Tap tones are too low! What to do next...

[BigFryMan]

Hi everyone!

Haven't posted for a long time, but have still been lurking and in the last few months getting back into making violin number #3.

I am most of the way through hollowing out a spruce top and have been trying to follow along with a working method that Davide Sora has been so kind to put online https://davidesora.altervista.org/videos/belly-back/

Currently my spruce top is 74 grams and the wings of the upper and lower bouts seem to be getting closer and closer to the flexibility I'm happy with. Not much flex longitudinally, but plenty of twist. The mode 5 tap tone is currently at around 289hz. This is where I am very far from the model that Davide is working with. I still have a little thinning out to do in-between the C bouts and would like to be somewhere in the 60-70g mark for the top. Davide's model at this stage has a mode 5 of 350-370hz. I obviously cannot put more timber back on and I'm not sure I'd want to even if I could. I have attached a few pics, one has the graduations marked on it.

A few things I'm thinking could have me where I am currently:
- I don't have stiff enough spruce for the weight
- my model is wider in the C bouts than I'd originally intended, perhaps this is pushing mode 5 down and the weight up
- my arching could be very weird
- I live in an area with high humidity

Anyways, the biggest questions I have now are: 
- What should I do with this spruce top now? Should I keep thinning down to where the numbers seem reasonable, or should I stop and cut the f-holes and keep moving.
- What did I do wrong and how can I improve for next time?

I know comparing Davide's model to mine is diamonds to gravel, but it is nice having a reference point to learn from.

Thanks in advance for any ideas and thoughts.

[Peter Lynch]

I think you are focusing on the wrong thing.  How can you  possible know that you did something wrong at this point?????  MoveOn.org  ... Clean up what you have done so far and make it beautiful, do your edge work, make your f hole fluting, Cut those f holes and get it to a decent weight. 

 

[Anthony Panke]

I am of the same opinion. Cut the f holes, you can always adjust the thicknesses later. In my opinion, 4mm is a bit too thick for the centre of the belly, 3mm is better. I would cut away around the blocks to form a curve rather than leaving them flat; this will reduce mass. Don’t worry about the exact tap tone frequencies.  Stiffness is more important, so if it flexes easily but doesn’t cave in then it’s good. 

In what way could your arching be weird?  Did you follow a particular model or is it by eye, what were you aiming for?

best of luck

[Peter K-G]

Two things to consider

1. Looking at the thicknesses and the weight you might have wrong readings of M5, if not the wood is really "low performance"

2. You cannot "decide" an M5 at the stage when you carve out the inside, it will be according to what wood you have and arching, assuming "normal" graduation.

[J.DiLisio]

22 minutes ago, Peter K-G said:

Two things to consider

1. Looking at the thicknesses and the weight you might have wrong readings of M5, if not the wood is really "low performance"

2. You cannot "decide" an M5 at the stage when you carve out the inside, it will be according to what wood you have and arching, assuming "normal" graduation.

Do you mind elaborating on the second point?  If you were starting with a piece of wood with low specific gravity how would you compensate with the arching?  Would you adjust the arching height or fullness to the edge?

[BigFryMan]

2 hours ago, Anthony Panke said:

I am of the same opinion. Cut the f holes, you can always adjust the thicknesses later. In my opinion, 4mm is a bit too thick for the centre of the belly, 3mm is better. I would cut away around the blocks to form a curve rather than leaving them flat; this will reduce mass. Don’t worry about the exact tap tone frequencies.  Stiffness is more important, so if it flexes easily but doesn’t cave in then it’s good. 

In what way could your arching be weird?  Did you follow a particular model or is it by eye, what were you aiming for?

best of luck

Thanks Anthony. Yes I still have a bit of wood to remove from the center, but was trying to decide whether to err on the side of a little or a lot more. 

I have a poster of the Del Gesu Plowden (1735) I've been using as a reference, but I'm a terrible copyist hah. 

[Peter K-G]

1 hour ago, DoorMouse said:

Do you mind elaborating on the second point?  If you were starting with a piece of wood with low specific gravity how would you compensate with the arching?  Would you adjust the arching height or fullness to the edge?

 

If you were starting with a piece of wood with low specific gravity how would you compensate with the arching?

I wouldn't, density is not what determines arching, wood stiffness properties does. Density determines plate thickness

Would you adjust the arching height or fullness to the edge?

Both, according to the wood's properties; arching longitudinal and latitudinal height/length/shape 

[BigFryMan]

1 hour ago, Peter K-G said:

Two things to consider

1. Looking at the thicknesses and the weight you might have wrong readings of M5, if not the wood is really "low performance"

2. You cannot "decide" an M5 at the stage when you carve out the inside, it will be according to what wood you have and arching, assuming "normal" graduation.

Thanks Peter,

I guess I was hoping people would chip in on nearly exactly what you're saying - either not great spruce perhaps I didn't get close enough to normal arching.

