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No M2


FiddleMkr

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10 hours ago, FiddleMkr said:

The m2 of the BACK is (in fact) two octaves below its m5 (not just one).  
       The TOP has a well defined M5 pattern and a high excitation of tea leaves. But as I said the nodal pattern for M2 doesn’t form. The thickness is a little over spec; 3mm where it calls for 2.8mm, but the weight is at the midpoint (66.9g, midpoint is 68g). Do you think I might could get an M2 pattern by reducing the thickness (by 0.2mm) on either side of where the M2 node should be? Or should I try reducing the thickness at the nodes, since you suspect that the plate is stiff? I have a +-10gram tolerance on the weight, if that matters. 

I think that even in the current state of your top plate you should obtain the nodal figure of M2, as @Evan Smith says it is one of the easiest to form. How do you detect modes? I suspect you're doing something wrong, follow Evan's suggestions and try again.

If you clearly hear the mode 2 note by ear while tapping, it means the pattern is forming, if it wasn't forming you wouldn't hear the note clearly.

Then, is your top plate without or with Fs? without or with bassbar?

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1 hour ago, Evan Smith said:

`The simplest and most reliable way to hold a plate to run over a speaker is with 2 small pieces of 0000 steel wool placed as such,,,,,,,,,,

 

 

So for mode 2,, which is one of the easiest to find, place the pads as such, lay the plate on them with the lower block directly over the speaker and scan,,,

 

Those are some nice looking nodal lines. Apparently the small opening and tapered hole makes a big difference (also). Curious; what size is your speaker? And, what are you using for “tea leaves”? 
 

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1 minute ago, Davide Sora said:

I think that even in the current state of your top plate you should obtain the nodal figure of M2, as @Evan Smith says it is one of the easiest to form. How do you detect modes? I suspect you're doing something wrong, follow Evan's suggestions and try again.

Then, is your top plate without or with Fs? without or with bassbar?

The top is without f’s and bass bar. I detect the modes by going through the frequencies slowly looking for tea leaf movement, and I know that m2 is about an octave away from m5, or it should be. 

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1 minute ago, FiddleMkr said:

The top is without f’s and bass bar. I detect the modes by going through the frequencies slowly looking for tea leaf movement, and I know that m2 is about an octave away from m5, or it should be. 

When I get to F# for M5 I would cut the F-holes anyway, it doesn't matter where the M2 is. Paying attention to the nodal lines doesn't make much sense to me, but it makes even less sense at such an early stage.

However, if you want to find the nodal pattern of the M2, you can locate the frequency by ear and tapping, then reproduce this specific frequency with the speaker and move a few Hz up and down to sharpen the nodal lines of the Mode. If you hear it by ear, it must form.

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2 hours ago, Anders Buen said:

Impressing, specially as the note fundamental is 140-160 Hz or so below the lowest note on a violin. Some are more bassy than others! :-)

E to F below middle C is in the lower end of a typical tenor and mid range for a baritone.  His mode 5 voice is ear-piercing. 

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3 hours ago, Davide Sora said:

it doesn't matter where the M2 is. Paying attention to the nodal lines doesn't make much sense to me

Edited to my viewpoint.:)

I have never failed to find M2 on any plate, but I don't use a speaker and glitter, which is a pain and less certain.  I hold the plate around where I know the nodal line should be, and tap/mic it where I know the antinode should be.  It's always somewhere around there.  I'm only looking for frequency, not nodal line shape.

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6 hours ago, Evan Smith said:

`The simplest and most reliable way to hold a plate to run over a speaker is with 2 small pieces of 0000 steel wool placed as such,,,,,,,,,,

 

IMG_9224.thumb.jpg.423f6ed67084fac67a9e6512272af8f4.jpg  

So for mode 2,, which is one of the easiest to find, place the pads as such, lay the plate on them with the lower block directly over the speaker and scan,,,

IMG_9225.thumb.jpg.d49f86483464c28161518311a774e290.jpgIMG_9226.thumb.jpg.ec3b1d0a3d4d3c4bcea81da720b8196e.jpg

 

To find mode 5, place the pads as such,,,put the plate over the speaker, and,,,

IMG_9227.thumb.jpg.e360290a6a97152bc018b2c063633d7b.jpg

IMG_9228.thumb.jpg.2a5e8f0996d37d61ee29fa52423bc500.jpg

 

All of these were done with 2, 0000 steel wool pads, only the speaker position changes. The only time the pads are changed is M 6 and upwards, when the highest amplitude is in the central part of the lower or upper bout. . There is usually a node in the vicinity of the upper eyes somewhere, move one of the pads there.

