Angling side panel 1st reflection absorbers so they're at less of an angle to speaker

[Max Dread]

Hi

I've touched on this in a couple of other threads but wanted to write a specific post about it......

I know that in some studio set ups the side walls are angled/splayed outward to reflect MF and HF away from the listener and toward the back of the room. But in most cases where absorption is used (from what I've seen) the absorbers tend to be flush - or at least parallel - to the walls. In such a scenario - if the speakers are toed in at a standard angle of around 30 degrees, sound will therefore reach the absorber at an angle of around 120 degrees. I appreciate that sound does not travel in a straight line and that this is therefore a vast over-simplification - but is it fair to also say that the absorber will not be as effective as it could be because of the high grazing angle?

Which leads me onto my point......

I plan to angle my side panels inward (i.e. in the opposite direction to the way walls are splayed in pro studios), reducing the angle from 120 degrees to something more like 90 degrees.

I wondered whether other people are doing this in their studios and whether it is generally a good idea or not?

Cheers

Max


PS - I will soon be measuring my room in more detail and will compare ETC measurements to see what differences there are. But as I won't have time to do that very soon, I just wanted to get a few ideas together first....

[tonio]

Right, take some ETC measurements and you can answer for yourself.

That said, I have my side panels angled in @ 90 or so degrees, and are actually adjustable. Have not yet taken measurments to that effect, but does seem to interact better ( oohh totally subjective) with side reflections.

[Max Dread]

Originally Posted by tonio

Right, take some ETC measurements and you can answer for yourself.

Yep, that's the plan. Just interested in hearing some thoughts before I get the chance and time to take the measurements (this will be a first for me and so I'm still learning at the moment).

Originally Posted by tonio

That said, I have my side panels angled in @ 90 or so degrees, and are actually adjustable. Have not yet taken measurments to that effect, but does seem to interact better ( oohh totally subjective) with side reflections.

I don't suppose you have any photos you would mind sharing of your set up with these side panels angled?

Cheers

Max

[mhch]

Originally Posted by Max Dread

Hi

I've touched on this in a couple of other threads but wanted to write a specific post about it......

I know that in some studio set ups the side walls are angled/splayed outward to reflect MF and HF away from the listener and toward the back of the room. But in most cases where absorption is used (from what I've seen) the absorbers tend to be flush - or at least parallel - to the walls. In such a scenario - if the speakers are toed in at a standard angle of around 30 degrees, sound will therefore reach the absorber at an angle of around 120 degrees. I appreciate that sound does not travel in a straight line and that this is therefore a vast over-simplification - but is it fair to also say that the absorber will not be as effective as it could be because of the high grazing angle?

....

Max


PS - I will soon be measuring my room in more detail and will compare ETC measurements to see what differences there are. But as I won't have time to do that very soon, I just wanted to get a few ideas together first....

Speaker emits sound in a cone (for MF and HF), some sound goes straight to the listener from the 30d angled speakers, but the 1st reflection panels in between the speaker and the listener will receive sound in between 90 and 120 (or more) depending on panel location and surface.

One can also say that sound arriving at more than 90 hits a thicker panel ...

So I'm not too sure this angling will have a significant absorbing effect.

But I'm still a newbie in Acoustics ... Expert's voice ?

[localhost127]

Originally Posted by mhch

So I'm not too sure this angling will have a significant absorbing effect.

i think the OP's reasoning for angling the panels was to decrease the chance of grazing (at high angles of incidence, approaching 90*).

OP will have to experiment and take ETCs to determine.
looking forward to the results!

[tonio]

Originally Posted by Max Dread

I don't suppose you have any photos you would mind sharing of your set up with these side panels angled?

Cheers

Max

No pics yet, but I got the idea from Andreas' set up .LEDE room with Haas trigger

Basically used a shelf bracket for stability while allowing easy adjustment of angle.

[avare]

Originally Posted by Max Dread

but is it fair to also say that the absorber will not be as effective as it could be because of the high grazing angle?

I plan to angle my side panels inward (i.e. in the opposite direction to the way walls are splayed in pro studios), reducing the angle from 120 degrees to something more like 90 degrees.

