How Sound Works In Rooms (Room Acoustics)

How Sound Works In Rooms (Room Acoustics)


Welcome to the Pod Sound School. You don’t
have to be great to start, but you have to start to be great. Okay, let’s get at it. Well hey there Podskis, welcome to episode
three: acoustics. I’m Studio Steve, and this is our first audio basics episode for beginners,
and it should prove to be a fun one. When someone talks about acoustic, they are
either talking about the branch of physics that’s concerned with the properties of sound,
or they’re talking about the qualities of a room, or a building. Wow Rhonda, this symphony hall has perfect
acoustics. It really does. As a podcaster, we are concerned with both.
We need to know basics about how sound waves and vibrations work, and we need to understand
the relationship those sound waves and vibrations have with the room they occupy. I once had acoustics explained to me using
the analogy of a pool table. Imagine that the cue ball, the white ball, is the only
ball on the pool table, and it represents our sound source. How hard we hit that cue
ball is how quickly it travels, the loudness of our sound source, the volume, or the decibel. If the cue ball is, say, a guitar amp cranked
to 10, then the ball is going to be propelled very quickly. But if it’s a ukulele, it won’t
be moving that fast. The propulsion, the speed, the vibration of that cue ball, that’s the
physics part of it. Now, the room acoustics part is the relationship
our ball has with the walls of the pool table. Let’s imagine our pool table again, and imagine
that there are not any pockets on the table for the ball to sink into. If the ball is
hit extremely hard, it’s going to continue to bounce off the walls for a very long time.
Hit hard enough, it may never stop. Hit soft enough, the ball may never reach a wall at
all. I like the analogy of a pool table when thinking
about the room that you’ll be recording in, and the analogy of a cue ball when you’re
thinking about the type of sound you’ll be recording, which in our case, is mostly speech. So, let’s talk about the room we record in.
This alone is a significant factor in how your recording will turn out, and there are
many inexpensive options that can turn a reverberated pingy, buzzy room into a smooth, pleasant
vocal studio. There are three main concerns that we have with our room’s acoustics. They
are reflection, absorption, and diffusion. Let’s start with reflection. Reflection really
refers to the materials that the walls are comprised of, and whether they will reflect
or add power to the sound. Are the walls made of sheet rock, brick, glass, are there mirrors
or glass picture frames hanging on the walls? Certain materials are more reflective than
others, and certain materials reflect or even increase the power of certain frequencies. Now, we haven’t discussed frequencies yet,
and if that term seems menacing to you, really it just refers to the pitch or the tone of
a sound. You’ve probably adjusted the frequencies of your car’s speakers, the lows, mids, and
highs. It’s important to understand how certain materials
react to sound, because your room adds the color and the characteristics to what you
record through that microphone. So, sheet rock, probably the most common American household
surface you’ll find, is very reflective of high frequencies, and just super reflective
in general. If you’re standing in an empty room with sheet
rock walls, it’s like you’re in a reverb chamber. The volume of your voice actually becomes
louder. The walls pick up the vibration from your voice, and reflect them back into the
room. For general recording purposes, this is not desired. The custom that we’re used
to hearing on podcasts and radio is that the voices are clear, and absent of effects, so
that they can be easily understood. So, we need to take a look at our walls. What
materials are they made of? We also need to look at the floor. Wood floor, tile, or laminate
flooring are going to be very reflective. Carpet or large shaggy rugs are going to be
very absorbent, which brings us to our next concern. Absorption. Absorption, simply put, is the opposite of
reflection. Rather than adding power to the sound, it absorbs the sound, and stops its
vibration. Imagine that cue ball hitting a bare wood wall, and compare that to it hitting
a pillow. Going back to the pool table analogy, we want that cue ball to come to a stop, and
we want it to come to a stop quickly. The denser and more sponge-like our walls are,
the quicker the ball with stop. The other thing that will bring our cue ball
to a stop is diffusion, our third concern. Diffusion is a process of scattering the sound
into multiple directions. Back to the pool table again, imagine instead of the table
being empty, we nail down random wood blocks around the table. Now imagine the course of
the ball. Rather than bouncing from one side to the other side over and over again, it
now has these obstacles that will change its course, and slow it down. Diffusion happens naturally in most rooms,
as does absorption, with the objects and the furniture we place in the room. Even our bodies
act as diffusers and absorbers of sound. Diffusion is a really nice way to color the sound of
the room without completely killing it. The balance of these three concerns will determine
the characteristics of your room, and will have a huge effect on everything you record
in there. So, you want to create a nice balance. You don’t want a room that’s completely reflective,
and you don’t want a room that completely absorbs all the sound with no character at
all. There are many DIY and low-cost solutions
