Brace height sound variation

Cereleste

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Every year or two I decide to tune my brace height and go through the whole shoot/listen/add a few twists/repeat scenario. Occasionally some high or low value causes a bit of a rattle, but other than that I've never really noticed a difference in sound as I go through the full range in increments of a few mm. Every tuning guide, video, and forum post makes it sound like there's one (or two) obvious sweet spots where everything is noticeably quieter, but embarassingly I've never noticed this. Could be my ears (I do play the viola, after all), or that the time to change from one brace height to the next is enough for me to forget the sound of the previous setting when comparing it to the new one, or that I've somehow got the one bow immune to string length. So I've generally then picked a nice looking number and gotten on with other things. I'm happy with my grouping and the sound of my bow, and wouldn't necessarily choose the quietest brace height if i could find it anyway. Setup is a standard olympic recurve with lightweight arrows that are bareshaft tuned. Only anomaly would be that it's a fiberbow riser with no extender.

Still, it's an itch that needs to be scratched, so this time I used a much wider range (20.5-25 cm for 68" bow) and started with a 5 twist increment (2mm at a time at 20.5, 6mm at 25), recorded each shot from a constant distance ( after an initial shot to settle the limbs), and edited out the clicker and target noises. So I can now listen to several brace heights side by side. I've linked to the audio from one test here. My ears are none the wiser however, and when I graph the shot noise (amplitude adjusted for frequency-dependent perceived loudness) I just get a slight decrease as brace height increases, which is expected due to the change in stored energy. I've repeated the test with a finer increment and more shots and different tiller settings but get very similar results. In contrast, when I shot a 605gr arrow instead of my regular 280gr ACE, I can clearly hear how quiet the heavy arrow is both while I'm shooting and in the recording, and the average calculated noise is about a third less. Similarly, I can hear the difference when I grip the bow or pluck the release.

Does you have a clear audible quietest point in brace height? If so, how wide is this minimum and how much quieter does it seem to be relative to neighbouring settings? I haven't found any other audio or videos online showing different brace heights on the same setup and it would be interesting to see how audible the effect can be.
 

Timid Toad

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I do, and it's very noticeable, but mostly through eliminating contact with the bow. Outside of this, as I shoot super recurves, they do have a very definite sweet spot connected to spine, mass and archer. Get it wrong and they sound like a gun going off. Get it right and it's very nice both in sound and feel. I too can hear a plucked loose etc.
 

Kerf

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I do, and it's very noticeable, but mostly through eliminating contact with the bow. Outside of this, as I shoot super recurves, they do have a very definite sweet spot connected to spine, mass and archer. Get it wrong and they sound like a gun going off. Get it right and it's very nice both in sound and feel. I too can hear a plucked loose etc.
Me too.
 

Rik

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I've never been able to hear it, apart from (as TT says) eliminating contact. Might just be too much other noise (nock separation for example).
 

dvd8n

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I can tell, but with my bow it's really subtle. Not sure if it's the sound difference that's subtle or just that my bow's a little noisy.
 

Cereleste

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I do, and it's very noticeable, but mostly through eliminating contact with the bow. Outside of this, as I shoot super recurves, they do have a very definite sweet spot connected to spine, mass and archer. Get it wrong and they sound like a gun going off. Get it right and it's very nice both in sound and feel. I too can hear a plucked loose etc.
In general, how far away from the sweet spot can you go before it sounds like a gun? Is the sweet spot independent of the overall trend of less sound as limb contact decreases, and is it quieter than just using the value with the minimum amount of limb contact tolerated by the manufacturer? I've attached a couple hypothetical graphs of perceived loudness vs brace height - which would you say your observations are closest to?
 

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Stretch

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Not much. There is a sweet spot just above 9 1/8” - anywhere between 9” and 9.25” is pretty good (72” bow). Above or below those ranges and there is a little extra vibration and a little more noise. But it is subtle. No gunshot.

Only bow I ever shot that sounded like a gun was a Browining Olympian with the original Samick made limbs (I should disclose that it was a 68” bow 32”) - one shot was enough then it was time for new undies and a trip to the dentist. No brace height made it quieter (which was the problem the owner was having).

I have had bows that were much more obvious, in particular a Hoyt Axis with FX limbs. Very noisy below 8 7/8” and very clunky over 9.25”. (70” bow)

I also had some Samick Extreme limbs that were pretty quiet at 9” and then 1/16” either way made it get ugly quickly in a number or risers.

So currently your bow 1 plot with less of a trough is about right for me.

Thing that makes the biggest difference to my current bow is strand count. I usually shoot 20 st Angel Majesty/777 his bow is much quieter with 18 strand. (Which means I have a lot of x10 Beiter #2 nocks that are as much use as a chocolate teapot). But the 18 str is a lot quieter with much less vibration.

It’s been a while since I tried it with anything else but with FF Plus there was a quiet spot much higher, near 9 3/4”, but the bow felt dead and dull. 8125 just felt OK across the range but never particularly good.

So I think it is very riser, limb, string, arrow specific.

Stretch
 

Kernowlad

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I feel like I’ve strolled into a nuclear physics lecture.
I shall quietly leave and ping some sucker arrows from our Decathlon bow...
 
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olis

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Having a strange tiller can make the bracing height hyper-sensitive. So it might be worth playing with that too.
 

