We’ve put this guide together to help explain some of the systems and technical terms used in commercial audio, whether that’s about loudspeakers, amplifiers, microphones, induction loop or something else!
Each section is also available to download as a PDF.
If you need any further information, please do not hesitate to contact us.
1. Low & High Impedance Loudspeaker Circuits
2. Loudspeaker Sensitivity and Why it is Important
5. IP Ratings
Low & High Impedance Loudspeaker Circuits
Download Guide Here
There are two types of loudspeaker and loudspeaker circuit that we can use when designing a sound system. One is “low impedance” and the is “constant voltage, high impedance” or more commonly known as 100v line.
Both systems have advantages and disadvantages, briefly explained below.
Low impedance “8 ohm”
Used for domestic hi-fi systems, professional live entertainment and music systems, car hi-fi and in Pro-Sound systems where high level playback of music is required. The amplifiers within a low impedance system will generate high current at relatively low voltages; therefore cable diameter is an important factor when designing a low impedance system.
Advantages
- Will produce full range sound (depending on equipment)
- Lower cost for basic setups
Disadvantages
- Cable diameter is a limiting factor in long cable runs
- Odd and multiple numbers of loudspeakers are difficult to fit or design into a low impedance system & require complex impedance matching calculations
High impedance or constant voltage (100v line)
Constant voltage systems are used within commercial audio & industrial public address sound systems. Best electrical practice is required when installing these types of system as the loudspeaker output from the amplifier is running at a relatively high voltage and low current compared with a low impedance system; therefore cable diameter is less of an issue, and long cable runs can be achieved without considerable loss of power.
Advantages
- Easy to fit odd and multiple numbers of loudspeaker to a single amplifier circuit
- Long loudspeaker circuits can be achieved using relatively thin cable
- The majority of 100 Volt line loudspeakers have multiple tappings to enable different volume levels to be set
Disadvantages
- Loudspeaker costs are higher than low impedance versions, especially when considering full range sound. Cheap 100v transformers within loudspeakers will saturate at bass frequencies, so to obtain equivalent sound quality to a low impendence system the loudspeaker transformer needs to be high quality.
- Not really suitable for pro-sound live applications where kilowatts of power are used and reproduction of very low frequencies required.
Loudspeaker cabling
When designing audio systems, loudspeaker cable if often not considered a being as important as the amplifier or loudspeaker to be used. This is a common mistake and more importantly can degrade the performance of the system considerably. There is no point in spending thousands of pounds on high performance loudspeakers and amplifiers unless a quality cable of suitable diameter is used.
This is most important in low impedance systems. Cable diameter and therefore resistance will have a direct effect on the loudspeaker circuit and overall response of the loudspeaker. It can also have a detrimental effect on the power of the amplifier and how it performs.
The following chart shows the size of cable that should be used with low impedance and 100v line loudspeaker loads. ‘YES’ is shown where the loss of power within the cable is acceptable. ‘NO’ is shown where the loss is unacceptable and will result in heating the cable instead of powering the loudspeaker.
An acceptable loss is judged to be less than 1dB attenuation in output at the loudspeakers.
Each chart shows the loudspeaker impedance, the power put into that loudspeaker and the recommended diameter of cable for each distance.
The cable length is shown in Metres.
Loudspeaker Sensitivity and Why It Is Important
Download Guide Here
Question: When is a 6w ceiling loudspeaker not a 6w ceiling loudspeaker?
Answer: When is only as loud as a 2w ceiling loudspeaker!
This question and answer may seem a little strange, but it is true if we disregard some of the loudspeaker specification data, especially regarding efficiency or sensitivity.
When being asked to quote and suggest equipment for a sound system design, a customer will normally send plan drawings and a system requirement specification sheet. If the design and layout of the sound system has already been done, then the specification sheet may contain details of the number and type of loudspeakers required.
