What causes different feedback when chopping?

This is mostly a curiosity question, but what exactly causes different knives to feel different when they hit the cutting board. I understand that the grind and other factors affect the feedback while actually cutting product, but why do knives feel different when they hit something solid? For example, if I was fast chopping an onion or tapping the tip of my knife on my cutting board (a bad habit), some knives seem a little hollow and thud, some feel solid and hard, and some bounce and vibrate. I feel like this feedback affects my preference for knives a bit, but just curious if anyone knows.

Maybe you're talking about the different feelings of soft san mai clad/honyaki(diffhardened)/full hardened mono. Myself I prefer the feeling full hardened mono have on board. But as you say, grind and mass plays a large role as well.

RDalman said:

Maybe you're talking about the different feelings of soft san mai clad/honyaki(diffhardened)/full hardened mono. Myself I prefer the feeling full hardened mono have on board. But as you say, grind and mass plays a large role as well.

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+1 to all of these (except I am yet to try a honyaki).

I find heavier mass knives with large core steel and thin lamination have provided the most feedback. You can also get good feedback from medium weight hardened mono steel knives.

Also worth adding sharpness will differ between metal types, heat treatment and hardness. I find screaming sharp knives will create greater acceleration through foods and will increase the feedback from edge back through the blade and handle.

I guess more than any cladding or alloy, thickness behind the edge is the cause of a damped feeling.

How sharp the edge is
How thick or thin the blade is
The type of grind on the blade

All of this is very interesting. I think it'd be cool if a bunch of people (or maybe someone with a massive collection) tried to separate knives based on different properties and see what exactly cause different types of feedback. I have a few knives that feel very different. My thinned 270mm Heiji feels like a solid slab of steel, really thick and heavy. Very different from a Kono Fuji that I have that has a much thinner grind and feels softer (gentler?) somehow. My most recent purchase, a Denka, seems to have this weird vibration, yet feels very stiff, which was similar to a Mizuno carbon petty I had.

I think you would get a better idea by blind testing.

From a materials science point of view clad or mono shouldn't make much of a difference geometry will.

I tend to think a lot of it is confirmation bias.. it is meant to feel like that so it does. Hence blind testing

Like others have said everything effects feedback. Some of us are more sensitive to it then others.

IMO there are a four main features that stand out the most

CLADDING vs MONOSTEEL:
Because clad knives have two different metals pressed together that vibrate in two different frequencies and one is sandwiched between two layers, that means when one metal is trying to vibrate the other is keeping it in check and vice versa. So with san mai there's a lot less vibration from the blade to your palm compared to a monosteel.

TANG TYPE:
Full tang means that you are actually holding in your palm the same metal that the blade is made of. So ass you cut and the metal vibrates (=feedback) you will feel it from your fingers thru your palm to the back of your palm. The more you have of the same metal that the blade is made of pressing in your palm the more feedback it vibrates given it's the same metal. If the tang and/or the handle is a different metal welded to the blade it will again vibrate at a different frequency and less feedback is coming thru. With a hidden tang the softer wood that wraps around the tang will dampen the vibration and mute the feedback. Also the softer the wood, the more muted feedback you will be.

HARDNES:
With a monosteel blade the harder the steel the more it vibrates and feels more alive. Softer steel will absorb the shocks and vibration more and so should provide less feedback.

FINISH:
Different finishes on the blade feels very different. The higher the polish is, the less feel you get. Personally I can't stand sand blasted or similar style finishes because they feel grainy and they feel like they ad friction. Even though it should ad food release properties too, but still it just has a wrong kind of feeling to me. So far a nice kasumi finish seems to work best for me. It feels slick with some feedback too.

These IMO are the major factors in the equation.
...but grind, thickness of the blade, thinness behind the edge, weight, handle material, sharpness etc. all bring their own little flavour to the mix.

malexthekid said:

From a materials science point of view clad or mono shouldn't make much of a difference geometry will.

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lus1:

Yeah, I did forget to mention geometry. I definitely agree with the geometry part of that statement. It certainly makes a big difference in feedback, but I would disagree with the the first part of the statement.

With two identical knives, with the only difference being one is clad and the other monosteel, the mono steel will always provide noticeably more feedback of the two. The laws of physics state that two different materials pressed against each other (core steel and cladding) will restrict either material from vibrating at their peak resonance frequency as the materials are holding each other down. as the core is trying to vibrate at it's resonance frequency the cladding doesn't vibrate at the same frequency and so is holding the core from vibrating and vice versa.

Any piece made of single material is free to vibrate at it's resonance frequency without restriction and in this case the monosteel knife can carry that as feedback thru the material in to your hand.

Make sense?

No it doesn't... reread my statement. From a materials science point of view there is no difference. Clad or not they are a single piece of steel. Hardening has minimal effect on your spring constants or youngs modulus. And if it did there would be bigger issues with differential displacement etc.

