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SOME THOUGHTS ON ACOUSTICS AND MY LISTENING ROOM
ACOUSTICS
I’ve been spending some time recently thinking about room acoustics. The
sources of my information are articles in UHF (Ultra High Fidelity) magazine
numbers 77 and 78. Both of these articles have information on room modes
and this has made me curious as to what sort of modes are occurring in my
listening room.
Room modes are those frequencies that create standing wave due to the
dimensions of the room. Every room has them.
There is a downloadable Excel program mentioned in issue 77 of UHF that will
calculate room modes based on the room’s size. I have tried to download it
but every time I do, Microsoft Internet Explorer tells me that it has a problem
and has to close down. (This has been happening a lot lately and I’m really
tired of it.) Try it yourself at www.uhfmag.com/Tech/roommodes.xls maybe
your luck will be better.
I have had better success running a more basic room modes program from
the RealTraps website. This program deals only with the axial modes of the
room: the height, width, and depth modes of the room. These are also the
most important modes acoustically. (www.realtraps.com) This program
prints out all of the axial modes less than 500 Hz as either a bar graph or as a
list of frequencies. You can use this program to ascertain just what modes
you have in your room or, if you are thinking about building a listening room,
to check the design for potential problems.
Once you have run the program, the question then becomes how to interpret
the results shown in the graph. There is not a lot of information provided on
analyzing the results, except that you do not want the height, width, and
length to have modes close to or at the same frequency. One way to get
some idea of how good or bad your room is is to run the program again using
one of the recommended room ratios noted on the RealTraps printout. These
ratios will give an example of what the modes look in a room with more ideal
dimensions. You can compare this printout to yours.
My listening room has a slightly over 7 foot ceiling (the highest that could be
built, unfortunately), a width of 23 feet and a length of 28.5 feet. I compared
the modes from my room to the modes of the largest room for which ideal
ratios were given. The ideal ratios are: 1:1.6:2.33; assuming an 8 foot ceiling,
this gives an ideal room of 8 X 12.8 X 18.6 feet. Frankly, not a terribly large
room. Certainly the width is just about the minimum that I would want to live
with.
My room graph has several modes where the room dimensions interact very
close to each other. For example, the length of the room has a mode at
198.25 Hz and the width has a mode at 196.52 Hz—pretty close together.
Looking at the ideal ratios mode printout, the room modes are clearly more
separate and have fewer points where they overlap or rub up against each
other.
I pulled out some measurements that I have done using the Stereophile Test
Record 1 in my listening room and compared these measurements to the
RealTraps room modes printout. There is a room mode on the printout near
80 Hz. I also have a 3 dB bump there in the measurements that I have
done. That would seem to be exactly what would be expected. The printout
indicates a mode at about 200 Hz, which should predict another bump, but
measurements indicate the opposite, a trough. It seems to me that while you
can predict the room’s modes, you can’t really predict what will be happening
at exactly the spot where you are sitting. You will be sitting in a
reinforcement of some frequencies and a cancellation of others.
I may hook up my frequency generator and do some further measuring with it
since I can target specific frequencies and see how those measurements
correlate with the predicted room modes.
I would certainly recommend playing with this program as well as reading the
UHF articles. This information will help explain some of the behavior taking
place in your listening room. I have found the RealTraps program easy to use
and feel like I have gained a better understanding of what is happening
acoustically in my room.
SPEAKING OF LISTENING ROOMS…
When you go to the RealTraps web site, follow the link on the home page to
an article by Stereophile reviewer Kalman Rubinson; it has photos of his
listening room. I always find it interesting to see what a reviewer’s room is
like.
Let me state that I don’t have a perfect listening room, although, I think it is
pretty good, nor am I taking a cheap shot at someone I don’t know, BUT I
was disturbed by a couple of things about Mr. Rubinson’s room. First, he has
a coffee table piled full of CDs directly in front of his listening position. Having
anything between the listener and speakers is asking for an acoustic problem,
especially something with a flat hard surface. I was also concerned by how
close to his left speaker his equipment rack sits. The left speaker has to be
working in a different acoustic environment than the center or right
speakers. At least the room is decent sized.
