Tiny Basement Mixing Room Woes

[epstudio]

Hello Everyone in Studio Land!

I haven't posted anything in a long time... Life has been quite busy for me since I joined this incredible and amazing forum so many years ago! Having said that, I have continued building small project studios in all of my various living arrangements over the years which leads me to my newest challenge...

We have purchased a modest 4 bedroom Bungalow which means we are hopefully going to be settled for awhile, as such my first priority has been to try and claim some square footage for my latest studio build science project!

The dirty details: (and by dirty I mean SMALL )

Room: 3.24 m Long 2.34 m Wide 2.24 m Tall

Isolation Requirements: 2 walls are completely underground (exterior) other two can be sealed without much difficulty so I am not concerned

Pre-built Soffits: Two Studios, ago I spent a significant amount of time researching and building a flush mount speaker system based on John's design and various other builds on the forum (I will post pics of that build for fun). The results of which are fantastic and ultimately ended up being portable! (my restrictions for building have been and continue to be space or lack there of)

I am reaching out to get everyone's input on my design so far (see attached pics) with the following specific questions:

1) Should I bother with the first reflection angled slat walls? (to get my 12 degrees of splay I've had to bring the soffits together... sacrificing sound stage)

2) Is it practical to use the extra space to the side of the soffits for hangers as shown? (or should I just stick to broadband absorbers with high frequency diffusion and use that empty space as part of the cavity?)

3) Is it realistic to put a panel absorber on the door? (to try and mirror some bass absorption from the corner trap opposite?)

4) I was planning to build a multi angle cloud into the room at 12 degrees over the mix position and then angle it back towards the rear wall (hopefully achieving some extra bass and low mid trapping functionality) Is there any suggestions on what the back wall absorption strategy should be?

5) I wanted to add two more Low-Mid/Bass absorbers on the last two parallel walls and was considering John's Curved Panel Absorber http://johnlsayers.com/Recmanual/Titles/Acoustics2.htm in order to retain some high frequencies in the room. Does anyone have any thoughts for or against?

I realize that my options are severely limited and any results I can achieve will be less than ideal given the excruciatingly miniature space my wife has allowed me to occupy for this latest endeavor...
so I greatly appreciate in advance any and all opinions, direction, advice, criticism, humor! assistance and time that the community my have for me.

Thanks in advance as always!

Lee

[epstudio]

Here are some Pics from the last build in my previous basement where I conceived of and executed construction on the now portable soffits...

[epstudio]

and the earlier ones... Sorry didn't realize 16 photos was the max!

[Gregwor]

Hey, another Albertan! Hope you got out to vote today!

Room: 3.24 m Long 2.34 m Wide 2.24 m Tall

Small sucks but at least you have a room. A small room is better than no room!

Pre-built Soffits: Two Studios, ago I spent a significant amount of time researching and building a flush mount speaker system based on John's design and various other builds on the forum (I will post pics of that build for fun). The results of which are fantastic and ultimately ended up being portable! (my restrictions for building have been and continue to be space or lack there of)

This could be more rigid overall in my opinion. Especially since you aren't decoupling your speakers. Could you add some 2x4's on edge underneath of the shelf?

1) Should I bother with the first reflection angled slat walls? (to get my 12 degrees of splay I've had to bring the soffits together... sacrificing sound stage)

Have you ray traced your SketchUp yet to see what you need to do to obtain an RFZ sphere around your head at mix position? The 12 degree thing does not help you here. That's a fine guideline for the rear half of your room or a live room, but if you're soffit mounting your speakers with large baffles, trying to obtain an infinite baffle design, you need to build your soffit wings to give you an RFZ and reflect sound towards your rear wall. Your rear wall will have to be very deep absorption in order to attenuate your first reflections.

Also, at what percentage depth-wise in your room will you have your head?

2) Is it practical to use the extra space to the side of the soffits for hangers as shown? (or should I just stick to broadband absorbers with high frequency diffusion and use that empty space as part of the cavity?)

The cavity looks small enough that you might be better off just filling that space with insulation.

3) Is it realistic to put a panel absorber on the door? (to try and mirror some bass absorption from the corner trap opposite?)

I don't see a door in your SketchUp so I can't comment on this.

4) I was planning to build a multi angle cloud into the room at 12 degrees over the mix position and then angle it back towards the rear wall (hopefully achieving some extra bass and low mid trapping functionality) Is there any suggestions on what the back wall absorption strategy should be?

