Extreme makeover - Listening room edition

Posted by: ClaudeP on 09 November 2015

In a previous post, Huge made the following comment about my listening room:

 

''3/4" air gap between drywall panels will definitely cause problems.  This will produce a resonant membrane / air compression chamber system between the two skins of the drywall.

 

The fundamental resonant frequency is difficult to calculate exactly as I don't know the drywall material spec and it is further complicated by the flexibility of the back wall of the chamber, but I would have thought a fundamental somewhere 500Hz to 950 Hz with harmonics to a few kHz.  There could be some complex phase behaviour as well (from the outer skin of the chamber being phase delayed).

 

The effect in the room will be extremely strong as all the walls will resonate like this.  Damping material between the two skins will reduce the effect but not eliminate it.  I would expect this to be so strong that, perceptually, it'll dominate over the fundamental room modes (i.e. resonances below 100Hz)."

 

Turns out he was perfectly right. Expensive sound panels helped, but the room remained fundamentally flawed. That was clearly demonstrated when I moved the system to the next room, where it sounded incredibly better... everywhere in the house.

 

After careful review of alternatives, I opted for this highly efficient - if somewhat radical - solution:

 

 

A sample of the infamous resilient bars can be seen on top of the rubble.

 

That's after Day 1 - the room already sounds much better!

 

Claude 

Posted on: 09 November 2015 by varyat

Awesome Claude!!!

For those of us afflicted with this hifi bug there will always be the tendency to double guess the limitations our rooms are imposing on the overall character of the SQ. Why do you think we buy so many silly/expensive tweaks that claim to solve all of our problems , but in reality, at best only mask/minimize our room's limitations. Your approach is heroic and I applaud your efforts!

Get the basic fundamentals right and it will be like a box upgrade!! Good luck and keep the pictures coming if you have a chance....

ATB,

Mark

Posted on: 09 November 2015 by andrewnielsen

You have nice, recessed downlights. If you used light roses then you would have been able to avoid having holes in the ceiling and thereby avoided having something that sound could leak through. 

 

It's no wonder you wife is looking fed up, after tearing out all those walls, and stacking them neatly, for you. 

Posted on: 09 November 2015 by hafler3o

Very interesting! I have a dedicated listening room but the walls are 3/4 metre thick granite and Caen limestone blocks. The floor is self levelling compound over concrete screed over blocks. Suspending panels / drapes / freestanding screens were the only option. Good luck!

Posted on: 10 November 2015 by Huge

Oops, seeing her expression, I feel really guilty now!

Posted on: 10 November 2015 by feeling_zen
If you did all that while she was out working in the garden for half an hour it would explain things.
Posted on: 10 November 2015 by Innocent Bystander

Looks like she's got her eyes closed waiting to be told "you can open them now" - or maybe best clear up the mess first...

Posted on: 10 November 2015 by ClaudeP

Actually she's thinking about the next step - now she has to take all that over to the dump!

 

Seriously Caroline has been extremely supportive throughout, and she's the one who insisted for the extreme makeover approach in the end.

 

Claude

Posted on: 10 November 2015 by Allan Probin

Just a thought, could you have squirted expanding foam into the gap behind the drywall?

Posted on: 10 November 2015 by ClaudeP

Allan,

 

We've considered it, but didn't settle for that solutionfor 2 reasons:

 

1 - As Huge points pout, nothing guarantees that it would have resolved the problem entirely, and

 

2 - The procedure is rather complex and ultimately would not have resulted in substantial savings - if any

 

Conclusion: do NOT install resilient bars, they are good to prevent the sound from getting out of the room, but bad for the sound

 

Claude

Posted on: 10 November 2015 by Allan Probin

I'm currently building a new house and it occupies most of my spare time. I'm almost into the third year of construction now. All the walls are 15mm plasterboard screwed to wooden battens at 600mm spacing. The 15mm board definitely feels heavier and stiffer than 12mm, though not perfect I'm sure. However, I'm certainly not ripping it out and starting again.

 

 

 

Posted on: 10 November 2015 by Innocent Bystander

Pack tightly with mineral wool, preferably high density acoustic type. Especially the listening room!

 

Walls between rooms need this anyway to minimise sound transmission, especially between bedrooms and other living rooms, toilets etc. Ditto ceilings.

 

Unfilled gaps in walls behind plasterboard is also undesirable for heat conservation reasons, as what is wanted is no space for air movement.

Posted on: 11 November 2015 by Huge
Originally Posted by Innocent Bystander:

...

Unfilled gaps in walls behind plasterboard is also undesirable for heat conservation reasons, as what is wanted is no space for air movement.

Unfortunately this turns each plasterboard panel and cavity into a resonant membrane chamber, partially damped by the mineral wool.  Tight packing of the mineral wool reduces (but does not eliminate) this effect.

 

A good idea is to vary the depth behind the plasterboard on each wall so the effect isn't so noticeable at just one frequency.  On an existing wall, an second layer of plasterboard (or even cement board) can be attached in front of the existing plasterboard to lower the resonant frequency.

Posted on: 05 December 2015 by ClaudeP

This has been a very frustrating period - I was listening to records I knew well and everything was messed up.

Good news: the brand-new listening room is now complete... without the dreaded resilient bars. We went the easy way - 3/4" Sonopan and 3/4" gyproc on forens, with screws every 18" or to keep things tight. No more vibrating walls for me, please. Yesterday, I added bass traps in the corners behind me to help control all the bass the Harbeth 40.2s generate. It worked just fine.

The end result is amazing - I never had such a great system, and now I'm hearing it at its full potential. Now everything I listen to puts a big smile on my face.

Posted on: 05 December 2015 by gary yeowell

Beautiful room and system Claude.

Posted on: 05 December 2015 by MDS

That room looks fabulous, Claude. If it sounds as good as it looks you must be absolutely delighted.  Enjoy.

 

Mike 

Posted on: 05 December 2015 by varyat

Looks terrific Claude.

Throw a cool rug down, might sound even better !!

ATB,

Mark

Posted on: 05 December 2015 by Hook
varyat posted:

Looks terrific Claude.

Throw a cool rug down, might sound even better !!

ATB,

Mark

+1.  A rug will help absorb the points of first reflection from the floor. 

Congrats Claude, your remodeled listening room looks great!

ATB.

Hook