Rerun: Shh! How Soundproofing Works

Producer Noel Brown joins the show to talk about the science, theory and practice of soundproofing. How does sound work? How can you protect a room from sound?

Learn more about your ad-choices at https://www.iheartpodcastnetwork.com

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:04):
Welcome to tech Stuff, a production of I Heart Radios
How Stuff Works. Hey there, and welcome to tech Stuff.
I'm your host, Jonathan Strickland. I'm an executive producer with
I Heart Radio and I love all things tech, and
we're going to take another look at a classic tech
Stuff episode of another one that published back in. This

(00:26):
one is called how Soundproofing Works, and Noel Brown joined
me for that episode to talk about the science and
tech behind sound proofing, which is a very important component
of our podcasting business. Here, I am currently baffled, or
at least I'm surrounded by baffling, so that we can

(00:46):
control the way that the sound bounces around inside the
studio so you guys don't get terrible vocal effects. But
Noel has a lot more to say about it, so
let's sit back and enjoy this classic episode. So one
of the things I like to do on the show
is at the end of every episode, I invite you
guys to send me requests ideas topics for future episodes,

(01:09):
and today's episode is due to that. So I'm going
to read a little bit of listener me. You know,
we used to have a whole claxon all right here
he goes, hey, you tech stuff. First off, I want
to thank you for putting out your content as I'm
a huge fan of this casual learning movement. Might need

(01:30):
a better term for that. I was wondering if you'd
be able to do an episode on acoustics and sound
dampening for studios, like how they're measured, tuned, made, et cetera.
It would be awesome and spectacular as I would be
able to harness the power to put together a kick
ass set up. Thanks again for what you do. Dub
nosis well dubed. We're going to do that for you.

(01:52):
And that's really the reason why I asked Noel to
come in here, because Noel, as a producer and sound
engineer type person, has had real world experience with this,
and so we're going to rely heavily upon his um
perspective some of the stories he has to tell about
the process of trying to make a room more soundproof

(02:13):
or tuning a room so that you're getting the sound
you want while you're recording, because, as it turns out,
sound is a pretty tricky thing. When you boil it down.
Sound is vibration, right, It's just particles banging together a
sentile thing you gotta wrangle. It is a thing you
gotta wrangle. We often consider sound to just be this

(02:35):
thing we perceived with our ears, But what's really happening
is a little more granular than that. Sound is particles
that are moving vibrating. Uh. Typically we're hearing things that
are coming through over the air, like actual air around us.
So you listening to this right now, you can hear
my voice. Well, what's actually happening is that some speakers

(02:59):
are vibrating some air molecules, and that is compressing and
decompressing those molecules. It's it's changing the pressure, increasing and
then decreasing the pressure at frequencies and amplitudes that your
ears pick up and then you perceive a sound. So
this is happening through all sorts of media, not just air.
It can pass through solid matter, it can pass through

(03:21):
liquid and depending on how the particles are packed and
the space between them, sound may move better through one
medium than through another. Now, knowing that sound can travel
through different media, you also need to know that it
can transfer from one medium to another medium. So for example,
if I'm shouting really really loudly in a little room,

(03:43):
some of that sound when it makes contact with the
wall actually causes the wall to move. Now it's not
causing the wall to move a lot, but it is
making the wall vibrate a little bit. Those vibrations get
transferred through the wall to the other side. And that's
why if you're in a place that has, you know,
flimsy walls, you can hear someone in another room. The

(04:05):
sound is actually transferring through, not to mention in the
room itself, that sound is actually reflecting back at you.
And the quality of the sound can depend, you can
vary greatly depending on the material that the room is
built out of or treated with. Right right, So some
of the sounds getting transferred through the materials, some of
the sound is being bounced back from the material toward you, um.

(04:26):
And a lot of that depends upon the the hardness
of the material, Like a really hard material is going
to bounce a lot more sound back at you, which
is why if you are in a large room with
a lot of hard surfaces you get that echoe sound. Um.
Or if you're out someplace like at a canyon and
you do a shout and you get that echo back,
it's because the sound is going out hitting the walls

(04:49):
of the canyon bouncing back to you, and that's when
you get to experience that effect. Well. Obviously, this means
that if you want to create a place where the
sound can't escape or leak into and a lot of
recording studios, you want both of those things right. You
don't want the sound from the studio to leak outward,

(05:11):
but you also definitely don't want outside sound to leak
into the important Then you have to figure out, well,
how do we limit how do we work within the
physical uh uh constraints of the way sound works, so
that we can limit that as much as possible and
try to have the purest experience as we can. Um So,

(05:33):
one thing you can remember is that sound, because it's
a physical activity and because it relies on on energy,
the way it works is that you've got a source
of the sound. Sound waves travel outward concentrically outward from
that source, and they get weaker as they travel out
that that energy starts to dissipate. You can think of

(05:54):
it kind of like um uh. You know, each each
time a particle has to bang up against the another
one to move it, some of that energy ends up
getting lost. So the further way you are from a
source of sound, the quieter it is. That's why that happens.
So one way you can limit the way sound comes
out of a room is you make an enormous room,
like you have a little room in a really big room. Um,

(06:18):
But that's not necessarily the most practical approach. Actually, there's
a studio I used to intern at in Athens, Georgia
called Chase Park Transduction, and they essentially built their studio
inside of a larger warehouse space. So they're renting a
space in the strip of big, giant, very high ceiling
warehouse spaces. But when you go into the studio, you're
in the warehouse. But then there's a smaller basically building

(06:43):
inside that warehouse that is the one that receives all
the acoustic treatments. But it's like you said, I mean
that is one way of dealing with it is air. Yeah,
the room within a room approach is often how it's
referred to, and sometimes it is not as obvious as that,
Like it may be that uh, it looks like the
the room you're walking into might be like it's it's

(07:04):
in a little uh alcove or hallway, but that hallway
is actually showing where the the walls are, where there's
an air gap between the two walls to to mitigate
any sound coming into the space. Here. Even this glass
window that we have in the booth that we're recording
in right now, it's a double paned window. So in
between these two relatively thick pieces of glass is a

(07:25):
little layer of air, which in and of itself acts
as a bit of a sound dampening insulation device, right exactly. So, uh,
some other little elements of sound that we need to remember.
There are two main components to a sound wave that
are important to keep in mind. One is amplitude or volume.
So if you are looking at the way we typically

(07:47):
show a sound wave which is on like an X
versus Y graph um, you know those those sine wave
style graphs, the height and depth of the troughs that
represents the amplitude how loud the sound is. Then you
have the frequency of sound, the number of times sound
cycles within a second that determines the pitch of a sound.

