Control Room For an Auditorium

Hello, I am analyzing a multipurpose church auditorium for acoustics and researching before making recommendations. I have used a program called CARACAD to come up with a treatment to recommend for the auditorium itself. The problems to be overcome are: - Bad echo off the back wall - Excessive reverb in the room - Bass-buildup along rear wall - Excessive stage wash - Excessive unbalanced natural room EQ What is driving this initiative is that a section is being removed from the existing auditorium to create a warehouse for a foodbank for the needy. This poses a double-edge sword. On one hand the auditorium becomes nearly a square which is bad. On the other hand, the new wall will be behind the new stage, so being constructed of good acoustical materials, it becomes a major component to the solution. Being an effective absorber, it will improve the stage wash significantly by not reflecting all the back sound out to the audience. Now on to the real problem. Since the auditorium room is multipurpose (also to be used as a gymnasium likely with balls flying around in it at times) the sound control will be moved into a control room with an opening off the second floor at the rear of the auditorium rather than being in a booth on the floor along the back wall. Sound control rooms like this are regularly used at theaters, but I don't know of any successful implementations at a church (all I ever hear on church worship discussion lists regarding sound control rooms are complaints). What else can be expected from situations where acoustics are usually considered as an afterthought. Looking at a few resources on control room design ratios, I think the ratio that I am most likely to succeed at carving from the upstairs is a 1:1.44:1.16. This is one of the more square ratios that still has decent spread of room modes. If I can get a 10' ceiling, it would be 14.4' long, 11.6' wide, 10' high. I doubt I'd get anything bigger. If 8' or 9' ceiling, a bit smaller. This becomes what I hear commonly referred to as a "small room" design - but I am sure that the aperture to the auditorium poses the real puzzle (not covered by CARACAD and I don't know if anyone has effectively modeled the acoustics of two coupled rooms. Perhaps the auditorium being much larger than the control room, I just model the control room like it has an open window to the outside. But part of the puzzle to solve is the transmission of sound into the control room from the auditorium - preferably natural and acoustically accurate. This almost resembles bandpass speaker design theory. ;-) Ideally, the aperture would be sized appropriately so that the sound transmitted through it would be equivalent to having near field monitors, but not mess up the relationship of room modes detrimentally. Also, the sound transmitted naturally through the aperture would have to be significantly louder than the acoustical effects the control room has on the sound. Now before I go too much further along this line of thinking, I am open for some input and advice and especially some pointers to really useful resources. Thanks in advance. Regards, Darcy

I'm no expert on acoustics, but from what I've learned here on this forum, in several books on the subject, and from years of personal experience visiting and trying to run live sound in numerous churches that have done exactly what you plan to do, it seems to me that you just cannot do what you are trying to do. I hate to be the one to tell you "You can't get there from here", but I really don't think you can. At least, I've never seen it done successfully. (Or maybe I'm just too much of a perfectionist...) No matter how you design your "control room in a connected box", no matter what you do with the "aperture" between the two, you are never going to get perfect coupling between them. I have run into this issue personally more times than I care to remember, and I've seen many attempted "solutions", but I have never seen one that works really well. Some are barely acceptable, but none are good, and "excellent" is totally out of the question. To my understanding, by putting your control room in a small "box" that is attached to the large "box" (auditorium), with an aperture in between, what you are REALLY doing is basically building a big Helmholtz resonator, and it will resonate at certain frequency(ies). Yes, by carefully designing the aperture you can probably tune the frequency(ies) out of the audible range, I suppose, but you will still have pretty lousy coloration of the sound. The control room just wont give you an accurate sound "picture" of what is actually going on in the auditorium. The only way that I have ever found of finding out what it REALLY sounds like in the auditorium, is to put your ears right there, in the auditorium itself, among the people! If you put your ears anywhere else, you won't be hearing the same thing as the congregation / audience is hearing. Even if you put your ears n the wrong place in the auditorium (especially in a badly designed one), you STILL wont get a true image of what the majority of the people are hearing. Now, having said that, this may or may not be important for your application. For example, if you only ever plan to use the "control room" as a true control room, for actual recording of events in the auditorium and nothing else, then forget about the aperture! Just seal off the control room entirely, isolate it from the auditorium acoustically with lots of mass, and you'll be fine! That would be excellent! Provided that you do NOT want to run live sound from your control room.... Or if the auditorium is only ever used for simple speaking events (never any music), then you might be fine with just a big "hole in the wall" aperture. But if you plan to use that control room to actually run good quality live sound for the auditorium, then I don't think you'll be able to accomplish that form a separate room. I've run live sound for enough years in enough locations to be able to tell you that, if you can possibly avoid it, you do NOT want to put your sound man anywhere else but right there in the audience, roughly centered side to side, and roughly one third or two thirds of the way back (between stage front and back wall), and slightly elevated above the heads of the audience. That's about the best possible place you can put him. If you put him anywhere else, such as in another room, under a balcony, on top of a balcony (or even worse, on the stage or behind the stage (yes, I've seen that too, believe it or not)), then he just isn't going to be able to do a good job, simply because he is not hearing what the audience is hearing. He needs to hear exactly what they are hearing, in order to give you a good mix. Sorry to be the bearer of bad tidings, and maybe one of the acoustic experts here will prove me wrong and suggest ways of dealing with your situation to minimize the coloration (maybe acoustic space couplers might help), but experience tells me that the chances are not very good at all that you will get an acceptable situation. I would suggest what I always suggest for such situations: A mobile sound booth that can be wheeled out of the way to a safe location for "ball throwing" events where sound quality doesn't matter, and wheeled back into place for "quality sound" events. You can hook it up in a couple of minutes in either of the two locations, using a couple of large multi-pin connectors that are protected in a recessed box under the floor, and which run all your cables to the stage, speakers, etc. That's about all I can suggest. Your other questions are totally outside of my area of expertise, but the issue of "putting your console and sound man in the right place for live events" is what I've been doing a couple of times each week for the last couple of decades, so maybe my suggestions there might be helpful for you, even though they are rather negative! - Stuart -

Thanks for your comments Stuart. Right now, I don't care if comments are negative or positive. I appreciate them all. When you warn me, you are not nay saying - but could be much better friend than one who simply says "go for it". The purpose of my initial post is to sanity check and to identify the types of problems I will have to be dealing with. I have thought of the rolling booth idea too. I'll be posting some more info on the facility soon. Darcy

