AVS Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
6,337 Posts
Discussion Starter · #1 ·
Just wondering how close to the corner the sub has to be to get the corner boost ? 2' , 1' , 6" ...


Does the boost help out more in small sealed rooms compared to large open rooms ?
 

·
Banned
Joined
·
3,677 Posts
Yes, usually the smaller the room the better, or should I say, easier, it is to get lots of bass. Whether that be from boundary gain, or having a smaller space to pressurize, either way, small rooms are the easiest way to get good bass.


I am in the process of trying to design a dedicated theater room myself. I plan to use my 27 foot by 14 foot room and divide it up into two completely separate rooms, one being a dedicated theater room, and the other side will be a dinning room. One of the decisions that I am having trouble with are what the optimal dimensions are for the theater side. I have 27' by 14' by 8' to work with.


I know absolutely nothing wrt theater design, but, I will probably go with a smaller room of around 12' by 14', or possibly 14' by 17'. Can't decide....
 

·
Registered
Joined
·
21,345 Posts
it is a little tricky because as you work your way down in frequency, first you get reflections some of which combine constructively and some of which create cancellations. the last of the cancellations occurs when the center of the driver is 1/4 distance from the boundary. for 80hz, that is about 3.5 feet. below that point, you get more and more constructive radiation. below about 1/8th of a wavelength, most of the wave is combining constructively, so you get the +3db per boundary from the reduced space. its never quite that high because walls tend to be lossy, but that's the basic idea.
 

·
Registered
Joined
·
4,835 Posts
Good advice above

Chalugadp, just be mindful of wavelength size for any given affected frequency ...


that thought process, the size of the sound, is inextricably linked to nearly every aspect of small room acoustics, from treatment including absorption and diffusion, to interference, blending and coupling between mains and subs, ...


yeah, if there's one concept to thoroughly and fully grasp, it sound "size".
 

·
Registered
Joined
·
4,835 Posts

Quote:
Originally Posted by Martycool007  /t/1523778/corner-boost-for-bass#post_24516695


Yes, usually the smaller the room the better, or should I say, easier, it is to get lots of bass. Whether that be from boundary gain, or having a smaller space to pressurize, either way, small rooms are the easiest way to get good bass.


I am in the process of trying to design a dedicated theater room myself. I plan to use my 27 foot by 14 foot room and divide it up into two completely separate rooms, one being a dedicated theater room, and the other side will be a dinning room. One of the decisions that I am having trouble with are what the optimal dimensions are for the theater side. I have 27' by 14' by 8' to work with.


I know absolutely nothing wrt theater design, but, I will probably go with a smaller room of around 12' by 14', or possibly 14' by 17'. Can't decide....

Marty, make the dividing wall a integral part of the HT's acoustic treatment ..i.e., either a diaphragmatic lossy trap, or something similar... if possible.


The HT needs to "see" the extra volume of the adjacent space at low frequencies, yet retain the remaining spectrum above.


Quite an opportunity ... non-starter?


IMO, a great way to implement the aforementioned sba (which requires total absorption the rear wall)
 

·
Registered
Joined
·
7,989 Posts
I'd say an 1/8th wavelength of 100hz because the XO isn't a dead stop at 80hz and a 1/4 wave distance will be a null. That's 42cm roughly depending on the ambient temperature. But you're close to sea level and indoors, so 42cm is gonna be close. That's the center of the cone to each boundary. Floor, left, and right walls. The best way to do this afaik is to use a small baffle and down firing sub. I use up/down dual opposed and get quite a reflection free room response.


Edit- or an IB will achieve this.
 

·
Registered
Joined
·
4,835 Posts
Chalugadp,

http://www.padrick.net/LiveSound/SubwooferInfo.htm


Here's a FOH engineer (near me I believe, never met) that's got an interesting web page, with good info on boundary summation etc., specifically how subs interact with the adjacent boundaries.
 

·
Registered
Joined
·
4,835 Posts

Quote:
Originally Posted by tuxedocivic  /t/1523778/corner-boost-for-bass#post_24516840


I'd say an 1/8th wavelength of 100hz because the XO isn't a dead stop at 80hz and a 1/4 wave distance will be a null. That's 42cm roughly depending on the ambient temperature. But you're close to sea level and indoors, so 42cm is gonna be close. That's the center of the cone to each boundary. Floor, left, and right walls. The best way to do this afaik is to use a small baffle and down firing sub. I use up/down dual opposed and get quite a reflection free room response.


Edit- or an IB will achieve this.

I like that better than the quarter wavelength point, improved wavelaunch with less smeared energy over time.


Also, great point wrt IB or baffle wall, I placed my quad 18" IB in the 1/8th space loading of a corner. Yes, it is (corner placement) contraindicated for modal excitation, but it's been fine.
 

·
Registered
Joined
·
749 Posts

Quote:
Originally Posted by LTD02  /t/1523778/corner-boost-for-bass#post_24516704


it is a little tricky because as you work your way down in frequency, first you get reflections some of which combine constructively and some of which create cancellations. the last of the cancellations occurs when the center of the driver is 1/4 distance from the boundary. for 80hz, that is about 3.5 feet. below that point, you get more and more constructive radiation. below about 1/8th of a wavelength, most of the wave is combining constructively, so you get the +6db per boundary from the reduced space. its never quite that high because walls tend to be lossy, but that's the basic idea.
I presume this is why stacked subs with drivers located at 1/4 heights of the room is recommended? (And, by extension, the SBA/DBA?)
 