Ignore the 12 degree rule here. You need to angle is such that you have an RFZ. That's the goal.

Your rear wall ideally should be 2 feet thick of hangers. If you can't spare that much space, make it as thick as possible. Minimum I'd ever go is 6". 24"+ is ideal.

5) I wanted to add two more Low-Mid/Bass absorbers on the last two parallel walls and was considering John's Curved Panel Absorber http://johnlsayers.com/Recmanual/Titles/Acoustics2.htm in order to retain some high frequencies in the room. Does anyone have any thoughts for or against?

That could be great. Obviously you're going to need something there. I wouldn't commit to anything at this point though. If you've followed many threads on the forum you'll see that the best way to treat a control room is one step at a time. Install a device, take acoustic measurements and then design/build the next device accordingly.

I realize that my options are severely limited and any results I can achieve will be less than ideal given the excruciatingly miniature space my wife has allowed me to occupy for this latest endeavor...
so I greatly appreciate in advance any and all opinions, direction, advice, criticism, humor! assistance and time that the community my have for me.

My biggest fear for you in HVAC. What is your plan with that? Clearly you don't have the space or maybe even the need for isolation.

Again, I'm glad to see another AB homie on the forum! Cheers!

Greg

[epstudio]

Hey, another Albertan! Hope you got out to vote today!

Howdy Greg! Great to see another Albertan indeed! I voted last week lol I couldn't wait to exercise my civic right!

Room: 3.24 m Long 2.34 m Wide 2.24 m Tall

Small sucks but at least you have a room. A small room is better than no room!

Yes you are totally correct! I am happy to have a small corner for my recording addiction!!

Pre-built Soffits: Two Studios, ago I spent a significant amount of time researching and building a flush mount speaker system based on John's design and various other builds on the forum (I will post pics of that build for fun). The results of which are fantastic and ultimately ended up being portable! (my restrictions for building have been and continue to be space or lack there of)

This could be more rigid overall in my opinion. Especially since you aren't decoupling your speakers. Could you add some 2x4's on edge underneath of the shelf?

Hmmm, I haven't noticed any rigidity issues? (each complete soffit weighs almost 400 lbs!!) although I suppose I could add even more mass by doing what you suggest if you think it would result in better infinite baffle response! Please advise?

1) Should I bother with the first reflection angled slat walls? (to get my 12 degrees of splay I've had to bring the soffits together... sacrificing sound stage)

Have you ray traced your SketchUp yet to see what you need to do to obtain an RFZ sphere around your head at mix position? The 12 degree thing does not help you here. That's a fine guideline for the rear half of your room or a live room, but if you're soffit mounting your speakers with large baffles, trying to obtain an infinite baffle design, you need to build your soffit wings to give you an RFZ and reflect sound towards your rear wall. Your rear wall will have to be very deep absorption in order to attenuate your first reflections.

Interesting, I hadn't picked up on that 12 degree distinction in previous threads but it works for me and does make sense (there seems to be a lot of designs and direction surrounding 12 degrees for splayed wings even with soffit mounted speakers...?) Also, I have not ray traced my sketchup yet but I will do so and post the results! Regarding the design of the Soffit wings (once I have the angle calculated)... Should I bother with a slat design? Even trying a tuned Helmholtz resonator? I'm worried about losing all my highs as the bass trapping is going to be as aggressive as possible in this tiny room...

Also, at what percentage depth-wise in your room will you have your head?

My head will be at the equilateral triangle peak (ideal listening position) so, approximately 40 to 45% into the room I would guess?

EP Studios SWEET SPOT.jpg

2) Is it practical to use the extra space to the side of the soffits for hangers as shown? (or should I just stick to broadband absorbers with high frequency diffusion and use that empty space as part of the cavity?)

The cavity looks small enough that you might be better off just filling that space with insulation.

3) Is it realistic to put a panel absorber on the door? (to try and mirror some bass absorption from the corner trap opposite?)

I don't see a door in your SketchUp so I can't comment on this.

Sorry I thought it was obvious from my drawing... LOL See below!

EP Studios DOOR.jpg

4) I was planning to build a multi angle cloud into the room at 12 degrees over the mix position and then angle it back towards the rear wall (hopefully achieving some extra bass and low mid trapping functionality) Is there any suggestions on what the back wall absorption strategy should be?

Ignore the 12 degree rule here. You need to angle is such that you have an RFZ. That's the goal.

