[lglura]

Wow guys, i think i `ll describe the build soon. i need a simple program to sketch it.
I`ll build the room airtight with no leaks, floating ceiling on floating walls attached with resilient clips to the concrete and a floating floor inside the wall. I`ll have two airtight doors. There is no weak point exept to little vertical height ( i hope). The acoustic treatment will be carried out when the room is done.

 

[lglura]

Keep in mind you're still going to hear subs.
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I can live it as long as my wife is happyaddle: and i can watch movies without any limitations:R

 

[paulspencer]

Is this a DIY project or are you having it done? This can have a big impact on the cost. If not diy, then labour cost will have a greater impact on budget.

When I looked into isolating mounting systems in the past, the cost was very high. It's a low profile option and the cost can look different if labour is factored in. However, if you can actually use staggered ceiling joists for example, you can completely isolate the false ceiling. Done cleverly, this will also be a low profile option where the staggered joists protrude just below the existing ceiling members. That would be my first choice in a DIY situation.

Bass traps are intrusive into a room, and it makes sense to try to turn the entire room into a bass trap. In essence, this is what we are doing in using drywall and isolating it from the existing cave-like envelope. So while I tend to disagree with ignoring the bass damping issue, thinking you can fix it later with bass traps, this is moot because isolated drywall walls and ceiling will in fact increase bass damping a great deal.

In terms of measuring, it actually makes sense. This allows a before and after - which you can't do later. You could measure sound transmission loss as well as internal acoustic response. Both will have value, and will give you some feedback on what you have achieved. You can't do this later if you get curious!

 

[Ted White]

What a great reply. I agree with all these points. Maybe not so much the measuring part, I'll admit. But for sure very good point about the decoupled system absorbing low frequencies.

You rarely hear about this. The max absorption occurs at whatever low frequency resonance point is present in a given partition. And you have the bell curve move out from there. Further away from the fundamental LF resonance point and absorption drops as well. I was involved with testing this very thing at Orfield Labs in Minneapolis.

This is all excellent that you brought this up as we're seeing amazingly large IB systems much more routinely, and of course this means they need more LF absorption as you say.

Do you like to use theater risers as bass traps? I'm not an in-room acoustics person but this topic comes up frequently.

 

[Ted White]

I`ll build the room airtight with no leaks,

Tough, but you know that obviously​

floating ceiling on floating walls

You mean independent ceiling joists as in the article? That's better than clips if you can do this.​

... floating walls attached with resilient clips to the concrete

Clips on stone = 1 5/8" air cavity. That small air space with clips and drywall will improve your high frequency performance but your low frequency isolation will worsen. I have the data on that if anyone's interested. There are other issues with that air cavity and the resonance point of that stone wall, but that's another post​

and a floating floor inside the wall.

This is for comfort? Getting the carpet and pad off the concrete?​

I`ll have two airtight doors.

When these two doors are closed, are they side by side or is there an airlock created?​

 

[Space]

The issue with any speaker that can generate enough pressure to rattle plates is that it had to rattle the structure to rattle the plates

Ted will be the first to say that before a build starts you should add additional mass to any and all areas that are part of the exterior leaf if possible. The interior leaf will not be effective enough to completely isolate the heavy rumblings of a sub woofer if this attention is not granted.

Is that not a fair assessment Mr. White? Windows, doors, that overhead floor and possibly the chimney should have a good look into before, if this were me, the build actually began.


Just trying to help you have the best you can Lgl.

 

[paulspencer]

What a great reply. I agree with all these points. Maybe not so much the measuring part, I'll admit. But for sure very good point about the decoupled system absorbing low frequencies.

Thanks :bigsmile:
I'm a little surprised about the measuring part. If you're talking about measuring the ambient noise level, I don't see the point. If we are simply talking about sound proofing, then all it will do is show what you have achieved. I'd say that's worthwhile, mainly for the sake of curiosity. Especially when one wants to see what happens at 50 Hz! Probably a bit disturbing ...

The most benefit in measuring will come when the room is actually done, and it's time to work on the bass.

This is a simulation of a room that I used in the past:

The dotted line shows worst case scenario if it were built like a bomb shelter/garage. The magenta line shows a more typical room. This would be easy to eq mostly, except two deep nulls. The red line shows what we want to see - a room where the modes are sufficiently damped that we have a good chance of getting it right with eq.

Of course, you can't rely on simulations, but they are illustrative still.

These settings were used to show the eq required to get the bass flat:

Note the actual room response is the inverse. As you can see, it's pretty tame. This is a lossy room with timber floor and light timber framed drywall as well as double glass doors and reasonably large windows. No bricks or concrete.

The two charts above are for the same room. Keep in mind the eq/measured chart is more complex also as it has mains and subs overlapping, the mains able to get down to 23 Hz.