We may see a list like this:
Zone 1: 45 x 6w ceiling loudspeaker
Zone 2: 10 x 20w projection loudspeaker
Zone 3: 6 x 30w music cabinet loudspeaker
This list looks like it will be easy to provide pricing, however let the seller, buyer and end user beware as there is not enough information!
Compare the specification of the 2 ceiling speakers in the table below:
| Model | TD06T | R06T |
| Type | 6w 100v ceiling speaker 200mm overall diameter |
6w 100v ceiling speaker 197mm overall diameter |
| Tappings | 6/3/1.5/0.75w | 6/3/1.5w |
| Sensitivity | 91dB 1w/1m * | 85dB 1w/1m * |
| Frequency response | 90 Hz to 18 kHz (+/- 10dB) | 80 Hz to 19 kHz (+/- 10dB) |
| List price | £ 25.70 | £ 19.25 |
These loudspeakers appear quite similar in specification. They are both rated at 6w 100v and have an overall diameter of around 200mm. One also has a slightly better low frequency response than the other. However, the sensitivity figures are very different.
Our list of loudspeakers from the project specification makes no mention of sensitivity but it is very important.
What is Sensitivity?
In basic terms loudspeaker sensitivity is a measure of input verses output, i.e. for an amount of amplifier input power, how much sound pressure level do I get out of the loudspeaker?
We need to also understand how sensitivity is expressed and its units of scale.
The sound pressure level (SPL) output of a loudspeaker is normally expressed in dB (decibels) and within its specification you will usually see its maximum output level and the sensitivity measured with a 1w input and at a 1m distance.
The scale of SPL is logarithmic, and for every additional 10dB you will effectively double the perceived volume level, so 90dB is twice as loud as 80dB, and four times as loud as 70dB.
To increase the SPL by 10dB would require 10 times the input power, so to achieve twice the volume level with a specific loudspeaker which is currently being fed with 10w would require an input power of 100w, not forgetting to consider whether the loudspeaker can handle this increase or not!
Looking back at the two ceiling loudspeaker models, we can see a 6dB difference between them meaning you will need considerably more power to achieve the desired SPL using the R06T model than the TD06T model. This would require an increase of 4 times the amplifier power, or it could mean that the TD06T model could be tapped down considerably saving money on high powered amplification systems.
However, There Is Always A But!
We are of course are at the mercy of the data published by manufacturers and must trust that what we read is correct, sometimes this is not always the case. The normal rule of thumb is that when something looks too good on a spec sheet, it normally is.
* For this document, we have assumed that the sensitivity of the loudspeakers shown in the example is consistent across the frequency and dispersion range. In the real world this is rarely the case and you should also consider frequency response and SPL in relation to dispersion, power compression, and many other things but hopefully you will now understand why sensitivity is an important factor.
Whilst designing a system, you should also consider the desired frequency response and coverage that is required, in addition to the sensitivity.
Designing a Sound System
We are happy to help design an audio system for you, but whether you prefer to tackle this yourself or enlist our help, there are a number of important factors that need to be considered to ensure the effectiveness of the resulting system.
No matter how simple the job appears to be, the more information you can gather about the location and function of the proposed system, the better.
Please determine whether the system is for public address use only. If it is for Voice Evacuation where emergency message broadcasting is the primary function, please contact us first.
What Will the System Be Used For?
- Volume: Low level background music, paging and announcements or performance
- Quality: Full range music, speech only or performance
- Coverage: Perfect coverage requires more speakers. Can this be compromised?
Will the System Be Zoned?
- Simple zones: The sound system may enable various areas of a building to have different volume levels with some control over the choice of input source to those areas.
- Complex zones: Different audio sources can be played in different areas, and there may be localised controls for the user to change the input and/or volume level in each area.
What Inputs are Required?