(08:09):
So a low frequency obviously would be a perceived as
a lower deeper note or tone, and a high frequency
with those peaks and troughs moving gradually more closer together
is going to be perceived as a higher pitch. A
good way to think about this too, is if anyone's
familiar with the instrument the theoremin. There are two controls
on a theoreman. One is the antenna that goes upward,

(08:31):
and there's an antenna on the side. Uh. The antenna
on the side you use your hand by moving it
closer to or farther away, you are changing the amplitude,
and that's perceived as a change in volume. The antenna
going up as you move your hand closer to it
or farther away, you are changing the frequency. So with
those two controls you can basically shape the way the
sound is perceived. Right, And it's important to remember these

(08:54):
things because uh, As it turns out different approaches to
sound proofing are effective for different frequencies. Definitely, right. So
there might be one that you're like, oh, this is
this is perfect, I can't hear my neighbors anymore. But
then it turns out that when your neighbors put on
a an album that has a lot of base in it,
it comes right through or start yelling at each other

(09:16):
for whatever. Yeah, the amplitude is loud enough, it maybe
that you're soundproofing isn't going to be uh. When people yell,
sometimes they tend to raise the pitch right right right,
the pitch goes up enough, but I got you. Yeah.
So these are things that you have taken to consideration
if you're trying to sound proof, and obviously what you
are trying to accomplish, like the reason why you're soundproofing,

(09:36):
that will play into it as well, because if all
you're trying to do is just make it quieter so
that you know, you don't have like you're designing a building,
maybe it's a hotel, and you want to make sure
that the the people talking in one room doesn't bleed
over into other rooms. That's one type of soundproofing. If
you're trying to make a professional recording studio, that's another type.

(09:56):
From a construction standpoint, like the base level soundproofing is dryewall,
So you have drywall, and that is where if you're
in a hotel that only uses drywall, people are gonna
be able to hear every single thing that's going on
next door. It's when you start basically stuffing that dry
wall with other denser materials or you know highly rated
soundproofing materials. That's when you can really cut down on

(10:17):
that transfer between the rooms, right, And also there are
other some other techniques you could use as well that
I'll get into that. And it's all about how do
you make it harder for the sound to travel from
one place to another because sound is going to travel
no matter what. It's not like we have created a
material that just sucks up sound totally. We've got a

(10:39):
lot of materials that resist vibration and that means that
they don't transfer sound very well. But in fact the
studio has some of that around us. But you know,
there's other stuff you have to take into consideration as well. Now,
there are four general elements to soundproofing and we've we've
kind of touched on a few of them, but one
of the big ones is called decoupling. Now, decoupling is

(11:04):
a construction term. When you're talking about decoupling, you're talking
about the way the walls of the soundproofed area are
actually constructed. So you were just talking about dry wall.
The typical way a wall is constructed is you've got
studs and attached to the studs are the anchor points
for the dry wall. And in a typical wall, the

(11:26):
studs are connected on either side by drywall for one
side of the wall and dry wall for the other
side the wall, So the h if you can think
of it like the interior wall versus the exterior wall
of a room. The problem with that is that when
sound hits the drywall, then sound can travel through the
dry wall through the studs, which transmit sound. They're pretty

(11:48):
good conductor for sound to the other side of the
dry wall, and then you get sound bleeding out or
you have sound bleeding in from the outside. So decoupling
is a process where you would build a wall so
that the studs don't touch both sides of the wall.
You would have a series of studs that one side
the interior wall are attached to, and a different series

(12:11):
of studs that the exterior wall are attached to. They
both extend well into the gap between the two walls,
but they don't touch the other side. So one side
could be receiving sound waves and potentially transfer those, but
since they're not touching, it's much more difficult for that
to happen. Right, because air is not as good a
conductor of sound as a solid object is, which is weird.

(12:33):
You wouldn't think that, because I mean, here we are
in a room talking to each other, and the air
is basically what's connecting us. But the interesting thing, though,
is that the way you can tell this, it's very
easy way to tell. It's the old kid game of
a telephone where you get two cans in a string, right,
you you punch holes in the bottom of the cans,
You run the string through the holes, you stretch it taut,

(12:55):
and then you can whisper into one can and here
it on the other side. But if you whisper that
same volume across the room, you can't hear it. So again,
that shows that the the physical media is actually more
or medium i should say, is actually more efficient at
transferring the sound than than air is. So air pockets
are actually really important when you're soundproofing, you know, designing

(13:19):
a soundproof room. Um, typically you would pair decoupling with
some of the other elements, and I'll go ahead and
mention what those elements are, and then we'll talk more
about how you would put it all together. So you've
got absorption another important element. This is obviously using a
material that slows down sound. Uh, it absorbs some of

(13:41):
the sounds, so that sound essentially loses some of its
energy and it thus is quieter. It doesn't it doesn't
leak out as much because the amplitude gets reduced as
a result. UH. So absorption you achieve usually through using
some sort of insulation material like UM. I mean, fiberglass
is a simple example where you would put that in

