8th March 2016

Sound Management

1 Preface

Church bell ringing is a part of the Church’s life and work. It has always been thus and it should remain so. The bells and the tower together form, in their acoustic combination, a public musical instrument belonging to the PCC officers and performed upon by church workers, the bell ringers.

English change ringing is a heritage musical activity which has been performed for centuries in public and for the public. In these times of rapid change it can be argued that our heritage artefacts and activities are deserving of care and support.

2 Sound Management Systems

External Sound Management Systems.
The steeples and the bells of churches were provided at considerable expense for the express purpose of proclaiming the continuing life and work of the Church to the public living and working in the neighbourhood and beyond. It needs to be borne in mind that actions taken to reduce the sound levels in the immediate vicinity of the church must be carefully planned and executed to avoid reducing the ultimate range of the sound of the bells into the community.

Internal Sound Management Systems.
Members of the public can and will distinguish good ringing from bad. Public musical performances given by the ringers must be of a good quality if members of the public are to tolerate the sound of church bells. This can be difficult to achieve if the internal sound of a ring of bells is heard too loudly, too quietly, too indistinctly or too unevenly by the ringers in their ringing chamber.

3 Background

The Towers and Belfries Committee of the Central Council of Church Bell Ringers has produced this document to set the scene for the Ringing Master who would like guidance in principle on the subject of sound management. It is not intended to be a technical reference on the improvement of internal and external acoustics of church towers and their bells.

Heritage Concerns.
The ringing of bells in changes by rope and wheel is a special feature of British life. Church bells are rung for many reasons, both ecclesiastical and secular, and the sound of bells ringing changes across town and countryside is part of the heritage. The art of change ringing will continue to flourish if both the public and the Ringing Master adopt reasonable attitudes.

In a world in which the public’s attitude towards environmental issues has changed, the Ringing Master should aim to manage the local regime of ringing in such a way that noise complaints are unlikely to be made. There should always be a presumption against muting the sound of church bells. Muting can turn out to be an irreversible process. There will be a risk to the heritage if permanent muting is allowed to become widespread in a given locality.

The Ringing Regime.
A reasonable local regime is based on a regular and non-varying schedule of ringing for practice night and services, effective advance publicity for all types of ringing including special ringing, adherence by visiting bands of ringers to the local constraints, consideration of the church tower’s closest neighbours, maintenance of good striking at all times, use of tied bells and simulators for novice-training, and holding open days for the public on a regular basis.

Tower Acoustics.
When a Parochial Church Council is considering carrying out acoustic modifications it is important that appropriate specialist technical advice should be obtained to suit the local circumstances. For this reason a number of broad statements of principle have been included, but numerical data have been excluded. In general, each sound management problem is different and must be considered in its own right.

Faculty Jurisdiction.
The PCC must obtain a faculty authorising proposals for works on or within the tower envelope. The Chairman of the Diocesan Advisory Committee will usually obtain the opinion of the DAC’s Bells Consultant prior to the DAC’s examination of the PCC’s faculty submission proposals. Work of acoustic modification to a church tower, if it in any way affects fabric or fittings, is likely to require the church architect’s approval.

Sound.
Sound usually travels from the source to the listener by way of a number of air paths. The most effective air paths are those having the shortest path lengths, providing they are uninterrupted and sufficient. Appreciable sounds reaching the listener by air paths other than the shortest can be confusing when heard mixed with shortest path sounds, although reflected rays are not always harmful and can provide a feeling of spaciousness.

Partial Sound Barriers and Sound Shadows.
Under external conditions, to insert a sound barrier such as a boundary wall or solid screen between the source and the listener, is to cast a sound shadow across the listener. The sound reduction will vary according to the difference between the shortest air path lengths with and without the barrier in position, and to the amount of diffraction taking place over the barrier’s top edge.

The sound reduction is less for low frequency sounds and more for high frequency sounds. For a single bell the ratio of the low and high frequencies emitted is about four to one, considering the five principal partial tones of the bell only. For a ring of eight bells the ratio of these frequencies is about eight to one. The sound barrier will reduce the volume of the higher partials of the small bells more than the lower partials of the large bells. The sound shadow effect may be small if there are secondary air paths, for example around the vertical edges of barriers, or if there are reflections into the shadow zone.