I am not clear on where you get the 120° from, or the idea that increasing the angle of incidence decreases absorption monotonicaly. The relationship between angle of incidence and absorption of porous materiasl is shown in the figure labeled fig 8 in its graphic, about 1/3 of the way down on this page. For most materials, the absorption increases as the angle of incidence increases, till a peak and then reduces to 0 at grazing.

Andre

[Max Dread]

Hi Andre

I'll give that paper some time when I have the .... erm ....time, but on first glance I must admit it looked a bit baffling!

When you say "I am not clear on where you get the 120° from" - how do you mean? Have I misunderstood my angles (again)? I don't mean precisely 120 degrees - but thereabouts. Do you think I have the angles in my diagrams all wrong? I thought the angle of incidence was calculated relative to the sound being admitted from the speaker......

See this as for why I thought that's the case:

Couple of questions about the Porous Absorber Calculator

RE: effectiveness - my current thinking is that LFs are absorbed more effectively as the angle increases toward 90 degrees, but the HFs are absorbed less effectively. Would you disagree?

Yours from an angle (sorry - couldn't resist)

Max

[localhost127]

Originally Posted by avare

The relationship between angle of incidence and absorption of porous materiasl is shown in the figure labeled fig 8 in its graphic, about 1/3 of the way down on this page.

Andre

thanks -

[localhost127]

Originally Posted by Max Dread

Hi Andre

I'll give that paper some time when I have the .... erm ....time, but on first glance I must admit it looked a bit baffling!

When you say "I am not clear on where you get the 120° from" - how do you mean? Have I misunderstood my angles (again)?
Max

0* would mean striking perpendicular to the panel
-90 to +90* in the illustration

[Max Dread]

Originally Posted by avare

I am not clear on where you get the 120° from
Andre

And just to clarify, when I talk about the 120 degree angle I'm referring to this kind of set up (which seems common):



I'm proposing a 90 degree angle like this:



Am I making sense?

[avare]

Max:
Your drawings are not showing up, but localhost shows it well.

If you had a chance to study the graph I referenced, the effect of angle of incidence on absoprtion should be clear now. Is it? Remember this acoustics, what drove Bayer to invent aspirin.

Andre

[localhost127]

max, i've amended your drawings:

reference 'angle 0*' is perpendicular to the wall.

[Audioactive]

i think the absorber should be angled the opposit direction

|/ Speakers \|

i wanted to ask a similar question, i had this idea that i could use side absorbers angled in a way that they could act at little bit as deflectors, mi room is 3.20m wide, so ...i figured out that could be an option to better fight early, but then, i've read that using deflectors and diffusors in not a good choice in small rooms.

My idea was to deflect the early towards the opposit back angles where bass traps are going to be, so that the distance they travel to go there, plus the absorption of bass traps will make early too weak to bother me.

what are your thoughts andre??

thanks

[localhost127]

Originally Posted by Audioactive

i think the absorber should be angled the opposit direction

|/ Speakers \|

i wanted to ask a similar question, i had this idea that i could use side absorbers angled in a way that they could act at little bit as deflectors, mi room is 3.20m wide, so ...i figured out that could be an option to better fight early,

does an ETC show that your current absorbers are not attenuating all of the specular energy to a sufficient level below the original source (at the listening position)?

as avare has noted, increasing the angle so the energy takes a longer path through the fiberglass will yield more absorption (up until a high grazing angle is reached).

Originally Posted by Audioactive

but then, i've read that using deflectors and diffusors in not a good choice in small rooms.
My idea was to deflect the early towards the opposit back angles where bass traps are going to be, so that the distance they travel to go there, plus the absorption of bass traps will make early too weak to bother me.

if the path taken from the speakers --> side reflectors --> rear wall to be diffused --> lisenening position is equal or greater than 20ms (~21ft) or so after the original signal, then that is a viable option, certainly.

and by reflecting the first reflection point sonic energy instead of absorbing it, you maintain higher levels of energy within the room which can then be diffused and returned after the ISD.

