Room dimensions - off the wall

[kach22i]

Item-1

Room dimensions are measured from the surface of a wall, floor and ceiling.

However under certain conditions and certain frequencies the room dimensions may seem to be different or react different - as in different lengths.

For Instance in my walk-out basement listening room I have on my left side a densely packed 3.5 foot wide CD rack that projects 7 inches out from the wall and just catches the "first reflection" on the edge closest to my listening position.

Is the acoustic center of the room now shifted to the right 7 inches or maybe 3.5 inches?

I'm going to do an experiment tonight and move my right speaker over to the right, already have the masking tape on the floor to mark the positions.

Item -2

Masonry walls below grade are the core foundation of my room for low bass notes. However, higher frequencies reflect off the furred-out drywall.

Therefore my room is several different sizes depending on the frequency, right?

Item-3

I'm using a 6'x6' Ikea Kallax as a record rack and rear area/zone room divider, another six feet of space lays beyond.

Low ceiling, only 9" higher that the record rack. Narrow room, 30" wide access from rear room entrance each side of record rack in the FUTURE.

Record rack has each cube filled to about 80% of opening.

Is the room divider that is 70% ish solid - counting flanking side openings my acoustic rear wall, or the true wall six feet beyond?

I will be adding sketches to explain clearer, see below.

 

[brad225]

George, when did you move your system down stairs. I thought I remembered your system had a stairway or room divider behind it as the front wall? Perhaps it was someone else.

In response to your question, my feeling is. Because the space is open to that wall 6' behind storage that would be the included in the total depth of the space. When playing music the entire space would be energized.

Do you have a 1st reflection device on the right side of the room?

I love seeing what people do with their listening room space.

 

[kach22i]

George, when did you move your system down stairs. I thought I remembered your system had a stairway or room divider behind it as the front wall? Perhaps it was someone else.

In response to your question, my feeling is. Because the space is open to that wall 6' behind storage that would be the included in the total depth of the space. When playing music the entire space would be energized.

Do you have a 1st reflection device on the right side of the room?

I love seeing what people do with their listening room space.

I think I know of a couple of members rooms with M/L's or Maggies and no wall behind them. I have never been one of them, but have an open mind.

I moved less than a year ago and resisted unboxing my stereo for six months because I wanted to build out the room first. Because I folded to my musical desires I have learned so much about the space that it has influenced future design plans for the better.

I agree about the room divider not being there for the bass. However when I had the room divider/record storage 18" closer to the front wall my head was only a foot or so off it. The sense of room space was smaller. The room seemed to get 10 feet longer by moving the storage wall less than 2 feet back.

Not a 1 to 1 ratio acoustically speaking.

Kind of like moving your speakers 6 inches more apart and having it sound like 6 feet more apart.



First reflection point is the vertical purple pool noodles at doorway.

The large white convex PVC reflectors are symmetrical in the room but unfortunately miss the first reflection points. However they are spot on for the second reflection points.

Things are changing in the room every couple of days, this has been going on for close to 2-months now.

Just moved my chair 6 inches forward last night, tonight will be 6 inches to the right along with the speaker - will see what happens.

My basic premise in this thread is that finishes and furnishings have an affect on acoustic room size, and that size varies with frequency.

I do not know if computer modeling adjusts for these parameters, but think the human ear does.

Edit:

I plan on mounting a homosote compact cassette rack on the door to the right. I just have to install some flat brass strips near the bottom of each shelf so cassettes do not go flying when door is shut hard. Also the hollow core will be replaced with a solid core door with acoustic seals. Leads to utility room, bathroom and outdoor side door.

EDIT-2:

New acoustic centerline is 4 inches to the right towards the utility room door.

Redid toe-in.

Adjusted centrally located subwoofer to follow suit.

Not sure yet if pushing the sub back 2 inches at the same time was wise, may have picked up more bass via front wall boundary reinforcement. Need to play more music on multiple mediums.

Speakers are the recommended six feet apart.

I don't think that I've had this level of soundstage cohesion before outside of a nearfield experiment a while back.

So, to answer one of my original ponderings -YES first reflection points influenced by solid furniture protrusions such as maxed-out CD racks and recessed door archways can shift the acoustic center of a room.

At least in my case it did (by four inches).

 

[BruceD]

First reflection points.

BruceD

 

[kach22i]

I updated my AutoCad file with what I think I've learned by this recent set of experiments.

My CD storage is overflowing and I'm trying to rid myself of red oak, so looking at something custom on door and flanking wall.



