Acoustic treatment alternatives

[Greg Cameron]

Hi guys. I posted this on the LAB too, but not much response over there that past day. I'm in a bit of a crunch, so I'm hitting up my comrades here:

I have been told by several people "in the know" that one of the best ways to go these days with acoustic treatment is eco insulation since it's sound absorption properties are outstanding and it's non-toxic to work with unlike fiberglass. Frame it up and use Guilford FR cloth for covering and you're good to go. At the venue I work in, we've done complete surface measurements and figured that the ballpark for raw materials is around the $16k range just for the insulation and Guilford. There are of course other costs for wood & labor, etc. I was wondering if there might be a lower cost alternative out there that might be effective as well for acoustic treatment. Any thoughts?

Thanks,
Greg

Response over there by Brad Webber:

" "Acoustic treatment" doesn't really define what you're trying to do or what the material needs to do and just randomly throwing materials up as "acoustical treatment" may affect the room acoustics but not necessarily in the most effective or desirable manner. Are there any specific acoustical properties that you are looking to obtain? Are you looking at absorption only or also at diffusion? If for absorption, are you just looking for 'soft stuff' or are you looking for something that offers specific absorption at certain frequencies? Are you looking for a certain thickness or density?"

My response:

- We're looking to deaden the room as much as possible, period. The idea was to apply damping materials to almost all surfaces except for the floor. The most problematic frequencies in the room are in the 400-500Hz range. But really it's necessary to squelch everything above that as well. So complete coverage of the ceiling & all walls was goal to really mitigate the RT60 across a broad spectrum and I was told the eco insulation was great for this. The floor will still be a reflective surface regardless, but it would be nice to have only the one bounce an then have all the other surfaces soak it up. The room isn't totally horrible and usually sounds decent if/when it's packed with warm bodies. But if it's a lightly attended show, the room does cause intelligibility issues with vocals. -

Thanks for any input,
Greg

 

[Greg Plouvier]

Re: Acoustic treatment alternatives

How big is your room? I am doing this treatment - still learning the method but in smaller rooms it's quite straight forward. This controls the 400-500 region( problems are almost always there) nicely without "deadening the room". Total cost of this treatment with volunteer supplied labor - $1600 for 300+ seat sanctuary.

 

[John Roberts]

Re: Acoustic treatment alternatives

Hi guys. I posted this on the LAB too, but not much response over there that past day. I'm in a bit of a crunch, so I'm hitting up my comrades here:

I have been told by several people "in the know" that one of the best ways to go these days with acoustic treatment is eco insulation since it's sound absorption properties are outstanding and it's non-toxic to work with unlike fiberglass. Frame it up and use Guilford FR cloth for covering and you're good to go. At the venue I work in, we've done complete surface measurements and figured that the ballpark for raw materials is around the $16k range just for the insulation and Guilford. There are of course other costs for wood & labor, etc. I was wondering if there might be a lower cost alternative out there that might be effective as well for acoustic treatment. Any thoughts?

Thanks,
Greg

Response over there by Brad Webber:

" "Acoustic treatment" doesn't really define what you're trying to do or what the material needs to do and just randomly throwing materials up as "acoustical treatment" may affect the room acoustics but not necessarily in the most effective or desirable manner. Are there any specific acoustical properties that you are looking to obtain? Are you looking at absorption only or also at diffusion? If for absorption, are you just looking for 'soft stuff' or are you looking for something that offers specific absorption at certain frequencies? Are you looking for a certain thickness or density?"

basically correct.

My response:

- We're looking to deaden the room as much as possible, period. The idea was to apply damping materials to almost all surfaces except for the floor. The most problematic frequencies in the room are in the 400-500Hz range. But really it's necessary to squelch everything above that as well. So complete coverage of the ceiling & all walls was goal to really mitigate the RT60 across a broad spectrum and I was told the eco insulation was great for this. The floor will still be a reflective surface regardless, but it would be nice to have only the one bounce an then have all the other surfaces soak it up. The room isn't totally horrible and usually sounds decent if/when it's packed with warm bodies. But if it's a lightly attended show, the room does cause intelligibility issues with vocals. -

Thanks for any input,
Greg

Do you have data on the eco insulation? Say compared to owens corning 703 rigid fiberglas? I ASSume this needs to be fireproof/fire resistant. If you're covering with cloth I guess it doesn't need to be cosmetic, but you probably don't want it to shed dust or make a mess.