Yup! I will get the ray trace done and submit my modified design around that!

Your rear wall ideally should be 2 feet thick of hangers. If you can't spare that much space, make it as thick as possible. Minimum I'd ever go is 6". 24"+ is ideal.

With that in mind I will amend my design to include a radical 24" cavity on the back wall /ceiling area to create maximum hanger space!

5) I wanted to add two more Low-Mid/Bass absorbers on the last two parallel walls and was considering John's Curved Panel Absorber http://johnlsayers.com/Recmanual/Titles/Acoustics2.htm in order to retain some high frequencies in the room. Does anyone have any thoughts for or against?

That could be great. Obviously you're going to need something there. I wouldn't commit to anything at this point though. If you've followed many threads on the forum you'll see that the best way to treat a control room is one step at a time. Install a device, take acoustic measurements and then design/build the next device accordingly.

This will be my Operating Procedure moving forward! Measure, Test, post results, build, install, test and Measure again! Rinse! Repeat!!

I realize that my options are severely limited and any results I can achieve will be less than ideal given the excruciatingly miniature space my wife has allowed me to occupy for this latest endeavor...
so I greatly appreciate in advance any and all opinions, direction, advice, criticism, humor! assistance and time that the community my have for me.

My biggest fear for you in HVAC. What is your plan with that? Clearly you don't have the space or maybe even the need for isolation.

Also, not shown in my drawing is the HVAC inlet above the mix position, I'm thinking I might have to do some sort of exhaust air vent type scenario (maybe over the door built into the ceiling treatment...) but in terms of isolation, yes I'm not too concerned!

Again, I'm glad to see another AB homie on the forum! Cheers!

I'm super excited for the help Greg! Thanks so much for responding, I apologize for my late reply (I was detained with work and my young children LOL) I will endeavor to respond sooner should you be able to keep working with me through my build!

Greg

[Gregwor]

Howdy Greg! Great to see another Albertan indeed! I voted last week lol I couldn't wait to exercise my civic right!

Crazy how Edmonton was all orange and the rest of the province was blue!!!

Hmmm, I haven't noticed any rigidity issues? (each complete soffit weighs almost 400 lbs!!) although I suppose I could add even more mass by doing what you suggest if you think it would result in better infinite baffle response! Please advise?

For the baffle, mass is EVERYTHING. This is necessary to properly direct the low frequencies as per the infinite baffle analogy.

Interesting, I hadn't picked up on that 12 degree distinction in previous threads but it works for me and does make sense (there seems to be a lot of designs and direction surrounding 12 degrees for splayed wings even with soffit mounted speakers...?)

12+ degrees is necessary as you're informed. However, due to the wavelength of low frequencies, you'd need an insanely long wall at 12 degrees for this to take effect at problematic frequencies. Basically, don't get hung up on it for your small room.

Regarding the design of the Soffit wings (once I have the angle calculated)... Should I bother with a slat design? Even trying a tuned Helmholtz resonator? I'm worried about losing all my highs as the bass trapping is going to be as aggressive as possible in this tiny room...

John Brandt incorporates a lot of slat design in the front half of his listening rooms. Personally, I'm not sold on the idea as maintaining high end in a room with insane amounts of insulation (required for bass frequencies) is difficult enough.

My head will be at the equilateral triangle peak (ideal listening position) so, approximately 40 to 45% into the room I would guess?

Like the 12 degree wall concept, ignore the equilateral triangle. It's a myth, kind of. What is most important is to try and have your head around 35-40% depth of your room. 38% is proven to be the sweet spot but some people have reported to enjoy being closer to ~35%. Having said that, position your head and design the angles and sizes of your soffits and wings around that!

Sorry I thought it was obvious from my drawing... LOL See below!

There is a room very similar to yours pretty much done on the forum somewhere. I don't have the time to look for it right now but I think it's in "other studios" forum.

With that in mind I will amend my design to include a radical 24" cavity on the back wall /ceiling area to create maximum hanger space!

Also, not shown in my drawing is the HVAC inlet above the mix position, I'm thinking I might have to do some sort of exhaust air vent type scenario (maybe over the door built into the ceiling treatment...) but in terms of isolation, yes I'm not too concerned!

Yes, you'll need supply AND return! Since isolation is not an issue for your, your low frequencies will be easier to control AND you can save a lot of money and time. Also, you could use simple residential HVAC concepts for your return.