Here is some additional info related to the facility... Planned Room Use: 1. Auditorium Live music events from church service each Sunday to rock-like concerts Live drama events Multipurpose / alternate uses - gymnasium - banquet facility - small convention open area - blood donor clinic (once per month) - occasional public meetings (nearby strata councils) 2. New Control Room Live mix of events in auditorium Use as CR with adjacent classroom as a recording room Music: Variety of genres (musically) - Christian mainly (thematically) We do get fairly loud especially when the teen bands are at work. Usual band setup: Live - Acoustic drums, digital keyboard, bass guitar, usually two E.guitars, one or two Ac.guitars a few vocals. Recording - have attempted live multitrack takes - too much bleed (and too much room reverb) Have also done multi take recordings of vocal ensemble and then a large crowd (extras) for a friend's movie Location; Port Coquitlam Vancouver area, BC Canada Climate: Moist moderate typical of Pacific Northwest (a bit cooler than Japan, California or New Zealand, warmer than Atlantic places like UK - I think) Space: Auditorium will be almost 60' square (60' long, 60' wide at rear, 52' wide at stage - two rectangular segments) Control room likely 10' high by 14.4' long by 11.6' high (if I can get that much from the upstairs). Isolation: Control room will need to be able to be coupled to the auditorium for live events. Otherwise there will be some form of a door/shutter to close it off. Drawing details: This will come later once I know I am not insane for even considering this. Existing Construction: The building is an existing structure (built 1994). Auditorium presently 90' long and 44' wide at the present stage - three rectangular segments (30 feet each at 44', 52' and 60' wide) Issues: 1. Acoustical treatment of the auditorium 2. Multipurpose facility 3. Proper spec of new control room - may have some "politics" to contend with when requesting the room size - some people's notion is that a closet is sufficient 4. Electrically very sound - hope to get wiring for pro lighting gear down the road

Hi Stuart, Perhaps if I could impose on you - the control room and aperture may not really be that negotiable, so I may have to just be happy with having input into design, size and the coupling arrangement. Please comment on the sizes, locations and coupling arrangements (e.g. aperture size, etc) you have dealt with in your experience and how effective (or should that be "ineffective") each has been. Also, please describe which ones were more workable (if any). Thanks, Darcy

