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QRD-2

Newport's QRD Well Sub-Assemblies
  • A 3-sided jig is very useful for keeping sub-assemblies accurately aligned during the set time.
  • Building the jig out of Formica-surfaced (or similar) material is helpful as the glue won't stick to it.
  • Only one single "bead" of carpenter's glue, spread evenly with index finger, is required per 1-1.5-in width of foam
  • Clamping, weights and pressure are absolutely necessary during the initial 2-3 hours set time
  • Remove sub-assemblies from the jig after no more than 3 hours to allow clean-up before excess glue hardens
  • Do not try to assemble all wells in one go -- the glue-prep process requires too much time and care per well
  • Start with single-well-width sub-assemblies -- then work up slowly to greater number of wells per sub-assembly
  • A reliable set-time is 3 hours. The assemblies are rugged enough to cure on their own and still allow easy cleanup.
  • Well sub-assembly sizes are determined by the positioning of full-depth (no foam well spacer) wells
  • Multiple sub-assemblies are fitted together then glued to the backer AFTER all wells are assembled
  • Assembling sub-sections with more than 5 wells becomes increasingly difficult


 

Glue Jig for building Well Sub-Assemblies
(3 foam blocks hold spacing while glue sets)
Gluing a 3-Well Sub-Assembly
(with 6 oak boards for weight on well bottoms)

 
 

QRD Final Assembly
  • At this stage there are 19 separate well sub-sections for one panel and there are 18 "spaces" between these sub-sections which will form "wells of either 0-in or 1/2-in height -- for a total of 55 wells.
  • Lauan is NOT flat. It warps, so foam spacer blocks and backer reinforcing help.
  • Carefully gluing of the well sub-sections to the backer will add stiffness and the long edges will complete the task. Bricks make great and inexpensive weights for gluing.

 
 
Checking sequence of well sub-assy's
(spacers necessary to keep Lauan straight)
Glue oak "hooks" and cross-supports
(even flat on floor, still some warping)

  • Glue the well sub-sections to the backer only after the backer is completely cured.
  • Maintain accurate alignment for each sub-section using a steel square
  • Constantly check fin alignment (90-deg) and keep spacing reasonably tight.
  • The design length is 62-in but the finish length is 65-in. The extra 3-in was accumulated because:
    • 1) the 1-in foam is slightly over 1-in thick
    • 2) glued surfaces add cumulative space and
    • 3) Lauan ply is warped so it's never completely flat on its own
  • The bottoms of well sub-assemblies will not always be flat -- just add a bit more glue as that surface is hidden
  • There will be some small variation in well-width -- just accept it as it is less important than well-to-well spacing
  • Clamp the assembly to a straight reference to remove any residual warp before gluing the sides
  • The sides are cut with a 1/4-in overhang at the front and 1/2-in in the back - the 1/4 is acoustically negligible
  • If the backer (and hanger strip) is not relatively straight the assembly won't be able to hang flush on the wall
  • Apply glue quickly for the long sides - there's 55 wells + edges to coat and the glue begins to set-up in 10-15 min
  • Again, there will be voids but don't sweat it -- finer cracks will be sealed by the polyurethane
  • Once the two long sides are glued and cured, the assembly will be straight and rigid
  • One QRD panel requires over 1/2-quart of stain and polyurethane to cover the large surface area
  • It takes about 4 hours to apply one coat to the surface using a 1-in wide brush

 
 
Gluing fin assemblies to backer
(note use of spacers and well-bottom weights)
Edge view of completed sub-assembly
(foam spacers and weights still in place)
 
 
Straighten any residual bowing
(gluing adds stresses which cause warp)
Glue first Lauan ply side panel
(individual weights to match side to edges)
 
 
Gluing the end panels
(clamp well to laminate flush with the end fin)
Assembled QRD Panel
(ready to finish sand, stain and urethane)
 
 
Back of assembled QRD panel
(showing long hangers + reinforcement)
Panel stained with 'Golden Oak'
(ready for polyurethane coat)
 
 
QRD panels installed below bass traps
QRD panel installed behind DAW

Room Measurements

The initial subjective impressions were positive. There was a sense of 1) more "openness", 2) more reflection, 3) more "live" / less "dead" and 4) more uniformity. However, it is too easy to "hear what we want to hear" so
the room acoustics needed to be measured again.


 
Room Freq Response - Before
Room Freq Response - After

Notice the following:
  • The QRD panels do appear to improve the frequency response flatness -- by ~3dB above 150 Hz
  • The room response now appears flat (above 150 Hz) to within +-4 dB -- at least at one location.
  • However, a notch appears at about 100 Hz. There is no explanation for this at present. It could be real or, because the QRD panels present more reflective surfaces, some additional phase cancellation has been added.
Now, consider the impulse response change:

 

 
Room Impulse Response - Before
Room Impulse Response - After

Notice the following:
  • The reflection at 3mS is gone
  • There is more energy in the first 10mS
  • The reflections are more diffused in time -- the objective of a diffuser
Finally, consider the low frequency response shown by the waterfall plots:

 

 
400Hz/500mS Waterfall - Before
400Hz/500mS Waterfall - After

Notice the following:
  • The room bass response below 300 Hz was smoother before adding the QRDs
  • The response above 300 Hz is now smoother
  • Ringing and flutter below 100 Hz has been improved