[Max Dread]

Hi guys and thanks for sticking with me! I don't know why - but my head just does not seems to "do" angles!

I've amended the uploaded pictures in Post 11, so hopefully they can be seen now.

Andre - I've had a read through the linked article and must admit I've fallen at the first hurdle when looking at Fig.8 as I am unsure what the vertical axis (0 - 100) is referring to, and therefore cannot make too much sense of it. If anyone could let me know I'll then take another look.

Localhost - thanks for the amended drawings, they help me to make sense of things (I think). So in the first one, that would be akin to an angle of incidence of 40 degrees, and if using the calculator to predict the absorptive-ness of a material placed in that situation, I would put 40 degrees in the angle incidence field - is that correct?

If so, what (roughly) would be the angle of incidence in the second picture? And would there actually be two angles - one for the sound on the way in and one on the way out?

If I'm right with this, I guess where I've been getting confused (and being stupid) is in measuring the angle of the direct sound from the speaker with relation to the panel. But it is not the direct sound I'm trying to absorb or am concerned with!!! I WANT that to reach my ears unobstructed! It is the indirect sound from the speakers that I want to absorb - which would otherwise reflect off the side walls and back to the LP. And of course this "indirect" sound "hits" the panel at an angle (well, in reality at lots angles because it is not a straight line) and it is these angles we are concerned with? Am I still talking sh!t and publicly revealing my stupidity? Or am I starting to make sense....?

Originally Posted by localhost127

as avare has noted, increasing the angle so the energy takes a longer path through the fiberglass will yield more absorption (up until a high grazing angle is reached).

But at high frequencies, increasing the angle seems to reduce the absorption.....


_______________________________________________________________

Incidentally, the significance of the angle of incidence for reflection point panels started for me when I made this post:

Foam instead of fabric for reflection point absorbers.....

....I thought I would add the link here as it seems to have a lot of relevant info.

Thanks one and all

Max

[localhost127]

Originally Posted by Max Dread

Andre - I've had a read through the linked article and must admit I've fallen at the first hurdle when looking at Fig.8 as I am unsure what the vertical axis (0 - 100) is referring to,

absorption (vertical axis/y) with respect to incident angle (horizontal/x)
as you increase the incident angle, you increase absorption - up to a certain point - as the specular energy is traveling through "more" insulation (a longer path through the panel)

as you get closer and closer to +/- 90* (parallel to the panel), then the specular energy grazes and skips off the absorber like a stone skipping off water - and you can see absorption thus drops to zero.

Originally Posted by Max Dread

Localhost - thanks for the amended drawings, they help me to make sense of things (I think). So in the first one, that would be akin to an angle of incidence of 40 degrees, and if using the calculator to predict the absorptive-ness of a material placed in that situation, I would put 40 degrees in the angle incidence field - is that correct?

sure

Originally Posted by Max Dread

If so, what (roughly) would be the angle of incidence in the second picture? And would there actually be two angles - one for the sound on the way in and one on the way out?

draw a line perpendicular to the panel. now measure the angle between the incident and that line. (like in my first photo).
eyeballing, i would say the 2nd photo incident angle is approx 25*??

yes, there are two angles, but angle of incident = angle of reflection, so they are the same.

Originally Posted by Max Dread

If I'm right with this, I guess where I've been getting confused (and being stupid) is in measuring the angle of the direct sound from the speaker with relation to the panel. But it is not the direct sound I'm trying to absorb or am concerned with!!! I WANT that to reach my ears unobstructed! It is the indirect sound from the speakers that I want to absorb - which would otherwise reflect off the side walls and back to the LP. And of course this "indirect" sound "hits" the panel at an angle (well, in reality at lots angles because it is not a straight line) and it is these angles we are concerned with? Am I still talking sh!t and publicly revealing my stupidity? Or am I starting to make sense....?

correct. the direct path angle/evctor is irrelevant. when using the porous absorber calculator, etc...you are inputting the incident angle of the specular energy with respect to the absorber panel. this incident angle is a parameter/variable that changes the effectiveness of the absorber.

you may not need to be terribly concerned with the incident angle.
do you have broadband panels installed now (to absorb first reflection specular energy?) or what is your concern for the need to angle the panels? have you verified with an ETC whether your broadband panels are functioning properly?