Hence why i said a blind review would be interesting.

JaVa said:

Make sense?

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Makes a lot of sense. However, it also begs the question: What about a monosteel blade that has been dif. HT with a very soft back and a very hard bevel. Would it still retain it's "toning fork" qualities or would the abrupt change in the fabric of the steel running lengthwise from heel to tip change the behaviour?

Not sure whether the same steel with different hardness -- indentation hardness -- behaves different in that respect.

tsuriru said:

...would the abrupt change in the fabric of the steel running lengthwise from heel to tip change the behaviour?

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There would not be a noticeable change in its "toning fork" qualities unless you hit it hard enough that the metal permanently yields.

In lay-mans terms: You'll end up bending or denting the blade if you hit hard enough to feel/hear the difference in resonance between soft and hard. The soft steel is easier to dent/bend, and of course you can push the harder steel further... but you won't be pushing the limits of soft steel in a well designed knife!

Sakon AS Nakiri, edge rings like a bell... Takamura R2, feedback as if you were cutting live wires.... both clad kives...

I have often wondered if knives, any kind of knives, could be analized in terms of resonance, but I lack the training or knowledge to even conceive such a set up, much less make sense of the results. Still, it is intriguing.

After thought: Perhaps the way to go would actually be to use the knife as a toning fork lined up with helmholtz resonator hooked up to a microphone and into an oscilloscope, but what would this yield? - no idea.

tsuriru said:

Makes a lot of sense. However, it also begs the question: What about a monosteel blade that has been dif. HT with a very soft back and a very hard bevel. Would it still retain it's "toning fork" qualities or would the abrupt change in the fabric of the steel running lengthwise from heel to tip change the behaviour?

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It will have some effect, but probably not enough to be significant. The harder part will carry the resonances easier thru the material, but it's still the same material. The softer and harder parts will have slightly different peak resonance frequencies due to the difference in hardness, but only a little so those resonances still overlaps enough to carry the information forward. So you prob loose some feeling, but not much. Unless the soft part is wildly softer, then it should start to make some difference as their resonance frequencies start move away from each other more.

@tsuriru much more interesting to get a sweep, or an step response

Measuring the speed of sound inside the steel (by phase delay) could be interesting too: If there is even a minute influence of temper or alloying content, this would make for easy quality control

Take an octave of worth of different length blades, in oscillator configurations, and wire up a keyboard...

LifeByA1000Cuts said:

Sakon AS Nakiri, edge rings like a bell... Takamura R2, feedback as if you were cutting live wires.... both clad kives...

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Sure, That's not in anyway impossible. Not all clad knives feel dead. There's a lot of variables that can affect that. Even if two materials are different and so will have different resonance frequencies there can be some overlapping where those frequencies reach each other and those vibrations can be carried thru the blade.

All materials have their natural peak frequency, which is the point where that material "wants" to vibrate. Let's say that's at 2 kHz. That's where it vibrates the easiest and the most. But it will actually have derivatives (new peaks) at certain intervals to both directions in it's frequency response. The further away from it's natural resonance frequency those peaks appear the less there will be vibrations and the more force is needed to make those derivative vibrations.

What mostly affects those characteristics are weight, density, hardness and thickness.

The core steel and the clad steel usually differ in all those characteristics, which should mean a higher dampening effect, but sometimes that equates to two sheets of metal with very similar resonance frequencies. That means some of those peaks just happen to hit the same spots and that means the knife would have a more monosteel like feedback.

That's very easy to test. It's the old "is it a forged knife" test. Flick the blade face with a finger nail. The clearer the sound the more feed back that knife could be able to provide. All my clad knives have a very dead thud except one. That's the Tanaka ginsan migaki. It just happens to have a clad steel and core steel that share some of those overlapping resonance peaks which makes it "ring like a bell" when cutting.

Here's the fun part. That means that probably no two clad knives from the same maker and line will have exactly the same feedback. Since they're hand made that means all those earlier mentioned characteristics will change with every piece. So I'm guessing there's prob someone out there with a Tanaka ginsan migaki gyuto wondering why his knife feels dead and I'm here cheering how great the feedback is on mine.

I haven't tried the finger flick test with my Takamura R2 and it's at work atm so I can't do it until tomorrow, but I'd say it's feedback when cutting is mediocre at best.

The sound of a ringing blade is cool and all, but seriously its a bit silly to see it as a sign of quality.

I mean, if you're gonna test for sound you'd better take the handle off your knife first so it doesn't deaden the vibrations. Then you'd better dangle the blade by a string or something... :razz:
I don't have a Global knife on hand, but I bet their one piece construction plays a nice tune!

LifeByA1000Cuts said:

Sakon AS Nakiri, edge rings like a bell... Takamura R2, feedback as if you were cutting live wires.... both clad kives...