If the ECO insulation is open cell with lots of surface area to capture sound. like proper acoustic treatment it could work, but insulation and sound treatment are not exactly apples and apples.

I don't know but might know someone who does. I just googled ECO insulation and it does not appear to be a single homogeneous product but a concept (recycled stuff). Cotten batting like from recycled denim (blue jeans) etc, could be pretty good, recycled plastic soda bottles I don't know.

Carpeting on the floor could help knock down room liveness too, but that may be beyond your budget.

JR

 

[Caleb Dueck]

Re: Acoustic treatment alternatives

I think Greg is talking about this (www.bondedlogic.com), which works well. In bulk it's under $1/sq ft for the 3.5" thick stuff. Spec-wise, similar to 4" OC 703.

I've used the smaller 'acoustic panels' made from this, and was happy with it. It's soft cotton, so will need something to hold it in place, like the cloth covering mentioned.

 

[Brad Weber]

Re: Acoustic treatment alternatives

How big is your room? I am doing this treatment - still learning the method but in smaller rooms it's quite straight forward. This controls the 400-500 region( problems are almost always there) nicely without "deadening the room". Total cost of this treatment with volunteer supplied labor - $1600 for 300+ seat sanctuary.

Greg, that looks like the Sonotube approach to diffusion, and in some cases bass traps, that some people promote. The biggest concern I have is that I have yet to see information showing that Sonotube (or whatever material they use) is appropriate for such use in public assembly spaces in terms of the Flame Spread and Smoke Developed ratings. Some people recommend simply covering the Sonotube with a fire rated material but the 'tubes' would seem to need to be closed at both ends and have all exposed surfaces covered with a properly rated finish.


As JR noted, there seem to be many materials that could fit the description "eco insulation" and not only board type materials as those Caleb linked or batt insulation such as http://www.ecobatt.us/ but also spray-on foams, injected foams, blown-in cellulose and so on.

At least in my experience, the fabric is often a greater portion of the cost than the core material. There are probably numerous less expensive options than Guilford of Maine FR701 for the fabric, although for many you may be guessing as to the effectiveness in an acoustical panel application unless you can get samples to assess. And make sure that whatever you use has the appropriate Flame Spread and Smoke Developed ratings for the space.

I understand just wanting to 'deaden down' the space but being significantly more 'dead' at some frequencies than others can have its own issues. If you look at the absorption data presented in http://www.bondedlogic.com/construction-products/acoustical-panels, you see that with the 1" panels you might get a lot of absorption at 1kHz and even 500Hz, but much less at lower frequencies which can lead to the room being 'boomy'. Also keep in mind that you can often get diminishing returns. Say you have some absorption in a room and add additional absorption to get twice the amount total absorption. To get that same change again requires going from twice the original value to four times that original absorption, which requires adding much more absorptive material than for the first step. When you combine these, unless there is some other factors to be considered then it is often more cost effective to treat the surface areas that will provide the most effectiveness first and see where that puts you rather than covering everything from the start.

By the way, ignore the absorption coefficients that are greater than 1.0 in the insulation product data as that is an anomaly of the testing method and how the samples are prepared and arranged. A 2" thick, 2' x 2' panel has an edge area of 1.33 square feet, so whether that edge is exposed, butted up against another panel, surrounded by a wood or metal frame, etc. can make a difference in the amount of total material exposed to the room for the same face area. Smaller, spaced samples versus one, large contiguous sample and other factors can also affect the results of lab absorption coefficient tests with the result that you can get values greater than 1 when that is not really physically possible. Of course, few real world rooms have true reverberant fields anyways so how well the absorption coefficient test values relate to real world performance is also imperfect, especially as the direction from a sound source approach grazing angles to the absorption material face.

 

[Greg Cameron]

Re: Acoustic treatment alternatives

Hi Greg. The surface area in need of coverage is 7000+ sf. if we cover the majority of wall and ceiling surfaces. It's an open gable style roof/ceiling system with wood truss. The room size is a about 45' wide and 65' deep plus an upper rear loft section that adds ~ another 14' of depth once the pipe organ and small office are ripped out (anyone want an historic pipe organ in need of TLC?).

Floor to truss hight is ~20'. So far the UltraTouch denim material with the Guiliford cloth works out to about $2.20 per sf. Not bad based on what I've seen for the Dow Corning sound stuff. Of course, it's still too much for the current funding, hence the shout out for possible alternatives.