Kalman is welcome to come over and dis my room at any time of his
convenience.
Over the years a number of magazines have run profiles on their reviewer’s
listening rooms. I have seen a number of these articles in The Abso!ute
Sound, Hi Fi News, and Hi Fi + and found them very interesting. In quite a
few cases, I have been shocked, yes shocked, to see the sort of room some
reviewers are listening in—not just listening, but making widely-read,
influential judgments regarding equipment and recordings. Some of these
reviewers have passed judgment on equipment, often very expensive
equipment, in rooms that should have gotten their opinions laughed at if not
readily dismissed. I remember someone at Hi Fi News (years ago) who was
listening in a ten foot square room. I have a spare bedroom that size and I
cannot even imagine how it could make a tolerable listening room much less
one in which serious evaluations could be done.
Alas, I don’t think reviewing in a “questionable” room is an uncommon
occurrence. While reviewers pretty much universally list the equipment and
recordings they are using for evaluating equipment, without knowing
something about the room they are in, you really can’t take their conclusions
too seriously. I think if we knew as much about a reviewer’s listening space
as we know about his equipment, we would be a lot less impressed by what
he has to say, which is unfortunate.
The listening room truly is another component of the audio system. Because
changing it is difficult, even impossible, we tend to ignore the whole issue of
the room and just pretend it isn’t there. This is wrong. While most of my
hardware components are fairly modest in high-end terms, I do have a good
listening room, which can realize my component’s potential. I think this is
musically far preferable to having the most expensive equipment available
situated in a lousy room*.
Since I like to think of what I do as reviewing, the time has come to provide
more information on my own listening room. Click here for a sketch. (A few
notes: the small boxes marked with a “B” are the bass boxes. Outside of
them are the MG 10s and outside of the MG 10s are my homemade room
lenses. A third room lens sits between and behind the speakers. There is a
table with a lamp to the left of my listening position. Note the axis running
through the listening position; this will be discussed below. My wife uses the
19 inch TV to run exercise videos. I hope everything else is self-
explanatory.) Click here for a photo that shows the equipment end of the
room.
My listening room is in a basement, it has thick Berber carpet and pad over a
concrete floor. The walls are half-inch drywall attached to metal studs. The
ceiling is half-inch drywall attached to resilient channel. The entire room is
insulated. The ceiling has six inches of insulation, the walls three. Bookcases
were planned for the back wall to help damp the energy in the room. I have
four dedicated AC lines available to me—three 20 Amp and one 15 Amp.
There are two support columns within the room, which I have managed to
work around fairly well.
There are two things that I gave a considerable amount of thought to while
planning this room. One was where to place the equipment rack and the
other was how to situate the speakers within the room.
It might seem retentive to spend a lot of time on something as seemingly
simple as locating the equipment rack but in fact the whole question of where
to put the equipment has a large bearing on the sort of equipment you use
and the costs involved in using it.
The simple fact is that there is no good place for the equipment rack within
the listening room. Most of the time, the rack is situated between/behind the
speakers. This has the advantage of keeping both interconnect and speaker
leads reasonable but the equipment is subject to all the acoustic energy
traveling throughout the room. Situating the rack along any of the other
walls requires either long interconnects, which requires a preamp with good
output, or long speaker wires, which can present problems for some amplifiers
that don’t like high cable capacitance. No matter where the rack goes, you
still can’t be sure your components aren’t getting their internal parts rattled
at some frequency.
The best location for components is actually outside of the room. They can
be ventilated properly and protected from acoustic energy. This isn’t terribly
practical, although as more and more equipment comes standard with remote
controls, it is at least potentially feasible. Certainly, if I could design a
listening space from scratch, I would give a lot of thought to putting
everything but the speakers outside of the room. I think it can be done.
What I decided to do in my listening room, I view as the next best
compromise. I built an alcove for the equipment rack, accessed by a door at
the rear. This has several practical and theoretical, i.e. I haven’t been able to
come up with any way to actually test them, advantages.
