Bad acoustics in my living room (with sound samples)

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Bad Acoustics In My Living Room (With Sound
Samples)
By sharing with you some samples of poor acoustics, you'll be able to recognize and diagnose them in
your own environment easier.
I had no idea just how bad the acoustics in my livin room were until I bought an ECM-8000 test mike
from Behringer. Listening to things through the mike rather than with my own natural ears, you can
hear all the flaws. Conversation and television become too garbled and "smeared" to understand.
Boomy at some frequencies, and thin at others, I was surprised at what I heard.
Our ears compensate for a lot of laws, but microphones are cold and unforgiving. It's better to fix the
problems in your room than to record them or allow your mixing environment to be influenced by
them. These sound samples are designed to open your ears to the problems you may be hearing
subtly now, but your ears and brain remove from the equation.
Flutter Echo
This is the echo that occurs between two parallel walls. High frequency sound bounces back and forth
without being absorbed or diffused and rings, very much like the feedback you get when you put an
open mic too close to the speaker.
Actually, it's very similar to feedback, only in a purely acoustical environment, so if there's no sound
source feeding it (like the amp), it eventually dissipates. Usually in a matter of seconds.
Think of this as like being between two mirrors, and looking at a reflection that goes on into infinity.
The better the reflectivity of the two surfaces, the longer the flutter echo lasts.
Room Modes
Bass frequencies also travel back and forth without dissipating. The difference here being that
because bass frequencies are so large - some the size of your living room - they create huge "waves"
of sound with high and low points in your room. Some people believe that making the walls non-
parallel will help eliminate room modes because the wave will be misdirected sleightly each time it
bounces and dissipate faster. While there may be some truth to this statement, what this does is
create a more unpredictable environment with "hot spots" in different locations.
Fill your sink 1/3 to 1/2 of the way full of water (or a plastic tub of water is even better because you
can shake the sides and rock it back and forth). Then use your palm to start moving the water in one
spot up and down. Your hand is now influencing the water the same way a low frequency sound
source influences the room.
You'll find that different frequencies - different rhythms - influence the water in different ways. Some
rhythms will cause the water to start rocking back and forth quickly, while others just sort of splash
around. Others work against the wave as it bounces off the opposite wall.
When you have the water going back & forth in a strong motion you'll find some areas are highly
affected, while others seem relatively calm. You'll also notice that different frequencies cause
different peaks and valleys, and where you start is less important than the dimensions of the tub.
Drop tiny pieces of paper in the water if you're having a hard time seeing the movements.
Comb Filtering
Comb Filtering is reverb that crowds the original signal. The peaks & valleys of it's waveform combine
with the original and emphasize certain frequencies while cancelling out others. A lot of people end
up with some nasty comb filtering when they apply reverb in a heavy handed manner, or don't add a
few milliseconds of delay in before they do it.
The result is a nasty, metallic, thin sounding signal. The extreme version is the "in the toilet" swirly
wooshy sound. I discovered a neat trick when recording guitar amps early on. I'd stick an empty
coffee can over the mic and you'd get a fun, thin sound. I've been trying to replicate that all day
today, but I don't have any empty coffee cans.
That reminds me, this sound is also similar to "putting a seashell up to your ear" or cupping your
ears. Very similar to your phase or flange effect isn't it? Well, in a sense, it is a phase effect because
it's delaying some of the signal by just enough to cause it to be out of phase with the original signal.
Samples
The following samples were made with my Behringer ECM-8000 test mic. It's omnidirectional and
reasonably flat. It makes my room sound a lot shittier than my ears normally do, though you can't

2. really tell from these samples what the room sounds like to ears. The noise around 16k is my
computer fan. I recorded them all at the same level without changing any settings, and did no post-
processing, other than to convert them to mp3's.
Note: The acoustics in your room will affect the way you hear these files. I recommend, especially for
the Room Modes file that you listen to them via headphones... and keep your finger on the volume
control.
Flutter Echo
I stuck the mic up by the ceiling, aimed at the corner. Then went to the opposite wall and
started clapping.
Room Modes
Sine Wave Sweep from 200 to 20hz. Around 20 seconds into the sample, a huge sound wave
came at me from all around and nearly made my ears pop. The noise you hear is me moving
around. Also take into account the limitation of the speakers.
Comb Filtering
I hung the microphone inside a metallic thermos bottle... no coffee cans being on hand.
Other Articles in this Series
Bad Acoustics In My Living Room (With Sound Samples)
Acoustics Crash Course 1 - Modes
Acoustics Crash Course 2 - Reflectivity
Room Mode / Standing Wave Calculator
Room Reverb / Sabine Calculator and Charts
See also Ethan Winer's article "Acoustic Treatment and Design for Recording Studios and Listening
Rooms"
page first created on Saturday, April 19, 2003
© Mark Wieczorek