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Acoustical Treatments Master Thread - Page 217

post #6481 of 10210
Would a 2D QRD be appropriate to replace 2" OC703 absorbers on the rear wall (at the first reflection point)? The rear seats are approx 6' from the rear wall.

Thanks,
Jeff
post #6482 of 10210
Quote:
Originally Posted by kevinzoe View Post

Mark,
Ok, I'll bite . . . allow my indulgence to show a little of my room's treatments.

Skylines are based on a prime number large enough to cover the intended wall area where the number of rows multiplied by the number of columns equals the prime number less 1. Max cell depth is 10" and block sizes are 1.5"*1.5". Blocks are polyurethaned to show the pine better.

Hemi-cylindrical diffusers double as bass traps as their concave interior is stuffed with OC 701 fiberglass while the outer side (facing into the room) is a red oak laminate hard enough so as not to absorb mid/high frequencies. Their humble beginings were from a 12 foot long, 48 inch diameter Sonotube. Five of them are in use and range from 160degree to 100degree arcs.

Cheers,
kevin

Nice work, Kevin- I like the "picture frame" around the rods. How long did it take you to build those skylines?
post #6483 of 10210
Quote:
Originally Posted by johnbomb View Post

Nice work, Kevin- I like the "picture frame" around the rods. How long did it take you to build those skylines?

Hi John,
Thanks for the compliment. The "picture frame" was designed to hide the 3.5" decking screws that secure the very heavy Skyline to the wooden 2"*4"s behind the drywall. I used velcro to stick the frame to the plywood backing that extends 3" around the perimeter from the Skyline blocks to allow enough room to put the required deck screws in.

The back wall with +1,500 wooden blocks took about 2-3 months working part time on it and working through a learning curve. The smaller one on the side wall near the back took but 2-3 weeks as a result of being smaller (less wood to cut) and improved learnings for better efficiency.

Although you didn't ask, the hemi-cylindrical diffusers were even less time. It involved cutting the right shape/size, sanding the exterior to remove the wax and glueing wood laminate to it and building a wooden frame on the back, stuffing it with OC 701 and wrapping it in plastic to prevent air borne fibreglass particles. Then polyurethaning it. One hemi took about 1 week of part time work in the evenings.
post #6484 of 10210
Quote:
Originally Posted by kevinzoe View Post

The back wall with +1,500 wooden blocks took about 2-3 months working part time on it and working through a learning curve. The smaller one on the side wall near the back took but 2-3 weeks as a result of being smaller (less wood to cut) and improved learnings for better efficiency.

What kind of learning curve did you experience? As I'm probably going to build several of these things, any tips/tricks are appreciated.

Thanks,
John
post #6485 of 10210
Quote:
Originally Posted by johnbomb View Post

What kind of learning curve did you experience? As I'm probably going to build several of these things, any tips/tricks are appreciated.

Thanks,
John

John - I've put together some thoughts on building a Skyline based on an existing patent and using the best online calculator I could find.

By the way, the 2D Skyline looks similar to an earlier post of a 2D QRD but I believe they are different beasts. The Skyline never has the same number of rows as columns, and vice-versa, whereas the 2D QRD has the same number of columns as rows due to the repeating pattern both vertically and horizontally. Skylines have no repeating pattern and appear more 'random' in their appearance to max diffusion effectiveness. I think the 2D QRD is meant to have the varying cavity depths point into the room while its Skyline-lookalike backing faces the wall. This would make sense and appears similar to RPG's Hemiffusor (http://www.rpginc.com/products/hemiffusor/index.htm).

On to building a Skyline . . .
**********
Creating a DIY Skyline Diffuser

Background: I wanted to add diffusion to my dedicated 2-channel stereo room rather than mid and high frequency (MF/HF) absorption to prevent over damping the room. This document walks the reader through how to build them and what's involved.

Why Use Skylines? A skyline diffuser is a two-dimensional tool - meaning it scatters sound waves vertically and horizontally - and is used primarily to add listener envelopment and to remove flutter echo. Diffusion and/or MF/HF absorption can also be used to improve timbre and localization of instruments in space by affecting 1st angle reflection points. The Skyline can work within smallish rooms due to the scattering abilities within the two dimensions allowing listeners to sit closer to them than a 1-dimension diffuser which requires positioning further away for the diffused sound to coalesce by the time it gets to the listener. I also was concerned about not creating a dead sounding' room as much of the MF/HF were already being absorbed by a low pile wall-to-wall carpet with underpad and a large number of resistive-type bass traps (i.e. fiberglass filled) that continue to absorb up into the mid-frequencies which is cumulative with the more bass traps you have.

