Noise is unwanted sound. Sound is the physical component and unwanted describes the emotional and psychological effect that noise has on a person. Home means different things to different people but is often described as the most personal and sacred place to shelter from the rest of the world. This is why many people find noise entering their home so intrusive and irritating. Not being able to relax in your own home, not being able to read a book or watch your favourite TV programme without hearing your neighbours or worrying that they might be hearing you is just depressing.
Noise is sound that is created when an object vibrates fast enough that it produces a disturbance in a gas, solid or liquid; this generates a pressure wave in the surrounding air. Sound is the term used to describe the vibrations as they enter the ear and are then interpreted by the brain.
Here is brief introduction to sound and theories of sound in relation to your home. This will give you a better understanding of unwanted noise and help you implement the ideas and concepts of soundproofing your home.
Humans’ sensitivity of sound is affected by three things:
- the frequency (or ‘pitch’)
- the loudness of the sound
- the length/duration of a sound.
Audible Frequency Range
What to do if your neighbours have installed a TV on party wall!
Frequency or ‘pitch’ is measured in hertz (hz). Sounds with frequency as low as 20hz can be felt by humans rather than heard. A teenager with good hearing can hear a frequency as high as 17,400hz. As we get older we find it more difficult to hear higher frequencies; a normal, middle-aged adult hears up to between 12,000 and 14,000hz. For this reason some convenience shops have started installing devices that emit high-frequency sound that is only heard by teenagers to discourage teenagers from hanging around inside or outside the shop. The voice of a normal male adult will range between 85 and 185hz and a normal female adult’s voice between 165 and 255hz. The human ear is most sensitive at frequencies between 2,000 and 5,000hz.
Most sounds we hear from neighbours occur within 125 and 5,000hz. Most present-day sound systems can produce low-frequency noise below 80hz and some people have deep voices that will transmit through a house’s structure. At present in the UK, government testing requirements for separating walls/floors to meet Part E of the building regulations only test in the frequency range 100hz to 3,150hz.
The good news is that 8,000hz sounds like a very high-pitched squeal, and most separating walls, ceilings or floors will barrier frequencies this high. These higher frequencies are actually quite easy to keep out through airtightness. High frequencies produce small sound waves that pass through small holes in the structure of your home. Low frequencies produce large sound waves that struggle to get through small gaps in the structure. Very low frequencies, between 20 and 100hz, travel the furthest and are the hardest to stop.
Airborne noise is noise transmitted through the air, such as TV or radio programmes, music, conversation. Airborne noise is regulated in the UK by the government to tackle the noise pollution in newly built homes and refurbishment projects, through the Building Regulations Approved Document Part E. Builders and developers are required to instal sound insulation to the walls, ceilings and floors separating some refurbishments and newly built homes and then have an acoustic test carried out. If the building passes the acoustic test, then the new development will be on its way to meeting building regulations and being signed off. Just like an electrical certificate the acoustic certificate is part of the inspection process.
DECIBELS: A decibel (dB) measures how loud a noise is.
The level of sound prevented from transmitting through separating walls and floors is measured (airborne sound insulation), and the higher the figure the better (the regulations require a score of at least 45dB Dnt’w +Ctr. The testing covers a wide range of frequencies, but unfortunately takes the average of the room. An amazing wall system on the party wall might achieve 70dB Dnt’w + Ctr but if you have not treated the suspended floor void, the ceiling void or other holes in the structure, these would let neighbour noise through. If the sound test found the overall sound insulation average of the room to be 50dB Dnt’w +Ctr, which is a pass, you might still be able to make out words and follow conversations from next door.
The acoustic test came into force on 1 July 2003 for refurbishment projects. To give you an idea what 45dB Dnt’w + Ctr means in real life, in a 1950s three-bedroom semi-detached house, Quietco paid an independent company to carry out a UKAS-accredited sound insulation test of the separating party wall beforeany soundproofing was installed. The sound insulation value of this wall measured at 47dB Dnt,w + Ctr, 2dB higher than the building regulations require for new dwellings, so better sound insulation than the standard required for properties newly built today. After the testing, I stood in our client’s neighbours’ dining room, the other side of the party wall, and managed to turn on our client’s smart speaker. (See https://quietco.uk/videos/)
Impact noise or structure-borne sound is most commonly associated with footsteps, for example footsteps on a wooden floor heard in the room below. Other examples of impact noise heard in the home are doors slamming, children running and jumping around, plug sockets and light switches, people using chopping boards, pots and pans clanging on a work surface, curtain and blinds being drawn, creaky floors and bangs against a wall or floor or ceiling: where the noise transmits through the structure.
When an object hits the structure of a building the sound energy is transferred to the structure and can then transmit through it: becoming a structure-borne sound. So, when your neighbours’ door slams, you are hearing the noise of the impact of the door leaf hitting the door frame as the door is closed. You may also be hearing the door latch (the metal parts of the door) hitting the strike plate on the door frame. Both these impact noises transmit through the structure of the building all the way to your property.
In the early days impact noise was measured by a steel ball being dropped from different heights on to a wooden floor; the higher the drop the more audible it would be in the room below. Later a ‘tapping machine’ was developed. The strict testing practices, standards and methods acoustic engineers have to abide by are outlined in the British Standard for measuring impact noise, BS EN ISO 140-7. The tapping machine uses a series of steel hammers tapping ten times a second. This machine is placed on the sub floor/temporary floor (not a finished or tiled floor) in the source room to be measured; acoustic engineers then measure the calibrated sound pressure in the room below. Impact noises can be reduced by isolating the surfaces generating them from the structure, using such as floating floors, floating walls and suspended ceilings.
The key things you need to understand about the two different types of noise is that both impact and airborne noise will get into the structure and transmit through the structure of the house. You can make a room airtight but still hear music, TV, conversation noise from next door because it is transmitted through the structure. These noises will still get through unless you isolate the finished surfaces from the structure.
There is no point in just applying sound insulation to a separating party wall if noise is getting in through the structure: you must apply soundproofing to any area that is connected to the source of that noise.
The impact sound pressure level is called Lnt’w. A maximum level of 64dB Lnt’w for impact noise transmission to separating floors also came into force on 1 July 2003 for converted properties. Confusingly, the lower the Lnt’w figure, the better. Since 1 July 2004 the regulations require airborne sound barriers to be a minimum of 45dB Dnt’w +Ctr for separating floors, ceiling and walls, and impact sound transmission to be a minimum of 62dB Lnt’w.
© Copyright Jim Prior
All rights reserved. No part of this publication may be reproduced, stored in or introduced into a retrieval system, or transmitted, in any form, or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the author.
The right of Jim Prior to be identified as the author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.