My initial idea was to test
impulse responses of various quality violins and compare frequency responses.
Unfortunately, I could not get a wide enough variety in quality of instruments. Also,
in the process, I
learned that you have to know what indeed is a good response in order to determine
whether or not you are seeing good responses because an expensive violin does not
necessarily mean that it has a good sound. Generally speaking, many
studies have already been done examining impulse responses of violin bodies and
this study focuses on information from those studies and others concerning the
quality of violins.
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Thoughts On The Sound Quality Of Violins
From physical measurements to close-eyed listening sessions to historical background checks,
there seem to be
many ways to distinguish good violins from not so well appraised violins. Musicians,
like myself, have an interest in determining the quality and worth of their instruments by
discrete and non-controversial methods. Violins, and other stringed instruments, come in an extremely
wide variety with regard to their sound in comparison to most other instruments. For most violinists,
the pure quality of the sound and the ease of playability determine the overall quality of a violin.
Engineering and physics researchers tend to concentrate their analyses of violins
solely on the instruments ability to produce pitches over its entire range.
This analysis is known as an instrument's frequency, or spectral, response (see picture). One simplified method for
determining the frequency response of a violin is to record the impulse response of
a violin. This is done by carefully tapping a hammer on the bridge of a violin (with tuned strings)
and recording the thud with a microphone a few feet away as well as with an
accelerometer attached to the violin body.
The way in which the accelerometer works
is analogous to how a pizo-electric transducer or pick-up works.
The frequencies found in the recordings (using a Fast Fourier Transform of the
amplitude vs. time data)
are ones in which the violin body resonates particularly well. Thus, when
playing notes containing those frequencies in their pitch, there is significant amplification
by the violin body and the frequencies come across as being louder. Other methods for determining
a violin's frequency response involve playing individual pitches and determining the power,
or amplification, of the various harmonic frequencies. Although much more accurate, these
methods require a lot more time because all pitches of the violin's range have to be analyzed
separately. (Bazant, Stepanek, Malka, 1993) Generally speaking,
a violin with a good frequency response is one that reproduces all frequencies evenly.
Measurement of frequency aspects alone to determine the overall sound qualities of a violin miss out
on many other aspects of sound. (Curtin, 1999) Research is currently being done to determine ways to measure
certain timbre qualities, tonal quality carrying capacity, modulation capacity, instrument radiation,
and other sound specific characteristics. (Muller, 1993) For the purpose of comparison, however, the current
method of analyzing frequency responses is good enough to give a general outline of a violin's sound.
On the opposite side of the fence, there are some violin makers who do not play
the violin and even sometimes do not hear what one of their own violins sounds
like. Their primary concern is with good workmanship and many other physical
characteristics. These characteristics concerning the physical aspects of a violin
are often overlooked
by engineering and physics researchers but can be very important when determining
the overall quality to a violinist.
The way a violin is built obviously determines
its frequency response yet very different violins can produce similarities
in their frequency responses. This leaves us wondering which physical characteristics
might be causing those responses and also which are better for overall quality.
Violin makers study many intricate details in
the art of violin making. The importance of a violin's outline, arching geometry,
f-hole position, wood-thickness graduations, wood properties, plate tuning,
bridge tuning, base bar placement and thickness, and varnish type (Schleske, 1989)
are but a few of the focuses of a professional violin maker. (Muller, 1993) (Caldersmith, 1985)
These physical characteristics affect the way players perceive the ease of
playability of a violin. Aspects such as weight distribution, string height off the finger board,
distance between the bridge and finger board, and general vibrational feedback
are important physical characteristics that determine the ease of playability. (Hancock, 1964)
They are also characteristics that directly reflect the general
workmanship of the violin
(characteristic mentioned in the previous paragraph).
With regards to playability, different violinists with varying physical stature
will desire different levels of playability. For instance, some very physical
violinists may want the violin to require forceful playing for a certain responses (feedback and input impedance)
while others may desire the opposite. The touch involved in playing a violin
has a great effect on the variance of the violin's response.
