Room needs more bass

[mustang guy]

 

This was the original post bhenry sent me which mentions room dimansions. I would guess about a 7 1/2' ceiling height.

 

bhenry: Thanks for the interest in my quest for more bass! Here are some pictures of the room, it is an "L" shape with the long part where the A/V equipment is being about 45/50' long and the short part around the corner is about 30' long.

 

long portion with sofa 12' x 50' = 600 sq ft

short portion with table in it 18' X 12' = 216 sq ft

600 + 216 = 816 sq ft

816 X 7.5 height = 6120 cu ft

stairway volume estimate 200 cu ft

total volume of room 6120 + 200 = 6320 cu ft, which is 320 cu ft over the 6,000 cu ft specification for two stacks of KW-120-THX subs.

 

If he builds a wall to block off back room, it would reduce the volume by:

 

12' X 30' = 360 sq ft

360 X 7.5 height = 2700 cu ft

 

And the remaining volume would be:

 

6320 - 2700 = 3620 cu ft for the HT room including volume of stairwell. With two stacks of KW-120-THX's, this would be well under the THX 6,000 cu ft specification you mentioned. There is no good way to build a door for the stairwell, but with this much overage, the room will still pressurize well if a wall is built.

 

Your thoughts?

 

Since the REW Room Sim utility doesn't do irregularly shaped rooms, I've just used the approximate dimensions (eyeballing the position of the couch and subs from the front wall).  The first image is the approximate low frequency response--at the listener's ears--for the current placement of the Khorns and subs, and the second image is for the same placement, except that the subs are simply moved to the front wall.  You might recommend just moving the equipment rack off to one side and placing (or stacking) the subs on the front wall between the Khorns, since the Room Sim shows a significant improvement in LF response doing just that.

 

imaged deleted

 

 

Which stack would you move, the one in the wall or the one behind the sofa?

 

I have read that in some theaters, the sub is placed slightly to the right of the center channel, and if there is a second sub, it is placed in the rear to the left of center.  Using that memory as my guide, the ones in the wall would be put to the right of the equipment rack. The ones behind the sofa would remain.

[Chris A]

All four subs on the front wall.

 

EDIT:  I guess I should explain rationale...

 

I see a lot of advice splashed about (including from Geddes, Toole, and others) on spacing subs around a room in order to "fill in the holes in coverage due to room modes".  For regular-shaped rooms that are shoe box shaped that approach may work.  For irregularly shaped rooms (like in this case with BHenry's room), I really don't advise that unless and until you get a configuration that works well without the scattered spacing.  I think that the rationale for this is complexity of implementation.

 

If you place the subs all on one wall, but spaced across that wall, you will, in effect, be dealing with the room modes that are longitudinally oriented (i.e., the 50' direction).  The width and height of the room have modes that are higher than 40 Hz (which is, in my not so humble opinion on this subject the better crossover frequency to the subs from the Khorns than a higher frequency crossover).  These are the main modes of the room that will dominate the LF coverage.  There are higher complexity modes (shown in the plots above), but their contributions are usually less than the main modes--by a large factor.

 

Secondly, by manifolding the subs together in one place, the Fc of the subs will broaden and deepen, in effect making a bigger and lower sub effectively (a very good thing). 

 

Thirdly, it simplifies the time delay settings for the listening position since you can set all the delays to be equal.  Then all you have to do is to get the Khorn delays right-making sure that you add about 7 feet to the distance of the DR subs' settings than the Khorns (i.e., the Khorn bass bin is approximately 8 feet in length by the time it emerges from the corner). 

 

Fourthly, you're not listening to the higher order harmonic of the subs as much if they are farther from your listening position - indicating a cleaner sound to the LF.

 

YMMV.

 

Chris

Edited April 29, 2015 by Chris A

[CECAA850]

All four subs on the front wall.

 

 

That would t least eliminate any phase issues.

[mustang guy]

There isn't room for them all unless he goes with different mains:

Edited April 29, 2015 by mustang guy

[Chris A]

Move the electronics...  Leave the TV where it is.