I apologize for my late reply (I was detained with work and my young children LOL)

I feel ya! Kids take up so much time.

Greg

[epstudio]

Crazy how Edmonton was all orange and the rest of the province was blue!!!

Definitely says something about the demographic of Alberta for sure... I work in Oil & Gas so you can guess which way I voted

For the baffle, mass is EVERYTHING. This is necessary to properly direct the low frequencies as per the infinite baffle analogy.

So, even though these soffits are completely built already, by adding lumber to the bottom of the individual speaker shelves you believe the low end response of the baffle itself could be improved? (I could add 2x6's glued and screwed together for the extra mass, it would just eat into the superchunk roxul that's currently under the speaker shelves...) Like this?

SOFFIT AS IS :

EP Studios SOFFIT MASS X.jpg

SOFFIT WITH ADDED 2x6 MASS

EP Studios SOFFIT MASS.jpg

EP Studios SOFFIT MASS F.jpg

12+ degrees is necessary as you're informed. However, due to the wavelength of low frequencies, you'd need an insanely long wall at 12 degrees for this to take effect at problematic frequencies. Basically, don't get hung up on it for your small room.

Here is my horizontal RAY TRACE.... WOW that took forever!! Still need to do vertical but I'm hoping this can start a conversation about any problem reflections that you see?... I'm happy with the RFZ so far? unless I am missing something?

This is with Soffit Wings at 15 degrees...

EP Studios TOP RAY H.jpg

EP Studios TOP RAY H ISO.jpg

EP Studios BACK WALL RAY H ISO.jpg

There is a room very similar to yours pretty much done on the forum somewhere. I don't have the time to look for it right now but I think it's in "other studios" forum.

I think this is the build you are referring to? and YES it is nearly IDENTICAL!! Thanks for that Greg!!
http://www.johnlsayers.com/phpBB2/viewt ... 10&t=21539

John Brandt incorporates a lot of slat design in the front half of his listening rooms. Personally, I'm not sold on the idea as maintaining high end in a room with insane amounts of insulation (required for bass frequencies) is difficult enough

In that small room build I just referenced he did "solid" soffit wings ... Should I do the same as a starting point you think? I feel like I should do the exact same superchuck treatment the whole length of the ceiling/wall angle just like he has done... Thoughts?

Similar Build Soffit Wings and Ceiling Chunks.jpg

Also, instead of "hangers" for back wall absorption he did the whole thing in one big superchunk as his research indicated higher bass absorption per square foot of space (as my research also concluded) Do you have thoughts on this?

Similar Build Super chunk.jpg

Thanks again Greg for working through this with me! I will keep updating my design and get my vertical ray trace done... I feel that designing my bass trapping like Martin has done in his build is a good baseline. Seems yourself and Stuart both helped him out a lot and he got fairly awesome results! (I fear my room is slightly smaller than his though...)

Please advise if you think this is a good design concept at this point?

Cheers!!

Lee

[Gregwor]

Definitely says something about the demographic of Alberta for sure... I work in Oil & Gas so you can guess which way I voted

I think I voted the same as you!

So, even though these soffits are completely built already, by adding lumber to the bottom of the individual speaker shelves you believe the low end response of the baffle itself could be improved? (I could add 2x6's glued and screwed together for the extra mass, it would just eat into the superchunk roxul that's currently under the speaker shelves...) Like this?

That's a LOT of mass. You COULD do that, but I think that is excessive. I would just use 2x6's around the perimeter and then one across the middle of said perimeter. The whole idea is to make it strong. Your version looks insanely strong haha

Here is my horizontal RAY TRACE.... WOW that took forever!! Still need to do vertical but I'm hoping this can start a conversation about any problem reflections that you see?... I'm happy with the RFZ so far? unless I am missing something?

That looks awesome. Is that the biggest RFZ sphere around your head that you can get? The fact that you got a sphere at all is promising. Just remember that the bigger the sphere, the more you'll be able to lean around without having reflections! The same goes for your cloud design (your vertical tracing fun filled adventure!)

I think this is the build you are referring to? and YES it is nearly IDENTICAL!! Thanks for that Greg!!
viewtopic.php?f=10&t=21539

That IS it!!

In that small room build I just referenced he did "solid" soffit wings ... Should I do the same as a starting point you think? I feel like I should do the exact same superchuck treatment the whole length of the ceiling/wall angle just like he has done... Thoughts?

Totally.