(14:02):
the wall, in the in the gap between the two
sides of the wall, the two pieces of drywall. I
saw one even saying denim. You can use different like
fabric type, interialt or something like. The important thing is
that whatever you use, you cannot pack two densely exactly,
because if it's too dense, that's going to transfer sound
and you're back to the same problem you were it before.
And you also want to have still have some air

(14:24):
gap there too. You don't want the material to make
contact completely through the gap. You would pack kind of
like half of the gap, a little more than half
of the gap. Typically with insulating material, you leave an
air gap, and that really creates a great cushion for sound. UM.
We'll talk a little bit more about how that can

(14:45):
go wrong though. Uh decoupling in particular can make certain
things UM a little more difficult. There's also damping. Sound dampening. Uh,
this is where you use some sort of material that
resists vibration. So like the foam we have here, there's
some we've got some dampening foam in here. But the
typically you look at a lot of things like adhesives
that are used to dampen sound. Um. One of the

(15:08):
ones I keep hearing about over and over as green glue.
Green glue is yeah, so so it's very popular, particularly
apparently in Canada, but it's popular along amongst sound proving technicians.
It is considered to be one of the most effective
for the least amount of money solutions for sound dampening material.

(15:28):
But typically this would be a layer that would also
be part of your wall that resists the vibration of
sound and so it won't transfer sound as well. Um.
It's again, uh, something that you would apply between two
constrained layers. So it's not like it's not like you
would cope this on the interior wall. That would be

(15:50):
a bad idea. It would be on the the the
back side of the interior wall. It might even be
something you could use as an adhesive for other sound
damping materials like acoustic foam or tile. And then the
last element is really the simplest, is mass. It's just
that heavier things are harder to move than lighter things, right,

(16:11):
It's just the basic idea like if if you had
a cart filled with concrete blocks, it would be a
little heavy to push, But if you had that same
cart and it was filled with feathers, it's easy to push.
So I've got something for you. He uses all of
those elements in a pretty perfect example, one of the
more perfect examples of soundproofing that we can see in
the real world. I'm not sure I think Microsoft has

(16:34):
maybe outdone them at this point. But there is a
place in Minneapolis, Minnesota called or Field Laboratories and it
contains um what was I believe again until recently, the
world's most silent room. This world record for the most
silent room. It is nine point nine nine sound absorbent.
In order to accomplish this, it uses a combination of very,

(16:57):
very very thick, heavy materials. It's got concrete walls, steel reinforcement,
and then on the inside of the room. I'm looking
at a picture right now, it has these alternating sort
of thin looking things, so You've got like three and
then going from left to right, and then three right
next to it, going vertically, and they alternate throughout every

(17:19):
panel in this room, um, and then even on the floor.
And the what you stand on is a metal grate
that goes on top of another series of these alternating,
um little little units. And apparently, um, the longest anyone
has been able to stand being in this room alone
with the lights out is forty five minutes, because people
start to hallucinate this level of silence. I've I've heard

(17:43):
such things. It's the sort of thing every time I
hear it, I have the reaction that I think people have,
which is bet I could go longer, And of course
I'd probably be in there for like three minutes and
be convinced I've been in there for three hours. Because
once you get to a point where something that you
have taken for granted, you know, just the ambient sounds

(18:04):
that you can hear once that's gone, that really does
make a big difference. And uh, it is a psychologically
powerful experience, but I still kind of want to do it. Yeah,
that's a great way of of kind of summing up
all of these elements. Now, if you want to really
sound proof a room, the best thing to do is
to incorporate as many of those as you possibly can,

(18:27):
because they're different. Ones are good for different parts of
that frequency range we're talking about, So some of them
are really good for those mid too high range frequencies,
some of them are a little better at the low frequencies.
So obviously you want to have a good combination. Otherwise
you're gonna have certain sounds come through even if you've
perfectly blocked the room for other ones, and that can

(18:48):
be really frustrated. Literally a cut off or a threshold
where if you looked on a graph that can show
you what frequencies are happening, you could literally track Okay,
this frequency, now I can hear it. Yeah, it's that specific. Nolan.
I will be back to talk a little bit more
about sound proving, but first let's take this quick break.

(19:16):
So kind of going back to to decoupling a little bit,
The size of the air cavity between the two sides
of the decoupled wall determines something called the resonant frequency
of that. So here's the here's one of the problems
with decoupling. That air cavity ends up acting kind of

(19:36):
like a spring, right, So springs actually have a resonant frequency,
and if you end up vibrating something at the resonant frequency,
it causes that thing to vibrate very very easily. The
big example of this that everyone is familiar with is
the crystal glass. The opera singer hitting that note, that's
the resonant frequency for it, and you can actually see

(19:57):
the glass to form and ultimately break. Now or even
someone that can play those glasses where they fill it
up with water and run their finger around the rim.
In order for it to start making that tone, it
has to reach that resonant frequency exactly to basically self
oscillate exactly. So so here's the problem with the decoupled
walls is that that air gap, because it's acting like

(20:18):
a spring, uh, and because it can resonate if it's
not at the proper thickness for the air gap, that
resonant frequency maybe within the range of sounds that you're
going to generate either inside or outside the room, within
the range of human hearing, which means they're going to
impact that sound proving. And if something actually is played

(20:38):
at that frequency, it will go not only will it
go through the wall. It'll go through the wall more
easily than it would have if you hadn't decoupled the
wall because that resonance. Uh So that is one of
the things you actually have to take into account. And
one of the solutions to that is don't make it
too thin of an air gap. Um. So another way

(21:02):
of experimenting this with this yourself, if you want to
just have some fun, and by fun, I mean, like
you know, Mr Wizard style fun. You get a bottle
and you know, if you blow across the the opening
of the bottle, it produces a tone. Well, it doesn't
matter how hard you blow, it's always going to play
that one tone. But if you add water to the bottle,

(21:23):
you have decreased the volume of air the bottle can
hold and that changes the tone. Again. Back to the glasses,
they could have, you know, the same size glasses, but
they generate different tones from each one by putting a
different amount of water in each right, Right, it's not
just the size of the glass, but how much liquid
is in the glass. So what you would love like
to do is make sure that your soundproofing UM technique

(21:48):
was going to take care of those maybe mid two
high range uh frequencies and then make sure that the
air gap would push would resonate at one of those
frequencies so that the other elements of your sound proofing
take care of it and it doesn't pass through. If
your resident frequency is too low and you didn't really
protect against that, it's going to pass right on in. Uh.

