Acoustics and background noise
Good acoustics and reduced background noise make all the difference to the way you hear, especially if you are listening to speech.
The process of hearing, listening and understanding is sophisticated and involves the physical properties of the ear and a complex series of interactions in our brain.
Something called ‘auditory processing’ must occur, which means that your brain recognises and interprets the sounds heard so that it becomes meaningful information.
For those with a full hearing range, auditory processing is typically done subconsciously and easily. It is done with the same ease with which most people breath.
For those with hearing loss or another condition that make processing of sound difficult, hearnig and listening take effort and thought. In an environment where there is background noise or poor acoustics then it becomes much harder still.
How we hear
Sound is made when objects vibrate and it travels in waves, spreading outwards from the source of sound. It varies in loudness (intensity) and pitch (frequency).
Loudness (intensity) is measured in decibels (dB). Frequency (pitch) is measured in Hertz (Hz). All sounds are made up of different frequencies.
There are three main acoustic criteria:
- Internal ambient noise
- Reverberation time
- Sound insulation
What it means for hearing aid users
Hearing aids are fantastic technological devices and there have been great leaps in recent years in how they can assist in different listening environments.
However, background noise and poor acoustics remain a massive challenge, no matter how sophisticated the hearing aid.
Background noise creates a problem because hearing aids amplify both wanted and unwanted sound. Hearing aid developers are continuing to work to create more sophisticated solutions for this issue.
Acoustics are a problem because hearing aids amplify any distortion. This is caused where sound bounces around a room, reverberating and echoing without the softening effect of such things as low ceilings and absorbent fabrics and features.
The bottom line is: no hearing aid can yet fully mimic natural hearing.
Internal & indoor ambient noise
There are lots of sources of noise that can impact on acoustics. This includes noise from:
- road, rail and air traffic
- people outside or in adjacent rooms
- nearby industrial or commercial activity
- building services, such as ventilation systems
- equipment that is being used in the space, for example, computers, overhead projectors, machine tools
- rain noise on lightweight roofs
People with a full hearing range need to have the speaker’s voice (the 'Signal’) 6 dB louder than the background noise (Noise) in order to make sense of what’s being said. This is a Signal to Noise (S/N) ratio of + 6dB.
For someone with hearing loss, this needs to be +16dB or more. Studies have shown that the more favourable the S/N ratio, the easier it is to understand what is being said.
Reverberation is the collection of reflected sounds from the surfaces of an enclosed space. It makes the sound persist after it has been produced. It mainly comes from low frequency sounds.
Speech includes lots of low frequency sounds. These are mainly the vowels - and they tend to sound louder when we say them than the consonants e.g. fish, cow, hut.
Consonants tend to be high frequency sounds. They give clarity to speech. If you cannot hear them then words are difficult to understand.
Where there is lots of reverberation, low frequency sound bounces around the room and makes it difficult for people to understand speech.
Reverberation is affected by the size, shape and nature of the enclosed space. Hard surfaces and high ceilings will typically mean more reverberation.
Rooms and spaces that are easiest to hear in will have good sound insultation to reduce the amount of low frequency sound bouncing around. Facilities open to the general public can become more 'hearing-friendly' by reducing:
- high ceilings
- hard surfaces
- sound travelling from one space to another e.g. rooms next door to each other
- sound travelling around a single enclosed space e.g. between tables within a restaurant
- the impact sound of floors