- Microphones: wireless or wired (hand held or paging)
- Background music: CD/MP3, USB/ SD, FM/DAB tuner, audio streaming
- Pre-recorded Messages: Automated announcements - triggered or timed
Description of the Location
- Dimensions of the area / areas to be covered including ceiling height
(Plan and elevation scale drawings would be really useful) - Acoustic properties: is the space reverberant or dull/dead?
- Ceiling type: solid or suspended
- Ambient noise: Background noise levels will effect the SPL and efficiency requirements
- Architectural constraints / permanent fixtures: Loudspeaker positioning and appearance may be compromised. eg, racking within a warehouse or pillars within a church.
Balanced Audio
Download Guide Here - (includes explanatory diagrams)
Audio signal cables can be either balanced or unbalanced, depending on their intended use. For long cable runs, especially when using low microphone levels, a two wire + screen balanced audio circuit reduces noise (XLR). Balanced audio cables use phase cancellation to eliminate noise whilst maintaining the original audio signal.
A balanced audio cable sends the same audio signal on two wires but inverts the phase of one signal by 180 degrees.
When noise is introduced into the cable, it is introduced equally to both the original and the inverted signal.
At its destination, the inverted signal is inverted again putting both signals back in phase. This causes the noise signals to be out of phase cancelling each other out.
The original signal gets a little stronger because it is sent on two wires and combined. This compensates for the reduction in signal strength that occurs naturally on a long cable run and any noise introduced into the cable along its length is virtually eliminated.
Note: Unbalanced cables have no way of eliminating noise and are therefore not as robust for long-distance cable runs, microphone signals, and other professional applications.
Unbalanced cables are only suitable for runs up to 10m & can still be affected by RF interference.
Balanced cable runs are suitable at mic level 1 to 5 mV for runs up to 100m (sometimes further depending on the quality of cable installed).
Line level 775mV signals should be treated in the same manner as microphone levels, although running slightly longer unbalanced lengths shouldn’t be such a problem as they would be with a microphone signal due to the signal to noise level. We would however recommend all signal cables are run balanced whenever they can be.
IP Ratings
Download Guide Here
On some product descriptions, you may see an IP rating. This rating, in accordance with IEC standard EN60529, classifies and rates the degree of protection provided against the intrusion of solid objects (like tools, dust or fingers) and water ingress in respect of electrical equipment enclosures.
The rating usually consists of a two digit number where the first number represents the solid particle ingress protection level and the second digit represents moisture ingress protection level. Whilst some product descriptions such as ‘waterproof’, ‘weather resistant’, ‘splashproof’ etc can be subjective, the IP rating gives a clear indication of resistance to particles and moisture. If either of the digits are unavailable, it is replaced by an ‘x’.
For example, a loudspeaker to be used outdoors in an exposed location would need to be at least IP64. One in a clean room which needs to be hosed down should be at least IP66.
There is sometimes a 3rd digit included in the IP rating - this relates to protection against impact and is rarely used. Values range from 1 (resists impact of weights up to 150g falling from 15cm) to 9 (resists impact of weights up to 5kg falling from 40cm).
| 1st Digit | Solid Particle Protection |
| 0 | No protection |
| 1 | Protection from a large part of the body such as a hand (but no protection from deliberate access); from solid objects greater than 50mm in diameter |
| 2 | Protection against fingers or other objects no greater than 80mm in length & 12.5mm diameter |
| 3 | Protection from entry by tools, wires, etc., with a diameter of thickness greater than 2.5mm |
| 4 | Protection from entry by solid objects with a diameter or thickness greater than 1.0mm |
| 5 | Limited ingress of dust permitted |
| 6 | Dust tight. |
| 2nd Digit | Liquid Ingress Protection |
| 0 | No protection |
| 1 | Protection from vertically dripping water |
| 2 | Protection from vertically dripping water when the enclosure is tilted up to 15 degrees |
| 3 | Protected against sprays of water to 60 degrees from the vertical |
| 4 | Protected from water splashed from all directions – limited ingress permitted |
| 5 | Protected from low pressure jets of water from all directions - limited ingress permitted |
| 6 | Protected from strong jets of water from all directions - limited ingress permitted |
| 7 | Protected against the effects of immersion between 150mm and 1m |
| 8 | Protected against continuous submersion at a specified depth |
Wireless Microphones
Wireless microphones are also known as radio microphones as most use radio waves to transmit the signal. (There are now some systems using infrared transmission.) Over the years, the evolution of thousands of radio & TV stations, microwave, Bluetooth, broadband and Wi-Fi services has made it necessary for communications regulators to reserve certain frequencies for different uses. Portions of the radio spectrum are now reserved for industrial, scientific & medical use. Many radio mics are now using this ISM band for transmission too as they are less susceptible to interference from other services.