(22:10):
So there's also something called the triple leaf effect. And
I had to look this up in a couple of
different locations to find out what the triple leaf effect
is because I don't know if you know this, Knuel,
I haven't built any houses recently. So the triple leaf
effect is all about a construction of a wall, like
a drywall, and they refer to each sheet of drywall

(22:33):
as a leaf. So you've got the interior wall that
is one leaf, You've got the exterior wall. There's a
second leaf. In a triple leaf approach, you actually have
a third sheet of drywall that's in between the two.
It's inside the wall. It's further compartmentalizing it essentially, right
and uh And you might do this and think, oh, well,

(22:54):
that's going to end up protecting against sound even better.
Not necessarily, um, it actually can cause a problem because
it can create If the air cavity between the middle
leaf and one side is too small, it can create
those resonance problems. So people actually refer to as the
triple leaf problem. So this is not necessarily a technique

(23:15):
you want to go for. This is describing a problem. Yeah. Yeah,
So there are some proof technicians who say, if you
have a triple leaf wall and you're having these resonant issues,
the the solution is actually to tear open the wall,
remove that triple leaf. That third sheet of dry wall,
the one that's in between the other two, take that out,

(23:35):
and then it will create a thicker air gap between
the two sides, and that will end up changing the
resonance problem. I Gauesse, I could see that. I mean,
it does introduce more of a variable into the equation,
and as opposed to just having to having a third
one there, there is more ways the sound could potentially
bounce around or catch that resident frequency. Right And you know, um,

(23:56):
we talked a little bit about echo and about how
sound can bounce off of hard services. We talk about
the BUNNEYMN. No we didn't talk about the Bunny Man.
You know they're playing in Atlanta soon, Are they really wow,
that I would much prefer to see them than insane clown. Posse,
you're already missed insane clown. I know they played earlier
this week, yesterday, day before yesterday. Yeah, I actually wanted
to invite them over so we could explain how magnets work.

(24:17):
But that's that's neither here nor there. No no in
their heart, I hope so well. You know, they made
a whole video about it. But the echoes can be
an issue obviously in recording studios, things like that. You
don't want there to be if there's gonna be any echo,
you wanted to be there on purpose, not because of
just that's the way the room was built. Same here
for our studio. We don't want too much echo here.

(24:38):
And we are in a building that's made out of concrete.
Now that in some ways that's good because it helps
dampen sound from other areas. Unless something is making direct
contact with the concrete, then we can all hear it everywhere.
Like whenever there's construction going on, you can hear it
move through the concrete columns and floors and ceiling. It

(24:59):
is disturbing. Their very strange. We play the game what
construction equipment do you think that is? Sometimes you just
don't know because the sound can mutate based on what
it's vibrating to. You know, right, it might be a
little drill that's vibrating a giant piece of metal, and
then that's vibrating something else, and by the time we
gets to us, it sounds like there's a giant playing

(25:21):
hop scotch up there. Yeah, it could be a little distracting. Fortunately,
most of the spaces in in the building where in
now have been built out because when we moved into
this building, we were one of the first offices here. Yeah,
and that just meant that we had construction noises pretty
much consistently throughout the whole experience. So that is been

(25:42):
reduced dramatically over time. But one of the other things
is that, you know, we when since we have all
this concrete, we have to figure out how to eliminate
that echo. And the way you do that is typically
by putting softer material on top of the harder material
and that that again dampens the echo. So you know,
if you if you have a castle, you probably are

(26:03):
hanging tapestries for a couple of reasons. One, it acts
like an insulator, so you don't lose as much heat
in those cold winters and do when you're screaming at
your servants because your food isn't on the table. When
the bad guys are attacking your castle. Yeah, you want
you don't want that to echo throughout the castle, unless
you're a villain, in which when I'm decorating my castle,

(26:24):
I tend to go with tapestry. I do. I do too.
I'm I'm tapestry heavy when I do that. Um, but
it's it's so sort of stuff you can do inside
like a home studio too. You can hang uh fabric,
heavy fabric to help kind of like a theater style
curtain is excellent not only because of its of what
it's the denseness of it. It bunches up like so

(26:47):
you can kind of squeeze it together where it creates
these natural kind of ripples which not only absorbed the sound,
they sort of diffuse it a little bit in the
same way what I was describing with that World's Quietest Room.
These alternating patterns of material that have little spaces in
between them, they act as a diffuser for the sounds. Right.
And there's there's one other thing that we can talk
about or I'll briefly mention which is sound cancelation. That's

(27:10):
a little different from soundproofing. Actually, in a way, it's
the opposite because you actually have to create sound with
sound cancelation. The way sound cancelation works is if you
were to look at that that graphic representation of a
sound wave, Let's say it's a steady tone, because that's
the easiest way to imagine it. So it's a stay
tone it I don't know, three hurts, and you're looking

(27:31):
at a three hundred hurts sign wave, and you see
where the peaks and troughs are. If you were to
create a a complementary side wave where it is out
of phase, so the peaks and troughs match up with
the troughs and peaks, then they cancel each other out.
That's the crazy thing about sound because you typically think

