A Detailed Guide To Constant-Voltage ("70v") Audio Systems

Clarifying and defining key power aspects with constant-voltage (or high-impedance) systems
crown

Electric power companies have a good idea that has been applied to audio engineering.

When they run power through miles of cable, they minimize resistive power loss by running the power as high voltage and low current.

To do this, they use a step-up transformer at the power station and a step-down transformer at each customer’s location. This reduces power loss due to the I2R heating of the power cables.

The same solution can be applied to audio communications in the form of a constant-voltage system (typically 70 volts in the U.S. and 100V overseas).

Such a system is often used when a single power amplifier drives many loudspeakers through long cable runs (over 50 feet). Some examples of this condition are distributed speaker systems for PA, paging, or low-SPL background music.

BACKGROUND
The label “constant voltage” has been confusing because the voltage is really not constant in an audio program. A better term might be “high impedance.”

A typical high-impedance system is shown in Figure 1. A transformer at the power amplifier output steps up the voltage to approximately 70 volts at full power.

Each loudspeaker has a step-down transformer that matches the 70-volt line to each loudspeaker’s impedance.

The primaries of all the loudspeaker transformers are paralleled across the transformer secondary on the power amplifier.

Figure 1. A typical high-impedance system using a step-up transformer on the amplifier output.

There are three options at the power-amp end for 70-volt operation:
• an external step-up transformer
• a built-in step-up transformer
• a high-voltage, transformerless output

These options are covered in detail later in this article.

The signal line to the loudspeakers is high voltage, low current, and usually high impedance. Typical line values for a 100-watt amplifier are 70 volt, 1.41 amperes, and 50 ohms.

How did the 70-volt line get its name? The intention was to have 100-volt peak on the line, which is 70.7 volts rms.

The technically correct value is 70.7 volt rms, but “70-volt (or “70V") is the common term. There are 70 volts on the line as maximum amplifier output with a sine wave signal. The actual voltage depends on the power amplifier wattage rating and the step-up ratio of the transformer. The audio program voltage in a 70V system might not even reach 70V. Conversely, peaks in the audio program might exceed 70V.

Other high-voltage systems might run at other voltages. Although rare, the 200V system has been used for cable length exceeding one mile.

ADVANTAGES OF 70V OPERATION
As stated before, a 70V line reduces power loss due to cable heating.

That’s because the loudspeaker cable carries the audio signal as a low current.

Consequently you can use smaller-gauge loudspeaker cable, or very long cable runs, without losing excessive power.

Another advantage of 70V operation is that you can more easily provide the amplifier with a matching load. Suppose you’re connecting hundred of loudspeakers to a single 8-ohm amplifier output. It can be difficult to wire the loudspeakers in a series-parallel combination having a total impedance of 8 ohms.

Also it’s bad practice to run loudspeakers in series because if one loudspeaker fails, all of the loudspeakers in series are lost. This changes the load impedance seen by the power amplifier.

With a 70V system you can hang hundreds of loudspeakers in parallel on a single amplifier output if you provide a matching load. Details of impedance matching are covered later. In addition, a 70V distributed system is relatively easy to design, and allows flexibility in power settings.

Let’s compare a standard low-impedance system to a constant-voltage system. Imagine that you want to provide PA for a runway at an airshow. A low-impedance system might employ 30 speaker clusters spaced 100 feet apart, each cluster powered by a 1000W amplifier for extra headroom. A high-impedance version of that system might use only one amplifier providing 140V. The cost savings is obvious.

DISADVANTAGES OF 70V OPERATION
One disadvantage of a 70V system is that the transformers add expense. Particularly if you use large transformers for extended low-frequency response, the cost per transformer may run $70 to $200. Low-power paging systems, or those with limited low-frequency response, can use small transformers costing around $4.95 each. Many loudspeakers are sold with 70V transformers included.

Another disadvantage is that transformers can degrade the frequency response and add distortion. In addition, a 70V line may require conduit to meet local building code.

TRANSFORMERS
The main component of a 70V system is the loudspeaker transformer.

Its secondary winding has taps at various impedances. You choose the tap that matches the loudspeaker impedance.

For example, if you’re using a 4-ohm loudspeaker, connect it between the 4-ohm tap and common.

The primary winding has taps at several power levels. These power taps indicate how much maximum power the loudspeaker receives. For example, suppose you have a 70V transformer with the primary tapped at 10W and the secondary tapped at 8 ohms. Then a loudspeaker rated at 8 ohms should receive 10W at its voice coil when the primary is connected to a 70V line.

Transformers have insertion loss mainly due to resistance. Precise system calculations should take insertion loss into account. These calculations are covered in the Appendix later in this article.

INSTALLATION
With this background in mind, let’s proceed to installation practices. Here’s a basic procedure that neglects transformer insertion loss:
1. Do NOT connect the 70V loudspeaker line to the power amplifier yet.
2. Install a transformer at each loudspeaker location, or use loudspeakers with built-in transformers.
3. Connect each loudspeaker to its transformer secondary tap. The tap impedance should equal the loudspeaker impedance.
4. Connect each transformer primary to the 70V line from the power amplifier. Choose the tap that will deliver the desired wattage to that loudspeaker.
5. Add the wattage ratings of all the primary taps. This sum must not exceed the amplifier’s wattage rating. If it does, change to a lower-wattage primary tap of one or more transformers, or use a higher power amplifier.
6. Connect the 70V loudspeaker line to the 70V output of the amplifier.

As an example, suppose you are setting up a 70V system with 8-ohm loudspeakers and a 60W power amp. Connect the 8-ohm secondary taps to each speaker. Suppose the total loudspeaker wattage is 55 watts. This is acceptable because it does not exceed the amplifier power rating of 60 watts.

Here’s a more detailed procedure that emphasizes impedance matching:
1. Compute the minimum safe load.

The minimum safe load impedance that can be connected to the amplifier is given by:

where
Z = minimum safe load impedance, in ohms.
E = loudspeaker line voltage (25V, 70.7V, 100V, etc.)
P = maximum continuous average power rating of power amplifier, in watts.

An example: For an amplifier rated at 100 watts continuous average power, the minimum load impedance that may be connected safely to the 70.7V output is:

2. Choose transformer taps.
Tap the primary at the desired power level for the loudspeaker, and tap the secondary at the impedance of the loudspeaker. The sum of all the power taps for all the loudspeakers should not exceed the power output of the amplifier.

Note: Changing the power tap also changes the load impedance seen by the amplifier. Raising the power tap lowers the load impedance, and vice versa.

