# 49 db Sound insulation



## collegetechie (Sep 10, 2010)

Hello,
The college I work at have just finished renovating an old hall in to a workable professional theatre space... I stipulated that I needed the control booth to be sound proofed for obvious reasons the plans came back and said that the insulation will be to a minimum of 49db. Now the room is finished and I have been in I can clearly hear what is going on out side and if i am talking to just above normal speaking level people can hear me when I'm in the booth. should this be right or are there some things that are compromising the insulation. For instance they have put ceiling lights that are cut into the false ceiling and not covered. Also there is an extra fan which has been placed on the side of the booth near the front. My question is at 49db should I still be able to hear outside noise or are these extra factors compromising the insulation.
Thank you for reading this and answering if you can. I need to tell the contractors before they leave and sign the building off...
Cheers


----------



## MNicolai (Sep 10, 2010)

While I don't know much about insulation, I do know that 49dB is very quiet. On this comparison chart, 40dB falls between 30dB (quiet whispering in a library), and is still quite a bit lower than 60-70dB, which is the loudness of a typical conversation.

Sounds like instead of getting a sound-proofed room, you just got a spec'ed level to which the room _would_ be sound-proof. In other words, the contractor installed the same insulation they would've before you said anything to them, but when asked about sound-proofing, they just provided the level of sound-proofing that would be available from the product they had already intended to use. Unfortunately, that's not really a practical amount of sound-proofing for you.


----------



## collegetechie (Sep 10, 2010)

Thanks for your reply.

Would padding the inside with acoustic panels help? at the moment the sound inside the booth is bouncing all over the place off all the hard surfaces. Would reducing the ping (for want of a better word) ant putting in bass traps help?


----------



## MNicolai (Sep 10, 2010)

Depends on what your goal is. If you want the walls to be insulated so that no sound enters (and subsequently leaves) the control room, insulation is probably the ideal way to go. If you want to dampen the interior of the control room such that it makes noises in the room quieter and makes it sound less like a someone hollering in a cave, then acoustical treatments in the room are ideal. You may want to get a mix of these, but you might be well enough off to just dampen the room -- it's not like you plan on playing a drum kit in the control room and need that level of acoustical isolation from the audience.

Other users here at CB specialize in this area (I am not one of them), who will probably see this thread later today and be able to give you more specific advice.

I've heard acoustics referred to as "dark art," which isn't wrong. People who specialize in this area have millions of tricks up their sleeves and lots of personal experience with how to apply acoustical treatments to rooms and how different materials affect ambient and active noise. You may want to contact the acoustician or theatrical consultant on the project (presuming you had one) or find one local to you who can come in and look at the room.


----------



## museav (Sep 10, 2010)

If you plan on making an issue of not meeting the defined criteria it is probably important to make sure we understand the criteria defined. So maybe we can start by getting some terminology straight so we are sure of what we are addressing.

One aspect is whether the 49dB noted is the sound isolation to be provided by the intervening construction or if it is the noise level to be achieved in the booth. In other words, is the 49dB defining the attenuation to be provided between the booth and adjacent spaces or is it defining the resulting level in the booth from activities in adjacent spaces?

Another potential factor is what the actual number represents. Is it 49dBSPL (Sound Pressure Level)? If so, is there a weighting such as 49dBA? If related to sound isolation might it actually be defining an STC (Sound Transmission Class) or NIC (Noise Isolation Class) or similar value? And if related to background noise is it 49dB or maybe other common descriptors for ambient noise such as NC49 (Noise Criterion) or RC49 (Room Criterion). STC, NIC, NC and RC are all curve fitting based values that incorporate frequency based considerations. STC is also a laboratory test and values such as NIC or FSTC (Field Sound Transmission Class) are more common for evaluating actual results in the field.


In any case, it does sound like it is quite likely that there are some details limiting the sound isolation performance of the existing construction. The lights in the drop ceiling may not matter much if the walls themselves go up to the structure rather than stopping at the ceiling. On the other hand, a fan opening in a wall could be a significant issue.