Hi Darcy. I haven't been able to respond for the last few days, as I've been tied up solid for the last 3 days recording vocals for a CD, in our own church, where the auditorium serves as both the tracking room and the control room, and the acoustic isolation out to the busy main street in front is maybe 40 dB on a good day... Anyway, back to your issues: it's really hard to get a mental image of the layout of your facility just from reading text. It would be good if you could post a diagram of some sort, and I'd really, really suggest that you do it in SketchUp, which is a free 3D design package that you can download from Google. It's pretty simple to use, but very powerful, and should only take you a couple of hours to learn. Then you can do a rough scale plan of your facility in 3D, so that we can get a better picture of exactly how it is laid out, where the CR will be in relation to the auditorium, shapes and dimensions of the rooms, etc. I think if you did that, it would not just help us to picture what you have, but would also help you to play some "what if" games with your designs, as you move forward. Some photos of the auditorium would help, too. One thing I noticed from your dimensions is that you are going to have some pretty bad acoustic issues in your auditorium, due to the "almost square" shape. At least it is not an exact square (52 feet at the stage, 60 at the rear wall), but to me it looks like it is close enough that you are going to have some serious issues with frequencies that fit in with those dimensions. I haven't done the math, but it's not hard to figure out where your problems are going to be. From what I see in your post, I think that the acoustics in your auditorium are going to be a much bigger problem than the coupling to the control room! If you have lousy acoustics in your auditorium, then it doesn't really matter at all if you have good coupling to your CR (control room): the sound will STILL be lousy, and there is no way at all that you can fix bad acoustics electronically. You cannot “un-salt” your food if you put too much salt on, and you cannot “un-color” sound that is full of reverb, resonance, artifacts, and other issues. I'm sure you already know that even the best graphic equalizer and fanciest compressor on the planet will not fix bad room acoustics. At very best, they can fractionally lessen one or two minor issues, but they can do nothing at all to fix excited nodes, flutter echo, resonance, standing waves, etc. The ONLY way you can fix those problems is with acoustic treatment in your auditorium. Period. And from they way you describe it, you are going to have plenty of those problems that need fixing! I guess that your comment about "52 feet at the stage, 60 feet at the rear wall" means that your side walls are not splayed (angled out like a fan), but rather that there is a sudden widening at some point: Is that correct? "Splayed" = "good", I think. "Sudden change" = "not so good". Maybe if you could angle that new side wall a bit, it might help to control flutter echo. Also, could you plan to NOT build it as a large flat surface, but rather to build it acoustically, to break up reflections? Since you are going to build it anyway, a change in the design costs practically nothing, and can make a big difference in the room acoustics. Is there no chance at all that you can change those room dimensions? Square = “Very Bad”!!! Question: You say that the chunk of the hall that is going to be cut off (behind the stage, for the warehouse) will be "constructed of good acoustical materials". What exactly do you mean by that? I'm concerned that if you don't do it right, you might actually make matters worse, since the part that you cut off could become a resonant chamber that is acoustically coupled to the main hall. How are you planning to build that wall that divides off the "warehouse"? Are you going to use separate double-stud wall construction with several layers of sheet rock only on the outsides of those two? Are you going to go for concrete or brick walls? Did you have something else in mind? You also mention three important issues where you already have problems: - Bad echo off the back wall - Excessive reverb in the room - Bass-buildup along rear wall Plus this other comment "Recording - have attempted live multitrack takes - too much bleed (and too much room reverb) " To my way of thinking, these are all actually one-and-the-same, and they will get worse, not better, with your new layout. Basically, they are just four manifestations of one single problem: Your back wall. I'm guessing that it is large, flat, smooth, and hard? Such as glass, brick, concrete, or sheet rock? If you ask me, this is going to be your biggest problem. I'm also guessing that your roof is going to be your second-largest issue, and that it, too, has no useful acoustic properties at all? The good news is that once you solve these two issues, the rest will probably not be so hard to deal with. The bad news is that these are not simple issues to deal with, and will cost money. This kind of treatment is not going to be cheap, even if you build it all yourself. I speak from experience, here! I helped to design acoustic treatment for a church here in Chile a couple of years back, after they really messed up their acoustics by installing a plywood ceiling across the entire roof, covering up the nice thick layers of rock wool insulation that had made the room sound really good prior to this. The auditorium seats about 800 people, and they had been building it slowly for years, but never got around to installing a ceiling. The ceiling was entirely made up of paper-faced rock wool batts, held in place against the roof by a twine grid. The room sounded pretty good, and I had run sound their several times very successfully, and ended up teaching their musicians and volunteers sound men how to use their equipment. It was a great space for sound . . . . until they covered the ceiling in plywood! That turned it into an acoustic nightmare. To fix it, they were planning to glue carpet all over their new plywood ceiling, and just called me to ask what kind or carpet they should use... (!) Fortunately, I was able to set them straight on some sad facts about acoustics, and managed to convince them that carpet would be a really, really bad idea. They have now "bitten the bullet", and are spending the time and money to install massive acoustical treatment all over the place, to mitigate the problem they created for themselves. Two years and thousands of dollars later, they are nearly finished, and the room is starting to sound reasonable again. But it will never sound as good as it did back then. I don't want to scare you, but acoustic treatment of large spaces is not cheap, not simple, and not intuitive. My intention isn’t to rain on your parade and scare you, but hopefully to point you in the right direction for avoiding some problems in advance, before you start building actual walls, at this stage while you can still fix things at no cost just by drawing lines on paper, rather than trying to do it later by tearing down walls or hanging lots of large and expensive acoustic panels! Changing acoustics in the design phase is a LOT cheaper than trying to fix it afterwards. And far more successful, too. From what I've learned about acoustics in large rooms, you are going to need some major diffusion and major absorption on the ceiling and side walls, but most of all on the rear wall. Corners are your worst enemies, and also your best friends, to a certain extent. That's where your nodes concentrate, so treating corners helps more than treating the center of a wall, (for absorption, at least, but not for diffusion). However, considering the size of your rear wall, you are going to need to treat a large percentage of that surface in order to control the reflections as much as possible, and you are probably going to need clouds on your ceiling, also to control reflections and break up the waves, as well as to absorb. The size and type and location of treatment is beyond my expertise, but maybe one of the REAL acoustic experts here can chime in with suggestions. I can give you some rough pointers, but you really need advise from an expert in large room acoustics, and that isn’t me! About all I can really tell you is that this is not going to be a cheap operation. Now, from long experience dealing with sound in churches, I think you have a problem that is far more important than acoustics. Unless you can get the pastor and steering committee to understand the importance and seriousness of the issues, you are going to be fighting a losing battle. Your FIRST priority should be to get the pastor and leaders educated on just how important sound is to the church. If you can do that, than you are much more than half way there. If you cannot do that, then there really isn’t much point. I can help you with the planning of your mics, speakers, equipment, setup of gain structure, EQ, and things like that to minimize acoustic issues (I have to do that al the time), but it won’t make a huge difference, and you really, really need to get the leaders on board to get the results that you are actually aiming for. One statistic that you might want to hit them with, is "seventeen percent". That is the percentage of your congregation that WILL walk away and not come back if the sound in your new hall is no good. I'm not inventing that number, and I'm sure you can find it yourself by googling around. It is an established and accepted number that shows how important good sound is in large spaces. That really is the statistical portion of your church members that will leave and not come back if they do not like the sound in the new church. If you can get your pastor and leaders to understand that nearly one fifth of the congregation WILL leave if they do not do a good job on getting the sound decent, then you might be able to get them to listen to what really needs to be done. No pastor wants the responsibility of explaining why one fifth of his congregation walked out…. This is not a "maybe one or two might not like the new sound" or "perhaps a couple of members will complain, then get used to it". Nope. It is the real number of real people who really will leave, if they cannot clearly hear and understand the message that the pastor preaches and the musicians sing. Get your church leaders to understand this, and they should be far more inclined to do what is needed to get it right the first time. Your comment that you "may have some "politics" to contend with when requesting the room size - some people's notion is that a closet is sufficient " is enough to trigger warning bells here! It sounds like you already have to deal with people in authority who just do not understand the issues of sound and acoustics at all, and unless you can resolve that "political" issue first, then the rest is all a moot point. Unless your church leaders understand the seriousness of the issues regarding sound and acoustics (both physical and spiritual issues!) and are prepared to do what they should do, then there really isn't much point in planning the kind of treatment that you actually need. Sorry that I'm not giving you the answers that you really need to hear, but experience tells me that the answers are not as simple as you are hoping they might be, that they are nowhere near as cheap as your church treasurer wants them to be, and that it will never be done right if the church leaders are not on board. Anyway, if you could post a sketch-up model of your current situation and another one of the proposed new situation, that would help to understand your issues a bit better!

Hi Stuart, Thanks again. I'll do a quick reply to some items and follow up with more info later. back ... . . . . . . . . . . . . ... front +-----------------+ | . . . . . . . . . . . | | . . . . . . . . . . . +----------------+ | . . . . . . . . . . . . . . . . . . . . . . | | . . . . . . . . . . . . . . . . . . . . . . | | . . . . . . . . . . . . . . . . . . . . . . | | . . . . . . . . . . . . . . . . . . . . . . | | . . . . . . . . . . . . . . . . . . . . . . | | . . . . . . . . . . . . . . . . . . . . . . | | . . . . . . . . . . . . . . . . . . . . . . | | . . . . . . . . . . . +----------------+ | . . . . . . . . . . . | +-----------------+ Control room most likely will be upstairs midway and behind the back wall. Present configuration is the above with a third yet slightly smaller rectangle (on the rightmost side). The new wall will likely be a rather expensive dense drywall on the warehouse side, then at least 4 inches of mineral fibre insulation. On the auditorium side will be some sort of perforated gypsum or perforated plywood. There may be a small air space needed too - I haven't done calculations yet. The CARACAD software proves that the room acoustics can be fixed, but the treatments I selected turn out to involve hard to find and very expensive materials. Still I am not certain as perforated construction materials are not near commonly available in Canada/USA as say in Australia, NZ or Europe. One supplier gave me contact info for a small CNC mill shop nearby who I could get to cut up panels - so I have to be flexible (either that or be drilling holes all night long for a few weeks). ;-) But if I can get it right, the wall not only will be an effective absorber but ought to provide a very effective firewall between the two rooms since the mineral fibre used for sound absorption is the same used for enhanced fire safety. I think fire codes may be on my side for this wall - except that they may limit my choices regarding the perforated construction material on the auditorium side. Regarding the 17% - I wish I had that info 15 years ago. We have lived with bad acoustics for that long. I suppose the converse is true too. If we fix the acoustics, we should start filling up the place faster. ;-) I think my second iteration will have to involve more sculptured room design changes. My first crack just involved existing wall treatments and the new wall. Probably the most important finding from this exercise is that the new wall, if made out of the right materials, contributes more towards an acoustical solution than the treatment applied to any existing wall. Just to summarize, my proposed treatment (so far) is: Upper back wall - Acoustic foam Lower back wall - Hardwood panels with 20mm air space Side walls - 20% perforated plywood with mineral fibre in space behind it (approx 50mm) New wall - 20% perforated gypsum baseboard with mineral fibre behind it. I suppose this is a brute force treatment and as you mention, applying certain treatments in corners and adding diffusers mid-walls may allow the same or better treatment using lower percentage of wall coverage. I am preparing a report. I'll upload a copy when it's done. The report includes a couple of photos and screen shots of CARACAD's rendition of the room change and the reverb time vs frequency plots. (It will be a while before I can get something drawn out using SketchUp. Oh yeah! I'd still like it if you can comment (rant away) regarding the different sound control rooms (and closets) you have had to deal with, especially the ones that were not as bad as (i.e. more workable than) you first thought. Thanks again. Regards, Darcy

