Theater room ratio

[Youngin...]

Is there a certain room size ratio that works better for a theater
room? I know that you should not have a square room or one where length
is twice the width but i'm wondering if there is a set ratio that real
theaters use. My room now is 16.5 x 18.5 x 8 but we're going to be
buying a new house soon and I will be building a dedicated room.

young...

[tavsec]

In Boral Plasterboard's Cinemazone Design Brochure, they quote 3 options:
Option Hieght(m) Width (m) Depth(m)
1____1.00______1.14______1.39
2____1.00______1.28______1.54
3____1.00______1.60______2.33

They quote the original source for this info as:
Sepmeyer L.W. Computed frequency & angular distribution of the normal modes of vibration in rectangular room, Journal of the Acoustic Society of America, Vol 37, No 3 (March 1965) Pages 413-423, and extracted from Widescreen Review June/July 1994 pge 65

[Ethan Winer]

Gary,

> This stuff only matters in the bass range <

Yes, up to about 300 or 400 Hz.

> that is controllable with EQ and a little diffusion. <

Not so. EQ can help tame the modal peaks at the very lowest frequencies -
say, below 100 Hz - but the mid to upper bass range cannot be improved
successfully with EQ. At those frequencies, basic acoustic interference
becomes as important as the modal behavior. The low frequency response
varies directly with position, and the frequency of the peaks and nulls
changes too. Over a span of one foot the response at 100 Hz can change by 10
or more dB. Further, EQ cannot help nulls which are at least as damaging as
peaks. Nulls are typically 25 to 30 dB deep, and no amount of EQ can counter
that.

Likewise for diffusion. The best diffusors I've heard are the RPG deep
"well" models. Those are effective down to 500 Hz. But most affordable
diffusors you'll encounter are effective no lower than 1 KHz.

Even if you could diffuse bass affordably and with a reasonable size panel,
or successfully EQ low frequencies, those won't solve what I consider to be
the biggest low frequency problem of all: modal ringing. Modal ringing can
cause some bass notes to ring out for half a second after the musician
stops, making it very difficult to distinguish which notes are being played
by bass instruments.

> the bigger the better ... What you want is a room at least 16 ft wide by,
say, 25 ft long <

Absolutely. And then you need to add substantial bass trapping to solve the
modal ringing. :->)

--Ethan

[Ethan Winer]

Young,

> My room now is 16.5 x 18.5 x 8 but we're going to be buying a new house
soon and I will be building a dedicated room. <

Tavsec has the right idea, and there are other good ratios as well to
consider. You can download my ModeCalc program for free (DOS & Windows) to
experiment with proposed sizes and shapes for your new room. Have a look at
the Acoustics FAQ, second in the list on my Articles page:

www.ethanwiner.com/articles.html

See the section about room modes, and also the sidebar that describes the
ModeCalc program with a link to download it. When you run the program it
shows several good ratios, not just the "big three" most often listed.

--Ethan

[Gary Eickmeier]

tavsec wrote:
> In Boral Plasterboard's Cinemazone DEsign Brochure, they quote 3
> options:
> Option Hieght(m) Width (m) Depth(m)
> 1 1.00 1.14 1.39
> 2 1.00 1.28 1.54
> 3 1.00 1.60 2.33

I wouldn't worry so much about these supposed ratios. This stuff only
matters in the bass range, and that is controllable with EQ and a little
diffusion.

Far more important is room size, the bigger the better. Imagine, for
example, that you followed the above advice for room ratios, with a home
with normal 8 foot ceilings. You would end up with a room that is about
10 x 13 feet. What you want is a room at least 16 ft wide by, say, 25 ft
long, regardless of ceiling height. With a room this size, you get your
15 or 16 foot wide image, plus great enough a size that bass frequencies
have no problem filling evenly. And enough room for a few people!

Gary Eickmeier
Just joined this group

[Gary Eickmeier]

Ethan Winer wrote:

> www.ethanwiner.com/articles.html
>
> See the section about room modes, and also the sidebar that describes the
> ModeCalc program with a link to download it. When you run the program it
> shows several good ratios, not just the "big three" most often listed.

OK, you've got me hanging - where is the section on "room modes"?

[Youngin...]

I had that exact question.

young...

Gary Eickmeier wrote:
>
>
> Ethan Winer wrote:
>
>> www.ethanwiner.com/articles.html
>>
>> See the section about room modes, and also the sidebar that describes the
>> ModeCalc program with a link to download it. When you run the program it
>> shows several good ratios, not just the "big three" most often listed.
>
>
> OK, you've got me hanging - where is the section on "room modes"?