Also, instead of "hangers" for back wall absorption he did the whole thing in one big superchunk as his research indicated higher bass absorption per square foot of space (as my research also concluded) Do you have thoughts on this?

Hangers have been proven to kick ass. If you're not handy, superchunk works great. Personally, I'd do hangers though. You won't be disappointed either way.

Thanks again Greg for working through this with me! I will keep updating my design and get my vertical ray trace done... I feel that designing my bass trapping like Martin has done in his build is a good baseline. Seems yourself and Stuart both helped him out a lot and he got fairly awesome results! (I fear my room is slightly smaller than his though...)

Smaller just means you'll need MORE treatment. So make your rear wall treatment as thick as possible and bass trap the HELL out of every single corner.

As you can see, with a ton of treatment and proper design, you can get pretty awesome results in rooms that are not ideal! I look forward to your build!

Greg

[epstudio]

Hello again Greg!

I have been swamped with life and not making a ton of progress on my build, although I did just start cutting the framing lumber for the back wall! In the downtime I have modified my design based on your previous suggestions and made some tweaks...

Hangers have been proven to kick ass. If you're not handy, superchunk works great. Personally, I'd do hangers though. You won't be disappointed either way.

I have added Hangers on the back wall (the cavity is just over 2' deep at the narrowest) What do you think of the Hanger sizes and orientation? I can't spare any more room than that unfortunately... The Hanger cavity front wall will be cloth covered roxul, and I will probably put a thin roxul panel on the back of the door to remove that reflection. Thoughts?

Hangers Front.jpg

Hangers Top.jpg

That looks awesome. Is that the biggest RFZ sphere around your head that you can get? The fact that you got a sphere at all is promising. Just remember that the bigger the sphere, the more you'll be able to lean around without having reflections! The same goes for your cloud design (your vertical tracing fun filled adventure!)

Here is the re-tweaked Horizontal RFZ... I managed to increase the sphere and this is probably the best it can get... Thoughts?

HORIZONTAL RAY TOP.jpg

HORIZONTAL RAY ISO.jpg

Here is my cloud design and Vertical Ray Trace... Had to get it pretty low in the front to achieve the right angles due to my low ceiling height but I think it will work... Thoughts?

CLOUD TOP.jpg

CLOUD LEFT.jpg

CLOUD BACK.jpg

CLOUD ISO.jpg

VERTICAL RAY RIGHT.jpg

VERTICAL RAY LEFT.jpg

VERTICAL RAY BOTT.jpg

VERTICAL RAY BACK.jpg

Smaller just means you'll need MORE treatment. So make your rear wall treatment as thick as possible and bass trap the HELL out of every single corner.

So, I am thinking of doing this with superchunks on the wall to ceiling angles where accessible... To maximize bass trapping outside of the hangars. What are your thoughts? is it too much or should I keep it in the design?

CIELING SUPERCHUNK.jpg

CIELING SUPERCHUNK ISO.jpg

CIELING SUPERCHUNK BACK.jpg

Hangers Back.jpg

Thanks again for your always helpful input Greg, hope things are great in your world... As I get the room framed in I will take acoustic measurements, starting with empty and continue measuring as treatments is added... Are you able to help me analyze the results? I will be using Stuart's guide and tools to do properly calibrated R.E.W. Acoustic tests... http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21122

Excited to get things moving finally! Take Care!

[Gregwor]

I have added Hangers on the back wall (the cavity is just over 2' deep at the narrowest) What do you think of the Hanger sizes and orientation? I can't spare any more room than that unfortunately... The Hanger cavity front wall will be cloth covered roxul, and I will probably put a thin roxul panel on the back of the door to remove that reflection. Thoughts?

Unfortunately the orientation of your hangers is incorrect. Try having them at around 40 degrees. If you can't make that work, have them all basically straight running front to back in your room. Remember, the sound hitting them is going to be coming from every angle imaginable.

Here is the re-tweaked Horizontal RFZ... I managed to increase the sphere and this is probably the best it can get... Thoughts?

So, I am thinking of doing this with superchunks on the wall to ceiling angles where accessible... To maximize bass trapping outside of the hangars. What are your thoughts? is it too much or should I keep it in the design?

You can never have enough bass trapping. Make them as big as you can!

Thanks again for your always helpful input Greg, hope things are great in your world

I'm hanging in there! Of course life throws curve balls but I can't complain!!

As I get the room framed in I will take acoustic measurements, starting with empty and continue measuring as treatments is added... Are you able to help me analyze the results?

