microphones – Diaconate of Church Technologists

As I found while researching this article, the statutory requirements relating to Hearing Augmentation Systems (sometimes referred to as Hearing Assistance Systems, or Listening Systems) in NZ buildings are Convoluted, Confusing and Contradictory. But I knew that – that was why I thought it would be a good topic for this column; I still wasn’t prepared for how much CC&C there actually is!

And to make it worse, compliance is signed off at the individual Territorial Authority level, and the interpretation of what is deemed to comply varies from Authority to Authority; sometimes from Building Surveyor to Building Surveyor.

Hearing Augmentation Systems are systems put in place to allow aural information to be conveyed to Building Users clearly and accurately. The Building Act and NZS4121 (Design for access and mobility – Buildings and associated facilities) are clear that the scope includes users who don’t require hearing aids; however, the Building Code clearly states the requirement is only for persons requiring hearing aids (G5.3.5). The guidance that is given in these documents and other related materials is that the Building Code is the minimum standard and the expectation is that an adequate solution will be designed for a given space, taking into consideration the requirements of the particular location and function of the space. There is also a requirement that Hearing Augmentation systems are maintained 6-monthly. In theory, they should appear on a building’s compliance schedule and are part of the Building WOF process. Also, because they are disability systems, the building must have prescribed signage.

Hearing Augmentation technology and Hearing Aid technology are both in the middle of the technological revolution – both are adopting “new” digital techniques and methods to implement the required functionality and feature set. Hearing Aids, in particular, are adopting new technologies rapidly such as linking to a user’s smartphone. The drive for miniaturisation, however, means that Hearing Aid manufacturers are increasingly leaving out the T-coil which has been the basis for Building Hearing Augmentation systems since the 1960s. The next 10-years will be interesting as the new technologies are trialled and adopted, and transition through the hearing aid population. Hopefully, it won’t take the legislation too long to catch up.

Hearing Augmentation Systems

So, what types of Hearing Augmentation systems are there?

Sound Capture

Firstly, all Hearing Augmentation systems require a system of microphones or other audio input. This can be built into the system itself or can be acquired via a sound system. In some circumstances, this means the sound system needs to be left on even though it is not needed in its own right.

Audio-Frequency Induction Loop Systems (Hearing Loops)

These loops are usually installed in meeting rooms or in other places where people gather. They assist people who have hearing aids fitted with a T-switch. They can also assist people without hearing aids if the user is provided with a loop receiver device.

In addition to permanently installed hearing loops, there are portable hearing loops available. These can be used in small spaces such as meeting rooms or motor vehicles. Loops are sensitive to building construction and other wireless frequency emitters (including other Hearing Loops, so they are not good in multi-room environments).

Infrared Systems

Infrared systems take the sound input signal and broadcast it on an Infrared frequency within the space, which is then picked up with a system-specific receiver worn by the user. These systems generally require a direct, unblocked, line-of-sight to the user and require users to obtain and wear a receiver with the appropriate attachment. They can be used by users without hearing aids. They are sensitive to very bright lights and sunlight and the receiver unit must be worn outside clothing etc.

Building operators need to keep a supply of receivers, batteries and headphones forbuilding users to use as required. Headphones or in-ear devices are subject to Public Health cleaning requirements.

FM Wireless Systems

Structurally, these are very similar to Infrared systems but use FM radio frequencies rather than Infrared frequencies. Consequently, they are not limited to direct line-of-sight. Receivers can consequently be put in a pocket or handbag with relatively minor impact to performance. While they are not impacted by sunlight, they can be affected by other wireless emitters.

There may be some old wireless systems around that use VHF radio frequencies. Given the recent changes in frequency allocation in favour of mobile phone service providers, continued use of this band is problematic.

Peter Lane is Principal Consultant at System Design & Communication Services and has over 30-years’ experience with Technology systems. We invite your questions, suggestions and ideas for articles. These can be submitted either through the editor or by email to dct@dct.org.nz. We also operate a website focused on building a community of people who are interested in improving the way we can use technology located at www.dct.org.nz.

A lot of us never need to get behind the business end of a microphone. But for those who have to present regularly, it is important to have a basic understanding of how different microphones work. Then we are able to adapt our speaking technique to suit the microphone in front of us as we deliver our message. This is a quick guide to using microphones effectively for presenters of all ages!

Microphones are components in virtually all audio systems.

Thus, you’ll hear about studio microphones for recording and PA microphones for live sound. There are boom microphones for broadcast or film shoots. Or instrument microphones which attach directly to guitars or other musical instruments. Then there are boundary microphones or boundary effect microphones for theatre work or conference systems, lapel mics for seminars and business meetings, and headset microphones for telephone call centres. (And this is just to mention a few options). The different types of microphones optimise a range of different requirements in different environments.

