Question about Golden ratios for HT room - AVS Forum
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post #1 of 25 Old 01-23-2007, 09:19 PM - Thread Starter
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I've been doing research for a HT in my basement where the height from the floor to the bottom of the 12" steel joists (concrete floor above!) is about 97 1/2", which would mean a finished ceiling height of about 7'11" if I just attached strapping and one layer of drywall to the joists. I won't be doing that, but to simplify things, let's pretend the finished ceiling height will be 8' (96").

I've been reading about Golden Room Ratios, and have come across 7 different ones (looks like 6 unique ones). These all are driven by the ceiling height, let's call that C. The numbers in parentheses would be my HT room size with C=8'.

Sepmeyer Room A: 1.14C x 1.39C x C (9'1" x 11'1" x 8')
Sepmeyer Room B: 1.29C x 1.54C x C (10'4" x 12'4" x 8')
Sepmeyer Room C: 1.60C x 2.33C x C (12'10" x 18'8" x 8')

from "figure 13-2 on page 277 of Alton Everest's Master Handbook of Acoustics":
Sepmeyer 1.28C x 1.54C x C (10'3"x12'4" x 8') -- same as Sepmeyer Room C??
Louden 1.4C x 1.9C x C (11'2" x 15'2" x 8')
Volkmann 1.5C x 2.5C x C (12' x 20' x 8')
Boner 1.26C x 1.59C x C (10'1" x 12'9" x 8')
(I don't actually have this reference, but found this on audiovideointeriors.com)

Question: How much does it matter if I deviate from these Golden Ratios?

I might not want to go wider than 12'10" (for instance) due to ducting that intrudes on the 8' height, but I might like to go longer than 18'8" - as I would like to have seating for 6 or 7 and a 100" or wider screen...

I assume that acoustical treatment of the room will be required no matter what room size is chosen. (I presume this is independent of the sound system, etc, as I can't imagine everyone having to redo acoustical treatment when the system is upgraded.)

Since my house is atypical construction (ICF, steel joists & concrete flooring - high mass radiant heat), I expect I will have some unique challenges.

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post #2 of 25 Old 01-23-2007, 10:17 PM
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I can give you fifty more "golden" ratios if you want...

These are dimensions in which each author has used their "golden" criteria such that the modal frequency spacing resulting from the wavelengths that fit into each dimension - do not have any significant gaps or overlaps - thus not creating a serious problem of peaks or nulls in frequency response - as long as you are sitting in the opposing corner as the speaker ....

The problem is that even these room ratios will have peaks and nulls in their frequency response that you can still hear - because small home sized rooms are not big enough to have well distributed and overlapped modes such that the room becomes diffuse. Room dimensions do not make room mode problems go away.

So you have to deal with peaks/nulls anyways with treatment, listener/speaker positioning, and EQ to tune the room. If you know what you are doing - you can make a concrete cube sound good - so don't design a room that does not fit your house or the intended purpose of the room because you used a golden ratio. You will want a seating array with suitable distances from speakers/walls with reasonable viewing/listening angles - something the first ratio on your list is unlikely to support.
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post #3 of 25 Old 01-24-2007, 04:40 AM
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Agreed. I'd go for the largest space you can get that will fit in what you have to work with.

That said, I am not saying that you shouldn't pay attention to dimensional interaction. It's just usually better to get the largest room you can and avoid particulary bad dimensional sets. Avoid things like:

8x16x24
12x12x8
12x24x8
16x24x8

Those direct multiples will cause the aforementioned modal issues that occur in every room to be stronger and more severe hence harder to deal with.

Keep in mind that we're only discussing axial modes here and most of the ratios you see listed also only dealt with axials IIRC.

If you want to stick with one of the ratios you listed, I'd say either the Sepmeyer C or the Volkman. I like the wider room but if you want 2 rows of seating, the longer room would potentially be of more benefit.

Personally, I'd likely do 12'10"x20'x8' and get the best of both.

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post #4 of 25 Old 01-24-2007, 06:09 AM
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As the other posters have said, golden ratios are highly overrated. The main virtue of such numbers is that no dimension is an integer multiple of another, which preventing room modes from overlaying each other and potentially creating extra problems.

I wish there were magic ratios that would greatly improve room acoustics. It would make my life much easier!

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post #5 of 25 Old 01-25-2007, 06:11 AM - Thread Starter
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Thanks for confirming that I don't need to feel constrained to these Golden Ratios. I expected that acoustic treatment would have been required anyway whether or not it was one of these magic numbers.

So instead of banging my head against the wall for these ratios, I will avoid any multiples of the ceiling height for the length and width.

