For what scale reeds does the tongue pass completely through plate?

[ttonon]

Greetings,

I have a question for the kind folk here, particularly the makers, or any one else very familiar with the details of tongue vibration with some kind of documentation lying around.  

When the vibration amplitude is large enough, the tip of the tongue passes completely through the slot, or vent.  Whether that happens depends on the playing volume as well as the length of the tongue in comparison to the slot thickness.  I'm interested in knowing how common such an occurrence is in normal playing.  Is there a tongue length above which this event occurs for most all playing volumes?  Is there a tongue length below which this event doesn't usually occur for normal volumes and maybe only the most loudest volumes would cause the event?  It would also be nice to know in any resulting discussion something about what portion of the length of the tongue makes it below the slot and for concertinas, what would be a normal range of bellows playing pressure, say in centimeters (or inches) of water column? 

This information would help me to decide on what kinds of calculations to make on the tongue vibration analysis I'm doing from a fluid mechanics approach.  Whether the tongue passes completely through the slot determines the kind of mathematical formulation to use, and it would be interesting to know how accurately the model describes this event.  

Now, may I be bold enough to also request whether anyone could share data - numbers - on the details of tongue vibration, say amplitude vs bellows pressure?  I doubt that, but if you do, I'd have to get downright greedy by asking for detailed tongue and slot geometry information to accompany it.  Yes, I know I should be doing that myself and I will, but I thought I'd get lucky by asking.

 

Best regards,

Tom

www.bluesbox.biz

[Dana Johnson]

Hi Tom, I find this circumstance at least up to f# 5 at a medium to high volume still within the normal playing range.  Most of my reed shoes are .063” thick, though I go to .093” for the long reeds below C3 in my low pitch instruments.  f#5 reed is .846” long x.090” wide.  I don’t know how far below the reed shoe bottom the reed travel is, and it is possible some reeds above that pitch  can travel below the shoe.  I only know this because the ports in the reed shoe for the f#5 reed are just barely longer than the reed window and the reed can begin to hit the wood at moderate volume, giving a wonky pitch change.  You can press down on the reed tip and feel it stop against the wood.  

   The stock thickness of the old Wheatstone reeds I have from an old duet are .080” thick, but I don’t think that is enough to cover reed travel in that same range.  Their brass is considerably softer than the brass I use, and I go up in thickness because long reed shoes are subject to bowing with my reed mounting method.  Also, I find that reeds in overly thin shoes can lack power, and the long reeds benefit from the added time the reed spend in the confines of the shoe vent.   What happens once the reed enters the port in the reed pan  I don’t really have a good idea of since the gap at the reed tip  becomes quite large in comparison to being within the shoe window.  Nor do I have any idea about the small slug of air in the port that goes from tight confines immediately to complete openness.  I wonder what might be reflected at this change in impedance.
   I tune my reeds at around 1” of water column, though bellows playing pressure can certainly go as high as 4”.   My target for starting to sound is .2” of water. In open air.  When in properly sized chambers they will start at half that.  Travel at those pressures is really minimal, just requiring the reed tip to enter the window.  

hope this information is useful.  Sorry I don’t have info on amplitude vs. bellows pressure.  Measuring audio amplitude is easy (ish, since reeds radiate sound differently depending on pitch and one mic position may not be ideal for all frequencies ). Measuring mechanical amplitude is much harder since the reeds are in a confined space when playing, either in a chamber or in the bellows.  If they were in the open you could use a strobe and make a feeler jig to gage the physical travel, but absent the chamber interaction,  it would hardly be representative of real world data.

Best Wishes,

Dana

[ttonon]

Many thanks Dana for what you've done here: a plethora of information that will be of much help.  To be sure, the notation f# 5 invokes the piano keyboard, so this reed has a fundamental vibration frequency of about 740 Hz, correct?  What I understand is that this seems to be about the dividing line between reeds that have their tongues that most often travel through the shoe, and those above that do not, generally, but not absolutely.  Since you make the vent for this f# reed slightly longer than the reed window (the hole in the wooden chamber wall), my guess is that you're not too concerned about the tongue hitting the wood during normal playing.  Is that right?  

 

On 1/23/2020 at 9:09 AM, Dana Johnson said:

Also, I find that reeds in overly thin shoes can lack power, and the long reeds benefit from the added time the reed spend in the confines of the shoe vent.

Yes, in my physical model, the time spent while the tongue moves through the vent is when the major portion of energy is transferred from bellows pressure to the vibration.  With analogy, this is the moment the father pushes on the swing his boy is riding.  There is a small contribution when a tongue exits through the vent, but still moving downward, due to the air jet passing through the vent and hitting the tongue.  But that small contribution is then largely cancelled when the tongue comes back up, before again entering the vent.  

On 1/23/2020 at 9:09 AM, Dana Johnson said:

Nor do I have any idea about the small slug of air in the port that goes from tight confines immediately to complete openness.  I wonder what might be reflected at this change in impedance.

My explanation above about the jet addresses this.  "Impedance" is not a good description of the underlying physics.  Impedance is a useful concept for understanding the behavior of wave motion.  Here, we're dealing with fluid mechanics, no waves.  

 

On 1/23/2020 at 9:09 AM, Dana Johnson said:

What happens once the reed enters the port in the reed pan  I don’t really have a good idea of since the gap at the reed tip  becomes quite large in comparison to being within the shoe window.

Yes.  This sudden widening of the gap is what ends the (static and dynamic) bellows pressure force on the tongue.  Without the vent, the action on the tongue from the bellows pressure is indirect.  When the tongue is below the vent, the air jet caused by the bellows pressure acts on the tongue.  And as I said, this aspect of energy transfer is both positive and negative, with nil net result.  When the tongue is above the slot, there is nil direct influence from bellows pressure.  There are small effects caused by air motion into the slot just before the tongue gets there.  

