Posted 15 February 2002
Baffles for Maccann Duet Concertinas:
Section I. Introduction
Robert Gaskins
1. Introduction
Baffles fitted internally can reduce the volume
and/or change the tone of a Maccann Duet concertina, and
the sound of each end can be controlled independently
so that the "balance" of an instrument can be altered.
By using different baffle techniques and
materials (leather and/or acoustical fabric)
it is possible to quiet the sound only slightly or to reduce it by up to half.
Some types of baffles change the sound-quality of the tone produced
(making it subjectively "sweeter" to most ears),
while others do not change the sound-quality appreciably.
Results in three example concertinas are given,
as measured by a sound level meter.
All baffles considered here make no change to the concertina,
and can be removed in moments leaving no trace.
This paper describes my experiments in fitting baffles to my Maccann Duet
concertinas in order to make them better suited to the music I want to play and
to my level of skill in playing.
When I began on this project, I could find only a few references to baffles,
and limited information about materials and techniques--mostly in a newsgroup
posting by Chris Timson, which is reproduced at the end of this note.
Since then I have
identified the proper materials and located sources for them (all on the web),
tried out various techniques to attach the baffles,
and measured with a sound level meter the changes produced. I hope that an
account of my successful experiences will help others with similar interests,
but there is still very much that I don't know. As is apparently true of all
topics in the acoustics of concertinas, there are many received opinions which
need to be examined critically, and the phenomena are complex enough that it
is easy for me to be mistaken in understanding the implications of any experiment.
This is not the definitive treatise on baffles; it is merely a personal report of
what I tried on some specific concertinas, and how it worked for me.
The specific problem that I wanted to solve was that
left-hand chords were too loud, so that they drowned out any right-hand melody.
(This is a situation that has long been known with duets.)
I found that a solution was to fix baffles of morocco goatskin
leather on short standoffs mounted under the fretwork of both ends,
and to augment the leather on the left side alone with layers of sound-absorbing
acoustical fabric placed on both sides of the reeds.
After this had been done, the left side was quieter than the right
so that a right-hand melody was clearly audible over sustained left-hand chords.
This particular use of baffles to quiet the left side more than the right
is clearly applicable only to Duets.
On an English concertina, where the scale alternates between right and left,
it would never do to have the notes grossly different in volume
on the left and right sides.
On an Anglo concertina it is necessary to mix notes from both sides
in playing most melodies so the notes should be the same volume on both sides.
And even on a Maccann Duet, passages in arrangements such as those of
David Cornell
use notes from both sides to gain flexibility and fluidity,
so they need to be the same volume.
Using baffles specifically to quiet the left side more than the right side is
feasible, or at least practical, only on a Duet
dedicated strictly to playing melody on the right and accompaniment on the left.
But this is not the only use for concertina baffles.
Other people have used the same or similar techniques
on English concertinas and Anglo concertinas
to make the volumes of the two ends equal if they are not naturally so,
or to quiet both sides equally to suit the volume to a singer or a smaller space,
or to alter the sound quality comparably on both sides.
I have fitted baffles only to Maccann Duets of various sizes (39-key to 67-key)
made prior to World War II by Wheatstone, Lachenal, and Jeffries,
but I believe that the information here would be relevant to other concertinas
of vintage English-style construction, not only Crane Duets and Hayden Duets
but also English and Anglo concertinas.
Certainly I have found
that the techniques described
in this note have different effects on different concertinas, so it would be
interesting to have comparable descriptions of other installations. I would
be very grateful for information about alternative ways of fitting baffles
and about historical uses of baffles on concertinas.
2. Motivation: Why I Fit Baffles
A player may want to change the relative volumes of sound from the two ends
of a Maccann Duet, referred to as the "balance",
depending on the style of playing--how
many notes are played at one time on each side, how long the notes are
sounded, and so forth. Different players will want different relative volumes
from the bass and treble sides. But there is no way for a player to control
the two ends separately, any more than there is a way to control individual notes.
The relative volume of the two ends is fixed at the factory.