Where to Locate Skylines? Current wisdom is to cover the back wall and rear parts of the side wall behind and up to the listening position. These locations help envelop the listener with a reverberant sound field that when mixed with the direct sound field from the speakers creates a balanced mix of both at the listening position. Ceiling first reflection points are another natural spot for them as the Skylines act as if they are raising the ceiling.

What Tools Are Needed?
 Measuring tape
 Mieter saw (sometimes called a Chop saw)
 Belt/Disc Sander
 Ear and eye protection
 Carpenter's Level and Square
 Stud finder
 Paint or wood stain (e.g. polyurethane)



What Materials Are Needed?
 ½ or thicker plywood for the backing - be sure to get the type with one side finished as you'll see the backing in the empty cells
 Lots of 2 * 2 wooden studs which are really 1.5 * 1.5. The least expensive is the construction grade with various pieces of wood finger jointed together - this is low grade/quality wood and you may prefer to paint it afterwards to hide blemishes etc. For my first project I used Pine and cut out the knots and painted it afterwards. It didn't look as good as my second project which used finished knotty Pine with a polyurethane finish. Any kind of wood should do.
 Some pieces of 1 * 4 boards that will form a picture frame-like trim - optional but I thought it finished the look.
 3.5 decking screws to secure the plywood backing to the studs behind your drywall as the Skyline will be HEAVY!
 Construction strength adhesive glue (e.g. Lepages PL Premium adhesive)
 Industrial strength Velcro to secure the picture frame-like trim to the plywood backing

What Steps Are Involved?
(A) Choosing a prime number & associated number of columns & rows for the chosen diffuser size you intend to build
(B) Cutting the wooden blocks
(C) Sanding the wooden blocks
(D) Painting or Staining the wooden blocks and empty cells
(E) Gluing the wooden blocks to the board
(F) Hanging the finished diffuser


(A) Choosing a prime number & associated number of columns & rows

For the definitive reference on the math formulas involved in this design, check out the US Patent office where RPG has filed their Skyline patent #5401921. You should be able to find it online by Googling it.

A general principle applicable to diffusers is that the less periodicity of the pattern, the more diffuse the scattering, which is a good thing. What this means is that you will need to find a large enough Prime number with corresponding column and row counts to fit within the size of the wall area you wish to cover with the diffuser, rather than several smaller diffusers put together. The less a pattern is repeated the better, hence try to find one prime number with enough columns and rows to cover your intended area.

See Appendix I for a partial list of prime numbers and dimensions (in inches).

I used the website www.oliverprime.com/prd.php to plan the diffuser.

Step #1: Click on Examples link to find a two column table. The left column titled P' represents sample prime numbers while the right column titled Grid' lists the corresponding column and row counts. The grid numbers are the number of cells, not the height or width in inches or centimeters. NOTE: the two grid numbers multiplied together should equal the Prime number minus 1. The grid numbers can be either columns * rows or vice versa, it doesn't matter.

Step #2: Determine the approximate area you want the diffuser to cover on your wall. Now take either the height or the width of your desired area and divide it by the dimension of the studs to calculate the number of cells you'll need. For example, let's say I want to cover a wall section roughly 48 high by 48 wide. If I divide 48 by 1.5 which is the size of my 1.5*1.5 blocks, then it equals 32 cells. So, ideally I would like to find a Prime number that is 32 cells high by 32 cells wide. However, looking at the list of Grid examples the only things that come closest are 30*19 or 33*20 or 36*31. I would elect to choose the last one (which corresponds to a Prime number of 1117 which is 1 cell (1.5) less than the desired height (or width) and 4 cells (6) greater than the desired width (or height). This is likely the best fit, providing you have the extra 6 otherwise you'll have to try different prime numbers until you settle on one that fits best.

Step #3: With the Prime number and corresponding grid size determined now click on the Links link and then click on the first hyperlink to calculate least primitive roots. This will open a window where you'll enter your Prime number and it will return a number that you'll use in Step #4. For my example, the prime number of 1117 has a least primitive root of 2.

Step #4: Now click on the Calculator link to play some what-if scenarios. Here is where you will enter various numbers that will all be considered to produce an output that tells you exactly what length stud to put where on your plywood.
Speed of Sound - leave this alone at 343 meters/second.
Lowest Frequency - put in how low you'd like your diffuser to work. Dr. Floyd Toole suggests in his latest book that the diffuser should work down to 300Hz and be a minimum of 8-12 inches deep. A 300Hz wavelength is 45.2 long and Toole suggests that the diffuser depth be a significant percentage of the wavelength. So at 50% of the 300Hz wavelength, you'd need a maximum cell depth of 22.6 which may be too long for typical residential rooms so 40% (18.1) or 30% (13.6) may be more appropriate lengths and still be good enough.


