Bass reed after-rattle

[Crank]

Dear friends

My LMMM 120 bass Scandalli (I guess 40-50 years old) has two bass
registers. One plays the fundamentals on two reeds an octave apart,
the other plays one reed - the higher pitch fundamentals. (For future
reference, what are the proper name for these registers?)

Only _after_ I release some of the fundamental buttons, using this 2-
reed register, I hear a loud, ugly rattle - a low frequency vibration
from the deeper reed of the pair. It sounds only slightly melodic and
fades away in a 1/4-1/2 sec. It seems to be associated with the deeper
notes in the octave - the heavily weighted reeds. The sound usually
occurs on draw and squeeze, but not necessarily equally. I can't bear
to use this register.

I bought the instrument a couple of years ago from a competent
technician who had overhauled, re-waxed, re-valved and tuned the
instrument - it generally sounds great. As he does not live close, I
have not been able to get back to him.

I am not convinced that these noises were present when I purchased the
instrument 2 years ago: as I became accustomed to it, I began to hear
things that were not apparent to me at first - or that gradually
developed. I live in S. New Mexico where it is VERY dry, which might
be a factor.

I have had the reed arrays out and examined them. I don't see any
valves obviously out of whack on the visible side of the blocks. Nor
can I find anything foreign or loose that might be vibrating
sympathetically (except potentially, another reed). It sounds to me
that when the air flow suddenly stops, the heavy reed keeps on
vibrating more slowly - not being adequately damped, or maybe not
stiff enough (these are supposedly hand-made reeds). What DOES limit
the vibration of a reed when air flow is cut off, normally?

I have read a great deal on the accordion (including the last 10 years
of this newsgroup), and have not encountered another instance of my
exact problem.

Does anyone have insight into the cause of this problem or how to
identify it and how to correct it?

I will be grateful for your opinions.

Crank

[Len Killick]

As you say the problem resolves itself in 1/4 to 1/2 second I would
check the tuning of the octaves: the best reeds sufficiently out of
tune will make the same sort of sound as a cheaper reed not starting
up properly, or even a similar sound to a loose reed or valve - the
fact that it corrects itself makes me lean towards a tuning problem.
Your other idea of the previously played reed still playing is also
possible, but not normally expected with a well made reed.

[Crank]

Thank you for your prompt comment, Ken.

To my ear, the 2 octaves are not out of tune with one-another on any
of the problematic fundamentals (In any case, I don't understand how
detuning could cause abnormal vibration of a reed only AFTER air flow
has ceased - my box has no leaks or bad felts). It's also hard to
imagine that something new would start vibrating when the button is
released.

So it seems to me that the vibration, whatever it is, can only be a
residual effect from activation of the reeds, after their air supply
is cut off. Another reason I think it is the reeds themselves is that
the "death rattle" has a distinct sound for each note sounded.

The only consistent explanation I can think of is that the inertia of
the lowest, heaviest, weighted reeds keeps them vibrating, albeit at a
slower rate, after air is cut off. I guess that normally the inertia
is overcome by the greater thickness/stiffness of the heaviest reeds,
or perhaps the leathers have a role in damping them.

This supposition suggests that the reeds at fault have lost some
stiffness, or that there is a problem with the leathers. Is loss of
reed stiffness with age and use a known issue, assuming quality reeds
(no corrosion is present)?

The leathers are all in good condition and have reinforcers. The reed
or leather gap might not be exactly correct (I can't tell), but they
do not appear wildly off.

Lacking a bellows, I can't rig something to safely sound individual
reeds, and narrow down what is happening.

Any further thoughts Ken, or anyone else?