In your second point about not deciding on M5, I think I am trying to learn what action would be best on where to go from here. Keep thinning out the graduation a little to get to the weight down and let M5 be what it will be, or leave it fairly heavy and try not to drop M5 much further. I am currently leaning towards thinning out the center a little more and bring the upper and lower bouts fairly uniformly down to 2.5mm

[BigFryMan]

I guess another course of action I could take to get M5 up a little bit higher would be to install a taller (stiffer) bass bar? 

[Jeff Jetson]

Good work!

[JacksonMaberry]

3 hours ago, Anthony Panke said:

I am of the same opinion. Cut the f holes, you can always adjust the thicknesses later. In my opinion, 4mm is a bit too thick for the centre of the belly, 3mm is better. I would cut away around the blocks to form a curve rather than leaving them flat; this will reduce mass. Don’t worry about the exact tap tone frequencies.  Stiffness is more important, so if it flexes easily but doesn’t cave in then it’s good. 

In what way could your arching be weird?  Did you follow a particular model or is it by eye, what were you aiming for?

best of luck

As regards the thicknesses, my best fiddle to date, in professional use, is 4.5mm thick in the thickest part of the belly. I think too much depends on your wood properties to say any thickness is preferred by default. 

I also disagree with working the arch right up to the block edges - just blend the transition line with a couple passes of a scraper. 

[Anthony Panke]

In which case the arching should be within a normal range. Are the thicknesses of the plowden approximately as per graduation of your plate? Also, is the density of your plates normal?

in any case I would not be too worried. 

[Don Noon]

5 hours ago, BigFryMan said:

Currently my spruce top is 74 grams ... mode 5 tap tone is currently at around 289hz.

I would be willing to bet large sums of money that you are not actually seeing M5... it is something else.

1)  My Walmart firewood top had a higher M5 than that, at that same weight, WITH the F-holes cut.  And that wood was some kind of pine with properties that were off-the-chart poor.

2)  There IS some other resonance that is excited when you tap the center of the plate and hold in the normal nodal line spot, and in my experience it is much stronger than the (eventual) M5 when the plate is thicker than the final.

3)  It's there even in the finished plate:

So unless you accidentally carved a top from a waterlogged wedge from a latex tree, carry  on and the real M5 will begin to emerge.  This is one of the problems of getting overly technical about specs... it can get you lost.

 

 

 

[uncle duke]

Hold the plate with the carved inside facing yourself with your left fingers holding the plate on the upper treble bout and tap the lower bass side outer bout with the pad of your index finger close to the edge and try to get a reading for the M1.  It should read somewheres from 95 to 105 if you are getting close.  Double that number for somewhat of a M2.  Then these guys will have an idea for where you may be at.

I'm not familiar with that graduating plan - looks heavy to me still but not all wood will conform to an ideal. 

According to Marty's plate weight to belly height comparison chart you're not in the ballpark yet.    

[Ken_N]

6 hours ago, Peter Lynch said:

I think you are focusing on the wrong thing.  How can you  possible know that you did something wrong at this point?????  MoveOn.org  ... Clean up what you have done so far and make it beautiful, do your edge work, make your f hole fluting, Cut those f holes and get it to a decent weight. 

 

Peter has the right idea here.  Listen to him. I wouldn't worry about the weight at all now.  It could be that the piece of wood you have will never get to 60-70 g.  So?  It's your number 3, and your work looks very good.  Look at your thickness numbers.  They are very even. I would leave the center alone.  I'm not afraid to leave the center at 5 mm.  But I'm not afraid of anything. I'm sure that you've learned a lot already.  Leave the center alone, and learn to let go if you have to.

I like to rough the inside, rough the outside, and then see what it is doing.  If it seems stiff, I'll leave the inside alone, and thickness it from the outside.  If it is already ALMOST flexing, I'll cut the inside deeper first, maybe even tightening the curves. 

Before I get near finishing; 4mm plus thick or so; I put the f holes in.  Then they will be incorporated with the arching.  After adding the bass bar, the plate will stiffen up.  I don't finish the recurve until the body is glued together, so I have no idea what weight, or tap tune I finish at.  

Every one that you do you will learn something.  I'm doing an arch top guitar now, and it is the same, but different.  The back is thinner than the vague thickness given in a book I bought, 2.5 - just under 6 mm, but it doesn't seem too flexible.  It taps around 330.  Maybe that's not the real note, but there are a lot of notes around there depending on where you hold, and tap it.  

Like Don said, maybe you are hearing something different.  When the back of that guitar was 450 grams and not 350 I thought the that tap tone was 330, and now it is STILL 330.  But is is far more opened up.  I used Flamed Birch for a violin back that was very low in pitch from the beginning.  But it was very resonant, just low.  It worked fine.

Cut the f holes.  Put in a bass bar.  Finish it up before, or after gluing it together, and move on to the next lessons: varnish and set up.  It's never ending learning.  But you have to just do it.  Don't let paralysis get you.

On the next one,  maybe try something different.  Or work on perfecting that model if you like it.  Don't be so hard on yourself.  It looks really good.

[duane88]

Looking good!