Be careful to plan by how much narrower or shorter your width and length of the room will become once the diffuser's long studs are on the wall. Keep in mind too that you should try and keep a minimum of 4feet between your listening position and the diffuser - the more distance the better. Finally, be sure that there are enough studs behind the drywall spaced across the diffuser's width to support its heavy weight.
Highest Frequency - put in 4,500Hz if you're using 1.5*1.5 blocks. While the longest length of the blocks determines the lowest frequency that the diffuser will work to, it is the block's dimension that determines the highest frequency. 4,500Hz is higher than the top note on a piano. If you can find a lumber mill to cut you 1*1 blocks then you can enter 6,750Hz. I wouldn't suggest anything smaller than 1*1 blocks.
Prime Number P - use the Prime number from Step #2
Primitive Root of P - use the least primitive root from Step #3
# of columns - use from Step #2
# of rows - use from Step #2
Quantize well heights within - this is where you indicate the incremental length that will be used for the studs. For example, 1.5 means that my stud lengths would be 0, 1.5, 3, 4.5, 6 etc. Note that the calculations are in centimeters so use 1=2.54 centimeters as your conversion factor. So stud length increasing by 1.5 corresponds to 3.81 centimeters.

What is outputted is a table of numbers corresponding to block length and their location based on the chosen Prime number.

For what it's worth, the George Massenberg designed Studio C at the Blackbird studios uses 1*1 dimensions and block lengths ranging from 1/10 to 30.



Border
For aesthetic reasons, I decided upon a picture frame-like border around the outer edges of the plywood. Of course a border can be any width you wish, but a 3 border width allowed the 1.5 cells to divide evenly into the remaining space of the plywood backing. Also, I can buy 1*4 lumber for the border which is really 1 by about 3.125 so I will have the border overhang the plywood just a tad. So, take your square and long straight edge which I used my Level for, to draw where the 3 borders will be and then all the cells inside the borders at 1.5 intervals. This takes a bit of time but will be helpful later on when it comes time to glue the right length stud to each cell. Finally, using the output from the website above, write the stud length in each cell. Be sure NOT to write a zero (0) in the empty cell because you'll see this empty cell.

(B) Cutting the wooden studs

Before getting ready to cut for a few hours, be sure to have a number of boxes, or bins, or buckets on hand in which to place the various length pieces of blocks being cut. I found several boxes and labeled them with a block length in order to find them easily when it came time for gluing. You might also consider a brand new saw blade given the hundreds of cuts about to be made.

Remember to think safety and wear ear and eye protection.


(C) Sanding the wooden blocks

If you can afford to purchase wood that is already dressed then you won't need to do the work in the following paragraph other than to sand one of the block's ends after cutting.

This is by far the most time consuming step depending on the quality level you want for the finished product. I had hoped to only have to sand the one end of the blocks that would be facing into the room but found that the four sides could also stand a sanding to smooth them out and remove minor blemishes. While many blocks will be pressed up against one another, you don't know how much of the sides will be visible so it's better safe than sorry and just do a quick sanding on 5 of the 6 sides. Furthermore, you may wish to get somewhat fancy and put a bevel on the end facing into the room by tilting the end of the block lightly on the sander to smooth the edge. Again be sure to wear ear and eye protection and also a mask to avoid inhaling saw dust.

It's a good idea to have a second/spare belt so as to minimize project delays. I used a 80 grit sandpaper and then a 200 grit to finish it off before staining them with polyurethane.


(D) Painting/Staining the wooden blocks

I thought a paint sprayer would be the fastest way to cover the wooden blocks in either a paint or stain. I'll admit I'm a novice to spray painting having thought how hard could it be . . . In actuality, too much paint came out and there are so many nooks and crannies to fill that I found myself quickly grabbing a paint brush to wipe the excess paint away and apply it to an unpainted area. I ended up painting each and every cell by hand with a long handled brush a little less than1 wide to allow it to fit into the deepest cells. Paint will hide the wood grain etc and for my first attempt at a Skyline helps hide my mistakes or shortcuts. For my next Skyline I opted to use Polyurethane to preserve the warmth and beauty of the wood grain. I simply dunked each piece of wood into the gallon can and set it aside to dry and then repeated the process a second time before glueing them onto the ½ plywood back board.

