#1647238 - 03/20/04 09:56 PM
Rear Wall - LF Absorption - Angled Slats
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jbr
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Loc: London, ON, Canada
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This idea warrants it's own thread. Andre mentioned building this for the rear wall of my 12x13x7'6" studio.
Andre wrote: "The rear wall is so close to the listening position that you will get comb filtering from reflections. Also 1" will not absorb low frequencies. What I would suggest is something like 4" MF (mineral fiber) covered with angled slats spaced to reflect the high frequencies AWAY from the listening position. Ray tracing would help determine the angles."
"For construction, consider a saw blade, and the shape made by the teeth. Not surprisingly a wave of this pattern in electronics is referred to as a sawtooth wave. Imagine the angled part of the sawtooth as being the slat, and the straight part (square with the other side of blade, or close to square) as being open to the absorbent material behind the slats."
"The simplest first version would be to cut top and bottom pieces with the sawtooth pattern and then attached slats across the angled portions and leave the straight portions open. Open meaning acoustically. You can cover it with fabric etc."
"The two variables in this design are the length and angle of the slats. Reflecting frequencies as low as 1kHz (AES TD 1001 table 2) would require surfaces about a foot wide. To avoid potential comb filtering vary the slat width. The angle would depend on the required direction of the reflected wave, hence my reference to ray tracing."
Q1. Would this design take up the entire rear wall, from side to side and floor to ceiling or directly behind the listening position only?...especially regarding the angled slats.
Q2. Do the slats run horizontally or vertically?
Q3. How do you attach the slats to the front of the 4"MF
Q2. Has anyone built a wall similiar to this or know web sites to view this design?
If you want to read the technical info regarding acoustics design see the links in the thread "Empty Room From Scratch"
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#1647239 - 03/21/04 01:16 AM
Re: Rear Wall - LF Absorption - Angled Slats
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Andre Vare
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Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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I had a nice inside of me when I started reading your post and the first three questions. The questions show good thought behind them.
Q1. Would this design take up the entire rear wall, from side to side and floor to ceiling or directly behind the listening position only?...especially regarding the angled slats.
Q2. Do the slats run horizontally or vertically?
Q3. How do you attach the slats to the front of the 4"MF
Q2. Has anyone built a wall similiar to this or know web sites to view this design?
Here is the link for people who aren't familiar with this topic and its threads:
Genelec Big Room
The links that I detailed for John Sayers and Francis Manzella help. At Manzella's site look at the studio room for Egan Studios. I seem to remember Russ Berger used a similar concept in one of the studios on his website:
Russ Berger Design Group
The height and location vertically are variable. Usual designs are starting about 2 feet to 3 feet above the floor to someplace near the ceiling. Remember ray tracing? 
The slats go vertically.
The slats do not have to be attached to the RW.
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#1647240 - 03/21/04 02:23 PM
Re: Rear Wall - LF Absorption - Angled Slats
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jbr
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Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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Thanks again Andre for your quick response. And yes, overloaded is accurate. I've forgotten where to look for some info, but that's okay because some/most was beyond my comprehension. I've saved some files to disk.
I feel were starting to close-in on the actual design details, which is quite exciting. The picture in my head is becoming clearer as we progress.
I understand the mirror technique, but was unaware it was technically called ray tracing.
I again looked at the Genelec illustration. Those slats seem a few feet wide. The photos from Francis Manzella Design show the slats quite well. The ones I saved are the Egan photo as you suggested as well as Masterdisk-Leon.
And so it continues:
Q1. Since the studio does not exist in a vacumm, the slats must attach phyically to something. Possibly hanging from the ceiling?
Q2. Regarding the rear wall, does the 4"MF attach directly to the wall or onto furring strips?
Q3. What type of wood is used for the slats?
Until next time,
Jim
PS the links for Russ Berger and John Sayers(Empty Room from Scatch thread)are not working.
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#1647241 - 03/21/04 02:43 PM
Re: Rear Wall - LF Absorption - Angled Slats
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jbr
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Loc: London, ON, Canada
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I added Q4. here and hit reply with quotes instead of edit post.
Originally posted by jbr:
Thanks again Andre for your quick response. And yes, overloaded is accurate. I've forgotten where to look for some info, but that's okay because some/most was beyond my comprehension. I've saved some files to disk.