Greg

 

[Greg Cameron]

Re: Acoustic treatment alternatives

Yes, that's the stuff. Sorry for lack of specificity. So far it seems like the best deal going and the absorption coefficients looks pretty good:

http://www.acousticalsurfaces.com/wall_insulation/ultratouch.htm

The concept was to build wood framing for the walls to so the Guiliford FR cloth would have nice lines after covering the insulation. The ceiling doesn't need to look as pretty but, it needs to be safely suspended & covered with black cloth. A potential cost savings might be to use Guiliford only for the walls and something less costly & black for the ceiling that still has an adequate fire rating. Any thoughts on that? And would tacking the stuff directly to the ceiling have a substantial effect on the absorption coefficients? I would thing that compressing it that would would reduce effectiveness.

Greg

 

[Greg Cameron]

Re: Acoustic treatment alternatives

I understand just wanting to 'deaden down' the space but being significantly more 'dead' at some frequencies than others can have its own issues. If you look at the absorption data presented in http://www.bondedlogic.com/construction-products/acoustical-panels, you see that with the 1" panels you might get a lot of absorption at 1kHz and even 500Hz, but much less at lower frequencies which can lead to the room being 'boomy'. Also keep in mind that you can often get diminishing returns. Say you have some absorption in a room and add additional absorption to get twice the amount total absorption. To get that same change again requires going from twice the original value to four times that original absorption, which requires adding much more absorptive material than for the first step. When you combine these, unless there is some other factors to be considered then it is often more cost effective to treat the surface areas that will provide the most effectiveness first and see where that puts you rather than covering everything from the start.

We'd be going for the thick UltraTouch stuff which appear to work down pretty low. I hear where you're coming from with potential 'boomyness,' but that's one area where the room doesn't appear to have issue. The neighbors might feel otherwise We figured with the thick stuff and going for a shotgun approach to the majority of surfaces that we could mitigate the issues once and for all without having to revisit and redo as you indicated. Of course, we may wind up having to take a piecemeal approach if we can't get the money together to do it all at once. And then it becomes a guessing game as to which surfaces to treat first to get the most benefit- something we wanted to avoid.

By the way, ignore the absorption coefficients that are greater than 1.0 in the insulation product data as that is an anomaly of the testing method and how the samples are prepared and arranged. A 2" thick, 2' x 2' panel has an edge area of 1.33 square feet, so whether that edge is exposed, butted up against another panel, surrounded by a wood or metal frame, etc. can make a difference in the amount of total material exposed to the room for the same face area. Smaller, spaced samples versus one, large contiguous sample and other factors can also affect the results of lab absorption coefficient tests with the result that you can get values greater than 1 when that is not really physically possible. Of course, few real world rooms have true reverberant fields anyways so how well the absorption coefficient test values relate to real world performance is also imperfect, especially as the direction from a sound source approach grazing angles to the absorption material face.

Thanks for the info Brad, much appreciated.


Greg

 

[Greg Cameron]

Re: Acoustic treatment alternatives

Here's a photo of the hall from the back when the new stage was being built last year for reference.

Greg

 

[Greg Plouvier]

Re: Acoustic treatment alternatives

Greg, that looks like the Sonotube approach to diffusion, and in some cases bass traps, that some people promote. The biggest concern I have is that I have yet to see information showing that Sonotube (or whatever material they use) is appropriate for such use in public assembly spaces in terms of the Flame Spread and Smoke Developed ratings. Some people recommend simply covering the Sonotube with a fire rated material but the 'tubes' would seem to need to be closed at both ends and have all exposed surfaces covered with a properly rated finish.

Brad - thanks for drawing attention to that. The tubes are coated with latex paint that contains fire resistant additive on both sides and edges. Do I have a flame spread number? - no. This method has been used in very large facilities all over the US and Canada including new builds so there is acceptance by building code officials. The problems with the absorptive materials are, as you pointed out, that to gain an acceptable amount of absorption at frequencies below 500Hz(where the problems inevitably lie) the panels would need to be ridiculously thick. Also those types of panels don't stop bounce very well - like the bounce off the back wall that comes back to the stage. I've seen facilities spend $20K to "fix" that kind of problem only to see it slightly reduced and the room become lifeless. I'm not claiming expertise in this area as I am still learning and the safety of souls in buildings is certainly important. I do think the tube solution is a cost effective and acoustically effective solution. They sometimes need to be combined with a little absorption and bass traps - usually in larger rooms.
Greg - where are you located?