 

On 1/23/2020 at 9:09 AM, Dana Johnson said:

I tune my reeds at around 1” of water column, though bellows playing pressure can certainly go as high as 4”.

Have you measured bellows pressure directly?  Years ago I attached a manometer to a full size accordion bellows and concluded that the larger pressures should be around 6".  That's for those bellows with a push area much larger than concertina bellows.  Aso, I didn't push with all my might, and I do know that some gorilla accordion players can be exceedingly loud.  I thus concluded that concertina maximums should be around about twice that.  Of course it depends on how strong the player is, and maybe the limiting pressures are determined by what happens to the reed.  What are your thoughts on this?  Do you think the reed can be damaged at such high pressures?  What happens to the sound of your reeds when you push or pull on your bellows with all your might?

 

On 1/23/2020 at 9:09 AM, Dana Johnson said:

My target for starting to sound is .2” of water.

I'm impressed with how low that is.  If you recall, I came up with a theory on how to predict the minimum starting pressure for a reed and published it here a few years ago.  I'll have to go back and look see that  post.  

 

On 1/23/2020 at 9:09 AM, Dana Johnson said:

Travel at those pressures is really minimal, just requiring the reed tip to enter the window.

I'm very curious now, concerning pitch, or vibration frequency.  Can I trouble you, or anyone else when you get a chance, to observe a real time reading on a pitch meter (tuner) to see how the pitch changes as you slowly increase bellows pressure (either plus or minus), from the very lowest pressures to the maximum pressure?  Just qualitative results, such as "higher" or "lower" would be very interesting from a theoretica point of view.  One complication here is the presence of the leather valve, which moves as pressure changes, and that might have an effect on pitch, so ideally there shouldn't be a valve.  

 

On 1/23/2020 at 9:09 AM, Dana Johnson said:

If they were in the open you could use a strobe and make a feeler jig to gage the physical travel, but absent the chamber interaction,  it would hardly be representative of real world data.

Yes, in my workshop, which currently is in disarray, I have an electric powered testing rig, with the reed mounted over a window.  The electric blower can suck steady air through the reed, with the tongue vibration freely visible and accessible.  The strobe is a nice touch.  The "real world" data I'm after does NOT contain a chamber, or any confined space.  I'm interested in the reed vibration by itself, without any other physical phenomenon going on.  Once I understand this, I can formulate the case when the reed is mounted on a cavity, or resonator, which is an entirely different problem.  I'm sure you'd agree that I cannot hope to analyze all real world effects, only to give an accurate-enough description.  

 

Best regards,

Tom

[Dana Johnson]

Sorry, I haven’t mastered responding to quoted sections.  I’ll just mash it all together.

i still get caught making incorrect analogies between the slugs of air in woodwind finger holes and the flow through the ports, though with reeds vibrating hundreds of times per second, sound waves kinda have to result somewhere in the process.

  I use a digital manometer to set my tuning pressure.  1” provides a reasonable volume, sufficient to avoid too much pitch change in the normal dynamic range of playing.  4” is quite loud for my concertinas.  I do measure it directly through a port in my tuning bellows, though I just use the bellows for mounting my reed pans and use a coaxial blower to generate the vacuum.

   My reeds generally don’t vary by more than 2-3 cents over the normal playing range.  I do find that under too much pressure they can go quite flat, but this requires quite a lot of pressure, and is only a bending effect I use purposely requiring extra effort.  Oddly the higher 6th octave reeds can actually go sharp instead of flat.  Go figure!.  

   I do find a lot of variation in pitch with the degree the bellows is extended, Maybe as much as 5-6 cents, even at constant playing pressure.  I have to be very careful creating my tuning charts to take this into account.

   Re f#5, yes you have the right pitch.  I cut my ports with a .125” end mill, leaving an arc at the ends.  For a couple reeds, the arc encroaches on the corners of the swinging reed.  I have to square off the ends because the reeds will hit in the mid part of the dynamic range or higher.  I can’t be sure how high this can happen since the progressively smaller reeds get more clearance in the ports.  I don’t find having the higher reed ports closely match the reed widths makes much difference, so I avoid an extra tool change.

   I do increase the window draft angle from 5 degrees per side at C3 to 20 degrees per side at G6.  For my reeds  I find this increasing draft angle is required to get a similar volume at a similar pressure over the entire note range.  I hypothesize that thinner reed sets may need less draft angle because they deflect more at a given pressure than heavier reed sets.  But they do max out in volume before the heavier sets.what my reeds need and max volume / pressure levels are empirical findings.  I have not experimented with light reed sets, though I have worked on instruments with overly thin reeds that both were kind of on or off as far as volume is concerned, and quite pitch unstable.  Reminding me that part of my choice for my reed stiffness/ pitch curve is my requirement that the reed be pitch stable even at higher volumes.  
   I don’t really know why varying the draft angle has the effect I find, just that it answered my question about keeping the high reeds volume comparable to the low at the same playing pressures.  The shoe thickness is the same from C3 to G6 even though the reed length goes from about 1.5” to .5” .

[ttonon]

14 hours ago, Dana Johnson said:

Sorry, I haven’t mastered responding to quoted sections.

Very simple.  Just highlight the text in my post that you want to quote and a little window will appear immediately with ""quote selection."  Click on it.  

14 hours ago, Dana Johnson said:

i still get caught making incorrect analogies between the slugs of air in woodwind finger holes and the flow through the ports, though with reeds vibrating hundreds of times per second, sound waves kinda have to result somewhere in the process.