·
Registered
Joined
·
1,380 Posts
I don't know the specifics and the names for it but I in my case it was almost a 10db gain just by having them in the front corners vs moving the subs away from the wall or by putting them against the sides of the listening area. If you recall my room is a long rectangle with openings off it to the hallway and the dinning room. The size of the actual room is about 14x35 with nothing but furniture and cabinets dividing it. My subs are both about 3" away from the wall. When I moved them forward 3' the level dropped. I would as close as possible in my case. Might be same in yours.
 

·
Registered
Joined
·
148 Posts
I have a semi open ended theater that has a bar half wall at the back. It's about 25x15. My two sealed 18's are placed at 1/3 and 2/3 along the front wall and I get some pretty massive room gain. I'm not even close to being an expert on accoustics, but I get a very flat response with no nulls. I'm guessing it has to do with the semi "open ended" room. You don't get the reflected waves cancelling each other out. I'm sure there's a drawback, probably having to do with pressurizing a larger space. The experts here can probably comment further on this.


If I had to do it all over again, I'd still put the bar seating at the back. It's been great for parites and sports events. With your space you could do two rows of seats and section off a tiled area at the back for a bar type area. Here are a couple of picks and the frequecy response. Let me know if you want any help on the design or more picks, i'd be happy to share. I got most of my ideas during the build from AVS forums. The guys in the home theater design are awesome and very helpful.


I just thought I'd give you more food for thought before you go and section the whole room off. Who needs a dining room anyway!




 

·
Registered
Joined
·
21,345 Posts
"I presume this is why stacked subs with drivers located at 1/4 heights of the room is recommended?"


that is actually another issue that has to with not exciting and or cancelling room modes.
 

·
Registered
Joined
·
21,345 Posts
"I'm not even close to being an expert on accoustics, but I get a very flat response with no nulls. I'm guessing it has to do with the semi "open ended" room. You don't get the reflected waves cancelling each other out. "


nice looking room...and response!


you are correct. side-to-side balancing the subs cancels or doesn't excite most of the modes that go side-to-side in the room. the open area behind the theater creates a zone where the waves don't bounce off a single wall and reflect back toward the front of the room (which would create peaks and nulls). your open area behind the theater is reflecting the wave and 'breaking it up' before sending what energy remains back into the theater area. it is actually a good design.
 

·
Registered
Joined
·
1,380 Posts

Quote:
Originally Posted by Gomdaf  /t/1523778/corner-boost-for-bass#post_24517340


I have a semi open ended theater that has a bar half wall at the back. It's about 25x15. My two sealed 18's are placed at 1/3 and 2/3 along the front wall and I get some pretty massive room gain. I'm not even close to being an expert on accoustics, but I get a very flat response with no nulls. I'm guessing it has to do with the semi "open ended" room. You don't get the reflected waves cancelling each other out. I'm sure there's a drawback, probably having to do with pressurizing a larger space. The experts here can probably comment further on this.


If I had to do it all over again, I'd still put the bar seating at the back. It's been great for parites and sports events. With your space you could do two rows of seats and section off a tiled area at the back for a bar type area. Here are a couple of picks and the frequecy response. Let me know if you want any help on the design or more picks, i'd be happy to share. I got most of my ideas during the build from AVS forums. The guys in the home theater design are awesome and very helpful.


I just thought I'd give you more food for thought before you go and section the whole room off. Who needs a dining room anyway!





Sorry this has nothing to do with the question at hand but this is a beautiful looking theater. I love the colors and the bar area. This is what I would do if I had a theater. I love it.
 

·
Banned
Joined
·
3,677 Posts
So with regards to my room, (currently 27' by 14') that I have been planning to separate into two rooms, one dedicated theater room, the other a dedicated dinning room, do you guys think I would be better off not separating the room into two, and instead possibly building a half wall approx 4' to 6' tall with the dinning room behind that wall so as to help with the reflections off the back wall?


What if I kept my current plan and made the room somewhere close to 12' by 14' or 16' by 14' and did a SBA on the front wall with lots of absorbing panels on the rear wall? I would prefer to do this so as to keep the room smaller, as I prefer smaller rooms when it comes to theater because you seem to get more bass with less subs, and the speakers used can be of the smaller variety.


Any thoughts on this? I could definitely do a SBA with some of my existing 4" thick OC703 panels that are 2' wide by 4' tall and space them 4" off the wall, or, I could pick up enough Safe-n-Sound to do 6" thick coverage along the entire wall.
 

·
Banned
Joined
·
15,491 Posts

Quote:
Originally Posted by Martycool007  /t/1523778/corner-boost-for-bass#post_24518529


So with regards to my room, (currently 27' by 14') that I have been planning to separate into two rooms, one dedicated theater room, the other a dedicated dinning room, do you guys think I would be better off not separating the room into two, and instead possibly building a half wall approx 4' to 6' tall with the dinning room behind that wall so as to help with the reflections off the back wall?

.
A six foot tall wall will be acoustically 'invisible' below roughly 180Hz.
 

·
Registered
Joined
·
148 Posts
I would say its personal preference. If you need or want a dining room I'm sure with the proper accoustical treatments you'd be good to go with a separate dedicated room and have the benefits of less bass needed to fill the room. I probably wouldnt have a dining room overlooking the theater though. Might also be a little goofy for resale on the house.


I would consider the layout of your house and what you want to accomplish. The half wall would be good if you plan on throwing a shelf bar on it with some stools overlooking the theater. I wouldn't go this route solely based on acoustics though.


Spend some time over in the theater construction area of the forums and you'll get plenty of ideas. The design phase can be a lot of fun and there are plenty of inspiring build threads on this site. Some of the theaters that members have built here are mind blowing.
 
1 - 18 of 18 Posts
Top