Sealed Enclosure.
A bell chamber is a relatively compact source of intense sound. In order to achieve a large degree of reduction of the sound levels experienced by all external listeners wherever positioned, it would be necessary to place the source within a sealed envelope. If there remained any openings through the otherwise continuous envelope then each one would behave as an intense source of sound in its own right, rather like a highly energised loudspeaker of the same effective area.

It would therefore be of primary importance to eliminate unwanted air paths through the envelope. Until the principle of a sealed enclosure had been satisfied the type of enclosing material would have only a secondary significance. Then, and then only, would the mass per unit surface area of the enclosing envelope become the key factor determining the amount of sound reduction.

For a semi-continuous barrier intended to cast a sound shadow over external listeners it is similarly important for the barrier to be solid and to have no chinks around its sides or its lower edge.

Material Types.
Material of high mass per unit area and low surface porosity will tend to reflect airborne sound. That part of the sound transmitted to the air on the other side of the material will be heavily attenuated.

Material of low mass per unit area and high surface porosity will tend not to reflect sound. That part of the sound transmitted to the air on the other side of the material will be lightly attenuated, especially if there are numerous capillary air paths throughout the material.

Material of high mass per unit area and high surface porosity will have intermediate reflection and air to air transmission characteristics which depend on the quantity and extent of capillary air paths within the material and on the frequencies of the incident sounds.

Care is needed when selecting materials for practical application. A material which is good for high reflection and low air to air transmission may give rise to reverberation problems in spacious chambers. On the other hand, a material which is selected for low reflection properties may have unexpectedly high air to air transmission properties. Some proprietary air-filled materials may have unexpectedly high air-to-air transmission properties.

Sound Levels.
Measurement of sound levels and the interpretation of results requires specialised equipment, knowledge and experience. In the wrong hands the use of sound level meters and the data they provide can be misleading, particularly when the readings are quoted out of their full and proper context.

An assessment of whether or not a given sound level could be considered disturbing depends on a number of circumstances including the nature of the sound under consideration, the season, the day of the week, the time of day, the weather, and the make-up and level of background noise. It is also true that the question of whether or not a disturbance is deemed to exist is a subjective judgement which could be influenced to a very large degree by the type of regime of ringing currently in operation.

4 Inside the Tower

Too Much Sound.
Reduce as far as possible the number of complete air paths between the bell chamber and the ringing chamber, and minimise the effective area of any air openings there may be in the floors between the bells and ringers.

Staircases, clock cases and clock weight shafts may provide unwanted air paths. Displaced boards in bell chamber floors must be replaced and secured. Boxed-in rope chutes between floors can act as excessive air paths and it may be advisable to modify them to become partial boxes or slap boards.

Too Little Sound.
Increase the number of complete air paths between the bell chamber and the ringing chamber, but aim to achieve an even set of sound levels, bell versus bell, and an even audibility of all the bells in all parts of the ringing chamber.

In some towers a false ceiling may have been installed instead of a sally guide frame, at a cost in terms of good audibility.

Uneven Sound.
Where there is an intermediate chamber between the bell chamber and the ringing chamber there is ample scope for achieving a satisfactory distribution of the sound before it passes down to the ringers. Adjustments of air paths in number, size and position will usually be sufficient.

It may be necessary to pipe bell sound from the upper tiers of multiple tier frames, either into the intermediate chamber or even into the ringing chamber itself.

Confused Sound.
Echoes and long reverberation times can result in a confused sound for the ringers when the bells are being rung. Reverberation time depends directly on room volume, and inversely on surface area and surface absorption. When there are parallel reflecting surfaces in a room they can cause flutter echoes which are disturbing.

The offending space may be the bell chamber, the intermediate chamber, the ringing room or a combination of them. It can be difficult to diagnose what is wrong. The cure is to cover a significant proportion of the total area of facing surfaces, including floors, in each reverberating space with a non-reflecting material.

When internal alterations in any of the tower chambers are carried out care needs to be taken to avoid introducing or exposing new areas of sound reflecting surface which may cause echoes and increase the reverberation time.