Also, changing the power tap changes the SPL of the loudspeaker. Reducing the power tap by half reduces the SPL by 3 dB, which is a just-noticeable difference in speech sound level.

If a particular loudspeaker is too loud or too quiet, you can change its power tap. Just be careful that the total power drain does not exceed the power output of the amplifier.

3. Connect the loudspeakers together.
Connect all the loudspeaker-transformer primaries in parallel. Run a single cable, or redundant cables, back to the power-amplifier transformer secondary. But DON’T CONNECT IT YET.

4. Measure the load impedance.
Before connecting the load, first measure its impedance with an impedance bridge (a simple low-cost unit is adequate). Here’s why you must do this: If the load impedance is too low, the power amplifier will be loaded down and may overheat or distort. It’s a myth that your can connect an unlimited number of loudspeakers to a 70V line.

If the load impedance measures too low, re-tap all of the loudspeakers at the next-lower power tap. This raises the load impedance. Measure again.

Usually, it’s no problem if the load impedance measures higher than the matching value (the calculated minimum safe load impedance). The system will work, but at reduced efficiency. Typically there is more than enough power available, so efficiency is not a problem.

If for some reason power the power is limited, then the system should be wired for maximum power transfer. This occurs when the measured load impedance matches the calculated minimum safe load impedance. If the load impedance measures above this value, you can re-tap all the loudspeakers at the next-higher power tap and measure again. This tap change lowers the load impedance.

Many people don’t realize that a transformer labeled for use with a specific voltage will work just as well at other voltages. See the constant voltage calculator here. It determines the power delivered from a transformer tap when driven with other than the rated voltage.

PRECAUTIONS
Since a 70V line is relatively high-impedance, it is more sensitive to partial shorts than a low-impedance line. Consequently, you may want to avoid running 70V lines in underground conduit which may leak water.

Use high-quality transformers with low insertion loss. Otherwise, the power loss in the transformer itself may negate the value of the 70V system.

Avoid driving small transformers past their nominal input voltage rating. Otherwise, they will saturate, draw more than the indicated power (possibly overload the amplifier) and will distort the signal.
You may want to insert a high-pass filter ahead of the power amplifier to prevent strong low-frequency transients which can cause core saturation.

The CTs amplifiers include a high-pass filter that can be selected at 70 Hz, 35 Hz, or bypass. The CH amplifiers insert a 70 Hz high-pass filter when placed in high-impedance mode.

POWER-AMPLIFIER OPTIONS
As stated earlier, there are three power-amplifier options for 70V operation: The amplifier might have:
• an external step-up transformer
• a built-in step-up transformer
• a high-voltage, transformerless output

Let’s consider each option.

Amplifier with external transformer
This system is shown in Figure 1 (on page 1). If you use an external transformer, select one recommended or supplied by the amplifier manufacturer.

If you have a conventional amplifier with low-impedance outputs only, and you want 70V or 100V operation, Crown has the needed accessories. The TP-170V is a panel with four built-in autoformers that convert four low-impedance outputs to high impedance. The T-170V is a single autoformer for the same purpose.

Choose a transformer with a power rating equal to or exceeding the wattage of the power amplifier. The turns ratio should be adequate to provide 70.7V at the secondary when full sine-wave power is applied to the primary. Use the following formula for a 70.7V line:

where
T = turns ratio
70.7 = voltage of constant-voltage line
P = amplifier power output in watts
Z = amplifier rated impedance
SQR means square root

Better yet, measure the amplifier’s output voltage at full power into its rated load impedance, and use the formula:

where
T = turns ratio
70.7 = voltage of constant-voltage line
E = measured output voltage at full power into the rated impedance.
Amplifier with built-in transformer
If the transformer is already built into the power amplifier, simply look for the output terminal labeled “70V,” “25V,” “100V,” or “high impedance.”

Amplifier with transformerless, high-voltage output
Figure 2 shows how a power amplifier with a high output voltage can power a distributed system without a step-up transformer.

Figure 2. A constant-voltage system using a high-voltage power amplifier.

Many high-power amplifiers can drive 70V lines directly without an output transformer. For example, Crown CH amplifiers have an auto transformer (except CH 4). CTs amplifiers can provide direct constant-voltage (70V/100V/140V/200V) or low-impedance (2/4/8 ohm) operation.

In Dual Mode, the CTs 600/1200 can power 25/50/70V lines; the CTs 2000/3000 can power 25/50/70/100V lines. In Bridge-Mono mode, the CTs 600/1200 can power 140V lines; the CTs 2000/3000 can power 140V and 200V lines.

With CTs Series amps, one channel can drive low-impedance loudspeakers, while another channel drives loudspeakers with 70V transformers. This makes it easy to set up a system with large, low-Z loudspeakers for local coverage and distributed 70V loudspeakers for distant rooms—all with a single amplifier.

The Crown CTs 2000 adept at providing constant power levels into various loads. In dual mode, it delivers 1000 watts into 2/4/8 ohms and into a 70V line. In bridge-mono mono, it delivers 2000 watts into 4, 8, or 16 ohms, 2000 watts into a 140V line, and 2000 watts into a 200V line.

Crown Commercial Audio series of amplifiers and mixer-amps provide both low-Z and constant-voltage operation. For example, the 180MA and 280MA mixer-amps offer 4-ohm, 70V and 100V outputs.

Pros and cons of transformerless systems
The high-voltage, transformerless approach eliminates the drawbacks of amplifier transformers:
• cost
• weight
• limited bandwidth
• distortion
• core saturation at low frequencies.

On the other hand, transformers are useful to prevent ground loops, ultrasonic oscillations and RFI. Some local ordinances require transformer-isolated systems.

Let’s look at the core-saturation problem in more detail. Sound systems can generate unwanted low frequencies, due to, say, a dropped microphone or a phantom-powered mic pulled out of its connector.

Low frequencies at high power tend to saturate the core of a transformer. The less the amount of iron in the transformer, the more likely it is to saturate.

Saturation reduces the impedance of the transformer, which in turn may cause the amplifier to go into current limiting. When this occurs, negative voltage spikes are generated in the transformer that travel back to the amplifier—a phenomenon called flyback. The spikes cause a raspy, distorted sound. In addition, the extreme low-impedance load might cause the power amplifier to fail.

Some Crown amplifiers are designed with high-current capability to tolerate these low-frequency stresses.

Production amplifiers are given a “torture test.” Each amplifier must deliver a 15-Hz signal at full power into a saturated power transformer for 1 second without developing a hernia!

