Index

Professional audio page

    Using audio equipments

    Do you, the musician, desire that everyone in the audience enjoy your music at an appropriate volume with good tone quality and with all parts in musical balance? In the ideal situation, the performance room.s acoustics would be sufficient to achieve these goals. In reality, even a concert hall cannot satisfy the needs of every performance, much less a church sanctuary, a school theater or a multi-purpose room! When the acoustics are not sufficient, a sound reinforcement system is required.meaning microphones, mixers, amplifiers and speakers.Since musical sounds are complex, reinforcing them is a challenge. Quality equipment and a knowledgeable, experienced audio engineer are foundational to accomplishing this task.A good reinforcement system will provide a variety of microphones from which to choose. Once the microphones are selected, they must be positioned so that the sound captured has a pleasing tone color. The task of reinforcing a musical performance is complex, requiring quality equipment and a good engineer. Yet, that is not all that is required. You are needed, too! In most cases, the complexity of the setup and the intricacy of the adjustments make critical a "sound check".a dress rehearsal with the sound engineer to insure that everything has been done right. In general, judgements are quite different when it comes to the definition of sound, because everyone has his/hers own listening attitude and individual preferences. Also the music itself sets specific conditions. Measurable parameters, influencing the sound, are the room acoustic and the speaker system itself, i.e. the technology of the cabinet and speaker design. To get good sound out of your system, you need to have gooddevices and know how to properly use them. Here you canfind more than a few tips for this.Many common problems in PA systems are noise and distortion. Distortion can come from a LOT of places. It can come from improperconsole / effect / amp gain staging. It can come from clipping your poweramp. It can come from trying to make a weenie speaker do the job ofa stack of much larger and expensive speakers. You have got to knowwhere your problem really is before you can solve it.Noise to the system can generally get there through not well shielded cables or wrong signal sensitivity settings in the system (or just noisy sound source).Vital practice should be done in the performance setting shortly before the program. The engineer needs to hear the way you plan to sound when performing, so the musical pieces should be almost all ready. Many times, musicians work hard on their pieces while forgetting to rehearse with the engineer. On stage, the impact of the performance is diminished by feedback, abrupt volume changes, poor tone quality or a part being accidentally soloed out. All these effects lessen the quality of the presentation, disappointing the performer and reducing the audience.s enjoyment. A completed "sound check" almost eliminates the likelihood of these problems.

      Speakers and amplifiers

      Power amplifiers are deisgned to amplify the line level signal that enters to them to a signal strong enough to drive the speaker elements at the desired power. The relationship between a power amplifier and a loudspeaker is symbiotic, that is, each depends on the other. The wattage sent to the speaker by the amp determines the speakers output level while the impedance of the speaker determines the amplifiers load. As long as everything remaines within "normal" bounds, quality audio is produced. However, when one element falls outside the boundary, system damage may occur. When clipping occurs, several things can happen in a conventional amplifier. In extreme cases, protection circuits kick in. When amplifier is loaded with too low impedance load, the amplifier wil be overloaded, which will result (sooner or later) amplifier overheating (up to amplifier damage) or protection circuits to kick in. Amplifiers are typical rated according to their RMS power. Music and speech require very little RMS power, but have much higher instantaneous peaks. Most loudspeaker spec sheets show a Program rating that is double the RMS Wattage.Three options for matching amplifiers to loudspeakers:

      • 1. Match amplifier RMS output to speaker Program rating divided by two: Economical, and safe as long as the operator does not try to play the system louder than the amplifiers will go, which causes clipping and driver failure. The system will not be as loud and clean as it could be.
      • 2. Match amplifier RMS output to loudspeaker Program rating. This will give the loudest cleanest sound your loudspeakers can deliver. The most expensive and dangerous method, because instantaneous peaks can destroy the loudspeaker. A properly adjusted Peak Limiter is required to prevent this.
      • 3. Pick an amplifier with RMS power rating about 60% of speaker Program power. A good compromise between safety, economy and performance.
      Typically, providing 100% (3 dB) more power than the RMS rating of the speaker system produces the intended result. As a caveat, a hard limiter in conjunction with moderate compression will keep things from getting out of hand.

