Brace height sound variation

Cereleste

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The short answer is I don't know. People talk about tiller/brace height being 'personal to your particular set up' i.e. that includes how you shoot.
The comment was more aimed at the people who have a very distinct 'best brace height' as a polite way of saying that you might want to look at your tiller choice.
I think the 3D plot is really interesting! Has it been done before?
You could use it to choose some different bow settings and then see if you get better groups. When you can shoot again of course.
3D plot - no, not that I've seen and I think I've turned over every stone. The closest is here, where someone used noise sensors mounted on the bow and measured noise duration at a smaller range of brace heights in 2mm increments and picked a value, then did the same thing with a bunch of tiller values at one brace height and picked a value, then repeated the process with brace height at the new tiller value. Unfortunately, even with 10 shots at each setting the data is so noisy that a large number of the brace height and tiller values could be chosen as the "minimum", and there must have been changes in experimental setup between the graphs as the noise for the loudest shot at the "ideal" brace height is less than the noise for the quietest shot in the second graph despite brace and tiller being identical to the first.
My plan is to pick a few points of interest in the 3d plot (any local minima and maxima in noise) and see if the grouping is different. Unfortunately it takes me a lot of arrows to notice a difference, unless the difference is at the level of group size changing to meters or mm.
 

Timid Toad

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Limb flutter is important to your shot efficiency, and if you have flutter you have vertical nock travel, which cannot be desirable.
 

Stretch

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I think limb flutter can come from different causes and you need to understand the cause. If there is a out of sync see-saw flutter between top and bottom then there is likely a tiller/ nockpoint issue (in the context of your form).

If the limbs are sync’d then most of the time it doesn’t affect how the bow shoots. And frequently neither does noise. What different does it make if you have a little energy lost in the flutter or you increase brace height, shorten the power stroke, lose the flutter but with less energy? Performance wise it is not measurable! (Unless you are really bored and have a chrono and a very accurate gauge). But you get limb designs and riser designs that can screw up that thinking.

Personally I like my bow to feel quiet, smooth and with minimal post shot vibration. I shoot better when my bow feels this way. It’s not the performance of the bow. It’s the performance of the idiot pulling it ;)

Stretch
 

Whitehart

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Limb flutter means the bow is not set up correctly nocking point tiller even limbs wound in to far possibly poor limb tip alignment Like noise it is wasted energy not transferred to the arrow.
 

Whitehart

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Would someone like to define limb flutter please. I think it is being used to describe different things. :geek:

Stretch
For me it after the arrow has left the string the limb tips wobble or flap around rather than recover quickly.
 

Cereleste

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Limb flutter - couldn't see any at 240fps in my bow at 0 tiller here, so I decided to see what it took to force it to happen. The main vibration of limbs (back and forth in sync) happens at about 110Hz with my setup, so I tried varying the tiller to see if that caused any prolonged flapping, which would be audible as the main limb vibration continuing at a higher amplitude for longer instead of disappearing quickly. I've attached the results from 10 tiller settings at one brace height - other than the setting of the limbs on the first shot at the more positive settings, there's no change in noise. So I put a 5lb weaker limb on one side and took another video, this time with a tiller of 28mm - is this what you mean by fluttering?
Either way, it seems like I have to go a long way out of any reasonable range of tiller value before extra movement sets in.
After Timid Toad and Stretch 's descriptions of the width of the sweet spot, I went back to 0 tiller and added 1 twist every 3 arrows. I've attached a graph showing how the sound level (average in colour, individual points in gray) changes with a much finer brace height. The three curves are just offset for visibility; they're equally loud around 21 cm. The difference in loudness from the lowest to highest brace height is definitely audible (from a sharp thwack to more of a thwack-hum), though it's still pretty linear. There are a few points that might be seen as local minima, but nothing that's above the level of random fluctuations. Though at least now I know that if there were a very narrow sweet spot, I should have found it.
 