There are thought to be many things that can be done during construction of a
concertina to affect the balance of the two ends: what size reeds are
chosen for each note, the size and shape of the tone chambers around each
pair of reeds, the depth of the chambers and whether the reedpan which is
their floor is flat or angled, the number and position of sound posts (under
the palm rest), the materials used for the reedpan, the materials used for
the ends, and more, are all thought to affect the balance. But once the
concertina has been shipped from the factory, these are all fixed.
Individual instruments differ quite a lot
in the balance of their two ends, but a player ordinarily doesn't get a
chance to choose among many instruments.
The most common need, I judge, is to make the bass quieter. On most
Maccann Duets, anyone who wishes to play sustained chords in the left
hand finds that three or four bass reeds drown out a
melody played on single treble reeds in the right hand. But depending on
the instrument, even playing
two single-note lines, one on each side, or playing chords on both sides
simultaneously, may require some adjustment to the balance.
Some people who use the concertina to accompany
their singing want to reduce the volume of both ends,
perhaps in addition to changing the balance,
for a better match to the loudness of a human voice.
Also common is the desire to make the instrument quieter overall, so as to make
it acceptable in a small performance space (especially for instruments which are
not very responsive when played gently).
Finally, there is the motivation to improve the tone of the concertina.
Chris Timson, a prominent advocate for adding baffles
to the English and Anglo concertinas that
he and Anne Gregson use to accompany their singing,
characterizes the tone of a concertina with added baffles
as "significantly sweeter". My experience on Maccann Duets is the same,
but it is hard to be any more precise about the change; the effect
is different on different instruments, presumably depending on properties of
their reeds, and whether the change is an advantage will be a matter
of personal taste.
Wim Wakker's website,
www.concertinaconnection.com,
suggests that baffles change the tone in part by differentially quieting
higher harmonics, and that one effect of that is to make close chords sound better:
"Close chords, e.g.
C-E-G, do not sound good on a concertina (or any other free reed instrument for
that matter). The harmonics of the three tones, being so close together, tend
to clash. Chords sound a lot better when played in a wide position, for instance
C-G-E. The spacing between the notes prevents the harmonics from clashing.
... Victorian
concertinas with steel reeds were suitable for close chords, because of the
leather baffle, which muted the higher harmonics."
I play close chords all the time, on steel reeds, and they sound fine to
me--perhaps because I have installed leather baffles.
So, any particular concertina, as it was made, may be louder than a singer
desires, may be too loud for smaller rooms,
may have a tone that can be improved (particularly for chords), or may need to
have the relative volumes of sound on its two ends adjusted. Fortunately,
there is a time-tested approach which can address these problems,
and that is to modify the sound of an existing instrument by fitting baffles
in one or both ends. I think of adding baffles to a Maccann Duet as "setting it up",
much as is done with other instruments, to tailor it to personal requirements
of the player. One listens, measures the volume of the two ends, and makes
adjustments as needed, by fitting baffles suited to the particular concertina
and its intended use.
3. Original Baffles on Vintage Concertinas
In fact, the very oldest duet concertinas
(which are the pre-Maccann Wheatstone "Double" duets made from about 1845)
were designed with one baffle on the right side and two baffles on the left
side, perhaps suggesting that the balance of sound on left and right sides was a
concern from the very earliest experiments with duet designs.
English-system concertinas in this very earliest period were customarily delivered
with pine or spruce baffles installed in both ends, beneath the fretwork.
Wes Williams showed me his remarkably-preserved
Wheatstone serial #1701 (around 1848) with original pine baffles in place. These pine baffles
are supported on three T-shaped padded struts which rise from among the action levers and which
hold the pine baffles firmly against bits of felt glued on the inside of the fretwork.
Wheatstone #1701 with original pine baffles (Wes Williams)
These “outer” wooden baffles continued in use for some years.
Paul Hardy has
provided me a photograph of wooden baffles in place in his old Wheatstone 48-key treble
English concertina serial #8461 (mid-1850s).
Wheatstone #8461 (Paul Hardy)
But in the early Double duet concertinas made at the same time, we find an additional
“inner” baffle on the left side—only. Wheatstone Double #23 (1847–1848)
has the customary pine or spruce baffles on both sides, and an extra shaped baffle (also of
spruce) screwed to a doughnut-shaped sycamore stand-off mounted around the central hole on the
inside of the left reed pan. This “inner” left-side baffle is asymmetrical and
covers all the larger reeds on the left side, leaving the left-side reeds which overlap with
the right end uncovered. This could have been an attempt to reduce the volume on the left
side smoothly, so that the same note was not quieter on the left and louder on the right.