[Ethan Winer]

Guys,

> where is the section on "room modes"? <

Sorry for not being more specific. It starts at the beginning of Section 2:
Room Design and Layout. The other part I mentioned, the sidebar about
ModeCalc, is listed in the Table of Contents so you should be able to find
that easily enough.

--Ethan

[Hyde]

Behold! Thus spake Youngin...:

| Is there a certain room size ratio that works better for a theater
| room? I know that you should not have a square room or one where
| length is twice the width but i'm wondering if there is a set ratio
| that real theaters use. My room now is 16.5 x 18.5 x 8 but we're
| going to be buying a new house soon and I will be building a
| dedicated room.
|



http://www.cinemasource.com/articles/room_modes/modes.html

http://tinyurl.com/3lm7w *

*Read thoroughly, but the info you're looking for is on Page 2.


--
Hyde
-
=====================================
"Of all the things I've lost, I miss my mind the most".
~ Ozzy Osbourne ~

[Gary Eickmeier]

Ethan Winer wrote:
> Guys,
>
>
>>where is the section on "room modes"? <
>
>
> Sorry for not being more specific. It starts at the beginning of Section 2:
> Room Design and Layout. The other part I mentioned, the sidebar about
> ModeCalc, is listed in the Table of Contents so you should be able to find
> that easily enough.

OK, I found it by doing a search. Not sure exactly how I got there, but
there it was:

http://www.ethanwiner.com/acoustics.html#part2

Pretty complete site. Must have been a lot of work. I must study it. But
in it, you agree with me that the room mode thing is not that big a
deal. Lots of more important factors, such as room SIZE.

Gary Eickmeier

[Ethan Winer]

Gary,

> you agree with me that the room mode thing is not that big a deal. Lots of
more important factors, such as room SIZE. <

Modes and size are both important. But I do agree that a large room with
poor mode distribution is usually better than a small room with a good
ratio. It all depends on how poor and how small. When the room is small,
even if the ratio is good, the modes are too far apart and start too high to
get a good low end response.

--Ethan

The main thing is to have a rectangular room, with your system on a SHORT
WALL, SHOOTING DOWN THE LONG AXIS.
This is important also for the sub, whose long waves need a "large area " to
shoot into.
Just go look at a church, long and narrow, they've known this since the
middle ages.
If YOU are spending the coin on a dedicated room (damn you :-)) I'd get
somebody in the field of audio , or at least a starving student from a
nearby college to dispense advice
"Youngin..." <youngmarin@rogers.com> wrote in message
news:ga2dnfXwBcrZ52HcRVn-2w@rogers.com...
> Is there a certain room size ratio that works better for a theater
> room? I know that you should not have a square room or one where length
> is twice the width but i'm wondering if there is a set ratio that real
> theaters use. My room now is 16.5 x 18.5 x 8 but we're going to be
> buying a new house soon and I will be building a dedicated room.
>
> young...

[Youngin...]

I've been since informed that all theater needs are to be put on hold as
baby #4 is in the oven. When we buy the new house it will now have an
extra bedroom with the hopes that I can still maintain a room for a theater.

young...

steve99@bellsouth.net wrote:
> The main thing is to have a rectangular room, with your system on a SHORT
> WALL, SHOOTING DOWN THE LONG AXIS.
> This is important also for the sub, whose long waves need a "large area " to
> shoot into.
> Just go look at a church, long and narrow, they've known this since the
> middle ages.
> If YOU are spending the coin on a dedicated room (damn you :-)) I'd get
> somebody in the field of audio , or at least a starving student from a
> nearby college to dispense advice
> "Youngin..." <youngmarin@rogers.com> wrote in message
> news:ga2dnfXwBcrZ52HcRVn-2w@rogers.com...
>
>> Is there a certain room size ratio that works better for a theater
>>room? I know that you should not have a square room or one where length
>> is twice the width but i'm wondering if there is a set ratio that real
>>theaters use. My room now is 16.5 x 18.5 x 8 but we're going to be
>>buying a new house soon and I will be building a dedicated room.
>>
>>young...
>
>
>

[C what I mean]

"Youngin..." <youngmarin@rogers.com> wrote in message
news:ysedncceAcAmvJvfRVn-vQ@rogers.com...
> I've been since informed that all theater needs are to be put on hold as
> baby #4 is in the oven. When we buy the new house it will now have an
> extra bedroom with the hopes that I can still maintain a room for a
> theater.
>
> young...
>
>snip<

Congratulations!