The idea of good craftmenship in woodworking is much more tangible than the frequency response of a violin,
so here is an example of how one might analyze the frequency responses of several varying violins.
(chart taken from Dunnwald, 1994)
Notes on Frequency Response Picture (shown to the right with Frequency on the X-axis and Amplification (dB) on the Y-axis):
1. Violin bodies characteristically have a minimum frequency response at 500 Hz.
2. Some violin bodies have minimum support for notes around 250 Hz and 350 Hz (creates low harmonic response from 650-750Hz).
3. Correction method: tune plates so that frequencies around 1500 and 4000 Hz (overtones) are strengthened.
Frequency response comparison:
P. Guarneri - 1749; big gap 250 - 350 Hz; gap at 500 Hz - made up for with some strengthening at 1500 and 4000
-end result - good overall response
H. Lacmann - 1989; gap at 475 (not much gap at 250-350 range) - huge peak at around 950 yet not much around 1500 or 4000
-end result - heavy lower overtone response but poor overall response - not a good response/quality
A. Stradivari - 1708; gap just below 500 and around 325 - fairly even response peaks from 1000 to 4000 - above 4000;
the frequencies are also boosted but not as much (this ties back to the Bark 17 - A7 weak response) overtones are helped
yet fundamentals are not boosted too much.
-end result - preceived overall response is very even.
H. Dunnwald - 1992; very small gap at 500. - good peaks at 1000 Hz, 1500 Hz, a little low response at the 4000Hz mark but over all
with a small gap at 500.
-end result - smaller response at 4000 Hz is acceptable for an overall good response.
These results correspond well with frequency response comparisons made by Gabrielsson and Jansson on 22 violins in 1977.
The following is a summary of their results characterizing what makes a good frequency response:
a. Strong low frequency range. (below 5 Bark)
b. Strong middle-high frequency range. (12-14 Barks)
c. Weak frequency response in the middle and high range. (above 17 Bark and around 10 Bark)
(2 Bark = G3 = 196 Hz; 2.8 Bark = D4 = 293 Hz; 4.2 Bark = A4 = 440 Hz; 6.2 Bark = E5 = 659.26 Hz)
(12 - 14 Bark is around C7; 17 Bark is above A7) see:Bark frequency scale for more info on the Bark Scale!
Summary:
Overall good responses can be characterized as having a linearly (or slightly exponentially) increasing frequency amplitude response from
700 Hz up to 4000 Hz with a measurable amplification in the 4kHz to 5kHz area. Since fundamentals on the violin occur most often between
200 Hz and 1000 Hz - it is important to have strong peaks in this region too - but watch amplifying one fundamental and its corresponding
overtones much more than other fundamentals!
In summary, there are many methods for determining the quality of a
violin in some measurable way. I think most of the methods boil down to two
main characteristics. The first would be variations in physical traits (such
as workmanship, weight, input impedance, wood characteristics, and other traits
mentioned earlier). The second would be the frequency responses.
Physical and frequency characteristics are duly important in determining the
overall quality of a violin. Good physical characteristics can affect the
frequency response too; environments are ever so changing. Climate variations
involving changes in humidity and temperature affect the wood of violins.
Even two violins that appear to be identical do not react in the same exact ways to these changes. An
explanation to that could be better initial workmanship creates a more even or
constant frequency response. (i.e. you could have two great sounding violins
and a slight change in weather makes one of them sound much worse than the
other.) In the end - the physical characteristics of a violin will help or
hinder the performer to be able to consistently reproduce good tonal quality
sounds.
The question that remains to be answered is how does a prospective buyer know
how one violin compares to another? There really are no current scoring methods
for determining the quality of a violin. The best one can do is to get the violin
appraised. Even then, there are several types of appraisals. Verbal appraisals include
a description of the instrument's origin and
its current market value.