There is further possible evidence of early concern to balance the volume of sound
from the two ends of a duet concertina. In his survey “The Wheatstone English Concertina”,
Neil Wayne mentions a sequence of three Double duets he has examined,
Nos. 5, 10, and 58. Of the earliest No. 5, he says that it “was probably a prototype instrument developed
by Wheatstone and has a partially completed baffle system in a deep central division in the
bellows. He had tried to perfect a method of splitting the bellows into two separate
compartments so that the larger, deeper left-hand reeds would not overpower the smaller
treble reeds. This instrument also has a circular wooden baffle screwed over the inner
face of the bass reed pan, presumably to further reduce the sound output of the deeper
reeds.” The second Double he examined, No. 10, appears to have closely resembled
Danny Chapman’s No. 14, also a 67-key duet. “It too has a centrally-placed
bellows baffle, but with the refinement of a pair of trap-door air valves, one each
side of the inner wooden baffle, which are operated by a brass switch mounted on the outside
edge of the central bellows fold that contains the baffle. In spite of this sophisticated
arrangement, the use of these baffles would only have had an effect on the relative pressure
head in each end of the instrument if the centre of the bellows was held rigidly relative
to the ends, otherwise the pressure would be identical in each half. There is evidence in
‘double’ no. 10 that the central bellows section could be secured to a
rigid mount to enable the separate ends of the concertina to be played at independent
volumes.” But by the time of Wayne's No. 58 the experimental attempt to divide
the bellows had been abandoned, and in fact it appears to have been abandoned by No. 23.
This idea of separating the halves of the bellows would only have been attractive for
a duet; on an English concertina, with notes alternating between the ends, both ends
must have the same volume.
(Neil Wayne, “The Wheatstone English
Concertina,” The Galpin Society Journal 44
(1991): 117-49. A copy is available on the web at
www.free-reed.co.uk.)
Another early material for baffles was leather, and this too was used
in very early duet concertinas. I have also examined a
well-preserved example of a Wheatstone "duett" concertina, the
rectangular 24-key pre-Maccann duets made in small quantities from at least the 1850s,
and found that it had original white leather glued tightly behind its open fretwork
with no standoffs or other way for air to get around the leather;
on these instruments the ends are very leaky (for example, with no
bushing around the buttons) so there is no problem.
Wheatstone Dutt #64 with glued leather baffles.
Leather baffles which evolved from these very early ones were used in Maccann duets.
These were pieces of leather or other material cut to fit inside the fretwork
of an end, and usually mounted on short stand-offs so as to not completely
block the flow of air. It seems that for instruments with rosewood or ebony
ends, frequently the baffles were made of a creamy-white "tawed" leather,
preferably goatskin. (Less-expensive instruments often had a cheaper leather
in white or red.)
For instruments with metal ends, frequently the baffles
were made of a dark-colored "Morocco" grained goatskin, such as dark red or
dark green, or brown or black. Both of these kinds of goatskin have very similar
properties: they are thin, fairly stiff but not rigid, dimensionally-stable,
and air-tight. When made into baffles they were mounted on standoffs made of
cork cut into tiny cubes about 1/8 inch in all dimensions and affixed
with a dab of glue on top and bottom.
I have seen the inside of one early Maccann duet with its leather baffles in place,
an early 39-key Lachenal Maccann of very modest quality, serial #885
badged for Jabez Gregory of Nottingham, with its original
factory baffles of red leather mounted on cork standoffs.
Lachenal ("Gregory") #885 with leather baffles on cork standoffs.
(I have been told by
Mark Davies of old rigid baffles made out of cork or wood (sometimes even balsa wood),
mounted on standoffs of cork glued to the back of the fretwork,
but I have never seen one of these myself.