(E) Affixing the wooden studs to the board

I used Lepages PL Premium construction adhesive found at Home Depot. Gluing is easy but tedious work. Having marked the length for each cell on the plywood ahead of time it was easy to know what length goes where. I'd pull all the required pieces for a single row and put them in their cell locations and then start gluing. This allowed the glue that came out to be quickly applied to the next block with minimal glue waste. Repeat the process for the next row etc. When gluing focus on the end of the block facing into the room to be sure it's square with the blocks around it. Sometimes a block will be warped and when the bottom is properly fit within its cell you'll notice that the other end which faces into the room isn't square with the blocks around it so use the end facing into the room as your guide for gluing and positioning the blocks.

.
(F) Hanging the finished product

Typically, a diffuser of 4 foot height will be hung two feet above the floor. Due to its weight, you will need to screw the diffuser into 2*4 studs behind the (dry)wall which are usually 16 apart from one another. Use a stud finder to locate the wooden studs. Then use your tape measure, a straight edge, and pencil to find and mark the top and bottom and sides of where the diffuser will go. You will need some strong friends to hold the diffuser in place while you put screws in the top border. Alternatively, you can use the scrap pieces of your blocks to build a temporary shelf at the 2 foot mark above the floor to rest the diffuser on while you screw in the top and bottom border of the diffuser. You can further secure the diffuser by putting a screw in an empty cell if it aligns with a stud, although I didn't need to. Then remove the temporary shelf and patch and paint the screw holes.

Next, cut the 1 * 4 wooden planks to become the picture frame-like trim. You'll need to set your chop saw to 45 degrees to get the correct angle, as one example of fitting the border trim pieces together.

With the diffuser securely fastened to the wall, place the industrial strength Velcro around the plywood's borders and also on the underside of the wooden 1*4 border trim planks. Place the border trim planks onto the plywood ensuring each corner lines up. This will now hide the deck screws from view yet gives you the flexibility of removing the trim to access the screws if/when you want to move the diffuser to another wall, room, or house.


Appendix I

Partial List of Prime Numbers and Dimensions (in inches)