[Audioactive]

Originally Posted by localhost127

does an ETC show that your current absorbers are not attenuating all of the specular energy to a sufficient level below the original source (at the listening position)?

as avare has noted, increasing the angle so the energy takes a longer path through the fiberglass will yield more absorption (up until a high grazing angle is reached).




if the path taken from the speakers --> side reflectors --> rear wall to be diffused --> lisenening position is equal or greater than 20ms (~21ft) or so after the original signal, then that is a viable option, certainly.

and by reflecting the first reflection point sonic energy instead of absorbing it, you maintain higher levels of energy within the room which can then be diffused and returned after the ISD.

i haven't done any proper test yet, at the moment there's just a room that i'm planning to convert in a small control room

My idea was to use an angled panel, done with some sort of light material, to deflect the early from cealing, which is only at 2.1m ..the cealing is too hard to drill and applying some floating panels its not an option, so..the first idea was to make an angled structure of some very light reflective material and glue it to the ceiling...

[localhost127]

Originally Posted by Audioactive

i haven't done any proper test yet, at the moment there's just a room that i'm planning to convert in a small control room

My idea was to use an angled panel, done with some sort of light material, to deflect the early from cealing, which is only at 2.1m ..the cealing is too hard to drill and applying some floating panels its not an option, so..the first idea was to make an angled structure of some very light reflective material and glue it to the ceiling...

using a reflector comes with its own set of additional issues to take into consideration. you would still likely need absorption between the reflector and the ceiling.

[johndykstra]

Originally Posted by Max Dread

And just to clarify, when I talk about the 120 degree angle I'm referring to this kind of set up (which seems common):

Attachment 232352

I'm proposing a 90 degree angle like this:

Attachment 232351

Am I making sense?

Max, I think you are thinking about this backwards. You show pictures detailing the panel on the same wall of the speaker. Generally speaking, that panel is used to augment signal arriving from the opposite speaker. You can play with this with a mirror. If you place a mirror on your left wall flush, you will not see your left speaker. However, angle it as you are suggesting, and you will at some point.

Regardless, the suggestion as you have drawn, will cause MORE reflections to enter the listening position than it would were it flat. Conversely, were it angled the opposite direction is would divert more reflections away.

Let's forget about reflective deflectors for a moment. Even raw fabric covered insulation is going to produce some level of reflection. Given that, increasing the angle of incidence will divert these remaining reflections. Decreasing the angle to attempt to avoid grazing seems it would be stepping over dollars to save dimes... so to speak.

[Max Dread]

Originally Posted by localhost127

absorption (vertical axis/y) with respect to incident angle (horizontal/x) as you increase the incident angle, you increase absorption - up to a certain point - as the specular energy is traveling through "more" insulation (a longer path through the panel)

Again, sorry if I'm being really stupid here - but if the Y axis relates to absorption, then why the different lines starting at 20/40/60/80? I don't understand what that relates to......

Originally Posted by localhost127

draw a line perpendicular to the panel. now measure the angle between the incident and that line. (like in my first photo).
eyeballing, i would say the 2nd photo incident angle is approx 25*??

That makes sense. And I think it supports what I was trying to say. The less of an angle = the better the HF absorption. However, saying that, it really only seems to be quite high frequencies that benefit. As Andre and others have pointed out, LFs and MFs are better absorbed as the angle increases up to around 60 degrees. So I guess it depends on what frequencies are the most important to absorb at first reflection and/or which are most problematic? As well as the dispersion of the speaker.....?

Originally Posted by localhost127

you may not need to be terribly concerned with the incident angle. do you have broadband panels installed now (to absorb first reflection specular energy?) or what is your concern for the need to angle the panels? have you verified with an ETC whether your broadband panels are functioning properly?