Many transformers are reactive, so their impedance varies with frequency. Some 8-ohm transformers measure as low as 1 ohm at low frequencies. That’s another reason for specifying an amplifier with high current capability.

CONCLUSION
Using a high-voltage system greatly simplifies the installation of multiple-loudspeaker PA systems. It also minimizes power loss in the loudspeaker cables. If you take care that your load does not exceed the power and impedance limits of your power amplifier, you’ll be rewarded with a safe, efficient system.

APPENDIX: HISTORY OF CONSTANT-VOLTAGE SYSTEMS
In early industrial sound systems, multiple loudspeakers were carefully configured to provide a matching impedance load to the amplifier. But as these systems grew in size, several problems arose: how to connect multiple loudspeakers to the same amplifier without loading it down, how to individually control the sound power level fed to those loudspeakers, and how to overcome the power loss associated with the typically long lines that ran between the power amp and loudspeakers.

By the late 1920s and early 1930s the “step-up, step-down” idea has been applied to loudspeaker lines in what has become known as “constant voltage” distributed systems. (Radio Physics Course 2nd Ed., Radio Technical Publishing co., N.Y., 1931).

Various voltages have been tried such as 25, 35, 50, 70, 100, 140, and 200 volts, but the 70V system has become the most widespread.

After World War II, we find constant-voltage systems depicted in such reference works as Radio Engineering 3rd Ed. (McGraw-Hill, N.Y., 1947). By the end of that decade, several standards had evolved to regulate 70V specifications for amplifiers and transformers. (Radio Manufacturer’s Association, SE-101-A And SE-106, both from July 1949). In the 1950’s we find the use of 70V systems very well established as evidenced by Radiotron Designer’s Handbook 4th Ed. (RCA, N.J., 1953 and Radio Engineering Handbook 5th Ed. (McGraw-Hill, N.Y., 1959).

As component design improved, 70V systems began to achieve high-fidelity status, but there were two weak links in the chain: the step-up and step-down transformers. Good broadband transformers that could resist core saturation and distortion were expensive.

Half of this problem was solved in 1967 When Crown International introduced the DC-300. It was most likely the first high-powered low-distortion solid-state power amplifier capable of directly driving a 70V line without a step-up transformer. And in June 1987, the Macro- Tech 2400 was introduced with the capability of directly driving a 100V line. Thus, today only loudspeaker needs a transformer to step down the voltage.

APPENDIX: TRANSFORMER INSERTION LOSS
Transformers have insertion loss (power loss due mainly to resistance). This loss should be included in system calculations for precision.

Converted to a power ratio, insertion loss can be expressed as

PR = 10 (L/10)

where
PR = power ratio
L = insertion loss in dB (always a positive number).

Some transformer manufacturers compensate for insertion loss by adding extra windings. In that case, the power delivered to the loudspeaker is the rated value of the tap. The primary draws the rated power times the power ratio of the insertion loss.

In this case, you can calculate the primary impedance as follows:

Pt = Ps + L

where
Pt = total power in dBm
Ps = power to the loudspeaker in dBm
L = insertion loss in dB

or

Pt = Ps * L

where
Pt = total power in watts
Ps = power to loudspeaker in watts
L = insertion loss (as a ratio).

Then the primary impedance is calculated as follows:

Z = (70.7)2/Pt = 5000/(Ps * 10(L/10))

where
Z = primary impedance in ohms
Pt = total power in watts
Ps = power to loudspeaker in watts
L = insertion loss in dB.

Other transformer manufacturers do not compensate for insertion loss. In this case, the primary impedance matches its rating. However, the power delivered to the loudspeaker is less than the power applied, due to the insertion loss.

Ps = Ptr/L

where
Ps = power to loudspeaker in watts
Ptr = power drawn by transformer in watts
L = insertion loss (as a ratio)

To determine whether a transformer is compensated, measure the power (E2/Z) delivered to the loudspeaker when connected to 70.7 volts. If it is less than the rated power, the transformer is not compensated for insertion loss.

When making loudspeaker SPL calculations based on sensitivity ratings, subtract the insertion loss in dB from the loudspeaker sensitivity rating (if the transformer is not compensated for insertion loss). In transformers that compensate for insertion loss, the speaker receives the power indicated. Consequently, each transformer draws a little more power from the line than is indicated. The final impedance will be too low if you add power equal to the amplifier power.

With non-compensated transformers, the labeled power is not the power received, so the loudspeaker SPL will be lower than calculated. The impedance will read correctly, but the acoustic output will be lower than expected.

APPENDIX: LINE LOSS
See the line loss calculator here.

REFERENCES
Daniels, Drew. Notes on 70-Volt and Distributed System Presentation, db, March/April 1988.

Davis, Don. Sound System Engineering, 2nd Ed., Indianapolis, Howard W. Sams Co., 1987, pp. 85-87, 402- 405. 138905-1 10-05

This article provided by Crown Audio, via ProSoundWeb.

Understanding Constant-Voltage ("70v") Audio Distribution Systems

25, 70.7 & 100 Volts; U.S. Standards; Just What is "Constant" Anyway?; Voltage Variations -- Make Up Your Mind; Calculating Losses -- Chasing Your Tail

by Dennis A. Bohn

constant voltage
Constant-voltage is the common name given to a general practice begun in the late 1920s and early 1930s (becoming a U.S. standard in 1949) governing the interface between power amplifiers and loudspeakers used in distributed sound systems.

Installations employing ceiling-mounted loudspeakers, such as offices, restaurants and schools are examples of distributed sound systems.

Other examples include installations requiring long cable runs, such as stadiums, factories and convention centers.

The need to do it differently than you would in your living room arose the first time someone needed to route audio to several places over long distances. It became an economic and physical necessity. Copper was too expensive and large cable too cumbersome to do things the home hi-fi way.

Stemming from this need to minimize cost, maximize efficiency, and simplify the design of complex audio systems, thus was born constant-voltage. The key to the solution came from understanding the electric company cross-country power distribution practices. They elegantly solved the same distribution problems by understanding that what they were distributing was power, not voltage.

Further they knew that power was voltage times current, and that power was conserved. This meant that you could change the mix of voltage and current so long as you maintained the same ratio: 100 watts was 100 watts—whether you received it by having 10 volts and 10 amps, or 100 volts and 1 amp. The idea bulb was lit. By stepping-up the voltage, you stepped-down the current, and vice-versa.