The practical advantages are short interconnects and reasonable length
speaker cables. The front and rear of the equipment is also easy to get to.
The theoretical advantages are that the rack is seen by the speakers as part
of the wall behind them, while the equipment on the rack is sheltered to some
extent from vibrations within the room. The alcove itself undoubtedly acts as
a resonator at some frequency but in over six years of listening, I have never
detected any coloration that I could identity. Is it a perfect setup? Of course
not but it is better than having the rack sitting in the corner of the room
being battered by bass frequencies. Actually, I thought it was a pretty clever
idea when I came up with it.
The second thing that I have experimented with is the location of the
speakers themselves. Typically speakers are set up on either side of an axis
that runs parallel to the side walls of the room. It’s a symmetrical orientation
around the center line of the room. In my room, the left speaker is just over
three feet from the east wall of the room while the right speaker is about
eleven feet from the west wall. This concerned me. My solution was to run
the speaker/listener axis non-parallel to the outside walls. You can see this
on the sketch. With his set up, the distance from either speaker to any wall is
unique. While I can’t do anything about the modes native to the room’s
dimensions, I can potentially not add to the problem with a symmetrical
speaker set up. Again, in six years of listening, I think this has worked out
very well. It is certainly worth experimenting with if you have the room to do
it.
What of the room’s weaknesses? I would list them as a ceiling lower than I
would like and a glass patio door that I should have gotten rid of when I built
the room. I was reluctant to give up the light the door brings in but it is
single pane glass and the heat it loses is just unacceptable. If I were staying
in this house indefinitely, I would remove the patio door and frame in the
opening to fit a large exterior door. The extra wall space would be useful for
more CD racks. I also wish the furnace/AC was in a different place. While it is
actually well-muffled by the wall insulation, air noise through the ducts can’t
be completely eliminated. I want radiant hot water heat in my next home.
A couple of more thoughts and then I’ll shut up.
While I am very concerned about global warming, I did not use any fluorescent
lights in this room. Fluorescents buzz, even the little ones that fit in your
table lamp. A fluorescent fixture placed in a ceiling will heat up, damage the
ballast, and buzz even worse. I also do not like halogen lamps as they can
also feed a 60Hz hum back through the electrical system. I used a halogen
floor lamp for a while; it had two settings—300 Watts and 150 Watts. On the
150 Watt setting, I could hear a buzz coming from the Tripplite LC-1200 Line
Conditioner and Stabilizer that feeds the Perpetual Technology equipment**.
There was no noise with either the lamp off or at the 300 Watt setting. I
hated to run a 300 Watt light source just to take notes or read a CD insert.
So I got rid of it for a table lamp that uses a 40 Watt bulb. Fortunately, I
rarely even use that. Beware also of dimmers at less than their full “on”
setting.
Do not assume that having dedicated lines will prevent noise feeding back
through your system. They don’t. All dedicated lines insure is that your
equipment will not be starved for power when your daughter turns on her hair
dryer.
I had some concerns when building my room that it might be too big. These
have proven to be totally unfounded. My amps have had no trouble driving
my relatively inefficient MG 10s to any level I have desired. The room really
looks larger on paper than it feels in reality.
I have had three prior listening rooms and this is by far the best, least
compromised of all of them. I didn’t have the budget to do everything I
would have liked to with this room but I was able to do those things I
considered most important. While I would leave Missouri tomorrow, I would
hate losing this room.
As always, I would be happy to hear from anyone with questions or
comments.
Kent Johnson
February 27, 2007
*To continue in this vein, I also get upset when I read where a reviewer has
recently had dedicated AC lines put into his listening room and, WOW!, it has
really made a huge difference. What are we to think of every judgment he
has previously made? Did that $12,000 amp he trashed as “lifeless and
lacking in dynamics” really have a problem or did his listening room’s electrical
system have the problem?
**The Tripplite is actually located in the laundry room as it clicks when it
reacts to voltage changes such as the refrigerator coming on. There is
enough clicking going on to make having it in the room annoying. Still, it is
one component that you know is earning its keep.