[ed]

What you may be describing is a normal after-vibration of a heavily
weighted bass reed. When the air supply stops and the reed skin is
just sitting there, there is not enough damping from the stiffness of
the tongue to stop the reed dead in it's tracks. It's a relatively
long lever and it goes through a few cycles in and out of the vent
before it stops. Just for jollies, I picked up six accordions that are
here on the table in various states of repair/restoration. Four of
them have hand made reeds. They all have substantial after-vibration
of the lowest pitches that is in the pitch of the sounding reed.
Generally, the bigger the reed (lower the pitch), the more aftervibe.
When it really does get nasty is if that big reed has gotten shifted a
bit in the vent and scrapes the side of the vent very slightly as it
goes through - then it's a noticeably metallic sound. If you listen
carefully to the lowest bassoon register reeds on the treble side, you
may hear the same after-vibration. I would guess that this might be
most apparent on a good quality instrument with full scale (longer)
reeds. Smaller scale accordions use shorter reeds and need more
weighting to sound the lowest pitches but the tongues, being shorter,
may have more self damping. They also take longer to speak because
they are less sensitive to the air supply. Sometimes on a really good
accordion well in tune, you can hear the sympathetic vibrations of the
bass reeds responding to the playing of the lowest bassoon reeds on
the treble side.

All of this is probably a very local phenomenon. I doubt that most
listeners hear it from a few feet away but I can see that it might
drive you nuts if you really get in to it. I think your supposition
that it's the inertia of the larger reeds is right on. If the pitch of
the after vibration is different than the playing pitch of the reed,
then that would be unusual in my experience. Let me know.

Ed

[Len Killick]

Sorry I misunderstood the second paragraph of your original question
and thought you meant the problem resolved itself after 1/4 -1/2
second of playing.

It is then most likely the weighting of the reeds which keeps them
playing after the sound should stop. This does get worse with age, but
there I mean normally 20 years or so, and quality reeds should be
better. The leathers don't normally affect this (unless you are
changing bellows direction), although a badly fitted leather can cause
noise all of its own. Of course the ideal reed would not have so much
weighting on the end... but would need to be a lot longer than they
are normally!!

If the problem is with one or two notes I would remove the offending
reedplate(s), clean them, fit a new leather, check the adjustment of
the reed tongue, wax it back it, cross my fingers, turn round three
times, and try it... It's also worth a quick check around the
instrument that there's nothing else loose which could vibrate in
sympathy.

[Crank]

Ed, thank you for your thoughtful analysis. It certainly is consistent
with what I hear.

Some reeds' after-vibe does seem to be in the same pitch as when
sounding properly - but in most cases it is hard to tell for sure - it
is more noise than musical. The worst reeds' vibe non completely non-
melodic. I have noticed none that vibrate in a recognizably DIFFERENT
pitch from the corresponding fundamental when the button is released.

"What you may be describing is a normal after-vibration of a heavily
weighted bass reed."

Sad if this is "normal", especially because I won't use 1 of the 2
available bass registers. These lowest reeds are pretty loud, so the
noise stands out, especially on the ugliest reeds and _especially_
when followed by a pause. I will have my tech take a look when I have
time for a 6 hr trip (one way). And I'll have him look for a shifted
reed in the worst cases. I have corresponded with him, and from the
questions he asked, I think he suspects the same as you do.

Len, I will also tell the tech to try your formula, refurbishing the
worst reed plate and, including your excellent advice, when all else
fails ... "cross fingers, turn round three times, and try it" ;-)

Thank you both for your help (and for not telling me I'm imagining
things). Oh, by the way, I'm hearing these voices .........

Crank

[Ike Milligan]

"Crank" <crikeycra...@gmail.com> wrote in message
news:57452d79-cafe-4213...@h23g2000pra.googlegroups.com...

In very old accordions, the bass reed plates may be thin enough so that the
rred tip will be more likely to hit the reed leather. Bass reeds nowadays
are often wedge shaped so that at the tip the plate is thicker. The booster
spring could be adjusted so that it does not close the leather as quick, and
softer leather could be tried. The reed leathers now are not brushed on the
nap side enough to soften them sufficiently, as the old way of making them
was hours of hand brushing. So a stiff spring, thin plate, heavy weighted
reed, and hard stiff leather can all combine to create a risk of the tip
hitting the leather.