Therefore to distribute 1 megawatt of power from the generator to the user, the power company steps the voltage up to 200,000 volts, runs just 5 amps through relatively small wire, and then steps it back down again at, say, 1000 different customer sites, giving each 1 kilowatt. In this manner large gauge cable is only necessary for the short direct run to each house. Very clever.

Applied to audio, this means using a transformer to step-up the power amplifier’s output voltage (gaining the corresponding decrease in output current), use this higher voltage to drive the (now smaller gauge wire due to smaller current) long lines to the loudspeakers, and then using another transformer to step-down the voltage at each loudspeaker. Nothing to it.

U.S. Standards—Who Says?
This scheme became known as the constant-voltage distribution method. Early mention is found in Radio Engineering, 3rd Ed. (McGraw-Hill, 1947), and it was standardized by the American Radio Manufacturer’s Association as SE-101-A & SE-106, issued in July 1949 [1]. Later it was adopted as a standard by the EIA (Electronic Industries Association), and today is covered also by the National Electric Code (NEC) [2].

Basics—Just What is “Constant” Anyway?
The term “constant-voltage” is quite misleading and causes much confusion until understood. In electronics, two terms exist to describe two very different power sources: “constant-current” and “constant-voltage.”

Constant-current is a power source that supplies a fixed amount of current regardless of the load; so the output voltage varies, but the current remains constant.

Constant-voltage is just the opposite: the voltage stays constant regardless of the load; so the output current varies but not the voltage. Applied to distributed sound systems, the term is used to describe the action of the system at full power only. This is the key point in understanding. At full power the voltage on the system is constant and does not vary as a function of the number of loudspeakers driven, that is, you may add or remove (subject to the maximum power limits) any number of loudspeakers and the voltage will remain the same, i.e., constant.

The other thing that is “constant” is the amplifier’s output voltage at rated power—and it is the same voltage for all power ratings. Several voltages are used, but the most common in the U.S. is 70.7 volts rms. The standard specifies that all power amplifiers put out 70.7 volts at their rated power. So, whether it is a 100 watt, or 500 watt or 10 watt power amplifier, the maximum output voltage of each must be the same (constant) value of 70.7 volts.

Figure 1 diagrams the alternative series-parallel method, where, for example, nine loudspeakers are wired such that the net impedance seen by the amplifier is 8 ohms. The wiring must be selected sufficiently large to drive this low-impedance value.

image

Applying constant-voltage principles results in Figure 2. Here is seen an output transformer connected to the power amplifier which steps-up the full-power output voltage to a value of 70.7 volts (or 100 volts for Europe), then each loudspeaker has integrally mounted step-down transformers, converting the 70.7 volts to the correct low-voltage (high current) level required by the actual 8 ohm speaker coil.

image

It is common, although not universal, to find power (think loudness) taps at each speaker driver. These are used to allow different loudness levels in different coverage zones. With this scheme, the wire size is reduced considerably from that required in Figure 1 for the 70.7 volt connections.

Becoming more popular are various direct-drive 70.7 volt options as depicted in Figure 3. The output transformer shown in Figure 2 is either mounted directly onto (or inside of) the power amplifier, or it is mounted externally.

image

In either case, its necessity adds cost, weight and bulk to the installation. An alternative is the direct-drive approach, where the power amplifier is designed from the get-go (I always wanted to use that phrase, and I sincerely apologize to all non-American readers from having done so) to put out 70.7 volts at full power. An amplifier designed in this manner does not have the current capacity to drive 8 ohm low-impedance loads; instead it has the high voltage output necessary for constant-voltage use—same power; different priorities.

Quite often direct-drive designs use bridge techniques which is why two amplifier sections are shown, although single-ended designs exist. The obvious advantage of direct-drive is that the cost, weight and bulk of the output transformer are gone. The one disadvantage is that also gone is the isolation offered by a real transformer. Some installations require this isolation.

Voltage Variations—Make Up Your Mind
The particular number of 70.7 volts originally came about from the second way that constant-voltage distribution reduced costs:

Back in the late ‘40s, UL safety code specified that all voltages above 100 volts peak ("max open-circuit value") created a “shock hazard,” and subsequently must be placed in conduit—expensive—bad.

Therefore working backward from a maximum of 100 volts peak (conduit not required), you get a maximum rms value of 70.7 volts (Vrms = 0.707 Vpeak). [It is common to see/hear/read “70.7 volts” shortened to just “70 volts”—it’s sloppy; it’s wrong; but it’s common—accept it.]

In Europe, and now in the U.S., 100 volts rms is popular. This allows use of even smaller wire. Some large U.S. installations have used as high as 210 volts rms, with wire runs of over one mile.

Remember: the higher the voltage, the lower the current, the smaller the cable, the longer the line. [For the very astute reader: The wire-gauge benefits of a reduction in current exceeds the power loss increases due to the higher impedance caused by the smaller wire, due to the current-squared nature of power.]

In some parts of the U.S. safety regulations regarding conduit use became stricter, forcing distributed systems to adopt a 25 volt rms standard. This saves conduit, but adds considerable copper cost (lower voltage = higher current = bigger wire), so its use is restricted to small installations.

Calculating Losses—Chasing Your Tail
As previously stated, modern constant-voltage amplifiers either integrate the step-up transformer into the same chassis, or employ a high voltage design to direct-drive the line. Similarly, constant-voltage loudspeakers have the step-down transformers built-in as diagrammed in Figures 2 and 3.

The constant-voltage concept specifies that amplifiers and loudspeakers need only be rated in watts. For example, an amplifier is rated for so many watts output at 70.7 volts, and a loudspeaker is rated for so many watts input (producing a certain SPL). Designing a system becomes a relatively simple matter of selecting speakers that will achieve the target SPL (quieter zones use lower wattage speakers, or ones with taps, etc.), and then adding up the total to obtain the required amplifier power.

For example, say you need (10) 25 watt, (5) 50 watt and (15) 10 watt loudspeakers to create the coverage and loudness required. Adding this up says you need 650 watts of amplifier power—simple enough—but alas, life in audioland is never easy. Because of real-world losses, you will need about 1000 watts.

Figure 4 shows the losses associated with each transformer in the system (another vote for direct-drive), plus the very real problem of line-losses. Insertion loss is the term used to describe the power dissipated or lost due to heat and voltage-drops across the internal transformer wiring. This lost power often is referred to as I2R losses, since power (in watts) is current-squared (abbreviated I2) times the wire resistance, R.

image

This same mechanism describes line-losses, since long lines add substantial total resistance and can be a significant source of power loss due to I2R effects. These losses occur physically as heat along the length of the wire.