Prime # X Y Least Primitive Root X (") Y (")
157 12 13 5 18 19.5
163 54 3 2 81 4.5
167 83 2 5 124.5 3
173 43 4 2 64.5 6
179 89 2 2 133.5 3
181 20 9 2 30 13.5
191 19 10 19 28.5 15
193 64 3 5 96 4.5
197 28 7 2 42 10.5
199 18 11 3 27 16.5
211 15 14 2 22.5 21
223 37 6 3 55.5 9
227 113 2 2 169.5 3
229 19 12 6 28.5 18
233 29 8 3 43.5 12
239 17 14 7 25.5 21
241 16 15 7 24 22.5
251 25 10 6 37.5 15
257 128 2 3 192 3
263 131 2 5 196.5 3
269 67 4 2 100.5 6
271 18 15 6 27 22.5
277 23 12 5 34.5 18
281 20 14 3 30 21
283 47 6 3 70.5 9
293 73 4 2 109.5 6
307 18 17 5 27 25.5
311 31 10 17 46.5 15
313 24 13 10 36 19.5
317 79 4 2 118.5 6
331 22 15 3 33 22.5
337 21 16 10 31.5 24
347 173 2 2 259.5 3
349 29 12 2 43.5 18
353 22 16 3 33 24
359 179 2 7 268.5 3
367 61 6 6 91.5 9
373 31 12 2 46.5 18
379 21 18 2 31.5 27
383 191 2 5 286.5 3
389 97 4 2 145.5 6
397 22 18 5 33 27
401 25 16 3 37.5 24
409 24 17 21 36 25.5
419 22 19 2 33 28.5
421 21 20 2 31.5 30
431 43 10 7 64.5 15
433 27 16 5 40.5 24
439 73 6 15 109.5 9
443 26 17 2 39 25.5
449 28 16 3 42 24
457 24 19 13 36 28.5
461 23 20 2 34.5 30
463 22 21 3 33 31.5
467 233 2 2 349.5 3
479 239 2 13 358.5 3
487 54 8 3 81 12
491 35 14 2 52.5 21
499 83 6 7 124.5 9
503 251 2 5 376.5 3
509 127 4 2 190.5 6
521 26 20 3 39 30
523 29 18 2 43.5 27
541 27 20 2 40.5 30
547 26 21 2 39 31.5
557 139 4 2 208.5 6
563 281 2 2 421.5 3
569 71 8 3 106.5 12
571 30 19 3 45 28.5
577 64 9 5 96 13.5
587 293 2 2 439.5 3
593 37 16 3 55.5 24
599 26 23 7 39 34.5
601 25 24 7 37.5 36
607 101 6 3 151.5 9
613 36 17 2 54 25.5
617 28 22 3 42 33
619 103 6 2 154.5 9
631 30 21 3 45 31.5
641 32 20 3 48 30
643 107 6 11 160.5 9
647 34 19 5 51 28.5
653 163 4 2 244.5 6
659 47 14 2 70.5 21
661 30 22 2 45 33
673 32 21 5 48 31.5
677 52 13 2 78 19.5
683 31 22 5 46.5 33
691 30 23 3 45 34.5
701 28 25 2 42 37.5
709 236 3 2 354 4.5
719 359 2 11 538.5 3
727 33 22 5 49.5 33
733 61 12 6 91.5 18
739 41 18 3 61.5 27
743 53 14 5 79.5 21
751 375 2 3 562.5 3
757 28 27 2 42 40.5
761 38 20 6 57 30
769 32 24 11 48 36
773 193 4 2 289.5 6
787 131 6 2 196.5 9
797 199 4 2 298.5 6
809 101 8 3 151.5 12
811 162 5 3 243 7.5
821 41 20 2 61.5 30
823 137 6 3 205.5 9
827 118 7 2 177 10.5
829 36 23 2 54 34.5
839 419 2 11 628.5 3
853 71 12 2 106.5 18
857 107 8 3 160.5 12
859 33 26 2 49.5 39
863 431 2 5 646.5 3
877 73 12 2 109.5 18
881 40 22 3 60 33
883 42 21 2 63 31.5
887 443 2 5 664.5 3
907 302 3 2 453 4.5
911 35 26 17 52.5 39
919 34 27 7 51 40.5
929 32 29 3 48 43.5
937 72 13 5 108 19.5
941 47 20 2 70.5 30
947 43 22 2 64.5 33
953 56 17 3 84 25.5
967 42 23 5 63 34.5
971 97 10 6 145.5 15
977 61 16 3 91.5 24
983 491 2 5 736.5 3
991 45 22 6 67.5 33
997 83 12 7 124.5 18
1009 63 16 11 94.5 24
1013 44 23 3 66 34.5
1019 509 2 2 763.5 3
1021 60 17 10 90 25.5
1031 103 10 14 154.5 15
1033 43 24 5 64.5 36
1039 173 6 3 259.5 9
1049 131 8 3 196.5 12
1051 42 25 7 63 37.5
1061 53 20 2 79.5 30
1063 59 18 3 88.5 27
1069 89 12 6 133.5 18
1087 181 6 3 271.5 9
1091 109 10 2 163.5 15
1093 39 28 5 58.5 42
1097 137 8 3 205.5 12
1103 38 29 5 57 43.5
1109 277 4 2 415.5 6
1117 36 31 2 54 46.5
1123 34 33 2 51 49.5
1129 47 24 11 70.5 36
1151 46 25 17 69 37.5
1153 36 32 5 54 48
1163 83 14 5 124.5 21
1171 39 30 2 58.5 45
1181 59 20 7 88.5 30
1187 593 2 2 889.5 3
1193 149 8 3 223.5 12
1201 40 30 11 60 45
1213 101 12 2 151.5 18
1217 38 32 3 57 48
1223 47 26 5 70.5 39
1229 307 4 2 460.5 6
1231 41 30 3 61.5 45
1237 103 12 2 154.5 18
1249 39 32 7 58.5 48
1259 37 34 2 55.5 51
1277 44 29 2 66 43.5
1279 71 18 3 106.5 27
1283 641 2 2 961.5 3
1289 46 28 6 69 42
1291 43 30 2 64.5 45
1297 48 27 10 72 40.5
1301 50 26 2 75 39
1303 42 31 6 63 46.5
1307 653 2 2 979.5 3
1319 659 2 13 988.5 3
1321 40 33 13 60 49.5
1327 39 34 3 58.5 51
1361 40 34 3 60 51
1367 683 2 5 1024.5 3
1373 49 28 2 73.5 42
1381 46 30 2 69 45
1399 233 6 13 349.5 9
1409 44 32 3 66 48
1423 79 18 3 118.5 27
1427 46 31 2 69 46.5
1429 42 34 6 63 51
1433 179 8 3 268.5 12
1439 719 2 7 1078.5 3
1447 241 6 3 361.5 9
1451 50 29 2 75 43.5
1453 44 33 2 66 49.5
1459 54 27 3 81 40.5
1471 42 35 6 63 52.5
1481 40 37 3 60 55.5
1483 39 38 2 58.5 57
1487 743 2 5 1114.5 3
1489 48 31 14 72 46.5
1493 373 4 2 559.5 6
1499 107 14 2 160.5 21
1511 151 10 11 226.5 15
1523 761 2 2 1141.5 3
1531 45 34 2 67.5 51
1543 257 6 5 385.5 9
1549 43 36 2 64.5 54
1553 97 16 3 145.5 24
1559 41 38 19 61.5 57
1567 54 29 3 81 43.5
1571 157 10 2 235.5 15
1579 263 6 3 394.5 9
1583 113 14 5 169.5 21
1597 42 38 11 63 57
1601 50 32 3 75 48
1607 73 22 5 109.5 33
1609 67 24 7 100.5 36
1613 52 31 3 78 46.5
1619 809 2 2 1213.5 3
1621 45 30 2 67.5 45
1627 271 6 3 406.5 9
1637 409 4 2 613.5 6
1657 46 36 11 69 54
1663 277 6 3 415.5 9
1667 49 34 2 73.5 51
1669 139 12 2 208.5 18
1693 47 36 2 70.5 54
1697 53 32 3 79.5 48
1699 283 6 3 424.5 9
1709 61 28 3 91.5 42
1721 43 40 3 64.5 60
1723 42 41 3 63 61.5
1733 433 4 2 649.5 6
1741 58 30 2 87 45
1747 97 18 2 145.5 27
1753 73 24 7 109.5 36
1759 293 6 6 439.5 9
1777 48 37 5 72 55.5
1783 54 33 10 81 49.5
1787 47 38 2 70.5 57
1789 149 12 6 223.5 18
1801 45 40 11 67.5 60
1811 181 10 6 271.5 15
1823 911 2 5 1366.5 3
1831 61 30 3 91.5 45
1847 71 26 5 106.5 39
1861 60 31 2 90 46.5
1867 311 6 2 466.5 9
1871 55 34 14 82.5 51
1873 52 36 10 78 54
1877 67 28 2 100.5 42
1879 313 6 6 469.5 9
1889 59 32 3 88.5 48
1901 50 38 2 75 57
1907 953 2 2 1429.5 3
1913 239 8 3 358.5 12
1931 193 10 2 289.5 15
1933 46 42 5 69 63
1949 487 4 2 730.5 6
1951 50 39 3 75 58.5
1973 58 34 2 87 51
1979 46 43 2 69 64.5
1987 331 6 2 496.5 9
1993 83 24 5 124.5 36
1997 499 4 2 748.5 6
1999 54 37 3 81 55.5
2221 60 37 2 90 55.5
2243 59 38 2 88.5 57

