The "Room Acoustics" thread

[santhosh]

We are seeing that more and more members are considering a dedicated room for A/V or even make some acoustic tweaks to their drawing room. So thought we can have a dedicated thread for this. If you have a question on Room Acoustics, post them here and members knowledgable in this will try and answer your queries. We even have a Sound Engineer on our forum, am sure he'll be happy to add his inputs here.

We have a lot of knowledge and discussion on the topic that are spread across so many threads. Would be good to have a single consolidated thread for questions in addition to all the interesting threads where members have documented their Home Theater build.

 

[PAVAN KADAM]

Good thread,

Now please explain me the difference in the feel of a 5:1 set-up and a 7:1 setup.:sad:

I am a novice into this part of the world. will it be expensive to have a 7:1 set-up compared to the latter.:sad:

 

[jitubisht]

Mods - is it possible to make this thread sticky?

 

[cmsajith]

@All Members, I request you not to dilute this thread with other questions which are not related to acoustics. Please stick to the purpose of this thread.

 

[S_Sridar]

Great, this is indeed a very good idea !!!!

The cross-flow of information would essentially be useful to all.

 

[sidvee]

My first contribution to this thread - unfortunately in the form of a question.
What are the methods of preventing sound leakage from doors and windows of HT or media rooms? I have seen rubber seals (similar to ones used on car doors) that can be placed at the gaps of door and window sills in the US in places like home depot etc, but am not able find them here. Note these are for HT's that used carpenter fabricated doors and windows as opposed the better method of using pre fab doors or windows (like fennesta).
Cheers,
Sid

 

[cmsajith]

Simple option would be to use 2 doors (One door towards inside HT room and another towards outside with a gap of 1ft) and frames on all 4 sides and deep/bigger lips with rubber gasket facing the door panel. The rubber gasket can be on both the surfaces to make it more air tight. The door face towards the gap can have absorbers to make it more effective.

 

[sidvee]

Simple option would be to use 2 doors (One door towards inside HT room and another towards outside with a gap of 1ft) and frames on all 4 sides and deep/bigger lips with rubber gasket facing the door panel. The door face towards the gap can have absorbers to make it more effective.

Any idea where these rubber gaskets could be sourced? Also this a good option for doors but what about windows, I know that a windowless room is best, but for ventilation purpose I prefer to have at-least 1 window.
Cheers
Sid

 

[S_Sridar]

The door-gaskets that would have to used are either the cam-profile gaskets, or larger sized Vee gaskets.

camprofiles are easily available.

Or one can get a rubber moulder to make these. The moulds are not very expensive, and the rubber could be extruded in the profile that you want.

 

[cmsajith]

Rubber gaskets can be found in any hardware shops.

The same way we can do for a window also. If you are using wooden windows which are having shutters opening outside, the same method can be used.
If you are having alum windows, make a similar frame around the window opening inside the room and make wooden shutters with frames having bigger lips.

 

[S_Sridar]

The double door solution is a little tricky.
It looks simple and obvious, but in implementation it is very tricky.

You may actually end up increasing the undesired noise transmission.
You would really have to do a lot of experimentation till you get the appropriate noise reduction effect.

 

[cmsajith]

The door-gaskets that would have to used are either the cam-profile gaskets, or larger sized Vee gaskets.

camprofiles are easily available.

Or one can get a rubber moulder to make these. The moulds are not very expensive, and the rubber could be extruded in the profile that you want.

Yes, corrugated surface with ~90degree angle for more effectiveness. Make sure to position the gaskets so that the corrugated portion of one surface gets into other to get a tight seal.

 

[cmsajith]

The double door solution is a little tricky.
It looks simple and obvious, but in implementation it is very tricky.

You may actually end up increasing the undesired noise transmission.
You would really have to do a lot of experimentation till you get the appropriate noise reduction effect.

Unless we have a ready made option available, there is no way other than trial and error. In most cases, this will solve the issue to a great extend. Also dont use wood for making the shutter as it can warp over a period of time.

Is there any ready made option available in India?

 

[S_Sridar]

Refrigerator door gaskets also are a good choice. These have the correct rubber hardness
( or softness ), and they seal air-tight ( also noise-tight ).

And they are known to last very long.

 

[sidvee]

One option for people considering new theater rooms is to use pre-fabricated widows and doors. I am not sure of doors but for windows there are manufacturers like Fennesta (not too sure of spelling), and their use of double glazed glass will contribute to significant (I have heard as much as 40db) reduction in both sound transmission into and outside the theaters through the glass, not to mention the saving in cooling due to the insulative properties of the glass. As for the door itself what do recording studios or radio stations use? I would imagine those doors would be sound proof. Also important is how well the door or window is installed into the opening and then sealed with a proper caulk.
Cheers
Sid

 

[S_Sridar]

The space between the two doors acts as the ideal space for a standing wave.
One has to put in wave breakers.
the ceiling of the space between the two doors should be provided with angular vees to kill the standing wave
the ceiling should be provide with sound absorbers.
the floor should be carpeted.
the distance between the two doors should be adjusted by trial and error.

 

[cmsajith]

One option for people considering new theater rooms is to use pre-fabricated widows and doors. I am not sure of doors but for windows there are manufacturers like Fennesta (not too sure of spelling), and their use of double glazed glass will contribute to significant (I have heard as much as 40db) reduction in both sound transmission into and outside the theaters through the glass, not to mention the saving in cooling due to the insulative properties of the glass. As for the door itself what do recording studios or radio stations use? I would imagine those doors would be sound proof. Also important is how well the door or window is installed into the opening and then sealed with a proper caulk.
Cheers
Sid

I dont think finesta doors can give a good result in an HT room. Moreover what will you do with the inner surface of the door, it will be totally a reflecting surface.

 

[sidvee]

I am not too sure I agree if all surfaces in a HT room have to be absorbent and or diffusive IMO. There has to be some reflection especially for rear surround speakers to create an effect of spaciousness. This is different for large commercial theaters but a HT needs a mix of absorption and reflection. A totally absorptive room will also need large amount of amplifier power which can get very expensive when you consider 7.1 or even 9.1.
Cheers
Sid

 

[cmsajith]

I am not too sure I agree if all surfaces in a HT room have to be absorbent and or diffusive IMO. There has to be some reflection especially for rear surround speakers to create an effect of spaciousness. This is different for large commercial theaters but a HT needs a mix of absorption and reflection. A totally absorptive room will also need large amount of amplifier power which can get very expensive when you consider 7.1 or even 9.1.
Cheers
Sid

It depends on the location of the reflective window \ surface.

 

[sidvee]

It depends on the location of the reflective window \ surface.

Yes I agree - it will be better to position it to the rear of the room, possibly behind the sitting position. One also has to consider blackout curtains - which are easily available fortunately in the fabric stores.
Cheers
Sid