‘Off the shelf’ wireless microphone systems are ideal if just one microphone is needed, However, the individual components of a wireless mic system can also be purchased individually to make up a bespoke system, giving the opportunity to add different microphone types to one receiver to suite different uses.
Hand held wireless mic transmitters sometimes have interchangeable microphone capsules with different pick-up characteristics or different frequency responses which may be better for speech or singing. A handheld mic is great as a Q&A roving mic but presenters on stage may prefer a tie clip or headset mic to keep their hands free. In this case, the mic plugs into a wireless bodypack transmitter worn discreetly within clothing or clipped onto a belt.
Some transmitters operate on standard alkaline batteries, but for more frequent use a rechargeable model offers better value for money. The chargers are usually specific to the range or brand so take care to select the correct one. Drop-in chargers are most convenient – instead of removing batteries to charge separately, the whole beltpack or handheld transmitter simply slots into the charger.
Wireless microphones operate on various frequencies, all of which have their own merits. We explain some of the benefits & drawbacks of the different transmission systems below.
Types Of Frequency Transmission
VHF (173.8MHz to 175.0MHz)
- Very few VHF systems are available now as the technology is very basic.
- Licence free to use within the UK.
UHF (approx 450MHz to 900MHz)
- Most wireless microphones use the UHF band for superior audio performance.
- A maximum of 4 systems will work together, intermodulation free, on a section of TV channel 70 (863 to 865MHz), licence free.
- At least 8 systems will work together, intermodulation free, on TV Channel 38. One licence is needed for the complete band at £75 per year.
- A licence for an individual frequency in the Interleaved spectrum of several other TV channels costs around £25 per year. (Call for more information)
Digital (2.4GHz)
- Up to 8 systems will work together, licence free.
- The wavelength limits the range from around 30m to 100m maximum.
- Shares the crowded Wifi band, so the more complex interference reduction technology may impact on the number of systems which can be operated together.
Digital (5.8GHz)
- Up to 12 systems will work together, licence free.
- The wavelength limits the range from around 30m to 100m maximum.
- Doesn’t use the crowded Wi-fi band, so a greater number of systems can be operated together.
Infra-red
- Licence free
- Operating range is limited to a maximum of 10m with standard systems
- Unlimited number of systems can be used in adjacent rooms (as long as there are no windows between the rooms)
- A very limited number of systems can be used in the same room, normally maximum of two
- Only really suitable for line of sight transmission from transmitter to receiver
Types Of Systems and Their Uses
Non-diversity
Low cost, non-diversity radio microphone receivers are equipped with a single antenna. Their operating range is limited to line of sight and suitable for small rooms only and simple applications where one or two systems are used together. Up to four non-diversity wireless microphone systems can be used together in simple room layouts.
Switching diversity (or space diversity)
Most entry-level radio microphone systems use switching where two antennae feed a single receiver module. The receiver constantly monitors the signal strength of both antennae to distinguish between a strong (line of sight) signal and a week (reflected) signal and reduce drop out.
True Diversity
True diversity technology offers increased performance by having a separate internal receiver for each of the two antennae. This results in improved sensitivity and accuracy and reduces dropouts.
