[95bcwh]

Russell brought up a comment on this thread about room shape:
http://www.audiocircle.com/index.php?topic=48361.msg433700#msg433700

Without hijacking that thread allow me to start a new thread to discuss what room shape/construction is best for two channel listening, assumming that one can design the room from ground-up - meaning a complete separate new building, with dimension of at least 23ft wide and 30ft long.

First, do people agree that a pentagon shape is the best for containing the bass mode? (Look at the first rough sketch below)

[bpape]

Rectangles are the most predictable.  People make the mistake if thinking if they build with non-parallel surfaces, the bass modal issues will go away - they won't.  They're just no longer axial (2 surface) modes and become different and harder to predict.  I'm not saying there isn't a benefit - it's just not a magic bullet that will fix all the problems.

If I could build any room I wanted, I'd build one that had the side walls splayed out at about 1" per foot of length on each side.  This helps push reflections away from you and toward the rear.  In the rear, the wall would be parallel with the front but have broadband aborbtion in the 2 corners and a large polycylindrical diffusor spanning the rest of the width. 

The ceiling would start at approx 9' in the front and go up at the rate of approx 1.5" per foot of length as it extends toward the rear of the room.  Trap the rear wall/upper ceiling corner with broadband.

After that, the treatment regimine is much the same but we've minimized the need for as much side wall absorbtion for reflections and directed the sound back toward a large diffusor that's effective well down into the vocal range to create a huge ambient soundstage around us to help support the focused soundstage in the front. 

Doing something like this in most normal sized rooms is just out of the question due to the space it takes up for the splaying of walls and ceiling.  But, if you have say a 20x30x15' shell to work inside, its great.

Bryan

[Ethan Winer]

First, do people agree that a pentagon shape is the best for containing the bass mode?

Sorry, no, all room shapes have bass modes. Better to go with slight angles within a standard shape. That gives you clean corners to put bass traps.

--Ethan

[95bcwh]

Bryan, you mean something like this is good enough..?

[nathanm]

Save your allowance and build one of these!

 

http://www.audiojunkies.com/blog/503/the-worlds-largest-anechoic-chamber

[bpape]

95

That's basically it but the front wall would be parallel to the original back wall.  The thing is there won't be much of anything left of the rear wall by the time you do the diffusor and the broadband.

If the room is wide enough to make a single poly impractical in the rear (and it likely will be), then you can make one about 8' wide and fill the gap between it's sides and the broadband absorbers with a series of well diffusors.

For a better look, instead of tubes, think solid chunks of absorbtion (triangles) going side wall to back wall.  Those will reach a LOT deeper than any resonably sized tube and take up a ton less space. 

Bryan

[Housteau]

Cathedral ceilings will work and they have a great visual appeal, but there are some important considerations.  On the positive side they will reflect energy at an angle.  The downside, in my room at least, was that this energy was such that it harmed the focus within the soundstage.  So, my ceiling and upper corner treatments were mostly placed to take care of those issues.

               

The ceiling treatments were made broadband and absorptive at all frequencies.  The rest of the room was a mix and consisted of solid filled corner traps, as Bryan has suggested above.  In fact most of my room was treated with DIY methods suggest by both Ethan and Bryan here on this forum.

[SET Man]

Hey!

    Hmmm.... a round circular shaped room? 

    But seriously will that work? Honestly I wouldn't mind have a round room in my house... well maybe if I won lottery than I think I will build one.

   Also, I remembered I saw something about the room shape and size on Cardas site where he show the what they considered a perfect Golden Ratio room... forgot how big was it but I'm sure it is still on his site.

Take care,
Buddy

[Glenn K]

Cathedral ceilings will work and they have a great visual appeal, but there are some important considerations.  On the positive side they will reflect energy at an angle.  The downside, in my room at least, was that this energy was such that it harmed the focus within the soundstage.  So, my ceiling and upper corner treatments were mostly placed to take care of those issues.

               

The ceiling treatments were made broadband and absorptive at all frequencies.  The rest of the room was a mix and consisted of solid filled corner traps, as Bryan has suggested above.  In fact most of my room was treated with DIY methods suggest by both Ethan and Bryan here on this forum.

Wow GREAT JOB!! I bet that is one great sounding room aa

Glenn

[Ethan Winer]

Hmmm.... a round circular shaped room?