You can go to a lot of trouble to calculate and/or measure each of these losses to determine exactly how much power is required [3], however there is a Catch-22 involved: Direct calculation turns out to be extremely difficult and unreliable due to the lack of published insertion loss information, thus measurement is the only truly reliable source of data.

The Catch-22 is that in order to measure it, you must wait until you have built it, but in order to build it, you must have your amplifiers, which you cannot order until you measure it, after you have built it!

The alternative is to apply a very seasoned rule of thumb: Use 1.5 times the value found by summing all of the loudspeaker powers. Thus for our example, 1.5 times 650 watts tells us we need around 975 watts.

Wire Size—How Big Is Big Enough?
Since the whole point of using constant-voltage distribution techniques is to optimize installation costs, proper wire sizing becomes a major factor. Due to wire resistance (usually expressed as ohms per foot, or meter) there can be a great deal of engineering involved to calculate the correct wire size.

The major factors considered are the maximum current flowing through the wire, the distance covered by the wire, and the resistance of the wire. The type of wire also must be selected. Generally, constant-voltage wiring consists of a twisted pair of solid or stranded conductors with or without a jacket.

For those who like to keep it simple, the job is relatively easy. For example, say the installation requires delivering 1000 watts to 100 loudspeakers. Calculating that 1000 watts at 70.7 volts is 14.14 amps, you then select a wire gauge that will carry 14.14 amps (plus some headroom for I2R wire losses) and wire up all 100 loudspeakers. This works, but it may be unnecessarily expensive and wasteful.

Really meticulous calculators make the job of selecting wire size a lot more interesting. For the above example, looked at another way, the task is not to deliver 1000 watts to 100 loudspeakers, but rather to distribute 10 watts each to 100 loudspeakers. These are different things. Wire size now becomes a function of the geometry involved.

For example, if all 100 loudspeakers are connected up daisy-chain fashion in a continuous line, then 14.14 amps flows to the first speaker where only 0.1414 amps are used to create the necessary 10 watts; from here 14.00 amps flows on to the next speaker where another 0.1414 amps are used; then 13.86 amps continues on to the next loudspeaker, and so on, until the final 0.1414 amps is delivered to the last speaker.

Well, obviously the wire size necessary to connect the last speaker doesn’t need to be rated for 14.14 amps. For this example, the fanatical installer would use a different wire size for each speaker, narrowing the gauge as he went. And the problem gets ever more complicated if the speakers are arranged in an array of, say, 10 x 10, for instance.

Luckily tables exist to make our lives easier. Some of the most useful appear in Giddings [3] as Tables 14-1 and Table 14-2 on pp. 332-333. These provide cable lengths and gauges for 0.5 dB and 1.5 dB power loss, along with power, ohms, and current info. Great book. Table 1 below reproduces much of Gidding’s Table 14-2 [4].

image

References
1. Langford-Smith, F., Ed. Radiotron Designer’s Handbook, 4th Ed. (RCA, 1953), p. 21.2.
2. Earley, Sheehan & Caloggero, Eds. National Electrical Code Handbook, 5th Ed. (NFPA, 1999).
3. See: Giddings, Phillip Audio System Design and Installation (Sams, 1990) for an excellent treatment of constant-voltage system designs criteria; also Davis, D. & C. Sound System Engineering, 2nd Ed. (Sams, 1987) provides a through treatment of the potential interface problems.
4. Reproduced by permission of the author and Howard W. Sams & Co.

Supplied by Rane via ProSoundWeb.

What You Need To Know About Wireless Systems

An in-depth yet easy-to-understand discussion of wireless systems, how they operate, issues that can plague performance, and solutions that do the trick in the vast majority of situations.

Editor’s Note: This article provides straightforward explanations of the primary issues that account for a full 80 to 90 percent of all wireless microphone system problems, while also presenting solutions that will do the trick in most cases.

However, keep in mind that the best solution is avoiding these problems from the outset. Certainly this won’t guarantee completely trouble-free operation, but the odds dramatically improve.

This compilation of wireless system knowledge is provided by several highly qualified professionals, with Gary Stanfill, who has worked with wireless and related technologies for more than 40 years, topping this list.


Part 1: PSW Wireless Primer

Getting Started
Anyone who has used wireless microphone systems for even a short time doesn’t need to be sold on their advantages. “Going wireless” allows concentration on the message rather than on the mechanics of delivering the message. (No more pesky mic cables!)

Yet wireless systems can be slightly mysterious, prompting suspicion among some users - particularly if they’ve experienced problems for unclear reasons.

The easiest way to understand wireless systems is to think of them as small-scale radio and TV broadcast stations – a transmitter sends out a signal that is picked up by a receiver.

For a number of reasons, including size, weight, battery life and government regulations, wireless systems operate at quite low power and thus have limited range.

The wireless microphone (or bodypack) is the transmitter, complete with a mic capsule, some audio circuitry, and an antenna (usually built into the case). It sends radio signals to its companion wireless receiver, which also has an antenna and some circuitry to select and process the signal, which is then sent via a cable to the sound system.

The transmitter and receiver of each wireless system must share the same frequency. Any other wireless systems in use in the same area must have their own frequencies as well. Ugly noise is produced if two wireless systems are using the same frequency in the same area.

The same goes for other transmitters, especially those of TV stations.

And because these transmitters send out very powerful signals, they are a common cause of interference for wireless systems.

Even though a wireless system needs a clear frequency for the area where it’s going to be used, every frequency is used again and again across the nation.

Again, this is because the power of the output signal of wireless systems is very low.

Keep in mind, however, that there is no absolute guarantee that a clear frequency in one area will be clear elsewhere, even just across town.

This is an aspect about wireless systems that sometimes puzzles users; the government takes care of the problem for the high-power signals of commercial broadcasting, but wireless system users are responsible for avoiding this problem on their own.

Fortunately, most modern wireless systems (developed in the past 15 years or so) offer some degree of frequency agility (also called frequency synthesis). This means that the user is able to select an operating frequency from a number of possible choices, ranging from as few as four frequencies to 1,400 or more, depending upon the model.

The more frequencies offered by a wireless system, the better the chance of finding a clear frequency that is not being used by someone else in the area. Further, in larger cities, where there are more frequencies occupied by numerous users, the ability to choose from a larger number of frequencies is especially important.

Having plenty of open frequencies also helps wireless system users get around another potential problem: intermodulation (or intermod for short). This can occur where the frequencies of two transmitters (of any type) “combine” in a wireless system receiver, resulting in noise and interference.