Here's more.  Impedance is defined as oscillatory pressure divided by oscillatory velocity, and the definition is sometimes useful, sometimes not.  Bellows pressure is not oscillatory, and it can be considered steady, or constant, for the purpose of examining its affects on tongue vibration.  The slugs of air going in and out of a finger hole in a woodwind is caused by the wave motion inside the body of the instrument.  This wave motion is characterized by standing waves - waves that are the additive result of forward and backward moving traveling waves - producing pressure and velocity oscillations that are a function of time, but not position (hence, "standing").  Thus a given finger hole, being at a fixed position ejects an air slug when the pressure just inside the hole, caused by the standing wave, rises (above atmospheric), and the motion there is periodic.  This is entirely a wave phenomenon and you can define an impedance for the air oscillations in and out of the hole (with time average flow being zero).  On the bottom of the vent in a free reed, there are pulses of air, but they are not caused by wave flow, but rather by the opening and closing of the tongue/vent valve.  In order to understand the nature of this oscillatory flow, we need to look at the equations of fluid mechanics, coupled with the governing equation for the tongue vibration.  The simplest equation for tongue vibration is the Euler-Bernoulli equation, which can also be called the tongue's wave equation.  Once the motion of the air slugs passing through the vent is calculated by this approach, you can now define an impedance for that oscillatory air motion, the same way as for a finger hole.  At this point, the oscillation does not care how it is produced.  In fact, we can use that definition of impedance for the underside of the free reed to couple it to the equations governing the air vibration in the cavity, or for resonators. I was maybe too restrictive to say that impedance is not helpful here.  My point is that it's not helpful in understanding how the pulses are formed and the effect of the reed geometry on those pulses.  Once we understand those pulses, we can define their impedance in order to do further study.  Trying to understand how those pulses are formed by invoking impedance can give the erroneous view that there is a sound wave passing through the vent and encountering a change of impedance because of the sudden area change.  That's not what happens.  But it does happen with the woodwind, when the forward traveling wave meets the end of the tube, or bell, and out to the atmosphere, where there is a large change of impedance.  There, impedance is a very useful concept.  The free reed is its own animal.  Very unique when it comes to musical instrument sound sources. 

 

14 hours ago, Dana Johnson said:

 4” is quite loud for my concertinas.  I do measure it directly through a port in my tuning bellows, though I just use the bellows for mounting my reed pans and use a coaxial blower to generate the vacuum.

 So you're not measuring bellows pressure generated by human muscle during playing, and my guess is that your judgement on the magnitude of driving pressure is made by the perceived volume you hear.  I wonder.  As I said, I measured the bellows pressure in an actual instrument, while playing.  The bellows I used measured roughly 18 x 6 inches, inside measurement.  Pushing on that "piston" with 20 lbs of force produces about 5 inches w.c.  My guess is that accordion players could produce such a playing force, though that's probably around the highest.  A concertina cross section is, my guess, around 6 x 6 inches, so that the same force produces three times the bellows pressure.  I doubt concertina players push anywhere near 20 lbs, but these figures to me suggest that 4 inches is well below the capability for the instrument.  All this may only prove that concertina players play for reasonable volume, and the difference from accordion players is interesting.  But all in all, the free reed can sound extremely loud with your ear next to it, and that perception is quite different from what we get when it's being played inside an instrument by a musician wanting to be heard above other instruments in a session.  It would certainly be an interesting experiment to fix an instrument with a pressure transducer and record the data during a session.  

 

14 hours ago, Dana Johnson said:

I do find a lot of variation in pitch with the degree the bellows is extended, Maybe as much as 5-6 cents, even at constant playing pressure.

That's surprising.  Do you see higher or lower pitch with extended bellows?

 

14 hours ago, Dana Johnson said:

I don’t find having the higher reed ports closely match the reed widths makes much difference, so I avoid an extra tool change.

You're saying that the precision with which the tongue fits the vent doesn't make much difference?  Intuitively, I would've guessed that a tighter fit would lead to more higher harmonics, but maybe they're just not noticeable.

 

14 hours ago, Dana Johnson said:

I do increase the window draft angle from 5 degrees per side at C3 to 20 degrees per side at G6.  For my reeds  I find this increasing draft angle is required to get a similar volume at a similar pressure over the entire note range.

This is most interesting, because I'm in the process of extending my model to include the effect of a draft angle on the sides of the slot, as well as the effect of a gap in the fit between the tongue and the vent.  Do you put the draft on all sides, including the tongue tip side?  Of course, there, the tip naturally pulls away from a non-drafted side as it travels through the vent, and this can be calculated.  But that effect is much smaller than that the draft angles you quote.  Incidentally, I find that the smallest fitting gaps are a couple thousandths of an inch.  Does that check with your fits? Except for the tip corners, which can go down to a thousandth.  

 

14 hours ago, Dana Johnson said:

I find this increasing draft angle is required to get a similar volume at a similar pressure over the entire note range.

Interesting.  You're saying that a draft angle increases volume, something that I'll look for in calculations.  

 

14 hours ago, Dana Johnson said:

I hypothesize that thinner reed sets may need less draft angle because they deflect more at a given pressure than heavier reed sets.

Confusion here.  If "thinner reed sets" means thinner tongues, they might bend with more curvature than thicker tongues.  Is that what you mean?  The higher curvature would mean that the tips pull away more from the tip side wall, suggesting that they would need less draft than thicker tongues, and I agree.  But your results seem counter intuitive, because as I mentioned above, tongue travel through the vent is prime time for which static bellows pressure can move the tongue.  When you cause more leakage between the tongue and vent wall, that pressure effect decreases.  Of course, some of the effects that happen during down-travel of the tongue through the vent are compensated for by up-travel a half cycle away.  This is something I need to ponder.  

