"Dead Spots"

[Pipedream Farm]

Yes, I'm a geek. After watching (and experiencing) poor listening and/or hearing on the "big field" around 2pm (and on several other fields) I wondered if there was any scientific studies on what we would call "dead spots". Sure enough there is lots of data on this. One area of special interest is the "natural selection" of animal vocalizations (especially tones) based upon habitat due to sound attenuation by the habitat ('sound

window' hypothesis of Morton). Generally, the speed of sound is attenutated by the ground, temperature, wind, and humidity. With localized changes in the speed of sound there is the possibiulity if constructive and destructive interference of these waves leading to "shadowing" (i.e. dead spots).

 

Tomographic Monitoring of Wind and Temperature at Different Heights Above the Ground

 

There are several meteorological effects that play roles in sound propagation. The most significant of these are atmospheric absorption, refraction, and scattering by atmospheric turbulence. Atmospheric absorption, due to the classical absorption and the molecular relaxation, causes a loss of energy, which depends mainly on frequency (the absorption increases with increasing frequency) as well as on the temperature and humidity. The refraction of sound waves occurs in the presence of sound-speed gradients. This causes a sound propagation at curved paths which leads to ray focussing or defocusing as well as shadow zones near the ground. Scattering of sound waves due to atmospheric turbulence causes fluctuations of the signal phase as well as the amplitude.

Tutorial on sound propagation outdoors

 

Concerns about noise in the community date back to the dawn of recorded history. Then, after centuries of relatively little activity, scientific interest grew during the 17th century and social concerns were again voiced during the 19th century. Many of the wave-propagation mechanisms relevant outdoors were understood at least qualitatively by the late 1800s. Today, knowledge of sound propagation phenomena is of great economic and social importance because of environmental and other concerns. Reality is more complicated than geometrical spreading above flat ground. Some grounds are acoustically hard like concrete, and others soft as snow. Corresponding reflection coefficients are complex and vary with angle. Grounds may not be flat, leading to shadow zones or alternatively multiple reflections at the ground. Gradients of wind or temperature refract waves either upwards (upwind or in a temperature lapse [decreasing temperature with height]) or downwards (downwind or in a temperature inversion [increasing temperature with height]). Atmospheric turbulence causes fluctuations in the acoustical effects. Many of these features mutually interact. Measured sound pressure levels owe as much to near-surface weather and to ground shape and impedance as to acoustical factors such as source and receiver heights and their separation. This tutorial paper emphasizes field measurements and simple physical interpretations.

Mark

[juliepoudrier]

Hey Mark,

Are you on the workingsheepdog list? They just had a discussion on this with respect to flat fields. Your post above would certainly add to the discussion. If you aren't a member, consider joining (it's a Yahoo group now) and posting. If you don't want to join and don't mind me forwarding the above to the list, I'd be happy to do so!

 

J.

[Pipedream Farm]

Julie,

 

what's the address?

 

Mark

[Pipedream Farm]

Julie,

 

nevermind, I figured it out. Untill I'm accepted you can cross post this to the workingsheepdog list. You can use my name.

 

Mark

[juliepoudrier]

Thanks Mark. I just cross posted. I hope it will generate more discussion as the original discussion got lost in a couple of other discussions on the finals and BBC.

 

J.

[Rebecca, Irena Farm]

OH! Is that where they went? Duh. Thanks Julie!

 

That is totally cool Mark. What about this- this bothers me all the time, since they had a discussion on sheepdog-l about it years ago:

 

How long does it take the sound of a whistle to reach a dog 800 yards away? It comes to about (I think) two and a half seconds. It's like one second for every 370 yards at 75 degrees F - slightly faster for colder air. That's a looooooooong time yet the dogs seem to respond almost instantly. I've marveled at this at the long-setout trials where I've been a spectator. I've even counted, thinking maybe it was just a perception problem. Nope, can't get to one-thousand-two, much less past it.

 

My math could be wrong. I am NOT a scientist. But I seem to remember a lot of science-types were bothered by this also during the discussion, so I'm not alone.

 

How do they do it?

[Pipedream Farm]

How long did it take for the sound to get to you? Did the sound travel directly from the source to you or did it bounce back to you?

 

Mark

[cgt]

I think your math is right, Rebecca.

 

I remember when I first started working at such distances and wondering why my dogs were always seeming to spend a moment or two thinking about my commands.

 

At 800 yards the dog is evidently not responding instantly. But if the dog is any good they are balancing on their own and it might *look* like they are responding appropriately. Although, if you listen to the whistles, many times they are not much more than constant steadying. Also, if the handler is any good, they are trying to "read the sheep" (as hard as that may be at 800 yards) and giving the needed instructions as early as possible. But I think, for the most part, it's all dog at those distances. Which is really great.

 

An amusing illusion I've noted many times when I've been setting sheep is that once the dog lifts the sheep and takes them down-field, you can watch the dog respond to the whistle before you even hear it (since the sound gets to the dog before it gets to you). That's always kind of unsettling.

 

charlie

[Firchow]

We had this discussion on another board after last year's finals. I tend to believe that "dead spots," while they may be physically possible, are more often what I would describe as "troublesome spots."

 

That is, frustrated dogs, tough sheep, frustrated handlers whistling, and the like.

 

In our previous conversation the esteemed Professor Torre submitted that:

 

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CGT said:

 

"In particular, I have one dog who seems to always find the dead spots and one who doesn't. How the heck does this happen? The dead spots seem to travel with this first dog from trial to trial and always appear right after the lift and generally continue until I've missed the fetch panels. Then the dog finally leaves the dead spot. Weird, eh? I'm not complaining though. Half the time the dog does better while in the dead spot than when it can hear and obey."

 

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Charlie is of the mind that dead spots travel with the dog, while I think they more often are affected by the sheep:

 

************************************

GF Said:

 

I suspect that dead spots do not travel with dogs at all, rather they travel with sheep.

 

I think tough range ewes have bigger, stronger travelling dead spots than dog-broke sheep and that the spots are magnified on long drives. I also suspect that the more sheep lean into dogs, the more effective they become.

 

I also think that the best dog/handler teams have an ability to render dead spots ineffective as they rarely seem to be affected.

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Anyway, while they may be physically possible, more often than not I think it's a euphemism for "I can't believe my dog wouldn't listen to me."

 

Glenn

[Pipedream Farm]

Glenn,

 

I have experienced a dead spot first hand at Hop Bottom. We were there at another time of the year playing tag. I was standing in the cross-drive line and could see Renee at the post yelling but I could hear nothing.

 

Generally, I tend to think that "dead spots" are often 1) places with huge pressure and many dogs don't want to listen or 2) places where the sounds are distorted or masked by more local sounds (i.e. sheep moving through tall grass). However, there are true "dead spots" in the sense that sounds from a distant point source are not audible at these locations and these locations come and go based upon local/temporal atmospheric conditions. Even more interesting the pitch of the sound can make a difference in how it penetrates these "dead spots" (based upon the studies I reviewed).

 

It is this belief and the common argument that you presented that caused me to search for scientific studies on this phenomenon.

 

Mark

[Rebecca, Irena Farm]

That's standing behind the handler - or directly beside the handler at a trainer, in some cases. Yes, I'm very bad to think about such things rather than the tast at hand.

 

That's wild, Charlie - I'd never thought about that one.

 

One thing I wondered about was, could the dog be reading the handler's body language. Impossible? I don't think so - I had a trainer demonstrate that he could get a dog to cheat over at 300 yards by simply shifting his weight and lifting a hand slightly.

 

Perhaps the dog can sense the handler's movements and takes some movement that usually precedes a whistle command as a sign that something needs correcting? Like I can say, "Cord" or even just "Eh-eh" and he'll get the sheep back online wihtout needing the series of commands needed to "show" him where the line is.