Most often, intermod is caused by a combination of the frequencies from two TV transmitters, or by the frequency of a TV transmitter combined with the frequency of a wireless system transmitter.

Because the source of intermod is usually not under the control of the wireless user, there is usually little choice except to change the frequency of the wireless system. This is yet another reason for choosing a wireless system outfitted with a wide range of frequency selections.

By law in the U.S., wireless systems are supposed to operate only on TV channels not in local use. If a wireless system happens to cause interference to TV viewers in the area of its use (and this can happen even with their lower output level), the interference is likely to be reported, resulting in the user drawing unwanted attention from law enforcement.

Thus it’s vital for the wireless system user to keep handy a list of local TV frequencies in use (available online at www.antennaweb.org/aw/Address.aspx), and to avoid those frequencies.

Although many wireless systems can “automatically” select frequencies or scan to see local RF activity, it is still possible to select the frequency of a local TV channel and get the innocent user into trouble.

Wireless systems are available for “VHF” and “UHF” frequency ranges (also called bands), roughly corresponding to VHF TV channels 7 though 13 and the UHF TV channels 14 through 69.

The question as to which range is “best” has pretty much been settled by the wireless manufacturers, who generally only offer systems with numerous frequency choices in the UHF band.

Additional bands used by wireless microphones include the “944 MHz” band between 944 - 952 Mhz. This is a band reserved for use exclusively for broadcasters.

Also, the “ISM” band between 902 - 928 MHz is an unlicensed band used by several wireless microphone products. Finally, the 2.4GHz band is another unlicensed area used by wireless manufacturers.

Although the UHF TV band classically extended up to channel 69, channels 52 to 69 (698 MHz to 806 MHz) has been converted to non-TV use - divided up by the U.S. government/FCC and auctioned to various companies for wireless devices available on the consumer market.

Accordingly, it is now against the law to use wireless microphone systems in this band. Even though a system has operated in this range without problems for years, it is illegal.

With all these competing signals in the air throughout the VHF and UHF bands, even high-quality wireless systems can run into problems when operating at distances of 100 feet or less between the transmitters and receivers.

Range problems usually appear as “fizzing” or “swishing” noises, perhaps followed by the complete loss of the audio signal. (This is called dropout.)

In addition to the low transmitter power, two other problems can limit the range of wireless systems. The first is signal absorption due to building construction and internal equipment, or shielding by metallic objects such as electrical wiring, air conditioning ducts, storage cabinets and the like between the transmitter and the receiver.

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Note the dual antennas on this wireless receiver, indicating it uses diversity.

The term “line of sight” is often used to express the idea that the signal path from the transmitter to the receiver should be open and clear of obstructions.

This simply means that if the wireless user can physically observe the receiver antenna, RF signal absorption is likely to be low.

The second problem is called multipath. It’s a phenomenon that results in numerous small areas where little or no wireless signal is present because of reflections and the resulting phase cancellations, and it often tends to occur within a fairly short distance between transmitter and receiver.

To overcome the problem, a majority of modern wireless receivers now use a technique called diversity. With diversity, two slightly separated receiver antennas are used, making it very unlikely that both will simultaneously be in one of the low signal (multipath) areas.

The receiver automatically selects the antenna with the strongest signal, not only solving multipath, but also increasing the reliable range of a wireless system.

A final note: most users are surprised to learn - despite urban myths to the contrary – that the U.S. government requires wireless systems to be properly licensed prior to use.

Unfortunately, the agency in change of issuing these licenses (Federal Communications Commission, or FCC) makes it very difficult for conscientious users to actually comply.

As a result, the vast majority of users don’t go to the trouble. But keep in mind that unlicensed wireless systems are in technical violation of FCC rules, and therefore are theoretically subject to fines.

As a practical matter, the FCC has neither the resources nor the inclination to go after the “average” wireless user, so the risk is low. But not zero. Due to the recent changes in spectrum allocation, this issue is being re-visited.

It appears that the FCC may make it easier for typical wireless microphone users such as churches, theaters, musicians, etc. to register their products.

This would also be beneficial in the event that additional types of consumer devices appear and complete for the same spectrum we are currently using.


Part 2: PSW Wireless Primer


Avoiding Wireless System “Issues”
Although the popularity of wireless microphones continues to grow, there’s no denying that they present more opportunities for problems than their wired counterparts.

In addition to the normal acoustic concerns that come with any mic are the complications of RF (radio frequency) transmission, interference, frequency selection, batteries and several other issues.

And technical improvements in wireless systems have not entirely kept pace with increasing frequency congestion, digital television and other recent complications.

Still, the hundreds of thousands of wireless systems employed in the U.S. is compelling evidence that the majority of users will live with the added challenges. Besides, many of the problems encountered by wireless users are largely avoidable, and happen primarily due to oversights, mistakes and misunderstandings.

Addressing the following common issues greatly improves the reliability of wireless systems and goes a long way toward ensuring trouble-free operation.

Issue: Frequency planning and coordination. Wireless systems share the RF spectrum with TV stations and several other types of authorized users. As a result, interference is very likely unless appropriate precautions are taken.

Solution: The first step is to determine the TV channels that broadcast over the air in your area.

When the local TV channels are known, they can be compared to the frequencies of the wireless systems. If there’s a conflict, the wireless frequencies must be changed. This is relatively simple for synthesized systems as well as ones that search for vacant frequencies, but the solution is more difficult for fixed-frequency wireless.

Despite the inconvenience, wireless systems should not be used on occupied TV channels. Not only is interference almost certain, the practice is illegal.

Issue: Intermodulation. Wireless systems can also experience severe interference even when operating on “vacant” frequencies. This is created by intermodulation distortion - basically two strong signals on other frequencies combining in the wireless receiver to create an interfering signal.

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In one variation of intermod shown here, the frequencies of two wireless systems can combine to “gang up” on a third system.

Called “intermod” for short, generally this type of interference is more common than direct on-frequency interference from other transmitters.

Intermod is typically caused by other wireless systems, or by other wireless in conjunction with local TV signals.

Even single systems can be affected, but the probability of problems grows roughly proportionally to the square of the number of systems in simultaneous use, plus the number of active analog TV channels present.

By the time eight or more wireless systems and six or more TV channels are involved, it can become quite challenging to find usable frequencies.

Solution: One or more wireless frequencies will have to change. There is generally no other practical solution.

Again, synthesized systems and “auto-search” frequency finding can be very helpful.