 

14 hours ago, Dana Johnson said:

I don’t really know why varying the draft angle has the effect I find, just that it answered my question about keeping the high reeds volume comparable to the low at the same playing pressures.

It's an interesting feature to explore.  My experience with accordions is very limited, but I've never noticed any draft angle with accordion reeds.  Maybe someone else here can add to that.  

 

Best regards,

Tom 

[Chris Ghent]

I am a world away from any of my gear and figures at the moment but by memory my numbers are wildly different to those quoted here. I like my lower reeds to start in the tuning rig by .11 “ . This figure climbs slowly to around .2 at high pitches. However it may reflect set height as much as anything and is almost certainly related to reed thickness and clearance. My tuning -pressure is 1.6”. This was not by design, it was all the rig could do flat out. I have not found any issue with that -pressure. 

 

A few years ago for no good reason I decided to find out the operating -pressure needed in the bellows and drilled a hole directly through a bellows frame and inserted a manometer tube. I was expecting high -pressures but never saw anything more than about .3”. I posted the figures here, so they could be found, it was some time in the last 6 years. This is so different from your figure Tom that it feels one of us must be wrong or we are comparing apples to oranges. 
 

As an interesting aside I once decided to try bedding a reed in so it would not need to be tuned so many times before it was ready to be sent off. I left it running in the tuning rig for hours. Over that time it dropped a few cents. I was pleased, thinking I would do it to all the reeds. The next day I somewhat idly put it back in the tuning slot and it had returned to its previous reading. My theory was the drop might be heat related.  I know Dana has different results to this. 

[Chris Ghent]

Just read your further post Tom, I think a good clearance is closer to 1 thou than 2.  I aim for .125 thou. 
 

Also, re draught angle, while it is not universal, accordion reeds often have more tapered reeds than concertinas. This increases the gap more quickly as the reed swings down and probably has the same effect as the draught angle in a concertina frame. 

Edited January 25, 2020 by Chris Ghent

[ttonon]

48 minutes ago, Chris Ghent said:

A few years ago for no good reason I decided to find out the operating -pressure needed in the bellows and drilled a hole directly through a bellows frame and inserted a manometer tube. I was expecting high -pressures but never saw anything more than about .3”. I posted the figures here, so they could be found, it was some time in the last 6 years. This is so different from your figure Tom that it feels one of us must be wrong or we are comparing apples to oranges. 

Hi Chris, so good to hear from you!  Yes, something seems amiss and I guess it's back to the drawing board.  A simpler experiment is to put a digital scale between one of your palms and the concertina and have someone read off the forces as you play steady notes.  My guess is that the pressure calculation from bellows cross section and force should be pretty accurate, but that should also be checked.  It should also be said that we need to use the same unit system, because far more disastrous results have occurred because of a mix up in unit system.  I'll look for your post.  

 

There are differences in construction between accordion reeds mounted in the common way using a reed block and the traditional concertina method.  With the accordion method, the reeds are situated with one end near the air hole (port) and the other end removed, at some angle not far from 90 degrees.  The concertina method places the reeds flat (zero degrees).  In my experience, the flat mounting produces louder tones, because some of the melodian-type accordions, such as the Louisianan Cajun type, place them flat, and I play both.  The question is, do the accordion-reeded hybrid concertinas with reed blocks sound at lower volume than the traditional concertinas (for same pressure)?  But I suspect any difference would be too small to explain these differences in normal playing pressure.  

 

Interesting comment about draft angles in accordion reeds.  

 

Best regards,

Tom

[ttonon]

Hi Chris, I think I found your post on bellows pressure, back in 2014, at

Quote

 

Okay, I went and did it and it took all of 20 minutes. So much for procrastination. This is the first thing I have done in a new workshop so a milestone of sorts. I used Terry's method number two, a piece of mdf screwed in place of the end and I ran an airtight tube from it to the Magnehelic gauge. This is a vacuum gauge made by Dwyer. It does not measure pressure so only worked on the draw.

 

The results...

 

Gentle quiet playing - 1"WC

Mid range playing - 2.5"C

Loud playing - off the scale. What a disappointment! My gauge only goes up to 3"WC. By the speed it hit the end stop I would say it was heading for at least 4.5"WC. Sorry, not very scientific.

 

So what is "WC.

Wikipedia -Inches of water, wc, inch water column (inch WC), edit a non-SI unit for pressure. Edit It is used for measuring small pressure differences across an orifice, or in a pipeline or shaft. OK, its old fashioned but the gauge is big and clear and helped monitor starting pressure for reeds back when I was unsure of how good they needed to be.

 

Gentle quiet playing 1"WC = .036 psi

Mid range playing 2.5"WC = .09 psi

Loud playing guess 4.5"WC = 1.6 psi

 

I have to say I find these numbers disappointing. I had hoped for something like 15lbs psi. Sorry, I can't talk hectopascals. It is the one metric measure no-one in this country has ever managed to assimilate. Service stations still calibrate tyres in psi even though it is illegal. Anyway, after a little thought I calculated the area of reedpan, it is 24.5 sq" x 0.09 psi (medium pressure 2.5"WC) = 2.2lbs pressure from the hands to create the note and that might be about right. Coincidentally 2.2 lbs is a kilo.

 

But... this is a very easy concertina to play. The reeds are very efficient, not the best I have done but very good. I would say a Lachenal would need twice the effort to play at the same medium volume and would never reach the same top volume.