(27:52):
if you add more sound to sound, it just gets louder.
Like if you've ever been in a restaurant that has
lots of hard surfaces, it becomes really difficult to have
a versation if it's a busy night because everyone everyone
starts to talk over everyone else and it just kind
of echoes. Well, it turns out that if you do
add sound to sound, but you make sure it's out
of phase, it cancels it and then it's as if

(28:13):
there's no sound at all. That's what noise canceling headphones do.
They create a sound, they detect the incoming sound waves,
they create complementary sound waves that phase that out, and
then you get silence as a result. So an example
of that phenomenon that you don't want that actually has
to be corrected. If you're in a recording studio. Let's
say you're recording an acoustic guitar and you want to

(28:35):
mike it in two places. So you might put a
mic on the soundhole of the acoustic guitar. Then you
might want to put a mike a little further up
on the next somewhere. If those mike, since they're recording
the same signal essentially, but they're spaced apart, there is
the potential for phase issues between those two mics. So
while it's not going to get straight up cancel out

(28:57):
the sound, it's going to change the quality of the
sound in a way that you might not like. It
might make it tinier, or it might give it almost
like one of those phaser kind of a jet engine
psychedelic guitar type sound. You know, you know where it's
filtered through that sound. Um, So what you have to
do is you can you can correct this after the fact.

(29:18):
But there are devices that you actually can test the
phase at the point you're recording and then space the
mics apart accordingly, and there's even ways to adjust the
phase using these devices. So it's interesting how you're describing
as sort of a practical use of this phenomenon. And
then there are also versions of that happened in a
recording situation that you actually have to be careful, right,

(29:40):
you have to correct for Yeah. So for for soundproofing,
there are a couple of different UH measuring systems to
determine how soundproofed a room is, and they may or
may not be useful to you if you are trying
to do something like create a recording studio. So, for example,
in the United States, the we typically use something called

(30:01):
the sound transmission class to explain how soundproofed a room is,
and that's really a measurement of how well sound within
the ranges of human voices travels through walls, so sounds
outside of those frequencies it sound transmission class isn't concerned
with them, because it's really more about building walls so

(30:23):
that sound doesn't pass or walls and floors and ceilings,
not just walls, but all the all the surfaces so
that sound does not pass easily through one uh and
into another. This would be like what hotels would be
really concerned with, or people who are building homes. UM.
That range, by the way, is about hurts to four
thousand hurts or four killer hurts. That's the that's the

(30:44):
typical range of frequencies of the human voice. So that's
really what sound transmission class is concerned with. And it's
designated by a number, and in general, the higher the number,
the better the quality of soundproofing is. So if you
were in a room that has it's like a really
kind of lousy dry wall partition, it doesn't have a
whole lot of you know, like it doesn't have that

(31:05):
that absorption insulation or anything like that. Uh, the number
might be somewhere around twenty. But let's say you're in
a high end hotel that has taken great pains to
create decoupled walls with good absorption insulation, some maybe some
dampening material in there too. That might be closer to sixty,
and so the higher number designates that it's more sound

(31:27):
proofed than the other one. But again for that given
range of frequencies. The stuff outside of that maybe not
so much. Outside the United States, people tend to use
was called the sound reduction index. Uh it's it's the
s r I. So that rating tells you how many
decibels in reduction the material will provide. So if a

(31:49):
sound is a certain amplitude, a certain amount of decibels,
which by the way, is not a not a it's
a logarithmic scale, so it's pretty complicated, but it'll tell
you how many decibels it will reduce a sound that
is generated from one space and into an adjoining space. UM.
It's depending also upon frequencies, because some are designed to

(32:12):
it's it's something that's specifically designed to cut out those
mid to high range frequencies. But it won't necessarily uh
like that material won't necessarily cut out low frequencies. So
if you get this s r I number, you have
to also ask, well, what what range of frequencies is
that for, Because it's not a blanket statement. It's not
saying that any sound at any decibel will be reduced
this amount, then you finally have noise reduction coefficient. Uh.

(32:36):
So this tells you how much sound of material can
absorb versus reflect Um. It's it's expressed as a percentage.
So really the percentage that you're looking at is the
percentage of sound absorbed by that material. A carpet with
a rubber underlay might have a point for rating. For example,
that means it would absorb of the sound that hits

(32:56):
it reflecting back. Um. Like a hard concrete wall might
be a point oh five, meaning it absorbs only five
of the sound that hits it and gets reflected back. So, uh,
those are those are how you would you know, that's
like the metrics you would use. You would use actual
instrumentation to detect how the sound is reverberating in the room,

(33:19):
and you would, you know, obviously use things like microphones
and stuff outside of a room to detect if there's
any sound leaking out. There are also some things you
gotta take into account, um, some natural weak spots. If
the room has a vent in it, which you kind
of hope it will because otherwise things get real stuffy,
real fast. Uh. The vent also may need to be treated. Ideally,

(33:42):
the vent will be treated with some of this material
to dampen some of the sound. Otherwise it's just a
conduit for sound to travel through. Yes, So the room
we're recording in right now, it was built out for
us with some of these specs in mind. Um. We
we chose the material based on the rating and we
went with oviously a higher number UM. And then this
glass window that I was telling about earlier that's specifically

(34:05):
designed for a studiotype environment. And what we have on
the walls in here are similar to the layout of
that World's Quiet room most talking about, except these are
acoustic tiles that are made up of their squares and
they're made up of strips in a single direction, but
the panels are alternating. So we have one where they're
facing up and down, the one next to it they're
going left to right, etcetera. And they altered it and

(34:27):
that helps break up the sound and um, you know,
make it a more uh dampened sound within the room
and keep the sound from escaping as well. But we
actually do have event in this room and it's not
particularly well treated. So what I actually end up having
to do is use a very nifty bundle of software
to take a print of the room tone, so you

