tomlinmgt
Lunatic Member
This is my second attempt at a 1D QRD diffuser with my first attempt being a 13-well unit. That first design....
http://www.audiokarma.org/forums/showthread.php?t=517397
....was very labor intensive and challenging to build, so for the second one I went back to the drawing board and came up with something that is a bit more compact, is easier to construct, offers the same performance (maybe even a little better), is lighter in weight, and looks better.
For the second unit I chose an 11N (or "11-well") design that has an effective range from 382 to 4526 Hz. Here are the performance parameters...
Scatter frequency range: 382 to 765 Hz, 3825-4526
True diffusion frequencies: 765, 1530, 2295, 3060, 3825
Minimum distance to seating position: 4.5'
Like the 13-well unit that preceded this one, this particular design is similar to commercial units costing several hundreds of dollars. I was able to build this unit for less than $70.
All materials came from Home Depot. The frame is 1"x8" rough cedar, the well faces are 3/4"x2" rough cedar and the fins and back plate are 3/16" (5mm) Luan plywood. I used a combination of wood screws and Loctite trim and panel construction adhesive (water based and dries clear). The overall dimensions are 48" tall x 20" wide x 7 1/2" deep and it weighs 15-20 lbs. I used rough cedar for its light weight and for the optimal adhesive bond its rough surface would provide (one side is smooth and one side is rough so the exposed/outer surfaces are smooth). I also happen to like cedar....a lot. I had the well fins cut at Home Depot and I highly recommend you do the same.
You can see the basic construction methodology in the pictures I attached. Basically I started by cutting the back plate, one side frame and both top and bottom frame pieces first. The side frame was glued and screwed into place. The top and bottom frame pieces were only screwed into place as they will need to be removed and reinstalled toward the end of the build. Once the partially completed frame was constructed I started installing the wells. Using pieces cut from the same 3/4"x2" cedar the well faces are constructed of, I made "pedestals" on which the well face sits. The height of the pedestal, less the thickness of the well face (3/4"), dictates well height (or depth, depending on how you look at it). In the second picture you can see that I have installed the pedestals for the third well. The fourth picture shows the third well with the well face installed, and the fourth shows the fin installed to complete the third well. The fourth picture shows initial construction of the fourth well with the pedestals in place. The fifth picture shows all wells now installed (note spacers in the empty wells) with only the remaining side plate left to install.
Up to this point everything has been glued in place and has started to set (it was in the upper 90's so it set up fairly quickly). However, I did not glue the ends of the well faces, fins or pedestals where they touch the top and bottom frame pieces. Allowing the top and bottom frame pieces to be removed enabled me to trim them as I wasn't exactly sure how much the glue would change the calculated width of the unit. Turns out not much as I only missed the calculated width by about half an inch. Even still, I'm glad I allowed for the removal of these pieces as they would've been a pain to trim if they had been glued to the other parts of the assembly.
The final step was to trim the top and bottom frame pieces, cut the right side frame piece, and glue/screw them into place. Be aware the wells need to be air tight, so before the last three frame pieces go on all surfaces that make contact with the frame will need to have glue applied to them.
If you want to construct your own QRD diffuser but want to try something a little less labor intesive I'd suggest you try a 7-well unit. It won't diffuse as much of the frequency spectrum as this 11-well unit, but it still offers effective diffusion and is usually what one finds when in the market for entry-level commercial units. There are several well configurations that can be constructed, but I strongly encourage you to familiarize yourself with the QRDude software to simplify the design process. The software can be found here...
http://www.subwoofer-builder.com/qrdude.htm
Ultimately I'll build three more of these so I can have a 40" wide array of two panels (butted one up against the other with one inverted) on the front wall behind each dipole speaker and the 13-well unit centered on the front wall between the speakers. I'll be updating this thread with installation, implementation, and performance details....so stay tuned.
- Michael
http://www.audiokarma.org/forums/showthread.php?t=517397
....was very labor intensive and challenging to build, so for the second one I went back to the drawing board and came up with something that is a bit more compact, is easier to construct, offers the same performance (maybe even a little better), is lighter in weight, and looks better.
For the second unit I chose an 11N (or "11-well") design that has an effective range from 382 to 4526 Hz. Here are the performance parameters...
Scatter frequency range: 382 to 765 Hz, 3825-4526
True diffusion frequencies: 765, 1530, 2295, 3060, 3825
Minimum distance to seating position: 4.5'
Like the 13-well unit that preceded this one, this particular design is similar to commercial units costing several hundreds of dollars. I was able to build this unit for less than $70.
All materials came from Home Depot. The frame is 1"x8" rough cedar, the well faces are 3/4"x2" rough cedar and the fins and back plate are 3/16" (5mm) Luan plywood. I used a combination of wood screws and Loctite trim and panel construction adhesive (water based and dries clear). The overall dimensions are 48" tall x 20" wide x 7 1/2" deep and it weighs 15-20 lbs. I used rough cedar for its light weight and for the optimal adhesive bond its rough surface would provide (one side is smooth and one side is rough so the exposed/outer surfaces are smooth). I also happen to like cedar....a lot. I had the well fins cut at Home Depot and I highly recommend you do the same.
You can see the basic construction methodology in the pictures I attached. Basically I started by cutting the back plate, one side frame and both top and bottom frame pieces first. The side frame was glued and screwed into place. The top and bottom frame pieces were only screwed into place as they will need to be removed and reinstalled toward the end of the build. Once the partially completed frame was constructed I started installing the wells. Using pieces cut from the same 3/4"x2" cedar the well faces are constructed of, I made "pedestals" on which the well face sits. The height of the pedestal, less the thickness of the well face (3/4"), dictates well height (or depth, depending on how you look at it). In the second picture you can see that I have installed the pedestals for the third well. The fourth picture shows the third well with the well face installed, and the fourth shows the fin installed to complete the third well. The fourth picture shows initial construction of the fourth well with the pedestals in place. The fifth picture shows all wells now installed (note spacers in the empty wells) with only the remaining side plate left to install.
Up to this point everything has been glued in place and has started to set (it was in the upper 90's so it set up fairly quickly). However, I did not glue the ends of the well faces, fins or pedestals where they touch the top and bottom frame pieces. Allowing the top and bottom frame pieces to be removed enabled me to trim them as I wasn't exactly sure how much the glue would change the calculated width of the unit. Turns out not much as I only missed the calculated width by about half an inch. Even still, I'm glad I allowed for the removal of these pieces as they would've been a pain to trim if they had been glued to the other parts of the assembly.
The final step was to trim the top and bottom frame pieces, cut the right side frame piece, and glue/screw them into place. Be aware the wells need to be air tight, so before the last three frame pieces go on all surfaces that make contact with the frame will need to have glue applied to them.
If you want to construct your own QRD diffuser but want to try something a little less labor intesive I'd suggest you try a 7-well unit. It won't diffuse as much of the frequency spectrum as this 11-well unit, but it still offers effective diffusion and is usually what one finds when in the market for entry-level commercial units. There are several well configurations that can be constructed, but I strongly encourage you to familiarize yourself with the QRDude software to simplify the design process. The software can be found here...
http://www.subwoofer-builder.com/qrdude.htm
Ultimately I'll build three more of these so I can have a 40" wide array of two panels (butted one up against the other with one inverted) on the front wall behind each dipole speaker and the 13-well unit centered on the front wall between the speakers. I'll be updating this thread with installation, implementation, and performance details....so stay tuned.
- Michael
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