Neil Wayne told me a number of anecdotes about baffles over
a chinese dinner when we were both in San Francisco, with mysterious tales of
solid and flexible baffles mounted below the reed-pans, as well as many different
ways of suspending wooden baffles under the fretwork, supported both from the end
and on struts from the pad-board. I wish that someone who has actually seen more old
baffles could write down what was observed.)
There have been other linings used inside fretwork, which seem not to have been
primarily intended
to function as baffles. Randall Merris has a metal-ended
Lachenal Anglo serial #140871 with
linen linings which were mounted on tiny cork standoffs just like leather baffles,
and closely-cut around the bushing-board and around all the sound-posts.
Joe Palof sent me a photograph of a very similar
linen lining from his Lachenal Edeophone 48-key English serial #55293, which because
it comes from a wooden-ended instrument without a bushing-board has actually been
cut out around every individual button! That is a challenging production step,
and certainly argues that someone thought the linen lining needed to be very
closely-cut indeed. But the linen material is not air-proof and so the lining and its
method of mounting may have had a small baffle-like effect, or may have
been mostly for appearance and for exclusion of insects.
Lachenal #140871 Anglo linen lining,
Lachenal #55293 English linen lining with button holes (Joe Palof).
Other older instruments, particularly
concertinas with large open areas in their fretwork, sometimes have very thin skived leather,
often red or white, mounted inside on glued cork blocks; this leather often seems to
be too thin and with gaps around the edges too large to ever have had much
effect on sound and it may have been mostly for aesthetics, but it can be difficult
to tell--the thin leather is so dry and rigid by now that it resonates. These
very-thin leather sheets were often original, because they had the
serial number of the instrument marked on them (and when the leather is later
removed, the serial number can be lost).
Many Wheatstone instruments in the 1915--1940 period were finished with
an open-weave material glued flush inside the fretwork; in the factory production
ledgers this is called "Gauze". It was often red, but was used in many other
colors such as blue and silver, and in special custom colors. Although it looked like a
baffle, the gauze was intended to be transparent to sound, like "grille cloth"
used now over speakers, and air passes through it easily so it required no standoffs
but was glued tightly against the inside of the fretwork.
Its purpose seems to have been partly cosmetic, partly to keep all foreign objects
and insects out of the inner workings.
Wheatstone #34366 with red "gauze" glued tightly on inside of fretwork.
4. Playing Without Baffles
Not all Maccann Duet players feel the need to fit baffles. Some players take the
view that the whole purpose of playing an antique instrument is to play
it as it was made, and that the proper approach is to adopt a traditional style
of playing for the traditional instrument, or invent a modern style that suits it.
These people would stress that, even if baffles had been used in the nineteenth century
on early concertinas, more than half of all Maccann Duets were made and played
in the twentieth century and did not customarily have baffles fitted to them.
On the cover of Tommy Williams's LP of his Maccann Duet playing, "Springtime
in Battersea" (Free Reed Records FRR008, 1977)--or at least on a transcript
of the cover that I received from Randall Merris--the claim is made
that "Stylistically, Tommy succeeds in overcoming the major limitations of
the Duet concertina, that of the tendency for bass chordal accompaniments to
overpower the right hand melody lines, by tasteful use of left hand chords
and by the use of arpeggio-style accompaniments or octave playing whenever
necessary."
Brian Hayden has recently explained this style of playing further,
in an
April 2001 interview with Wes Williams:
Wes Williams:
"The old Duet players would talk about 'balance' as a technique, between
the bass and treble. What's that all about?"
Brian Hayden:
"You play the treble notes more or less joined up together, with tiny
little spaces between them, and you play the bass notes about half of what
the note indicates on the music.
"Thats what I would always do for any sort of folk thing. You'd be playing
a tune, where tune is played continuously but with tiny little gaps, and the
bass is played like 'Um, rest, Pah, rest. Um, rest, Pah, rest' ... and keeping
it very light.
" ... Its just when you are playing by yourself maybe, you've
got to balance it up. As I say, keep it short and light on the bass."
A logical alternative to making the left side of a Maccann Duet
quieter by using baffles
would be to make the right side louder by adding reeds.
There is evidence that this has been tried at least once.