 

[Greg Cameron]

Re: Acoustic treatment alternatives

Greg - where are you located?

Nevada City, CA. The venue is the Miners Foundry: http://test.minersfoundry.org

Greg

 

[Tim Padrick]

Re: Acoustic treatment alternatives

It's my understanding that a device made from A rated components is not necessarily A rated, or rated at all. Look into these: http://www.primacoustic.com/index-panels.htm

 

[Greg Cameron]

Re: Acoustic treatment alternatives

It's my understanding that a device made from A rated components is not necessarily A rated, or rated at all. Look into these: http://www.primacoustic.com/index-panels.htm

Hmm. Even their least expensive product, the Primafoam is 3x the price per sf. of the method we were looking at. I hear what you're saying about fire rating, but I don't think we're inserting anything into the mix here that would degrade the insulation and Guiliford cloth unless I'm missing something.

 

[Arthur Skudra]

Re: Acoustic treatment alternatives

Without much further acoustical measurement information or the luxury of modeling this room in EASE, I'd say slapping fibrous absorbers like the ones mentioned above may create an acoustical imbalance in the room where the high frequencies are attenuated too much in the quest to control the more difficult lower frequencies. The approach I would take is finding treatment that is particularly effective at the problem frequencies. In this case, if you're looking to tackle a 400-500 Hz problem, I would be inclined to use a 6 lb fiberglass panel encapsulated with perforated vinyl like those made by MBI products, that way you're not killing the high frequencies while trying to tame the lower ones. Space them off the wall or ceiling about 3-4 inches to improve their efficiency at 400-500 Hz.

 

[Greg Cameron]

Re: Acoustic treatment alternatives

Without much further acoustical measurement information or the luxury of modeling this room in EASE, I'd say slapping fibrous absorbers like the ones mentioned above may create an acoustical imbalance in the room where the high frequencies are attenuated too much in the quest to control the more difficult lower frequencies.

If I have full coverage of the venue with the high frequency horns on my boxes so that direct sound is reaching the entire audience, how would having HF bouncing around be beneficial? I've always been under the impression that the less reflection, the better. When running PA outdoors on an open field, It always seems beneficial to not have high frequency reflection. Is that not ideal? Or should I be concerned that the low end will truly "outrun" the high end? For reference, the room won't be totally dead. The floor will still be a hard smooth surface. There will also be windows about 12 feet above the floor on one wall. Some of the back loft wall area will also be left uncovered since it's a mortar and stone wall which is not parallel to the stage. Other than the 400-500Hz range, standing waves have not been an issue below that range.

Thanks for the insight,
Greg

 

[Rob Timmerman]

Re: Acoustic treatment alternatives

If I have full coverage of the venue with the high frequency horns on my boxes so that direct sound is reaching the entire audience, how would having HF bouncing around be beneficial? I've always been under the impression that the less reflection, the better. When running PA outdoors on an open field, It always seems beneficial to not have high frequency reflection. Is that not ideal? Or should I be concerned that the low end will truly "outrun" the high end? For reference, the room won't be totally dead. The floor will still be a hard smooth surface. There will also be windows about 12 feet above the floor on one wall. Some of the back loft wall area will also be left uncovered since it's a mortar and stone wall which is not parallel to the stage. Other than the 400-500Hz range, standing waves have not been an issue below that range.

Thanks for the insight,
Greg

Too much absorbtion will change the feel of the room, possibly dramatically, and doesn't really help matters. And the contributions from the floor may not help as much as you think - if that's the only reflective surface, you're basically standing in a large paved parking lot.

You've got a relatively small room, and I'm having a hard time believing it really needs 7k sq ft of absorbtion to sound decent. Have you considered hiring an acoustical consultant? They may be able to save you much more than their fee in material savings.

 

[Arthur Skudra]

Re: Acoustic treatment alternatives

If I have full coverage of the venue with the high frequency horns on my boxes so that direct sound is reaching the entire audience, how would having HF bouncing around be beneficial? I've always been under the impression that the less reflection, the better. When running PA outdoors on an open field, It always seems beneficial to not have high frequency reflection. Is that not ideal? Or should I be concerned that the low end will truly "outrun" the high end? For reference, the room won't be totally dead. The floor will still be a hard smooth surface. There will also be windows about 12 feet above the floor on one wall. Some of the back loft wall area will also be left uncovered since it's a mortar and stone wall which is not parallel to the stage. Other than the 400-500Hz range, standing waves have not been an issue below that range.

