I have wanted to add diffusers behind my bipole Magnepans for a long time to diffuse the backwaves. I have 2 rooms with larger Magnepans and would like to experiment with the HT room first which has a flat screen in the middle so the diffusers would be on each side of the flatscreen on the front wall, or could straddle 45 degrees on the corners covering the corner traps. The 2-channel room could have diffusers behind each speaker and the center of the front wall, but that would be later if the former works well. I already have absorption in the room half way up the corners of the wall. The absorption helped including one-note bass. If I added too much absorption, I would get an uncomfortable pressure in the room that detracted from the sound and made the room too dead.
I have looked at and read a lot of designs (originally inspired by PDR's design/build
http://www.audiocircle.com/index.php?topic=96222.msg1035197#msg1035197) and played around with QRDude. I then saw the Leanfuser design (both metric and imperial implementations) and their design philosophy of using regional "standard dimensional" readily available building materials. After that, I played around with QRDude again and was not able to model their wide effective frequency ranges (@ 400 Hz to 8 KHz) using their shallow well depths and wide well widths that appear in the designs.
I then tried to get QRDude to generate as wide a frequency range as I could (goal to cover a piano's frequency range) using 2", 1.5" and then 1" readily available stock without generating warnings from QRDude's software. I tried automatic and manual settings and found the automatic settings the best to avoid the "squeeze toy" errors generated by tweaking one parameter to much.
Below is the best I could get from QRDude and it turned out to be with 1" stock. I could get slightly lower with the wider stock, but the top end was lowered to 3,372 Hz.
I would appreciate any critiques on this design.
Piano Frequency Range: 27.5 Hz - 4186.01 Hz
Scatter: 207 Hz, Diffuse: 415 Hz, HF cuttoff 6615Hz
True Diffusion Frequencies: 415 830 1245 1660 2075 2490 2905 3320 3735 4150 4565 4980 5395 5810 6225
I plan on using 1" EPS painted with a hardener additive to paint. I would try the cement coating method that PDR used, but am afraid it would not adhere well for me (read: user error). The 2" and 1.5" material appears to be easier to build and more rigid/durable, but the frequency range is restricted further. Maybe the 1.5" width EPS may be a better compromise ???
TIA for your helpful insights.
1.5" compromise