Darcy, I guess I'm a little confused about the dimensions: In one place you say that the auditorium is "presently 90' long and 44' wide at the present stage", and that it will end up being "60' long, 60' wide at rear, 52' wide at stag". I assume that, since it is currently 44´wide and will end up being 52 wide at the front and 60 wide at the back, that you are planning to add something on to one side? Maybe knock down existing side walls to gain extra space? Also, can you provide some details about your current ceiling? It must be at least 16 feet high, I guess, since you mentioned that the CR will be on the second floor, but how high is it? Does it slope, or is it flat? What is it made of? Also, what are your current walls and the floor made of, especially the rear wall?

Existing... 90' long 60' wide at rear 52' wide at middle 44' wide at stage ...each width for 30' think of it as three rectangles in sequence. Ceiling heights are 25' at rear then 22.5' in middle section, then 20' at the stage section. The existing stage section rectangle will be walled off to become a food bank warehouse leaving us the existing rear and middle rectangles. The new wall will be between the existing middle section and the existing stage section. What I have figured out so far is that our single greatest opportunity lies within how we build the new wall (materials used, construction, etc). We still have to treat the existing walls to complete the acoustical solution for the audorium, but for the new wall it is better to build it to be part of the acoustical solution rather than to simply put up a normal dry-wall and then try to treat it afterward.

I have submitted to the church leadership, a report that describes the changes to the auditorium. Available from my web site at: http://www.xstreamworship.com/resources/grace-auditorium-acoustics-p1-Rev-A.pdf It describes the present auditorium, proposed changes, the problems we have lived with for the last 15 years and a proof-of-concept solution (that needs further work for improvement, availability of materials and local building codes, etc). It has plenty of diagrams, pictures, photos and plots in it. I submitted this report based on discovery that the new wall to be constructed would be more effective if designed and built for acoustics rather than to be built as a typical hollow dry wall and then treat it afterward. I wanted to convey that thought to leadership so that it could be communicated to the architect / engineer who would do the design, plans, drawings, etc. The report was well received and passed to the architect, builders, etc. Now my next steps are: 1. Source the materials for the new wall - find an alternate equivalent solution if I cannot source perforated gypsum in North America 2. Refine the room design, treatment, etc based on treating existing walls and having the new wall be a good part of the solution 3. Start analysis regarding the control room. I bought a couple of good books on Acoustics and am reading the first one... Master Handbook of Acoustics, 4th Edition, F. Alton Everest (and contributors) - McGraw Hill - 2001 Now a couple of questions... 1. Anyone know of good supplier of perforated gypsum in North America? (location in order of preference - mainly due to added complexities when importing) - Western Canada - Canada - North Western USA - USA - rest of world 2. In the book, I saw staggered stud construction. Does that seem reasonable? I know it's not as good as a double wall, but it's still way better than using studs that are in contact with both wall surfaces, right? Regards, Darcy

Hi Darcy,

streamworship wrote:

I have submitted to the church leadership, a report that describes the changes to the auditorium. Available from my web site at: http://www.xstreamworship.com/resources/grace-auditorium-acoustics-p1-Rev-A.pdf

Great! I downloaded, and read it through. I have some questions and concerns, though. See below...

The report was well received and passed to the architect, builders, etc.

That's good too. I assume the architect will hire an acoustic engineer to do some testing and confirm your findings? Did the committee specify who is the final responsible authority for taking decisions on the acoustics?

1. Source the materials for the new wall - find an alternate equivalent solution if I cannot source perforated gypsum in North America

I'm not sure why you are specifying perforated gypsum board! Why exactly do you need that, specifically? What specific specs does it have that make you want it so badly? I didn't see any details of the wall construction you are proposing, but from the report I presume that you are planning on using two stud walls, separated by an air gap filled with insulation (mineral wool or fiberglass), with a couple of layers of ordinary drywall (gypsum board) on the outer sides of your studs? And then some kind of sealed resonator structure on the stage side of the inner leaf, with the perforated gypsum board attached to that? Is that the plan? If so, why do you think that perforated gypsum board would be superior to, for example, slot resonators, which would be easier and cheaper to build with normal, easily obtainable building supplies? To my way of thinking, slot resonators have several other advantages: You can build them in sections, and tune them as you go if you need to, or you can build them more broad-band, as needed. They are also nicer, aesthetically.

