[avahifi]

Well Nyal, what would have better low frequency room damping than an an anechoic chamber?  Are you telling me that we want great damping at some low frequencies but not at higher frequencies?  Where is the appropriate frequency where we should switch over from damping to reflective?

Obviously we can't have a perfect interior listening room in a rational private home, but the goal should be to get as close to this as reasonably possible. By the way, when I say stiff room, I am meaning something like concrete - no flex or mechanical resonance at all.  Room node reflections and boom control requires careful room dimension design.  I have no problem with double layer wallboard with careful inert bonding layers.  It is a step in the right direction at some frequencies, but there is much more to solving the problems then this.

Of course one could just say screw all this and just invest in $5000 power cords.

By the way, I can demo the room treatment improvements I use if you just call me, you can hear the difference even over the telephone. 

Frank

[redjr]

...

But - - - if you record yourself talking in a normal live room and then play the recording back in that anechoic chamber, it will sound just fine.  The recording includes the acoustics of the original live room along with your voice...

Great feedback and points Frank.

So, I guess it goes without saying that recording studios are designed much like an anechoic chamber with sound absorption walls and other treatments.  This helps reduce any natural reflective and echo characteristics of the music being recorded and puts the emphasis back where the musician and/or recording engineer wants it.  The music as pure as possible.  And with close miking, you virtually record the instruments moments after they are produced.

But, having said that...does this scenario really capture music in it's natural habitat - so to speak?  With all the natural reflective and absorption surfaces it encounters before it reaches our ears.  Does all of this help the accuracy of the sound or hinder it?

I think my plan/design is becoming clearer.    The $64mil question remains.  How far do I take it?   

Rick

[avahifi]

We can't do better with our playback system then not screw up what the recording engineer gave us on our source material.  Not until our playback systems have skilled artificial intelligence.

Until then we are stuck with closely miked studio performances where there is essentially no room acoustic involvement at all or at the other extreme of a distantly and perfectly miced pipe organ and solo violin performance is a great huge stone European cathedral.

Don't second guess the second example.  I was there hearing this performance live and the violin could fill the cathedral and the duet was just magnificent.  I wonder if any recording engineer could capture this performance adequately

But in either case the acoustics of our listening room can do nothing but detract from the performances, so that is why my sound room has acoustic fabric wallpaper on all horizontal surfaces, thick carpet, acoustic foam ceiling, and as irregular hard interior surfaces as possible.  It sounds pretty good because it does not sound all that much at all even though it is far from perfect

Frank

[JLM]

Avoiding the isolation 'confusion' (keeping outside sound out and inside sound in)...

IMO the #1 priority is room size/shape.  Having been in anechoic chambers, a 11 foot cubic room (at an audio shop!), and (3) 45 foot diameter domes; I'd avoid them all!  Again, we are used to traditional sized/shaped spaces for home listening (many different opinions, just avoid the room dimensions being in simple ratios to each other and then go as big as possible).  Larger spaces designed for musical performances can either be concert halls (good) or cathedrals (that make organ sound great but speech less intelligible).  Read Floyd Toole's 'Sound Reproduction' (cheaper than a case of Green Glue or stack of studs).  Proper room design deals with inevitable reflections (room reverberation).  Reverb is natural (sound of a great hall) and connects what you see with what you hear.  The standard reverb measure is RT60 (how fast echo decays).  The 'best' value at the proper frequency is a matter of room size, debate, and personal taste.  This is where wall/ceiling design (materials, construction, stiffness) comes into play.

After achieving a good sized/shaped room and applying traditional furnishings (avoiding the coffee table in front of 'the' chair), the next most important issue is proper bass reproduction (read 'Sound Reproduction').  Toole pushes for use of multiple subwoofers to avoid standing waves (search for 'swam' here at AC).  Of course during construction is the time to address isolation, but in your case really seems like a much lower priority.

[youngho]

Well Nyal, what would have better low frequency room damping than an an anechoic chamber?  Are you telling me that we want great damping at some low frequencies but not at higher frequencies?  Where is the appropriate frequency where we should switch over from damping to reflective?

Sure, that's easy. Anechoic chambers all the way down to the deep bass regions is extraordinarily difficult to achieve (NRC, Harman, etc), so low frequency damping through pressure absorption is far easier to achieve.  Yes, great damping can be more desirable at low frequencies than higher frequencies, though that will depend on loudspeaker directivity and setup, also room furnishings. The appropriate frequencies for maximal damping would be below the transition zone (poorly approximated by the Schroeder frequency, probably around 300-500 Hz, depending on room size). Above that, gradual switching over would depend on loudspeaker directivity and setup, direction of reflections (usually desirable to heavily damp the front wall with conventional speakers, also at least the central portion of the back wall), also room furnishings.