Installing absorptive materials in the room will help, I typically do include acoustical treatment in booths, but in respect to sound isolation the improvement would likely be very limited. A $5 to $10 tube of acoustical sealant or acoustical caulk can often have much more impact on the sound isolation provided than thousands of dollars worth of acoustical panels being added in the room.

You mentioned that the project was renovating an old hall into a professional theatre space. You might want to ask if the acoustical consultant on the project could take a look at the situation. Hopefully they ca help you. If it turns out that there was no acoustical consultant involved then you may have a different set of issues to address with the Architect.


----------



## collegetechie (Sep 14, 2010)

in response to my questioning the integrity of the sound isolation in the booth the architect said:

_The booth is almost identical in construction to a booth installed in a
commercial theatre that we completed a while ago. We have received no
adverse comments regarding the acoustic performance of that booth.

At the time that we were working on the Commercial theatre we were told
that the construction should be appropriate for whispered conversation
between the theatre technicians.

The floor and 'roof' construction of the Reigate booth exceed the acoustic
performance of the booth installed at the commercial theatre.

The glazed window is identical to the commercial theatre booth.

The wall construction as shown on the drawing has theoretical dB rating of
56dBA._

I feel I have been duped by the achitect. at the planning stage I asked for a room the would retain the sound level of normal conversation. I should have done my own research on the sound level of 49db before the construction of the booth. Any-hoo lesson learnt I feel.

I'm now on to another battle of trying to get access for all my audio and visual cables into the booth. onwards and upwards!

Cheers for your detailed responses the information came in real use when arguing my point.

c


----------



## museav (Sep 14, 2010)

collegetechie said:


> in response to my questioning the integrity of the sound isolation in the booth the architect said:
> 
> _The booth is almost identical in construction to a booth installed in a __commercial theatre that we completed a while ago. We have received no_
> _adverse comments regarding the acoustic performance of that booth._


*Almost* identical. I get the feeling they are looking just at the basic wall construction and no one is even considering flanking paths, penetrations, construction details, etc. which may actually differ significantly. Just because the basic elements are the same does not mean the overall situation or application of those elements is the same, failure to recognize that may reflect very limited expertise and knowledge in acoustics.


collegetechie said:


> _At the time that we were working on the Commercial theatre we were told that the construction should be appropriate for whispered conversation between the theatre technicians_.


If that other theatre had said that they wanted a specific number of seats did the Architect then also assume that applied to your project? Their perspective might be more understandable if it was based on the sum of multiple past experiences but applying a specific design goal from one past project to another project without confirming the validity of it's applicability seems poor design practice.


collegetechie said:


> _The floor and 'roof' construction of the Reigate booth exceed the acoustic performance of the booth installed at the commercial theatre._


So they have actually field tested the sound isolation of both venues and shown you the comparison? Or is their opinion based on listening tests? Or is it simply based on what they put on their drawings?


collegetechie said:


> _The wall construction as shown on the drawing has theoretical dB rating of __56dBA_.


And theoretically they were going to be paid, perhaps the one 'theory' should be confirmed before the other is.


So apparently they have stated that their design assumed a 56dBA isolation. The fact that dBA is not usually relevant to sound isolation shows a lot but regardless of that, if they are saying that 56dBA of sound isolation was the design intent then that should be what you get. Maybe things are different there but here in the US the Architect's role is typically not just creating an appropriate design but also extends to verifying that the design intent they defined is maintained throughout the work provided and reflected in the final result. What an Architect or Consultant put on the drawings is of little meaning if what you actually got differs and I am used to part of the Architect's job being to verify that those are the same, or at least do not negatively impact the Owner. Maybe things are different there.


----------



## avare (Sep 14, 2010)

Brad gave great detailed for non acoustics professionals' response. From what I have read, flanking seems to be the culprit. Think of a tank of water. Three sides are solid glass. There is a hole in the fourth side. Despite how watertight the other three walls are, the water will get around the walls through the hole. My suspicion, and that is all it can be with the information given, is that there are holes, or weak spots in the construction. 