I feel were starting to close-in on the actual design details, which is quite exciting. The picture in my head is becoming clearer as we progress.
I understand the mirror technique, but was unaware it was technically called ray tracing.
I again looked at the Genelec illustration. Those slats seem a few feet wide. The photos from Francis Manzella Design show the slats quite well. The ones I saved are the Egan photo as you suggested as well as Masterdisk-Leon.
And so it continues:
Q1. Since the studio does not exist in a vacumm, the slats must attach phyically to something. Possibly hanging from the ceiling?
Q2. Regarding the rear wall, does the 4"MF attach directly to the wall or onto furring strips?
Q3. What type of wood is used for the slats?
Q4. When you mentioned "The height and location vertically are variable. Usual designs are starting about 2 feet to 3 feet above the floor to someplace near the ceiling." does that include the 4"MF as well as the slats?
Until next time,
Jim
PS the links for Russ Berger and John Sayers(Empty Room from Scatch thread)are not working.
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#1647242 - 03/22/04 07:58 PM
Re: Rear Wall - LF Absorption - Angled Slats
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Andre Vare
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Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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PS the links for Russ Berger and John Sayers(Empty Room from Scatch thread)are not working.
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#1647243 - 03/22/04 10:17 PM
Re: Rear Wall - LF Absorption - Angled Slats
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AudioMaverick
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Registered: 05/19/01
Posts: 1790
Loc: Outskirts of Big Bear, CA,UNIT...
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I have a now dead link to John Sayer's "Recording Manual". It was good stuff. Let me know if you find out where it is. I'll update my link.
_________________________
"It's all about the... um-m-m, uh-h-h..."
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#1647244 - 03/25/04 06:49 PM
Re: Rear Wall - LF Absorption - Angled Slats
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Andre Vare
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Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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Q1. Since the studio does not exist in a vacumm, the slats must attach phyically to something. Possibly hanging
from the ceiling?
in his "Build a Better Bass Trap." The fronts would be the angled slats instead of the solid plywood.
Q2. Regarding the rear wall, does the 4"MF attach directly to the wall or onto furring strips?
construction or aesthetic reasons, but it is not important acoustically.
From the last couple of posts you have written I think that you are starting to comprehend the theory and principles we
are using quite well. In this case, the purpose of the MF is to try and absorb as much of the low frequency sounds so
that they do not reflect back. The highs will be directed by the slats. That is why there is no need to sculpt the front of
the MF. Because we are dealing with the sound coming straight at the absorber, we do not have to worry the effect of
closing off the sides of the space where the MF is.
Q3. What type of wood is used for the slats?
sound itself. I worded the last part that way to emphasis the acoustic characteristic required to keep your mind open as
to what material you can use. It can be wood, plywood, LDF, MDF, HDF, OSB, Formica, aluminum, lead, steel for a
few examples. If it is a somewhat porous surface. like wood, it should be sealed to make it more reflective. If it is a
material that has low damping, like thin steel, it will some additional damping to prevent it from ringing. The ringing is an
example of a material adding sound by itself.
When you get onto John Sayers site and look at the studios in "Studios Under Construction" section, you will see a
couple of pictures in one studio (I forget its name) where the diffusers at the back of drum/live room are steel.
You can use your creative mind. You can make a strong aesthetic statement with your choice of material. you can even cover the slats with an acoustically transparent fabric if you want to visually hide them, or paint a design on the surfaces.
Q4. When you mentioned "The height and location vertically are variable. Usual designs are starting about 2 feet
to 3 feet above the floor to someplace near the ceiling." does that include the 4"MF as well as the slats? 
Its a little indirect to answer your question, but the reason I am answering this way will make sense when you get to the
end. It will also answer at one question that you have not asked yet, if you have thought of it already.
The design is worked out according to the specific situation and factors of cost and labour. In this case the purpose of
the MF is to absorb initial reflections at low frequencies. The MF at 4" would cover the entire wall from floor to the ceiling. Below the slats there would be additional MF to bring the surface to the front of of the slats. In other words the front of the MF in this section would be flush with the front of the slats.
So what are the length and height in this case? We work from the ceiling down. The hard ceiling is is at 7.
