[sleepysurf]

As seen in my system pic, I have recently added acoustic panels (and large silk trees for diffusion) behind my ML Summits. Overall, the bass, soundstage, and imaging were much improved (vs. plain walls), but the music now lacks what I call presence (not as live sounding). I'm pretty sure it's from the front wall being a little too "dead" now.


Turns out, I'm about to re-do my home office, and the cabinetmaker says he can build me 2' wide open bookcases (8" deep) for the space behind my Summits. He would design it to match my center console cabinet (for WAF!) The bottom-most section would be 24" x 24", to accommodate the lower acoustic panels of that same size (angled out from wall for additional bass trapping). See draft below.


I'd then fill the rest of the shelves with scattered books, and cut-up portions from my upper acoustic panels. I would get rid of the silk trees.  This would allow me to add and subtract books/absorption and "tune" the front wall to get the exact sound I want. The only potential downside is that I'd have 8" less space from the stat panels to the front wall (would be 37" vs. 45" that I currently have).  Moving them farther out would be ideal, but I can't, as that blocks the lateral view to my HDTV from side chairs.

I'm already using a GIK Pillar Trap in the left corner, and GIK Table Trap next to a side chair (not visible in pic).

What do y'all think?
 

[Ethan Winer]

This would allow me to add and subtract books/absorption and "tune" the front wall to get the exact sound I want.

The only way a bookshelf will be much of a diffusor is if it exactly emulates a QRD or other proven design. I recently made a video comparing a number of surface types, including a "typical" bookshelf, and you can hear it for yourself. Find All About Diffusion about halfway down the list on the RealTraps Videos page. This video is presented from the perspective of recording studios, but it applies equally to audiophiles.

--Ethan

[sleepysurf]

GREAT video Ethan!  It's clear my front wall panels are deadening the sound too much, just as in your video.  My idea is to simulate the QRD diffusor as much as possible, but with "high WAF".  Even if I get sound that is only in-between a plain wall, and true diffusor, it would be better than the over-damped sound I have now.  I'll still be able to use the 2' x 2' absorbers on the bottom, and the functional storage of the shelves will be an added bonus.  Thanks!

[sleepysurf]

My cabinet guy installed the bookshelves yesterday. His woodworking skills are incredible, evidenced by the intricate lattice design he recreated (matching the center console sliders). I'm starting off with 2' square panels angled in the bottom section (for bass trapping), and will stagger books on the shelves directly behind the stat panels, to see how diffusion works. The shelves are designed so I can (optionally) still use my two 4' panels, if that proves best. I now have endless possibilities for acoustic "tweaking" by combining acoustic panels, books, CD's, etc. I'll eventually use my XTZ Room Analyzer for final tweaking, but need to address some reproducibility issues with that device first.  Here's a sneak peek of the shelves thus far.

[twitch54]

Lookin' and 'hopefully' sounding good Alan !

[sleepysurf]

Another update. After a couple weeks of tweaking/listening, I'm quite pleased with my acoustic bookshelves. 

Firstly, despite the asymmetry of my room (open arch/door front right, sliding glass on left wall), the soundstage is now perfectly centered (was always skewed to the right), and twice as deep. That was a complete surprise!

I was also surprised by the degree of SPL boost. I expected things to be slightly louder (vs. using pure absorption), but once I dialed in the speakers, they were ~20% louder, and more live sounding.  However, they were also a tad brighter than I prefer.  On a whim, I hung my 4' tall absorption panels behind the wall-mounted HDTV (see pic). That took the edge off the highs, and gave me a razor-sharp image, probably by eliminating some reverb from sound bouncing between the wall and cantilever-mounted TV.  I also positioned the 2' square absorbers to be fully upright (rather than tilted) at the bottom front of each unit, with 9" of dead space behind them, for better bass trapping. That tightened the bass further, but I still might add some cotton batting behind the panels to see if that offers any further improvement.

I'm still not done tweaking, but can honestly say this combo acoustic/decor upgrade has had the greatest impact on my soundstage since getting the Summits. I know that absorption, absorption, and absorption is commonly preached by many on this forum, and I fully understand the logic. However, if you already have a somewhat dead room, and are able to pull your speakers out at least 36-40" from the front wall (distance from bookshelves in my case), don't underestimate the power of diffusion for improving the imaging, attack, decay, and overall energy, of your setup (especially with dipole speakers)!

Next up will be XTZ Room Analyzer measurements for final tweaking.

[bpape]

Diffusion absolutely has a place in a design scheme - especially with panels like that.

Understand that you do have absorption behind the speakers below and in terms of the books themselves which are absorbers, not diffusers except at very very high frequencies.  The rest of the bookcase is certainly scattering some sound but not really diffusing evenly in terms of the physical or time domains.  That said, it's still better than a flat wall and it seems to be working in your case.

Congrats.

Bryan

[sleepysurf]

...Understand that you do have absorption behind the speakers below and in terms of the books themselves which are absorbers, not diffusers except at very very high frequencies.  The rest of the bookcase is certainly scattering some sound but not really diffusing evenly in terms of the physical or time domains...

I guess I should call this WAF_abfusion    Whatever, it's definitely a major improvement!