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Brian Prunka
Oud Junkie
Posts: 2916
Registered: 1-30-2004
Location: Brooklyn, NY
Member Is Offline
Mood: Stringish
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Yes, I would think that discrepancies would be magnified at higher volumes. Due to the subjectivity of experience, however, I think it might be hard
to play with exactly the same force on successive trials.
Perhaps playing one string about a dozen or so times in succession and then averaging the results would be a way to compensate for variation.
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jdowning
Oud Junkie
Posts: 3485
Registered: 8-2-2006
Location: Ontario, Canada
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Mood: No Mood
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My lute is designed for fingertip plucking so the course pairs are relatively widely spaced and would not work well with a risha. However, consistency
of plucking force should be more important than striking intensity. Ideally some kind of mechanical device for plucking the strings would be best but
that would mean more complexity than I currently have time for. In this case I tried - with experience - to be consistent in striking each string
using about the same force and for each test the chord was sounded three times in succession i.e. there were 18 strikes to be averaged for each
analysis. Not laboratory standard testing by any means though - just using what I had readily to hand to obtain some quick results.
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jdowning
Oud Junkie
Posts: 3485
Registered: 8-2-2006
Location: Ontario, Canada
Member Is Offline
Mood: No Mood
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Another promising audio analysis software is the free 'Sonic Visualiser' available for Linux, Windows and Mac. - designed for musicians to visualise
and analyse audio recordings. It is more versatile (and complex) than Audacity and supplemented with many third party 'plug-ins'.
I have not yet spent time in reading the operating manual or tutorials to be able to use the software effectively but it looks as though it may be
very useful for the current objective of this thread in analysing, from audio recordings, the effect acoustically of adding or removing sound board
plates.
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jdowning
Oud Junkie
Posts: 3485
Registered: 8-2-2006
Location: Ontario, Canada
Member Is Offline
Mood: No Mood
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Before I hang this test lute back on the wall, I will do another series of tests - as suggested by Brian - just plucking the 5th course wound string
a number of times using a plectrum (to obtain a louder response than with fingertip) but also to attempt to measure sound pressure levels with an SPL
meter.
Basic SPL meters are available on EBay for between $15 and $30 - not laboratory grade (meters that can cost hundreds if not thousands of dollars) but
good enough for comparative rather than absolute measure. They are not loudness testers but have filters (A filter) that approximate (roughly!) to the
human perception of 'loudness'
The meter that I will be using is this one that records maximum values in sound pressure recorded in dB. Should be interesting to have another
reference for comparison.
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jdowning
Oud Junkie
Posts: 3485
Registered: 8-2-2006
Location: Ontario, Canada
Member Is Offline
Mood: No Mood
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The SPL meter is a low cost one of Chinese manufacture - a 'Wensn' ws 1361. It has a digital read out and appears to be quite well made. It measures
sound pressure levels in dB for frequency weighting A and C - the dBA weighting is supposed to represent human hearing that is more sensitive to
frequencies in the 2000Hz to 5000Hz range. The meter comes with software that records readings to a PC via a USB connection. Unfortunately the
software will only work with either Windows 7 32 bit or 64 bit operating systems not Linux so I can not take advantage of this feature at present. The
meter has a stand alone maximum level feature so will record the highest measured dB value over a period of time.
This feature was used to determine dB levels for a series of tests on my lute this time using a stiff leather plectrum to repeatedly pluck the wound
string of the fifth course in an effort to produce a 'louder' sound than with using soft fingertips.
Two trials were made one without contact film the other with film measuring 10 cm X 16 cm (as used in the previous trials).
The SPL meter and Zoom H2 recorder were both placed at a distance of 18 inches facing the sound board of the lute (constant distance is important for
comparisons as sound pressure diminishes with increasing distance from source). The recorded signal was subject to Audacity spectrum analysis for
comparison.
The SPL meter measured a range of 57dBA to 59dBA (slightly louder) for the lute without the film and 53 dBA to 55dBA for the lute with contact film.
Comparison of the spectrum graphs indicated that for the lute with film, in the lower frequencies (94 to 472 Hz range where the resonant peaks were
most prominent) sound pressure levels were slightly greater but only by about 4 dB or less. In the 1000Hz to 3000Hz range it was difficult to judge as
the dB levels at peak frequencies varied greatly in some cases in others not so much. However, on balance the lute without film appeared to have
somewhat higher sound pressure levels so would tend to confirm the maximum SPL meter readings recorded.
So I have to conclude that given the relative inaccuracies inherent in the test equipment and procedures, the addition of contact film to the sound
board appeared to make little difference, if any, to perceived loudness levels for this instrument.
Time to move on!
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