      Power amplifier have several controls. First, its imperative to understand that amplifier level controls are not "gain" controls. They do not control the amount of gain the amplifier produces. All power amplifiers are designed to produce a set amount of gain. The function of the level control knob is to adjust the signal level coming into the amplifiers input stage.Gain controls do not affect amplifier power. The amp has exactly the same power capability as with the controls turned up all the way; it just takes more signal level to hit full power. If the amplifier has a sensitivity setting, set it to match as closely as possible the output of our mixer and other gear (usually around 1.4v). Now turn on the amplifier and adjust the level controls to the desired sound level.Gain controls in aplifier allow you to optimize the gain structure of your audio system to maximize dynamic range and minimize noise and hum.

      Loudspeakers expect a source impedance somewhere near zero (a voltage source). Audio amplifier drive our speakers from essentially pure voltagesources, and the speakers are design to provide their responsefrom a constant voltage transfer, not a constant power transfer. Thus, as far as speaker systems are concerned, conjugate loadmatching is not only unnecessary, it's a bad idea. However, WITHIN speakers, conjugates are important becausepassive ladder-type crossovers ARE sensitive to the loadimpedance. Thus, in such cases, conjugate loadmatching IS used, and referred to as "zobel" networks.This is a matter internal to the speaker and one forthe designer of the speaker to deal with.Driving your typical speaker from typical voltage-cource amplifiersconjugate load matching simply is not an issue. A "mismatch"between the speaker and the rated load of the amplifier is notparticularly important unless you are trying for the ultimate inoutput power. If the speaker impedance is too high, the output levelwill be a bit low. If the impedance is low, you could get someoverheating in the amplifier.

      A considerable amount of distortion is caused when you try to make a modern a amplifier to give out more power than it can. This will sound bad. When an ideal amplifier clips, the input signal becomes flat-topped waves.Those flat-topped wave often but not always have more HF content than the input signal. The direction of the change depends on how much HF content the input signal hadto start with. The process of squaring sine waves tends to produce square waves which havea spectral content that falls off at 6 dB/octave. Modern music is often very bright, so in some cases clipping does nor cause the HF content so considerably cange.

      PA is designed for sound distribution. Our goal as professional sound engineers is to make quality sound delivery available to as much of the venue as possible or necessary. Speaker placement is integral to this end. Bass cabinets tend to be omnidirectional whereas upper cabinets tend to be uni-directional. Better cabinets are wedge designed to distribute sound in a wider pattern while maintaining a uniform appearance. Audio voids are to be avoided as much as possible.Today's pro grade speakers are designed by accoustical engineers and constructed to exacting specifications with the aid of computerized manufacturing techniques. Speaker arrays used to be sinonymous with flown, permanent speaker installation. PA manufacturers have adapted these advanced designs into an affordable, portable, road-worthy product.

      When connecting amplifiers to speakers look at the speaker impedance and the minimum impedance that the amplifier can handle. For example if your amplifier says that it's minimum impedance it can drive is 4 ohms, then you cna attach a spaker with impedance of 4 ohms or more to it safely. Attaching a spaker with higher imoedance than the imepdace to which amplifier is originally designed (the rated power is tols), just means that the available output power will tail offusually pretty linearly. If you attach a speaker with lower impedance than the minimum impedance of your amplifier, you risk in overloading and damaging your amplifier. Modern amplifiers generally work nicely without any load connected to them. Please note that some older amps don't like not having a load and canoscillate (those are rare, but such amplifiers have existed).

      Note on Hifi amplifier: Many home receivers/amplifiers have connections for two set of speakers. If those speakers are connected in parallel, many home amplifiers paralell the speakers! This meansthat two set of 8 ohm speakers show as one 4 ohm speaker load to the amplifier.With two sets of 4 ohm speakers you, this will be 2 ohm "nominal" loadto amplifier. Any home hifi amplifier/reciever will hate that load.