2. Refine the room design, treatment, etc based on treating existing walls and having the new wall be a good part of the solution

I think you might be over-treating your side walls, and it seems to me that you are concentrating way too much on a few frequencies that are merely "predicted" to be problems by US$ 75 software that is designed for home theaters! And all that based only on room dimensions and theoretical proposed treatment, using theoretical materials and theoretical values. I'm not so sure that I would rely that much on cheap software that was not designed for the purpose for which you are trying to use it. I'd suggest that you spend a few days using something like ETF to do a complete analysis of the existing room, and see exactly where your problems are at present, then compare that to a Caracad prediction for the existing room. My bet is that the two will not even be close. If you get an exact match, I'd be EXTREMELY surprised! That would convince you that predicted behavior probably does not match reality very well. Your proposed treatment does not seem to fit well with what I've read and learned about large room acoustic treatments. For example, you specifically mention in your report that the ceiling will remain untreated, yet most large room acoustic treatments that I've seen use the ceiling heavily, usually with some form of diffusion, absorption, clouds, etc. You have a very large area up there that you are not using as part of the solution, and untreated you are going to have mode problems in the vertical plane. You make no mention at all of the roof / ceiling construction, nor of the predictions made by your Caracad program for axial nodes or tangential nodes that involve the ceiling and the floor. What exactly does Caracad predict for your floor / ceiling modes? Also, you are proposing basically 100% treatment of your side walls, plus 100% treatment of your front wall, plus about 75% treatment of your rear walls. That amounts to well over 60% treatment of the entire room surface, whereas I've seen recommendations that you usually don't need to treat more than about 30% of the surfaces, maximum, unless you have some rather unusual problems. And 20% perforation across your entire side wall treatment seems to be rather high, from what I've read about. Common treatments seem to be in the range of around 2% to 10%. Why do you need so much perforation? Also, you did not specify the hole sizes. What size perforations do you need, according to Caracad? Also, why did you decide to treat only specific predicted problem frequencies with tuned perforated absorption? Would it not have been better to go with broadband treatment? In such a large room, I would think that you'll have more than just a couple of frequencies that you need to treat, despite what Caracad is telling you!

3. Start analysis regarding the control room.

That control room is still going to be your biggest nightmare. I still don't see your proposed "hole in the wall" solution as being viable, especially in light of the comments in your report. You say that, at present, your sound engineers already have serious problems hearing the room, and cannot even do a decent mix without needing to get out and walk around the room, then head back to the console to make adjustments! And that is with the console positioned IN the room, with the only limitation being that it is against the back wall!! You already have serious, serious acoustic problems with your current mix position, which isn't ideal but is also not too bad. That problem will get ten times worse if you put the console in a box, located high up in the middle of the back wall. No matter what you do up there, you just CANNOT couple those two spaces acoustically. It will be terrible, always, regardless. In effect, you are going to be putting your console inside a Helmholtz resonator that is attached to your room. To be honest, I cannot think of a worse possible place to put it. That's not just theory talking, but many years of personal experience running live sound in all kinds of venues. It simply is not going to work. For live sound, you MUST have your engineer right in the audience / congregation, more or less two thirds of the way back (or one third), roughly centered side-to-side, with his head no more than about 50 cm or so above the heads of the crowd. In other words, he has to be part of the crowd, hearing what they are hearing. Sticking him in a resonant cavity up in the rear wall just isn't going to work. that might be a great location for a recording studio control room, but not for live sound.

I bought a couple of good books on Acoustics and am reading the first one... Master Handbook of Acoustics, 4th Edition, F. Alton Everest (and contributors) - McGraw Hill - 2001

That's a great book. Some call it the "Bible" of acoustics. It is heavy going in places, but gives you a pretty good basic understanding of acoustics. I bought it a few years back, and have read it several times. But I'd suggest that you also buy Rod's book. It is not about large rooms at all, and is very specific to studios, but some of the basic principals that he teaches there are also applicable to larger rooms.

Now a couple of questions... 1. Anyone know of good supplier of perforated gypsum in North America? (location in order of preference - mainly due to added complexities when importing) - Western Canada - Canada - North Western USA - USA - rest of world

See my doubts above about using this. I'm not sure why you think you need it, nor why you have discarded easier and less expensive construction materials. How about if you post a SketchUp diagram detailing how you plan to actually build that wall?

2. In the book, I saw staggered stud construction. Does that seem reasonable? I know it's not as good as a double wall, but it's still way better than using studs that are in contact with both wall surfaces, right?

It's better, yes, but still falls far short. If you need good isolation, then you need separate stud walls, a couple of layers of drywall on the outer sides of each, with an insulation-filled air gap in between, and your acoustic treatment on the outside of that. You could also build one (or both) of the walls "inside-out", meaning that the layers of drywall go in the inside faces of the studs (the side of the studs that directly face each other, inside the wall). That way, you can use the stud space for acoustic treatment. Once again, that's not quite as good as building the wall normally (you lose a few dB of isolation), since it reduces the size of the air gap, but it might be an idea in your case. In any event, the cost of two single stud walls vs. one staggered double stud wall is about the same. The only thing you save is a few dollars on top plates and bottom plates in your framing, but with a double stud wall you need much larger dimension plates anyway. To be honest, in your case I think I'd go with two totally separate walls, each one with 24" OC studs, and a large air gap between, at least 6 inches, filled as much as possible with mineral wool. Don't forget that you absolutely have to seal up both leaves of that wall totally hermetically, with lots of caulking all around. - Stuart -

The target RT60 seems very low. What is it based on? Andre

Hi Andre and Stuart, Lots of comments so I will have to take my time to reply. First answer to Andre's q? since it was short and is a good lead in to response to some of Stuart's comments. (I think it will take multiple posts for me to consider all of Stuart's comments and questions - especially since I want to do it justice and learn the most from valuable input from others - but I think there may have been some misunderstanding I hope I can clear up). The target RT60 does seem low. It is based on the CARACAD program which appears to use one criteria for all (or at least that is the impression I get). I have two concerns regarding the CARACAD software. 1. I think it underestimates the reverb problem in our room (large) 2. The target RT60 doesn't appear to be adapted based on room uses. I expressed the first of the two in my report as a comment at the end of section 4.5. As Stuart has rightly pointed out, CARACAD appears to be intended for home theatres and I think also for clubs, restaurants and other "small" rooms - and is not really intended for hall like auditoriums. In large halls, reverb actually takes on a sense of directionality - something I am able to perceive in our existing auditorium acoustics, but not considered in any of the models I have seen so far. I have been using CARACAD software for the first round (preliminary) analysis based on the following assumptions. 1. It should steer me in the right direction (qualitative) even though I cannot rely on it for exact estimates (quantitative). This is based on the experience of this program used to help with improving the acoustics at a different campus (eluded to in last paragraph of section 4.6 in my report). 2. It is known to and accepted as a tool by some of the recipients of the intended audience of the report. They understand its strengths and limitations. So it makes sense to use this as a start and then go from there - especially since I came onboard as part of the merged-in organization so I am still sort of "new" to the greater whole organization. To this extent, I believe the software served me well. It showed me the following: 1. Decorative curtains / drapes (which cost lots and people used "acoustics" to justify the expense in the past at my church) are not effective as acoustical treatment. If people want to propose curtains - they now have to propose it strictly on basis of aesthetics - not piggyback it as acoustical treatment. I won't fall for that one again. 2. It showed me that constructing the new wall as an absorber is more effective than waiting to be handed a hollow dry-wall and then having to treat it afterward. Since that info needed to be communicated immediately - I felt it most important to convey that information even though the rest of the analysis would have to be done over again. 3. It also generated the rough concept sketches of how the room would appear after renovations. I fully understand that before construction starts, more analysis is needed and I will most likely perform these calculations manually and just use CARACAD just as a sanity check to back up. In the report I commented that it should be possible to achieve effective treatment using less coverage (since I had not considered any corner or ceiling treatments yet). I will post later regarding the wall's construction and my rationale behind it. Regarding the control room, I fully understand that it is a bad idea so I hope that you can appreciate that I am just deferring the decision. When it really comes down to it, the only driving factor behind the control room is to secure the sound / multimedia equipment from damage when part of the room is used as a gymnasium. The gymnasium room use also drives a requirement for a rather expensive room divider to protect the stage and musical instruments, etc. I think that if I were to point out that this expense all ties to room use as a gymnasium, some may decide that it may not be worth it. This will likely be part of the subject in a later report - it could involve controversy, not something I wanted to have entangled in the first report considering my main point was to avoid being stuck with a quickly slapped together hollow dry wall. more to come later... Regards, Darcy