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These two knives? If you were holding them by the handle while you did the test I bet the width of the emoto/neck is the main reason they sounded so different. The one on the Sakon looks very thin in comparison to the Tak.
If you hold them both in a pinch grip and repeat the test, I bet they'll both sound like crap haha! :biggrin:

JaVa may i ask what is your background? Because unless you have a much higher understanding of materials than i do (which is reasonable but far from extensive, so I'm not being a d!!k i just really want to know more on this and from my reading and engineering materials knowledge this doesn't compute so trying to ascertain the trustworthiness of information) i think you are spreading misinformation.

The properties of steels that relate to natural frequency are going to be almost identical across the types meaning a monosteel or clad have effective the same point natural frequencies and same reaction. As far as I am aware hardness does not affect anything pre-yield point aka they react identically in the elastic range we are working in.

Happy to be wrong here but from the reading i have done there should be no difference in how the blade feels from use. Hence I maintain I would love to see a blind test done to see if this is more psychological than material performance.

My back ground?
Sure, no probs.

I used to be a serious hifi enthusiast since I was fifteen years old. That led me to work for a few different home and car audio companies in Finland for ten years From (25 - 35 years old). I've designed home speakers, car speakers and car amplifiers for hifi brands. I've designed and built speaker cabinets and subwoofers. I've been a part of European and World champion competition car sound quality team. I've also competed regionally in car spl competitions. I've designed and built several sound quality competition cars.

During that ten years I've had training by the likes of Focal, Alpine, DLS and Onkyo Which are just some of the companies I worked for or with. All that time I've studied frequency response, vibrations, How to control vibrations and dampen them, how different materials react to vibrations and how those resonances travel thru different materials and how sound waves travel in different circumstances.

Here is just one example of a case where this principal was used.
One subwoofer we designed for car audio company we used pressed cellulose as the cone. It was a heavy duty subwoofer that could move a lot of air. The problem is while the cone moves back and forth with great force the cone starts to resonate and develop unwanted distortion in the frequency response. The pressed cellulose is a very tough and irregular material that is VERY "dead" so those unwanted resonances can't appear. The client wanted the speaker to look more high end and demanded a metal cone.

The metal cone is not the best material since it very easily develops those extra resonances. Our cure for that was pressing two metals together. That made the cone much more stable for the reasons I mentioned in the earlier posts. In our measurements this approach provided almost as good results as the "paper" cone and the client was happy.

Sure I'm talking about sound pressure and sound waves, but it doesn't matter if the impact to the material that causes those resonances is made by sound pressure or a touch, the same basic laws of physics apply.

Some very interesting notions here. Some of the science is way over my head certainly the mathematical basis is over my head. Also, Im also trying to look at this from a practical point of view. I think, in a way, some of the discussions here remind me of what musicians sound like when they are discussing instruments. Especially bowed strings like violins or cello or violas. I always found it amazing that violin makers did not make bows - just violins - and that bow makers where a different art altogether. And it was also amazing to listen to musicians discussing their bows as a completely different topic than their instruments. Do violin players judge their bows the same way knife users judge their knives?

Now bear in mind that these conversations did not include any scientific proof or method - but there was a lot of common experience and intuition and a vague sense of unity regarding certain desirable and undesirable traits. Is there a point? - Of course there is:

Short of compiling a lexicon that defines each and every "type" of feedback from a knife, there is no common language here, and one must fall back on science - or statistics - or both. And even science cannot provide all the answers where individual experience and intuition is concerned, and statistics can be used to manipulate the truth. I think there is too much emphasis on Clad Vs. Mono steel to begin with, and even if this emphasis was really warranted, I think there are not enough realistic parameters or a valid (read minimal) sample to allow for any statistical extrapolation. So we are stuck. And its very hard to go back to the basics since there are still a lot of unknowns here besides the knife:

1) What is the cutting surface?

2) is it wood? If so is it dry or wet? and does that even affect "feedback"?

3) Is one person as sensitive as the next? or do some of us have a higher sensitivity to this so called "feedback"?

4) What are the desirable (and also undesirable) traits one would look for in "feedback"?

5) Can a known state of "feedback" be reproduced over and over again using the same geometry on different materials?


.... And quiet possibly a number of other questions that I didnt even think about.

I'm out of my depth here, but this is way too interesting to pass up.

JaVa said:

What mostly affects (resonance) characteristics are weight, density, hardness and thickness.

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Shouldn't this be stiffness/rigidity instead of hardness?
What I'm trying to be sure of here is the distinction between the properties of a constituent material (e.g hardness), and the properties that also depend on the shape of a structure (stiffness/rigidity).