At this point in the game, tap tones are moot, or perhaps should be mute...Record them, finish the violin and see how it sounds. There is not only one single path or set of measurements that will allow you to create a good violin.

[donbarzino]

The large thick flat areas you have left for the upper and lower blocks could be interfering

with the usual mode 5 vibrations.

[Marty Kasprzyk]

55 minutes ago, donbarzino said:

The large thick flat areas you have left for the upper and lower blocks could be interfering

with the usual mode 5 vibrations.

That's what I've found too.  

[JacksonMaberry]

1 hour ago, donbarzino said:

The large thick flat areas you have left for the upper and lower blocks could be interfering

with the usual mode 5 vibrations.

It worked for Strad (and has for others also). Granted on Strads the line is blended, rather than so stark as in this case.

[francesco piasentini]

Hi there.

How do you measure M5?

Hold and tap, record on a PC, smartphone? Guitar tuners, ecc...?

[BigFryMan]

6 hours ago, Don Noon said:

I would be willing to bet large sums of money that you are not actually seeing M5... it is something else.

1)  My Walmart firewood top had a higher M5 than that, at that same weight, WITH the F-holes cut.  And that wood was some kind of pine with properties that were off-the-chart poor.

2)  There IS some other resonance that is excited when you tap the center of the plate and hold in the normal nodal line spot, and in my experience it is much stronger than the (eventual) M5 when the plate is thicker than the final.

3)  It's there even in the finished plate:

So unless you accidentally carved a top from a waterlogged wedge from a latex tree, carry  on and the real M5 will begin to emerge.  This is one of the problems of getting overly technical about specs... it can get you lost.

 

 

 

Thanks Don, I think you might be on the money there! It was the loudest, clearest resonant frequency so I had just presumed it was M5 and wasn’t paying a huge amount of attention except to the pitch. I’ll review the tapping/holding positions and fire up my recording rig today to check properly. Maybe I’m not so far off the norm after all. 

[BigFryMan]

4 hours ago, Ken_N said:

Peter has the right idea here.  Listen to him. I wouldn't worry about the weight at all now.  It could be that the piece of wood you have will never get to 60-70 g.  So?  It's your number 3, and your work looks very good.  Look at your thickness numbers.  They are very even. I would leave the center alone.  I'm not afraid to leave the center at 5 mm.  But I'm not afraid of anything. I'm sure that you've learned a lot already.  Leave the center alone, and learn to let go if you have to.

I like to rough the inside, rough the outside, and then see what it is doing.  If it seems stiff, I'll leave the inside alone, and thickness it from the outside.  If it is already ALMOST flexing, I'll cut the inside deeper first, maybe even tightening the curves. 

Before I get near finishing; 4mm plus thick or so; I put the f holes in.  Then they will be incorporated with the arching.  After adding the bass bar, the plate will stiffen up.  I don't finish the recurve until the body is glued together, so I have no idea what weight, or tap tune I finish at.  

Every one that you do you will learn something.  I'm doing an arch top guitar now, and it is the same, but different.  The back is thinner than the vague thickness given in a book I bought, 2.5 - just under 6 mm, but it doesn't seem too flexible.  It taps around 330.  Maybe that's not the real note, but there are a lot of notes around there depending on where you hold, and tap it.  

Like Don said, maybe you are hearing something different.  When the back of that guitar was 450 grams and not 350 I thought the that tap tone was 330, and now it is STILL 330.  But is is far more opened up.  I used Flamed Birch for a violin back that was very low in pitch from the beginning.  But it was very resonant, just low.  It worked fine.

Cut the f holes.  Put in a bass bar.  Finish it up before, or after gluing it together, and move on to the next lessons: varnish and set up.  It's never ending learning.  But you have to just do it.  Don't let paralysis get you.

On the next one,  maybe try something different.  Or work on perfecting that model if you like it.  Don't be so hard on yourself.  It looks really good.

Thanks Ken, very encouraging. 

I wasn’t at the point of paralysis over it, more just making sure that if I’ve ended up in a weird place I wanted to learn from it for next time and take the best course of action. As Don mentioned, it’s possible that this resonance is not actually M5, but another modal resonance. I do like to learn my lessons well because making a violin is so time consuming and I aspire to making a decent one before I hit 40.

[BigFryMan]

2 hours ago, donbarzino said:

The large thick flat areas you have left for the upper and lower blocks could be interfering

with the usual mode 5 vibrations.

 

1 hour ago, Marty Kasprzyk said:

That's what I've found too.  

Thanks for the pickup, I didn’t actually realize mine were so stark. I might blend them a bit. I’ve heard a few people mention to leave the corners alone and I’m presuming for the sake of support.

[BigFryMan]

33 minutes ago, francesco piasentini said:

Hi there.

How do you measure M5?

Hold and tap, record on a PC, smartphone? Guitar tuners, ecc...?

Hold and tap and compare to a sine wave frequency. 

[curious1]

The only true confirmation of M5 would be by vibrating the plate and observing the modal pattern.

M5 without bass bar: