Striation of sound at a distance?

[Coytee]

Some may recall me dragging a LaScala outside to play into a field a while back. While doing so, it sounded fantastic.

Several weeks ago, I did it again, this time for a friend who came by to hear the Jubilees. (he'd never heard the Khorns while I had them)

Ok, so he's outside, I crank it up and walk out to his location.

It sounded very very different this time. While walking out there, the sound changed dramatically.

The speaker was NOT at the same location and was angling more downward than the first time.

What I experienced was the division of the sound so to say.

Meaning, as I walked away from the speaker (50' to 100') I was walking in the range of the midrange horn and then when I got out to the field, the midrange petered out and I was in the range of the tweeter.

I've never noticed that striation of sound. I really expected the entire sound to have melted into a single unit at that distance.

Does that sound reasonable that the sound would be dramatically different like that?

In fact, as we were walking back to the house, I noticed the area where the midrange "came in" (probably 100' out) and my friend even made comment that the sound suddendly changed.

[Duke Spinner]

....Throw .....

[DrWho]

What time of year and day did you do the experiment last time / this time? The temperature of the air and the relative temperature of the ground to the air can have a large effect on the steering of the sound at those distances. I'm surprised you heard the midrange drop off first though? What happened to the sound from the bass bin?

You might also try the same experiment with the speaker in the same spot firing at the same angle too. Though it's still wierd that the tweeter held out longer than the squaker - it's usually the other way around.

[D-MAN]

Both Duke and Who are right on the money. Both effects are occuring.

The mid energy is being absorbed/dissapate faster due to its wider dispersion pattern and frequency wavelengths. Temp and humidity could alter this quite a bit and its closer to the ground.

Check this website out...

http://www.du.edu/~jcalvert/waves/wavhom.htm

DM

[Coytee]

As I recall, the first time I did it was probably more in middle of day until the latter half of the day. The second time I did it, was something like 11:00 am.

Also, it seemed to be more "height" affected. The field is sort of bowl shaped and from my house to the FAR side of the field, you are then sort of on the same plane. The field dips between those two points.

My reasoning is the first time I did it, the speaker was firing more straight into field and the second time, it was probably firing more downward into the field.

It seemed, just like when you go through thermal layers when diving, that there was a sonic layer.

I noticed it as I was walking OUT to the location and we both noticed it on the way back.

so, my presumption that it was more height dependent gets less points, than perhaps temp/humidity?

very interesting.

COULD the height of it have something to do with it and if so, would you say 10% or 80% of it as a guessing point?

[mark1101]

Richard,

Did you by chance have the ES networks in there this time, but not the first time?

[mas]

Well, I made the mistake of relying upon this lousy website engine (sorry folks, but I call 'em as I experience them, and right now after wasting far too much time...well, sorry for my bad 'mood') instead of independently saving what I wrote, and since it hangs upon trying to attach files it is lost.[:@]

In a sentence or two, you are most likely dealing with a combination of possible thermal refraction, and the basic polar patterns of the drivers, but I suspect that the more important phenomena is comb filtering. And I will note that most folks never recognize comb filtering except in a large setting such as a concert hall or a large outdoor setting. The fact that you say the HF remain while the MF are gone points to comb filtering, as thermal effects act most profoundly on the higher frequencies. Thus, if the MF are 'gone' due to thermal refraction, you will not have the HF.

All of this tends to point to comb filtering caused by superposition. You can indeed have a strange mix and match of frequency passbands present with a comb filtered environment - as this is exactly what characterizes comb filtering.

Check out pp. 151, 154-7.

On the other hand, if this is correct (no mids with highs) and you are only using one LaScala which would rule out comb filtering (unless the crossovers are shot), you have a demonstration worthy of 'saving'! []

ConcatSSE.AcousticEnvironment.Pt1.p145-154.pdf

[mas]

Here is the second part.

ConcatSSE.AcousticEnvironment.Pt2.p155-166.pdf

[Coytee]

Mark: Hmmm... I wasnt sure but was able to brighten one of the pictures I had. The OLD AAs were indeed in there (the first time...when it sounded "good" []). The ES networks were in there the second time.

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Might I ask how that might make a difference?

Mas: We all love the search engine! [:@]

For the record, it was a single LaScala, fed a mono signal. Crossover the SECOND time was one of Al Ks extreme slope ES600 + ES5800 networks. (I think Ive got those numbers right). The original time I did it I can now verify, I was using the original AAs that were in them (1979).

So, here was my take and I guess no one is finding merit in it?

I had surmised that the FIRST time I did it, I was probably not hearing much if any tweeter. Simply that the midrange was firing out directly across the field, it was spraying overhead and covered everything. Tweeter (sound) was flying even higher, perhaps blending in.

I further surmise that the second time I did it, the speaker was angled a bit more downward, as such, was driving the midrange into the field say, 100 short of where it was the FIRST time through. As a consequence, only the HF carried further, making it seem as though the midrange petered out?

(I also don't think I was driving it as hard, in the event THAT fact makes a major difference)

This is intresting to me. All I can say is (the second time) it sounded pretty good in the middle of the field and real tinny on the far side. The first time I did it, even with the old crossovers in it, it really sounded very nice all over the field. I mean ALL over the field, top, bottom, side to side.