 

It's odd, I've seen so much evidence of how sensitive and responsive these dogs can be and yet I still can't resist yelling louder when I'm not getting the result I want. I'm trying very hard to change this but it's trying to undo ten years of bad habits.

[airbear]

Oh thank goodness that I'm not the only one plagued by the roaming dead spot. Mine shows up on the turn after the first drive panel, regardless of right or left drive. Hills, flats, sunny, rainy, plague of locusts ... there it be, a dead spot, that generally affects only my dog. I find the whole thing very mysterious.

 

Also am very glad that I have never had to stand on a bale at the post, as am sure would fall and cause most grievous harm to head.

[Pipedream Farm]

In one study, the researchers were examining why a cricket that lives in grass lands only mates in the cool of the day (morning or evening) and they found that their "singing" did not carry across the grass land once the day heated up.

 

In another study they looked at the pitch of bird songs used by birds in different habitats. Birds that lived in grass lands used a more restricted pitch range than birds that lived in marshes. The study reveled that sounds of a wider pitch range carried better and farther over the marsh than over the grasses.

 

Mark

[Rebecca, Irena Farm]

I've seen dead spots in action - true dead spots, had to be a physical location because it corresponded to the exact moment the DOG entered that spot. "Moving" dead spots would actually move, since different dogs handle sheep from different physical locations. I could almost see a line at some of them. I agree though that these true dead spots are rarer than may generally be proposed.

 

Yes, pearls of wisdom from the lifetime backseat driver.

[Rebecca, Irena Farm]

I'm also glad I wasn't the only one looking at that bale of hay and thinking, I SO wouldn't be doing that. Not because of falling off but because of vertigo. I was at a trial where for Ranch and Open you had to get up on a little stand - I think to see the cross drive - for once I was thanking Heaven that I hadn't moved up yet. I just can't handle standing on anything taller than a few inches.

[Pipedream Farm]

Charlie,

 

this one is for you

 

Sound Propagation Outdoor: Comparison between Numerical Previsions and Experimental Results

 

Mark

[Firchow]

Originally posted by Pipedream Farm:

However, there are true "dead spots" in the sense that sounds from a distant point source are not audible at these locations and these locations come and go based upon local/temporal atmospheric conditions.

I conceded that point but still believe that "dead spots" as they relate to working dogs are in most cases more aptly described as troublesome spots.

 

As a tongue-in-cheek a side note, it's interesting that this is a discussion relating to the NF just as it was last year. Perhaps the more competitive one is the larger they become and the more frequently they occur.

[Sue R]

Perhaps the more competitive one is the larger they become and the more frequently they occur.

Then, when you become VERY competitive (think "top handler"), maybe they become smaller and less frequent again.

 

I'm just a novice and I think I carry my own dead spots around with me. Either that, or the dog thinks I'm ignorant and figures he knows better than I (and he's probably right).

[Firchow]

Originally posted by Sue R:

Then, when you become VERY competitive (think "top handler"), maybe they become smaller and less frequent again.

That's it, exactly. They're an eerie phenomenon.

[Sue R]

Mark, I think you're on to something! I guess that's another reason why top handlers tend to "anticipate" on the fetch, etc., as they have to also factor in the distance and response time (referring back to that long and contentious thread on Sheepdog-L).

 

This makes me think of the concepts of concert halls, and what distinguishes the great ones from lesser ones. Some are more appropriate for choral or orchestral music of different types, and there are acknowledged "dead spots" in definite places. A different setting, but I'm sure the same principles apply.

 

NPR had an article on replacing the stage floor in a concert hall in Boston, that was famous for acoustics and quality. Any time there has been a renovation, extreme care has been taken to "not change anything" because of its quality of sound. In fact, the stage floor had never (I believe) been replaced until now, when they could duplicate the wood, etc., hoping it would not lessen the quality of sound.

 

Now, if I ever progress, I'll have something more to be concerned about...