This is literally history at its finest. Someone taking a lifetime of wisdom in a specialized field and sharing it in a way many many people can understand it. God bless
Not only is he sharing his knowledge, Dave always does an incredible job for visualizing all the concepts. Often time these experiments are so good and cool they should be adopted in school physics classes
The demonstration was enough to make my jaw drop. 38 years on stage and would never have understood how much difference a temperature differential could make. Thank you Dave!
It's amazing how audible the difference is! Seriously cool (pun intended) 😁 Just a wee correction though, if I may - hot air is less dense than the cooler air above it. Rather than sound bouncing off the hot air layer, it's actually the cool air bending the sound upwards like a banana. This diverts some acoustic energy away from the listener (as you say). HF bends more, so more HF energy is diverted away than low frequency, causing the loss of HF that you demonstrate. By angling down, the 'banana' effect (not a scientific term!) still occurs but not in a big way because of the ratio you talk about. If anyone wants to read more, check out stuff on refraction', particularly refraction of sound. It's amazing we can hear refraction in such a 'try this at home' set-up. Thanks for another great demo! 👍 So glad you're doing these again. Keep 'em coming!
@@DaveRat Bob Hiel's book has info on a sound system designed to take advantage of this at a large racetrack. I think that may have been the first big sound system that was flown to exploit this diffraction effect. If I could find my copy of the book I would give more details. I do remember that the horns were about 5' long and we're pointed down about 30°. The horn's axis intersected the pavement about half way to the first spectators. Earlier systems had used ground stacks in the infield. In the mornings it just about ripped people's heads off because it was way too loud. But that was not enough when it got hot. The power required then was huge and people miles away could hear the announcements better that those in the stands because essentially the sound just bent over the top of the stands, bypassing the audience.
James Drissel that’s incredibly interesting. I live in indianapolis and have gone to several races at the world famous Indianapolis Motor Speedway. As a live reinforcement sound engineer for several years, even I can tell the sound system for all those in the infield is absolutely garbage. I never thought about the air density though. The temperature of the track can become incredibly high during the day, so it makes so much sense now.
If I may correct this even further. Some brief background on sound propagation: Density variations of air can be ignored. Sound refraction is related to the velocity gradient of air, following Snell's law in a first order approximation. Ignoring wind and humidity, the speed of sound simply relates to temperature (of dry air), named in literature the adiabatic speed of sound. In that case, sound refraction is related to the temperature gradient. For horizontally propagating sound through a vertical temperature gradient you can state that "sound refracts up for a negative gradient and down for a positive gradient" and steeper the gradient, the stronger the refraction. To generalize this a bit more you do also need to take the relative orientations between the direction of sound propagation and the temperature gradient into account. So the effect is strongest when the direction of sound propagation is orthogonal to temperature gradient (or velocity) and is zero when sound propagation is tangential to the temperature gradient. In case of the latter, sound propagation will only notice a velocity decrease (or increase) but no directional change occurs. An awesome book (for experts) on the physics of acoustics is the book by Allen Pierce doi.org/10.1007/978-3-030-11214-1 To go back to the equally awesome demonstration with the candles: The audience (or candles) near the ground cause a negative temperature gradient and sound propagation from the ground stack to the microphone is orthogonal to this temperature gradient, maximizing the refraction upward. For the flown speaker, the relative angle with respect to the temperature gradient is smaller than 90degrees reducing the refraction. Also equally important for the flown speakers in the nonlinear gradient. It's likely weaker for the path from the flown speaker to the microphone (further away from the candles) than for straight through the heat source for the ground stack.
Wow man. I always learn something new from your videos but this was like learning a whole new field of study or something. I never would have thought you would have to factor in sound refraction due to different temperature layers. That's a whole other level.
I have finally met someone that I could talk to for hours about sound... Most people get a deer in the headlights look when I talk for 30 seconds about this stuff... Thanks for your contribution Dave!
Thats a great demo...I have been trying to get this across to bands / engineers for years that a room changes as it fills up and the temp changes......thank you...i will be passing this along
Hi Dave thank you so much for all your replies. I’ve read and liked them all. Great that your videos popped up in my general searches on RU-vid and yes what a learning channel this has become. Master class. Much appreciated 👌
thank you for making this video. the number of young sound engineers and artists i have explained this too that dont believe me is a big number haha. Awesome video
never realised just how significant the difference is with flown PA. ive only done engineering in a small-ish venue before so the stacks tended to not have any trouble unless a fat guy stood directly infront of them. really good demo of the effect :)
Every touring engineer has experienced that difference between the empty room of sound check, and the full, moisture filled Dense air of a packed venue. We all expect to have to add high-end back into our system EQ after the room is full. Your points about a flown system are very well taken. Especially about the distance differential. Really fun presentation. Thanks for that.