ACOUSTICS
I’ve been spending some time recently thinking about room acoustics. The
sources of my information are articles in UHF (Ultra High Fidelity) magazine
numbers 77 and 78. Both of these articles have information on room modes
and this has made me curious as to what sort of modes are occurring in my
listening room.
Room modes are those frequencies that create standing wave due to the
dimensions of the room. Every room has them.
There is a downloadable Excel program mentioned in issue 77 of UHF that will
calculate room modes based on the room’s size. I have tried to download it
but every time I do, Microsoft Internet Explorer tells me that it has a problem
and has to close down. (This has been happening a lot lately and I’m really
tired of it.) Try it yourself at www.uhfmag.com/Tech/roommodes.xls maybe
your luck will be better.
I have had better success running a more basic room modes program from
the RealTraps website. This program deals only with the axial modes of the
room: the height, width, and depth modes of the room. These are also the
most important modes acoustically. (www.realtraps.com) This program
prints out all of the axial modes less than 500 Hz as either a bar graph or as a
list of frequencies. You can use this program to ascertain just what modes
you have in your room or, if you are thinking about building a listening room,
to check the design for potential problems.
Once you have run the program, the question then becomes how to interpret
the results shown in the graph. There is not a lot of information provided on
analyzing the results, except that you do not want the height, width, and
length to have modes close to or at the same frequency. One way to get
some idea of how good or bad your room is is to run the program again using
one of the recommended room ratios noted on the RealTraps printout. These
ratios will give an example of what the modes look in a room with more ideal
dimensions. You can compare this printout to yours.
My listening room has a slightly over 7 foot ceiling (the highest that could be
built, unfortunately), a width of 23 feet and a length of 28.5 feet. I compared
the modes from my room to the modes of the largest room for which ideal
ratios were given. The ideal ratios are: 1:1.6:2.33; assuming an 8 foot ceiling,
this gives an ideal room of 8 X 12.8 X 18.6 feet. Frankly, not a terribly large
room. Certainly the width is just about the minimum that I would want to live
with.
My room graph has several modes where the room dimensions interact very
close to each other. For example, the length of the room has a mode at
198.25 Hz and the width has a mode at 196.52 Hz—pretty close together.
Looking at the ideal ratios mode printout, the room modes are clearly more
separate and have fewer points where they overlap or rub up against each
other.
I pulled out some measurements that I have done using the Stereophile Test
Record 1 in my listening room and compared these measurements to the
RealTraps room modes printout. There is a room mode on the printout near
80 Hz. I also have a 3 dB bump there in the measurements that I have
done. That would seem to be exactly what would be expected. The printout
indicates a mode at about 200 Hz, which should predict another bump, but
measurements indicate the opposite, a trough. It seems to me that while you
can predict the room’s modes, you can’t really predict what will be happening
at exactly the spot where you are sitting. You will be sitting in a
reinforcement of some frequencies and a cancellation of others.
I may hook up my frequency generator and do some further measuring with it
since I can target specific frequencies and see how those measurements
correlate with the predicted room modes.
I would certainly recommend playing with this program as well as reading the
UHF articles. This information will help explain some of the behavior taking
place in your listening room. I have found the RealTraps program easy to use
and feel like I have gained a better understanding of what is happening
acoustically in my room.
SPEAKING OF LISTENING ROOMS…
When you go to the RealTraps web site, follow the link on the home page to
an article by Stereophile reviewer Kalman Rubinson; it has photos of his
listening room. I always find it interesting to see what a reviewer’s room is
like.
Let me state that I don’t have a perfect listening room, although, I think it is
pretty good, nor am I taking a cheap shot at someone I don’t know, BUT I
was disturbed by a couple of things about Mr. Rubinson’s room. First, he has
a coffee table piled full of CDs directly in front of his listening position. Having
anything between the listener and speakers is asking for an acoustic problem,
especially something with a flat hard surface. I was also concerned by how
close to his left speaker his equipment rack sits. The left speaker has to be
working in a different acoustic environment than the center or right
speakers. At least the room is decent sized.