Here's some references for what I mean:
http://www.audioxpress.com/article/Plastic-Speaker-Cone-History
http://www.nutshellhifi.com/library/speaker-design2.html



This kinda stuff is fascinating to me. I have half a mind to go out and take two pieces of steel with different material properties and grind them to identical dimensions just for testing this out with a drumstick... only I don't want to waste my knife-making steel. Shits expensive yo!

Sorry if this is too off topic.

Problem is you wont find two pieces of steel with different material properties. In terms of the material properties that effect stiffness for most types of steel, especially those that are used for knives, are basically identical and hardening doesn't effect them, pre-yield.

Thats exactly what I mean. I should be able to differ their hardness and keep their sound the same - hardness being the material property that changes without effecting the resonance (as the elasticity remains constaint).

JaVa said:

Our cure for that was pressing two metals together. That made the cone much more stable for the reasons I mentioned in the earlier posts. In our measurements this approach provided almost as good results as the "paper" cone and the client was happy.

Sure I'm talking about sound pressure and sound waves, but it doesn't matter if the impact to the material that causes those resonances is made by sound pressure or a touch, the same basic laws of physics apply.

Click to expand...

This is really interesting. Were the two different materials made of the same metal or were they different metals like steel and aluminum? I wonder if hardening changes the natural frequencies of the steel any or if maybe the hardness of the material affects anything. Does a higher rockwell hardness relate to a noticeable change in stiffness of the steel or is this more a property of the thickness/construction of the blade? Would a blade that uses nickel liner between the core steel and the cladding in a sanmai blade have any noticeable effect on feeling the way binding two metals together affect the subwoofer? I have a biology background, so material science is quite a bit out of my depth and I don't really know what I'm talking about here.

Oh man, what did I get myself into? :IMOK:

One thing I really want to address first is something that is really surprising to me in all this discussion. The thoughts that hardness/softness would have no effect to the resonance frequency if the metal is the same? That claim really is puzzling to me as hardness is one of the biggest attributes that effect the frequency.

softer = lower frequency response
harder = higher frequency response

also
softer = higher dampening factor
harder = lower dampening factor

dampening factor = materials ability to carry those vibration forward (or not to carry forward).

So a softer metal will have lower frequency response and on top of that it's ability carry those vibrations forward are much worse due to it's higher dampening factor. This is the most basic fundamentals of frequency response.

Kippington said:

I'm out of my depth here, but this is way too interesting to pass up.



Shouldn't this be stiffness/rigidity instead of hardness?
What I'm trying to be sure of here is the distinction between the properties of a constituent material (e.g hardness), and the properties that also depend on the shape of a structure (stiffness/rigidity).

Here's some references for what I mean:
http://www.audioxpress.com/article/Plastic-Speaker-Cone-History
http://www.nutshellhifi.com/library/speaker-design2.html

This kinda stuff is fascinating to me. I have half a mind to go out and take two pieces of steel with different material properties and grind them to identical dimensions just for testing this out with a drumstick... only I don't want to waste my knife-making steel. Shits expensive yo!

Sorry if this is too off topic.

Click to expand...

Good catch! :thumbsup:

I completely spaced on stiffness/rigidity earlier and I definitely should have mentioned it as it is another major factor. Although in it's own right, not instead of hardness. And yes, shape too is just as important as it has a direct effect on rigidity.

Very good and informative links you found.

JaVa said:

Oh man, what did I get myself into? :IMOK:

One thing I really want to address first is something that is really surprising to me in all this discussion. The thoughts that hardness/softness would have no effect to the resonance frequency if the metal is the same? That claim really is puzzling to me as hardness is one of the biggest attributes that effect the frequency.

softer = lower frequency response
harder = higher frequency response

also
softer = higher dampening factor
harder = lower dampening factor

dampening factor = materials ability to carry those vibration forward (or not to carry forward).

So a softer metal will have lower frequency response and on top of that it's ability carry those vibrations forward are much worse due to it's higher dampening factor. This is the most basic fundamentals of frequency response.

Click to expand...

I think you are confusing terms of and hard and soft)

Yes in general terms you are right but hardness is not a measure of softness/hardness as you discuss it, the better term for that would be malleablity.

Again I will repeat hardness does not affect steels material properties which relate to stiffness.

Stiffness (EI) is determined by two key things firstly geometry (second moment of inertia, I) and secondly a materials properties (such as young's modulus, E).

Natural frequency is basically controlled by mass, stiffness (EI) amd length? As well as some constants like pi to determine what mode of frequency you are looking at.

In your cone example you altered the frequency by essentially adjusting tje length. The two cones still retain the same stiffness but by inserting into each other they are now interacting together and sharing load (as in the cone can't freely oscillate without engaging the other cone therefore altering your frequency of the system).

In a san mai blade the metal is forged into a single piece of steel which will have the same stiffness, and therefore natural frequency as a monosteel blade of identical dimensions. Your weight is basically identical (assuming identical handles).


http://imechanica.org/node/2285