(34:49):
can there's a base level where if Jonathan and I
were quiet right now, you probably and we sent this
out without running this process, you would hear that base
level room tone, air conditioning ound, whatever. So what I
can do with the software is analyze thirty seconds a minute,
the longer the better of that baseline sound than the
computer analyzes that, and then I apply it to the

(35:11):
whole audio file and it gets rid of it and
no artifacting at all. When I want to say artifacting,
I mean there's no digital debris leftover where you can hear.
Oh there, here's the sound of the effect working. It's
completely transparent. And this sweet software is about two thousand dollars,
so right, they're a really good job. There are a
lot of suftware packages out there that that attempt to

(35:32):
do something similar to that, like a Audacity has the
noise removal tool, which is a very similar thing. It's
looking at specific frequencies and then it looks through the
entire track for those frequencies to remove those. Problem is,
of course that if you have other stuff laid on
top of it. Audacity doesn't necessarily it's not necessarily able
to go in and remove just the stuff that you

(35:54):
want removed and leave everything else untouched. So, uh well,
my experience with things like this has has always been,
Now it doesn't work, you can always tell. You can
always hear it kicking in or whatever. But just in
case anyone's interested in, this software i'm talking about is
by a company called Isotope, and it's a package called
r X Advance, and it's a suite that has multiple
um little modules that can do different things like let's

(36:16):
say you're picking up a hum or some kind of
radio interference. It can isolate things like that. But the
one I always used to give it to that air
conditioning noise is it's called de nois Er and it's
it's fantastic cool. And the other thing that you have
to worry about besides the vents are obviously doors. You
want to have. Make sure that your doors have proper
ceiling all around it. Ceiling s S E A L

(36:37):
that kind of seal. Yeah, Like in a recording studio
control room, you might see a door that has a
heavy rubber um strip on the bottom of it that
when you close it, it literally makes a seal between
the door jam and the bottom of the door, so
it's air tight. Yeah, because otherwise sound will just travel
underneath right underneath it the gap. You've done all this

(36:57):
other work and then you have a gap in the
bottom of your door. Yeah, you might as well have
done nothing right. It's it's not gonna it's not gonna
give you the results you want. So no, you know,
we were talking before we start recording that, you know,
the concept of making sure the sound within a room
sounds right, and this goes beyond soundproofing, but it was

(37:18):
also part of of the question sent into us. Noel
and I have a bit more to say, but before
we get to that, we're going to take another quick
break to thank our sponsor. So walk us through kind
of the process. If you were setting up, say a

(37:39):
recording studio for music, that would be obviously you would
want to make sure that everything is just right to
capture the music as the artist intended. You know, you
might do some alteration on it on the back end,
but you want it captured as pure as possible at
the recording session. Yeah. This this goes into kind of

(38:00):
philosophy in some ways. Some people might want more of
a live room that has some character, some nice acoustics
or something like that. And for certain things, like say
recording a vocal, you might want a room with as
little character as possible. So you're just getting the quality
of that voice through that really nice microphone and microphone preamplifier,
which is what you plug a microphone in that kind

(38:21):
of boost that signal and makes it audible and makes
it at a level that can then be recorded into
the computer or tape machine or what have you. UM.
So that's one way of looking at it. Like for
a quiet room, like a completely dead sound booth, let's say, UM,
then you might have different little tricks you can do.
Like so at a drum room, for example, there are

(38:43):
ways you can use panels of wood on the floor.
You might take a strip of wood and place it
right underneath the kick drum the bass drum, and have
a microphone kind of at the end of that, so
you're the sound of the drums are sort of reflecting
off of that wood and creating kind of a cool
diffew room sounds. So you when you mike drums, you're

(39:03):
making them up close. You're putting a microphone right up
on the tom tom or the snare of the kick,
and then a lot of times people will mix in
the sound of the room, which is the whole kit,
and then kind of blend those signals together so you
get that direct sound, which you also get this nice
roomy tone. So in that situation, you might want a
little character in your room, and you might use things
like I'm talking about these strips or what have you

(39:24):
to achieve some sort of character. Now, let's say we're
talking about a control room, which is where you're going
to be mixing your your music. So you have really
high end, very nice, high fidelities studio monitors which gives
you your playback. And you know, the best studio monitors
are considered to be very um flat. That's that's the

(39:45):
word that's used, where the frequency response isn't particularly um
it's not it's not messed with on the speaker side.
So everything that's coming out of there, you know, is
going to be accurate based on what you're doing, what
you're putting into it, the frequencies you're adjusting on your
mixing console or in your computer. The monitors themselves aren't
imparting any tone or quality beyond what you're doing to

(40:09):
it right there. They're just they're just neutral and only
presenting the stuff that you've told it to mean a
lot of times they're referred to as reference monitors because
you the idea is, and it's not always the case,
um that the way it sounds on those monitors, it's
going to sound like that anywhere you play it. Obviously,
there are things that happen after you finish a record

(40:29):
called mastering, where you you kind of adjust to account
for different types of systems that might be played on
to make sure it sounds as good as possible on
any system. But in a control room when you're playing
back your music, you don't want bad reflections. You don't
want that sound coming out of the speakers to bounce
back at you in a way that changes the quality

(40:52):
of that sound. You want it to be as flat
and clean as possible. So there are little extra touches
you could put in a control room that absorb certain frequencies.
Like you said, certain materials will absorb certain frequencies better.
There are things you might put in the back corners
of the room that fill up a corner where two
walls meet, called base traps, and they are these kind
of tall. They can be round or squared off UM

(41:15):
and they're made of kind of dense fibroglass material covered
in a particular type of fabric, and those absorb some
of those base frequencies so that it's not bouncing back
at you and muddying up your mix. Then you might
have a lot of times you'll see in a recording
studio in the control room where you have your big
mixing console, and then directly behind it against the wall,
a lot of times there's a couch, and then above