@@DaveRat Hey, you're welcome. My band is only small, but I'm always striving for getting the best sound, with what we have. So someone that can explain something which is quite complex, and me get it within seconds, is worth gold. 💯☺️
Hi Dave, my description focussed on cool night air with a distinct warm barrier at crowd level. I am a radio wave propagation specialist as part of my profession with sound engineering being a serious hobby of say 6 years with loads to learn on audio. I spend my nights learning from you! Cape Town South Africa. The next level of experiment would be pulling out a high tech frequency spectrum analyser
My favorite experience was running sound for the Romantics at Western Washington University in Bellingham Wa. As the crowd brought the heat in the room to a higher level, someone decided to open the ocean side windows to cool off the room. the inrush of humid air immediately condensed on the cement beams overhead, and it proceeded to rain in the building....including on my trusty 40 channel Gamble console.....ah, fun memories. The show survived and yes, you could hear a different audio characteristic with each change of the weather.
This is a perfect example and the point of the video is proven. Why would 7 people dislike a simple experiment? Oh let me guess, they prob wanted to see purple candles. Mr rat thank you for always experimenting and keeping it simple...i decided to double stack my CC on a 10 feet truss and shade them until i get real arrays speakers. Great video
I actually had that issue happen at a baseball field in Sacramento- they had plastic flooring and it was hot and my smaart measurements were so weird . I could see the heat in the floor of the plastic .. thanks for this info sir ..
Dave Rat we wait for you here asap. Anytime you are here the sound is always the best. Keep up the excellent work on youtube, SoundTools and Rat Sound. Stay safe
Hi,Dave. I from China, I am trying to learn English watch your video,Thank you for sharing your experience. you are my sound hero,Looking forward to seeing you.-------your five year fans.
On some large racetracks the speakers are flown and aimed at the track surface. When it is cold the sound reflects off the pavement into the stands. As it get hotter the sound refracts because the hottest, least dense air is closest to the pavement. The sound then curves up into the stands. In musical venues you may have a similar thing happen with the sound going to a balcony.
I remember seeing Wilco several years ago. They had all their amps aimed everywhere but at the audience, including one speaker pointed skyward. Crazy how all this stuff works
Hey Dave, just heard about you the other day and already have watched many of your youtube videos, including the Mighty Headphone Quest. As a live engineer myself, I got curious about trying those Denon AH-D2000, but my guess is that they're discontinued. What are you using these days?
Well, I still have some of those demons and the Sony cd3000 so I stopped searching as I've retired from live touring. But I do keep an eye out for quality cans. I really should just get some made and add them to the sou stools products. Will ponder that
Ha! Very clever simulation. I do simulations, videos and listening tests for my Live Sound students, but I am going to make them watch this video for this particular comparison. This topic often comes up and I just explain it to them, but here they can actually hear what is happening. Cheers!
@@DaveRat Yours is required watching. I have plenty of viewers for my live sound vids and in one of them I suggest they 'listen to other people as well, with different experiences, like Dave Rat', because we can't just listen to 1 person....I guess 'cause there are people who 'poo poo' some of my remarks; thankfully that is the minority (some people just object to the science part of it) Great channel, man! Stay safe.
Those concert experiences you describe re heat of the day plus hot ground level scenario I would think has a super high temperature at knee level with a more gradual temperature transition to say 20 metres up. This I think opens the playing field between FOH ground stacks merging with flown arrays, the flown arrays having major height and throw advantages. hence you say you actually had to reduce the height and levels of the flown during the day. Back to night time observation... one would need more power and angle of attack (like you say you raised them at night) to counter the refractive index from upper cool air into the less dense warmer air environment at crowd level. Cold into warm creates dispersion and loss of energy.
This assumes that there are ground stacks and ignores the easily demonstrate able refraction that is occurring and well known. Typically for large events, we do not deploy ground stacks. Especially for delay clusters where the complexities of merging multiple sound sound sources at various environmental temperatures is quite complex and in a constant state of flux. As far as the heat source and elevation, that is quite variable as well. During the day, a hot field or parking lot will have heat radiating upward from the ground. Separately and unrelated, a mass of humans can generate significant heat, even in very cold temperatures. The abruptness of the thermal differential and the vastness of the area that the differential occurs has significant impacts on the severity of the refraction.