 

Any thoughts welcome...

 

Terry McGee also posted (I wrote in the English units):

Quote

 

Right. Did the same thing as you, Chris, bolted a piece of craftwood across one side of the bellows of the Simpson anglo. Dusted off my trusty manometer. Amazingly it's had the same water in it for years and the level hasn't changed. This is highly calibrated water! Plugged the manometer into a hole through the craftwood.

 

Here's the results:

 

Squeezing or pulling just enough to sound the reed as quietly as possible - 10mm (0.39 inch) of water pressure

Playing (left hand only) - 30 to 40 mm (1.2 to 1.6 inch) of water pressure

Playing really loud (but still single notes) - 140mm (5.5 inch)water pressure

Not playing, but pushing or pulling pretty hard - 200mm (7.9 inch) of water pressure

 

(That's close to the limit of my manometer.)

 

Obviously we can convert those figures into any other system we need.

 

Happy to run any other tests now that I have the setup.

 

 

The conclusion I come to is that normal concertina bellows pressures are about the same as I expected for accordions.  In light of the fact that a concertina player needs to supply only about a third of the muscle force to produce the same bellows pressure, that extra reserve is not utilized and it's the volume of the note that determines how hard the musician pumps.  Rather obvious, I guess.  Big box accordion players have to supply about three times the muscle power for the same volume as concertina players, and realizing that makes me wonder whether playing force is a factor in limiting the largest size of big box accordions   If you also consider that big box accordion playing involves many chords, incorporating maybe 5 - 8 times the number of notes that concertina players use, accordion playing can be much more strenuous than concertina playing.  This incidentally is the reason why big box accordions can be used to play good tango music, it can never produce the dynamics produced with the smaller bandoneon, the traditional tango instrument, especially when the bandonistos slam the instrument down on their knees.  

 

Best regards,

Tom

 

 

 

[alex_holden]

My starting pressures on the tuning bellows are similar to Chris's, maybe slightly lower. My tuning pressure is lower, around 0.5". I also try a much harder yank on the bellows after each adjustment to check that it doesn't choke. The bellows are the same size as used on a typical 6 1/4" concertina. I haven't measured the maximum bellows pressure in an assembled instrument, but 3" or 4" sounds plausible based on how much force it takes to make my pressure gauge max out at 2".

[Chris Ghent]

Tom,

seems I have remembered the psi figures as WC figures so not as much difference as I thought.

[Dana Johnson]

On 1/25/2020 at 1:13 PM, ttonon said:

But all in all, the free reed can sound extremely loud with your ear next to it, and that perception is quite different from what we get when it's being played inside an instrument by a musician wanting to be heard above other instruments in a session.  It would certainly be an interesting experiment to fix an instrument with a pressure transducer and record the data during a session.  

Concertinas radiate most of their sound from the ends, away from your ears.  You sound much louder to people on either side.  If you want to hear yourself in a session, sit in a corner, like harpists sit with a wall behind them to hear the sound as it bounces back to you.  Most decent concertinas are plenty loud enough for sessions.  Mine certainly are without having to exert much effort.  Both violins and flutes are right next to your ear when playing and are much easier for the player to hear.  I tune my reeds in the reed pans with a plate with one pad hole over the chambers.  It sits about the same distance from me as normal playing position.  I think it is quite close to what the concertina produces fully assembled, especially since  I often will hold the concertina end up facing me if I am listening for any reed or valve issues.

 

On 1/25/2020 at 1:13 PM, ttonon said:

On 1/24/2020 at 9:51 PM, Dana Johnson said:

I do find a lot of variation in pitch with the degree the bellows is extended, Maybe as much as 5-6 cents, even at constant playing pressure.

That's surprising.  Do you see higher or lower pitch with extended bellows?

I’m trying to visualize the readout, but only see the numbers.  I often have to recheck the readings because I forget to write down the sign. I am thinking that the pitch is dropping though.  Now I think about it, I don’t think the deviation is that large.  Again I am fooled by the readout which is in tenths of cents.  It does vary by a couple cents though.

 

On 1/25/2020 at 1:13 PM, ttonon said:

Confusion here.  If "thinner reed sets" means thinner tongues, they might bend with more curvature than thicker tongues.  Is that what you mean?  The higher curvature would mean that the tips pull away more from the tip side wall, suggesting that they would need less draft than thicker tongues, and I agree.  But your results seem counter intuitive, because as I mentioned above, tongue travel through the vent is prime time for which static bellows pressure can move the tongue.  When you cause more leakage between the tongue and vent wall, that pressure effect decreases. 

Thinner refers to the tongues.  I do find that thin sets tend not to be able to reach the same volume as thicker sets, which does connect to the pressure required to drive the reed through the thickness of the vent.  Concertinas with thin reeds trade responsiveness for maximum volume.  The vent angle change is a way to get the most out of a reed.  I once did an experiment measuring the output of a reed ad the vent angle changed and how belling the vent instead of using a straight taper.  I measured the voltage out of the mic and thought I’d really found something when the amplitude doubled in the belled reed shoe.  Then I remembered that in audio, one db increase is x10 .  The belled set was noticeably louder, but just.  It did change the volume / pressure  curve, jumping to high volume more quickly.  Good for some music, bit makes dynamic control more fifficult.  
  I did arrive at my current draft angles  by testing to find the point where increasing draft started to reduce power.    Re: accordion reeds, they generally have little or no draft angle  because it eats more air than an accordion with multiple reed banks sounding at once can afford.  This is from an accordion maker.

