Speakers

Speakers are usually classified as full range, tweeter, midrange, woofer, or sub-woofer. A full range speaker is designed to handle the full range of sounds most people can hear. A single amplifier is all that is needed to power a full range speaker.
However, tweeter, midrange, woofer, and sub-woofer speakers are only designed to handle a portion of the sound spectrum. These speakers require a device called a Cross-over to work properly.
Cross-Over - The Cross-over splits the full range audio signal into two, three, or four ranges to be delivered to separate speakers. A 2-way speaker system consists of only a tweeter and a woofer. A 3-way system consists of tweeter, midrange, and woofer. And, a 4-way system consists of tweeter, midrange, woofer, and sub-woofer.
There are two ways that the Cross-over can be connected: either after the amplifier or before. Most low to medium power speaker systems connect the Cross-over after the amplifier. Frequently, the Cross-over is inside the speaker cabinet. High power speaker systems often use a Cross-over connected before the amplifiers. This also makes it necessary to have a separate amplifier for each speaker. A 2-way system must be bi-amped (that is, 2 amplifiers). A 3-way system must be tri-amped (that is, 3 amplifiers). If a sub-woofer is used, it also requires a separate amplifier if the Cross-over is connected in front of the amplifiers.

Sub-Woofer - The Sub-Woofer reproduces extremely low frequencies from about 100 Hz down to 20 Hz. These frequencies are "felt" more than heard. The Sub-Woofer gives the bottom end "beat" to music and the thunderous effects to movie sound tracks. If your sound system is not used for music with a heavy beat or movie sound tracks, then you may not need a Sub-Woofer.
Sub-Woofer may be placed wherever it is convenient since the human ear cannot tell what direction bass sound comes from

Woofer - The Woofer reproduces low frequencies from about 500 Hz down to 100 Hz, the bass sounds. Speaker placement is not critical because Woofers are omnidirectional.

Mirage - The Midrange speaker reproduces midrange frequencies from about 500 Hz to 6000 Hz. The midrange area contains most of the sound for voices and instruments. Speaker placement is more critical because mid-range sound is more directional.

Tweeter - The Tweeter reproduces high frequencies from about 6000 Hz to nearly 20,000 Hz. It is responsible for the brilliance in the sound, mostly associated with harmonics. Speaker placement and angle are critical because high frequency sounds are very directional.
Full Range - A Full Range speaker is a single speaker which attempts to reproduce the entire audio spectrum, usually not as well as a multi-speaker arrangement. Full range speakers are practical for low power speakers, but not for high power.

Main or House Speaker System - The Main or House Speakers deliver the sound to the audience. Usually the a combination of tweeter(s), mid-range(s), woofer(s), and possibly sub-woofer(s) designed for smooth frequency response over a wide frequency range and able to operate at high volume levels is used for the Main or House Speaker System.
Usually, a central cluster is best for the main speaker system. A number of multi-speaker cabinets are arranged in an arc and suspended from the ceiling just in front of the center of the performance area.
The number of cabinets, angle of speakers, and angle of cabinets is critical for even coverage.
If the room is not suited to a central cluster or the main system must be portable, a distributed system with one or more multi-speaker cabinets just in front of each side of the performance area should be used. The height of the cabinets, angle of speakers, and angle of cabinets is important for even coverage.
A distributed system will experience the "comb filter" effect to some degree. Each audience member hears sound from both the left and right speakers. These sounds arrive at different times and therefore are out of phase with each other. The amount of phase difference depends on the frequency of the sound. Therefore, from each individual audience seat, some frequencies are louder (in phase) and some frequencies are quieter (180 degrees out of phase).

Monitor System - The Monitor Speaker System is located in or aimed at the performance area. Monitor speakers enable the performer(s) to hear themselves and other necessary elements of the program (i.e. music).
Usually Monitor speakers consist of a combination of a tweeter and a woofer in a slanted cabinet designed to aim the sound back toward the performers.

Monitor speakers should be placed to satisfy the performer(s). Wedge shaped monitor speakers should be placed on the floor in front of the performer so they aim the sound towards the rear of the performer's mike. Sometimes side fill monitors are needed to cover a larger area (i.e. if the performer moves around). Avoid placing monitor speakers where they face the front of a microphone.

If multiple monitor mixes are required, each performer may have their own monitor speaker(s).

Fire Alarm Detection System Design

In order to undertake the process of designing a fire system for a building it is necessary to have a sound understanding of the relevant design standards, the legal framework surrounding building safety legislation and a sound working knowledge of product application theory. The importance of consultation with all relevant parties cannot be overstressed, neither can the importance of specialist advice in relevant areas. The following system design process is intended to give a reasonable overview of all the areas of knowledge required for the successful design of a fire alarm system.

OVERVIEW OF THE DESIGN PROCESS:
The following describes a typical fire alarm system design process
• Understand the reasons for installing the fire alarm system in the specific property
• Conduct a risk assessment to help determine requirements
• Consult with all interested parties
• Decide on the relevant design standard
• Establish if third party approval is required - for equipment and/or installation.
• Decide on the type of alarm technology to be used
• Decide on the appropriate protection category and extent of coverage where relevant
• Discuss and agree the fire strategy
• Plan the zoning of the building
• Select and position relevant system components
- Select the appropriate detectors for each area
- Position the detectors- Select suitable callpoints and position at appropriate locations
- Agree on the means of summoning the fire authority
- Plan the alarm signalling arrangements (sounders, beacons, pagers etc)
• Select a suitable panel (suitably sized and rated with adequate standby autonomy)
- Review the design such as to - minimise the potential for false alarms
- Select Contractor- Ensure suitable wiring of the system
- Make suitable arrangements for commissioning
- Appoint/Establish responsible person
- Make suitable arrangements for ongoing maintenance and monitoring of system performance

I will explain each one of the previous items in more detail