WOW! This might explain why I noticed my instruments sounding different on a very hot day. Im gonna use this if I ever get around to recording that song I complain about the heat. Just have to make sure I dont bbq the condensator
Dave Rat, if the angle from a flown array is what helps the sound waves fight this refraction, why do arrays always curve heavily at the bottom and become more vertical the farther up it goes? Is this just a compromise instead of having more delay towers at the same height and angle for a more uniformed coverage of sound?
Line array sound systems point more speakers far and less speakers close to try and offset volume drop with distance. The height of the PA vs the listening area is what helps increase the angle of incidence.
Interesting experiment. I was always told that if you fly a bass bin it becomes a midrange because there is no mechanical connection to the floor and consequently the building. How do you get good low end with a flying array?
Dave, thank you for another great video. Given your explanation about flown PAs giving better ratios of distance from the nearest listener to the most distant listener, do you have a specific front-to-back ratio in mind that tells you when some audience is simply too far away and delay towers will make more sense than trying to throw all that volume from the main PA?
The distance you throw sound outdoors is very dependent on the environmental factors. If you're in a place that has a consistent temperature no wind no rain you can throw much farther then if you're in a place which is unpredictable may have a lot of wind and some severe temperature changes.
To piggy back on this question, is there a suggested front to back ratio for flown speakers in an indoor venue? Just interested as in our church we have a mono flown speaker array and it wasn't getting sound well enough to where the sound desk near the back! So we got the guys that did the install to fly two more delayed fill speakers for the rear and now it is much better.
The max usable distance from pa to listener is highly dependant on venue acoustics and reverberation as well as system size. Outdoors it an be a 1000 feet or more with a large system on a grass field while a room with all hard surfaces it could be a struggle at 50 feet. Churches are quite often designed with little or no soft absorbing materials so relying on delays and distributed sound is beneficial
@@DaveRat thanks Dave. We had acoustic guys involved in modelling the acoustics and testing / tweaking the system so I think that is why it has come out so well. Sometimes we wonder if the rear delay speakers are on (and they are) which I think is the sign of a good system as you can't really notice them!
watch the bending sound waves with heat as it is a worthdwhile watch, loike the rest of Dave's videos. it's like he has a magic touch. the delay and the point source vs line array videos were eye opening, not to mention same sound from two sources :)
Remember too that warm air, especially where I live (South Florida), has more humidity. There is that factor as well. This also goes to the guy who made the warm air is less dense comment. There is still the humidity factor. Which could be even worse I'd think. P. S. Dave, thanks for another informative and interesting video.
Humidity actually has less of an impact than heat, in that the variations in sound frequency response and diffraction between the coldest and warmest environments we as humans provide sound for, is less than the impact of the most and least humid environments we encounter. There are quite a few graphs and data sets out there that are worth a google
Love the videos! The demonstration was very clear and easily heard. I do have a question about your explanation, since hot air would be less dense than cold air... Although sound would travel through the denser medium better... I guess the analogy of a stone skipping off water confused me. I am easily confused though.
"Why are you setting it up that way?"...DON'T ASK QUESTIONS! THIS IS JUST THE WAY IT'S DONE!'...Thank you Dave for giving us grumpy & opinionated sound guys the education necessary to explain the science behind our actions.
In my opinion, 99% of all "sound engineers" are actually operating on lore, rather than engineering - doing things because they saw somebody else do it. Dave is the rare "sound engineer" who is actually doing the engineering. This reminds me of the first time I actually heard a flown sound system, ELO's _Out of the Blue_ tour. The speakers were stacked inside of big metal cages, long before they figured out how to incorporate the hanging hardware into the speaker cabinet.
@@DaveRat Thanks for making these. The one where you showed how the same sound from two different speakers is an unnatural event absolutely blew my mind. I've been trying to share it with people, audiophiles specifically, and none of them seem to actually *get it.*
Many thanks for taking the time and effort to do such a great video. So we tune the system to an empty room using pink noise and a RTA. I'm curious to know what other engineers do to compensate for the heat factor when the room fills with people. Or if the speakers are flown, is any compensation really necessary?
Dave, how much of an issue is this in an indoor venue? I can certainly see how this would be VERY problematic at a festival show. But what about an indoor venue with a ground stacked system above the heads of the crowd and only a few Degrees of temperature rise?
Flown helps reduce slap back echo when the room has crappy acoustics (concrete box). That was an audible difference. What happens when AC kicks in? Amazing video.
