| Subject: | Re: [RESOGUIT-L] Intonation question | | Date: | Wednesday, January 4, 2006 22:55:56 (-0800) | | From: | Richard DeNeve <richard_d13132 @.....com>
|
| In reply to: | Message 2005 (written by John Risdon) |
John,
The reason the bridge saddle on a flattop is slanted
is due to the dosplacement of the plucked string.
That is, the side-to-side movement of the strings.
The treble strings have little side-to-side movement,
so they can lie closer to the fretboard without
buzzing against it. The heavier strings have gfreater
amplitude of movement, and are more prone to buzzing
or rattling against the frets. These strings are
raised by elevating the bridge, to give them more
clearance. But then, as you pull the string down to a
fret, you increase tension on the string, which causes
the note to go sharp. Slanting the saddle lengthens
the string from the fret to the saddle, flattening the
note again to bring it back in tune. It is a
compromise, but usually a pretty good one.
In the reso, we don't have that problem, as the bar
places approximately equal tension on all strings,
stretching (and sharpening) them all to an
approximately equal amount. I don't know about other
builders, but I offset my bridges about 1/16th of an
inch to compensate for this, while keeping it
perpendicular to the strings.
Another problem those folks have is the stretch
inparted to a string between frets. That is, the
frets behind and in front of a fretted string holds it
above the fretboard. Finger pressure pushes it down
to the fretboard, adding more stretch. I recently
"adjusted" an electric guitar for the above mentioned
string sway, saddle height, etc., but the G string
especially went sharp when fretted. I told the owner
that she could use lighter finger pressure or use a
heavier string, that would stretch less, but would
also press into her finger more and hurt her
uncalloused fingers. We replaced the .017 plain 3rd G
string with a .022 plain. The problem went 90% away;
she could live with the compromise.
On the reso, we trade in these problems for other
ones. When we play, say, a D note on the 3rd string
while doing a roll on the first two strings, the bar
has to be placed just a bit flat of the 7th fret,
because the tip of the bar is depressing the 3rd
string more than it would if we were fretting all the
strings. This causes the 3rd string to go sharp, so
we slide down a bit to compensate. The amount varies
from player to player (due to differences in bar
pressure) and from guitar to guitar (different mass in
the 3rd string will require different tensions to
bring them in tune, and they will be varied in the
amount of added tension by the same amount of bar
pressure.) Practice with your own machine will
minimize these effects in your playing.
Some folks have written about flattening the B string.
This is done because we can. Most guitars are tuned
to frequencies that are what are called "equal
tempered" chromatic scales. That is, each note's
frequency is increased by a given amount (105.9463094
times the frequency of the next note lower) to attain
the next note. All notes are separated by the same
mathematical amount. But chords sound best to our
ear when the notes are exact multiples of ofe another.
This results in a D note not being a D note. That
is, on the tempered scale, with a 3rd string G note at
196.00 cycles per second (Hz for you modernists), a D
first string is listed as 293.66 cps. But if you tune
them to unison with harmonics, twice the 1st string
frequency should be 3 times the 3rd string harmonic.
That is, if the 3rd string is tuned to 196 cps, the 1
string should be 294 cps, not 293.66cps. Now, 0.33
cps isn't a lot, but the notes will "clash" once every
3 seconds.
The case is a bit more extreme for the B string. You
can tune to the harmonics of either the 3rd string, or
the 4th. I prefer to use the 4th harmonic of the D
string (chimed at the 4th fret) to the 2nd harmonic of
the B string (chimed at the 7th fret). That is, 5
times the frequency of the 4th string (146.63 cps)
should be 3 times the frequency of the B string.
Doing the math says the B string should be at 244.38
cps, but the tempered scale of your electronic tuner
would have you tune to 246.94 cps. Using your tuner,
you would clash about 2-1/2 times a second with a B
and D note which most ears would detect as dissonance.
The difference between A# (233.08 cps) and B (246.94
cps) is 13.86 cps. The 2.56 cps difference between
the tempered scale and the mathematically derived
value based to a G or D note is about 18% of the
difference between the A# and B notes. Quite a bit, a
sixth of a fret. So we tune flat ==> because we can,
and because it sounds better! We tune to an oipen
major chord, and the straight bar maintains this
mathematical relationship all up and down the neck.
(It might get a little off on slant chords, but still
isn't bad.) On a flattop, and other instruments, they
try to deal with the lack of proper frequency with
compensated nuts and bridges; we compensate by tuning
the B just a bit flat. The B note is a different
frequency in a B chord than in a G chord; both are
different than than the B note in an E chord. They
vary the lengths of their different strings (by
fretting them at different frets at the same time)
trying to get a good sounding chord, but it is always
a compromise. We tune true to an open chord, and
shorten all the strings the same amount at the same
time. Makes things easier.
Using the G of the 3rd string at 196.00 cps, and
chiming the other strings to get the guitar in tune
with itself, the first string D would be 294.00 cps,
the 4th string D would be half that (147.00 cps), and
the 6th string G would be 98.00 cps. The second
string B would be 245.00 cps, and the 5th (B) string
would be 122.5 cps. Neat and easy.
Once again, more than you need to know.
Dick DeNeve
--- John Risdon <john_marie.risdon@sympatico.ca>
wrote:
> I have what may be a silly question, however here
> goes:
>
> On non-reso electric guitars the bridge is either
> adjustable for
> individual string intonation, or on most acoustics
> (and some electrics)
> the bridge is at a slant to allow for the
> differences between the high
> strings and the low ones. Resonator guitars that I
> have seen all appear
> to have a bridge that is straight (perpendicular to
> the body).
> Shouldn't it be at a bit of a slant to compensate as
> in other acoustic
> guitars? or does the use of a steel across the
> strings reduce the
> difference in the strings that occurs when they are
> played by pressing
> down against the fretboard?
>
> John
>
> John Risdon, B.A., PMP, CRM
> PM Consultant
> (613) 282-5240
>
>
>
>
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