      There are many methods used to connect speaker cables to amplifiers. For amplifiers, the most popular termination device on professional products has been the dual banana. However, recent regulatory requirements in Europe have outlawed the use of the dual banana plug and forced users to terminate speaker cables with spade lugs or bare ends?an approach that is clearly not advantageous to the customer who wants to reconfigure his system or quickly change out a defective product. It is possible that similar regulatory controls will appear worldwide over the next few years. Neutrik? Speakon? connector is a special connector specifically designed for speaker connection applications (manufacturer says that it should not be used for other applications). The Speakon? connector meets all known safety regulations. Once wired correctly, the connector cannot be plugged in backwards, causing the type of inverted polarity situations that are common with banana hookups. It will provide a safe, secure and reliable method of interfacing your amplifier to the load. The Speakon? connector is nowadays widely used in professional audio field.

      On the audio amplifier market there are different kind of amplifiers, most important of them being PA amplifiers and HiFi amplifiers. PA amps tend to be optimized for heavy duty higher-power use. Hi-Fi amps tend to be designed for home use. PA amplifiers are designed usually so that they will deliver lots of power reliably to the load. PA amp will be designed for far greater output than a Hi-Fi amp. It may have a cooling fan which would be audible in a home situation. PA amps are frequently more noisy physically: mainly the cooling fans, but sometimes buzzing transformers, etc. This noise is not a problem in noisy environment where PA systems are generally use, nut could be annoying at home. The mechanics of PA amplifier is typically heavily built rack-mountable case that can take hard use on the road. PA amplifiers generally have professional audio connectors, typically balanced XLR connectors or 6.3 mm jacks. PA amps may have lower sensitivity (+4dB professional line level vs. -10dB consumer line level). This makes them more difficult to interface to things like consumer preamps, etc. A PA amp will normally be fed from a mixing board. A home system probably needs a front end with switching for various inputs. PA amps are frequently more noisy electrically: Optimizing them for high power sometimes involves trade-offs with low- level signal to noise ratios. Note that most PA amps are never heard at the distances and quiet ambience where Hi-Fi amps are usually found. Being a "PA" amplifier does not impart any inherent superiority or inferiority to any particular "Hi-Fi" amp in sound quality. There's absolutely no reason why a powerful PA amp can't sound perfectly smooth and detailed - and many of them do. The only downside is that they usually have quite noisy cooling fans. There are good and bad products on both categories. A small, quality PA amp can be a useful substitute for a Hi-Fi power amp.

      PA speakers are generally quite unsuitable for home listening. They're often designed to be loud, not to be smooth and detailed. PA speakers are also often designed in such way that they sound good on some distance, and still sound good on longer distance. A large PA speaker could sound very bad if you sit just few meter away from it. A lot of PA speakers sound rather rough in a living room. PA speakers may not be what you want for domestic music replay. Many PA speakers are designed with certain directivity pattern in mind more than very accurate frequency response, because controlled directivity is needed when building spaker system that consists of many speakers stacked or hanged together. If the directivity is not right in those situations, the overall sound quality will be bad. Slight frequency response errors can easily be fixed in PA system with a proper equalizer if needed. Mechanical construction of PA speaker is usually very rugged for life on the road.

      If you are lookign for good speakers for home use, you might find it interesting to look at speakers sold as studio monitors rather than ones sold as hi-end hi-fi. Even a medium-priced pair of nearfield monitors placed the right distance from your ears (a few feet) may give you a VERY pleasant surprise.

      And remeber always that you usually get what you pay for. Be aware that $1,000 is peanuts in the world of high-quality speakers. And when buying speakers it is always a good idea to listen to the speakers well with the intended material you plan to play for them before buying them. All speakers have their good and bad sides, some spakers are better for some uses than soem other, and no speaker will do all situations well.

        Amplifier specs and operation

        When people refer to "amplifiers," they're usually talking about stereo components or musical equipment. But this is only a small representation of the spectrum of audio amplifiers. Amplifier is in general just an electronic device that simply produces a more powerful version of the audio signal that is coming in to the amplifier. In other words the amplifier generates a new audio signal based on the input signal and the amplification factor defined to amplifier circuit (can be adjustable or fixed).