IMG_2463a.thumb.JPG.a59407d48dd1f691d8294de552a06787.JPGIMG_2463.thumb.JPG.eae57ac6ffff005c359f9c27e0025e91.JPGIMG_2462a.thumb.JPG.d5d1cc7aff497025abc2016c6be59a19.JPGIMG_2462.thumb.JPG.04d05be49310010f947298e118484bfe.JPGIMG_2461a.thumb.JPG.66e1d87fd8c47bcfad77ce80ff884150.JPGIMG_2461.thumb.JPG.9814fddcf9ed20e4ce1cf89ca1249140.JPGIMG_2460a.thumb.JPG.c35399f364d85d0a553f9d82f7323a84.JPGIMG_2460.thumb.JPG.6a266d69f4e9856b1f6aa09e103adaca.JPGIMG_2457a.thumb.JPG.e8ba5de6befba847ff4fa7b883951010.JPGIMG_2457.thumb.JPG.b2896688bdcdd592a3cd0e159fad661e.JPGIMG_2241a.thumb.jpg.1092b68a43f9b1af2727e0b537839a71.jpgIMG_2242ajpg.thumb.jpg.4d1ddde557bf12f719d9b86ec746415e.jpg

It looks like that it could possibly work. It is by far the easiest and fastest with the cleanest lines, and I can't find one hertz difference, from any other method.

I think that too often people have the speaker opening way too large, and it cancels itself out. Also the thickness mounting of the hole is minimal, I have it beveled away to nothing, with a sharp edge at the surface. Too thick with straight sides creates phase cancellation and distortion, and hard to find clean lines.

Does it help, does it make a difference, to be able to see,, that discussion is in another world at the moment.

 

What a great post!
This deserves the maestronet medal of achievement :)

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1 hour ago, Don Noon said:

Edited to my viewpoint.:)

I have never failed to find M2 on any plate, but I don't use a speaker and glitter, which is a pain and less certain.  I hold the plate around where I know the nodal line should be, and tap/mic it where I know the antinode should be.  It's always somewhere around there.  I'm only looking for frequency, not nodal line shape.

Same here. Although I used the glitter test in the past, I soon stopped. The only real use I got from it was to identify the various Modes to understand which ones to attribute the various frequencies that you hear in a plate when you tap it.

This can be particularly useful in cellos, where it is easy to make a mess; for example, for some years I mistook the M3 or M4 for the M2, because they were louder and clearer than the M2 (which doesn't happen in the violin). Then doing the glitter test I discovered which was which, and I corrected my data.

Luckily I didn't give too much weight to the M2, otherwise I would have made a real mess.:lol:

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I will get back to y’all later (I had to take down my setup) after I improve my test; move the excitation point to the rear of the plate and rest the plate on steel wool. 
id feel better if I had a m2 nodal line, whether it matters or not. 
 

Edited by FiddleMkr
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On 12/2/2023 at 2:36 PM, Don Noon said:

If I'm reading this correctly, I'd agree with the opposite.

This has been attempted a number of times with "tonal copies", with questionable results.  My attempt and Sam Z's copies I think lead to the same place:  if you take a specific instrument and carefully copy it, you can get some of the general character of it's tone.  But, with wood being wood with all of its large numbers of variables (including damping), you won't get an identical twin.  And I think age does some things that are likely impossible to copy.

Is damping something that is expressed in some way in tap tones?

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4 hours ago, Nick Allen said:

Is damping something that is expressed in some way in tap tones?

It would be in how quickly the "ring" of the taptone dies off, which can be quantified as how many cycles it takes for the amplitude lose half of its value.  Unfortunately, the way the plate is supported will add some unknown damping, and it varies a lot with EMC.  It's not easy to measure, so most people don't.

A taptone is some unknown mix of longitudintal (low) and crossgrain (high) damping, to further confuse things.

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On 12/3/2023 at 4:34 AM, FiddleMkr said:

Those are some nice looking nodal lines. Apparently the small opening and tapered hole makes a big difference (also). Curious; what size is your speaker? And, what are you using for “tea leaves”? 
 

Yes the small opening is much easier to direct the assault. When I tapered the hole the results were dynamic.

What is this iteration of the speaker?  I'm not sure anymore.