(41:36):
that couch there might be a weird looking wooden panel
that has smaller arrays of these alternating little UM tiles
sort of like what I described we have in our
room here, but smaller and and a little more dense,
and those are designed to do different things to other
frequencies like the mid range or the high um. Another
thing that's really important in UH these control room settings

(41:58):
is where the monitors speakers are placed. So what you
might do is have an engineer UM that specializes in
you know, do building out recording studios and tuning room
that's what they call it. Go in there and use
a device that that measures the way frequencies bounce around
the room and you would generate what's called a test

(42:18):
tone or some white noise even um which is just
like you know, static kind of sound. And then you
can use this device, this handheld device, it might be
cooked up to a computer. There's lots of different ones
UM that will then take a print and analyze, Okay,
this is what the sound's doing. This is where this
room needs some work, where we need to move the
monitors a little further away or a little closer to

(42:39):
the wall, et cetera. So that's just a few of
the ways that you can um affect how the sound
is actually heard within a room for different situations, whether
you're recording, whether you're mixing and listening, it's all about that.
There are different scenarios that require different treatments. Sure, and
and anyone who's listened to you know, live albums versus

(43:02):
studio albums, or for me, even just with classical music,
Like if you ever listened to classical piece that was
recorded in a big sound studio where you know they
got the whole orchestra in there, it can sound really amazing.
But then if you hear the same sort of thing
but it's played in a concert hall, even without an audience,
the effect is measurably different. You get that character you

(43:24):
were talking about of the space, and different spaces have
very different characters. Just as musicians may have a favorite
type of amplifier that they like to use because of
the tone that it helps, uh, the tones that accentuates
versus the ones that it doesn't accentuate as much. Uh.
You have the same sort of stuff with these these rooms. Now, no,

(43:46):
let me ask you this. Let's say that some of
our listeners out there are wanting to set up like
a little home recording area. Maybe they want to do podcasting,
maybe they want to record some acoustic music, nothing to complicated.
What would be some general guidelines you would give somebody
who wants to set up a space in their house

(44:08):
meant for recording, Like, what were what would just be
some general tips, not like the super like you're gonna
go and remodel your home kind of approach, but but
more simple ways that you can at least limit problems
with sound from exterior sources or uh interference with the
sound that you're creating in the room. What are some

(44:29):
of your tips you would give. I mean, there's a
lot of different ways that you can um make spaces
in your home work, and all depends on what kind
of music you're trying to record. UM, So the choice
of microphone would make a big difference. For example, so
the microphones that we use in the podcast studio or
what are called dynamic microphones, and we've talked about this
in the past episode. I believe um they tend to

(44:50):
record best things that are very close to them and
don't necessarily pick up as much ambient room sound as
what's called a condenser microphone would. Now, some might say
the condenser microphone gives a richer, bigger sound, but it
also depends on how you use it. UM, So I
might recommend for recording vocals trying to go with like
get a really nice dynamic microphone, like one of these

(45:13):
a sure SM seven B microphones will use and there
you know, they're about three hundred bucks. They're not cheap,
but um they allow you to record uh much closer proximity.
So if you're recording a guitar, for example, through an amplifier,
you put it right up next to that amplifier and
crank it so that it's not recording. The signal to
noise ratio is what's called is in favor of the signal,

(45:36):
So the sound of the amplifier is uh the main concern.
There's really no worry about recording any room tone. And
you don't even have to crank the amp up that
high because the mic is so close. But in terms
of little things you can do for dampening, I mean,
get get a pack of egg crate or like some
acoustic tiles from or lex, you know, and it's not

(45:56):
cheap either. But then just make some little clusters, you know,
make a few little squares on your wall if you can,
like if you have a closet door, maybe put three
or four panels and then record facing that, you know. Um,
there are also these shields you can get you can
attach to your mic stand and basically is like a
um almost like a half moon shaped shield that goes

(46:18):
behind the microphone so you're facing it and that cuts
down on reflections. Um. There are lots of little tricks
like that that you can do. But at the end
of the day, UM, it's just about how you use
the stuff that you have for podcasting. Definitely go with
a dynamic microphone, talk very close to it so that
it's only getting your voice and it's not recording your

(46:40):
cats or the sound of your conditioning things like that. Um,
the lower you can turn up the mic and still
get a really good signal, the better off you are,
because if you have to crank it up really high,
you're really far away from the mic, you're gonna be
picking up a whole lot of that room sound. Yeah,
I I can tell you from experience. I record a
couple of shows from home just for fun that that

(47:01):
aren't work related, and I used to use a condenser
mike because they were they were easy. I had a
USB condenser mic um and and there's nothing wrong with
the MIC's. I'll even tell you I had a blue
Snowball for a while, and we have one here we
we've used it occasionally, mostly to connect through Skype or whatever.
We don't record through it, but we use it to

(47:22):
to pick up our voices so people on the other
end can hear us. UM. And I also had a
blue Yetie microphone. Both of them are great. I love them,
but for podcasting, like you were saying, they pick up
pretty much everything. And in fact, if you were to
go back and listen to some of those podcasts I did,
you would hear, like, what's that weird clicking noise and
hearing in the background, And that clicking noise would have
been my dog's toe nails clicking against the hardwood floor

(47:45):
as as he just ran across the floor and he
wasn't making any other noise. It's just click click click clicklick.
But that condenser mike picked up everything. And it all
comes back to what we talked about sound being sort
of this organic thing that moves. I mean, you're never
going to completely get rid of every bit of room
noise unless you are going above and beyond. You're going
to that crazy world's most silent room approach. But you

(48:07):
can mitigate how much of the sounds you don't want
are recorded based on where you set up the mic.
You want to be as far away from any noisy
sources as possible. You certainly wouldn't want to record a
podcast right next to your fridge. If you have an option, uh,
if you have an internal room where it doesn't share
an external wall, that would be a good choice. Um