Kalman is welcome to come over and dis my room at any time of his
convenience.
Over the years a number of magazines have run profiles on their reviewer’s
listening rooms. I have seen a number of these articles in The Abso!ute
Sound, Hi Fi News, and Hi Fi + and found them very interesting. In quite a
few cases, I have been shocked, yes shocked, to see the sort of room some
reviewers are listening in—not just listening, but making widely-read,
influential judgments regarding equipment and recordings. Some of these
reviewers have passed judgment on equipment, often very expensive
equipment, in rooms that should have gotten their opinions laughed at if not
readily dismissed. I remember someone at Hi Fi News (years ago) who was
listening in a ten foot square room. I have a spare bedroom that size and I
cannot even imagine how it could make a tolerable listening room much less
one in which serious evaluations could be done.
Alas, I don’t think reviewing in a “questionable” room is an uncommon
occurrence. While reviewers pretty much universally list the equipment and
recordings they are using for evaluating equipment, without knowing
something about the room they are in, you really can’t take their conclusions
too seriously. I think if we knew as much about a reviewer’s listening space
as we know about his equipment, we would be a lot less impressed by what
he has to say, which is unfortunate.
The listening room truly is another component of the audio system. Because
changing it is difficult, even impossible, we tend to ignore the whole issue of
the room and just pretend it isn’t there. This is wrong. While most of my
hardware components are fairly modest in high-end terms, I do have a good
listening room, which can realize my component’s potential. I think this is
musically far preferable to having the most expensive equipment available
situated in a lousy room*.
Since I like to think of what I do as reviewing, the time has come to provide
more information on my own listening room. Click here for a sketch. (A few
notes: the small boxes marked with a “B” are the bass boxes. Outside of
them are the MG 10s and outside of the MG 10s are my homemade room
lenses. A third room lens sits between and behind the speakers. There is a
table with a lamp to the left of my listening position. Note the axis running
through the listening position; this will be discussed below. My wife uses the
19 inch TV to run exercise videos. I hope everything else is self-
explanatory.) Click here for a photo that shows the equipment end of the
room.
My listening room is in a basement, it has thick Berber carpet and pad over a
concrete floor. The walls are half-inch drywall attached to metal studs. The
ceiling is half-inch drywall attached to resilient channel. The entire room is
insulated. The ceiling has six inches of insulation, the walls three. Bookcases
were planned for the back wall to help damp the energy in the room. I have
four dedicated AC lines available to me—three 20 Amp and one 15 Amp.
There are two support columns within the room, which I have managed to
work around fairly well.
There are two things that I gave a considerable amount of thought to while
planning this room. One was where to place the equipment rack and the
other was how to situate the speakers within the room.
It might seem retentive to spend a lot of time on something as seemingly
simple as locating the equipment rack but in fact the whole question of where
to put the equipment has a large bearing on the sort of equipment you use
and the costs involved in using it.
The simple fact is that there is no good place for the equipment rack within
the listening room. Most of the time, the rack is situated between/behind the
speakers. This has the advantage of keeping both interconnect and speaker
leads reasonable but the equipment is subject to all the acoustic energy
traveling throughout the room. Situating the rack along any of the other
walls requires either long interconnects, which requires a preamp with good
output, or long speaker wires, which can present problems for some amplifiers
that don’t like high cable capacitance. No matter where the rack goes, you
still can’t be sure your components aren’t getting their internal parts rattled
at some frequency.
The best location for components is actually outside of the room. They can
be ventilated properly and protected from acoustic energy. This isn’t terribly
practical, although as more and more equipment comes standard with remote
controls, it is at least potentially feasible. Certainly, if I could design a
listening space from scratch, I would give a lot of thought to putting
everything but the speakers outside of the room. I think it can be done.
What I decided to do in my listening room, I view as the next best
compromise. I built an alcove for the equipment rack, accessed by a door at
the rear. This has several practical and theoretical, i.e. I haven’t been able to
come up with any way to actually test them, advantages.