What ever it is it will work better if it has a long excursion with a large magnet.(4 to 6 inch, or 10,, maybe 8.29748321", sounds perfect.

 

You need to pump air,,,

I've got a 100 watt amp.(works easily),(20 or so will do) a lower wattage speaker will work,,, unless you plan to spend hours with it cranked up  anywhere near 12 to 120 Bazillion volts or so. At which point you could also tan your wood, and heat your hide glue.

Tea leaves, can't I have a few secrets of my own?

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Here is a top, still a bit heavy,,

IMG_3173.thumb.jpg.d875b4e4184055711bb50a6e4f61943f.jpg

IMG_3212.thumb.jpg.e3ddd07ee06ba06d69793eb509f8e41b.jpg

The bar added 4.4 gms

 

IMG_3247.thumb.jpg.dadc359b3c9134791a2c09acffc42604.jpg

 

 

I  removed the weight of the bar (4.4) +.1 gms excess wood, and raised M5 by 20 Hz.

It's difficult and I'm slow so I have to be able to see the node lines to do that.

Notice that as the plate became more active, the lower bottom line was pushed out a bit further, and the upper lines are on the verge of breakup. Forget I said that. Pay no attention to me. I don't like it when a plate leaves piles of glitter every where, not enough activity for me.

 

 

IMG_3252.thumb.jpg.e597200993c0ad19cf4382a4e084582b.jpg

 

 

Next is a victim of personality recognition disorder, otherwise known as a problem. Mode 5 and 6 are too close together. Too close and a problem can occur with the E string evenness, it can develop some real hot spots.

They started out at 438/390, then ended up at 415/390, before I got distracted and stopped documenting. I was pulling down 6 to five, and you can often pull them together, and then a different 6 will show up and 5 will then look normal, at a lower hz..

IMG_1695.thumb.JPG.66070d815f34ab05274af901af106213.JPGIMG_1700.thumb.jpg.53a7ba2e9db40f88d83c15fb6df10ec8.jpg

 

 

You can see how they are almost a reverse mirror of each other. I had pulled this fiddle back apart because I was dissatisfied with the sound.

It's good now.

 

 

IMG_1710.thumb.jpg.286277663e45f5288f2dcbd4a0f9126e.jpgIMG_1711.thumb.jpg.b86c0b81c4a65f8b445649aa9ebde029.jpg

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On 12/5/2023 at 8:05 AM, Evan Smith said:

Yes the small opening is much easier to direct the assault. When I tapered the hole the results were dynamic.

What is this iteration of the speaker?  I'm not sure anymore.

What ever it is it will work better if it has a long excursion with a large magnet.(4 to 6 inch, or 10,, maybe 8.29748321", sounds perfect.

 

You need to pump air,,,

I've got a 100 watt amp.(works easily),(20 or so will do) a lower wattage speaker will work,,, unless you plan to spend hours with it cranked up  anywhere near 12 to 120 Bazillion volts or so. At which point you could also tan your wood, and heat your hide glue.

Tea leaves, can't I have a few secrets of my own?

Wow! You have the natural frequency testing perfected! I’m using an 8” speaker that I bought from radio shack. It has a 2-3/4” diameter magnet, 70 watts. I assume this is in the range of workability? 
     I do need to resize the hole and taper it. When you said “a long ‘ excersion’ and taper it “, did you mean a thick piece of wood with a tapered hole in it? Like a 2x10” joist with a tapered hole in the Center, maybe 3” tapering to 2” diameter?

 

On 12/5/2023 at 8:05 AM, Evan Smith said:

Yes the small opening is much easier to direct the assault. When I tapered the hole the results were dynamic.

What is this iteration of the speaker?  I'm not sure anymore.

What ever it is it will work better if it has a long excursion with a large magnet.(4 to 6 inch, or 10,, maybe 8.29748321", sounds perfect.

 

You need to pump air,,,

I've got a 100 watt amp.(works easily),(20 or so will do) a lower wattage speaker will work,,, unless you plan to spend hours with it cranked up  anywhere near 12 to 120 Bazillion volts or so. At which point you could also tan your wood, and heat your hide glue.

Tea leaves, can't I have a few secrets of my own?

Right now the hole is 7-3/4” or 8” diameter.
     When I can get back to solving this problem, the first step is just to move the rear of the plate over the speaker. (I forgot this detail from the last time. My age is catching up.)

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I may have been a bit unclear, I apologize.