**********
post #6486 of 10210
Skylines and flutter free seems somewhat straightforward to DIY - anyone done a DIY BAD? any tips on how to do it (other than learning CAD and getting a laser cutter/cnc to do it?). Dont suppose anyone has a CAD file for the grating?

I had thought about getting pegboard and using that as a guide i.e. use the existing holes as pilot holes and drill (or route) through multiple sheets at a time, just a concept, need to look at pegboard hole spacing
post #6487 of 10210
Quote:
Originally Posted by Elill View Post

Skylines and flutter free seems somewhat straightforward to DIY - anyone done a DIY BAD? any tips on how to do it (other than learning CAD and getting a laser cutter/cnc to do it?). Dont suppose anyone has a CAD file for the grating?

I had thought about getting pegboard and using that as a guide i.e. use the existing holes as pilot holes and drill (or route) through multiple sheets at a time, just a concept, need to look at pegboard hole spacing

Hi Elill,

Personal preferences aside, what do you see as special or attractive about Binary Amplitude diffusers?

While the peg board would appear as a good starting 'template' it's holes are likely not the right size and are spaced too regularily and not near random enough in their appearance for proper diffusion. Sorry, haven't BAD experience to pass along . . .
post #6488 of 10210
Hi Kevin, they cater for my needs to diffuse and absorb at certain frequencies in a small room.

Let me clarrify the point around the pegboard - its got a linear patten of holes, now I bet they're not centered in the same spacing as a BAD, but say if it was, buy some chance, I'd draw the BAD pattern on the pegboard sit that over something (thin ply) and drill through 1/2" holes.