to a reverby, nasty room. I’ve mentioned rugs. Many people hang up sound blankets, or the
blankets you’ll see in moving trucks, usually the blue ones that you buy at Home Depot.
Some people experiment with egg cartons, or camping foam pads. These DIY solutions will help the reflection
problems and soften your room sound. But if your room is to be used for any other purposes,
these solutions aren’t very easy on the eyes, and it’s a quick way to piss off your spouse,
or roommates. Another solution that can be very effective
are curtains. Curtains can hang over doors, windows, walls, they can even divide rooms.
And of course, when you’re done recording, they can be pushed to the side. Way easier
on the eyes, and your spouse can even pick out the color. Now, if your budget allows for it, there are
also many different acoustic panel options available, both absorption panels and diffusion
panels. There are people on Etsy that custom build diffusion panels that are eye-catching,
and can really add a real studio feel to your room. One company that’s worth checking out is Auralex.
They have many different packages and designs to choose from for their absorption panels
that really add that studio look to your room as well. It makes you and your guests feel
like you’re in a nice recording studio. These, again, are all considerations that are going
to be dependent on your budget, and you want to do something that’s practical, and make
sure that you go through your whole checklist before spending all your money on your room. So, before we finish up with our quick discussion
on acoustics, we need to talk about noise and soundproofing. When I say noise, what’s
the first thing that comes to your mind? Is it the kids playing in the other room? The
cars driving by outside on the street? Those are the kind of things that first pop into
my mind. Combating these issues can be difficult and,
in many cases, out of reach. You’re just set up to record your new episode, and the neighbor
starts thumping base and stomping on the floor above you. Or in the middle of a wonderful
interview, a truck drives by and rumbles the room. However, in most cases, just using some cost
effective sound treatment items, like curtains and acoustical panels, will make these issues
tolerable. Mostly because of the proximity or closeness these noises have to your microphone.
So, complete soundproofing isn’t really a necessity, but sound treating is. Now, there are many more concerning noises
that maybe we don’t always think about right off the bat, like computer buzz, fluorescent
lights, the refrigerator, the air duct or ventilation systems. These little nasties
are one of our biggest enemies. These are perhaps the most overlooked, yet cheapest
noises to eliminate. Although, it might require some creativity. Take the time to sit in your podcast studio
when no one is home, or it’s late at night and quiet. Close your eyes and just listen.
The longer you pay attention and really focus on those hums and buzzes, the more you’ll
realize that even the quiet times in your room are actually very loud. And these buzzes
and hums will be even louder to a microphone, and impossible to get rid of later in the
editing. The solution? Find the source of the noise and, if possible, remove it from
your studio. This may require some creative workarounds. If you’re a round table podcast that gets
together in the dining room in close proximity to the kitchen refrigerator, maybe meet in
the basement, or the garage instead. Or you can unplug the refrigerator for an hour or
two, but maybe have your guests put their car keys in the fridge, or set a reminder
on your phone to plug it back in. This is done all the time on film and TV sets. The
fridge will maintain its temperature for a surprisingly long time if it isn’t opened
after unplugging it. If you’re recording on your PC tower, or an
old school Mac Pro, move the CPU out of the room and purchase some monitor and USB extensions.
Get those CPU fans away from the microphone. What about air filters, or air vents? Eliminating
offensive air vent murmur can be as simple as just shutting the air off manually before
recording. Post a reminder sign where you’ll see it to shut it off every time before recording.
You don’t want to get through an hour of great conversation to find out that the air’s been
running the whole time. And that beastly, hissing that comes from
those fluorescent lights, get a couple cute lamps, and have the girlfriend pick them out.
That can be your podcast studio mood lighting. This is your podcast, you decide what goes
into that microphone. Keep those sneaky little monster noises out of your show. They buildup,
and buildup, and soil your show very quickly. Especially in multi-microphone situations. That about does it for your crash course in
acoustics. I hope you feel like you’ve learned a little. Setting up your space has got to
be one of the funnest parts of this process. So, now that we’ve covered some acoustic basics,
we’re ready to move on to microphones. I’ll see you over on episode four. Well, there you are [inaudible 00:12:16].
Remember, success usually comes to those who are too busy to be looking for it. Opportunities
don’t happen, you create them. See you next time.

8 thoughts on “How Sound Works In Rooms (Room Acoustics)

  1. When starting out in podcasting we're very quick to think about the mic we'll need, the interface, and the software, but before all of that: it's so important to control the sound of the room we record in.

  2. This is such helpful information. I would not have even thought about fluorescent lights or the refrigerator noises.

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