Neil Wayne owns a Maccann Duet, perhaps a prototype made by an amateur maker
at an indeterminate date using some salvaged Lachenal parts internally,
which is unusual in many ways--it is ten-sided,
it is held by carved elevated palm-rests containing thumb-loops, and it
contrives through intricate construction to use the same reeds for both push and pull.
In addition to all those oddities,
it is built with double reeds on the right side only, so that any button on the left
sounds a single reed
while the corresponding button on the right sounds two identical reeds in unison.
It is hard to avoid the conclusion that this design was intended to make the right side
permanently louder than the left side, correcting a perceived defect in conventional construction.
If so, the complexity of doubling reeds
on the right turns out to be far greater than that of adding baffles on the left.
Certainly, any plan to fit
baffles should require no modification of the original instrument, and should
be wholly reversible without any residual damage, so that a future player of
the same instrument can remove the baffles leaving no trace at all.
5. Traditional Leather on Standoffs, Plus Modern Acoustical Materials
I have found two different ways of creating the volume-reducing effect of baffles.
The first, the traditional way, is to mount a thickness of air-tight leather inside
the ends on short standoffs, as was done in the old days. This redirects the air
moving through the end to go through the slits left all around the edge between the
leather and the end. This has the effect both of reducing
the volume of sound, and also of changing its character to be more
"mellow" or "sweet".
A first surprising finding is that the precise width of the slit left around the
leather appears to be critical to the amount of reduction, so that much more than
ordinary care must be taken in cutting the leather.
The other way is not known to me as a traditional method, and that is to
install a layer of thicker sound-absorbing fabric on both sides of the
reedpan. Once upon a time it could have been some kind of thin knotted
or woven carpeting; today we have high-tech acoustical fabrics which can absorb
sound a great deal better. These materials are not air-tight, so they
require no standoffs and the sound passes through them rather than around them.
Exactly how these are fitted is explained below,
but basically the outer layer of acoustic fabric goes in the end, like a
baffle (lining the inside of the baffle if both are used), and the inner
layer is fitted below the reedpan protruding slightly into the bellows frame.
A second surprising result is that such layers of acoustical fabric can
produce much the same reduction in volume as leather, but do not produce
the "mellow" or "sweet" change in tone.
That provides a choice of effects, and an additional discovery--a third
surprise--is that these two methods can be combined, and each retains its
independent efficacy. So fitting a leather baffle, plus fitting layers of
acoustic fabric on both sides of the reed pan, provides a total reduction
in volume approximately equal to the sum of the two methods used alone, and
also gives the "mellow" or "sweet" effect.
A number of variations of these two methods, and combinations of them, provide
the ability to choose many levels of volume reduction. One good combination for
solving the common balance problem in Maccann Duets is to install leather on both
ends, and acoustical fabric on the left end only; this produces the
"mellow" tone on
both sides, reduces the volume on both sides to make a better accompaniment for
quiet singing, and reduces the volume of the left side still further so that the two
sides are more nearly balanced for playing a melody with chord accompaniment.
6. Choice of Leather
The first step is to acquire the proper leather. The range of leathers with
different properties is astonishingly wide, but not many of them are useful
for concertina baffles. All the leather varieties made for clothing or for
upholstery are too soft--they drape easily, and they stretch, and both of
these properties are fatal for baffles. Leathers which are sturdier are
often thicker and thus not as useful in the constricted space available in
a concertina end, or else so rigid and stiff that they might resonate.
What is needed is leather that is thin, strong, fairly stiff but limp (not rigid),
dimensionally-stable, and air-tight.
Such leather is surprisingly difficult to find. I tried out samples of every
plausible leather from Tandy Leather Company (now selling online
exclusively) without finding a suitable choice, and had similar results from
other online sources, including suppliers of leather for organ repair. I bought
leathers with mixed success from specialist stores in London. Finally I found
the ideal supplier: J. Hewit & Sons Ltd. of Edinburgh. These folks create
wonderful leather, mostly for bookbinders but also for other purposes
as various as bagpipes, and are traditional suppliers to concertina makers
(the business goes back to at least 1806). Hewit has an comprehensive website
with an admirable online store, making prompt and accurate deliveries to any
part of the world. Full details are below under Suppliers.