Alternatively I could draw a grid and then drill, but that wont be as accurate in terms of getting the hole centers in the right spot (one thing I suck with is drilling accurately like that)

I am however thinking about the DIY skylines, I dont think it'd take me that long really, once you get into the swing of it. Depends on type and quality of finish. It is was paint thats easy, if I go for a timber, that'd be a little longer, but still quick if you set it up right. I'd-

- pre-sand and finish the 50x50 lengths
- cut a lot of the 6 different sizes
- stand them together and sand ends and finish
- glue to a backing board using construction adhesive
- let dry, screw through from the rear
- hang

The other thing I thought of was buying a bit of flutter-free, using that as a template for router bits and height and then spending a day running timber over a router table
post #6489 of 10210
Wow, Kevin, thanks!

John
post #6490 of 10210
Quote:
Originally Posted by johnbomb View Post

Wow, Kevin, thanks!

John

You're welcome. I trust the info was/will be helpful.

Be sure to post pictures of your finished Skyline product(s) for all the world to see . . .
post #6491 of 10210
Pegboard will behave more as a low pass filter rather than a diffuser.
post #6492 of 10210
Wow Kevin. You are a wealth of information. Very, very cool.

Frank
post #6493 of 10210
Quote:
Originally Posted by Dennis Erskine View Post

Pegboard will behave more as a low pass filter rather than a diffuser.

Hi Dennis, understood, I was going to use the pegboard as a hole centre guide for making a diffuser i.e. it would ensure manually drilled or routed holes were centered....can i be bothered? probably not.

General question though - how does one determine what frequency a perforated board will absorb? or rather how do I determine what hole depth and size will absorb certain frequencies? if someone can point me to a book/reference that'd be appreciated.

I like the perforated veneer look, but you can get it in all manner of shapes, sizes, designs

I have found this?

Freq = 200 x square root of (P/(D x T))

where:
P = perforation percentage (eg, 5%)
D = depth of air space (in inches)
T = PT + 0.8 x HD
where:
PT = panel thickness (in inches)
HD = hole diameter (in inches)

for absorbers with slats:

Freq = 216 x square root of (P/(D x PT))

where:
P = perforation percentage (eg, 5%)
D = depth of air space (in inches)
PT = panel thickness (in inches)
post #6494 of 10210
Hi Eill,

Keep in mind, there is more going on as well. The diffusive element requires a certain backing behind the material and the the "holes" act to DIFFUSE not absorb by their pattern, depth and size. Trevor Cox and Dr. D'Antonio wrote a textbook called Active Absorption and Diffusion. But be forewarned, this is essentially a Masters level text and a STRONG fundamental background in mathematics (i.e. ODE's) plus it is expensive. As with any math based text, it isn't all spelled out for you. It wasn't meant to be a DIY book. Many "fill in the blank calculations" i.e. what looks like a simple equation explodes into a 14 page derivative when you start working the equation. No "a" times "b" in that book. The only way to ensure you got it right is to measure it...with very expensive equipment and in an acoustic chamber. Testing new concepts is expensive which is why some of these types of panels cost so much...not to mention the assembly required and the R&D. All costs money, but you know it's right. Not everything is best done DIY unless you like to waste money and lots of time. If that is your cup of tea...go for it! Perfsorber is also a lot cheaper than a BAD panel and you can do a lot more "things" with it. FYI, RPG is geared more towards commercial, not residential treatment. Just my 2 cents. Best wishes!
post #6495 of 10210
Hmm, ok thanks SMB (for the record one of my majors was in physical chem (read quantum mechanics).....could I still apply the math.....probably not

You and Dennis sure do a good job of scaring the ________ out of me!

Nothing is cheap in this country, well when it comes to this stuff (what does a perf-sorber panel cost in the US?) - The wife has read me the riot act again re the ever expanding "budget" so I'm leaning back to DIY territory
post #6496 of 10210
Quote:
Originally Posted by Elill View Post

Hmm, ok thanks SMB (for the record one of my majors was in physical chem (read quantum mechanics).....could I still apply the math.....probably not

You and Dennis sure do a good job of scaring the ________ out of me!

Nothing is cheap in this country, well when it comes to this stuff (what does a perf-sorber panel cost in the US?) - The wife has read me the riot act again re the ever expanding "budget" so I'm leaning back to DIY territory

Then you should be ok regarding the math. It takes quite a bit of reviewing the 'ole texts, but it often comes back. I started with my 1st grade math book as a review and worked my way back up from there. If DIY is on the budget, what I would do is consider buying the perfsorber or BAD panels outright, then DIY the rest. Saves lots of headaches and time etc. Cost is roughly 2/3 of what a BAD panel costs. When it comes to planning a budget, I guess it is best to know what things really are worth the money and what things aren't. I would put these (perfs), a proper design and good equalizers as my top three. The other things can always be upgraded and replaced at a later date. Again, just my 2 cents. I think the reason Dennis and I scare you with equal propensity is that we are on the same wavelength (i'll wait for the proper banter from Mr. Erskine...although he complains that he can't leave me alone for 5 minutes) . Best wishes!
post #6497 of 10210
I would greatly appreciate some help with this one. I'm currently trying to figure out how to build an air return for my theater. I have a soffit running along the upper left wall/ceiling line, and I'm building a mirror image of it in the upper right wall/ceiling line.

