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Discussion Starter · #1 ·
Happy New Year Everyone,


This is the year for my basement HT project. I've got a light controled space of 10' wide x 15' deep to work with. After scouring this site I've decided on the follow budget design.


92" dia screen

1080 projector (TBD)

rear seating against the back wall

front seating at 10' (80" wide screen x 1.5)


I'm looking for some confirmation on my layout. Any suggestions would be greatly appreciated. Thanks in advance.


Jeff
 

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Hello. One observation is that 10' x 15' will cause serious acoustic concerns. 10' and 15' are both even multiples of 5. You want to avoid even multiples when considering length, width and height.


So a 18' x 24' room is bad, 12 x 18, 11 x 22, etc... all problematic.


10x14 isn't perhaps so bad, but still even multiples of 2. Better perhaps would be 10' x 14.5'
 

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With 1080p you will have easy opportunity to scoot seats a bit if need be.

Main seating at 10 ft may help you moderate some of the potiential stupids with room modes. Don't sweat it, just be prepared to move subs / mains a bit to help with seat to seat variations in lower frequencies.


As you may know, typically anything up against the wall is a "throwaway" seat as far as audio goes.
 

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Discussion Starter · #4 ·
Thanks for the responces guys. I think I'm going to go with a 100" dia. screen with only one row of seating (4 across). I'll put these at 11' from screen. I can use some bar stools behind these for additional seating.
 

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Look at my sigs for more info/inspiration on small theater builds, which is what you have.


Victor
 

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Quote:
Originally Posted by Ted White /forum/post/15438557


Hello. One observation is that 10' x 15' will cause serious acoustic concerns. 10' and 15' are both even multiples of 5. You want to avoid even multiples when considering length, width and height.

Could you explain further? 10 is 2x5 and 15 is 3x5. 3 is not even, but odd. 5 is odd as well. How are 10 and 15 even multiples?
 

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I have a hunch that the correct phrase could have been "---both integer muliples of 5".


The basic idea behind "proper" dimensions being that a more "uniform spacing" of modal frequencies would provide a space with a more even modal support across the frequency range. Dimensions with a common factor will create coincident modal frequencies.


In small rooms the modals are sparse and it would be quite difficult to space them such that there is a well distributed collection providing even support. In fact I have seen rooms where the coincident pile up was somewhat beneficial since dealing with a single troublesome peak in the response was essentially all that was needed.


For some reason though I think you may know this Roger
 

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Yeah, ok it is spelled "multiples"


Also, all of the above is predicated on the dimensions being the actual low loss acoustic dimensions of the space. Think fully reflecting walls as opposed to lossy or absorptive.


EDIT: can't spell fer ....
 

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Quote:
Originally Posted by jamin /forum/post/15481573


I have a hunch that the correct phrase could have been "---both integer muliples of 5".


The basic idea behind "proper" dimensions being that a more "uniform spacing" of modal frequencies would provide a space with a more even modal support across the frequency range. Dimensions with a common factor will create coincident modal frequencies.

Yes, I am aware that when room dimensions are even multiples of each other, it can cause problems. But 15 is not an even multiple of 10. So I took a quick hop over to this handy room mode tool: http://www.bobgolds.com/Mode/RoomModes.htm

To see what looks bad I plugged in a room LWH 16x8x8 and it lights up all the piled up room modes. Then I plugged in 15x10x8 (I'm not sure what Jeff's ceiling height really is), and while it is not optimal, it doesn't appear to cause "serious acousticsl concerns." However, I am not sure how serious it is to fail one of the three BBC ratio criteria, for example.


- 1.1w / h
- l
- no integer multiple within 5%: Pass


Interestingly, it passes the integer multiple test.
 

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I will apologize in advance as I am using a darn cell phone and tiny keyboard so I can't really get busy with the whole cut and paste thing at the moment.


One point was that both 10 & 15 have a common factor, which is 5. Therefore they are each integer multiples of that factor. As a result, for example, the second width mode would be the same frequency as the third length mode -- if I am thinking clearly ( could be iffy). And I am surprised that Bob's calculator doesn't see that one. I will double check all this later.


You have also discovered the beauty of "rules" for rooms. That is that there are so many of them! Bonnello crtieria, Bolt, BBC (Walker), .....Some interesting work also came from Salford U ok this very thing not too long ago ( I'll hunt for the link).


Ok- enough of this keyboard-
 

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Quote:
Originally Posted by jamin /forum/post/15482110


One point was that both 10 & 15 have a common factor, which is 5. Therefore they are each integer multiples of that factor. As a result, for example, the second width mode would be the same frequency as the third length mode -- if I am thinking clearly ( could be iffy).

You are quite correct. There is overlap at 113 Hz, 226, etc.


It may also be useful to point out that these mode calculators assume all modes are excited equally and heard equally. That is not the case in actual use, so the sonic effect of these modes cannot be known until the room is evaluated based on actual speakers and seating locations. Your earlier point about wall construction affecting the modal response is another variable in the final equation.
 

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Quote:
Originally Posted by Roger Dressler /forum/post/15482002


Yes, I am aware that when room dimensions are even multiples of each other, it can cause problems. But 15 is not an even multiple of 10. ..snip......Then I plugged in 15x10x8 (I'm not sure what Jeff's ceiling height really is), and while it is not optimal, it doesn't appear to cause "serious acousticsl concerns ." ...snip..

Ah yes, bold and snips are mine and I agree --
 
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