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post #6 of 25 Old 01-25-2007, 10:22 AM
 
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Although, room ratios do matter. You can calculate the various modes, and ratios that keep too many modes from piling up together are flatter, which is better. But there are many many ratios that are good, and others that are not so good, and the best way is to just run the numbers on a bunch of dimensions near what you're shooting for and see if some are a lot better than others.

I just didn't want the above posts to perhaps mistakenly leave the impression that room dimensions weren't that important. They are, but limiting yourself to some single good ratio, or a handful of good ratios is not always the best thing. And of course there are other shapes than rectangles too...
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post #7 of 25 Old 01-25-2007, 10:30 AM
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That is not true in the interior of the room but only at the boundaries. On the boundaries all modes are the same phase and will build together. On the interior of the room - many modes at the same frequency is a good thing - it promotes diffusion because all of the modes are different phases. At some point you reach statistical equilibrium as they all cancel each other out such that none is dominant over the other and does not color the spectrum or decays.

This is the problem with many of the rules - they are naturally using the boundary response of the room - which is an unnatural place to have your ear.

The modal density increases exponentially with frequency which is the very reason that low frequency is a problem in small rooms. There simply are not enough modes for them to go away as a problem. Now some of the metrics do have a not enough modes in bandwidth criteria - but when it comes to subwoofer frequencies - no ratio in small rooms can ever distribute them enough.
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post #8 of 25 Old 01-25-2007, 10:32 AM
 
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Quote:


On the interior of the room - many modes at the same frequency is a good thing

No, they most certainly are not a good thing at all. That's why a cube is the poorest shape.
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post #9 of 25 Old 01-25-2007, 10:36 AM
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No a cube is the poorest shape because the phases of the modes at certain interior positions are the same. But a cube is also the best shape if you plan to use four sub woofers and broadbrand treatment simply because it is predictable.

The ratios really are more about which ratios are bad - not which ratios are good. Which is why the BBC (Walker) made a ratio range rule to avoid bad ones. But it is a design guideline that does not eliminate the need for treatments and placements design.
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post #10 of 25 Old 01-25-2007, 10:41 AM
 
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A cube is no more or less predictable than other rectangular shapes. It is, however, a terrible shape to use. But I can see I'm not going to convince you of that.
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post #11 of 25 Old 01-25-2007, 10:43 AM
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I do have a masters thesis in this topic - so you can debate with me all you want. I enjoy an intellectual debate. My cube example does not come from me - it comes from Dr. Toole - so argue with him if you want. And his comments are backed by the latest AES paper from the Harman crew regarding computer modeling on room ratios with subs/seats positioning away from the usual corner-corner modal response.

Many of the conventions of modal design date back to the time when computer modeling was horribly expensive to do - and emperical rules were used. Most of these rules do not even compute the modal frequency response because it was very difficult to do so at the time. When these methods were designed - the spreadsheets we implement them with now did not even exist - so even the spacing/density rules were difficult to implement.
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post #12 of 25 Old 01-25-2007, 12:38 PM
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Terry,

> I wish there were magic ratios that would greatly improve room acoustics. It would make my life much easier! <<br />
You don't really mean that, right? If that were the case you'd be out of a job!

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post #13 of 25 Old 01-25-2007, 01:47 PM
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Quote:
Originally Posted by Ethan Winer View Post

Terry,

> I wish there were magic ratios that would greatly improve room acoustics. It would make my life much easier! <

You don't really mean that, right? If that were the case you'd be out of a job!

--Ethan

Fortunately, there are about a gazillion other factors to deal with in architectural acoustics design.

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post #14 of 25 Old 01-26-2007, 09:58 PM - Thread Starter
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Okay, I remeasured the area in the basement where the home theatre is planned, without worrying about the Golden Ratio.

Constraints:

ceiling height, assume finished height is 7'11 (95") with double drywall - assuming finish flooring (carpet) is zero height.

Room width: there are some cold air return plenums that start to intrude around 15', that would drop the ceiling height by 8". If I can box in soffits around this, I can widen the room by that boxed in amount. (E.g. 2' soffit would enable a 17' wide room.)

Room length is constrained by a gas shutoff valve at 21.5 (that must be accessible).

So how does this sound? (haha )
H=95" (7'11"), W=17' (w/2' soffits on each side), L=21.25'

I still need to find the guidelines for seating, viewing angles, etc.

Does one have to have the electronics (speakers, projector, etc) selected before designing a room including where the speakers are located?

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post #15 of 25 Old 01-27-2007, 10:02 AM
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Most HT rooms have soffits anyways - just check with your local code if that soffit is over a walkway will they allow it? Even if they do - do you have any 7'+ relatives?

Your chair area depends on what chairs you get - they could take up a 2'x2' footprint or a 6'x6' footprint. Do you want snack tables in between? Will you buy an attached curve row because you got a deal - or jump on a pullout seats from the latest dead cineplex - that can dictate your theater design. Do you want 1' walkway for the local multiplex experience, or the 3' walkway so nobody is squished?