However, any frequency can potentially interact with any other, so changing one frequency can solve one problem can create another - or several others.

When changing frequencies or searching, it’s absolutely critical that all RF systems of any type at the location be turned on and operating.

As one clear wireless frequency is found, that system must be left on, and the next system tested until all are operational. Otherwise, the situation can quickly become a snarl of changes and more changes, “phantom” problems, confusion and frustration.

Some manufacturers offer assistance in selecting usable frequencies, and as always, don’t hesitate to get your sound contractor involved.

In addition, there are a number of readily available software packages that are designed to aid in calculating your frequencies so that intermod problems are avoided.

Several manufacturers of wireless microphones offer this kind of software, and there are third-party options as well. Often, the third-party solutions are the most flexible – offering coordination of many types of systems by most manufacturers.

Issue: Shielding or covering antennas. In order to properly launch a radio wave, a sizeable volume of free space is required around an antenna, and in general, they must be unobstructed.

Solution: For efficient operation, all wireless system antennas must be kept clear of metallic objects that can weaken and distort signals in addition to reducing range. With bodypack transmitters, the antenna must be kept away from the mic cable, the bodypack case and ideally, the wearer’s body.

Securing antennas to the transmitter case and tying antennas to cables, as is sometimes done, can be absolutely deadly to range. Skin and flesh can absorb RF energy, so it is best to have the transmitter case and antenna away from the body.

Further, receiver antennas must extend away for the receiver case, as well as away from other antennas, equipment racks, other equipment, cabling and, again, metallic objects.

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Large metal structures like ductwork can create serious multipath issues.

It’s best to mount receivers at the top of the rack so that the antennas extend above and away from the rack and other equipment. Using rear-mounted antennas inside a metal rack will almost always result in very poor reception.

For multiple receiver installations, the common practice of positioning front-mounted antennas in a “V” configuration, with all the antennas parallel, will also reduce range. It causes them to function together somewhat like a TV antenna that’s pointed upwards.

Even worse is when antennas from two different receivers touch. Not only will range be seriously compromised, interference becomes much more likely. In such a situation, it is much better to incorporate a single pair of antennas and then an antenna splitter to distribute the signals to the receivers in the rack.

Issue: RF path. A clear path between the receiver and the transmitter is also required. This is sometimes called a “clear line-of-sight,” but remember, light will pass in a straight line through a small hole while radio waves will not.

Solution: Similar to the free space needed around an antenna, radio waves require a sizeable space in which to travel.

The amount of space necessary depends upon frequency - the lower the frequency, the more space needed.

Create an imaginary tunnel of open air between the transmitter and the receiver antennas.

For UHF systems, a tunnel diameter of 3 feet or so is usually adequate, but for VHF systems, it should be at least twice as large. There also should be no metallic objects - scaffolding, iron beams, cables, cabinets, pipes, etc. - within this space.

In particular, large flat metal objects such large ducts, rows of cabinets, truck bodies and the like that are parallel to the path should also be avoided.

Even though they might not be in the direct path, they can still act similar to a mirror, reflecting RF energy away from the direct path. Systems with diversity reception help avoid dropouts in these situations, but range still can be reduced considerably.

Issue: Long antenna cables. Sometimes it’s necessary or desirable to locate antennas at a farther distance from a receiver. RF coaxial cables can be used to connect the remote antennas to the receiver inputs.

However, they typically have considerable losses that will reduce operating range. The amount of loss depends upon the size, construction and quality of the cable, and upon the operating frequency.).

Even high-quality RG-58 cable will have a loss of about 8 dB per 100 feet at 200 MHz, and about 17 dB at 700 MHz. Since every 6 dB of loss cuts range by half, the working range with 100 feet of this cable will be only 40 percent of normal at 200 MHz, and a mere 14 percent of normal at 700 MHz.

Premium RG-58 type cables, such as Belden 7806R, are better, offering about 4.7 dB loss at 200 MHz and 8.9 dB at 700 MHz. Still, at 700 MHz, only 68 feet of this cable will cut range in half.

Solution: If long cable runs are s necessary for your wireless systems to work properly, skimping on the cost of the highest quality cables available is a bad decision. For the best results, a premium foam-dielectric cable such as Belden 9913 should be used. This cable has only 1.8 dB of loss per 100 feet at 200 MHz, and 3.6 dB at 700 MHz.

Generally, it’s preferable to run audio cables out to remote receivers, keeping RF cables short. This is particularly true with runs longer than 75 feet or so. If remote location of the receivers is not feasible, go with the high-quality, low-loss cable noted above.

In-line RF amplifiers can also be used to boost the signal before the long cable run. These devices require power, and add cost. So before thinking that RF amps are the way to go, consider how the system can be configured to avoid using them and still keep your cable loss to a minimum.

Issue: Batteries. Simple but true and most certainly the number-one cause of wireless problems the world over!

Fortunately, it’s the one that’s easiest to fix.

The most common cause of short battery life is poor quality or old age, along with mixing used batteries with new ones and simply losing track of how long a battery has been in use.

Some sound operators also fail to understand that, when turned on, wireless transmitters draw power even if not being used, and that the “mute” switch does not affect the current drain.

Solution: Check transmitter batteries prior to every use. Get a battery tester to help you determine a good battery from a bad one. And when in doubt, change to a new battery!

Name-brand alkaline batteries such as Duracell and Eveready are the best bet. While private label batteries are often nearly as good, their useful life can vary considerably from purchase to purchase.

Make sure that to buy batteries that are date coded, and don’t accept any whose expiration date is less than three years away. And never use zinc carbon or toy batteries; most can’t even properly power up a modern wireless transmitter.

Classically, many techs recommend against use of rechargeable batteries, and for good reason. Rechargeable batteries used to have much lower capacity than alkalines, and the useful life was usually short. This was particularly true of 9-volt units, whose operating life was a fraction of that of an alkaline.

In the past five years, the technology for rechargeable batteries has improved dramatically. Now, NimH and LiPoly batteries are every bit as good as alkalines, and in some cases even better.

Still, it is important to recognize the added complexity of using rechargeable batteries – a clear strategy will be needed for keeping them charged, tested, and removed from the pool when the time comes. By doing this, you can save considerable costs and it’s also better for the environment.

Even more issues that are relatively simple to address can impact wireless performance.

Part 3: PSW Wireless Primer

Downsides Of Digital
Issue: Digital interference. Modern digital audio equipment, including processors, equalizers, controllers and other gear, operate at high clock frequencies that generate considerable radio frequency (RF) noise. (By the way, this noise is often termed RFI.)