System Planning
Questions to ask when proposing a wireless radio microphone system might include:
- How many systems do you want to run together?
- What are the operating conditions; size and layout of the room and location of the building, and will remote antenna and distribution systems be required?
- Are there any other radio microphone systems in use in the same building or adjacent buildings?
- What types of microphone are required; handheld, head-worn or lapel?
Frequently Asked Questions
“How far will my radio microphone transmit?”
Normal expectations are 75 to 100m line of sight. This range is reduced considerably if the transmitter and receiver are separated by a wall, and if the room of operation is full of people and other obstructive objects.
Some systems feature a high power switch, which will increase the RF output, but will shorten the battery life.
If a receiver can only be installed in an adjacent room, then you will most likely need to employ remote antenna, cable and probably antenna boosters.
“When should I use an antenna distribution amplifier?”
If you are operating several radio microphone systems in the same area, it is strongly advisable to use an antenna distribution amplifier. This will minimize the number of receiving antenna in the system which improves system performance and appearance, and it can also distribute power to each receiver from one mains point.
“My radio microphone systems interfere with each other when multiple systems are switched on together”
This is normally the result of trying to run multiple systems too close to each other when talking about transmitting frequency and channel numbers. It may also be a result of one system producing a harmonic which then interferes with another system.
Careful consideration must be made to system planning and how many systems you are expecting to use together. Usually, the more expensive systems provide the possibility of running a higher number of systems concurrently as the receiver section of the wireless system incorporate more sophisticated RF filters.
Operating a wireless transmitter too close to their receiver may also affect system performance; normally it is advisable to leave at least 5m distance between the two components.
“I have heard a lot about changes to radio microphone use within the UK. How will I know if this affects my system?”
There have been many changes to the frequencies that you can operate wireless microphones on in the UK, and to the uninitiated it can appear daunting and complicated.
If you do not own a licence and operate a radio microphone then you should only be using the licensed free frequencies of 863 to 865MHz for UHF systems, 173.8 to 175.0MHz for VHF and 2.4GHz for digital systems. Use of frequencies outside this band is illegal unless you have the correct licence. Further details of radio microphone licensing can be found from JFMG, www.jfmg.co.uk
This is intended as a basic guide to the different wireless microphone systems available.
Please contact us for more information and guidance if required.
For licensing enquiries, please contact JFMG, www.jfmg.co.uk
Microphone Pickup Patterns
Omnidirectional
An omnidirectional microphone picks up sound equally from all around it. This is ideal for studio recordings for a natural sound, or for larger group performances such as a choir or orchestra.
Many tie-clip lavalier mics are also omnidirectional – this ensures that the speakers voice is picked up clearly regardless of the direction they are facing.
However, this makes an omnidirectional mic unsuitable for live performances where they may also pick up unwanted extraneous sound from the audience or amplified instruments. This can also cause problems with feedback.
Cardioid
A cardioid microphone probably has the most useful pickup pattern of all and is widely used for professional microphones, both for vocals and instruments.
The greatest sensitivity is directly in front of the microphone, dropping off around the sides before reaching a minimum at the base.
This pattern ensures that the singers voice or whatever instrument is in front of the mic is clearly heard, without interference from adjacent instruments / voices or feedback from nearby speakers.
Supercardioid
The pickup pattern of a supercardioid mic is similar to a cardioid one with an even tighter pickup area at the head of the mic, rejecting even more sound from the sides but with a small area of sensitivity near the rear of the mic. This provides an even narrower focus and is ideal for isolating a singer’s voice or particular instrument reducing competing sound from nearby and further reducing the risk of feedback.
However, the ‘tight’ pickup pattern makes this type of microphone unsuitable for inexperienced or guest users who have a tendency to move ‘off axis’
Additionally, the small area of sensitivity at the rear means that stage monitors cannot be placed directly in front of the performer, but should be off to one side and pointing away from the mic.