KidCurry

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Although, shooting barebow I live with a noisy bow, I have found the cheaper limbs are not as noisy as performance limbs. If shooting them normally my Synergy Air limbs are very tolerant of bracing height. My Winex limbs not so much, but the noisiest are my Xtour limbs if they go too far from an ideal brace height. The Synergy limbs are also tolerant of string walking where as the xtour limbs don't like it at all. Infact the synergy air limbs are so tolerant of string walking I'm thinking of using them for indoors instead of my Winex.
 

Cereleste

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Having a strange tiller can make the bracing height hyper-sensitive. So it might be worth playing with that too.
Any particular tillers where it may be more sensitive?
I've repeated the 0 tiller (my normal setting) test with 2mm changes in brace height for tillers of +6mm and -4mm and am partway through +3mm. Taking a while as I need my partner to be out of the flat getting groceries to get a long enough distance for the bow and target noise to be separated. -4 gives a very straight diagonal line as higher brace heights get quieter, +6 increases very slightly from 20.5-22.2cm then decreases. Tiller 0 (repeated with a finer increment than the test in the audio) has a slight decrease until 21.8 after which it decreases more rapidly. My plan is to eventually have a surface plot of loudness at varying tiller and brace heights that I can visualize in 3d.
 

olis

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Any particular tillers where it may be more sensitive?
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.
 

Whitehart

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I would suggest set the bow up(for established archers you will have a good idea where to start with tiller nocking point height arrow selection) and get it shooting with no limb flutter, this is just noise and a reduction in the bow efficiency. From then on concentrate on your arrow group size (this is where you gain points) changing the BH by one or two twists at a time and plotting how your groups get bigger or smaller.
 

Timid Toad

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In general, how far away from the sweet spot can you go before it sounds like a gun? Is the sweet spot independent of the overall trend of less sound as limb contact decreases, and is it quieter than just using the value with the minimum amount of limb contact tolerated by the manufacturer? I've attached a couple hypothetical graphs of perceived loudness vs brace height - which would you say your observations are closest to?
My findings, I think are not generic. In my case, with a super recurve, I'm using low brace heights and the second button hole. So I think I'd have difficulty giving a fair comparison to you.
Each set of arrows I have are quiet at different brace. Some will give me a few millimetres either side. Some not that.
Generally speaking, the heavier the arrow the quieter the shot, regardless of tune - that much is a no brainer - noise is wasted energy not getting behind the arrow. More massive arrows are taking more energy with them. And the reverse is also true. Don't expect stupidly light arrows to be quiet.
Very noisy bows can be the result of wrong spine. Some people say too weak. But my experience suggests that too stiff can also cause heavy back end contact with the bow and that is very loud but can still group well out to say 50m. So if someone is complaining about breaking rest arms or damaging fletchings along with a noisy bow, look at spine.

As an aside, I've also found twisted risers make for noisier bows (and hard to cure) and people like me who torque strings (ie pull the ring finger away from the face so the string dog-legs) have noisier bows and people who torque their risers have noisier bows.
 

Cereleste

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My findings, I think are not generic. In my case, with a super recurve, I'm using low brace heights and the second button hole. So I think I'd have difficulty giving a fair comparison to you.
Each set of arrows I have are quiet at different brace. Some will give me a few millimetres either side. Some not that.
Generally speaking, the heavier the arrow the quieter the shot, regardless of tune - that much is a no brainer - noise is wasted energy not getting behind the arrow. More massive arrows are taking more energy with them. And the reverse is also true. Don't expect stupidly light arrows to be quiet.
Very noisy bows can be the result of wrong spine. Some people say too weak. But my experience suggests that too stiff can also cause heavy back end contact with the bow and that is very loud but can still group well out to say 50m. So if someone is complaining about breaking rest arms or damaging fletchings along with a noisy bow, look at spine.

As an aside, I've also found twisted risers make for noisier bows (and hard to cure) and people like me who torque strings (ie pull the ring finger away from the face so the string dog-legs) have noisier bows and people who torque their risers have noisier bows.
It's the width and depth of the sweet spot that I'm interested in; I wouldn't expect any comparability between bows. But knowing that in at least some cases with your super recurve, the width of the sweet spot is maybe only 2mm at the minimum, and the depth is quite deep (normal to gunshot), is quite valuable. It means that there's the possibility of missing a minimum in noise when the increment is 2-3mm. I'll print out a finer scale for my bowsquare and see if a 0.5mm increment shows anything new.
 

Timid Toad

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I definitely adjust my brace height to within 1mm. If it's that much out the bow may be noisier and groups are definitely poorer.
 

Cereleste

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I would suggest set the bow up(for established archers you will have a good idea where to start with tiller nocking point height arrow selection) and get it shooting with no limb flutter, this is just noise and a reduction in the bow efficiency. From then on concentrate on your arrow group size (this is where you gain points) changing the BH by one or two twists at a time and plotting how your groups get bigger or smaller.
I'm not currently looking for an optimal position, just understanding how it varies. Sometime later I will try to analyse group size outdoors for a few loud and quiet combinations of brace height and tiller to see if there's a noticeable difference at my level. But with only 291+-15 average last summer at 70m, and up to a 20 point difference between two halves of a 720 in similar weather, I estimate it would take at least 9 dozen arrows per brace height (divided between 3 sessions and alternating with my normal setup) to get any statistically significant results about group size. As some Korean coach said, "shoot 1300 then tune" - better focus and consistency, not fiddling with equipment are what'll get me those 33 points.

Does limb flutter matter besides its contribution to bow noise and how long the sound lasts? I already have those in my graph (both maximum loudness and the rate at which it decays affect the root mean square (A weighted) value over the first 50ms).
 
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