Salmonsc,
If you'd like to view pictures of my room with its hemi-cylindrical (poly) diffusers and Skyline diffusers, then you can do so under my System link.
If you'd like to build your own Skyline then here is a write-up I did to help others. Be sure to share with us pictures of your final product.
On to building a Skyline . . .
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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 whats 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
Carpenters 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 youll 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 didnt 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 doesnt 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 youll need. For example, lets 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 youll 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 youll enter your Prime number and it will return a number that youll 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 youd 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, youd 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 diffusers 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 diffusers width to support its heavy weight.
Highest Frequency put in 4,500Hz if youre 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 blocks 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 wouldnt 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 its 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 youll 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 wont need to do the work in the following paragraph other than to sand one of the blocks 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 dont know how much of the sides will be visible so its 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.
Its 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. Ill admit Im 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. Id 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 its square with the blocks around it. Sometimes a block will be warped and when the bottom is properly fit within its cell youll notice that the other end which faces into the room isnt square with the blocks around it so use the end facing into the room as your guide for gluing and positioning the blocks.
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(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 didnt 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. Youll 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 plywoods 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
