How Sound Works (In Rooms)

How Sound Works (In Rooms)


Hi, I’m John Calder of Acoustic Geometry.
Let’s talk about Acoustics, which is basically how sound works in rooms.
It may seem complicated, so let’s make it simpler.
Most rooms have flat walls and flat ceilings and sound bounces off of these.
So how does that affect the sound? I’ll use these two Nerf guns to demonstrate.
I’ve got this one aimed so this disk goes directly to the ear.
That represents direct sound. I’ve got this one aimed so that disk bounces
off the wall and it represents reflected sound. I’ll shoot them both at the same time.
Reflected sound arrives at our ears later than direct sound, even though it started
out at the same time, because it’s traveling farther.
And this wall is only one flat surface. There are at least 6 in the average room and
that’s a lot of reflected sound. But why is reflected sound bad?
I’ll demonstrate using these two identical patterns.
The blue pattern represents direct sound waves. The red pattern represents reflected sound
waves. They start out together, but when I move the
red one backwards, like a delayed sound reflection, it creates destructive interference patterns
which changes the original sound wave. Here’s the problem.
Original sound waves are distorted by strong later-arriving reflections.
Also, sound travels really fast. About 1130 feet per second.
A sound wave will bounce back and forth between these two walls about 60 times in one second.
Sound travels so fast it fills a room almost instantly.
This is only one bounce angle, every room has thousands.
How can we make our rooms sound better? Remember our Nerf guns?
I’ll shoot these at the same time, again representing a sound wave bouncing off a wall.
Both discs bounce together in the same direction, which means the reflected sound is at full
strength. Now let’s use the first of our two acoustical
tools, an absorber, to reduce the strength of sound bounces.
To a sound wave, an absorber looks a little like a hole in the wall, so some of the energy
doesn’t come back. An absorber works by reducing the strength
of reflected sound that would otherwise cause more destructive interference.
But if we use only absorbers in a room it makes it sound dull and unnatural.
Historically, humans don’t like overly absorbent rooms.
So, let’s use the second of our two acoustical tools, the curved surface diffusor.
It also reduces the strength of sound bounces. A diffusor works by scattering the sound reflections
in different directions, smoothing out destructive interferences throughout the room.
Room acoustics are greatly improved using a combination of absorption and diffusion. It’s all about reducing those flat-surface reflections.
Use a combination of absorbers and diffusors and your room will sound a lot more natural.
Thanks for watching.

100 thoughts on “How Sound Works (In Rooms)

  1. thanks so much for this video. as a hobbyist trying to make improvements to my recording space this video definitely changed my ideas on how to go about it. fuggit. add some absorbent and diffusive pieces and then move stuff around til' you like how it sounds? use a few built-for-the-purpose items and then the indigenous contents of the room?
    aside from acoustic panels, etc , think i'm going to put up some shelves with old paperbacks? maybe add an overstuffed chair? how bout stuffed animals? worth a try anyway.

  2. you could use that clip of the wood clappers for an 80's inspired music video…reminds me of some of back when MTV used to play music videos. Kinda funny.

  3. well I too studied for many years the acoustical problem and if what this channel says is the absolute truth then Bose would be out of business because that's what made them the empire they have become today _Direct Reflecting Technology, their flagship the 901

  4. This is what I figured after playing instruments for so long. Simply having a fan set to low messes with sound frequencies too. It's interesting how it causes them to sound. Thanks for the video!

  5. Mr. Calder seems like, AND IS, such a dedicated, industrious (20th centuryisque) genius who simply loves his craft.
    wish youtube would have more of THESE instead of the over animated 'fake' exuberant ones whose charade is all about fame, name and being up on the game.

    youtube, please have more of the likes of Acoustic Geometry, the Engineering Guy http://youtube.com/user/engineerguyvideo , Grand Illusions http://youtube.com/user/henders007 and the likes.

  6. Interesting and somewhat helpful. You should have mentioned Standing Waves and Room Modes and their effect on the sound. I find that my irregular shaped room is best for music reproduction. You do want some reflected sound to make it more natural. Also avoid "exact" distances between speakers and boundaries. The old equilateral triangle position is another fallacy for good sound. Just place your speakers where they sound best, but not the middle of the room. Fuhgeddaboudit!

  7. 3:18 – "More natural" – That's funny to hear.
    Sound is supposed to bounce. It must be living inside of a box that isn't natural.

  8. Fascinating and informative! We are currently in the middle of recording at our home studio and trying to get our sounds right and this puts a wonderful visual on WHY things happen the way they do.

  9. This is what bugs me most:
    fArther = fUrther
    Eleven hundred and thirthy = One Thousand one hundred and thirty

    Why do Americans make everything sound stupider with their slang

  10. You're saying all this about flat walls causing bad sound, but you're in a room with flat walls and the sound on the video is perfect

  11. I always wondered why there were curved and flat thing on the walls of band rooms. I knew it was for sound, but this really helps. Thanks!

  12. what a clown….."humans dont like full absorbed room" wot? i have full absorb room and i love it so much…commercial of bullshit defusers

  13. If you add to this video the knowledge that often the two reflections arriving closest in time to the direct sound are high frequency reflections from the ceiling and the floor. This causes an unpleasant hardness to the sound and confuses the sense of direction, To counter this simply buy a suitable rug for the floor between your speakers and you listening position and place some simple absorbers on the ceiling in the reflecting areas. This way reproduced sound quality can be substantially increased. Settle for electrically well made but cheap cables and spend your money on getting the acoustics right instead. I promise it will work wonders!

  14. Great Thanks ! How was processed the positioning of this red absorber please ? – – Measuring ? Counting ? Akustic use or visual just for fun ?
    THX 😊

  15. One of the best explanations I heard.

    And now im going to demonstrate how the sound reflects using this AK-47 hitting a pig alive and on the other hand I have a grenade that is going to explode inside that fridge filled with live monkeys.

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