If the bell chamber sound outlet windows are closed off with blockwork, stonework, brickwork or wooden boarding the sound outlets will cease to behave as “black holes” for transmission of the sound energy produced by the bells, reverberation within the bell chamber could become a problem and the sound of the bells heard by the ringers might become confused.

In the ringing chamber the removal of carpet from the floor or curtains from the windows is likely to result in a loss of clarity of the sound heard by the ringers. In all chambers with concrete floors heavy carpet should completely cover the floors.

The installation of a full height permanent glass screen, between the ground floor or gallery ringing room and the nave of the church, opposite the west window of the tower, might introduce the problem of confused sound due to reverberation.

The Sound Comes and Goes.
In ringing rooms with low ceilings it is common for the sallies to interrupt the air paths as they pass through the rope holes, with disconcerting results in terms of audibility.

A false ceiling which serves simply as a sally guide should be removed and a sally guide frame should be installed.

Boxed-in rope chutes passing through a low intermediate chamber should be replaced by partial boxes or slap boards. In other cases it may be necessary to provide additional parallel air paths to offset the problem.

Unwanted Sounds.
A false ceiling installed as a sally guide may drum and rumble if it is of light construction. A flimsy sally guide frame may rattle. Rope bosses may rattle if not secured to the ceiling or guide frame properly.

In a few towers one can hear the shock of clapper blows transmitted through the headstocks and frame to the tower structure itself. If this problem is severe then advice from a firm of professional bellhangers must be obtained.

5 The Intermediate Sound Attenuation and Balancing Chamber

The sound attenuation and balancing chamber, interposed between the bell chamber and the ringing chamber, is included in the design configuration of a church tower with these objectives:-

  • To attenuate and balance the sound levels of the bells as heard by the ringers in the ringing chamber. The ringers will not be able to produce high quality musical performances unless they can hear each bell evenly and neither too loudly nor too quietly.
  • For health and safety reasons, including the need for reduction of sound to a safe level and the need for protection of the ringers from bells and/or clappers falling out of the bell frame if a mechanical failure were to take place.
  • To enable adjustments to be made to the fall of the bell ropes to improve the rope circle in the ringing chamber.
    Such a chamber should preferably be about 2.5m (8ft) tall, bounded above and below by substantial wooden tongued and grooved or closely butted boarded floors. The two floors should each be supported by wooden joists spanning the tower in accordance with Building Regulation requirements. Neither of the floors should be boarded across underneath the joists.

The upper floor should be designed to sustain violent impacts when for example, due to component failure, a clapper falls onto it after becoming detached from a bell while swinging full circle. The lower floor should be of similar construction, and should be structurally and acoustically independent of the upper floor.

Both floors should be continuous sound-opaque membranes except for the essential bell rope holes, each of which should be fitted with a cast iron rope hole boss. There should be no superfluous air paths (as evidenced by light paths) through the floors, around the trap door or at the floor edges where they meet the tower walls whose surfaces are often uneven.

In a tower of insufficient height to accommodate an intermediate sound attenuation and balancing chamber, where a single floor between bell chamber and ringing chamber has been boarded above and below the joists, and where the interspace so formed has been filled with sawdust or a proprietary air-filled material, it is common to find that vertical tubes have been installed between the two sets of boarding, i.e. between the upper and lower rope holes, to stop sawdust or a proprietary air-filled material falling through into the ringing room.

However each tube then acts as a transmitter of unbalanced sound energy from the bell immediately above it. The acoustic situation may be improved by removing the tubes altogether, installing instead a half-height “fence”, around and well back from each rope hole, to retain the layer of sawdust or proprietary air-filled material.

6 The Tower Staircase as an Unwanted Sound Path

Musical sounds are best transmitted to our ears along air paths. The intended and proper route for the bell sounds to pass from the bells in their bell chamber to the ringers in their ringing chamber is firstly through the rope holes in the bell chamber floor, then into the intermediate sound attenuation and balancing chamber, and lastly through the rope holes in the ringing room ceiling i.e. the intermediate chamber floor. This design configuration usually results in the sounds of all of the bells being heard evenly and at a reasonable volume.

