[jmpsmash]

Hi all.

I have a 20ftx20ftx9ft room. While nice and spacious, the dimension causes a HUGE suckout at 40-50Hz and doesn't recover until 30Hz. I want to resize it to 20x15x9, but due to presence the room features (doors, windows, HVAC inlet, attic access), there is not good way to put up a proper permanent framing and drywall. I wonder if it is possible to line up a bunch of IKEA bookshelves and do a fake wall. They will be backed with thin backing, and likely 6 foot tall only so there will be gap on top. Will that be effective against the 40-50Hz sound waves?

TIA.

[Letitroll98]

I doubt that will do a thing to reduce your suckout.  The dip occurs because of interference from out of phase wall reflections, so the best strategy would be to place bass traps in the corners.  Another successful strategy is The Swarm, using four subwoofers in various positions around the room.  Just Google it.  Both much cheaper and easier than building walls.

[JLM]

Your idea of wanting a rectangular room would be an improvement. Can you adjust the width down? Fibonacci ratio would put it between 12'-3" and 14'-7".  Or can you put one or more notches or skew(s) into the new partition?  (The best rooms aren't perfect rectangles.)  Perfect rectangles are often modeled as easier to standardize.  No one said rectangular rooms are ideal, just easier to design/build.  What should be avoided is small cubic/spherical shapes.

My first favorite audio shop put a skewed (angled) wall between listening rooms to help break up standing waves in both rooms.  Paul Allen commissioned an all out ideal room that consisted of a large room with dozens of skewed wall sections inside a barn.  My 8ft x 13ft x 21ft room has a 3ft x 5ft notch into the back corner that may actually help the sound.  Note that I have ten GIK 2ft x 4ft 244 panels that do little good here (in a near ideal room) but works wonders elsewhere.  Also have 3 subwoofers and use Dirac room correction as a final tweak. 

What you're proposing is to build a huge resonating chamber behind the partition that will attenuate one frequency.  The thin backing would also resonate.  Suggest getting creative.  Notches can be sized to hold those Ikea bookshelves.  Recommend reading Floyd Toole's "Sound Reproduction" (either edition) which is an audiophile primer for learning how loudspeakers and subwoofers behave in-room.  The Swarm Letitroll98 mentions is one of ideas Toole brings up.

[richidoo]

20 foot wavelength is 56.5 Hz.

The IKEA will not reflect low frequency effectively even if it was perfectly sealed the sound would go right through the thin backing. 50Hz will go right through a stick built wall too. Concrete would reflect it, as you may already know? Is the room concrete? 

Even with a reflective partition at 15 feet you will still have LF modes inside the room that could be improved. So a better way to deal with it is to cancel/absorb the reflections.

The only methods I know that will efficiently absorb sound at very low freq are: Carbon absorber and active absorber. They work best placed near the LF speakers.

[jmpsmash]

Hi all, thanks for the replies. Let me try to respond and clarify.

The room is in a standard American wooden structure house. Ie. wood framed and drywall, not concrete. While there are more leverage in making changes to the room, there are also limitations. There are doors and windows at the corners so cutting them off completely is a no go. There is certainly flexibility in the dimension.

The ideas of active bass trap or sub array are interesting and while it might not cost less than building walls they certainly will be less destructive to the room's structural layout. Let me give those some research!

[Tyson]

Bass traps are going to give you the best results.

[jmpsmash]

Bass traps are going to give you the best results.

Many have said bass trap won't work down to 40-50Hz.

I have tried putting a big bundle of Rockwool (16"x24"x48") that was destined for some panels as a trial. Putting them in the corner and the 40-50Hz suckout didn't move a bit. Perhaps too small?

[richidoo]

Did you measure the room response, or are you going by ear?

Are you using separate subwoofer(s) crossed over to main speakers?

Did you already try moving the speakers and the listening position around, even just as temporary experiment?

[jmpsmash]

Did you measure the room response, or are you going by ear?

Are you using separate subwoofer(s) crossed over to main speakers?

Did you already try moving the speakers and the listening position around, even just as temporary experiment?

I use REW. I don't have separate subs at the moment. my main speaker has a pair of 15" JBL drivers. I have moved them around quite a bit. Right now they are at the most optimal location but they are only optimal for frequencies outside the 40-50Hz range. I have never found a place where the 40-50Hz works aside from me standing at the corners. I have used REW to generate sine waves 40Hz, 50Hz, all are cancelled out at my sitting position. I also moved sitting position (within reasonable limits) and that doesn't help either.

[richidoo]

Well that sounds perfectly frustrating!
Do you want to post your room measurement?

[Tyson]

Bass traps can work but they have to be pretty big.  You could also do a bass trap based on it being a Helmholtz resonator tuned to a specific frequency.  GIK sells a version like that. 

I'd also buy 2 or 3 additional subs and scatter them about the room in a swarm approach. 

Last but not least I'd use EQ to knock down any peaks that might pop up after you make these changes.

[Doublej]

What about a room divider like this, https://roomdividersnow.com/products/hanging-room-divider-kits?variant=15868701254, or a build a wall kit, https://www.everblocksystems.com/everpanel-modular-walls or https://www.everblocksystems.com/simple-walls.

[youngho]

Try four of these, one in each corner if possible: https://www.psiaudio.swiss/avaa-c20-active-bass-trap/

[Rob Babcock]

Try four of these, one in each corner if possible: https://www.psiaudio.swiss/avaa-c20-active-bass-trap/

I didn't see any pricing info, what do they run?

[Doublej]

I am not sure if this is the same item but it's $2769 each

https://www.bhphotovideo.com/c/product/1352278-REG/psi_audio_avaa_b_active_velocity_acoustic_absorber.html

[Big Red Machine]

BTW, the ideal room dimensions are 17 wide, 23 deep, and 10 high. No multiples in there. There is other math, but for another day. You could go 20 x 17 x 9 and still be in good shape.

I'd personally make it 17 wide with new stud walls if I could. Splaying them would be even cooler. You might fill that 1.5 feet on each side full of insulation and add a double door. Resale could be a problem but acoustics are way more important!!

[rockadanny]

Helpful link. Check it out:  https://amcoustics.com/tools/amroc?l=23&w=17&h=10&ft=true&re=DIN%2018041%20-%20Music

[richidoo]

Nice link! Thanks rockadanny.  Don't need to run modecalc program anymore. 

I forgot to put this link in my post, wavelength/frequency converter.

[Kevin_X]

I had a 10x10x8 square room in the house we rented while shopping for our current home.  That was audio purgatory.  Kids, don't try this at home.     Plus, I have an Ikea Fredde desk.  Maybe it wasn't purgatory after all; maybe it was actual hell.

I find the Harman Excel spreadsheet easier to interpret than Amroc, but both tools can be useful:  https://www.harman.com/search-results?k=room+mode+calculator

Drywall sheets are cheap (and can probably be returned if it isn't cut).  If you have a few friends to bribe (beer and Firehouse subs work wonders) and some spare time, for around $100 you could buy 5 or 6 sheets of drywall and have them held in place in different positions to see if those reductions improve the room acoustics.  As was mentioned, even attempt an angled false wall to see if it re-orients the modes out of cancellation position.

Some folks have tried a 45 degree rotation to defeat standing waves.  Placing the speakers on perpendicular walls, firing diagonally into the room.  I actually tried this with the aforementioned desk in the aforementioned room.  I'll spare the details of the aesthetics and feasibility.  But you have 4 times the square footage I did.

[abomwell]

I have a 15' square room with a big suck-out at 50Hz. Putting two subwoofers in diagonal corners solved the problem entirely.

Al