So if you get the room right first, this should be the first thing for the bass. Then I'd experiment with eq and placement. There's a good chance this will get a good result. Ideally if funds permit you'd do this in conjunction with a multi sub arrangement. Here is a measured example:

http://mehlau.net/audio/multisub_geddes/

Geddes suggests 3 subs are ideal. You can start with one sub which mostly meets your performance demands on its own. It's placement is less critical since it will most likely operate below problemmatic zones. The other subs will give some boost, but their main function is to improve the room response by "spatial averaging." They can in fact be compact, and this is a good place to diy since you can cleverly hide them if desired, and integrate them into the room creatively. You could have a stair riser sub, coffee table sub etc.

If after doing all this you are still having a case of audiophilia perfectionitis, then it's time to think about adding bass traps.

Do you like to use theater risers as bass traps? I'm not an in-room acoustics person but this topic comes up frequently.

The idea makes sense, but I haven't done it due to practical restraints. I also don't actually need add on bass traps. Chances are I will experiment with them to see if I can get an improvement. In that case I'd certainly measure before and after.

 

[Ted White]

Ted will be the first to say that before a build starts you should add additional mass to any and all areas that are part of the exterior leaf if possible. The interior leaf will not be effective enough to completely isolate the heavy rumblings of a sub woofer if this attention is not granted.

Is that not a fair assessment Mr. White?

That's fair, sure enough. Having said that, you could mass load the existing structure, decouple, mass load the second inner structure and still hear bass. It is not likely that the resonance point of the resulting new assembly will be lower than 30Hz. This means we won't have as much effect on frequencies below 45Hz.

That's what I was meaning several posts ago. You're still going to hear the low bass, since it just isn't practical to build partitions whose resonance point is extremely low. Too much air cavity depth and mass is needed.

 

[Bruce Fisher]

this is very educational! good stuff!

 

[lglura]

What can I say, I am very grateful for all the answers.:hail::hail::hail:
I am not a beginner, and certainly not an expert, so please contribute, even if it flies over my head.
I would agree, this is very educational.

 

[lglura]

When these two doors are closed, are they side by side or is there an airlock created?​

It will be an airlock between the doors, indipendent ceiling joist as in the article.
I plan to build a floating floor for insulation and decoupling.
I shall try to describe with a sketch before the nails and screws fly

 

[Ted White]

I would not take up valuable headroom for that floor.

 

[lglura]

I know it but I need to isolate, it is cold in Norway

 

[Ted White]

You're below ground? Or no? Cold in the states and canada as well but a few feet below ground it's all same temp all year. Small point, as many do this for thermal comfort nonetheless.

 

[lglura]

You're below ground? Or no? Cold in the states and canada as well but a few feet below ground it's all same temp all year. Small point, as many do this for thermal comfort nonetheless.

Have not thought of this, the floor in the room is two feet below ground.
Possible a thick carpet is solution,I get two inches extra ceiling and the height is 230 cm.

 

[Space]

That's what I was meaning several posts ago. You're still going to hear the low bass, since it just isn't practical to build partitions whose resonance point is extremely low. Too much air cavity depth and mass is needed.

I am a bit confused on what it is you are saying then.

I saw a guy(Lgl) that is doing a remodel on an existing ht...there is a reason people do this And at least part of that reason is house rattling not in the basement...in the upstairs area. But we did not know this for sure until the ground shaking subs were mentioned, after the measurement comments.

Your preaching to the choir. It is the easy answer to mention doing a room in room construction, it can be the most effective weapon against low frequency energy. But all parts of the build must be entertained as being interactive with this wall system or it is just another wall that isolates but does not address the specific issue/problem that seems to be the current concern.


In a nutshell, that is all I am saying

 

[Ted White]

Adding the mass as you pointed out is a good idea. I am saying that you cannot build a room in any basement that will completely stop low frequencies even after adding said mass.

 

[paulspencer]

From a thermal comfort point of view, a concrete floor on the ground is a good thing. It acts as thermal mass, and when the room is heated it stores the heat - a flywheel effect. Some houses are designed with this in mind to avoid or eliminate conventional heating. It also works in cooling. Radiant cooling is the most natural and pleasant kind - ever been down deep in caves on a stinking hot day? Feels better than an air conditioned room. Of course, in a cold room it will feel cold, but rugs where you put your feet will help.

Concrete is very reflective acoustically, and should have something to tame it since the ceiling will normally not have anything. There are two schools of thought on acoustic treatment in general:

1. The first is the only one that many seem to know. Use whatever speakers you like best without considering the room as a factor then make the room fairly dead. Use a lot of acoustic treatement, mostly to absorb, but also some diffusion, with specific focus on the reflections that will cause the most problems.

2. Choose speakers with a room interaction which is optimal in a normal room. Speakers like dipoles, omnis or with controlled directivity and a very well behaved polar response. In this arrangement, reflected sounds are desired and radiated in a controlled and planned way, rather than trying to just kill them. You might still use treatement with this approach, but it becomes less critical.

 

[paulspencer]

Quick thought about the shaking things upstairs - what happens if you lay the sub across a couch? This will mechanically de couple it - what kind of difference does it make?

 

[Space]

That is an area that may need some thought. I don't know if I would give up a whole couch to the sub even if the couch could do the job but it needs decoupling to reduce the structure borne vibration.

It may be as simple a thing as volume reduction.