        The amplifiers are generally divided to preamplifier amplifiers. Pre-amplifier is an amplifier that takes a quite weak signal (typically from milliolts to few volts) and outputs an amplified signal (typically 1-4V signal level). The pre-amplifiers have often adjustable amplification factor (volume control) and possibly other controls (for example audio source selector, tone control etc.). Power amplifier is an amplifier that is designed to drive the speaker. It can supply the neeeded power to the speaker (signal level typically few volts to tens of volts and currents typically up to many amperes). In a small amplifier -- the amplifier in a speaker phone, for example -- the final stage might produce only half a watt of power. In a home stereo amplifier, the final stage might produce hundreds of watts. Output amplifiers are generally designed to have fixed amplification (some models have adjustable attenuators in front of final state). Most home hifi amplifier are devices where pre-amplifier and and power amplifier are built into same equipment. In professional amplifier world the pre-amplifiers are typically inside house mixer, and the amplifiers that drive the speaker include just the power amplifier part.

        The component at the heart of most amplifiers is the transistor. The goal of a good amplifier is to cause as little distortion as possible. The final signal driving the speakers should mimic the original input signal as closely as possible.

        There are many different kind of amplifiers and techniques for amplifiers. Sound enthusiasts are fascinated with variations in design that affect power rating, impedance and fidelity, among other specifications. The amplifier operation is generally divided to different amplifier classes:

        • CLASS A: The positive and negative output transistors each handle 100% of the audio signal- they are biased so their zero-signal output current idles halfway between zero and maximum. When the audio current in one transistor increases, the current in one transistor increases, the current in the other decreases; as a result, their voltage move together. In some designs (in preampkifiers for example) on the of the transformers is replaced with a resistor. The primary advantage of class-A operation is inherent lack of distortion. However, a serious flaw is the extreme heat loss at idle. Class A amplifiers are generally only used on pre-amplifiers and some "high-end hifi" amplifiers.
        • CLASS B: Class B amplifier has two output transformer, one for positive and other for negative half of the audio signal. So each transistor control only its half of the waveform. When the waveforms are combined properly, we still get the complete output waveform, but we have eliminated the large idle current. If the waveforms don?t joined together perfectly, we get annopying zero-crossing distortion (frequently called crossover distortion and heard as slight gargling or rattling sound during quiet parts of the program).
        • CLASS AB: One popular method is to compromise between class A and B and operate the amplifier in class AB. Bu permitting a small idle current to flow, we get a small amount of idle heat, but we eliminate any chance of "dead space" between the positive and the negative waveforms. Most professional and hifi power amplifiers nowadays operate in AB mode. This amoplifir class provides both acceptable power consumption and well acceptable sound quality.
        • CLASS C: When each transistor controls less than 50% of the waveform, we call this mode class C. This mode is not usable for audio.
        • CLASS G: This mode uses two or more sets of output transistors connected to different supply voltages. The goal is to reduce the heat loss in class A or B amplifiers. The main problem is to ensure seamless transfer from the low-voltage to the high-voltage transistors to avoid any small glitches similar to zero-crossing distortion, but this techniques has been successfully used on some amplifier (for example QSC Series Three and original QSC MX series)
        • CLASS H: This class uses a single bank or output transistors connected to a low-voltage supply, along with some means of switching them to a higher-voltage supply when required. This method has the same thermal benefits as class G, but it avoids the second bank of output transistors, thus reducing the size and cost of the amplifier. The QSC EX series uses this technique.