5'. The ceiling corner treatment comes down 1.5' (1' 4.97' actually, but 1.5' is acceptable for the precision needed in
this post). This brings the top of the slats to 6'. The bottom is based on what the reflected waves would hit, and how
important it is. The sound from the bottom of the wall would hit the floor. This is also a common location for sofas,
chairs, etc blocking the reflecting waves also. So the bottom of the could be as low as the floor, or as high as 3',
roughly the height of the back of seating furniture. Where do we put the bottom of the slats then? Think about
construction ease and cost. 4' long slats can be easily made by cutting 8' lengths in half. They could be 3.5' long, but
hen we are adding a cut and throwing away a foot slat material. They could be 5' long, and then 3' of material would be
thrown out, assuming 8' long as purchased. Taking all these factors together, the slat length would be 4'. This bring the
bottom of the slats to 2'. The bottom of the wall would be MW.
You will see similar designs in a couple of the pictures at John Sayers' site.
Till the next post!
Andre
ps: Audio Maverick, John;s site is up again!
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#1647245 - 03/25/04 07:32 PM
Re: Rear Wall - LF Absorption - Angled Slats
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Ethan Winer
MP Hall of Fame Member
Registered: 06/12/00
Posts: 5406
Loc: New Milford, CT, USA
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Andre,
Thanks for doing such a great job in this thread. If I ever meet you in person at an AES show or whatever, remind me that I owe you a drink. 
--Ethan
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#1647246 - 03/25/04 09:08 PM
Re: Rear Wall - LF Absorption - Angled Slats
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Andre Vare
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Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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Thanks for doing such a great job in this thread.
One of my intents with these threads is to give an example of the details involved in trying to get the best possible performance out of a room design. Tying in with that, all the links so that people can get greater depth of knowledge of
the theories, ideas, and specifications involved. And of course the links to pretty pictures of studios (I like pretty pictures).
Even though there has been a lot of design work on the acoustics of the room, all the constructions discussed so far all fall within the realm of projects constantly mentioned here. Adding sound absorption, how much what type, building absorbers based on a box (the slat wall) etc. The thing that brings it to the next level is working on the details. Avoiding the "cut it twice, still too short" sort of situation.
Is it permitted to post graphics in posts here? There are some things that a graphic would clear up a lot.
If I ever meet you in person at an AES show or whatever, remind me that I owe you a drink.
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#1647247 - 03/25/04 10:16 PM
Re: Rear Wall - LF Absorption - Angled Slats
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jbr
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Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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Gotcha!
Let's consider the rear wall being "reversed" meaning I remove the drywall so the studs are visible. A 2nd layer might be added to the adjacent room in order to have same mass as before.
4"MW between each studded cavity. But, since the 1.5" edge of the stud would still be visible, a 1"MW could be added across the entire wall or just across stud edges only, but with a 2"(arbitrary number)overlap on each side. Two angled slat panels each 2'x4'x3.5" would be fastened at the top & bottom in front of the 4"MW by screws which would penetrate the 4"MW into a wood stud(if planned correctly). An addtional 4"MW would then be added under the slat wall panels in order to make that area flush. This would only encroach into the room by 4.5" at the slatwall sections. And would not interfere with the door swing. Not too bad.
Please confirm or not my opening "Gotcha!"
I'll probably use MDF for the slats then. It's inexpensive, easily shaped and takes paint well.
If two slat panels are used, lets say 2x4x3.5", are they constructed as mirror images?
...it's getting better all the time.
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#1647248 - 03/26/04 01:50 PM
Re: Rear Wall - LF Absorption - Angled Slats
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Ethan Winer
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Registered: 06/12/00
Posts: 5406
Loc: New Milford, CT, USA
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Andre,
> I was getting a little concerned that you might consider these threads a little to deep for the forum. <
Not possible. 
> Is it permitted to post graphics in posts here? <
Yes, but this site does not host them. Rather, you need to host them somewhere else and then you can imbed a link in your post. If you have an occasional "important" image and no place to host it, email it to me and I'll find a place for it and give you the link. Email it via the Contact page on my company's site listed below.
--Ethan
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#1647249 - 03/28/04 10:05 AM
Re: Rear Wall - LF Absorption - Angled Slats
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Andre Vare
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Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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Gotcha!
Let's consider the rear wall being "reversed" meaning I remove the drywall so the studs are visible. A 2nd layer might be added to the adjacent room in order to have same mass as before.