Dana

[Dana Johnson]

Regards trying to figure out reeds in isolation,  I am not sure how easy it is to get to a place where you can afford to discount the reed’s environment.  The pitch change with bellows extension is one example, but once I thought once I’d be clever and build a foot powered tuning bellows ( or really a dropping weight one ) using a smallish accordion bellows about twice the area of my concertina bellows that could be used both with or without the blower.  I was surprised that my reeds would not sound with that big a bellows.  Given the requirement to have the positive side of the reed isolated from the negative.  Just how do you look at the acoustics of the system ?  I know you can’t look at wind instruments without considering the upwind side, be it vocal tract or mouthpiece cavity design.  I know others have had tuning bellows with larger areas, but I could not use the same setup I use with the blower / concertina bellows mount just transplanted to that accordion bellows.  I do have separate chambers on the plenum I use with reeds being rough tuned, not in the reed pan.  I have three chamber sizes in the plenum, each works best with a certain pitch range.  Reeds stop sounding when the chamber gets too big .  I could probably do better with 4 sizes, but having the chamber on the backside makes a huge difference to whether the reed operates or not.  When getting too close to the reed too small for the chamber pitch, the reeds get muted and lose their harmonic richness.  I cover the unused slots with flaps of silicone rubber, and when I get to some notes, especially at the transition zone.  I find that as the notes dull, partially opening the adjacent port will allow the reed to sound clear again.  I know chambers etc  complicated things, but I am  not sure  how possible it is to ignore the kind of spaces reeds need to work.

    I know people have brought up different thoughts about resonance, mostly discounted because the sizes involved don’t really fit the wavelengths involved, and are far from critical dimensions, but some property of the spaces involved  has a very large influence on reed function.  

well, have fun with it all.

Best wishes,

Dana

[ttonon]

I recall an incident when I was experimenting with free reeds in my jig, with the reed isolated and freely exposed over a port through which airflow traveled downward.  A friend came by with her toddler son to say hello, but she shortly had to leave after only a few minutes because she feared the sound was too loud and might damage her son's hearing.  She was standing a few feet from the apparatus.  I then realized how really loud the sound was and it became annoying, after which I reduced the driving pressure down from about 4 - 5 inches w.c., which I think we established here is not uncommon in normal playing.  I wonder if she would've had the same fears if the reed was inside an instrument, with the same driving pressure.  

 

On 1/26/2020 at 8:55 PM, Dana Johnson said:

The belled set was noticeably louder, but just.  It did change the volume / pressure  curve, jumping to high volume more quickly.  Good for some music, bit makes dynamic control more fifficult.  

Dana, I'm not sure I understand what you mean by "bell," but if it means that the draft of the vent sides has a bell-like curve rather than straight-line angle, I'm very surprised, maybe even suspicious.  There's no mechanism I can think of based on fluid mechanics that could explain such an effect to the extent that it would be noticeable or measurable, and so I'd have to question the measurements themselves.  No offense, of course.  Experimental physics isn't trivial, if we want to be certain about results that are accurate, reliable, and reproducible by others.  

 

On 1/26/2020 at 8:55 PM, Dana Johnson said:

Re: accordion reeds, they generally have little or no draft angle  because it eats more air than an accordion with multiple reed banks sounding at once can afford.  This is from an accordion maker.

This checks with my own experience.    

 

On 1/26/2020 at 11:13 PM, Dana Johnson said:

Regards trying to figure out reeds in isolation,  I am not sure how easy it is to get to a place where you can afford to discount the reed’s environment.  

Before getting into a lot of detailed discussion, it's very common for both theoreticians and experimentalists to eliminate extraneous conditions.  It would be silly, even impossible, to try to include all real world effects when trying to understand any given phenomenon.   The wisdom here is in realizing the essential elements of the phenomenon.  That's what makes a good researcher.  What's the point in including the feature of open or closed bellows?  The sensible approach is to first understand the essentials, then if worth it, try to include less essential aspects, especially if those aspects have their own explanation, as in the case of bellows volume?  For the free reed, it can indeed be excited as it sits freely outside bellows and away from the traditional cavity geometries.  You can excite its vibration without any effect of a cavity.  So why not understand first that arrangement?  You can then add other features.  

On 1/26/2020 at 11:13 PM, Dana Johnson said:

 I was surprised that my reeds would not sound with that big a bellows.

I'm not sure your conclusion that the size of the bellows is the reason your reeds didn't speak.  But if you're right, the only theoretical explanation I have is that the bellows volume and port opening over which the reed is mounted form a Helmholtz resonator that has resonance near the reed fundamental frequency.  Did you check that?  That's my guess, but not seeing the complete geometry of the apparatus, I can't say for sure.  I assure you that your experience can be explained by acoustic theory, and the underlying effect can be eliminated in an investigation on how the free reed vibration itself occurs, given tongue and vent geometries and a uniform, steady pressure difference across it.  

On 1/26/2020 at 11:13 PM, Dana Johnson said:

 I know you can’t look at wind instruments without considering the upwind side, be it vocal tract or mouthpiece cavity design.

Really?  But you could look at numerous papers in scientific journals that do just that.  Of course, the investigative history of any given instrument gets more inclusive with time, and it's the early papers that will have the simplest investigations.  Whether those simpler investigations are adequate can be judged by the effects included in subsequent papers.  But with many woodwinds, it's not necessary to consider upwind effects for a basic understanding, and the inclusion of such effects are done sometimes more out of a luxurious curiosity, on a special case basis, by people who are paid to come up with new ideas. 