The excursion is in reference to the flexibility of the speaker. The excursion of the cone itself. (Some speakers without a lot of excursion are very stiff, and have to be pushed hard to get an adequate  response.) I am speaking of a speaker with a foam edge typically used in car or home stereos, they are typically relaxed and move easily. I also referenced a larger magnet because that has more strength for the coil to work against.

However,  almost any speaker will do, and only after using one that works exceptionally well in this application , would you even know there could be a difference.

The taper is referring to the hole in my bench that the sound comes out of. For years I just had a box with a speaker in it, a thin piece of plywood with a 2.5" hole in it ,screwed on top, it worked great. When I mounted a speaker under my bench, it didn't work well at all, at tremendous volume it would barely illicit a response from the plate. The bench is almost 2" thick. After awhile of futzin with it, I decided that the air was damping itself and causing havoc in the 2" tube I had created. So I tapered the underside of my bench at more than 45 degrees into the hole, leaving just enough at the bench top for a snap ring to hold a piece of linen the keep debris out of the speaker. Suddenly it worked fantastic. The table top is flat, I carved out from underneath to get rid of my tube.

I have seen so many try to use some giant hole for the speaker, and I've tried to use their stuff, it gets crazy nasty, even with experience it barely works good enough to be useful,,,the smaller the better. If both sides of a node line receive energy it will try to cancel it all out.

Small directed and precise is what works well. You will enjoy a smaller hole for the speaker.

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On 12/5/2023 at 4:00 PM, Evan Smith said:

 Next is a victim of personality recognition disorder, otherwise known as a problem. Mode 5 and 6 are too close together. Too close and a problem can occur with the E string evenness, it can develop some real hot spots.

They started out at 438/390, then ended up at 415/390, before I got distracted and stopped documenting. I was pulling down 6 to five, and you can often pull them together, and then a different 6 will show up and 5 will then look normal, at a lower hz..

IMG_1695.thumb.JPG.66070d815f34ab05274af901af106213.JPGIMG_1700.thumb.jpg.53a7ba2e9db40f88d83c15fb6df10ec8.jpg

 

 

You can see how they are almost a reverse mirror of each other. I had pulled this fiddle back apart because I was dissatisfied with the sound.

It's good now.

 

 

IMG_1710.thumb.jpg.286277663e45f5288f2dcbd4a0f9126e.jpgIMG_1711.thumb.jpg.b86c0b81c4a65f8b445649aa9ebde029.jpg

I had a top with similar behaviour. The odd frequency patterns was present also before i started hollowing out. Decided not to use it and made another top.

Took some images of it right now and I like it even less, short fibers and it looks like it has defects. Maybe crushed/broken somehow.

IMG_2341.thumb.jpeg.b851486325d7d8b41ccf0fb6d6c93dc0.jpeg

IMG_2340.thumb.jpeg.ad3b26e16ff6e9fd9d7265164db95bc3.jpeg

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On 12/7/2023 at 10:46 AM, FiddleMkr said:

 

Right now the hole is 7-3/4” or 8” diameter.
 

What Evan said us good advice. The approach also depends on what you can get your hands on. I have an approx 4" 10w long throw speaker with a big magnet I salvaged from a top end computer presentation speaker system. It was in a column speaker box with two of these plus tweeter. With a small speaker its more efficient to mount it set in flush to the top of your board than have the sound go through that organ pipe from underneath. You need less power to drive it this way. With something like an 8" speaker mounted under a 4" wind tunnel you get complications from the height of the tunnel plus the volume of air trapped between the cone and the tunnel opening.  It's a Helmholtz resonator. 

 

Rex Thompson had a speaker under a thinnish plywood baffle mounted in a drawer under his bench. Open the drawer, pump the tea leaves, close the drawer. 

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42 minutes ago, LCF said:

What Evan said us good advice. The approach also depends on what you can get your hands on. I have an approx 4" 10w long throw speaker with a big magnet I salvaged from a top end computer presentation speaker system. It was in a column speaker box with two of these plus tweeter. With a small speaker its more efficient to mount it set in flush to the top of your board than have the sound go through that organ pipe from underneath. You need less power to drive it this way. With something like an 8" speaker mounted under a 4" wind tunnel you get complications from the height of the tunnel plus the volume of air trapped between the cone and the tunnel opening.  It's a Helmholtz resonator. 

 

Rex Thompson had a speaker under a thinnish plywood baffle mounted in a drawer under his bench. Open the drawer, pump the tea leaves, close the drawer. 

If you were going to buy a speaker, what size would you get?