I am not married to any particular 1st reflection point wall treatment as I have tried three different things so far.

I am resolved to do something "smart" despite myths of 30 degree dispersion for my speakers.

I kind of like the Flex 48's, but also would dig a highly textured diffraction statement there.

 

[kach22i]

I've slept on the problem, did a mark-up and fought the CD rack Vs diffuser issue to the point of looking at cutting holes in solid concrete walls and adding steel beams just to get recessed CD storage out of the first reflection area.

Then it hit me, why fight it?

Let the CD storage and diffusion device become one in the same - combine them.

Start with a vertically running Quadratic diffuser pattern and scale it to accommodate CD's.

Horizontal shelves would hold the CD's but in a fore and aft pattern mimicking the quadratic diffuser.

I'm doing a search right now, but if I don't find anything will start some design study sketches.

I do have concerns about reading covers and accessing the jewel cases without them falling all over the place. Would be nice if somebody else worked this all out already.

I'm just not confident that even sparsely loaded CD racks are effective diffusers at first reflection points.

Of course one can always add absorption behind the rack and offset it from the wall to get a proper acoustic balance.

Looking for a KISS solution here, not a DIY science project.

EDIT:

Perhaps something like this QRD-D1 scaled to fit loosely stacked CD's. Mount two vertically on each wall.



http://www.decoacoustic.com/diffusion/diffusion49.html


EDIT-2:

Looking at 8-12 of these (going all way to front wall), so it's got to be cheap, most likely DIY.



EDIT-3:

Looks like good diffusion pattern to me, and adjustable depending where one puts the CD's.

http://www.racksandcabinets.com/avmomwamodoc.html


I bet I could fit some acoustic foam in the empty spots if I wanted to.

Product above is no longer made.

Boltz is similar, maybe even better but it does add up.

 

[kach22i]

Unless I find something off the shelf that I can buy that will serve as both media storage and diffuser/absorber I'm setting in the direction of building something myself.

A few sketches from the sketchbook, a work in development.



It's just a box really, fabric wrapped homosote back, two most likely aluminum plates vertically, and a few plywood shelves.

If I want more absorption, will make deeper to accommodate fabric wrapped mineral wool over the backer, backer might be plywood in lieu of homosote. Still debating strength and weight issues in my mind.

I've used all these materials before in other furniture and audio related projects.

Some of the images came out sideways or upsidedown - oops.

 

[Addicted to hifi]

I've slept on the problem, did a mark-up and fought the CD rack Vs diffuser issue to the point of looking at cutting holes in solid concrete walls and adding steel beams just to get recessed CD storage out of the first reflection area.

Then it hit me, why fight it?

Let the CD storage and diffusion device become one in the same - combine them.

Start with a vertically running Quadratic diffuser pattern and scale it to accommodate CD's.

Horizontal shelves would hold the CD's but in a fore and aft pattern mimicking the quadratic diffuser.

I'm doing a search right now, but if I don't find anything will start some design study sketches.

I do have concerns about reading covers and accessing the jewel cases without them falling all over the place. Would be nice if somebody else worked this all out already.

I'm just not confident that even sparsely loaded CD racks are effective diffusers at first reflection points.

Of course one can always add absorption behind the rack and offset it from the wall to get a proper acoustic balance.

Looking for a KISS solution here, not a DIY science project.

EDIT:

Perhaps something like this QRD-D1 scaled to fit loosely stacked CD's. Mount two vertically on each wall.

View attachment 65102

http://www.decoacoustic.com/diffusion/diffusion49.html
View attachment 65103

EDIT-2:

Looking at 8-12 of these (going all way to front wall), so it's got to be cheap, most likely DIY.

View attachment 65104

EDIT-3:

Looks like good diffusion pattern to me, and adjustable depending where one puts the CD's.

http://www.racksandcabinets.com/avmomwamodoc.html
View attachment 65105

I bet I could fit some acoustic foam in the empty spots if I wanted to.

Product above is no longer made.

Boltz is similar, maybe even better but it does add up.

Great cd holder.

 

[MTB Vince]

At that tight a distance between both the sound source and MLP vs the primary reflection treatment along the sidewall immediately adjacent each loudspeaker, you should be using a 4-6" depth absorptive trap for that first treatment rather than a diffuser. The pair of poly diffusers this would free up might come in handy on the front wall directly behind each Martin Logan in order to diffuse the dipole's rear wave.