I know it sounds cool, but round is the worst shape possible because it focuses all the sound to the center. Focusing (bad) is the opposite of diffusion (good).

--Ethan

[bpape]

Hey!

    Hmmm.... a round circular shaped room? 

    But seriously will that work? Honestly I wouldn't mind have a round room in my house... well maybe if I won lottery than I think I will build one.

   Also, I remembered I saw something about the room shape and size on Cardas site where he show the what they considered a perfect Golden Ratio room... forgot how big was it but I'm sure it is still on his site.

Take care,
Buddy

Yeah - round isn't reallly good at all for just the reasons Ethan stated.

The Cardas setup is based on the Fibonnaci numbers and his whole line is based on the Golden Section.  If you want to learn more than you ever cared to about these things - go here:  http://www.mcs.surrey.ac.uk/Personal/R.Knott/Fibonacci/fib.html

Bryan

[richidoo]

Taking the "round" idea to the max, how bout a sphere? haha  No corners, no parallel walls, should be great, right?


Here is the comparison of resonances inside a sphere vs a cube of same volume. No clear advantage. Article.

Two important disadvantages with curves:
1. Less corners to concentrate bass for trapping
2. It's impossible to use software for statistical analysis.

Great topic 95!

[richidoo]

Here's George Cardas' article about his Golden Trapagon room dimensions.

[JLM]

I've been in two 45 foot diameter geodesic domes.  Whispers on one side travel very effectively to the opposite side.  Standing in the middle gives an "underwater" sense of resonance, with the resonance greatly increasing at the right frequency.

I moved into my man cave 2 years ago, which is proportioned and setup to the Cardias formulas for rectanglar rooms (didn't want to give up the extra room to go trapagon).  It is fully insulated with fiberglass exterior door and ductwork (and except for the ceiling that the builder refused to use Z-channels to "float" it from the floor joists above) it works incredibly well. 

I'm fortunate to have the room.  It has multipled my audio enjoyment immensely.  It has also brought to realization how fustrated/limiting it was to set up in far from ideal rooms.

[bpape]

Pretty much any concave shape is a bad idea in a listening room.  A round room just takes that to another level.  A sphere?   

Bryan

[Housteau]

Wow GREAT JOB!! I bet that is one great sounding room aa
Glenn

Thank you.  It has been quite a journey to reach this point.  People often speak of the Golden Age of audio as if it was a time in past.  However, I believe that time is now.  Before audiophiles had to really dig to find good sources of information in books and magazine articles that were few and far between.  Most of the time it probably came from an acquaintance also involved with this hobby.  I did get some good info before the age of the internet, but also got led astray many a time by well meaning, but incorrect facts on different things.  For example:  I remember some of the earlier articles on room acoustics by J. Gorden Holt.  I had thought them to be the first few book of the listeners bible, only to find out later that a lot of what he wrote was just plain wrong.  Facts can be gotten wrong on internet forums such as this also, but the chances of them being almost immediately corrected by someone else is quite good.  With the sharing of such good information, the growth potential for everyone involved is so much greater than any time in the past.

[Glenn K]

Wow GREAT JOB!! I bet that is one great sounding room aa
Glenn

Thank you.  It has been quite a journey to reach this point.  People often speak of the Golden Age of audio as if it was a time in past.  However, I believe that time is now.  Before audiophiles had to really dig to find good sources of information in books and magazine articles that were few and far between.  Most of the time it probably came from an acquaintance also involved with this hobby.  I did get some good info before the age of the internet, but also got led astray many a time by well meaning, but incorrect facts on different things.  For example:  I remember some of the earlier articles on room acoustics by J. Gorden Holt.  I had thought them to be the first few book of the listeners bible, only to find out later that a lot of what he wrote was just plain wrong.  Facts can be gotten wrong on internet forums such as this also, but the chances of them being almost immediately corrected by someone else is quite good.  With the sharing of such good information, the growth potential for everyone involved is so much greater than any time in the past.

I totally agree, but one bad point of the internet is if a person does not take the time to TRULY research things they COULD end up  wasting tons of money on snake oil. I am still amazed that so many companies can stay in business when it is clearly FRAUD/BS. The worst part is it not only takes sales from companies that are trying to be on the up and up, but (talking about acoustics here) if a person buys something that is BS they loss hope in the whole “acoustic matter”, which we spend so much time trying to promote.


Glenn