However the staircase of a church tower is usually offset from the central vertical axis of the tower and is often located at a corner. If there are superfluous air paths between the bell chamber, the staircase, the intermediate chamber and the ringing chamber, then the staircase will transmit a significant proportion of unbalanced sound from that corner of the bell chamber downwards and into the ringing chamber.

Each door into the staircase needs to be well designed and fitted so that there are no air ways through it, around it, over its top edge or under its bottom edge. The general rule is that if light cannot pass through any of the doorways, then unbalanced bell sound will not pass through or around any of them. It should be noted that it is important for the tower staircase to have a slight amount of natural ventilation, usually achieved by equipping both the entrance door at ground level and the exit door onto the tower roof with a small vent, but guarded to prevent entry of wind-driven stormwater.

7 Tower Alterations and their Acoustic Effects

Attention is drawn to the importance of adopting a carefully planned, measured and recorded procedure during any programme of internal acoustic improvement.

Each change to be made should be fully detailed in writing and with accompanying dimensioned drawings. Only one change should be made at a time. Sound measurements should be taken before and after each change is made. A written log should be kept of the details of every change made, the effects it had, the date, the method of measurement, and who made the entry in the log.

Unless such a procedure is used it will be difficult to manage a programme of internal acoustic improvement effectively. If more than one change were to be made at time it could be difficult afterwards to determine which change produced a particular acoustic result for the better or the worse.

A ring of church bells is, at any given time, as acoustically satisfactory as the church tower’s design, construction and present contents permit. Alterations to the internal acoustics of the tower can affect what the ringers hear in the ringing chamber, but they can also have an indirect effect on what is heard outside the tower.

If the internal acoustics are worsened, then the quality of the ringers’ musical performances are of course worsened as a direct result. This will be noticed by members of the public in the neighbourhood of the church. The main influences on the tower’s internal acoustics are the physical properties of the ringing chamber, the intermediate sound attenuation and balancing (ISA&B) chamber, the bell chamber, the tower staircase, and also the physical properties of their respective contents.

The features which have marked effects on the acoustic properties of the church tower include:-

  • The relative sizes and proportions of the three chambers above-mentioned, and of their interconnecting staircase.
  • The ceiling materials, construction and surface finishes of each chamber.
  • The wall materials, construction and surface finishes of each chamber.
  • The materials, proportions and surface finishes of the window recesses and windows of each chamber.
  • The floor materials, construction and surface finishes of each chamber.
  • The sizes, proportions, and design configurations of the sound outlet windows in the bell chamber walls, and of their louvres for limiting ingress of wind-driven stormwater.
  • The materials, construction and surface finishes of the tower staircase.
  • The size, proportions, materials and construction of the ISA&B chamber (positioned between the ringing chamber and the bell chamber) are crucial in influencing the sound of the bells heard by the ringers during ringing. These design details directly control the general sound-level of the bells and also the sound-level of each bell relative to the others.
  • The sizes, positions, materials, construction and degree of fit of the tower staircase door surrounds and the doors themselves.
  • The sizes, positions, materials, construction and degree of fit of the trapway surrounds and trap doors themselves through the floors of the bell chamber and the ISA&B chamber.
  • The material, sizes and positions of bell rope hole bosses, clock wire holes and clock weight shafts through the floors of the bell chamber and ISA&B chamber.
  • The contents of each of the chambers in the tower.

8 Outside the Tower

External sound management action may be required to modify the sound level and the sound spectrum of the bells as heard by external listeners in the immediate vicinity. The upper partials of the bells (each bell has at least five principal partial tones when struck) can be a source of annoyance to listeners close outside.

A simple method of reducing the intensities of the upper partials relative to the lower partials is to install around the ring of bells an imperforate semi-continuous sound-barrier to a height just above the mouths of the bells when they are up. In this context the term semi-continuous means that the barrier is continuous and sound-opaque from its top edge downwards, but is open and sound-transparent from its top edge upwards. The tower walls can form most of this barrier, with window openings protected as described above.

Too Much Sound.
The full set of sound outlets should not be closed-off completely as a solution to this problem. It could be an irreversible step. It could encourage those who advocate the silencing of church bells at large. The preferred solution, if there is no spire, is to combine the closing-off of the sound outlet windows with installation of a tower roof sound lantern which, in conjunction with the parapet, produces a sound shadow in the immediate locality of the tower.