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KidCurry

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Nice results. You can't beat properly acquired data.
When I bought new limbs some time back I couldn't wait for my new 8125 spool to arrive so I bought a really cheap string. It had a similar elasticity of a post office rubber band. I shot it for an hour or so but was amazed at how the limbs took so long to settle. You could turn the bow after the shot and watch the limbs settling it took so long. I went through the whole range of tiller from 1/2" to -1/2" with no effect. But it was quiet. I set it back to zero tiller. A week later I made a 8125 string. No vibration, limb settle was almost instant. It was louder. I also shot a 452x string material from my compound days. The result was instant, even harder and louder.
The cheap string allowed one type of limb flutter that I would say was synchronous; both limbs over reacting and returning at the same time.
The other type of limb flutter I have come across in my short BB experience is non synchronous flutter. This was where one limb finishes its travel and returns before the other. This was almost all corrected by tiller, but some is always present when string walking.
Once tiller was set, bracing height had no effect on limb flutter but it did get noisier from high to low bh. For the most part I think noise is from the string hitting the limb. More string around the recurve more noise. I did have a Bodnik slick stick. It was a hybrid with no recurve. It was virtually silent at 50lb. No recurve/ no limb slap.
 
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Stretch

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Firstly, yes, in my opinion flutter is when the top and bottom limb are out of sync. It would be symptomatic of poor tiller selection or issue with the limb design or construction. But I think I agree with what you are saying, most modern limbs just don’t seem to do this, choose the tiller you like and the limbs will deal with it. When you have some balanced after shot vibration I don’t consider that flutter but others do.

On the noise front, I admire your tenacity! Can I ask what limbs and riser you are using? I could imagine that something like a carbon riser or even heavily damped stabilisers *could* neutralise patterns.

There are also a lot of other factors that if wrong have a bigger impact on noise - so again could neutralise in a bad way. My Prodigy RX 27” riser is a bit twisted. As a 72” bow it was quiet (spooky quiet) with 44# woodcore Quattro limbs. But swap to 72” 39# Velos and it was noisy. The wood limb coped with the twist in the riser. The faster, lighter bamboo limb did not. To get it quieter I had to manipulate the limb to an extraordinary level with it’s the multi axis adjustment. However, the thing that made the biggest difference was dropping from 20 strand to 18 strand. (Angel Majesty... which was the quietest/nicest when noisy). Now that is the opposite of what you’d expect, so there could be a frequency issue going on there too.

So it’s kind of a 4D (or more) puzzle and when you work in 2D the 2D you’re not looking at can be more influential and cause you to not see what you think you should see.

So just chuck it together and shoot (haha :ROFLMAO:)

Stretch
 

Kerf

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However, the thing that made the biggest difference was dropping from 20 strand to 18 strand. (Angel Majesty... which was the quietest/nicest when noisy).
Funny you should say that about Angel. I’ve been playing with my bow using different strings. Out of 8125g, a FF+ double loop Flemish twist, a FF+ endless and an Angel Majesty 777 (all 18 strand) the Angel gave me the quietest rig.
 

Stretch

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I’ve been using Majesty since it came out. I didn’t see any benefit in Majesty Pro, similar results with a slightly weaker tune. 777 is amazing on my bows. Quieter but still with the really tight feel of original Majesty. (I know, what the F*** does tight mean... go with it, it’s a feeling!) I periodically try other strings but always end up back on Majesty.