There are lots of people on the forum that can chime in and help you out. If I see it first and have time to check it out I'll gladly throw my thoughts out at ya!

Greg

[epstudio]

Unfortunately the orientation of your hangers is incorrect. Try having them at around 40 degrees. If you can't make that work, have them all basically straight running front to back in your room. Remember, the sound hitting them is going to be coming from every angle imaginable.

Thanks for that Greg... I was trying to maximize number of hangers! Have a look below, if I orient them 40 degrees to the right I can fit 10 hangers, as compared to 9 if I swing them to the left... Which way would be better for the room?

RIGHT AT 40 DEGREES:

Hangers Top 40 R.jpg

Hangers Top 40 R B.jpg

LEFT AT 40 DEGREES:

Hangers Top 40 L.jpg

Hangers Top 40 L B.jpg

You didn't comment on the cloud design from my last post... Am I to assume therefore, that you approve? It's such a small space the cloud design was really giving me grief so some feedback would be helpful and put my mind at ease!

Thanks in advance as always Greg! You're AWESOME!

[Soundman2020]

Have a look below, if I orient them 40 degrees to the right I can fit 10 hangers, as compared to 9 if I swing them to the left... Which way would be better for the room?

Either way will work. Go with whichever is easier, and whichever gives you the greatest total surface area of hanger.

Here is the re-tweaked Horizontal RFZ...

Are you sure that your surface normals really are perpendicular to the reflective surfaces? Many of those reflections seem to not be at the correct angle, for both the soffit wings and the cloud. I would double check that you are doing your ray-tracing correctly.

- Stuart -

[epstudio]

Hello Stuart!

Thank you so much for your time and valued input, it is greatly appreciated!

Are you sure that your surface normals really are perpendicular to the reflective surfaces? Many of those reflections seem to not be at the correct angle, for both the soffit wings and the cloud. I would double check that you are doing your ray-tracing correctly.

When you ask if I'm sure that my "surface normals" really are "perpendicular" to the reflective surfaces? I gasp and my mind starts doing back flips as I spent hours scouring the forums and searching your posts on the subject of ray tracing to ensure I was understanding the technique completely! Now, I fear that maybe I missed something entirely...

I utilized your rainbow trace pic as a guide as well;

Rainbow-raytrace.png

and if I am interpreting your comment correctly, the surface normals would be the soffits (speakers) themselves? therefore whatever "angle" the soffits are at (mine happen to be 12 degrees) that would be your baseline with the flat face of the speaker representing the full 180 degrees? (Probably not the best explanation... )

For my trace, I then created the rays at 5 degree intervals starting at the full "flat" 180 degree and fanned them out back to center. The reflections themselves are following the laws of reflection in that the angle of incident equals the angle of reflection... (at least I thought so anyway!!?!)

So, where a ray would hit the soffit wing, the incidental angle would be say, 25 degrees I would mirror the 25 degree angle for the reflected ray, Like this:

Ray Trace Top EDIT.jpg

Ray Trace.jpg

Are you able to tell me if I completely mucked it up? Am I way off base? Here is my Sketchup file if it would be of any value...

https://drive.google.com/open?id=1mQuBY ... LjEVWCME7V

Thank you again in advance for engaging and enlightening me! I absolutely LOVE this forum and everyone who participates... It is a great blessing to the community at large!

Lee

[Soundman2020]

When you ask if I'm sure that my "surface normals" really are "perpendicular" to the reflective surfaces? I gasp and my mind starts doing back flips as I spent hours scouring the forums and searching your posts on the subject of ray tracing

I hope I didn't scare you too much with that comment!

OK, "surface normals" are just imaginary lines that come out from the surface that is reflecting the ray, exactly perpendicular to the surface at that point. In other words, 90° from the tangent to the surface at that point. That's what you use to make sure that your angle of reflection does indeed match your angle of incidence. Every time you change the position / rotation / tilt of the surface you need to draw new normals that are perpendicular to the surface in it's new location. The reason I say that, and the reason I questioned your diagrams, is because I very often see that somebody did the normal correctly at 90° to the surface, drew guidelines in SketchUp, figure out the ray bounce, didn't like the result, and moved the panel... but then use the SAME guidelines as before, without updating them to the new angle and position! That, of course, will give you the wrong answer... It's easy to make that mistake when you are moving fast, trying lots of adjustments one after the other: I've done it myself more than once ! Since it's such a common mistake, and since some of your diagrams seemed to show strange angles of reflection, I asked the question.