Obviously we can't have a perfect interior listening room in a rational private home, but the goal should be to get as close to this as reasonably possible. By the way, when I say stiff room, I am meaning something like concrete - no flex or mechanical resonance at all.  Room node reflections and boom control requires careful room dimension design.  I have no problem with double layer wallboard with careful inert bonding layers.  It is a step in the right direction at some frequencies, but there is much more to solving the problems then this.

Incredibly stiff or concrete walls would result in maximal standing wave formation, regardless of room dimensions. Although concrete itself would have little mechanical resonance, it would support maximal acoustical resonance between parallel surfaces. Basically, divide ~565 by each room dimension (in feet) and multiply by integers to get axial room modes. More flexible room boundaries would reduce the Q (or narrowness of the frequency curve) and level of the modes.

By the way, what are "room node reflections"?

Any discussion of what recording engineers might have intended inevitably leads to some consideration of the circle of confusion: http://seanolive.blogspot.com/2009/10/audios-circle-of-confusion.html

[TRADERXFAN]

  Are you telling me that we want great damping at some low frequencies but not at higher frequencies?  Where is the appropriate frequency where we should switch over from damping to reflective?

Yes. And the answer is the specific  Schroeder Frequency of the given space.

[Nyal Mellor]

Room node reflections and boom control requires careful room dimension design.

You can spend as much time as you like optimizing room dimensions. Fact is you will still have room modes, that's an unavoidable fact of physics. And if you have extremely stiff concrete walls then those room modes will be undamped and extremely peaky resulting in boomy, low articulation bass.

No offense but I've learnt my lesson that for an industry person it is best restricting one's posts to areas where you have expertise.

[Nyal Mellor]

Yes. And the answer is the specific  Schroeder Frequency of the given space.

Exactly. Glad someone else got there before me.

With well designed speakers with a spectrally consistent off axis response (unfortunately not a lot fall into this category) I have been going increasingly towards room acoustic designs with minimal lateral plane (side walls in particular) absorption above 250ish Hz. Below this there is a lot of absorption provided by different mechanisms including damped double drywall on isolation clips (yes these act as pretty good bass absorbers), pressure based absorbers (metal VPRs) in conjunction with active room mode cancellation through multiple subwoofers where the client is amenable

[youngho]

would be below the transition zone (poorly approximated by the Schroeder frequency, probably around 300-500 Hz, depending on room size). Above that, gradual switching over would depend on loudspeaker directivity

Sorry, 150-400 Hz would have been more accurate for transition zone frequencies. Toole argues that Schroeder frequency may not be the best measure here, but the basic physics still apply.

Young-Ho

[redjr]

I'm 're-opening' my thread because I'm at the point of 'no return' with respect to my walls.  I've got one layer of 5/8" DW up, with Safe-N-Sound insulation on interior walls and between ceiling joists.  As stated in my OP I'm not going for total isolation and will have a drop ceiling and french doors.  But I do want a dead room.  I'm still torn on whether or not use GG due to the cost and current budget constraints.  My question is... What other acoustical caulk (damping substance) products will work in place of GG - even if not as effective?  An earlier poster mentioned a DAP product for gutters and other uses.  Is that okay to use between DW sheets too?  IOW - what alternatives exist instead of using GG?  Could I install the 2nd layer without caulk of any kind?

BTW, after putting up the Safe-N-Sound and one layer of DW, I can already tell a huge difference in the sound deadening qualities of the room.  I figure it can only get better once the 2nd layer is up, acoustic ceiling tiles in-place, doors on and carpet installed.  I'm getting excited!   

[BobM]

I recommend putting some insulation between the joists above the drop ceiling. Worked for me.

[redjr]

I recommend putting some insulation between the joists above the drop ceiling. Worked for me.

Already done.

[mcgsxr]

Well, since you ask... I did not go beyond what you have done (single layer of 5/8ths drywall, and Roxul safe n sound in the joist bays, and stuffed completely my bulkhead with pink insulation) and I am happy a year later.

A solid core door to close off your room will help too.

[redjr]

....A solid core door to close off your room will help too.

