Ceiling Speaker Calculator Guide

This 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

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.

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.

Listening Area 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.

Listening Area 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).

Speaker – Select the speaker model you wish to design into your project. The Speaker Calculator includes all current Extron ceiling speaker models

Select Audio Content – Select the typical content that will be presented in the room, whether speech, music, paging, or program. Each of these content types has an approximate maximum frequency. As the content's 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
Speech - default	7 kHz	Full-range voice reproduction
Paging	3 kHz	Only basic speech intelligibility is required. Paging generally requires the fewest speakers for coverage.
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:

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 user 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 specified audio content and the maximum allowable attenuation.

Recommended Tap Setting - The power tap setting to be selected on the speaker to acheive the specified requirements

Amplifier Power Required (APR) includes 25% headroom - This is the recommended tap setting multiplied by the recommended speaker quantity, plus an additional 25% for headroom.

Coverage Map

The coverage map provides a visual depiction of the recommended speaker layout. This recommendation is an approximation; the integrator will need to 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.

Essential Formulas Used in the Calculator

• R_C = (H_C - H_L) tan (A)
• D_C = (H_C - H_L) / cos (A)
• ΔL_A = 20 log [D_R / (H_C - H_L)]
• ΔL_E = 20 log (D_R / D_C)
• L_MINREF = L_MIN - ΔL_E + Isobar
• L_MAXREF = L_MAX - ΔL_A

Where:

• R_C = Radius at coverage angle and listening plane
• H_C = Ceiling height
• H_L = Listener height
• A = Coverage angle at isobar
• D_C = Distance from speaker at coverage angle and listening plane
• ΔL_A = Distance loss for listener on-axis (inverse square law)
• D_R = 1 meter or 3.28 feet reference distance
• ΔL_E = Distance loss for listener at isobar
• L_MINREF = Minimum target level on-axis at reference distance
• L_MIN = Minimum needed level for listener at isobar
• Isobar = Boundary with a specified SPL attenuation
• L_MAXREF = Maximum target level on-axis at reference distance
• L_MAX = Maximum target level for listener on-axis