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

Distributed Sound Systems

Distributed Sound Systems
Distributed sound systems are used in commercial applications as an efficient means to distribute sound. These systems are commonly referred to as constant voltage (CV) systems or 70-volt systems. In some cases, usually schools or correctional facilities, 25-volts is used instead of 70-volts.Almost all 70(25)-volt systems are made up of the following components:
1. Source Components - microphones, CD players, tape decks, etc.
2. Mixer Amps - these provide input selection, signal control, and power to drive speakers. They have a 70(25) volt output that is usually just two screw terminals on the back, "+" and "-".
3. Wire - most installations use 18 gauge, two conductor, stranded, jacketed wire. There is no need for a shield.
4. Volume Controls - these are only necessary when sound levels need to be changed in various areas on the same system.
5. Transformers - these are almost always mounted to the back of the speaker frame and the step the 70(25) volt signal down to an 8 ohm signal; commonly called step-down transformers. The input of these transformers is referred to as the primary side and the output is called the secondary side. Therefore, a transformer with a 70 (25) volt primary and an 8-ohm secondary would have a 70(25) volt input and an 8 ohm output.
6. Speakers - these can be almost any kind of speaker available. They need a transformer to change 70(25) volts into the signal they are designed to operate on, usually 8 ohms, sometimes 4 ohms.

Tap Settings Rules of Thumb
A. Amplifier Rule - The sum of the tap settings should never exceed 80% percent of the amplifiers' rated output.For example, if there are 23 speakers tapped at 2 watts, the load would be 46 watts (23 x 2 watts = 46 watts). To arrive at the needed power for this number of speakers, simply divide the total load by .8. In this case, 46 ¸ .8 = 57.5 watts. Therefore, a standard 60 watt amp would safely drive this load. To calculate the amount of usable power an amp offers, simply multiply the rated output by .8, i.e., 60 watts x .8= 48 watts.
B. Volume Control Rule - The sum of the tap settings on a volume control should not exceed its power rating.If the volume control is rated for 10 watts (i.e., AT10), then it could handle 10 speaker/transformer assemblies tapped at 1 watt. If the same assemblies were tapped at 2 watts each, then the resultant 20 watt load would need to be controlled by the next size up, the AT35.
Wire Rules of Thumb
A. The most common wire used on commercial 70(25) volt systems is 18 gauge, 2 conductor, stranded, and jacketed without a shield. Shielded wire is only needed with low level signals.
B. The wire starts at the amplifier location and is paralleled past each speaker location. One of the two conductors is connected to the positive lead of the step-down transformer on each speaker assembly, and the other conductor is connected to the common or negative lead (usually black).
C. Wire Length -18 gauge is appropriate up to 700 feet with a 100-watt load. If you double the load (sum of your tap settings), you will reduce the footage by half, to 350 feet. Conversely, if you half the load, you may double the acceptable wire length, i.e., a 50 watt load is safe over 1400 feet of 18 gauge. Stepping up to 16 gauge wire extends the allowable run length by approximately 35%. For example, a 100-watt load can go 700 feet on 18 gauge; the same load may be placed on 1100 feet of 16 gauge.

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Understanding Sound System Design and Feedback

To provide a good design for sound system, you must have a good knowledge of the following subjects:

1- The audio system chain.
2- The products of sound systems.
See the catalogues of the suppliers and the study (introduction to the sound system)
3- The dimensions of the place which we design a sound system for it.
See the architect's drawings.
4- The good distribution of the selected sound system components in the place.
By determining the accurate distances between the elements of the sound system as we will see.
5-The basic laws of sound system design.
There are many laws of sound system as we will see.

Use this knowledge to determine:
1-PAG (potential acoustic gain).
2-NAG (needed acoustic gain)
3-NAP (needed amplifier power)

By only two methods:
1-by using math. Equations.
2-by using the GAINCALC computer program.

The design will cover the most popular two sound systems:
1-conference system.
2-paging system.