[Chris A]

A secondary objective (one that may actually solve the room mode problems) is to implement a "double bass array" that would eliminate the longitudinal modes of the room, albeit with some loss of room gain, but making the entire room a "sweet spot".  This would mean placing two subs on the back wall (with the table and chairs) and setting them out of phase to cancel the longitudinal LF waves coming from the front wall.  It's a really cool and neat idea that apparently works well in shoebox-shaped rooms.  It might work in this instance.

 

EDIT: For those of you not familiar with this technique, it is an application of the same principles used in noise-canceling headphones.

 

Chris

Edited April 29, 2015 by Chris A

[mustang guy]

A secondary objective (one that may actually solve the room mode problems) is to implement a "double bass array" that would eliminate the longitudinal modes of the room, albeit with some loss of room gain, but making the entire room a "sweet spot".  This would mean placing two subs on the back wall (with the table and chairs) and setting them out of phase to cancel the longitudinal LF waves coming from the front wall.  It's a really cool and neat idea that apparently works well in shoebox-shaped rooms.  It might work in this instance.

 

Chris

That certainly sounds easier than moving that custom electronic stand. It looks like it is part of the built up floor. Only bhenry can answer that.

 

I was also thinking that the subs could be side by side under the electronics. He has more electronics than would fit, but two of the electronics could be placed on top of the KHorns. It would give him room for a much larger screen also.

 

edit: I did a quick drawing of what I thought the front wall would look like with the subs all on the floor. The only other component is the RC-7. What this tells me is that ALL of the electronic equipment which is currently on the floor will have to be relocated to above the KHorns or somewhere else. There is most definitely room for more screen either way.

Edited April 29, 2015 by mustang guy

[Chris A]

By the way, the rack and electronics in the middle of the front wall also degrades the Khorn imaging in the midrange frequencies.  I'd recommend placing some absorption tiles good enough for 200-2000 Hz on that front wall (and on the sides of anything) in between the Khorns, and on the side walls nearest the Khorn midrange horn mouths.. 

 

I could also recommend diffusion tiles, but they won't be as effective in the near field as absorption tiles. 

 

It's the near field reflections in the midrange which are the ones that confuse and degrade the stereo imaging.

 

Chris

[LarryC]

1) The dog is sucking up the bass

You beat me to it! 

 

I've seen a staircase and more than one floor cause a big loss in the bass.

 

I can't explain it, or fix it, either.

Edited May 4, 2015 by LarryC

[bhenry]

I moved the subs behind the couch about 3' off the outside wall and matched the phase on both sets of subs and it helped a bit. I would love to be able to move these things all over the place but I don't think that's going to happen. I thought about trying all four on the front wall but that would require a TON of effort and I'm not sure I want to get involved with that.

I thought about dumping this gear but I think I'll just get it as good as I can and if I ever move then I'll hope for a better result. It's nice gear so I think that makes sense because I'd hate to have to buy this stuff again!

[derrickdj1]

That sounds like a good plan.  Most of us have to make a few compromises in our setup due to gear foot print, aesthetics, cost, ect.  The last 10% of improvement may cost more than everything else, lol.  Due to being in a large basement, I got bass shakers.  Much cheaper than more subs, putting up wall, ect.

[mustang guy]

I moved the subs behind the couch about 3' off the outside wall and matched the phase on both sets of subs and it helped a bit. I would love to be able to move these things all over the place but I don't think that's going to happen. I thought about trying all four on the front wall but that would require a TON of effort and I'm not sure I want to get involved with that.

I thought about dumping this gear but I think I'll just get it as good as I can and if I ever move then I'll hope for a better result. It's nice gear so I think that makes sense because I'd hate to have to buy this stuff again!

I hear ya. Having all the subs in front would require a monumental amount of work and may not pan out. It would look pretty cool though.  

 

If you had nothing else to do with your life except make that room the acoustical version of heaven, it would be different. By the sound of it, you are done fiddling with it, and as Derrick so wisely said you are compromising. There aint nothing wrong with that!

 

If you ever get a second wind and decide to put all those subs up front, definitely take a picture even if it fails miserably. HAHA