Interesting difference.

Why would this demonstration be worthy of saving? (exactly what are you finding of interest, if anything?)

[mark1101]

Mark: Hmmm... I wasnt sure but was able to brighten one of the pictures I had. The OLD AAs were indeed in there (the first time...when it sounded "good" []). The ES networks were in there the second time.

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Might I ask how that might make a difference?

Richard,

I'm not really sure. I was just wondering. The ES networks sound completely different than the AAs and there is no frequency overlap on the drivers. Each driver only puts out its "assigned" frequencies. In the AA all the drivers are duplicating portions of the frequency spectrum. I would expect some sound differences.

The explanations above sound plausible. I can hear a noticable difference in my outdoor sound once it gets dark. But I haven't heard a difference due to the weather....yet. You guys know I speak of using my cornwalls outdoors all the time. But, I place them in the same spot and use everything the same each time.

[garyrc]

When walking from a great distance to the bands during the free concerts / dances / clothes optional be-ins in Golden Gate Park in the 60s, one heard upper midrange and lower treble first, battered by the wind, wavering over, say, a 35 dB range of phasey, drifting sound. There were no buildings anywhere close, just trees. Upon getting close enough to see, and more or less on axis, the treble and shimmering overtones became more prominent, and the music became stable (non-wavering). It was not until we would get rather close that the deep bass came up enough to sound truly balanced, and then it was sometimes loud enough to make the dirt bounce up and down off of hard surfaces like concrete / asphalt walkways. We liked the fact that the dirt danced in rhythm with the music. It was a trip.

The speakers were usually tall and wide stacks of very large Altecs, JBLs, or boxes containing their drivers. Occasionally they would use La Scalas, or supplement with them. Once Klipschorns were used, in artificial corners. I heard the Dead borrowed some Khorns very early on, but found them and the artificial corners too unwieldily to move around.

Ahh such days. The Dead, Airplane (later Starship), Loading Zone, Country Joe and the Fish, many others --- for free! Chants and poetry readings by Alan Ginzberg, Michael McClure, and the rest. Once in Provo Park in Berkeley, Country Joe did Rock 'n Soul Music while slamming the stage with his microphone on the long whip of its cord. They had the bass turned way up for this. Indescribable. I think it was one of those mics they used to advertise by driving nails with it (RE-15??).

With all of this, I'm not aware that they ever blew a speaker. JBL ran a glossy ad showing such a Rock set-up in a park, with a cautionary tale about the time a passing griffin stopped by, coughed into the microphone, and left nothing except a crater. It was a time of passing griffins.

[Groomlakearea51]

It seemed, just like when you go through thermal layers when diving, that there was a sonic layer.

Correct, it could be, at least partially, the same phenomenon with diving; there is a definite "density" issue with salinity related in the thermoclines (10% between fresh and salt at the same temperature, generally regardless of depth), but it's also related to the water's temperature, thus how much salt is in solution; coupled with the density.

Humidity plays a great part, but I've noticed that baro pressure and temperature plays a great part also. On a cold night right after a front went through, say 50 degrees and 65% humidity, I can hear a CD playing (provided my wife's not home...) at the end of the pasture (250 yards) as if I was on the porch. But..... on a hot Florida night, low humidity (still about 90 degrees out..., no rain for a week), I cannot hear anything really intelligible until I'm almost back to the barn.

From the "water" point of view, with temperature layers (especially differing more than 1-2 degrees C), sound has a marked tendency to "bounce" off these thermoclines especially the high freq's associated with, shall we say, machinery in subs, metal hitting metal, divers banging their tanks, etc. That's why we taped off and soundprooofed (in the day, in another life...) anything that may "clank" when underwater. On the job as the Dive Officer down here, however, we started using an underwater comms system (divers can't drop down and just sit on the bottom and screw off anymore...[]), but the old one lost the low end really bad in the audible speech area (sort'a like the midrange?...) as distance increased (inverse law); the new one, however has a higher freq range transducer and while things are "tinny", we can get further from the topside tender. We did notice that if we poked our heads through a t-cline, we would pick up the lost bottom end, but again this is associated with "speech" freqs on this piece of equipment.

That being said, in water, as most know, since it does not compress like air, sound travels much faster, and due to the scattering effect, it's very difficult to pinpoint the source the further away without arrays of multiple transducers (mic's). Also, the "comb" interference effect is very evident at low freq's in water, making low "rumbles" very difficult to pinpoint because they drop in and out, dependent on the freq, depth, and presence of thermoclines.

So...

Could it be a combination of ambient temps, humidity, and the effects of the crossovers on the drivers. There is a possibility that given your description of the "bowl", that there very well may be a high humidity and cooler (more dense) layer from the low point in the bowl to several feet off the ground, or at least until it really warms up in the afternoon. Was what you described very "directional" or was there a noticiable loss of directivity (close your eyes and point to the speaker test) at all?

I'm curious because it's getting cool enough down here in the swamp in the Sunshine State for a fall Oktoberfest party...; and if I drag my LaScalas outside on the porch, put the 6 kegs for all 3 of us out in the middle of the pasture, put the horses in the barn, grab the lawn chairs....... just kidding... it's only 2 kegs....

Ask Mr. Klappenberger about the ES's, he may have an idea.