The best leather for baffles is goatskin, which has all the desired properties;
this was traditionally referred to as "morocco" leather, which is goatskin
treated to emphasize its natural grain (so-called "French Morocco" is a
sheepskin imitation, to be avoided.) Hewit supplies "Chieftain Goat", which
is traditional East Indian goatskin, re-tanned in Edinburgh, processed to a
ravishing grain pattern, and colored with vegetable dyes to traditional colors.
For light colors, they supply a very similar goatskin which is "alum tawed"
(rather than tanned) to produce an etherial creamy white leather.
After I finally found and bought some of this distinctive leather,
I handed a small scrap of it to Steve Dickinson of C. Wheatstone & Co.,
who without any prompting immediately identified Hewit by name and went on
to name the specific type of goatskin and even the specific color;
it is the same leather that he sometimes uses for bellows. I should
have known earlier to look for bookbinder's morocco leather if I had studied
my concertina history more closely:
"The bellows on these very first Wheatstone concertinas [to 1842] were of the
finest glazed green morocco leather, of a similar quality to that used by
bookbinders. The Wheatstone workshop ledgers show regular purchases of
morocco leather and payment of bookbinders' bills for the production of
these fine bellows. Indeed, similar techniques of neatly skiving, lapping,
and folding the leather were used as in fine bindery practice, producing
the neat joins and thin bellows folds found on all concertinas up to the
end of 1842." Neil Wayne, "The Wheatstone English Concertina," The
Galpin Society Journal 44 (1991): 117-49 (online at
www.free-reed.co.uk).
Buying goatskin is not like buying an industrial product--this is a natural
material, with lots of variations in the leather and in the processing and
finishing. Rather than some neat rectangle, one buys a whole skin, in the
shape of an animal with four legs and so forth, and every skin varies in
size; pricing is by actual area, so each skin also varies a little in price,
as it is bigger or smaller. The skins are roughly half a square meter to
two-thirds of a square meter each, so the unit of sale is about half a
square meter. Any skin in this size range should cut up into at least four
baffles for a very large concertina (say, a 72-key AEola), or into at least
nine baffles for a small concertina (say, a 46-key hexagon), so even the
smallest skin should make two to four sets of baffles. Skins are priced
by the square meter, about GBP 100 per square meter in standard grade II;
since a typical skin is a bit over half a square meter, the price of a
typical skin is around GBP 55 (USD 80, EUR 90).
7. Choice of Mounting Tape
So, with the leather found, I now needed the standoffs because baffles
won't work if they are flat against the fretwork. Chris Timson has suggested
the correct choice, namely double-sided thick foam tape--this works like the
little cubes of cork, but with the glue already applied on two opposing sides.
I tried out about a dozen different kinds of double-sided foam tape--vinyl,
acrylic, polyethylene, polyurethane, open-cell and closed-cell, with a variety
of different kinds of adhesives. The best choice turned out to be a 3M product,
3M number 4416, "closed-cell PVC foam with acrylic adhesive" in black. This
tape is sturdy and doesn't come apart, and its adhesive is strong enough to
hold the tiny standoffs but comes off cleanly from wood and metal so as
not to damage a concertina. It's not possible to buy this directly from 3M
online, but there is an excellent distributor on the web, McMaster-Carr, who
have a fabulous online store (stocking 350,000 products), outstanding customer
service, and are very experienced in rapid delivery to all parts of the world.
(See below under Suppliers.) A single roll costs
USD 22.35 (GBP 16, EUR 25).
The 3M closed-cell PVC foam tape comes in several widths, but the easiest to
use is the narrowest, the 1/4" width. A standoff 1/8" x 1/4"
is a size that fits under
typical fretwork well; to make this size, just take a length of 1/4" tape
and cut 1/8" slices off of it.
The tape also comes in three thicknesses: 1/32", 1/16", and 1/8".
I tested
all three, and concluded that the 1/16" is the correct thickness. A thickness
of 1/32" is too thin--it can leave too small a slit at the edges. The old cork
bits were 1/8", but this is probably because there is a limit to how thin you
can easily slice cork without its crumbling. And if you have 1/16" and want 1/8",
there is a simple recipe:
take a length and bend it back upon itself, adhesive to adhesive,
to make yourself a half-length of 1/8" double-sided tape. I found that the 1/16"
tape worked well in a number of different concertinas.