        The newest player in the aqmplifider game are so called "digital amplifiers". Sometimes those are referred as amplier classes D, E, F and T. The so-called "digital" or class "D" amplifiers use pulse-width modulation of a square wave that is then filtered to analog. A class-D amplifier is one in which the output transistors are operated as switches. When a transistor is off, the current through it is zero. When it is on, the voltage across it is small, ideally zero. In each case, the power dissipation is very low. This increases the efficiency, thus requiring less power from the power supply and smaller heat sinks for the amplifier. Pulse width modulation is a process that generates different length pulses. A square pulse can have any width: It can smoothly go from "always off" to "always on". The output pulse width is determines by the input signal voltage. The output filter "integrates the area under the curve" The speaker gets an analog signal, just like any other amplifier output. The advantages of class "D" are very high efficiency (lower power consumption and less heat) compared to traditional class "A", "AB" or "B" amplifiers. The have been around in experimental form since the '70s, but they seem to be gaining in popularity due to the large number of power amplifiers required for multichannel surround sound and because of power saving possible on the portable equipment. There has been also some trials in using the class D technology with professional audio amplifiers, and there has been some amplifiers that are built to very small case, weight almost nothing, do not need massive colling fans, and still generate considerable amount of power. The primary disadvantages of class D technolofy is the complexity and sound quality. The speed requirements for the switching transistors are 50 to 100 times greater than for linear audio amplifiers. The high-frequency switching causes radio interference, and many practical problems must be solved to attain the same audio fidelity that we expect with linear amplifiers. Today the class "D" switching amplifiers don't attain the performance of the highest quality traditional designs, but they might eventually. The complexity of the designs also nowadays causes the class D designs to be somewhat more expensive than traditional designs, but this is changing as this technology comes more and more in mass production. The term digital amps" is a misnomer. There are two categories: Analog-controlled class D (switching amplifiers with an analog input signal and an analog control system) and Digitally controlled class D (amplifiers with a digitally generated control that switches a power stage).

        All amplifiers have a maximum power limit. The voltage at the amplifier output can only go as high as the voltage in the dc power supply. If the signal tries to exceed this limit, it "hits the ceiling", and the waveform becomes flattened. This problem, called clipping because it looks like the top of the waveform has been clipped off, results in the familiar ?blatting? sound of an overdriven amplifier. Increasing the supply voltage adds cost and weight to the amplifier, so amplifier power has a big effect on price. Amplifiers have a minimum rated output impedance, which should be equal or less than the impedance of the loudspeaker load. As the impedance of the loudspeaker gets lower, more current will be drawn from the amplifier. This is why, up to a point, the amplifier power rating increases into lower impedances. However, the increased current puts a greater strain on the amplifier components and the power supply. At some minimum impedance, the strain will get so high that the power-supply voltage sags or the transistors overheat. Any further decrease in impedance will cause the amplifier circuitry to collapse, resulting in less power, or it could even cause amplifier failure.

        The ac power comes into the amplifier through the ac cord, is controlled by the on/off switch, and usually goes through a fuse or circuit breaker, which cuts off ac power in case of massive overload. It then reaches the power transformer, which is in the heart of the power supply. The simplest and least expensive transformer is the E-I type, which is generally cubic-shaped (roughly equal height, length, and width). This type is widely used. The U-I type is more expensive, but it is easier to make in a flatter shape that can fit into low-profile amplifiers. The toroidal type is built on a donut-shaped core, which has the best magnetic properties. It can be made quite flat, it weighs somewhat less and is has low hum emissions, but it is the most expensive. Once we have scaled and isolated the ac power through a transformer, it is rectified with a rectifier. Typical large capacitors are connected to the output of the rectifier. The capacitor fills, or charges up, to the peak voltage of the rectified wave-form. If the capacitor is large enough, it stays pretty full between the peaks, and we get an almost perfectly smooth dc voltage. The size and weight of power-supply components has been somewhat reduced over the last 20 years, but progress has been slow because we are only refining the same basic technology.

        The only great change in power supply technology has been switch mode power supply used on some amplifiers. A switch more power supply first rectifies the incoming ac and smooth it with capacitors. Then high-speed switching transistors to convert the dc power to a high-frequency ac waveform that is passed through the switchign transformers. The switch mode power supplies typically operate at 50kHz to 100kHz frequency. Higher freuquency needs a specially constructed amplifier but allows usigg a smaller size transformer. In addition to the primary benefit of greatly reduced weight, switch mode power supplies can control the operation of the high-frequency transistors to compensate for variations in ac voltage and load currents, thus improving both kinds of power-supply regulation. The ultimate result will be more consistent amplifier performance, but the audio industry must solve problems of cost, reliability and radio/TV interference caused by the high-frequency switching.