Another issue to be aware of for surfaces that have absorption on them (for example, your hard-backed cloud), is which surface to use? The face of the absorption, or the face of the panel behind it? Do you ray-trace from where the ray hits the insulation surface, or from where it hits the rear panel on the other side of the insulation? The answer to that isn't easy at all, since it depends on several factors, such as the frequency, the angle, and the insulation. For example, if we are talking about dense insulation, grazing angles (close to being parallel to the surface), and mid to high frequencies, then use the surface of the insulation, and ray trace on that. But if we are talking low frequencies, angles close to the normal, and low density insulation, then use the panel behind the insulation for your ray-tracing. Often the easiest thing to do is just to ray trace for BOTH surfaces, to get a better idea of which way things will go for a variety of frequencies, angles, and densities.

and if I am interpreting your comment correctly, the surface normals would be the soffits (speakers) themselves? therefore whatever "angle" the soffits are at (mine happen to be 12 degrees) that would be your baseline with the flat face of the speaker representing the full 180 degrees? (Probably not the best explanation... )

Wellll..... sort of! See above: the surface normal is the imaginary line that pokes out of the surface, perpendicular to it, at the spot where you are doing the ray-tracing. It's conventional to use the surface normal, rather then the surface itself (even though that is valid too), simply because for curved or irregular surfaces, it's easier to do with normals than to try to figure out where the flat part of the surface is, to work the angles from there. For flat surfaces, you can do it your way, but for curved or irregular surfaces you'll find it easier to use surface normals. It's also easier to do it that way in SketchUp, as you can simple select the normal itself, rotate-with-copy (select the line, hit "Q" to select the "rotate" tool, then tap the Ctrl key once to make it copy the line then rotate the copy), using the point of intersection as the fulcrum. Rotate that guideline until it lines up with your incoming ray, read off the angle, rotate the line back past the normal position, type the same number and hit enter. Done! You can do it fast like that.

For my trace, I then created the rays at 5 degree intervals starting at the full "flat" 180 degree and fanned them out back to center. The reflections themselves are following the laws of reflection in that the angle of incident equals the angle of reflection... (at least I thought so anyway!!?!)

Yup! As long as you are certain that your surface normal (the line you are reflecting around) really is perpendicular to the surface at that point... and remember to update the surface normals if you move or angle the object. If you have your object created as a "component", then you can edit it at the geometry level, and create your surface normal lines there, then close the component and move/rotate/flip/whatever that object as much as you want, and the normals will stay attached to the surface, and perpendicular to it.... as long as ou do not SCALE the component, you'll be fine!

So, where a ray would hit the soffit wing, the incidental angle would be say, 25 degrees I would mirror the 25 degree angle for the reflected ray, Like this:

Right, but use the normal, not the surface itself. And since your example seems to show fabric on top of the surface, use the surface itself, not the fabric, for your ray-tracing... I may be wrong, and that really is the surface in this case....

But you DO have the problems I suspected! The very first ray I chose on your model, is wrong:

At random, I chose this ray and its reflection:

epstudio-any-bounce-1.jpg

I added the surface normal as a guideline, and you can already see the problem: your angle of reflection is NOT the same as your angle of incidence.

On this second image, I placed another guideline at the correct reflection angle:

epstudio-any-bounce-2-wrong!.jpg

Your angle of incidence is about 40°, so your angle of reflection should also be 40°, but it's only about 27°...

Also, your reflection does not line up with the incoming ray: the reflection should be emitted from the exact same spot where the ray hits the surface, but your reflection is off by a few mm....

There might well be more.... that's just the first one I chose.


- Stuart -

[epstudio]

Stuart! You are a gentleman AND a scholar!! Thank you so much for this thorough and explicit explanation... I completely get it now! The surface normal is totally the key, and yes the majority of those ray reflections will most likely be wrong ... I can't thank you enough!

Regarding the cloud absorption, I was going to use our standard Roxul mineral wool here in Canada ( which has a density of > 2 lb/ft3 or > 32 kg/m3 ) covered in breathable fabric, so I was reflecting the rays off of the hard plywood (or MDF) lid. Should I use "lighter" or less dense insulation in the cloud in your experience?

I will now go and "correctly" apply your instructions to my Rays and FIX my glaring errors!

Thank you again Stuart, sincerely appreciate and value your assistance!

Lee