Written appraisals, insurance appraisals, include a signed document
describing the instrument, stating its dimensions, and verifying its current
value.
Certifications give a complete history and description of the instrument,
including color photographs from various angles.
Appraisals, however, are more or less a measure of an instrument's richness of
history and brand. The possiblity exists of finding a Stradivari appraised for several million
dollars that sounds no better than a ten-dollar violin from the local flee market!
Because of this, several people have proposed methods for rating violins
that require certain groups of people listening to and playing the violins. This is not entirely
realistic for the average violin makers or buyers wanting to know how their violin
compares in quality.
Since it is easy to separate physical and frequency characteristics, one possible
scoring method could be derived that lists the ratings for the two main
characteristics separately then offers a combined score.
The approximate frequency
response of a violin could be easily calculated and compared to a desired response.
Relative closeness to the desired response could formulate the score.
For a score on
the physical attributes (generalized from overall woodwork quality),
some research would have to be done to
find a simple method for evaluation, but since a violin maker is often consistant
in design from one violin to the next, the score could be based on a sample violin
that underwent a standardized test. Essentially this would give the violin maker a
personal score. (Today's methods of appraisals could suffice for this score until
a better standardized test were developed to rate violin makers).
Musicians could then
determine, based on these scores, an approximate level of quality for a violin.
For instance, a small and feeble player might want an instrument with
a very high physical rating because this could be interpreted as an
instrument that is very easy to play. Opposite to this rating would be a violin
with a high frequency response rating and a low physical rating. This would translate
as an instrument that is hard to play
but once you can play the way it needs to be played, it will demonstrate a very
good frequency response. The current method of appraising violins
will most likely continue to determine the sale price of famous name violins.
However, some good sounding violins with not so rich a history could
dramatically increase in worth when their excellent qualities are realized!
REFERENCES
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Bazant, P., Stepanek, T., Malka, A.; Predicting Sound Quality Of A Violin From Its Frequency Response; 2.4:42,
The Catgut Acoustical Society, November, 1993.
Caldersmith, Graham; The Violin Quality Debate: Subjective And Objective Parameters; 43:6-12, The Catgut Acoustical Society, May, 1985.
Curtin, Joseph; Innovation In Violin Making; 3.7:18-22;
The Catgut Acoustical Society, May, 1999.
Dunnwald, H.; Discussion of "The effect of the musical key on perceived violin tonal quality," by Oliver Rodgers;
2.6:33; The Catgut Acoustical Society, November, 1994.
Gabrielsson, A., Jansson, E. V.; An Analysis of Long-Time-Average-Spectra of Twenty-two Quality-Rated Violins; 27:13-19,
The Catgut Acoustical Society, May, 1977.
Hancock, Maurice; Thoughts On The Response Of A Violin; 2:7-8, The Catgut Acoustical Society, November, 1964.
Harajda, H., Fedyniuk, P.; Sound Response Of Violin Instruments: The Spectral Structural Changes In Violin Sounds During The Attack Stage;
2.4:45; The Catgut Acoustical Society, November, 1993.
Jansson, Erik V.; On The Acoustics Of The Violin: Bridge Or Body Hill; 3.7:23-27;
The Catgut Acoustical Society, May, 1999.
Meyer, Jurgen; Tonal Quality Of Violins; 41:10, The Catgut Acoustical Society, May, 1984.
Muller, H. A.; The Acoustic Quality Of The Violin With Respect To Its Physical Properties;
2.4:42; The Catgut Acoustical Society, November, 1993.
Rakowski, Andrew; Subjective Evaluation Of The Quality Of Musical Instruments; 25:5-6, The Catgut Acoustical Society, May, 1976.
Schleske, Martin; The Influence of Typical Violin-Varnishes On The Acoustical Qualities Of Thin Spruce Strips; 1.4:38,
The Catgut Acoustical Society, November, 1989.
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