I want to put a 12 inch duct in the mirror soffit, and leave both ends open: the end inside the theater will be "capped" with a perforated or cloth covered end piece to allow air to pass into the duct. The other end of the duct will pass through the rear theater wall and allow air to pass from the theater into the adjacent room (where a real return that feeds the HVAC lives).

This duct will be about 16 feet long.

I'm concerned that my theater will act as a giant speaker box, and the the duct will act as a "port" for this box. I ran a calculation on WinSD, and the predicted resonance for a port this long is around 30 hz or so. I have a double bass array as my subwoofer solution.

Will this be a problem? If so, do you have any suggestions as to how to avoid it. To put another way: what is the best way to return air from a theater?

Thanks,
John
post #6498 of 10210
We used alot of this for supply and returns

http://www.specjm.com/products/ductboard/enviroaire.asp

http://www.owenscorning.com/quietzon..._DataSheet.pdf

Super easy to install and you can do it yourself, not sure about having them turn into giant ports, if anything they would add to the volume of the room and making them out of Duct board would give you huge bass traps?
post #6499 of 10210
BAD panels (unlike PerfSorber) are better in larger rooms. Much like the Skylines, you have to be far enough way from them to acquire a fully randomized, homogenous sound field. In other words, sitting too close and (a) you can hear the panels; and, (b) at close distances they are doing more damage than good. Far enough away...they are great.
post #6500 of 10210
So my 13 x 17 x 7.5 foot room is probably not big enough for diffusion no matter where I am sitting, eh?
post #6501 of 10210
No. You just need to be careful about what product you use and where you use it. PerfSorber would be a good product for a room of this size.
post #6502 of 10210
Quote:
Originally Posted by nathan_h View Post

So my 13 x 17 x 7.5 foot room is probably not big enough for diffusion no matter where I am sitting, eh?

I used to think that, and it's the conventional wisdom, but even in a very small room diffusion can add a nice sense of spaciousness. As an experiment I tried adding massive amounts of diffusion to a small room, and I liked the results a lot. This first video explains more about diffusion and lets you hear what it sounds like 6 inches away:

All About Diffusion

This video lets you hear what microphones pick up at the listening position in a room almost the exact same size as yours:

Hearing is Believing

--Ethan
post #6503 of 10210
Quote:
Originally Posted by Ethan Winer View Post

I used to think that, and it's the conventional wisdom, but even in a very small room diffusion can add a nice sense of spaciousness. As an experiment I tried adding massive amounts of diffusion to a small room, and I liked the results a lot. This first video explains more about diffusion and lets you hear what it sounds like 6 inches away:

All About Diffusion

This video lets you hear what microphones pick up at the listening position in a room almost the exact same size as yours:

Hearing is Believing

--Ethan

Very cool Ethan
post #6504 of 10210
Due to space limitations, my L/R front speakers are inches from the side wall. Would acoustical treatments on each respective wall be beneficial in any way?
post #6505 of 10210
Quote:
Originally Posted by Tooj View Post

Due to space limitations, my L/R front speakers are inches from the side wall. Would acoustical treatments on each respective wall be beneficial in any way?

Probably.
post #6506 of 10210
Quote:
Would acoustical treatments on each respective wall be beneficial in any way?

In this case, more like required...particularily on the boundaries around the speakers.
post #6507 of 10210
What software/hardware would I need to be able to create these spiffy response graphs for my theater room? Is there a link or thread to look at?

Thanks.

post #6508 of 10210
Quote:
Originally Posted by Scamps View Post

What software/hardware would I need to be able to create these spiffy response graphs for my theater room? Is there a link or thread to look at?

Thanks.


Room EQ Wizard.
post #6509 of 10210
post #6510 of 10210
Quote:
Originally Posted by Scamps View Post

What software/hardware would I need to be able to create these spiffy response graphs for my theater room? Is there a link or thread to look at?

I made those graph by plotting all the data manually after measuring sine waves. That was before REW was available. The advice you got here to use REW is correct. This article explains how I use the older ETF software, but all of the explanations apply to REW too:

Using ETF

--Ethan
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