Thanks for the insight,
Greg

IMHO, making a room extremely dead makes it an unpleasant experience for the musicians as well as the audience, for musicians it becomes difficult to hear each other, for the audience, cheering and any other participation in the event becomes hindered. Constructive early reflections are good, it's the late echos that need to be controlled and managed, and any resonances in the room "balanced out" with the appropriate treatment. When outside, people have the unconscious expectation that there are no nearby reflective surfaces. Place them in a room and the expectation will be there that there should be some reflective energy. Don't mess with people's minds!! It's sound *reinforcement* that you should doing here, not sound replacement!

 

[Greg Cameron]

Re: Acoustic treatment alternatives

You've made some really good points which I'm taking under advisement. I know quite a bit about sound reinforcement but admittedly I'm not an expert in acoustic treatment. It never occurred to me that the room could be made "overly dead." The point about potential cost savings hiring a consultant and not treating most of the surfaces is an excellent one. So that leads to my next couple of questions: what should one expect to pay for initial consulting and, anyone have a lead on a reliable consultant in the Sacramento or Reno/Lake Tahoe area (we're in between).

I will say we have a competing venue in town that has done extensive sound treatment by completely batting the ceilings a well as a bunch of panels. It is for all intensive purposes a "dead" room. And though they don't have the best or most powerful PA in there, the room sounds great for rock shows and theater arts. That said, it's a much different shaped room which of course may have required extensive treatment.

Greg

 

[Tim Padrick]

Re: Acoustic treatment alternatives

Hmm. Even their least expensive product, the Primafoam is 3x the price per sf. of the method we were looking at. I hear what you're saying about fire rating, but I don't think we're inserting anything into the mix here that would degrade the insulation and Guiliford cloth unless I'm missing something.

My concern is not a change in the flame spread or gas/smoke release, but merely having rating documentation to show to your insurance carrier and the authorities.

 

[Brad Weber]

Re: Acoustic treatment alternatives

It never occurred to me that the room could be made "overly dead."

http://www.churchproduction.com/go.php/news/15929#

There was also a church here that added a lot of very thick absorption to address some acoustical problems. Talking to the people involved, that led to several discoveries including that even thick absorption has a practical low frequency cutoff and that too much mid band absorption can make a room aurally uncomfortable. So after spending big bucks on the acoustical treatment they ended up having to spend even bigger dollars for an electronic acoustic enhancement systems.

In both of these cases, an overly 'dead' room led to quite large expenditures. Not necessarily relevant in your case but this is why it is so important to get someone to look at acoustics early in a facility design as trying to address acoustics as an integral part of the room design is often much more cost effective than trying to address them after the room is already designed.

The point about potential cost savings hiring a consultant and not treating most of the surfaces is an excellent one. So that leads to my next couple of questions: what should one expect to pay for initial consulting and, anyone have a lead on a reliable consultant in the Sacramento or Reno/Lake Tahoe area (we're in between).

Cost depends greatly on how detailed their analysis and recommendations get, how challenging the space is and whether they perform site measurements before and possibly after the treatments are installed. I will say that most consultants are likely to be somewhat wary of DIY treatments as there is no laboratory derived acoustical performance for the overall assembly. They may be able to calculate or estimate the performance and the results may be very close, but there is always the spectre that you are then calculating something based on another calculation or estimate that you hope is accurate. An example of the risk is basing an analysis on panels made of fiberglass board with no backing that are then furred off the wall to benefit on low frequency absorption only to have the person constructing the panels make them with a solid plywood back.

There are a good number of qualified firms in California, but I don't know that area that well so I'm not sure which may be close to you.

I will say we have a competing venue in town that has done extensive sound treatment by completely batting the ceilings a well as a bunch of panels. It is for all intensive purposes a "dead" room. And though they don't have the best or most powerful PA in there, the room sounds great for rock shows and theater arts. That said, it's a much different shaped room which of course may have required extensive treatment.

The room shape. volume, etc. were likely factors but so is the use. An acoustically 'dead' room may be acceptable or even desirable for rock shows and many theatrical productions but not for symphonic, orchestral or choral music or for audience/congregational response and interaction or for organ music. The challenge with many space, including many churches, is that they are not necessarily dedicated purpose in this regards, they often have to support a range of uses and musical styles thus they need to achieve an appropriate balance or flexibility for the acoustical environment.