[machine]

Made the decision to use 6lb, mineral wool (Roxul) for corner bass traps and 4lb, 2" mineral wool for first relection point.  ($0.80 sq' and $0.40 sq')

One of my front corners has a door on sidewall starting 16" from the front wall which screws up using solid 34" triangles (4 of these per 2' x 4' sheet).  I could go with the smaller 24" triangles (8 of these per 2' x 4' sheet), but was wondering if I could just put rectangle traps in each corner to save dealing with all this cutting.

For the corners I would build a floor to ceiling rectangle in each corner.  these would be 2' wide and 1' deep.

Would this be as good as doing the 24" solid triangles, floor to ceiling in front and 34" in rear?

Does the triangle shape help with bass absorbtion?  Any other benefits vs. rectangluar shape.

Thanks for any help

Edit: 12'w x 17'l x 9'h room

[klh]

Why not laminate 6 2'x4'x2" peices together... no cutting and you have a unit 1' deep, 2' across and 4' tall. Same effect but exceedingly easier. That's what I've done except I'm only 6" deep with 8# MW. I just tied a string around them and it holds them together wonderfully. You could stagger them for added strength, so if you wanted to go floor to ceiling the back would be a 2' tall peice, with a 4' peice above it, and a 2' peice above that. The next layer would have a 4' peice above another 4' peice (so it would be 242, then 44, then 242, then 44, etc., until you are 6 panels deep).

[machine]

I'm able to get the 6lb MW in 3" thickness and was in either case going to try and glue them together and then wrap with 4oz black polyester batting and black burlap.  I should be able to just set these in the corners with minimal attachment.  I think the 6lb density should work using this approach.

I can build these slabs and angle them also, which gives me the flexibility to experiment.

For the 1st reflection point, I need to think about what I'm going to do.  I like the idea of just wrapping this stuff for ease of construction, but I think the 4lb may be too flimsy to do this with.

[samplesj]

For the 1st reflection point, I need to think about what I'm going to do.  I like the idea of just wrapping this stuff for ease of construction, but I think the 4lb may be too flimsy to do this with.

Steven Helm has a http://www.radford.edu/~shelm/acoustics/bass-traps.html'>walkthrough on using drywall corner bead for trap frames.

They are very lightweight and pretty cheap too.  I just ran a couple of wires out the screw holes and hung them from that.

[MaxCast]

I followed the link to Stevens site.  The before and after graphs look like a reduction in scale.  The dips and peaks are still there, just a lower db reading.  Couldn't the same be done with the volume control?

[bpape]

The peaks and dips are in the same place but not of the same intensity in relation to each other.  Some of them may be seating position related and more difficult to deal with and require more surface area.  Peaks can be EQ'd down to assist also.

The other thing that the absorbtion provides that those graphs don't show is the reduction in decay times at different frequencies which is a significant benefit in many ways.

You can certainly go solid squares in the corners.  It will expose more surface area and give better overall average depth to each square foot of absorbtion exposed.

[MaxCast]

Thanks, bpabe.
It just seems if you slide the mustard colored curve up you would be covering up most of the red.  I guess I would have expected more attenuation.  That's why you accoustic guys always say the more the better.


I can see how absorbtion effects peaks.  Does absorption also effect dips?

Decay time.  Is that like echo?  the time it takes a tone to reverberate out of the room?

What is modal ringing?

Thanks,

[bpape]

Yes.  Treatments deal with peaks and dips.  Think about WHY you have dips (nulls).  It's because you have 2 waves colliding at opposite angles from different directions that cancel each other.  OR, you have 2 waves coming from the same direction but 180 degrees out of phase with each other.  Treatments will help attenuate those bounces so the intensity of the null is less.  Same with the peak but it's when 2 waves align but are IN phase with each other.

More bass control is better usually.  It's hard to get too much.  Just be careful when using broadband absorbers that you don't also do too much to the mids and highs that have already been knocked down with things like carpet and curtains that only affect high frequencies.

Decay time (RT60) is the amount of time it takes a sound to decay by 60db - not as some people think TO 60db.  Modal ringing is a phenomenon where waves that have lengths at fractions or multiples of room dimensions (or combinations of dimensions in the case of the non-axial modes - tangential and obliques) that reinforce each other by aligning at a place and in phase with each other as I described above.  Non modals tend to die out quicker by them selves since they don't reinforce each other in phase as often due to not being aligned with room dimensions.

If you look closely at your plots, you'll likely see that the one big null is  at the approx same place on the scale as it was before - even though the rest is reduced in level.  So, I've eliminated several db of variation overall AND reduced my decay times in the process.

[MaxCast]

Thanks B.