Dedicated HT Dimension question

[Phantomgto]

Hello everyone. I have been researching this forum for a few days on what dimensions to make my room and just keep getting more confused by crazy acoustical math... Basically I'm dealing I only need to determine the length of the theater. The Width with be approx. 12' and the head is 8'. I will mostly likely be soundproofing through the use of a sub floor and staggered studs or room inside a room technique. My question is what would be an ideal lenth for the room and along with that length a good screen size? I'm sorry if this has been answered before.

 

[TLS Guy]

Hello everyone. I have been researching this forum for a few days on what dimensions to make my room and just keep getting more confused by crazy acoustical math... Basically I'm dealing I only need to determine the length of the theater. The Width with be approx. 12' and the head is 8'. I will mostly likely be soundproofing through the use of a sub floor and staggered studs or room inside a room technique. My question is what would be an ideal lenth for the room and along with that length a good screen size? I'm sorry if this has been answered before.

Twenty to twenty four feet would be great.

 

[ParadigmDawg]

I am building mine 28' deep and 18' wide with 10'ceilings but I don't remember how I came up with this.

 

[Phantomgto]

Thanks a lot guys, now I have a good idea on what dimensions to aim for. Thanks again.

 

[AVRat]

Based on your 8 x 12 front wall and approximately 20' - 22' length, assuming in room front speakers, I'd suggest max screen size of 110" dia.

 

[mperfct]

I remember seeing either a website or a spreadsheet that can tell you what the best dimensions are for your room given 2 of the measurements.

I'm still looking for it, but this is a great site with a terrific spreadsheet that will help you get started.

http://www.carltonbale.com/home-theater/home-theater-calculator/

 

[mperfct]

Here's one...

http://www.componentacoustics.com/Room_Dimensions_Calculator.xls

There are lots of them out there, just google for "home theater room dimension calculator".

Good luck!

 

[mike_wassell]

The room dimensions should not be evenly divisible by each other in order to prevent standing waves. You are already stuck with 12 x 8. A good measurement would be 13 x17 x 8. For your room I would chose a length of either 17 or 19.

Also non parallel walls (like in a movie theater) are great for diffusion and can help prevent standing waves.

 

[Savant]

The room dimensions should not be evenly divisible by each other in order to prevent standing waves. You are already stuck with 12 x 8. A good measurement would be 13 x17 x 8. For your room I would chose a length of either 17 or 19.

While the intent is correct, the explanation is not. Room dimensions that have a high common factor should generally be avoided. This is to prevent overlapping room modes, not standing waves. (Standing waves are going to be present in the room regardless of the dimensions.)

While 12' x 8' is less than ideal, it is better than 8' x 8' or 16' x 8'. But regardless of what the dimensions turn out to be, the room will need acoustical treatments, including treatments to control low frequency problems. Therefore, I would suggest that the room size is selected with an emphasis on viewing and seating. It's less important to worry about dimensioning for acoustics at this stage. Of course, if there is ample flexibility to consider both at this point, then by all means!

 

[mike_wassell]

While the intent is correct, the explanation is not. Room dimensions that have a high common factor should generally be avoided. This is to prevent overlapping room modes, not standing waves. (Standing waves are going to be present in the room regardless of the dimensions.)

While 12' x 8' is less than ideal, it is better than 8' x 8' or 16' x 8'. But regardless of what the dimensions turn out to be, the room will need acoustical treatments, including treatments to control low frequency problems. Therefore, I would suggest that the room size is selected with an emphasis on viewing and seating. It's less important to worry about dimensioning for acoustics at this stage. Of course, if there is ample flexibility to consider both at this point, then by all means!

Room modes (sometimes called nodes) are the result of standing waves which result from sound being reflected back off the walls of a room and interfering with the original traveling wave radiated by the source.

 

[Savant]

Room modes (sometimes called nodes) are the result of standing waves which result from sound being reflected back off the walls of a room and interfering with the original traveling wave radiated by the source.

With all due respect, it might behoove you to review the basic acoustical terms and concepts you are trying to describe.

Room modes do not "result from" standing waves; they are room resonances. These resonances are inherent physical properties of the room.

The term "nodes" refers to areas of minimum sound pressure in a room's modal sound field. (Conversely, "antinodes" are areas of maximum sound pressure.)

While your description of standing waves (by itself) is fine, modes and standing waves should not be treated as synonymous. Modes are a form of standing wave, but "standing wave" itself is a more universal descriptor of an acoustical concept that is not restricted to describing room resonances. I.e., not all standing waves are modes.

 

[mike_wassell]

The only standing waves in room are going to result from room modes.

Two waves with the same frequency, wavelength, and amplitude traveling in opposite directions will interfere and produce a standing wave or stationary wave. The reflective wave has to have the same amplitude and frequency as the incoming wave.