 

Progress in scientific investigation is aided by knowing what to include and what not to include.  Many heroes in physics and engineering found just the right mix and their names are memorable.  It takes real talent to realize what's important and what's not.  Just because some feature of a real instrument can influence the sound of the instrument doesn't mean that the feature is essential and must be included for a basic understanding on how the instrument works.  You first cleverly identify the essentials, figure out the results, then add in other "real" effects.  With tongue vibration of the free reed, first understand how it works in isolation, without a cavity (or bellows), then add in more.  Then move on to acoustics, and you can then deal with the acoustical effect of the cavity, which can be noticeable, but not largely.  And concerning tongue vibration, we already know that the effect of the cavity and bellows is normally small, except in those instances when a resonance occurs, which in turn is also a well understood phenomenon. 

 

To me, the Western free reed is an enigma.  On one hand, it's one of the simplest sound sources - just a vibrating cantilever involving little companionship with other vibrating systems - but on the other, just its vibration alone has withstood a complete-enough understanding.  On one hand, its musical tone can be largely understood without bringing in its geometrical environment, on the other the details on how the acoustic sound is made solely by virtue of its own vibration is extremely complicated.  The Asian free reeds are more complicated because in addition to what happens to the Western version, you do have a system coupled with a resonator.   So to me, the complexity of the free reed, unlike other sound sources, is largely confined to itself, whereas with other sound sources, additional vibratory elements must be considered.  

 

But I think I know what you mean, and I can be more accommodating by noting that in some instruments there are some real world effects that must be included for a more-or-less complete understanding of its tone.  The harmonica is a good example, and it's brethren to the concertina.  Without understanding the acoustic effects of the musician's body parts, one cannot get a realistic understanding how harmonica tones come about in actual playing.  It's again the wisdom of the investigator, knowing what to include and what not to include.  But if all you want to understand how the harmonica reed vibrates subject to a steady pressure difference, you don't have to look upstream. 

 

There are some instruments that are borderline cases.  Organ pipes are one.  For a hundred years there were claims that the body of the pipe flexed to the degree that it affected the sound.  But we're talking now about nearly imperceptible acoustic effects.  It was only fairly recently that the issue was mostly settled.  And then it was discovered that in some cases, because of construction details, the funnel shaped connection between the shallot (mouth) and the pipe could vibrate in acoustically noticeable ways.  But that was exceptional.  Then it was discovered that in some rare cases, the pipe walls could noticeably contribute to the tone.  But that was happenstance, due to exceptional construction details.  I don't recall the exact details, but while I'm at it, and concerning the issue of whether materials of construction affect musical tone, musical instruments cover the full spectrum, from stringed instruments in which materials are key to the tone, to woodwinds, where materials have very little affect on the tone, except some of the brass instruments that have large bells (the bells vibrate and affect the tone directly and sometimes indirectly by feedback to the musician's lip vibration), with organ pipes intermediate, involving uncommon occurrences.  

 

In many of these studies, simplified approaches are taken, with a focus on what your goal is (say mechanical vibration vs acoustical sound spectrum) and in some cases further study is needed to obtain a more comprehensive picture.  You often see the titles of investigations with the format, "Investigation of the tone of the X, for the case of Y," where X is the instrument and Y is the added element.  We might see in the future something like, "The vibration of the free reed, including the effect of a cavity."  

 

On 1/26/2020 at 11:13 PM, Dana Johnson said:

I know chambers etc  complicated things, but I am  not sure  how possible it is to ignore the kind of spaces reeds need to work.

It depends on how accurately you want to understand the sound of the instrument.  If the criterion is only to understand the vibration of the tongue, the issue is enormously simplified, as compared to a criterion to understand the perception of our ear/brain system.  Moving on to the acoustical effect of the vibration is an added complication.  The ear/brain system is phenomenally sensitive, and that raises a high bar for theoretical understanding.  But acousticians have methods to deal with that.  Right now, I'm working on the vibration problem of the tongue, a relatively simple aspect, and believe me, the lion's share of understanding can be gotten with the isolated reed.  Such a solution can be incorporated into the acoustic issues, which can involve the effects of the cavity, as well as the bellows.  If you want, you can also consider the acoustic effects of the wood structures, the end plates, the fact that the instrument is played on the lap of a human, the presence of a wall or corner behind the musician, the presence of the musician's hands in front of the end plates, the presence of other musicians in a room with furniture, wall hangings, the clothes the musician wears, the hearing response of the ear of the listener, and so on.  At what point do you stop?  Well, we all know the answer to that.

 

Best regards,

Tom

Edited January 28, 2020 by ttonon
Modify response to 11:13 response by Dana

[Little John]

On 1/25/2020 at 6:17 PM, Chris Ghent said:

... I like my lower reeds to start in the tuning rig by .11 “ . This figure climbs slowly to around .2 at high pitches. ...

 

This might be going slightly off-topic, but as a duet player this is of considerable interest to me. Often, with a duet, balance is a problem - the bass can overpower the melody. One "solution" is to fit a baffle to the left hand end to reduce the volume; but that's a bit of a fudge. I have owned several Crane duets over a period of more than 30 years, but it was only about six or seven years ago when I bought a 55 button Crabb that I realised where the problem lay. On that instrument the reeds all started to sound at the same pressure. It didn't have a balance problem. In the light of that I had the reeds on my Dipper re-set so that they all started to sound at the same low pressure. Big improvement. When Alex built me his #4 instrument he was careful to make all the reeds sound at the same pressure. That instrument has great balance.

 

Getting the reeds sounding at the same pressure also increases the dynamic range of the instrument because you can play quietly. If the low reeds start to sound first you have to play fairly loud to get the high reeds to sound at the same time; but at any volume it seems that the low reeds, having started louder, stay louder.

