Architectural Acoustics 4 of 4: Sound Moving In a Room

Architectural Acoustics 4 of 4: Sound Moving In a Room



so can we please answer my her journal question why does it sound different when we speak outside than inside put on your headphones so that this demonstration isn't contaminated by the uncontrolled character of the room you're sitting in alright imagine a scenario with a source and receiver outside in a free field with no reflecting surfaces nearby it would sound something like this in language infinitely many words can be written with a small set of letters now put a few walls in in language infinitely many words can be written with a small set of letters now and close it totally can we play those again in language infinitely many words can be written with a small set of letters in language infinitely many words can be written with a small set of letters we can launch the sound move through these enclosure conditions using ray tracing will use the Ray or line model to represent sound though it omits the frequency differences and multi directionality content of sound this is good for showing propagation and reflection starting with the free field we can model the paths the sound takes from the source to the receiver that's it I mean just a straight shot yep the free field is an anechoic environment wait wait wait Anna echo with Anik one without an echo ah okay I get it in the absence of reflecting surfaces the direct sound is the only kind of sound arriving at the listener it arrives at the listener sometime after the source creates it the delay pursuant to the distance between the source and the receiver and with a single surface added say the ground plane in an outdoor environment we see the direct sound followed by the reflected sound off the plane adding a second reflective surface we see the direct sound followed by reflections off the floor and wall they've arrived later than the direct sound because they've traveled farther right because the shortest distance between two points is a straight line right so the reflected sound arrives later than the direct sound also some of the sound energy has been lost to the surfaces sound transmission through the material and sound absorption in the material so the reflected sounds not only arrive later but weaker the sound has undergone the twin phenomenon of time and attenuation in this case we've chosen smooth concrete as our simulated surfaces so only a tiny portion of the sound and pinching on those two surfaces is either lost to transmission or absorption almost everything then is reflected yeah ninety-eight percent so two surfaces baguettes two reflections no we've only looked at the one bounce reflections called first-order reflections there are reflection paths that include more than one surface well let's look at second-order reflection that arrives later than the first-order reflections you know because it's travelled farther and is weaker than the first-order reflections because it's hit two surfaces instead of one in this case yes on average higher-order reflections are weaker and arrive later than first-order reflections when taken in aggregate this is how endure sound lingers for just a bit just enough that you can sense it then fades in some rooms it lingers longer than just a bit but I wanted to see how complicated it gets with total enclosure it's complicated but not very complex if you can follow the concept behind the partially enclosed room you can follow the concept behind the fully enclosed room there are just orders of magnitude more paths for sound to take and still arrive at the receiver loud enough to be audible we can start with the first-order reflections then hire multi order reflections until the sound level of the reflections weakened by successive impacts on the surfaces that absorb sound is either below the noise floor in the room or below the threshold of hearing altogether


6 thoughts on “Architectural Acoustics 4 of 4: Sound Moving In a Room

  1. I am a third year undergraduate in Architecture School and these videos are giving me a great launching point for my research in designing a performing arts center. Thank You!

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