring schemes allow for longer wiring runs with many speakers in sequence, low impedance systems tend to deliver better low frequency response.

Calculate – When the Calculate button is pressed, the Speaker Calculator generates the results which can be viewed on the right. The View/Print Coverage Map opens a new window with a speaker coverage map and a summary that includes the input parameters and additional calculation results.

Reset – Removes distance parameters and sets all other input values back to their defaults.

Results

Recommended Speaker Quantity – The number of speakers recommended for delivering sound coverage, based on requirements defined by the user.

Coverage Area per Speaker – The approximate area that each speaker covers, defined by the frequency range of the audio content and the maximum allowable attenuation.

Minimum Needed Power Level - The output wattage per speaker, tap setting, and amplifier power required to achieve the minimum needed SPL as established earlier.

Maximum Target Power Level - The output wattage per speaker, tap setting, and amplifier power necessary to meet the maximum target SPL as defined by the user.

Coverage Map

The coverage map provides a visual depiction of the recommended speaker layout. This recommendation is just an approximation; the integrator will need consider all practical mounting limitations and make adjustments as necessary. A row is defined as a group of speakers with a common Y coordinate, while a column is a group of speakers sharing the same X coordinate.

Distance Wall to First/Last Row – The distance between the first or last row of speakers and the nearest room wall.

Distance Wall to First/Last Column – The distance between a side wall and the first and last column of speakers. For a hexagonal speaker pattern, distances are provided for odd and even (offset) columns.

Row Spacing - The distance between each row of speakers.

Column Spacing – The distance between each column of speakers.

Column Offset – The amount of offset between successive columns.

Display Isobars – Allows the user to select isobars for display on the coverage map. This can be helpful in illustrating variations in sound coverage throughout the area.

Coverage Calculation Inputs – Provides a summary of the user input parameters, including any defaults in the advanced options section.

Radius of Coverage – This section provides the radius of coverage for the 3, 6, 9, and 12 dB attenuation isobars.