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  Project 1.
Improving acoustics using
sound absorbent walls

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Note:
The projects described on this site relate to the specific situation concerned, and may require adaptation to suit other situations. The information does not necessarily include all relevant Health and Safety information and guidance. No responsibility is accepted by the author(s) or by PAforMusic for any consequence arising directly or indirectly as a result of information provided or omitted.


The project information presented on this page has been kindly submitted by Mike Holt and Martin Mason of Elim Church, Coventry, England. Any queries should be addressed to them (contact information is provided at the bottom of the page).

Take great care when working at height. Follow the Health and Safety Regulations and Guidance and, where relevant, the Building Regulations, that are applicable in your country or region.


Solving Church Acoustics

Demands on Church acoustics have changed radically in the last two decades. The church has moved from no sound reinforcement and the use of purely acoustic instruments with modest sound levels to a situation where a great variety of instruments and voices are used, all amplified sometimes up to levels peaking at 100 dB C. The church environment is becoming more akin to a theatre rather than the traditional concept. This increase in sound levels and complexity together with a requirement for higher standards, and of course the Church is more concerned with clarity and intelligibility than the normal music venue, has brought with it excessive demands on the sound engineering.

This is the situation that the Elim Pentecostal Church, Coventry found itself in recently, ahead of a major refurbishment of the worship area and hence the opportunity to address these issues. The specific problems at the church are unpleasant room resonance in the upper bass area, a thickening of sound textures and a general lack of clarity. This was particularly bad in specific congregational positions such as adjacent to side walls and other locations dependent on resonant frequency being produced.

The main Church built in 1980 and therefore of a modern design, is essentially square in plan view with a vaulted roof. The worship area where the platform of musicians and singers are is set into one of the corners of the square. The roof, being multi-faceted, was good from an acoustic point of view, but the square section plan of the congregational area was the worst possible proportions. Two side areas are provided so that the seating area can be extended from 270 to 350, which turns the shape of the building into a rectangle, which improves the acoustics slightly. The construction of the church is that all of the walls are plain brick, with wood cladding on the roof plus some large expanses of glass. This was a very pleasing modern design but introduced some inherent acoustic problems. The floor was wood block except the platform area, which was carpeted. However the Church was not known as being 'poor' acoustically on the contrary, but increasing demands were producing problems that could not be solved with conventional sound engineering available to a small church.

The music was produced by a worship band comprising electric piano, electric guitar, bass guitar, drums, alto sax, flute plus vocals of worship leader and up to three backing vocals. All musicians were connected to the sound system with three microphones on the drums. No digital sound processing was being used.

This picture shows the bare platform area prior to modification.

The problems were isolated to the 'direct' sound from the musicians located in a recessed corner of the building as the main problem and also, as a secondary issue, the problems associated with the main building shape. With a 'revamp' of the worship area it was decided to explore improvement possibilities. The aim being to reduce the resonances and nodes being set up in the platform area.


platform

This picture shows church being used for a Youth event.

Part of the refurbishment project was for the platform area to have the walls changed visually from brick to a white plaster surface so that wall washers could be introduced and so enable changeable colours to be used to improve the visual aspects.


event

The idea actually adopted was for all the 'wall' area on the platform to be transformed into a sound absorbing area, so that only direct sound emanated from the platform. The 'muddying' of the reverberant sound from the walls would be nullified by being absorbed thereby reducing resonances from the sound emanating area.

The final design comprised a white canvas outer skin onto which the coloured light from the wall washers could be projected, under which were 2 layers of 45 mm of 100 Kg/m3 sound-absorbing felt mounted within studding to maintain its position. Sound would therefore have to travel through 180 mm of absorbing material if it was to reverberate into the room.

Outcomes

The sound quality has been transformed by the implementation of the above design. The musicians have been very complimentary about the changes, as have the congregational members. In other words not only can the congregation hear the music better and more clearly but so can the musicians hear each other better on the platform. Foldback levels have been reduced. The resonant frequency aberrations have been eliminated much to the appreciation of congregational members. Acoustic improvements have occurred in all areas and the solution was far more cost effective than any other solution to the problem.

The issue of a canvas wall being vulnerable to misuse has not materialised as a problem. The kick-board trough has accomplished its function of keeping people and damaging objects away and no serious damage has occurred in the initial years of use. The area does not experience traffic from the general public and the area is restricted. Damage could occur in an area more accessible to the public. The construction has remained taut and provided the function excellently. No drawbacks have been discovered beyond the obvious. For others experiencing problems such as those described above, this would appear to be an excellent solution.


Construction of the Sound Absorbent Walls

It has been suggested that I place on the Web some recent practical experience of covering a brick wall with sound absorbent material finishing with a flat finish suitable for lighting effects.

The wall lit in pink was standard brickwork, as can be seen on either side. It measures 11 metres wide by 6 metres high at its highest point and consists of 90 mm of sound absorbent wadding supported by a wooden frame attached to the wall, and finished in heavy duty canvas, as used in stage scenery.


finished

This picture shows the start of the operation with some framing in place. The framing consists of 50 x 50 mm sawn softwood battens screwed directly to the wall using 125 mm frame fixings. To each of these is screwed another 50 x 50 mm batten using 90 mm x 10 screws.

This should give a top surface to each batten 100 mm from the wall surface. [Should the timber size be marginally under 100 mm it is suggested that 12 mm slats are nailed on top to make sure the surface of the wadding doesn't touch the canvas when taut.]


frame

This photo shows the framing packed with 90 mm wadding.

Please note that a tough plastic netting, as is sold in most garden centres, is stretched tightly across the timber battens and frequently stapled to ensure that the wadding is unlikely to fall forward and spoil the flat surface of the taut canvas.


wadding


This shows the heavy duty, un-shrunk canvas being fixed.

It is fixed temporarily with nails at the top, and then pulled in each direction to remove wrinkles and frequently stapled [e.g. every 150 mm.], but only around the edges of the canvas. Do not attempt to stretch the canvas by hand, but ensure any loose canvas is flattened by merely pulling out the wrinkles, so that the final surface is as flat as possible.


tower


Following this a coat of fireproofing spray is applied, which itself begins the process of tightening, followed, when dry, by a liberal coat of PVA adhesive mixed 1:1 with water. This should produce a completely flat, taut surface, if the wadding has been so fixed that it does not fall against the canvas.

Finish the edges with 50 mm rounded architrave [to avoid shadows] and paint with 2 coats of emulsion. For lighting purposes a stone coloured matt emulsion is effective. This produces a finish which responds well to lighting effects but is also effective in allowing sound to pass through into the wadding.


This photo shows an option for dealing with the bottom of the wall.

In the instance photographed, the framing for the canvas finished 300 mm above the floor so a kickboard 450 mm high was used for the whole 11 metre width. Apart from providing a good place for loose cables it keeps people away from the canvas, which is remarkably resilient but it is best to minimise human contact.

kickboard

Any queries on the above should be directed to:

Mike Holt at mike.holt8@talktalk.net

Martin Mason at martin_mason@talk21.com   (Note: That's martin_mason)

or to the following address:

Mike Holt,
c/o Elim Church, The Butts,
Coventry CV1 3GR
England

UK Tel. 024 7622 6493
International Tel. (+44) 24 7622 6493


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This page last updated 04-Feb-2016.