 

LJ

[Dana Johnson]

On 1/28/2020 at 1:39 AM, ttonon said:

Dana, I'm not sure I understand what you mean by "bell," but if it means that the draft of the vent sides has a bell-like curve rather than straight-line angle, I'm very surprised, maybe even suspicious.  There's no mechanism I can think of based on fluid mechanics that could explain such an effect to the extent that it would be noticeable or measurable, and so I'd have to question the measurements themselves.  No offense, of course.  Experimental physics isn't trivial, if we want to be certain about results that are accurate, reliable, and reproducible by others.  

The draft angle varies with depth so the cross section shortwise across the reed shoe looks mildly shaped like a musical instrument bell.  All this means is that the reed sees side clearance increase faster than a single angle draft.  I found the amplitude increase over straight draft held over most of the note range from about b3 on up though I didn’t  graph the values.  When concertina reeds have too low a draft angle, they require more pressure to get to max volume.  Whatever happens in a belled vent, it happens sooner in the cycle than in a straight one.  I originally tried it because the reeds on my old Bb/F Jeffries had all the reeds carefully belled by hand.  It was a lovely. clear sounding instrument.  I did vary the amount of belling with shoe size.  What I found as far as the sound goes is that the belled reeds go from quiet to loud more quickly with increasing pressure.  If you are looking for a more honky sound, that helped.  
   As far as mechanisms go, I can’t see a curved draft is really any different than a straight one except that whatever is happening at the side clearances sees a gap that increases at a accelerated rate.  

 

On 1/28/2020 at 1:39 AM, ttonon said:

But if you're right, the only theoretical explanation I have is that the bellows volume and port opening over which the reed is mounted form a Helmholtz resonator that has resonance near the reed fundamental frequency.  Did you check that? 

that may have been the case, but I seem to remember that it affected more than one reed. ( of course things can gave multiple resonances.)   I am quite aware of the issue though.  My current tuning setup has a resonance around G4, which I get around by opening a second chamber.  It extends about halfway to G# but heavily influences the affected reeds.  An earlier setup I used with a more powerful blower that could easily get to 4” and above, had a exit pipe of 4 inch pvc about 6 feet long.  Had to ditch it because of the resonance problem.    Even room resonances can cause problems.  
    I am coming at this from the wrong direction for any kind of mathematical analysis.  As a player and maker,  I pay attention to the things that get musical results which have to include the complete unisolated package.  I am stuck poking around things until they seem to give the best subjective result, with modest experimentation  to home in on the desired result.  Not practically being able to separate out very much and still tell anything has been frustrating.  It is relatively easy to make general statements about chamber depth and size,  the general effect wood species has on both tone and damping,   But I have pretty much given up on trying to understand the mechanisms by which it all happens.  Trial and error can be an effective way of coping with  complex interactions without really understanding them.  When I was younger and more ignorant of my lack of critical thinking powers.  I was invested in “understanding” how it all worked.  The more I learned the less I knew.  Now, I get my enjoyment from the craft of making concertinas and getting lost playing them.  I’ll leave the ciphering to cleverer folk.

Best Wishes,

Dana

[ttonon]

Hi Dana, sorry for the delay.  I'm glad to see your post because I actually suffered remorse for the possibility that I was too harsh in my last response.  I do like to be direct with people because I no longer have the patients to worry about personal issues.  To me the important thing is the subject matter and finding a way to explain it in the most direct way, which I agree can sometimes be toned down.  So I apologize if I was lost in my own head.  

 

On 2/4/2020 at 12:59 AM, Dana Johnson said:

When concertina reeds have too low a draft angle, they require more pressure to get to max volume.

This surprises me because the major amount of energy addition to the vibration is during the downward movement of the tongue through the slot.  With high draft angle, there's a lot more air flow between the edges of the tongue and the walls of the vent, lowering the pressure driving the motion. 

 

On 2/4/2020 at 12:59 AM, Dana Johnson said:

I originally tried it because the reeds on my old Bb/F Jeffries had all the reeds carefully belled by hand.

In fact, my model does predict that for straight sides, the thicker the shoe, the larger the vibration amplitude.  I suppose it's possible that you might hear a louder volume for a lower vibration amplitude, and that's particularly intriguing.  Understanding the vibration of the tongue is not the same as understanding the acoustic effect on our ears.  So yes, I'm intrigued.

 

On 2/4/2020 at 12:59 AM, Dana Johnson said:

I originally tried it because the reeds on my old Bb/F Jeffries had all the reeds carefully belled by hand.

Just how do you do that?  Do you use a ball mill cutter?  I can't see that you're cutting the sides with some kind of file or scraper, so maybe I really don't understand what you mean by a "belled" relief angle.  

 

On 2/4/2020 at 12:59 AM, Dana Johnson said:

As far as mechanisms go, I can’t see a curved draft is really any different than a straight one except that whatever is happening at the side clearances sees a gap that increases at a accelerated rate.  

I agree.  Would you agree that the effect is a little like that of a thinner shoe (plate)?

 

On 2/4/2020 at 12:59 AM, Dana Johnson said:

Even room resonances can cause problems.

I didn't see in your description a possible effect of the sound produced by the air delivery system, when there's a powered blower.  I know in my own set up there are interference resonances with the SOUND the blower makes, for whatever reason, the sound of the motor, it's fan, or in the air flow noise.  It can be pretty complicated.  

 

Regards,

Tom

Edited February 10, 2020 by ttonon
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[ttonon]

Dana, I forgot to ask, do you put a belled draft angle on all of the vent (slot) sides, or only on some of them?  Thanks.

 

Regards,

Tom