4"MW between each studded cavity. But, since the 1.5" edge of the stud would still be visible, a 1"MW could be added across the entire wall or just across stud edges only, but with a 2"(arbitrary number)overlap on each side. Two angled slat panels each 2'x4'x3.5" would be fastened at the top & bottom in front of the 4"MW by screws which would penetrates 4"MW into a wood stud(if planned correctly). An additional 4"MW would then be added under the slat wall panels in order to make that area flush. This would only encroach into the room by 4.5" at the slatwall sections. And would not interfere with the door swing. Not too bad.
There will be more than 2 panels. At least 6.
The reason I haven;t posted too much on this thread is because the size, angles, etc. are a function of the monitor and listening positions, which we are firming up.
Please confirm or not my opening "Gotcha!"
I'll probably use MDF for the slats then. It's inexpensive, easily shaped and takes paint well.
If two slat panels are used, lets say 2x4x3.5", are they constructed as mirror images?
Do you have a CAD or graphics program you can use? We are just about at the stage in both threads where words are not enough (why does that sound like a movie title? Also do have file hosting ability? I do not have one that I have figured out how to use.... It would help a lot for people following our discussion as we get more and more into the details.
As an excellent example of how important graphics can be, consider the posts on John Sayers' site with plans. How would you even start to describe all of that data in clear and concise manner?
...it's getting better all the time.
Total agreement!
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#1647250 - 03/28/04 06:28 PM
Re: Rear Wall - LF Absorption - Angled Slats
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jbr
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Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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I accidentally erased everthing I just typed(of course it was accidental, why would I purposely do it). How frickin' annoying. So the following is the abridged version because I'm not typing all that out again. It was so brilliantly written too.
By "gotcha" I meant "I understand".(abridged)
When I wrote "Two angled slat panels each 2'x4'x3.5" I meant 2 sections. I thought it might be easier to install in 2 mirrored sections.
Having said that, the top & bottom sawtooth patterned pieces will span the entire horizontal span required. The various sizes of slats will run vertically along the horizontal span.
When you wrote "There will be more than 2 panels. At least 6." you meant 6 slats.
I use Vectorworks CAD software as a sideline job. I think I have 5Mb personal web space with Sympatico, but have no idea how to use it, nor care to at this tinme.
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#1647251 - 04/01/04 04:45 PM
Re: Rear Wall - LF Absorption - Angled Slats
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Andre Vare
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Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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I accidentally erased every thing I just typed(of course it was accidental, why would I purposely do it). How frickin' annoying. So the following is the abridged version because I'm not typing all that out again. It was so brilliantly written too.
Why did you not consider re entering the post? All we have is what we write back and forward. Each piece of information may be important. If it is worthwhile to write once, why not again? We are writing about your spending a lot of money to do your studio as good as possible. Do you really want to have shortcomings for years because you chose not to spend an extra 15 minutes at the design stage?
When I wrote "Two angled slat panels each 2'x4'x3.5" I meant 2 sections. I thought it might be easier to install in
2 mirrored sections.
Having said that, the top & bottom sawtooth patterned pieces will span the entire horizontal span required. The various sizes of slats will run vertically along the horizontal span.
When you wrote "There will be more than 2 panels. At least 6." you meant 6 slats.
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#1647252 - 04/01/04 10:20 PM
Re: Rear Wall - LF Absorption - Angled Slats
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jbr
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Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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Good idea about writing offline
What email graphic are we talking about? I have Jim2 and Jim2 Reflections, but I have not received details of the slats themselves.
The stuff I accidentally erased in my previous post was just yada yada, nothing regarding the design elements of the room.
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#1647253 - 04/02/04 02:06 AM
Re: Rear Wall - LF Absorption - Angled Slats
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Andre Vare
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Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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You should have the detals by email. No insult meant but the details are much easier to to show by graphics.
I would love to hear the room once it is complete.
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#1647254 - 04/02/04 11:35 AM
Re: Rear Wall - LF Absorption - Angled Slats
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Ethan Winer
MP Hall of Fame Member
Registered: 06/12/00
Posts: 5406
Loc: New Milford, CT, USA
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Guys,
> Good idea about writing offline <
I have learned to always copy to the clipboard what I'm about to submit. Just before you click "Add Reply" press Ctrl-A then Ctrl-C to select all text and copy it. Then if your post gets trashed you can just paste it again easily.
--Ethan
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