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1 hour ago, FiddleMkr said:

If you were going to buy a speaker, what size would you get?

Probably 6" or 4" in 20 or 30w or whatever matches your amplifier . I've used all sorts to 8". Larger ones under the baffle through a hole as above. Fine dust inevitably works it's way down into the voice coil when they face upwards in a workshop with tea or whatever bouncing around nearby so they can have a short life. Fasten a bit of speaker box cloth over the top to help with that. 

 

 

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6 hours ago, LCF said:

Probably 6" or 4" in 20 or 30w or whatever matches your amplifier . I've used all sorts to 8". Larger ones under the baffle through a hole as above. Fine dust inevitably works it's way down into the voice coil when they face upwards in a workshop with tea or whatever bouncing around nearby so they can have a short life. Fasten a bit of speaker box cloth over the top to help with that. 

 

 

Do you have a cone above your 4” speaker to focus the sound to 2” diameter, or is the 4” a small enough focus of sound?

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On 12/6/2023 at 8:52 PM, Evan Smith said:

I may have been a bit unclear, I apologize.

The excursion is in reference to the flexibility of the speaker. The excursion of the cone itself. (Some speakers without a lot of excursion are very stiff, and have to be pushed hard to get an adequate  response.) I am speaking of a speaker with a foam edge typically used in car or home stereos, they are typically relaxed and move easily. I also referenced a larger magnet because that has more strength for the coil to work against.

However,  almost any speaker will do, and only after using one that works exceptionally well in this application , would you even know there could be a difference.

The taper is referring to the hole in my bench that the sound comes out of. For years I just had a box with a speaker in it, a thin piece of plywood with a 2.5" hole in it ,screwed on top, it worked great. When I mounted a speaker under my bench, it didn't work well at all, at tremendous volume it would barely illicit a response from the plate. The bench is almost 2" thick. After awhile of futzin with it, I decided that the air was damping itself and causing havoc in the 2" tube I had created. So I tapered the underside of my bench at more than 45 degrees into the hole, leaving just enough at the bench top for a snap ring to hold a piece of linen the keep debris out of the speaker. Suddenly it worked fantastic. The table top is flat, I carved out from underneath to get rid of my tube.

I have seen so many try to use some giant hole for the speaker, and I've tried to use their stuff, it gets crazy nasty, even with experience it barely works good enough to be useful,,,the smaller the better. If both sides of a node line receive energy it will try to cancel it all out.

Small directed and precise is what works well. You will enjoy a smaller hole for the speaker.

You said that you are using a speaker that would be used in a car stereo system. About what size (diameter) is it? If I am reading correctly the best option is to have a small diameter speaker and focus the sound further with a cone?  
 

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14 minutes ago, FiddleMkr said:

Do you have a cone above your 4” speaker to focus the sound to 2” diameter, or is the 4” a small enough focus of sound?

I just measured the spare it's only 3"! 10w, 8  ohms. Can't get much tighter than that.  Pic below.

 

I also have used the powered speaker box in the next pic as-is for chladni demos. That's about a 120 mm speaker with  a 30 w integrated amplifier. Solves all the problems. Just put a pile of books next to it if you need more support. It's horribly loud. 

JPEG_20231209_233102_6881856811859209738-1.jpg

JPEG_20231209_233451_2282910996427365189-2.jpg

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21 minutes ago, LCF said:

I just measured the spare it's only 3"! 10w, 8  ohms. Can't get much tighter than that. 

Looks exactly like a speaker I used.  This might shock some folks, but I actually made a plate testing table and messed around with glitter and mode shapes within the last year or so...  just to see if there was anything that might be of interest.

Although it's kinda fun to see the glitter dance around and form patterns, it's annoyingly lound, and I can't see anything that is meaningfully connected to producing a decent violin more useful than tracking wood properties, arching, grads, and weights.

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22 minutes ago, Don Noon said:

Although it's kinda fun to see the glitter dance around and form patterns, it's annoyingly lound, and I can't see anything that is meaningfully connected to producing a decent violin more useful than tracking wood properties, arching, grads, and weights.

I don’t doubt what you’re saying, and maybe it’s just coincidence, but when the plates are made to the specified weight, and thicknesses, arching, etc, their dominant natural frequency falls right in the middle of the violin’s range (1st position). That is the frequencies from an open D string to G.   
        Out of interest; have you tried to measure the natural frequency(s) of the plate(s) with them glued down around their edge(s)? 

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