hello,

moving along on my iso booth here.

i have a question: let's say there is 3/8" thick carpet padding and
then 3/8" pile carpet on top of that. would you count that in the
vertical height of the room dimension?

meaning, if the room height is 80 inches, would you subtract 3/4" inch
to consider the room height as 79 1/4"?

i'm trying to figure out how tall to make the walls to get a "golden
ratio". since the top coating of the floor will be carpet/padding, i'm
wondering if it's a factor or not.

On 3 Jan 2005 21:32:33 -0800, wrote:

let's say there is 3/8" thick carpet padding and
then 3/8" pile carpet on top of that. would you count that in the
vertical height of the room dimension?

Maybe we should rephrase the question as "How different is the
speed of sound through these materials than through air?", and
then to factor in their relative contribution to room dimensions.

Framed a different way, room modal Q's start to rear ugly heads.

meaning, if the room height is 80 inches, would you subtract 3/4" inch
to consider the room height as 79 1/4"?

Subtract? Fibrous tangles have a slower speed of sound than
fresh/raw/natural/God-given air.

i'm trying to figure out how tall to make the walls to get a "golden
ratio".

You're going to get a lot of BS about this; hang in there. There
is a reason why all natural packing dimensional ratios fall towards
a particular number (or that number plus one). It's religious, but
it's a deep religion that predates us mammals.

Chris Hornbeck
"They'd meet at the Tout Va Bien, a cafe just off the highway."
-JLG, _Bande a part_, 1964

so maybe split the difference and consider 3/8" padding + 3/8" carpet
to be 3/8" total rather than 3/4" ?

wrote:
i have a question: let's say there is 3/8" thick carpet padding and
then 3/8" pile carpet on top of that. would you count that in the
vertical height of the room dimension?

meaning, if the room height is 80 inches, would you subtract 3/4"
inch
to consider the room height as 79 1/4"?

i'm trying to figure out how tall to make the walls to get a "golden
ratio". since the top coating of the floor will be carpet/padding,
i'm
wondering if it's a factor or not.


For the purposes of dimensioning your room for acoustical
considerations, you take the finished height of the room minus any
furnishings or floor coverings. "Golden Mean" room ratios are appealing
because of their even modal distribution, a phenomenon which is only
sonically meaningful at frequencies below those where carpet and carpet
pads make any significant difference. Your room is 80" tall.

However, when it comes time to install your racks, remember your room
is definitely only 79.25" tall!

wrote:
i have a question: let's say there is 3/8" thick carpet padding and
then 3/8" pile carpet on top of that. would you count that in the
vertical height of the room dimension?

meaning, if the room height is 80 inches, would you subtract 3/4" inch
to consider the room height as 79 1/4"?

From an acoustic prediction point of view, the thickness of the carpet
is not significant, however, its absorption coefficients are highly
significant.

If you are planning to use porous absorption in the walls, then their
thickness is significant. A porous absorber of a given thickness will
have a measurable impedance which will, in turn, affect its absorptive
properties. However, the hard wall behind the absorber (with or without
an air gap), is considered to have an infinite impedance.

The impedance of the porous absorber layer(s) on the walls can then be
modelled using a transfer matrix, and you can then arrive at the porous
absorber's absorption coefficients.

I have written a couple of spreadsheets that will predict:
1) The basic acoustic properties of a rectilinear control room
2) The absorption coefficients of a porous absorber

You can download these free of charge from
http://www.rmmpnet.org/members/ChrisW/index.html

Please read the instructions on the download pages carefully!

i'm trying to figure out how tall to make the walls to get a "golden
ratio". since the top coating of the floor will be carpet/padding, i'm
wondering if it's a factor or not.

Don't get too hook up about these "golden" ratios. Recent research by
Trevor Cox et al from the University of Salford (Manchester, UK) has
redefined the meaning of an acoustically "suitable" room. This
completely alters the perceived benefit that many of these ratios are
supposed to provide.

This is because a room's modal frequencies will vary depending on not
only the ratios, but also the absolute dimensions. Therefore, Trevor
Cox has defined the suitability of a rooms dimensions on the basis of
the degree of bass resonance (The lower the better). In the spreadsheet
"Control Room Calculator", there is a diagram on sheet "Room Ratios"
taken from Trevor Cox's website that shows this.

Bolt produced a set of ratios that were considered good (these are often
incorrectly attributed to Sepmeyer)

H:W:L 1.0 : 1.14 : 1.39
1.0 : 1.28 : 1.54
1.0 : 1.60 : 2.33

Of these, the first (1.0:1.14:1.39) is the closest to being considered
good according to Cox's new definition.

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--

GP,

Chris has the right answer, but to summarize succinctly:

Room dimensions for mode calculations are always to the rigid boundaries.
Carpet doesn't count, nor do soft porous absorbers (foam, rigid fiberglass)
mounted on the walls or ceiling. So if you have a suspended grid ceiling
with ceiling tiles, the modal height is to the rigid ceiling above that.

--Ethan

wow, thanks Ethan.

at the likelihood of looking really stupid:

i should count neither the carpet nor the padding in my room dimension
calculations.... pretend the floor really "starts" at the hard stuff
under the carpet padding.

do i have that correct?

wrote:
i should count neither the carpet nor the padding in my room dimension
calculations.... pretend the floor really "starts" at the hard stuff
under the carpet padding.

do i have that correct?

Yes, you are correct.

If you give my Control Room Calculator spreadsheet at try (see my
previous post for the URL), you can put your room dimension ratios in,
and then the width of the room, and it will calculate all the modes for you.

You can also noodle around with different wall, floor and ceiling
materials, and it will plot the absorption curves.

Have fun!

Chris W

--
The voice of ignorance speaks loud and long,
but the words of the wise are quiet and few.
--