Generally I would design seating anywhere from 1x to 2x your screen width - there are SMPTE/THX viewing angles for worst row of commercial theater - but you want to sit as close as you can before pixel technology and bad sources become apparent - resolution and brightness for bigger screens is expensive! These visual rules are counterbalanced with audio rules - as mentioned earlier - modes create hot/cold spots in the room.

Your screen size depends on if screen is perforated or if you have to leave room above/below or to side for speakers. Your seat locations will thus depend on perfed screen or not. Your riser heights and distance depend on ceiling/soffit heights and ear line to center speaker and sight lines to screen bottom.

There are many variables to consider in theater design with compromises to be made - what you think you know and what you don't know are what will get you. This is why many of us are professional theater designers even if you want to be the theater builder. Or you can hang out for a year here and work on a plan and another year of build - plenty of threads in here to attest that it makes for a great hobby - some of the threads seems they enjoy the design/build more than the movies themselves!
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post #16 of 25 Old 01-27-2007, 07:35 PM - Thread Starter
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Quote:
Originally Posted by krasmuzik View Post

.... There are many variables to consider in theater design with compromises to be made - what you think you know and what you don't know are what will get you. This is why many of us are professional theater designers even if you want to be the theater builder. Or you can hang out for a year here and work on a plan and another year of build - plenty of threads in here to attest that it makes for a great hobby - some of the threads seems they enjoy the design/build more than the movies themselves!

We just moved to a house that we designed and had built and I am kinda bored now, so I can totally relate to enjoying the design/build part.

From your very informative reply, it seems that there are a lot of dependencies, so I really need the equipment details sorted before I can have a plan for the room.

At the very least, I thought that I could at least build the box for the room. I've lurked on this site on/off for several years, but perhaps I need to do more reading and planning.

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post #17 of 25 Old 07-18-2008, 10:55 AM
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I am not trying to bust your chops here but I for one would love as many ratio as you could muster.....My math skills leave a lot to be desired.


Quote:
Originally Posted by krasmuzik View Post

I can give you fifty more "golden" ratios if you want...


If you know what you are doing - you can make a concrete cube sound good - so don't design a room that does not fit your house or the intended purpose of the room because you used a golden ratio. You will want a seating array with suitable distances from speakers/walls with reasonable viewing/listening angles - something the first ratio on your list is unlikely to support.

If you know what your doing.

Thats just not fare. As a seller of acoustical products for 10 years I think I know what I don't know. And thats a lot, even with dealing with room acoustics nearly every day. This is a public forum. That being said the number of readers capable of "fixing" that concrete box is so small as to be statistically insignificant.

I like a lot of the other advice. I think there is some good info here. But I would compare that statement with "anybody can build a car with 2000hp".

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post #18 of 25 Old 07-18-2008, 11:47 AM
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You realize you are responding to a thread that is over one and a half years old, right?

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post #19 of 25 Old 11-12-2008, 08:52 AM
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This has been brought up to me more than a few times.

Why does the age of a thread matter if it interests me?

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post #20 of 25 Old 11-12-2008, 11:10 AM
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Let me make it simple for you, oh seller of acoustical stuff. In a small room, ratios aren't going to make a twits worth of difference. You can go from "good" to "bad" in one foot and the "Q" of a modal response is going to overlap the difference in any case.

As to the cubic room, it is absolutely fair. You have to make a rectangular room sound good as well, and the principles used in the rectangular room are exactly the same as found in the cubic room. Strangely enough, after many years of research, I've discovered the laws of physics don't change with room dimensions. Nuts.

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post #21 of 25 Old 11-12-2008, 12:19 PM
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Quote:
Originally Posted by Dennis Erskine View Post

Strangely enough, after many years of research, I've discovered the laws of physics don't change with room dimensions. Nuts.

Of course they do, you just haven't gone to a small enough room. At the subatomic level, Newtonian physics goes out the window and quantum mechanics (probably) apply.
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post #22 of 25 Old 11-12-2008, 12:56 PM
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Spent four years playing with Pi Mesons (lab rat for Gene Loh) ... not a one of those little critters changed the sound of a room.

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post #23 of 25 Old 11-12-2008, 01:51 PM
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Thanks for clearing that up fellow seller of acoustic stuff.

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post #24 of 25 Old 11-13-2008, 04:53 AM
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Actually, I don't sell acoustic stuff. I do teach acoustics; but, don't sell the stuff.

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post #25 of 25 Old 11-13-2008, 07:28 PM
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Quote:
Originally Posted by dennis erskine View Post

strangely enough, after many years of research, i've discovered the laws of physics don't change with room dimensions. Nuts.


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