        Many amplifier use protection circuitry. The lower the impedance of the load, the greater the current drawn from the amplifier, and the greater the heat generated in the output transistors. If too many loudspeakers are connected to the amplifier, or if the ends of the loudspeaker wire touch together by accident, the load impedance goes very low, and the current flow becomes dangerously high. If the flow is not limited, the output transistors will burn out. Therefore, amplifiers need some kind of short-circuit protection. There are also other thing where protection is needed. Common protective circuits include turn-on and turn-off muting, shut-down or muting in case of excessive temperature, protection against radio pickup (RFI), and dc fault protection.

        Speaker specs

        The ohms in a loudspeaker's specification tells you in broad terms whetherthe 'speaker will suit your amplifier. Ohm is a measure of resistance (ormore accurately for alternating currents, impedance) The higher the number,the higher the resistance, and therefore the less current the 'speaker willdraw.Today, most speakers are rated at 8 ohms, some at 4 ohms, so today'samplifiers tend to be designed to work with 'speakers of nominal impedance4-8 ohms.Speaker impedance ratings are very "nominal" and most'speaker's impedance will go down by almost half its rating, and up byseveral times it's rating depending on the design. The nominal power for speakers is defined as the continous power that can be applied to the speaker for 24 hours. This nominal power is measured by pink noise signal. The nominal power is applicable to both a single chassis/driver and complete box. Sometimes nominal power is also referred as thermal power, (according AES/ANSI specs). The maximum power is defined for woofers and boxes only. It is measured by applying sinusoidal signals of 250 Hz and lower such that the speaker is neither damaged nor produces unwanted output.

        Distributed speaker systems

        100V- or 70V-Systems are referred to as 'constant-voltage distributed audio systems'. The constant voltage system is the most economical way to install a multi-speaker sound reinforcement system. This was typically used (years ago) to power large numbers of horn type speakers in outdoor events and as a cheap and cheerful way of running speakers for musack purposes around large buildings or even show relays. This system is still used nowadays for some applications because it allows many speakers to be attached to one amplifier without running into impedance problems. In an installation where you need to run a large number of lower volume loudspeakers, such as a paging system, a restaurant background music system, or a church install, the easiest solution is often a 70-volt speaker distribution system. 70V/100V line systems are easy to wire, easy to expand and are still used in a major way in factories, shopping centres, schools and other environments to this day to play background music, do paging and for evacuation systems.

        The term "100V system" or "70V system" relates to the maximum output voltage of the amplifier. 100V is the usual voltage in Europe, 70V in the United States. The actual voltage used is pretty much the highest local regulations don't consider mains so in the EU we mainly use 100v, presumably in the US the cut offs 70V. A higher voltage up to 200V can be used too for very long cable runs and higher power requirements. To generate this high voltage, the amplifier is equipped with a step-up transformer, which transforms the regular output voltage, in the 15 to 30 Volts range, up to the necessary 100V or 70V respectively. There are direct 70 volt amps out there, and there are normal amps powering the 70 volt systems. A bigger amp can deliver more current and hence drive more speakers, but it won't be any louder with a same set of speakers.

        The main difference to a regular low-impedance system (4 or 8 Ohms) is the way, individual loudspeakers are connected to the loudspeaker line. A large number of single loudspeakers, each equipped with a step-down transformer, can be connected to one single output line. Individual speakers have transformers of suitable ratios to draw their rated power from the line. Each speaker's step-down transformer has a relative high impedance at the primary side to connect to the 100V line. The secondary side of the transformer matches to the speaker itself (mostly 8 Ohms). There are speakers with multi-tap tranformers and volume controls in them, so with suitable speakers it is possible to adjust the volume levels of different speakers locally without affecting the rest of the system operation.

        Also a much smaller wire diameter (AWG) can be used in 70/100V than in a low-impedance system, because increasing voltage and decreasing current minimizes the amount of current flowing in the wire. This solution was borrowed from the electrical power line distribution system years ago. Requirements for long audio distribution came about and the 25 and 70 volt line levels were developed for this purpose. The higher the distribution voltage the lower the losses because of the resistance of the wire to the speakers.A distribution transformer is required to step up the output voltage of the amplifier so that the current flow is kept as low as possible. 25V, 70V, 100V and sometimes even more than 200V are used.

