Stage Curtains Draped Along Wall

[Esoteric]

If there is one thing I have learned in my years it is that I still have a lot to learn.

Mike

[pdc]

Originally Posted by cw4u

Well, we're trying to reduce the "echo" in the room. It's not so bad during musical performances, but for speech, it's pretty noticeable. That is our biggest concern. I was hoping by adding a thick, soft surface in front of the drywall would help to eliminate some of that.

Btw, the curtains are just coming down because the school is buying new ones. However, one school is shutting down for good and is just being used for district storage.

Thanks.

There are a couple of terms being used and they are two different things. Soundproofing is keeping noise from coming in or going out. Acoustic treatment is compensating for the acoustics inside of a space. You can have an acoustically neutral space with tons of leakage, a terrible sounding space with no leakage, etc.

Heavy sound curtains are built for sound. If you do a seach for an STC chart of building marerials, you will find standard lite draperies and carpets are only are absorptive in very, very narrow bands of high frequencies. You need to know how frequencies are delayed and where, then you can realize what your treatment options are.

When you have two parallel hard surfaces, you will have flutter echo between them. You can knock this down by splaying the walls in 1' per 10' of length (roughly). If you cannot do that, you will need use diffusion materials to diffuse the waves. If you want to deaden it, and can do so without creating other freqency response issues for your room, you can use broadband absorption. The types of diffusors are very important. Some diffusors will not work in small quantities, must be grouped together and will not yield any benefits if closer than 12' to the adjacent wall. So, the form must match the function.

If you go to studiotips.com you will find some calculators for determining your rooms RT60 time, which is based on your room's dimemensions, boundary materials, etc. So a 14' x 24' x 10' room made of concrete and glass will have a different RT than one of gyp board and wood.

One of the calculators will tell you the room modes. These are standing waves. If you trap for the wrong frequencies, you could make your room completely unusable. Too much high frequency trapping will just darken and muddy up your room.

[Brad Weber]

Originally Posted by pdc

There are a couple of terms being used and they are two different things. Soundproofing is keeping noise from coming in or going out. Acoustic treatment is compensating for the acoustics inside of a space. You can have an acoustically neutral space with tons of leakage, a terrible sounding space with no leakage, etc.

This is a gross generalization, but salespeople and Architects often talk about "soundproofing", STC and NRC while acousticians instead speak in terms of sound isolation, transmission loss, sound absorption coefficients and so on. "Acoustic treatment" can be addressing any of a wide number of areas, adding lined ductwork to reduce HVAC noise would be an acoustic treatment, so would building a barrier wall around an outdoor noise source. Room acoustics is probably a better terminology for reverberation, echoes, etc. within a space. And Architectural Acoustics could accommodate room acoustics, interior and sound isolation, HVAC noise and vibration isolation and any other acoustical aspect relevant to a building.

Originally Posted by pdc

Heavy sound curtains are built for sound. If you do a seach for an STC chart of building marerials, you will find standard lite draperies and carpets are only are absorptive in very, very narrow bands of high frequencies. You need to know how frequencies are delayed and where, then you can realize what your treatment options are.

STC is Sound Transmission Class, a single number rating for sound isolation based on a standard curve fitting predicated on isolating speech frequencies and it has nothing to do with absorption. And when looking at absorption coefficients for materials, one has to consider the test conditions such as the the mounting of the material and for draperies, the fullness. Such factors can significantly affect the acoustical performance of many materials.

Originally Posted by pdc

If you go to studiotips.com you will find some calculators for determining your rooms RT60 time, which is based on your room's dimemensions, boundary materials, etc. So a 14' x 24' x 10' room made of concrete and glass will have a different RT than one of gyp board and wood

One of the calculators will tell you the room modes. These are standing waves. If you trap for the wrong frequencies, you could make your room completely unusable. Too much high frequency trapping will just darken and muddy up your room.

First, there are differences between small and large room acoustics, something that based on what I see in many forums that even some 'experts' don't seem to recognize. One of these is that small rooms tend to be modally controlled while larger rooms are more reverberant controlled. In small rooms, it is difficult to achieve a diffuse, reverberant field at all locations, in fact you probably don't want that in a studio, while in large spaces the room dimensions often drive the room modes down to much lower frequencies.

In addition, most of the free and online Reverberation Time calculators are simple Sabine formula calculators. The Sabine Formula assumes certain conditions such as a diffuse sound field and even distribution of absorption that are not valid in many worship spaces. The further a space varies from those assumptions (e.g. a rather dead space or one with the absorption primarily in one or two areas), the more inaccurate the results.

[cmchamp]

An additional comment on room modes in larger spaces. . . many "acousticians" don't comprehend the depth and dynamics of contemporary worship music and resulting spaces are uncomfortable and lack any attention to the LF frequencies and modes. Yes, larger spaces (dimensions and cubic feet) have lower modes, but they still can have modes, especially if they are basically a box.

[Brad Weber]

Originally Posted by cmchamp

An additional comment on room modes in larger spaces. . . many "acousticians" don't comprehend the depth and dynamics of contemporary worship music and resulting spaces are uncomfortable and lack any attention to the LF frequencies and modes. Yes, larger spaces (dimensions and cubic feet) have lower modes, but they still can have modes, especially if they are basically a box.

