[bpape]

If they were angled with drywall, then you could do something thicker as an inverted triangle to make it APPEAR as a square or rectangle again - but give you some good, broadband bass control in the process.  IMO that would be a step in the right direction.

Bryan

[youngho]

CAK,

Sorry, I'm not an expert, so forgive my intrusion, but it seems a little hard to explain the relative null you're measuring in terms of modes from the room dimensions. Do you find that the null goes away significantly as you move the microphone away from the midline and towards one of the sidewalls? Usually, modes are approximately calculated by dividing 565/x, though wall construction and other details will often shift these down slightly. If the null is due to cancellations from standing waves, changing positions should significantly change the measurements.

In terms of the bass trapping columns you have there, these look like they can basically be considered to be panel absorbers. According to Everest's Handbook, you can calculate the resonant frequency of a panel absorber as 170 divided by the square root of the product of the panel's surface density and the airspace behind the panel. For 1/4" plywood, that density is 0.74 lb/sq ft. Since the dimensions you gave for the columns were 15" x 18", if we substitute these into the equation, we get 46 Hz and 51 Hz, so the panels should resonate at these frequencies but ultimately convert some of the sound energy to heat due to frictional losses from the fiberglass. However, this equation only gives you a rough approximation, and since you've framed out the corners, this may shift these frequencies up, which I don't know how to calculate. Sorry. In any case, you can see that the columnar construction that you've chosen focusses, perhaps inadvertently, on a relatively narrow frequency range.

The advantage of arranging them as a triangle, rather than a rectangle, is that you have variable airspace depth behind the panel (maximal in the middle of the panel, less so as you move towards either wall), which allows for broader absorption of bass frequencies, though probably less so at a specific frequency. In terms of higher frequencies, however, a plywood panel straddling the corners would have the theoretical disadvantage of making tangential modes more prominent because you now have a wider area of parallel surfaces to bounce off.

I believe that this may answer a few of your questions, but I'll leave it to the experts to address the rest.

Young-Ho

[CAK]

Just to clarify, which of the two designs is less likely to have a negative effect on bass.  I realize traps will be necessary in both, but from an acoustical scientific perspective would it be better to have an angle on the front/side wall joint rather than introduce another corner with the column design?

Thanks,

CK

[bpape]

If you're going to chop off the corner with the angle, then fill it back in to make a 'fake column', you have the corner issue whipped and no new REAL corners created.

The membrane type absorber youngho refers to would be very unpredictable in this situation with obstacles behind it, different fillings from left to right, etc.  Don't get me wrong, those can be very very useful in tuning a room - but I wouldn't do it in this situation.  I'm quite sure you're getting some of that membrane type effect right now - just impossible to predict how much and where it's centered.

Bryan

[CAK]

Thanks Byran.  You think 703 cut into triangles (or whatever angle will reform the column) and stacked in each corner from floor to ceiling sufficient?

Thanks again!

[bpape]

That's what I'd start with.  I'm not sure that will solve all of the problems but it will certainly take care of some of the room issues.

Bryan

[bocephus]

Off-topic a bit, but I just wanted to chime in and repeat what some others have already said; great-looking set-up!  What type of rack is that?

[CAK]

Thanks 

That’s a home made rack. I like the minimalists approach and just needed something small and simple.

[Housteau]

I have been giving this some thought.  I also like the look of your room.  For me that is nearly as important as the sonic signature, as it can set a certain mood for listening.  So, I understand your reasons for visual and sonic symmetry.  Your room is already trimmed and finished off so well that it would be a shame to tear back into it once again.  But, if you do, well, this is what I would do.

I would first soundproof that AC ducting with several inches of 703, then solidly enclose it as you have done.  Only this time make it as small as possible.  Then, you need to fill in the two corners created by this square enclosure with triangular sections of 703.  When you are finished it should look as if that corner just consists of a singular column of triangular cut pieces of that 703 from floor to ceiling.  You can then cover that corner with a fabric stretched frame.  The opposite corner can just be filled with the triangular 703 and covered in the same way.  This is how I did my room.

Visually this will be symmetric and acoustically nearly so.  The higher frequency absorption should be close to the same.  However, as you get lower in frequency there will be an imbalance, but it should not happen such that imaging would be impaired at all.  As your room sits now there is already an imbalance.  This modification will take care of the corner issues you have now and add in more broadband value to the treatments.

[CAK]

Housteau, thanks for the suggestions.  I'm still contemplating what to do with the corners.  I think I'm leaning towards triangulation as that way opens up more room behind the speakers giving them a bit more air to breathe... so to speak. I can make 4" thick panels from floor to ceiling that cover the angles. That should do well for broad band bass control I would think.

I'm still interested in how the angle would affect response vs. the two corners created by the column. For example, would an angle decrease bass response since you lose the convergence of the corner (x2) ? Anyone have any clue as to what angles like this do to a room?  I'm trying to figure what negative anomalies I will create (if any) with the corner triangulated vs. the column before I deconstruct. Anyone have a program that allows me to change the front corners and see what happens with reflections and such?

CK

[bpape]

If the angles are covered with thicker absorbtion, anything that would 'reflect' purely off the angle would be absorbed.  Anything that's not, the waves are so large it will go right around it.

Bryan