Yes, I've already made some panels of Mineral Wool 60kgm3 (Knauf Rocksilk RS60) which are 100mm with a small air gap of around 50mm (although this would obviously be larger in places if I angle them - or I could even add more mineral wool behind in a wedge type shape). As soon as I have some time off work I will be learning how to make and read ETC measurements and will then try the panels flush and angled and see what the difference is. Watch this space!

My concern/idea about angling the panels is to reduce the grazing angle and minimize reflections. Granted - there might not be a problem and I won't know until I measure. But in the meantime I was interested to hear people's thoughts and more so to see whether others have done this (because it is not something I recall seeing too often). As I mentioned above, it was mainly in this thread:

Foam instead of fabric for reflection point absorbers.....

that I read about the effect of grazing angles and the idea of angling panels (although I'm sure I've read it elsewhere too).

Originally Posted by johndykstra

Max, I think you are thinking about this backwards. You show pictures detailing the panel on the same wall of the speaker. Generally speaking, that panel is used to augment signal arriving from the opposite speaker. You can play with this with a mirror. If you place a mirror on your left wall flush, you will not see your left speaker. However, angle it as you are suggesting, and you will at some point.

Hi John

I'm not sure I follow this - but that could be because of the confusion caused by my crappy picture! In my picture, the panel is on a side wall. The speaker is the left speaker and is toed in to point at the LP which is roughly where the underlined text is. Think of the top horizontal of the picture as the front wall. Is that how you saw the picture or did you see it differently? And does that change what you wrote in the part I quoted above?

Originally Posted by johndykstra

Regardless, the suggestion as you have drawn, will cause MORE reflections to enter the listening position than it would were it flat. Conversely, were it angled the opposite direction is would divert more reflections away.

Same question really!!! - otherwise I'm not too sure what you mean tbh.

Huge thanks to all for taking time to share their views and bearing with me while I try to get my head around all this.


Cheers

Max

[localhost127]

Originally Posted by Max Dread

So I guess it depends on what frequencies are the most important to absorb at first reflection and/or which are most problematic?

http://www.gearslutz.com/board/6424136-post4.html

[Max Dread]

Fair point and thanks for reminding me of that. But I'm not sure if that post covers the issue of reflection due to grazing angles. Here are some quotes from the same thread that do:

"Reflections tend to increase as the incidence angle deviates from 90 degrees (perpendicular). So the first thing to try if you have reflections off the panels would be to re-orient your panels to reduce the grazing angle (Angle one side by spacing one side of the panel so that the panel is a little further out then the other side).” SAC

“we already discussed how the amount of absorption decreases and the amount of reflection increases with increasing incident angles until the degree of reflection is maximized in the ‘grazing’ incident range of between about 60-85 degrees from normal (perpendicular). Thus, the single most effective technique we can use to increase the degree of absorption in a panel is to orient it so that it is as near to perpendicular to the source as possible. But we often accept reasonable compromises here.” SAC

“But in all, with regard to this particular situation, which is easier? Obsessing over which brand of material is imagined to magically solve a potential issue, or would paying a bit more attention to incident angles and thus potentially minimizing any negative impact throughout the process such that it would have been easier to have avoided creating the problem to begin with?” SAC

“Grazing angles. Essentially from 60-85 degrees off perpendicular (for those not aware, this is referred to as the "normal" angle), you encounter the region defined as grazing. In this region almost every 'flat' material will reflect.….. But suffice it to say, that the amount of reflectance is reduced (although it may not be totally eliminated!), by changing the angle of incidence to an angle closer to normal (90 degrees).” SAC

“Thus, while you want a material covering with sufficient porosity, the basic orientation of the panel is a MUCH greater factor in maximizing absorption and minimizing reflections.”


I'm in no way confident that I'm right in any of this - just merely thinking aloud at this stage and trying to make sense of it all!

[avare]

Again, sorry if I'm being really stupid here - but if the Y axis relates to absorption, then why the different lines starting at 20/40/60/80? I don't understand what that relates to......

The numbers refer to absorption of materials at 0°. A porous absorber that has an absorption coefficient of 0.2 at 0° has an absorption coefficient of 1.0 at 87°.

Obtusely,
Andre