The carrying power of the bells and the ventilation of the tower are preserved by this solution. The sound is reflected off the tower roof surface and directed upwards rather than downwards.

Where there is a spire with open sound outlet windows it is usually sufficient to close off the tower outlets only.

Where neither of these is feasible the sound outlets can be closed off from the bottom to a height just above the mouths of the bells when they are up. It is important to leave enough outlet area at the top of each window to preserve satisfactory carrying power.

If the tower’s design configuration permits, a floor could be built above the bells and below the sound outlets. The total effective airway area of the sound-path openings through this floor would need to be large, and greater in total area than the total effective airway area of the original sound outlet windows. The floor’s permanent apertures and trapways for sound must be properly and permanently guarded around.

Too Little Sound.
Efforts at sound limitation in the environs of the tower may have resulted in closing too much of the outlet windows and it is of course a matter for regret if the audible range of the bells has been reduced.

The preferred solution of installing a tower roof sound lantern after completely closing off the outlets should be considered. Failing this, some judicious opening of the upper parts of the outlet windows may suffice.

Uneven Sound.
When some or all of the bells are hung above the sills of the sound outlet windows, or above the level of the boarding or blockwork, there will be a tendency for those bells nearest the listener to shout out above the others. The uneven effect can be disturbing.

On the other hand when all the bells are hung with their upturned mouths some way below the sills, even when the bells are hung in tiers, the external listener will hear them evenly. Improvements can be made by boarding around bells which are hung in upper tiers alongside the outlet windows.

Harshness of Sound.
A listener near the tower may find the sound of the smaller bells harsh especially when they are hung above the level of the sills or boarding of the outlet windows.

The technique of boarding around these bells will produce a partial sound shadow for the higher pitched, and therefore more disturbing, sounds. Steeply inclined sound outlet louvre boards can intensify harshness of higher frequency sounds close to the tower. Replacement with less inclined louvre boards fitted with high back-lips can reduce the problem without impairing weather protection. Replacement with perforated weather boards and back canvas is acceptable in some localities.

The Sound Lacks Carrying Power.
Those carrying out installation and care of bells must have in mind the need to limit local annoyance, but must recognise the need to preserve their carrying power and the range of reasonable audibility. A properly designed tower roof sound lantern meets these needs.

When a lantern is to be installed it is important to remove any existing barriers between the bells and the lantern, such as those provided above the bells during earlier attempts at external sound control.

Where there is a large space above the bells, their range can be increased by suspending an inverted timber cone below the tower roof which will act as a sound reflector, increasing the sound output through the bell chamber windows.

Clapper Rattle and Mechanical Noise.
Clapper rattle or other mechanical noises coming from the bell chamber can be an unrecognised cause of local annoyance. A routine of regular inspection, maintenance and record-keeping must be operated to ensure that such problems are diagnosed and corrected promptly.

Variable Means of Control of the Sound of the Bells Outside the Tower.
When it is not practical to install a tower roof sound lantern and it has been decided that the sound outlets must inevitably be largely closed off, the idea of providing variable traps in the sound envelope may be attractive.

The basis is that the ringers will open the traps during service ringing and weddings but will close them during practices and other ringing. Experience has shown, however, that unless a set of remote controls for the traps is provided within the ringing room itself, this opening and closing is hardly ever done.

The ringers are unlikely, after a brief initial enthusiasm, to make the climb to a bell chamber which may not be clean and safe to enter. This being so, the traps remain closed and the bells are no longer heard at any great distance from the church.

The remote control in the ringing chamber, whether it is mechanical, hydraulic or electrical, must be conveniently positioned and easy to use. It must be professionally designed and engineered and it must continue to work satisfactorily throughout the life of the traps.

The variable traps in the sound envelope must themselves have well designed and engineered heavy-duty actuating gear. The wind forces on variable traps during storm conditions must be taken into account. The traps must stay-put in the open, closed and intermediate positions, and they must be capable of full and satisfactory movement throughout their designed stroke during such storms. The actuating gear must be weatherproof and its satisfactory operation must not be reliant on frequent lubrication and maintenance. Simple rope-operated shutters are often the best, provided that they and their operating gear have been properly designed and constructed.