(48:30):
like like the place where my microphone is set up.
I don't have a room that's into All of my
rooms face outward one way or the other. So I
don't have a room that I can that is that
is isolated where I could record from. UH. So my
mine is not ideal because I also live across the
street from UM railroad tracks and Marta tracks UH and

(48:52):
a busy road. So I'm just fortunate that when my
house was being built, they built it with that in mind.
They were building the external walls so that they would
dampen that sound as much as possible, because the home
builders new while we're right next to some train tracks,
so we have to take that into account when we're

(49:13):
designing this. Unfortunately, it doesn't often impact my recording. Once
in a blue moon, if there's a freight train going
by blasting its horn, you're gonna hear it. But otherwise
it doesn't come through. So just to wrap up on
this whole you know home podcast set up, I can
give you a really good practical example of our show
stuff you miss in History class Um. The host live

(49:33):
in different cities. Holly Fry lives here in Atlanta and
records in our studios, and Tracy Wilson lives in Boston
and records from her home. And so when she was
getting ready to move, we had to figure out how
we were going to set this up. So I kind
of looked into it and did some research and recommended
what to get, and what we ultimately went with is
she has this It's called the sound shield, I guess
it is the best way of referring to it. A

(49:55):
company is called sc Electronics. The product is a reflection
fill to ex portable vocal booth and the idea is
that the way it's pitched on on Sweetwater, which is
the music equipment site that I'm looking at. Um, it
is a portable acoustic treatment to reduce room ambience in
untreated recording spaces. So it works pretty well as advertised.

(50:17):
So it's this thing that kind of wraps around the
back of the microphone connects to the mic stand. Um.
So she has one of those behind her against the wall.
She has a heavy curtain like we talked about earlier
as well, and so that helps dampen the sound that way. Uh,
And she's using this sm seven b um dynamic sure
vocal mic or microphones on doesn't have to be a

(50:37):
vocal mic. But she is next to a window. So
whenever the trash pick up comes or if there's a
motorcyclist something like that you know, we've got to stop,
so you deal with what you have. And I think
she's a pretty good example of a successful home set
up as well as as as is yours. Jonathan. Yeah,
if you if you listen back to um some of
the episodes that we recorded before we move to pot

(50:59):
City Market, there was a brief period where we were
set up in an office, uh like an actual It
wasn't designed to be an audio recording studio, but was
an office at the old office space and Buckhead that
shared a a window facing Peach Tree or near Peach Tree.

(51:21):
And if you listen carefully to some of those old podcasts,
not just Tech Stuff, but all the other ones we
record at How Stuff Works, you might occasionally hear a
little high pitched noise and wonder what that was, And
that was Baton Bob. There was also sirens. Those were
the bane of our existence. YEA, sirens we would stop for,
like we if we heard the siren the whistle. Baton Bob. Yeah,

(51:44):
Beaton Bob is a a kind of a fixture here
in Atlanta. He is quite the character and often can
be seen marching up and down the various streets of
Atlanta in a tutu and twirling a baton and blowing
a whistle and he's a smile all ambassador. I love
baton Bob, Absolutely love him. Great guy. Uh, not fantastic

(52:06):
to have to record a podcast. Was you're hearing is
in whistling up and down the street and talk about
d I y setup. We had those windows covered over
with I made these panels out of that pink panther
foam installation for construction, and I nailed them and stapled
them to pieces of luan and then had them attached
to the window to cover them over. And then on

(52:28):
top of that we had this bright red um acoustic
foam in sheets that would be you know, staple on
top of that, and it still didn't block out and encies.
We couldn't do anything permanent because that that wasn't something
we were allowed to do in that space. It wasn't
meant to be a recording studio. So we were just

(52:49):
doing the best with what we had um. But yeah,
it was, it was. It was difficult, so it can
be a challenge, but the stuff is out there. It's
not like like Noel is saying, it's not necessarily cheap.
You can do some relatively inexpensive things to limit U
sound issues. But obviously you get what you pay for
the more that you are able to spend on that.

(53:12):
But do your research. But the more you're able to
spend on that, the better result you are going to get.
In general, just make sure that whatever outlet you're going
with is highly rated. You know, don't just hire a
general contractor and and go with that, because that's probably
not gonna give you the results you want. But obviously,
you know, these are things that people in all sorts

(53:35):
of of jobs and and positions, uh, worry about. Whether
it's professional recording artists, whether it's podcasters like us home
podcasters you just want to record a demo. I mean,
these are the sort of things you got to think about.
So thank you very much for writing in and requesting
this episode, and Noel, thank you for joining me today.

(53:57):
Usually you're on the other side of that window we
were talking talking about. It's true, it's nice, too nice
to pass through. Yeah, it's it's great to be on
this side once in a while and not stay so
long that the room gets super stuffy. Uh. This that's
one of the things that this room in particular, it
does get a little warm. Now we we fixed the
stuff you should know podcast room because it used to
get blistering lee hot, and now it gets very cool there,

(54:22):
and now the opposite seems to happen here. But I'm
afraid to ask for anything because I don't want to
end up getting Gail Force winds into the podcast studio.
That wraps up another classic episode of tech Stuff. Hope
you guys enjoyed it. If you have any questions, comments, requests,
you can send me an email the addresses tech stuff
at how stuff works dot com, or pop on over

(54:42):
to Facebook or Twitter. They use the handle tech stuff
HSW that message will get to me. Don't forget. You
can visit our website that's tech stuff podcast dot com
that has a link to every single episode we've ever published,
and it also has a link to our online store
where every purchase he make goes to help the show
and we greatly appreciate it. I'll talk to you again
really soon. Text Stuff is a production of I Heart

(55:08):
Radio's House Stuff Works. For more podcasts from I Heart Radio,
visit the i heart Radio app, Apple Podcasts, or wherever
you listen to your favorite shows.