Very true, I certainly did not mean to imply that room modes were irrelevant in large room acoustics, I was only pointing out that while there are many similarities there can also be significant differences between small and large room acoustics. Acoustical recommendations and suggestions for small home studios abound on the Internet but those do not always apply or translate well to larger public spaces.

[kfhoech]

Adding to my note of thanks to Esoteric for pointing out learning opens the mind to new questions, would anyone care to point out some good references for the beginner in learning the science of acoustics? I know I'm interested.

Thanks.

[cmchamp]

F. Alton Everest's Master Handbook of Acoustics. McGraw-Hill publishing, I believe. I have the 4th edition. Should be available from any larger public library or through their inter-library loan program.

[pdc]

Originally Posted by Brad Weber

This is a gross generalization, but salespeople and Architects often talk about "soundproofing", STC and NRC while acousticians instead speak in terms of sound isolation, transmission loss, sound absorption coefficients and so on. "Acoustic treatment" can be addressing any of a wide number of areas, adding lined ductwork to reduce HVAC noise would be an acoustic treatment, so would building a barrier wall around an outdoor noise source. Room acoustics is probably a better terminology for reverberation, echoes, etc. within a space. And Architectural Acoustics could accommodate room acoustics, interior and sound isolation, HVAC noise and vibration isolation and any other acoustical aspect relevant to a building.


STC is Sound Transmission Class, a single number rating for sound isolation based on a standard curve fitting predicated on isolating speech frequencies and it has nothing to do with absorption. And when looking at absorption coefficients for materials, one has to consider the test conditions such as the the mounting of the material and for draperies, the fullness. Such factors can significantly affect the acoustical performance of many materials.


First, there are differences between small and large room acoustics, something that based on what I see in many forums that even some 'experts' don't seem to recognize. One of these is that small rooms tend to be modally controlled while larger rooms are more reverberant controlled. In small rooms, it is difficult to achieve a diffuse, reverberant field at all locations, in fact you probably don't want that in a studio, while in large spaces the room dimensions often drive the room modes down to much lower frequencies.

In addition, most of the free and online Reverberation Time calculators are simple Sabine formula calculators. The Sabine Formula assumes certain conditions such as a diffuse sound field and even distribution of absorption that are not valid in many worship spaces. The further a space varies from those assumptions (e.g. a rather dead space or one with the absorption primarily in one or two areas), the more inaccurate the results.

We can split hairs on the terms all day. But if you call an acoustical engineer and tell them that you want to sound proof a room, they will ask questions for clarification. As for architects, my father is an architect and I trained for that field. We all know that most architects have no idea about acoustics and the proper terminology. We fix what architects do to church and performance spaces all the time. So I do not care what they call things. CMChamp even got the spirit of the message.

As for the STC...just use some simple logic. What I said is still true. For something to have an STC rating above infinity, it must have .some form of absorption or reflective properties. Since there is no publishedtesting data (and we all know that acoustic testing is standardized and unbiased...not) STC was the only thing that I could point to.

As for the large room comments, that's true. Time and energy are more of an issue than frequency in most cases. The low end is less of an issue. However, the OP did not specify a large room, unless I missed something.

[cmchamp]

khfoech and others wanting to have access to some acoustical science material without trying to find a book, Dr. Dan Russell, at Kettering University in Flint, MI has this wonderful page with simple animations, explanations, calculations, etc. I use it in my classroom and workshops.

http://paws.kettering.edu/~drussell/demos.html

C.

[Brad Weber]

Originally Posted by pdc

We can split hairs on the terms all day. But if you call an acoustical engineer and tell them that you want to sound proof a room, they will ask questions for clarification. As for architects, my father is an architect and I trained for that field. We all know that most architects have no idea about acoustics and the proper terminology. We fix what architects do to church and performance spaces all the time. So I do not care what they call things.

The use of correct terminology is a basic skill in any profession and incorrect terminology is a common cause of misunderstandings. The proper or improper use of terminology can be an indication of one's professionalism and relevant knowledge and skill. I wasn't trying to 'split hairs' but rather to take advantage of the opportunity to potentially help educate people rather than allowing misunderstandings or misconceptions to perpetuate.

Originally Posted by pdc

As for the STC...just use some simple logic. What I said is still true. For something to have an STC rating above infinity, it must have .some form of absorption or reflective properties. Since there is no published testing data (and we all know that acoustic testing is standardized and unbiased...not) STC was the only thing that I could point to.

STC values address sound transmission rather than absorption and there is no direct correlation between the two, in fact STC values are typically applied to a construction rather than to a single material. An STC rating above infinity is impossible, I think you actually mean above zero. And while there are definitely issues with some of the standard methods and not everyone tests to the standards or publishes the results appropriately, there is a huge amount of published sound isolation and absorption data that is provided by independent, certified testing labs in accordance with numerous relevant standards. Testing in acoustics is much more standardized than it is in audio, however the standards are not always applied and that is something that both practitioners and consumers should recognize.

Originally Posted by pdc

However, the OP did not specify a large room, unless I missed something.

They also did not say it was a small room, which is why I was identifying that the two are different.

[EmilBarnabas]

Rather than messing with dying a flame-proofed curtain, why not just get some cheap black fabric to hang in front of the curtains?