9 A Tower Roof Sound Lantern

Objectives:-

  • To reduce the sound levels in the immediate vicinity of the tower.
  • To project the sound upwards and outwards into the sky whilst keeping out rain, hail and snow.
  • To preserve the carrying power and ultimate range of the bells.

Design Considerations.
The original sound outlet windows in the bell chamber walls must be completely closed off with imperforate sound barriers.

A sufficient area of sound outlet opening must be provided through the tower roof into the base of the sound lantern. It must at least be equal in effective area to the total of the original openings in the four walls’ sound outlet windows.

The height and louvred perimeter of the sound lantern must, subject to appearance considerations, be designed to be sufficient to provide a total effective area of openings at least equal to the tower roof opening in plan and, by implication, at least equal to the total of the original openings in the sound outlet windows.

The reduction of sound levels close to the tower will be marked. It is a result of closing off the sound outlet windows and thereby increasing the air path length by an amount roughly equal to the distance from the sound lantern outlets measured over the tower parapet to the old bell chamber wall outlets.

In addition, two successive sound shadows operate in series, the first created by the sound lantern’s positioning at the top of the tower and the second created by the tower parapet itself. The sound lantern and parapet combination has the function of projecting the great majority of the bells’ sound upwards into the sky in the form of an inverted pyramid.

The extent and intensity of the overall sound shadow are affected by many factors. Examples are the height of the parapet, any slots or perforations in the parapet which reduce its effective height as a sound barrier, the height of the lantern, the horizontal distance between the lantern air openings and the parapet, and the position and local surroundings of the tower.

A tall sound lantern, in combination with a tower parapet of small height, will produce a slight sound-shadow of small extent. A short sound lantern, in combination with a tower parapet of great height, will produce a dense sound-shadow of great extent.

In all cases, ornamental perforations through the parapet will reduce the density of the sound-shadow.

The extent of the sound shadow around the tower in plan view may be estimated roughly by making a set of elevation sketches of the tower and surrounding topography.

Comparisons of air path length difference, with and without the sound outlet windows closed off, and with and without the interposition of the tower parapet effective height at the correct position between the lantern and listener, will give an indication of sound shadow intensity for various listener locations.

For large distances from the tower the air path length difference becomes negligible in relation to the air path length itself. Consequently the carrying power of the bells will be shown to be little affected, subject to the care given to sufficiency of sound outlet air openings and the geometry of the tower parapet and lantern combination.

10 Sources of Advice

Professional Firms:-
Established firms of bell founders, bell hangers and other technical specialists advertise regularly in the weekly newspaper of the Central Council of Church Bell Ringers, “The Ringing World”, 35A High Street, Andover, SP10 1LJ, UK, telephone 01264 366620.

The Central Council of Church Bell Ringers:-

  • The Towers and Belfries Committee can be contacted through its Chairman, c/o The Editor, “The Ringing World”, address above.
  • The Public Relations Committee has prepared a document “Guidelines on Ensuring the Acceptability of the Sound of Church Bell Ringing”. The PRC’s Complaints Advisers can be contacted through its Chairman, c/o The Editor, “The Ringing World”, address above.

Complaints by Members of the Public:-
If there is a complaint about your bells, do respond promptly, sympathetically, courteously and reasonably, and then seek experienced help from the Public Relations Committee Complaints Adviser for your area. In the event that advice on sound levels is needed, the Public Relations Committee has access to specialists in measurement of sound levels and the proper interpretation of results.

The Local Territorial Association:-
The bells adviser of the local territorial Association of Church Bell Ringers can be contacted through the Association’s General Secretary c/o the local Diocesan Office.

The Diocese:-
The specialist advice of the Diocesan Advisory Committee’s Bells Consultant may be sought by the Chairman of the DAC in response to a query from a principal PCC officer i.e. the Incumbent, Churchwarden, PCC Treasurer or PCC Secretary.

11 Reference

The Towers & Bells Handbook 1990 Edition. Editor A J Frost AADip RIBA DCHM.

Print Friendly