Hi Stuart, I would like to make use of some tests / measurements as you mentioned and not rely only on software modeling. As I read further into the Master Handbook of Acoustics I believe I will get a better idea as to what I can test based on equipment I have on hand and what sort of SW / HW I would need to purchase. Is ETF described in my book? I don't know who the final authority for taking decisions on acoustics will be. My pastor made an interesting observation that there are many who are willing to make measurements and recommend treatment (some even sell the stuff) but none (as in no one) would guarantee that results would match their predictions. In other words, it's still, "Buyer beware!" I am still going to have to learn the math and do it. You asked about treating only the predicted problem frequencies. Actually the problem frequencies are whole ranges. The side wall treatment has a rather broad peak intended to tackle a rather broad peak in the room's characteristics. But you are right, these are all based on modeling and theoretical properties. For purposes of a preliminary report this was OK. Before actually specifying for the construction, I would want to better understand the room's natural response and then would likely pattern hole sizes and perforation percentages accordingly. As I mentioned in my previous post, I think that effective treatment should be possible using less coverage but adding some to ceiling, corners, and some other treatment. The proof-of-concept solution is really just a proof that it can be done, far from determining what is the best. It was based on no structural changes apart from the wall and the control room (and for this analysis, the control room wasn't even added - just the reflective characteristics of the shutter when closed). I think I am not going to respond to your comments regarding the control room other than that I take it under advisement. When I discuss the control room with people, I tell them that I only hear people discouraging us from doing it. The biggest counter argument I run into is a control room at one of the other campuses that does work. I think they lucked out. They have a square room with stage in one corner and the control room in the opposite corner. They installed a small wall to make the corner into a triangular shaped control room. I think they lucked out in such a way that the bass buildup inside the corner-room cancels the loss of bass through the aperture. This would not be something working in our favor in our auditorium though. The more I think about it, the more I think that the gym room use idea should be abandoned. If I cannot prevail regarding this, and all my concerns regarding protection and security are met, and I can get a real control room - not a tiny closet, then I'll have to figure out the control room. Yeah it is a two room coupling problem - most likely as you say a Helmholtz resonator - but likely the control room is big enough that it is like the earth and moon in orbit around each other (each room a helmholtz resonator to the other) as opposed to a tiny satellite orbiting the earth (simple case). If the control room goes ahead, I will likely have to resort to some real nasty math to figure it out. But I think it is more likely that the cost of the control room plus a room divider will be too much to justify gym use. If they counter propose that equipment be packed away and restored, etc. then I will have to point out the costs of hiring people to do it, to guarantee that it works when needed and that the increased rate in wear and tear is properly accounted for in budgets. I think that when costs are really considered, the gym use is a hard sell. I did elude to these things in section 8.1 in my report and concluded that these things have to be figured out before we start the renovations. More to come later regarding "the wall"... Regards, Darcy

xstreamworship wrote:

The target RT60 does seem low. It is based on the CARACAD program which appears to use one criteria for all (or at least that is the impression I get). I have two concerns regarding the CARACAD software. 1. I think it underestimates the reverb problem in our room (large) 2. The target RT60 doesn't appear to be adapted based on room uses. I expressed the first of the two in my report as a comment at the end of section 4.5.

What is being done in the space? Have a look at pages 150-154 in MHoA for better guidelines. Andre

Hi Andre and Stuart, Andre, thanks for the pointer. I read through that the other day. I am at around p179 (ch9) in MHoA. I plan to take those charts into account during the next pass at it. For our style of church (mellow rock style of music for the singing part of the service and speech for the sermon) I think we would be just below the line dividing the two regions on the graphs. This is definitely livelier than the goals for a home theater. If these criteria are all based on empty rooms then I suppose I shouldn't bother taking into account people in the room either. Now the promised comments about "the wall". The wall in question is the new wall to be constructed between the auditorium and the warehouse. I think there may have been some misunderstanding here. First - what the wall is for. Unlike the typical wall between a live room and a control room, this new wall does not have to maximize transmission loss. In fact, the transmission loss just has to be sufficient to prevent the two rooms from coupling through it. Fortunately it will likely have to be a fire barrier so it will have a very dense wallboard on the warehouse side and be filled with mineral fiber. Since the warehouse and the auditorium are used at different times, I don't have to worry too much about what noise would make it through, so my two main objectives are. 1. Keep the two wall surfaces decoupled (staggered studs will suffice) 2. Use the mineral fiber absorption material to absorb sound from the auditorium (hence the perforated wall board on the auditorium facing side). So in a nutshell, the wall is designed more to be an acoustical panel for the auditorium more than a sound-proof barrier between two rooms. I think this explains my rationale behind the new wall construction (at least I hope it explains it and I hope it is rational - pun intended). :lol: Regards, Darcy

1. Keep the two wall surfaces decoupled (staggered studs will suffice) 2. Use the mineral fiber absorption material to absorb sound from the auditorium (hence the perforated wall board on the auditorium facing side).