Double-sided tape not made of foam doesn't work because it's far too thin.
The sticky dots sold for mounting light posters on office walls don't work
because they're not strong enough and too thin.
Velcro hook-and-loop material doesn't work because it's very
much too thick, and bits small enough to be concealed behind the fretwork
are too small for the velcro material to work effectively (except perhaps on instruments
with extremely-coarse fretwork). Double-sided foam (and non-foam) tapes made
to replace glue in manufacturing sometimes have very-sticky adhesive comparable
to epoxy, which can mar the wood of a wooden end or remove the plating from a
metal end and damage the concertina. Also, these very-strong adhesives "grab"
the surface of the leather immediately, and will not allow it to be adjusted,
or removed for slight re-cutting. The acrylic adhesive on the recommended
tape will allow the leather to be removed (gently!) for up to 24 hours after
installation without marking the leather, for inevitable adjustments to be made,
but is strong enough for the tiny bits to hold firmly.
The black color is correct for baffles of all colors, even white leather. The
black tape disappears into the dark shadows under the fretwork, and even if a
bit is visible by mistake it is unnoticed. White tape (which I also tried) is
far more visible.
8. Sound-Absorbing Acoustical Fabric
Leather baffles are the traditional way, and work very well, but I wanted
also to try other materials, to see whether
it was possible to make a bigger reduction in volume.
A promising sort of material would be one that absorbed sound (rather than
re-directing the air flow as leather does). Traditional sound absorbers are
fabrics, such as batting, or knotted carpets. More recently, a number of
high-tech sound absorbing fabrics have been devised which may work somewhat
better, and are quite a lot thinner--very important in the restricted space
of a concertina end.
The material I tried is a rough ribbed polyester fabric made by JM Lynne Co.
and sold on the net by Netwell Noise Control under the name "silence
wallcovering" for application to the walls of rooms; it is said to be
"designed for light sound absorption where the human voice and other
mid range sound sources are a culprit". It is thin: 0.175" (about 4.4mm).
The mill width is 54 inches, so a single linear yard at that width will
cut out into a dozen or more pairs of baffles, even large ones; it is light in
weight, with a linear yard (54" wide x 36") weighing 24 ounces. The
fabric is available in 24 colors ( I have used black and ivory.) A
yard costs USD 22.50 (GBP 15.85, EUR 25.60).
See below under Suppliers.
This particular acoustical fabric is not at all air-tight--if you hold it
to your lips you can blow through it just about as easily as through a single
layer of ordinary t-shirt fabric.
The way that I have mostly used the acoustical fabric is to make
a "baffle lining" out
of it, a layer mounted inside of a leather baffle. When used in this way,
the material is never visible because it is covered by leather, so the
color and appearance are completely irrelevant.
Measurements show that the front surface must face toward the reeds, into
the source of the sound--the fabric has almost no measurable effect if placed
with its acoustically-active surface facing the other way. When I add a second layer
of the fabric inside the reed-pan, it is again with the front surface facing
the reeds.
It would be possible
to use the fabric alone, without leather, leaving its back visible, but the
back is covered with an acrylic coating, intended apparently to provide
a gluing surface for attaching it to walls, which is not beautiful
(different batches of the fabric have had backings which varied more
or less from the color of the fabric). If used alone, the back would
probably need to be covered with an acoustically-transparent cloth,
such as speaker grille cloth. (There are sites on the web offering
reproductions of 1920s table-radio grille cloths, which might be
appropriate choices.) The acoustical fabric could be readily
used alone in a Wheatstone whose fretwork is already lined with the
factory "gauze", which would conceal the back of the fabric.
The results of experiments with this acoustical fabric were most surprising:
(1) used alone, the acoustical fabric reduces the volume of sound by just
about the same amount as standard-cut leather baffles--but without
affecting the tone appreciably;
(2) used in addition to leather baffles, the acoustical fabric has
approximately as much effect as when used alone, adding to the reduction
in volume while leaving the tone as changed by the leather.
This is a very fortunate result, because it means that leather and fabric
can be used together to give a wide range of effects.