That said, all microphones have one thing in common: “microphones convert a sound wave into an electrical signal in which the voltage and current are proportional to the original sound”. To perform this task microphones use a thin membrane, known as a diaphragm, which mimics the function of the human eardrum. Sound waves strike a microphone’s diaphragm and cause the diaphram to move. Harnessing this movement creates an electrical signal.

A sound is essentially a change in pressure that varies in specific ways over time to create specific sounds (sound waves). When sound waves strike a microphone’s diaphragm, they cause it to move, which movement, in turn, creates a variance in an electrical current (aka signal). The electrical signal is transmitted to output devices, which either process the electrical signal (store it, or make it louder, or make it sound like Darth Vader on a bad hair day), or use the signal to recreate sound waves (loudspeakers).

Microphone Types

Microphone engineers, over the course of “recorded” history, have developed 3 fundamental techniques for detecting sound waves and “transducing” sound to electrical signals.

Dynamic Microphones

A dynamic microphone uses the diaphragm to move a coil of wire within a magnetic field to create the electric signal. It’s advantages are it’s relative simplicity and good voice frequency characteristics. A dynamic microphone is quite sensitive to interference from external electromagnetic fields. If your venue has a hearing aid loop, you don’t want to try dynamic microphones.

Condensor Microphones

A condenser microphone uses the diaphragm to move one side of a capacitor plate thus causing the capacitance to vary. This creates an electric signal. The advantages are it has good resiliency, can cope with large variances in the sound loudness and tends to have a larger frequency response. Condensor microphones are often used for instrument microphones, however, are the basis for many vocal microphones as well. The disadvantage is that the capacitor requires a power source to keep it charged. Therefore, a condenser microphones require either batteries or a power supply delivered from the connected equipment.

Ribbon Microphones

Ribbon microphones consist of a thin strip of metallic foil suspended in front of a magnetic plate. Sound waves cause the foil to vibrate, producing fluctuations in the electrical current, creating the audio signal. This extremely sensitive configuration picks up a wide range of frequencies and produces an extraordinarily rich representation of the original sound. The trade-off for this sensitivity is the delicacy of the mechanism – ribbon microphones are very sensitive to physical impacts and power overdrive. (Oh, and very expensive).

System Engineering

The other factor that effects using microphones is the system engineering. A system engineered for voice reinforcement usually uses rather sensitive microphones and try to “hide” the microphones away so they don’t distract from the presenter. A vocal microphone for a rock band vocalist, by contrast, can have much lower sensitivity. In this case, however, the microphone is held within millimetres of the vocalist’s mouth. This means that the microphone “hears” only the voice and not the other instruments around it.

Principles for Presenters

So, as a speaker/presenter, how do you make sure you are heard and understood?

Learn to recognise – or at least be able to take a good guess – at what internal configuration and pick-up pattern the microphone has. If you have the opportunity to research beforehand, do so. Then adjust your speech style accordingly – speak “firmly” to dynamic microphones, but more relaxed and rounded to condenser microphones.
When you have a sound operator, work in cooperation with them. A good sound operator will usually have a better understanding of the capabilities of the microphones they can offer.
While standing normally, move the microphone so you are “looking down the barrel” of the microphone. If you can’t move the mic, move yourself. For guidance in using voice reinforcement systems, a hand-held microphone should be about a handspan from your mouth. Stand-mounted or Lectern mics should be about 15”/400mm away from your mouth. A microphone on a stand will typically be setup for voice reinforcement. Taking the microphone off its stand and useing it as a hand-held will result in excessively loud sound-levels. A good sound operator can help here. However, don’t assume they can read minds, so try to give them some warning what you intend to do.
Ensure your voice production is clear and controlled. The microphone doesn’t make the sound for you – it reinforces the sound you make. If the sound you make is muddy, mumbled and unclear, so will be the amplified sound.
Watch your dynamic control. By all means express yourself dramatically – just stay within the bounds of the system capability. If all your drama only bursts your audience’s ear drums, they won’t “hear” anything else. In either sense of the word.
Watch you don’t move off orientation to the microphone. It’s fine to walk around if you are comfortable with that – so long as the microphone walks with you and stays properly oriented to your mouth. (If you are able, use a wireless microphone such as a lavaliere clipon, developed specifically to address this issue. However, they still need care to setup and use.) Some microphones are more tolerant than others, but just turning your head can make a big difference.

You speak to deliver a message – don’t let the technology become a distraction to that message.

Tag: microphones

What Was That? – Hearing Augmentation Systems