[jeffc]

I'm searching for a new house to live in, and one of the criteria is a nice
room to be used as a dedicated stereo room (2 channel). I'm looking at one
house that doesn't have a room yet, but has the space for it. It's a
prewired for power and prevented for HVAC. Basically an unfinished bonus
room over the garage.

The problem is, it's not exactly a rectangle shape. Although it is
symmetrical. But I just don't know how the shape of the room might affect
the acoustics. Basically it has 2 rafters that would jut below the ceiling
at one end of the room (this could be either the listening end or speaker
end). I don't have photos, which I could get next time I look at the house,
but in the meantime is there a starting point for me to learn more about the
negative (or positive) affects of these sorts of room idiosynchrasies?

[Harry Lavo]

"jeffc" wrote in message
...
I'm searching for a new house to live in, and one of the criteria is a
nice
room to be used as a dedicated stereo room (2 channel). I'm looking at
one
house that doesn't have a room yet, but has the space for it. It's a
prewired for power and prevented for HVAC. Basically an unfinished bonus
room over the garage.

The problem is, it's not exactly a rectangle shape. Although it is
symmetrical. But I just don't know how the shape of the room might affect
the acoustics. Basically it has 2 rafters that would jut below the
ceiling
at one end of the room (this could be either the listening end or speaker
end). I don't have photos, which I could get next time I look at the
house,
but in the meantime is there a starting point for me to learn more about
the
negative (or positive) affects of these sorts of room idiosynchrasies?

A few:

* You don't want it to be approximately square...that will almost certainly
create an obnoxious set of bass standing waves.
* An open, so-called cathedral ceiling would definitely be a plus.
* The set of rafters probably would not be an issue (but this is based on
imperfect understanding from your description).

Let us know more. Dimensions or a link to photos would definitely help.

[[email protected]]

Some info on room acoustics can be found at

http://www.audioasylum.com/audio/gen...ges/73758.html

On non-rectangular rooms I've found two papers

Noise control engineering
1979, Nov., p.112 : Van Nieuwland : Eigenmodes in non-rectangular
reverberation rooms

Journal of the Acoustical Society of America
1989, vol.85, p.772 : Milner : An investigationof the modal
characteristics on nonrectangular reverberation rooms

The main difference between the rectangular and the nonrectangular
room is the fact that the axial and tangential modes are not existing,
only the oblique modes are active. This results in a more regular
distribution of the modes than one would find in a rectangular room
with optimum dimension ratios. A regular distribution of modes avoids
the occurrence of large dips or peaks in the frequency response curve.
This led to the conclusion that nonrectangular rooms are superior
(Nieuwland). Milner determined optimum dimensions of a nonrectangular
room with parallel floor and ceiling to be : a = 6,30 m, b = 5,24 m, c
= 10,35 m , d = 7,00 m, e = 7,91 m, with a height of 4,93 m (see Fig.
14 from Milner).

The pressure variation from maximum to minimum for each individual
mode will be the same as in a rectangular room. The superposition of
modes, however, will yield smaller spatial variations.

Figures 5a and 5d (from Nieuwland) show modal patterns of a two-
dimensional room of 5 by 7 m for two different frequencies. The lines
connect points with equal sound pressure. The thick lines represent
the nodal lines of the standing waves.
Figure 9 (from Nieuwland) shows the pattern for a three-dimensional
room. Again, the lines connect points with equal sound pressure. The
dotted lines represent the nodal lines of the standing waves.

Due to the somewhat unexpected behaviour of the modal characteristics
of nonrectangular rooms, the resonance frequencies for each particular
room shape have to be calculated (Finite Element methods) in order to
know whether the frequency distribution is as desired.

Klaus

[WindsorFox[_2_]]

Harry Lavo wrote:
"jeffc" wrote in message
...
I'm searching for a new house to live in, and one of the criteria is a
nice
room to be used as a dedicated stereo room (2 channel). I'm looking at
one
house that doesn't have a room yet, but has the space for it. It's a
prewired for power and prevented for HVAC. Basically an unfinished bonus
room over the garage.

The problem is, it's not exactly a rectangle shape. Although it is
symmetrical. But I just don't know how the shape of the room might affect
the acoustics. Basically it has 2 rafters that would jut below the
ceiling
at one end of the room (this could be either the listening end or speaker
end). I don't have photos, which I could get next time I look at the
house,
but in the meantime is there a starting point for me to learn more about
the
negative (or positive) affects of these sorts of room idiosynchrasies?

A few:

* You don't want it to be approximately square...that will almost certainly
create an obnoxious set of bass standing waves.
* An open, so-called cathedral ceiling would definitely be a plus.
* The set of rafters probably would not be an issue (but this is based on
imperfect understanding from your description).

Let us know more. Dimensions or a link to photos would definitely help.


I agree and I have seen all manner of rooms have their effective
shape changed with acoustical panels. Also if it is a true "bonus room"
with no other function, you can throw up a wall or ceiling anywhere you
like.