And the yellow 777 is the dogs doo-dahs o_O

Stretch
 

Cereleste

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Limbs are 40lbs samick extreme, wound down to 41.2 lbs on the fingers. Second hand so don't know their full history.
Riser is a fiberbow 6.3, bought new in 2012. Has the old style eccentric tiller bolts. I removed all but one of the logos when I redid the chipped varnish.
Stabilization is nothing fancy though maybe a bit heavy - HMC+ long rod and cartel triple sides, but about 250g weight on the sides and 270g in front, plus 3/4in mini dampers.
I've read that the Extreme limbs were known for being loud, and the fiberbows are meant to be quiet, not sure which would dominate there. It's possible the system is too heavily damped, and might be more sensitive to brace/tiller if less stable.
Stringwise, I've always used dynaflight97 (a spool lasts forever and it's my colour) but have a FF+ and a dacron lying around somewhere. Might fiddle around with strings and less stabilization and see if I can get a (not necessarily competitive) setup to show a clear minimum - it's a bit of a white whale.
I suppose with a rubber band string, the bow vibration mostly stays in the string, which can vibrate a lot without producing much sound, while a perfectly stiff string transfers all that energy to the rest of the bow. So I'd expect a stiffer string to be more sensitive to brace height etc.
 

olis

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I've attached a graph showing how the sound level (average in colour, individual points in gray) changes with a much finer brace height. The three curves are just offset for visibility; they're equally loud around 21 cm. The difference in loudness from the lowest to highest brace height is definitely audible (from a sharp thwack to more of a thwack-hum), though it's still pretty linear. There are a few points that might be seen as local minima, but nothing that's above the level of random fluctuations. Though at least now I know that if there were a very narrow sweet spot, I should have found it.
Full marks for effort! The specific best brace height clearly doesn't apply to your set up
Maybe the differences in people's experience is what they mean by loudness. A harsh sound with lots of discordance would seem 'loud' compared to a pure note of equal volume. I suppose a happy sounding bow will generally shoot better than an unhappy one, and be nicer to shoot. Also, surely all this noise happens after the arrow has left the bow, so maybe much of the effect is actually on the archer and then (indirectly) on the arrow.
 

geoffretired

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I suppose a happy sounding bow will generally shoot better than an unhappy one, and be nicer to shoot. Also, surely all this noise happens after the arrow has left the bow, so maybe much of the effect is actually on the archer and then (indirectly) on the arrow.
For some time now, while reading this thread, I have been thinking the same thing. It's a bit like bow vibration and using dampers. The vibrations are there after the shot has gone; not before.
Then I had another thought???!! heehee. An archer's follow through also happens after the arrow has gone. But the shape of the follow through is really a more obvious " view" of how the shot was executed... warts and all... if relevant. Perhaps the bow's noises are really an amplification of something that we would rather didn't happen. I know that if my sight was loose and it rattled after the shot, I would tighten it.
What the bow string gets up to in the power stroke, is about moving the arrow. Most of that journey is too fast to see and just about silent. The noise at the end will represent something. Two( or more perhaps) suggestions have been made on this thread. Separation of nock from string and string slapping against the recurve of the limb(s).
Many recurve bows make a really nice sound at the end of the power stroke.... is that the sound of a well executed shot? Is it the sound of a bow that is performing really well?
 

Stretch

Active member
I shot a set of Samick Extremes in a Hoyt Helix, they were actually pretty quiet for me. I only let them go as they increased from 41# to 44# in the last inch (70” bow at 32”). Led to some very tight groups but a lot of fliers.

Strange but true, these were quietest with BCY452x. So a no stretch vectran blend. They also had a very obvious brace height sweet spot at 9” to 9 1/16”. They were easily as quiet as by G3s but less clunky on release.

I have never shot a Fibrebow but is the reputation for a soft shot feel? So that could suppress the behaviour and impact the effect of brace height etc on the overall system.

You also have the low mass between the limbs, I get that is why you have so much rod weight but the energy has to travel through the stabilisers to get to the mass. Have you ever tried stiffer rods? The HMC+ is a great rod but relatively quite soft. Not sure I have ever seen more than 5 or 6oz on one of these and most HMC+ fans (eg most of the Korean women over the past few years) tend to shoot them light. No idea about the Cartel sides but I’d also be curious to how they’d react with that much weight on them. Not saying it is - just that it could be a root cause.