As a result, it’s not at all unusual for such equipment to interfere with wireless systems.

Symptoms include low-level spurious tones, buzzing sounds, hissing and a varying noise floor.

Digital interference can also cause an unexplained loss of range and other problems.

Although FCC rules require that such equipment be tested to meet spurious emission standards, it’s a fact that not all units are indeed tested.

In addition, loose covers and casings, warped metalwork, lax grounding and other mechanical shortcomings can greatly increase spurious RF emissions.

Even properly approved digital equipment, in good working order, may generate enough RFI to affect wireless receivers located nearby.

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Digital audio equipment in close proximity to wireless systems can sometimes result in interference.

When wireless interference occurs, one of the first things to do is to temporarily turn off digital devices to see if they are the source of the problem.

Solution: As a general precaution wireless receivers should be located as far as possible from digital gear. Often just moving the equipment a few rack spaces apart is enough to solve a problem.

More severe cases may require separating the wireless power, signal and RF cables from those going to the digital equipment.

Using remote antennas with the wireless systems may also be helpful.

And finally, try tightening up the covers on any offending digital gear and also adding a ground strap to the cabinet or other local ground point.

Issue: Lapel (or lavalier) (microphone sound quality. Lapel mics can cause a number of different problems. A common complaint is thin sound quality, which often occurs when the user has previously used only mics intended primarily for vocal applications.

These mics generally boost low frequencies to make the voice sound warmer and fuller, but the omnidirectional mics normally used with wireless bodypack transmitter systems don’t have this boost and thus can sound noticeably different.

Another cause of “thin audio” from lapel mics is interference. RF energy can “couple” into the mic cable and affect the preamplifier circuitry in the mic capsule. A high percentage of all lapel mics exhibit this problem under at least some circumstances.

If the voice quality and level varies when the mic and cable are moved around in close proximity to the wireless transmitter antenna and body, it is almost certain that RF interference is present.

Solution: In all cases, the manufacturer of the wireless system exhibiting this problem should be first contacted for specific recommendations. However, the problem is often solved with the addition of small RF bypass capacitors to the mic connector. Note that this should only be done by a qualified service professional only.

Issue: Lapel mic feedback. Users new to wireless often complain that a system is defective because feedback occurs where none was present before. Part of the problem is that the lapel mics typically used with wireless are not directional and thus provide little feedback protection.

However, the larger problem is usually that the mobility of wireless allows users to walk into zones more likely to cause feedback.

Solution: Use lapel mics with a unidirectional pattern, or use headset mics. Moving the mic closer to the mouth and lowering gain is also helpful. Many users think headset mics are unsightly, but unidirectional mics can suffer from sudden drops in level when wearers turn their heads.

The better solutions are acoustic, either by training users to avoid feedback zones, or by modifying the loudspeaker configuration to put feedback zones out of reach.

Issue: Lapel mic mechanical problems. This is common to lapel mics, in particular because their cables are small, often delicate and typically get considerable abuse.

Even if not damaged outright (i.e., the cable pulled out of the mic connector), lapel mic cables eventually wear out.

Most often this wear occurs first at the connector end, but keep in mind that it can also happen at the capsule end. Usually the cable shield fails first due to constant bending in the area where a cable leaves the connector’s strain relief.

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A headworn mic can be an option in some cases, and there are a wide variety of lapel mics to choose from. (Upper photo couresy of Electro-Voice, showing the company’s RE97 headworn mic.

When this happens, clicks, pops, other noise and “lost audio” are experienced. Even before there’s a complete break in the shield, pops and clicks due to RF disturbances can happen.

Therefore, it’s always prudent to check the cables when experiencing lapel mic noise of any type. Breaks at the connector end can usually be repaired (and don’t forget the bypass capacitors), but a break at the capsule end may not be fixable.

Mechanical noise due to lapel mic capsules rubbing on clothing is relatively common and can usually be eliminated by using the right type of mic clip, one that holds the capsule away from the fabric.

It may also be necessary to carefully secure the cable near the mic capsule. Static electricity sometimes creates audio noise, especially with certain types of fabric. Clothing anti-static spray usually solves this problem.

Issue: System quality. It may seem strange to list “system quality” as a wireless problem, but a great many wireless difficulties start with inferior equipment. Inexpensive systems can often work well in rural areas and/or in relatively undemanding applications.

But in larger cities and their surrounding suburbs plagued by typical frequency congestion and myriad interference sources, something better may be required.

The same is usually true when more than a few systems must be operated at the same site. And, this situation is going to worsen, with more and more digital signal sources going on the air almost daily.

The adoption of digital technology has greatly lowered the price of many audio products, but the impact of these advantages on wireless systems has been relatively small to this point. Wireless systems are still largely analog-based, and their manufacture is more labor intensive due to the requirement of considerable tuning, testing and tweaking.

Quality components also tend to be expensive in comparison to digital components and are less adaptable to low-cost automated assembly.

Unfortunately, there is yet no new magic technology that can cut the cost of a quality wireless system significantly - say 30 to 40 percent. Right now, if cost goes down, so do quality and performance. And it’s easier and cheaper for manufacturers to promote their mic capsules and “features” rather than build in better performance.

Consequently there is a growing tendency to regard the RF portion of a wireless system as being relatively unimportant. This is a serious mistake.

Solution: If a wireless system doesn’t have the selectivity and interference rejection to cut through all of the “junk” in the air, it doesn’t matter which mic elements it has, how neat the feature set, or how much money was “saved”. You’re simply left with something that doesn’t work like it should.

The recommendation is to pay a little more and go for performance over features. High-quality wireless systems cost less than half of what they did 10 years ago, and they work better in virtually all cases.

Final Thoughts: All in all, wireless microphone and in-ear monitoring systems can significantly enhance the experience for audiences and performers alike. Freedom of movement for actors, musicians, minsters, orators and politicians is a major benefit.

However, the complexity, cost and potential problems are the risks of using microphones. By following the guidelines presented in this series of articles, you should be well on the way to flawless operation from wireless systems.

Don’t forget that this is a changing world with respect to the RF spectrum and thus the operation of wireless mic systems. What works today may not work tomorrow.

Your best bet is to stay informed and educated. Watch for announcements about RF issues related to the FCC and potential other users of the spectrum. Keep up with the technology as manufacturers introduce new systems.

And most of all, stay up on troubleshooting skills so you can identify where the problems originate. Sometimes the wireless will be at fault, and sometimes not. It’s best to know the difference.