Yeah, I intend to get some 2' french doors that are solid core - or as solid core as possible.  I haven't found a suitable door yet, nor purchased it so that's an outstanding item, but it's on my list.    Just haven't had the time to look locally, or online.  Most of the ones I've seen are frame and glass, which is not what I'm after.  I'm sure there are some out there, just haven't found them yet.  I hope they're not a pricey special order. 

[JLM]

Just buy two solid doors (recommend insulated exterior fiberglass oak grained doors that can be painted/stained) and a removable mullion (if you have big items to move in/out).  Add rubber weather stripping/door sweep as sound seals.  If you don't need an extra wide door opening, recommend just buying a pre-hung insulated exterior fiberglass door.  If sound transmission is a really big deal, provide two such doors (can be on the same wall with one swinging into the room and the other swinging out of the room, if the wall is thick enough the door handles won't hit or else hinge them on opposite sides of the opening).

[redjr]

Back to my OP.  In my particular situation(drop ceiling and french doors), is GG 'really' necessary to damp the sound further, or would it have little effect?  Should I have something between the sheets of DW, or just hang the 2nd layer right over the first overlapping existing joints, mud and tape and call it a day?  Keep in mind, I'm not after total isolation, and what I have (including 2nd layer of DW) will be good enough.  - Rick

[Scottdazzle]

Back to my OP.  In my particular situation(drop ceiling and french doors), is GG 'really' necessary to damp the sound further, or would it have little effect?  Should I have something between the sheets of DW, or just hang the 2nd layer right over the first overlapping existing joints, mud and tape and call it a day?  Keep in mind, I'm not after total isolation, and what I have (including 2nd layer of DW) will be good enough.  - Rick

redjr,

I'm coming to this post late but maybe this will help.  I posted about the construction of my listening room here: topic=116979.40.  I had the same questions you have and the room turned out to be a musical success.  Some of the replies to your op have made these points, but here is my two-cents' worth.

I recommend green glue between double layers of sheetrock.  You get great isolation and resonances seem to be minimized.  Suspending the ceiling with isolation clips to the joists is hugely effective in removing noise (mechanical and acoustic) transmission between floors. Insulated ducts and pipes are a must. Above all, pay attention to room dimensions to minimize nodes.  Avoid multiples (e.g. 8' ceiling and 16' wall length).  My room turned out to be 18'6" x 12'11" x 7'2" and is remarkably neutral acoustically for a smallish basement listening room.

Best of luck to you!

[Big Red Machine]

I don't see you being able to take full advantage of the double drywall unless it has been isolated from the structure on hangers and each layer separated by a viscoelastic compound.  That's my experience and those of many others in my neck of the woods.

[redjr]

Hi Scottdazzle - Appreciate your comments.  I recognized your avatar so I must have read some of your previous posts.

The room dimensions are already set, as are the decisions to have a drop-ceiling and french doors.  I'm also aware that these two items are not at all helping my isolation efforts.  But since this is a multi-purpose room that is the path I'm on.  However, I have taken some measures to help minimize sound coming in and going out.  Not total measures mind you, but things I trust will help after doing a bit of research.  Such as; double 5/8" DW, insulation in all walls, between overhead floor joists and offset studs on my primary forward TV wall.  The room size is not a rectangle, but is 10' wide at the screen end and 14' at opposite end with and angled wall on one side where the french doors will be.  It will be on the small..ish side, but my man-cave nonetheless. 

My basic question remains... If I haven't taken measures A and B, will C even matter?  If I've got 2 big holes in my fishtank (using that analogy) - my drop-ceiling and french doors, does double DW even matter, much less what I put between them?  Or, am I simply going after a < 5% additional improvement in isolation, mass, and absorption qualities for which there will be little difference noticed?  If I can save $400-600 on GG and use something else because of the minimal % improvement factor, I'd rather spend that same amount on, say, nicer speakers - for instance.  Are there other compounds in the marketplace that are similar to GG, cheaper and still work as a damping agent between DW sheets?

Rick

[redjr]

I don't see you being able to take full advantage of the double drywall unless it has been isolated from the structure on hangers and each layer separated by a viscoelastic compound.  That's my experience and those of many others in my neck of the woods.

I was posting when yours came through.  That's the $64K question.  However, since I'm not going after the double DW from an isolation perspective only, but also to improve the qualities of the sound inside the room, DD is going up.  One way or another.  And I agree that the benefits will not be as great without the other isolation measures in place.  But, it will not be a total waste of time and money either.  Maybe nothing between the sheets is the best answer for my situation.  I simply don't know.

Edit:  I know GG won't hurt, but will it's benefit be out-weighed, not necessarily negated, by the lack of other isolation measures?