That doesn't sound like a two-leaf wall to me! If I understand you right, you are planning to build a wall with only ONE leaf, and a perforated panel resonator next to it. From your description, I think you are planning this, starting from the warehouse side: normal drywall - studs - airgap with insulation - studs - perforated drywall That is NOT a two leaf wall. It is mostly likely a tuned resonator! Why are you going that path? I'd be concerned that you might actually be helping to COUPLE the two spaces like that at certain frequencies, instead of DECOUPLING them!! Is there any reason why you do not want to go for a normal two leaf wall? The way I see it, your entire wall will resonate at whatever frequencies you happen to have tuned it to, depending on perforation hole size, panel thickness, and the size of the air gap!!!! I don't think that is what you are trying to achieve at all!

xstreamworship wrote:

I have two concerns regarding the CARACAD software. 1. I think it underestimates the reverb problem in our room (large) 2. The target RT60 doesn't appear to be adapted based on room uses.

That's why I'd suggest that you get ETF or maybe even Room EQ Wizard, spend a few days analyzing your EXISTING room, and produce a set of waterfall plots that show you where your REAL problems are already, instead of just relying on predictions. After all, you are only changing the position of one of the six "walls" in your room, so many of the nodes will remain the same, even after the new wall is built.

As Stuart has rightly pointed out, CARACAD appears to be intended for home theatres and I think also for clubs, restaurants and other "small" rooms - and is not really intended for hall like auditoriums.

Exactly. That's probably why it is suggesting such low RT60 times. IT is designed for home theaters, mainly, where you really do want very low RT60.

I have been using CARACAD software for the first round (preliminary) analysis based on the following assumptions. 1. It should steer me in the right direction (qualitative) even though I cannot rely on it for exact estimates (quantitative).

I think it might have pointed you in roughly the right direction, but it is a PREDICTIVE tool, not an ANALYSIS tool. It can give you a very rough estimate of what might, possibly, maybe happen in your new room, but you'll never know until you actually ANALYZE your room with analysis software.

To this extent, I believe the software served me well.

Probably, but I'm wondering if you have already reached the limit of how helpful it can be!

It showed me the following: 1. Decorative curtains / drapes (which cost lots and people used "acoustics" to justify the expense in the past at my church) are not effective as acoustical treatment. If people want to propose curtains - they now have to propose it strictly on basis of aesthetics - not piggyback it as acoustical treatment. I won't fall for that one again.

Well, at least they didn't want you to stick egg cartons all over the walls! :) Drapes actually can help a bit, provided they are made of thick, heavy fabric, and are deeply pleated, but you are right that they don't do a lot, and will only deal with high frequencies, which probably isn't the problem in your case! Drapes used wrongly might even make the situation worse, as you'd end up with a muffled clunky cave, instead of a bright clangy cave... Hard to say which is worse.

2. It showed me that constructing the new wall as an absorber is more effective than waiting to be handed a hollow dry-wall and then having to treat it afterward.

Yes, but the design you outlined does not seem to be an absorber to my way of thinking. Rather it seems to be very large perforated panel resonator, which is probably not what you want! You still need two completely sealed leaves, separated by an air gap that is filled with mineral wool. MASS - AIR - MASS. The air acts as a spring, but it can only do that if the entire air cavity is sealed, meaning that both leaves are solid and hermetic. If one of them is a perforated panel, then you no longer have an isolation wall with mass - air - mass. You now have a resonator. The wall MUST be sealed. Any holes at all in it, and you no longer have an air spring in the middle, so your wall no longer isolates. It resonates instead. What you need to do is to build your M - A - M wall, then build your absorption onto the auditorium side of that wall.

I fully understand that before construction starts, more analysis is needed and I will most likely perform these calculations manually and just use CARACAD just as a sanity check to back up.

Once again, I wouldn't put too much faith in calculated predicted performance. I would put a lot more faith in actual measured performance. Let me put it this way: you can calculate all week how to ride a bicycle, but that won't help you to actually ride it! In order to actually ride it, you need to actually ride it! Calculations can give you an idea of fast you need to ride to not fall off, and how far you can lean over for a given speed, and how hard you can brake, etc. But all of that means very little, unless you actually get on the bike and start peddling. I think you need to do that: do some REAL analysis of your existing room, five of whose walls will remain the same.

Regarding the control room, I fully understand that it is a bad idea so I hope that you can appreciate that I am just deferring the decision. When it really comes down to it, the only driving factor behind the control room is to secure the sound / multimedia equipment from damage when part of the room is used as a gymnasium.

I still think a mobile "sound booth on wheels" with a couple of high density connectors in boxes under the floor would be a LOT more cost effective, and much simpler in the long run. It would also allow your soundmen to actually do a decent mix! Anyway, it seems like you need to re-think your wall design as the first priority. Using perforated gypsum board (drywall) as one of your leaves means that it isn't a leaf at all. You need two completely sealed (airtight) leaves, with the air gap filled with insulation of some sort, and your acoustic treatment goes on the OUTSIDE of that wall.

Hi Darcy,

For our style of church (mellow rock style of music for the singing part of the service and speech for the sermon) I think we would be just below the line dividing the two regions on the graphs.

Let me guess: "Mellow rock music" means that you will have a full acoustic drum kit on stage, plus a bass guitarist with his amp, an electric guitarist with his amp, perhaps an electro-acoustic guitarist with another amp, probably a keyboard of some type with yet another amp, and a few singers with floor wedges? Does that sound about right? That's the normal kind of group that I run live sound for all the time. And all of those musicians will be just a few feet from your "perforated panel resonator wall"? It sounds like you need to rethink that wall! :shock:

Unlike the typical wall between a live room and a control room, this new wall does not have to maximize transmission loss.

I beg to differ! The ONLY way to fully de-couple your rooms is to maximize transmission loss! If there is a lot of transmission of sound through the wall, then by definition the two rooms are coupled! :) Even more so if you place a resonant wall between them, as you are proposing to do...

In fact, the transmission loss just has to be sufficient to prevent the two rooms from coupling through it.

OK, so how much is that? What amount of transmission loss have you calculated that you need? Don't forget that an average acoustic drum kit played hard by your average totally deaf drummer can easily produce 115 dB SPL(C). Add to that all of the other instruments, singers, amps and monitors, and you could be getting quite close to 120 dB peak. What level is acceptable on the other side of the wall? What are your design parameters? Have you done the math yet? Does Caracad predict the curve for the wall? What does the curve look like, especially at the lower end of the spectrum, where your kick drum, toms, and bass guitar live?

