An easier way to make double muffles for bell ringing practice

The Kent County Association website describes a method of creating double muffles from old motor cycle tyres.  This gives good results but is hard and dirty work , and need the use of an angle grinder, which is a dangerous tool to use.

This note describes making similar rubber clapper muffles cheaply and more easily from relatively compliant 6mm sheet neoprene rubber.  Experience of use is limited, but tests so far are good.  Even if it turns out that they don't last as long as the Kent ones, they are so easy to make it doesn't matter.

The rubber sheet can be bought cheaply on ebay - search for something like "Rubber Sheet Material" - a "value" (i.e. cheap) grade of material is good enough.  A sheet 300x300mm is enough to make double muffs for 4 bells. Look for something like this:

Each double muffle also needs 2 300mm x 3.6mm plastic cable ties to hold it in place round the clapper ball. 

The sheet can be easily and quickly cut with a Stanley knife to provide 2 strips each 3 inches wide and 6 inches long.  (This size suits a ball of 4.5 inches across. )

Holes are drilled drilled at the corners half an inch in from the edges and ends.  The cable ties go through the holes,

and the unit is fitted into the clapper ball with one tie above the ball and another below it.  The ties are then tightened up but leaving enough looseness so the unit can be moved through 90 degrees. 

This takes only seconds to fit in the first instance, and just seconds to change from muffled:

to unmuffled:

If removal is ever required the ties (which are very cheap) are simply cut with a knife, and new ties used to put the muffles back on. 

(Alternatively, if the muffles cannot be left in place for some reason, they can be tied on (inner side):

(and outer side  - is here shown with a second muffle layer for greater sound reduction)

 but this tying on method is not recommended, as it is more fiddly and less reliable)

The rubber fits closely onto the ball in this configuration, is very neat and effective and is much easier than using motor cycle tyres. 

It also has the advantage over motorcycle tyres that the quietening is very consistent as the material is of consistent specification, and very closely attached to the ball.

If the sound is still too loud for your neighbours , use two layers of rubber.  If the clapper bounces producing audible multiple strikes, try adding an additional muffle made from old carpet - this version was made longer, so it fits over a rubber muffle:

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The more you muffle the less satisfactory the ringer's experience of the sound becomes

Improving the sound

The timing of the sound of muffled bells is hard to hear accurately in the ringing chamber.  When using muffled bells it is a good idea to have a microphone in the bell chamber linked to the sound card on the ringing room computer and piped through to some powerful loudspeakers in the ringing chamber .

Place the microphone well away from any individual beel to avoid sound imbalance.  A cheap electret microphone will do - try to avoid overloading it with sound, pack some felt around it if need be.  Experiment to get good sound.  (please feedback your experiences!)

The required software to do this is "SOX", which is open source software available for different platforms.  This runs a "console" program (which makes it fast).  On windows open a cmd ("Dos") window and run the sox executable program with this command line: 

sox -r 16k -c1 --buffer 512 -d -d  

This will send the microphone input to the loudspeakers, using rate 16k samples per second (-r 16k), for a single channel (-c1) with buffer size 512 (--buffer 512).  The use of 16k rather than the standard 44.1k was to reduce the load on the computer and reduce latency on an old computer - it seems good enough.

There may be a slight delay in the sound depending on how far up the bells are from the ringing room.  The delay can be adjusted by changing the buffer size in SOX - change the number 512 in the line above - if it is too small, there will be audible glitches.

You will also need to ensure that the audio settings for the microphone input and the loudspeakers are correct.  The SOX program has an indicator to show whether the sound is overloaded or not.

It is also possible to filter the sound to make the strike notes easier to hear:  Our setup works better using this:

sox -r 16k -c1 --buffer 512 -d -d  equalizer 1200 0.7q +11

The following CMD batch routine (call it runrox.bat) (works on WinXP) does all this, and opens the audio settings automatically and records the sound to a file all at the same time and tidies up the windows using a program called CMDOW:

@ECHO off
set mytest=ring

rem test for file already exists, if so add a _ to name
:2
if not exist %mytest%.wav goto 1
set mytest=%mytest%_
goto 2

:1

rem get a filename from user
set /p mytest="provide filename (no extn), followed by [ENTER] - default = %mytest%
echo Using filename :  %mytest%
echo setting up microphone to loudspeakers, using modified sound:-
start sox -r 16k -c1 --buffer 512 -d -d equalizer 1200 0.7q +11
echo setting up microphone to sound recording file "%mytest%.wav":-

rem NB this records original sound not modified
start sox -r 16k -c1 -d "%mytest%.wav"
echo open the recording applet to adjust microphone level
echo make sure sound bars in the black windows are loud enough but don't max out!

rem this is the version for Winxp SP3,  Win7 is sndvol.exe rather than sndvol32.exe
start c:\windows\system32\sndvol32.exe -r
ECHO When finished, terminate the programs in the other black windows using CTRL-C
Echo when those are closed, continue by pressing ENTER to play back recording
cmdow /tv
pause

rem play back what was recorded

start sox "%mytest%.wav" -d

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Examples of sound heard in ringing chamber through the microphone loudspeaker set up

Here are some examples recorded at Tiverton St Peter (25cwt 1920s Taylor 8) - which uses Kent Association type muffles.  The microphone is in one corner of the bell chamber and about 2 m above the bells and points up towards the centre of the bell chamber.  This ringing was recorded during a early learner training session, and the  striking is not good.

All 8 bells rung open - this overloads the electret microphone, consequently creating a wave form which is displaced from being centred on zero, but it sounds reasonably ok.

Front 6 bells rung open

Front 6 bells with muffles as used for muffled practice.  The initial strike point is followed by additional impact sounds which probably reflect clapper bounce and engagement with the Hastings stay slider rail, but this is not too much of a problem for practice purposes.

Front 6 bells with sound modified to improve audibility as above

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Please notify any issues in this paper, thanks

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R H Johnston 26.8.2015.