Nearly 10oz is a lot on most rods :unsure:

Stretch
 

Cereleste

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I shot a set of Samick Extremes in a Hoyt Helix, they were actually pretty quiet for me. I only let them go as they increased from 41# to 44# in the last inch (70” bow at 32”). Led to some very tight groups but a lot of fliers.

Strange but true, these were quietest with BCY452x. So a no stretch vectran blend. They also had a very obvious brace height sweet spot at 9” to 9 1/16”. They were easily as quiet as by G3s but less clunky on release.

I have never shot a Fibrebow but is the reputation for a soft shot feel? So that could suppress the behaviour and impact the effect of brace height etc on the overall system.

You also have the low mass between the limbs, I get that is why you have so much rod weight but the energy has to travel through the stabilisers to get to the mass. Have you ever tried stiffer rods? The HMC+ is a great rod but relatively quite soft. Not sure I have ever seen more than 5 or 6oz on one of these and most HMC+ fans (eg most of the Korean women over the past few years) tend to shoot them light. No idea about the Cartel sides but I’d also be curious to how they’d react with that much weight on them. Not saying it is - just that it could be a root cause.

Nearly 10oz is a lot on most rods :unsure:

Stretch
That's fascinating about the string material - if you have some BCY452x or any other no-stretch materials lying around (either in string form or loose) I'll happily buy a few meters off you to see if it makes my setup more sensitive to brace height variation (and in general, whether it's louder or quieter). I tried the fastflight+ string (18 strands, unknown history) last night and the loudness was the same at both a high and low brace height as my regular dynaflight 97, which is not surprising as they're supposedly similar materials. the pitch was a bit higher on the FF+, perhaps because that string was also 14gr lighter.

I've heard the fibrebow described as vibration dampening, but also very responsive and sensitive to the other components used. Realised I couldn't give you a real answer on this so I compared it to my partner's SF premium (die-cast Al). If I hold each riser by a limb bolt and tap it, the fiberbow rings slightly while the Al riser gives a thud. When set up as barebow, this behaviour is reversed and the fiberbow gives a thud on release while the Al riser rings (about 220Hz) for seconds. With all the stabs and my heavy weights and dampers, both are quietened the same amount, but effect of adding stabilisation is much less than the difference between the risers. Subjectively, I would say the fiberbow feels both soft and non-resonant and the perceived energy going into the hand was much less.

The weights are just there for aiming stability (and perceived wind stability though that may be a placebo effect); I haven't tried to optimise for vibration. I've found I prefer the feel over the standard 30-60g per rod setup, and as I end up at the same total mass as a standard Korean women's bow, i'm not worried about injury. I can't hear or feel a post-shot difference between 60g or 250g on the ends. With the heavy end weight, it deflects by perhaps 0.5mm, and no signs of fatigue after 8 years. The cartel sides deflect far less as it's proportional to the cube of the length. Both rods could likely cope with far more weight than I could lift without any damage.

I haven't tried any stiffer rods, but intend to at some point for the sake of it. Though I am slightly dubious about the difference. Looking at the HMC+ rod here in slow motion, it wobbles about 3mm at the centre from the pressure wave. The stiffest rods still give around 1mm flex - their modulus is up to 2.5x higher than the HMC+, and the second moment of area is the same or less (smaller diameter and thicker). I don't notice my current rod flexing, so I don't see how I could notice the increased stiffness of a different rod, though I expect the better dampening technology would be noticeable.
 

Timid Toad

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I wouldn't recommend shooting any *x* string material off a recurve these days. Several manufacturers, including Hoyt (in a roundabout way), Border and Uukha advise against as their properties are not good for limbs. They were designed for compounds that are permanently strung, and whose limbs are short, thick, and wide, with a different construction, so take sudden stops much better. Yes, the material is a tiny bit faster, but much harder on the limbs and has been attributed to failures.
For a basic rod experiment. Take all your rods off and shoot with just you sight. It's an illuminating experience, not just from the noise point of view.
 
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