Have you visited the other facility? It may be something as obvious to the trained eye (ear?) as the doors not being identical, or yours not sealed.

Andre


----------



## collegetechie (Sep 17, 2010)

Hi guys.

I had the architect in yesterday to look at the sound isolation in the control booth... he told me that during the planning he consulted a few 'acoustic specialist books' (made me worried straight away) and came to the conclusion that 70dB sound isolation was almost impossible to achieve! I argued that between 50 - 70dB would be the volume of normal conversation to which he flustered and said he could only go on what information he had. I didn't continue with the argument, this is after all the same guy who thought a parquet floor would give students with bare feet splinters?!?

There is, as andre suggested, some flanking in the room which will be addressed with acoustic caulk and the doors do need acoustic seals on them so this will greatly improve the quality. I then recieved this email this morning


_"I have now spoken the an Acoustic Consultant we are using on another project and he thought (without me prompting) that the acoustic level that we have specified for the construction of the booth was more than appropriate.

He said that for the wall between cinemas ( which was the most extreme example that he could think of) you would aim at 75dB for the construction and said that for all practical purposes 100dB reduction is unachievable"_

So what about drum rooms in recording studios? 
Any way I have decided to drop this issue with them. We are not going to get the room re-built and I will see what happens when all the other flanking issues are sorted.

Cheers Guys
C


----------



## avare (Sep 17, 2010)

Welcome to the world of acoustics. You have my sympathies. 

One of the difficulties with sound isolation is that one number is rarely adequate to describe the performance of sound isolation. You mentioned drumes in studios. To give an idea of the sound isolation levels achieved in studios, and what the wall construction entails, have a look at BBC RD 1987-01. For starters look at figs 3, 4 and 5. You see the single number averages and the constructions involved. Figs 8 and 9 show high isolation, up to 100 dB, and the masive walls and support mechanisms involved.

Using STC numbers, 49 is quite achievable, and normal conversation on one side would be inaudible on the other side. This type of isolation is what is specified between party walls in condominiums. That is done all the time.

Putting perspective on what levels, a good modern recording studio will have background sound levels of around 30 dBA, and first class studios 20 dBA. With conversations at 70 dBA, you can see that an STC 55 (I think the design spec used) will reduce the speech to inaudibility, as it would be 5 points below the (impressively low) background level of 20 dBA.

If you want to try and do troubleshooting yourself, set up a radio ro other sound source at the talking position at the equivalent level, and go into the booth and listen to the various areas of teh walls, ceiling, vents etc to determine wher the main sound source is. 

Good luck!

Andre


----------



## collegetechie (Sep 17, 2010)

Yeah, who would choose to work in acoustics! 

Thanks for the article, I can see now how difficult it is to achieve certain levels of sound isolation. 
After testing the booth just now with a set of speakers and an ipod I can tell where the sound is escaping, most of it is coming from the air-vent in the side of the wall. I'm sure we will get to a point that is bare-able soon. Thanks again for both your help, i'll up date what we did and how effective it was later
Cheers
Chris


----------



## avare (Sep 17, 2010)

collegetechie said:


> Yeah, who would choose to work in acoustics!
> 
> Thanks for the article, I can see now how difficult it is to achieve certain levels of sound isolation.
> After testing the booth just now with a set of speakers and an ipod I can tell where the sound is escaping, most of it is coming from the air-vent in the side of the wall. I'm sure we will get to a point that is bare-able soon. Thanks again for both your help, i'll up date what we did and how effective it was later


 Congratulations on identifying the (at least main) source of the leaking sound. Please keep us posted on the progress, both to assist you in your correction, and to share with the people here your experience.

With all that you have gone through in this thread, I believe you have good idea of why acoustics is so non-intuitive. If you don't mind, next time you communicate with the architect, would you ask him if the air-vent is identical to the control he based your design on? If it wasn't, then his copy of the design was not a copy in significant areas. That is ignoring the isolation standard of "whispered converstions between theatre technicians."

Well isolated, well on the the other side of the pond,
Andre


----------