The practical advantages are short interconnects and reasonable length
speaker cables. The front and rear of the equipment is also easy to get to.
The theoretical advantages are that the rack is seen by the speakers as part
of the wall behind them, while the equipment on the rack is sheltered to some
extent from vibrations within the room. The alcove itself undoubtedly acts as
a resonator at some frequency but in over six years of listening, I have never
detected any coloration that I could identity. Is it a perfect setup? Of course
not but it is better than having the rack sitting in the corner of the room
being battered by bass frequencies. Actually, I thought it was a pretty clever
idea when I came up with it.
The second thing that I have experimented with is the location of the
speakers themselves. Typically speakers are set up on either side of an axis
that runs parallel to the side walls of the room. It’s a symmetrical orientation
around the center line of the room. In my room, the left speaker is just over
three feet from the east wall of the room while the right speaker is about
eleven feet from the west wall. This concerned me. My solution was to run
the speaker/listener axis non-parallel to the outside walls. You can see this
on the sketch. With his set up, the distance from either speaker to any wall is
unique. While I can’t do anything about the modes native to the room’s
dimensions, I can potentially not add to the problem with a symmetrical
speaker set up. Again, in six years of listening, I think this has worked out
very well. It is certainly worth experimenting with if you have the room to do
it.
What of the room’s weaknesses? I would list them as a ceiling lower than I
would like and a glass patio door that I should have gotten rid of when I built
the room. I was reluctant to give up the light the door brings in but it is
single pane glass and the heat it loses is just unacceptable. If I were staying
in this house indefinitely, I would remove the patio door and frame in the
opening to fit a large exterior door. The extra wall space would be useful for
more CD racks. I also wish the furnace/AC was in a different place. While it is
actually well-muffled by the wall insulation, air noise through the ducts can’t
be completely eliminated. I want radiant hot water heat in my next home.
A couple of more thoughts and then I’ll shut up.
While I am very concerned about global warming, I did not use any fluorescent
lights in this room. Fluorescents buzz, even the little ones that fit in your
table lamp. A fluorescent fixture placed in a ceiling will heat up, damage the
ballast, and buzz even worse. I also do not like halogen lamps as they can
also feed a 60Hz hum back through the electrical system. I used a halogen
floor lamp for a while; it had two settings—300 Watts and 150 Watts. On the
150 Watt setting, I could hear a buzz coming from the Tripplite LC-1200 Line
Conditioner and Stabilizer that feeds the Perpetual Technology equipment**.
There was no noise with either the lamp off or at the 300 Watt setting. I
hated to run a 300 Watt light source just to take notes or read a CD insert.
So I got rid of it for a table lamp that uses a 40 Watt bulb. Fortunately, I
rarely even use that. Beware also of dimmers at less than their full “on”
setting.
Do not assume that having dedicated lines will prevent noise feeding back
through your system. They don’t. All dedicated lines insure is that your
equipment will not be starved for power when your daughter turns on her hair
dryer.
I had some concerns when building my room that it might be too big. These
have proven to be totally unfounded. My amps have had no trouble driving
my relatively inefficient MG 10s to any level I have desired. The room really
looks larger on paper than it feels in reality.
I have had three prior listening rooms and this is by far the best, least
compromised of all of them. I didn’t have the budget to do everything I
would have liked to with this room but I was able to do those things I
considered most important. While I would leave Missouri tomorrow, I would
hate losing this room.
As always, I would be happy to hear from anyone with questions or
comments.
Kent Johnson
February 27, 2007
*To continue in this vein, I also get upset when I read where a reviewer has
recently had dedicated AC lines put into his listening room and, WOW!, it has
really made a huge difference. What are we to think of every judgment he
has previously made? Did that $12,000 amp he trashed as “lifeless and
lacking in dynamics” really have a problem or did his listening room’s electrical
system have the problem?
**The Tripplite is actually located in the laundry room as it clicks when it
reacts to voltage changes such as the refrigerator coming on. There is
enough clicking going on to make having it in the room annoying. Still, it is
one component that you know is earning its keep.