        Many loudspeakers can be placed across the output by using distribution transformers. The input taps of the distribution transformer let one choose the power drawn from the line and the output taps let choose the connected loudspeaker (4 Ohms, 8 Ohms, 16 Ohms). The downside of the use of those transformers is, that they always degrade the sound quality in a certain way (especially the low end). Most audio transformers pass a low frequency of 100 Hz without major loss. If the amplifier is producing power at 30 Hz and feeding it to the transformer it will saturate the core and reflect a short to the amplifier resulting in a loud, possibly damaging, surge or crack to the speaker or a blown speaker fuse on the amplifier. So you won't get big thumping bass or very high output powers with a 70/100V system, but there are many applications that do not need those properties.

        The 70 volt system offers the following benefits compared to "low impedance" system: Lots of speakers on one amp, no need to home run each speaker, higher voltage allows use of smaller wire, speakers can easily be added and removed, economical, no need to calculate impedance (just total power) and EASY to design. Disadvantages of 70 Volts system are: Limited frequency response and the system is considered high voltage by codes.

        There are many commercial products that operate at a constant voltages using transformers. Usually found in 25V, 70V and 100V sizes, these transformers are connected to the amplifier on the primary side and then send one pair of relatively thin stranded wire from device to device. In the case of the 70V audio transformer, a mono audio signal is fed and kept at a constant 70V signal. The 70V voltage is either generated directly with a special amplifier with 70V output, or using conventional 4/8 ohm power amplifier wired to suitable transformer to boost up the voltage to 70V.

        The 70V keeps the signal from degrading but does not have the same fidelity associated to a standard 4 or 8 Ohm system connection. Less wire, longer distances without degradation, better coverage capabilities and easy installation.

        The speakers used in these constant voltage systems will have a transformer with connections called taps. Taps (usually you can find find multiple choices) on those transformers are based on a Wattage specification. The number of speaker transformers and the size of amplifier connected at the head end determine what tap is used. You will be surprised at the amount of volume available from a one Watt tap. In most cases, the sound systems you see in malls, amusement parks, office building and paging systems use this form of wiring at low wattage taps. If you need to adjust the volumes on different speakers different, you can tune the soudn putput levels by selecting different wattage taps.

        Distributed audio systems are often mono systems. The fact that the system is mono does not mean that sound is "bad" or AM quality. The audio quality of mono system can be as clear as with a stereo system, is it just lacking the "stereo image". Often time?s a mono signal will provide you with more information and more fidelity than a stereo signal in applications where multiple speakers are used and listeners are not in the "sweet spot" for sound (stereo sound will sound good only on limited "sweet spot" are between left and right channel speakers).

      Compressors, limiters anf gates

      The audio compressor, is a pretty useful item, and one which you need to add to your system at some point if you are recording any type of audio, but especially vocals. The Compressor automatically adjusts and maintains the signal levels as they go to H/Disk or Tape to be recorded. If you use a normal compressor, nothing occurs until the threshold is breached. But when that happens, the compression cuts in. On a Hard Knee compressor, this full amount of compression (as set by the Ratio) is applied in full, as soon as the input level rises above the threshold. Lets say you have set a RATIO of 4:1, this means that compressor allows only 1db of signal level increase at the output, for every 4 db in input singnal level rise above the threshold setting.Soft Knee compressors apply compression gradually as the signal approaches the threshold level. As the input signal gets within about 10db of the threshold level, the Soft Knee compressor starts to gently apply compression, but with a very low Ratio, which increases proportionately as the Input level gets nearer to the Threshold setting, so that by the time the Input level actually reaches the Threshold level, the compressor is applying its gain reduction at the full level as set by the Ratio Control.Hard Knee compressor is the most commonly used compressor type.Some units allow you to switch between a Hard & Soft Knee function.

      Equalizing

      Equalization means selectively boosting or cutting bands of frequencies to improve the performance of a sound reinforcement system. Equalization can do when used properly:

      • Improve the naturalness or intelligibility of a sound reinforcement system by emphasizing the frequency ranges most critical for speech (improveme