Fortunately it will likely have to be a fire barrier

If it is full of holes on one side, then I doubt that it will pass code as a fire barrier! Have you checked with your municipality to see what they require for a fire barrier? I'll bet that "wall with lots of holes in one side" does not quite meet code.

so it will have a very dense wallboard on the warehouse side and be filled with mineral fiber.

When you say "wallboard" do you mean drywall, or are you talking about something else?

Since the warehouse and the auditorium are used at different times,

Well, that's fine for today and maybe the next year or two, but what happens when things change in the future? What if the warehouse is re-purposed in a couple of years, as, for example. a printing press? Or a classroom? Or a Sunday School room? Or a library? What if your church decides to hold meetings / events at the same time the warehouse is being stocked / used.

1. Keep the two wall surfaces decoupled (staggered studs will suffice)

I'm not sure why you insist on staggered studs, when two separate stud walls are so much better, easier to build, and wont cost you any more at all. Have you figured out the cost of using double 2x12 base plates and top plates for your staggered wall, compared to normal 2x4s for separate walls? That's the only real difference. In any event, the two surfaces wont be decoupled if one of them is a perforated panel.

2. Use the mineral fiber absorption material to absorb sound from the auditorium (hence the perforated wall board on the auditorium facing side).

Once again, if one of the leaves has holes in it, then it isn't a leaf: it is a perforated resonator. In order to be a leaf, it has to be airtight.

So in a nutshell, the wall is designed more to be an acoustical panel for the auditorium more than a sound-proof barrier between two rooms.

But the way you describe it, it isn't either of those! I'd still recommend that you go with a normal double wall, with two sets of studs, and two layers of drywall on the outer faces of each set of studs. sealed airtight, and the gap filled with mineral wool. Then attach your acoustic treatment to the auditorium side of that wall. - Stuart -

The reverb time graphs are for when occupied. That is why absorption co efficient tables include "audience" in different densities and seating. With all the questions you asking, I suggest you get Architectural Acoustics by Marshall Long. It is not expensive, because it is worth it. Or turn the project completely over to an acoustician. Andre

The dense wall board on the warehouse side is a material that is equivalent to three or four layers of dry wall, but in normal size sheets. It is rather expensive but has high transmission loss and is very fire resistant. Regards, Darcy

Thanks Andre for the book suggestion. I will be looking into it since I doubt that an acoustician would be hired. You have to understand that most church organizations operate on shoestring budgets and this is complicated by the fact that there are always people on committees and boards who know just enough to be dangerous... And to be honest - that very likely includes me which is kind of why I expose my ideas to input and critique here - pride notwithstanding. :x Darcy

To sum things up, what I get out of the input and critiques so far are: 1. Revisit calculations to independently verify some of the model predictions. 2. Do some room analysis based on measurements - don't rely too much on predictions from modeling software. 3. Make sure that the target RT60 is realistic for the hall size and usage. 4. Mixing live sound in a control room off the back is likely to be problematic. 5. Should be able to achieve good acoustics using much less treatment coverage than in my proof-of-concept solution. 6. Further research needed regarding the new wall as an absorption panel since incorrect choices could cause more problems than solve problems. Thanks (and this doesn't close out discussion - I am still open to input and suggestions). Darcy

Hey Darcy, Yep, I reckon your summary pretty much covers all the major points! :) :thu: Regarding the "dense wall board" that you mention: as long as it is the equivalent density or better, and has characteristics similar to drywall (flexibility, simplicity of working with it, etc.), then it's probably OK, but I'd check your cost / benefits very carefully to make sure. Will it really work out substantially cheaper than the same mass of drywall? If not, then go with drywall, which is a known factor, acoustically. If it is a LOT cheaper than drywall, then do some careful research on its acoustic properties to be certain that it will work the way you expect. Below is a graph that shows the total thickness of double-panel wall (two sets of studs) that you need in order to get a certain level of acoustic isolation. This implies, in the case of gypsum board (drywall) that if you have two sheets of drywall on each side of the wall, then you need to have the entire overall wall thickness at about 11.5 inches in order to achieve decent isolation, but if you could replace that drywall with the same mass of lead plate, then your wall would only need to be about 3 inches thick (or 4 inches in the case of steel plate). Note that this "11.5 inches" and "3 inches" and "4 inches" does NOT refer to just the thickness of the drywall, lead or steel: It refers to the overall total thickness of the entire wall, including the studs and airspace as well. So denser materials will only mean that you can have a thinner wall, not that you get better isolation. Important point. So, if your "high density wall board" falls on that curve substantially lower down than "gypsumboard", and is also much cheaper for the same total mass, then it should probably work, but even then the only advantage it will give you is that your wall can be a bit thinner overall than if you would have just used the same total mass of gypsumboard. Using that expensive wallboard won't improve isolation: it just lets you build a thinner wall. However, I doubt that your "wallboard" fits those characteristics, because if it did then I'm sure the acoustic experts would have heard about it already! :) So it might be more dense, for example, but work out more expensive for the same mass, or it might be cheaper but less dense: Either way, you are wasting your money. Unless it is both more dense AND much cheaper, AND also has good acoustic isolation properties, then just stick with the known quantity: standard drywall. It's easy to handle, easy to cut, easy to install, and easy to finish. Anyway, at least you now have a rough plan of how to move forward, and things you need to concentrate on!

... that very likely includes me which is kind of why I expose my ideas to input and critique here - pride notwithstanding.

If you ask me, that is the absolute smartest thing you have done! Coming here, laying out your plans, asking intelligent questions, being open to accept constructive criticism, and being prepared to re-think concepts and make substantial changes, bodes very well for success in the end. The very fact that you are still here even after many of your ideas have taken a severe pounding(!), and that you are taking into account all the suggestions with a view to getting it right, is very good, and very smart. (And also rather unusual in church situations, in my experience.) If you stay on this track and can convince the steering committee to back you and fully implement what really needs to be done, then I think you are virtually assured of success, and will end up with a good sounding auditorium. (But we still have to talk about your sound system and how it interacts with the room acoustics, which is where I can really help you most! Even though it would be totally off topic for this forum... :) ) - Stuart -

Hi Stuart, Where did the graph come from? Thanks again. Regarding the sound system, I am most certain that once acoustical problems are resolved, we will discover that we are a bit under powered to achieve the same sound levels - only clean now. Also, our main mixer is showing signs of excessive wear and tear so I imagine that once we recover from the renovations, we will need to consider some upgrades in the sound system as well. Regards, Darcy