Room modes are the result of standing waves which result from sound being reflected back off the walls of a room and interfering with the original traveling wave radiated by the source. At certain frequencies there will be some points in the room where the waveforms will add to produce an antinode or loud spot, and others where complete or partial cancellation occurs to produce a node. Where the radiated wave can bounce back and forth, causing repeated reinforcement and cancellation strong nodes and antinodes will arise, the simplest example being the longitudinal mode along the length of a room in which a speaker is placed at one end. Since there can be no air movement perpendicular to a wall, pressure nodes will always arise there.

 

[Cruise Missile]

Nice cut and paste from Wiki, Mike... mention sources if not your own, it goes a long way for your credibility.

 

[Savant]

There are many things (just about everything) wrong with that post / citation. I guess this is proof, yet again, that not everything on the Internet is true. Especially when it comes to acoustics.

 

[Soundman]

Odd Shaped room

How about odd shaped rooms? Many of these calculators used use length x width x height. But I have a future project that may involve an odd shaped room. It is possible to make some modifications to the rooms shape, but it may be easier just to treat the room. I'm not sure. Here's the layout: Perimeter walls= 5.8+6+5.8+5.1+16.2+5.1+6+6+6+16.2, height=9ft, but slopes down to about 7ft on the front and back sides of the room. This room is on the third floor and was originally the attic. That is the reason for the odd shape. I may start a new thread on this later if necessary.

 

[Savant]

There is no convenient method to calculate room modes for non-rectangular spaces. It can be done, but requires sophisticated software as opposed to (relatively) simple calculators.

What should be avoided is to get sucked in by the "non-rectangular rooms don't have mode problems" myth. I see this one from time to time on the (oh-so-reliable) Internet. All rooms have modes; they're just much more difficult to predict in non-rectangular spaces.

What non-rectangular rooms are very good for is minimizing problems with flutter echo. Fewer parallel surfaces help enormously with this. The sloping ceiling—provided the low part is in the front (screen) and the high part is towards the back (seating)—is also a boon.

Whether or not some approximations can be made about your particular space will depend on the exact layout, which I assume you'll be providing to us in that new thread, yes?

 

[mike_wassell]

Savant:

I’m sorry I got so defensive. I hate when people do that. I’m not an expert. I can defiantly be wrong and I did use Wikipedia as my source. However I have put in many hours investigating acoustic and acoustical treatments on the web. I have read your articles but did not realize that it was you. I recently made 24 acoustical panels and 8 bass traps for my home theater. I consider myself to have a high end audio system and mediocre video system because I don't have a projector. I love listening to good music!!! I did have a “hobby job” at a high end stereo/home theater job for over 5 years.

Right now I am running:
Onkyo DTC-9.8 preamp
Parasound HCA-3500 2 x 350w amp for front mains (large speakers)
B&K EX4420 2 x 200w amp for rear surrounds (small speakers)
B&K TX4430 3 x 200w amp center and side surrounds (small speakers)
Carvin DCM2000 2000w amp for Buttkickers
Focal (JMLab) Electra 7.1 system I guess I actually have a 7.6 system
2 M&K MX-350 subs
2 M&K MX-700 subs
2 Buttkickers
JVC 61” HD-ILA TV
Pioneer BDP-51FD Blu-ray player
Denon DVD-2900 DVD, SACD, DVD-audio player
Panamx M5400-EX surge protector/line conditioner
Harmony 890 universal remote
Mostly Monster Cables
DYI acoustical room treatment
12000 Series Berkline Home Theater Seating

Again sorry for getting so defensive – that’s not me I can always learn something.

Can you briefly explain the difference between room nodes and standing waves? Thank you.

Mike

 

[Soundman]

There is no convenient method to calculate room modes for non-rectangular spaces. It can be done, but requires sophisticated software as opposed to (relatively) simple calculators.

What should be avoided is to get sucked in by the "non-rectangular rooms don't have mode problems" myth. I see this one from time to time on the (oh-so-reliable) Internet. All rooms have modes; they're just much more difficult to predict in non-rectangular spaces.

What non-rectangular rooms are very good for is minimizing problems with flutter echo. Fewer parallel surfaces help enormously with this. The sloping ceiling—provided the low part is in the front (screen) and the high part is towards the back (seating)—is also a boon.

Whether or not some approximations can be made about your particular space will depend on the exact layout, which I assume you'll be providing to us in that new thread, yes?

I can definitely get a thread going on that, but I'd like to take some pics first. I haven't actually moved into this house yet, but this is something I'd like to start working on once I am moved in and settled. Thanks for the info.

 

[mike_wassell]

Try

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

 

[Savant]

I’m sorry I got so defensive.

No worries.

Can you briefly explain the difference between room nodes and standing waves?

I thought I already had!

Room modes (not nodes - see previous posts for explanation) are the resonant frequencies of the room. A standing wave is a description of a certain type of wave interference, which does in fact occur with room modes. It's just not exclusive to them.

I think you generally have the right idea. It's just some concepts and terms that are getting muddled a bit.