Sound effect on people: good or bad?

In 1999, the World Health Organization (WHO) released the technical report ‘Guidelines for community noise’ and it concludes that for most spaces within the healthcare segment, critical effects of noise are sleep disturbance, annoyance and communication interference. The guideline demands that the LAmax (A-weighted, maximum sound level) should not exceed 40dB(A) during the day and evening – and during the night the guideline value is 30dB LAeq (A-weighted, equivalent sound level).

 

But how is it in reality? Research¹ has shown that from the 1960s to 2005 the sound levels in hospitals have increased on average 15dB during the day and 18dB during the night and the sound levels are way above the recommendations. In some cases the sound levels are measured to be above 60dB during the night and 70 during the day. According to the WHO it is then impossible to sleep and the recovery of the patients is threatened at the same time as the staff need to stress their voices to be understood.

 

Money

It is difficult to put numbers on wellbeing – but the price of bad sound environments can also be explained with money. Studies²  have shown that medication intake can increase with noise – that patients simply require more sedative medication when sound pressure levels are too high. A study from Sweden also shows that patients suffering from chest pain need extra intravenous beta-blockers in rooms with long reverberation time (0.9 seconds) in comparison to what they need in rooms with short reverberation time (0.4 seconds).³ When you have short reverberation time you do not feel ‘echo’ in the room and you perceive speech more clearly. 

 

 

Standards and regulations in healthcare

Standards, regulations and guidelines on room acoustics in hospitals are lacking in a lot of countries, which is also the case in Finland where 21 hospital districts decide themselves what acoustic targets to reach (if any!). Finland actually has a standard – but not an official requirement and the importance of knowledge about the impact of acoustics can then be crucial for the planners, project participants and architects – since good acoustics have to be prioritised in the design phase to secure the right solutions for the purpose. This was the case at Satakunta Central Hospital and Vaasa Central Hospital. 

 

Satakunta Central Hospital: better working environment and wellbeing of staff

“The staff know what works and what doesn’t!”, maintenance director Tapio Kallio says and continues: “a hospital has complex tasks to solve and it can be difficult to prioritise the right design.” The refurbishments and new buildings of the hospital took place from the end of 2012 and opened in 2015. The old hospital was replaced by a modern women’s and children’s hospital and from the beginning of the transformation the staff took part in the discussions. It was important to the staff and management to create a welcoming friendly environment at the same time as patient privacy and a peaceful atmosphere were highly prioritised. ‘You cannot sleep very well if there’s a lot of noise”, Evelliina Mäki-Opas – the interior decorator concludes – “…and we know that good acoustics have a healing effect on patients”.

 

Absorbing class A wall panels for design and good acoustics in combination with a class A acoustic ceiling.

 

Good acoustics were considered a design opportunity

How do we combine lively colourful spaces with privacy and silence? After all it is also a children’s hospital. To obtain good acoustics in healthcare premises, normally hard surfaces need to be explored. Walls, ceilings and floors are hard and reflect the sound energy that then builds up and creates unwanted noise and high sound levels in a lot of older hospitals. In Finland there has been a long tradition of using metal and plasterboards but the desire for better acoustics made the architects and the planners choose differently. 

 

Class A absorbing glass wool ceilings and wall panels could solve the acoustics, the hygiene demands and the requirement for a lively yet peaceful design. Class A material is the best acoustic material according to ISO 11654 – and the material absorbs up to 100% of the sound energy. The big hard walls were decorated with absorbing ‘photos’ (made by local artists) and together with the class A ceiling, the acoustics were secured without compromising the visual thoughts of both the architects, the staff and the planners. “The sound is softer now”, the staff evaluate, and Tapio Kallio is happy with the success. 

 

Colour and creativity in combination with class A acoustical ceiling.

 

Our hearing and good room acoustics

Our hearing hasn’t changed for thousands of years (actually hundreds of thousands years!) and therefore we are not ‘ready’ to spend up to 90% of our lives indoors in sound environments where hard surfaces reflect and build up the energy of the sound. It stresses our system. Outside the sound will pass our ears once and then it is gone, speech clarity is perfect and natural sounds make us relax. Inside we will hear the direct sound plus the reflected sound again and again if we don’t take care of the acoustics. Speech intelligibility will be bad at the same time as the sound levels increase. 

 

In a lot of guidelines and regulations in general (not only in the healthcare segment) reverberation time is the only acoustic descriptor used to evaluate a room. Reverberation time is defined as the time it takes for a sound to decrease in level by 60dB after the source emission has stopped – and it is often communicated as the ‘echo’ of a room. A big cathedral has long reverberation time – outside there is nearly no reverberation time. At Vaasa Central Hospital they focused on how to decrease the reverberation time.

 

Fig. 1: Measurements of one of the therapy rooms shows that the acoustics treatment shortened the reverberation time remarkably – going from close to two seconds to under one second in all octave bands. Even though the desired target was not attained the end users, patients and staff, were pleased. Only 60% of the ceiling was changed and covered with acoustic class A baffles.

 

Joensu Central Hospital: rooms suitable for speech and recovery 

In this hospital, refurbishments together with new buildings should secure a calm working environment, and tranquility and privacy were considered as a security factor since the hospital also has a psychiatric department. The planning coordinator of the hospital district, Menna Kärnä, states: “The patients should be able to talk without being afraid of being heard”, and explains that in psychiatric wards good room acoustics actually are more important than hygiene factors. 

 

Measurements before and after acoustic treatment were done in one of the old refurbished buildings, and when analysing the reverberation time it is clear why the end user statements are so positive. The measurements revealed that therapy rooms were especially inappropriate for speech (and for sensitive listeners in general!) before the refurbishments – and the long reverberation time and poor speech clarity made the room sound like a big cathedral. Everyone who has been to Notre Dame de Paris knows that it is really difficult to understand speech here and the late reflections and echoes mask the information. 

 

 

Acoustic descriptors and standards

The human ear hears so much more than just reverberation time and when measuring it according to the standard (ISO 3382-1/2) it is measured over a 20 or 30dB range starting 5dB below the initial level and then extrapolated to the full 60dB range. Starting 5dB below can be problematic since this part of the decay contains a lot of information. It actually means that we do not analyse the direct sound and the very first reflections of the sound, despite the fact that they are really important for speech clarity and perception of sound. 

 

Knowing that standards and national building regulations are lacking in the healthcare segment, it would be relevant already from the beginning to include more acoustic descriptors than just reverberation time to secure a healthy working environment for staff and recovery spaces for patients.

 

1. Busch-Vishniac et al. Noise Levels in John Hopkins Hospital. J Acoust Soc Am 2005;118(6):3629–45.
2. Minckley BB. A study of noise and its relationship to patient discomfort in the recovery room. Nurs Res 1968;17(3):247–50.
3. Hagerman I et al. Influence of intensive coronary care acoustics on the quality of care and physiological state of patients. Int J Cardiol 2005;98(2):267–70.