church building bass traps

[bobmurphy]

I hope it's ok to ask a little about auditorum/church bass trapping here... ( i cant find another forum with the knowledge available here and i think i saw some other posts on them )

( in the past i also build my own studio with great help from this site and im really happy with the room thanks so much )

.......Now my church is moving into a new building and the builders are working at a rapid pace and my pastor asked me advice about how to get it sounding nice. I feel at this stage that bass trapping is the most important of all ( and the one that i need to get right during construction stage if possible ). It would be great to get a bit of advice and a few questions answered.

What we are trying to achieve is clear and nice sound. There are no real audiophiles to be seen ( except me perhaps ) but we did have a temporary stay in a building which was mostly glass, tile and cement with little or no absorbtion ( ugly yes i know, and it was electric music too, not just vocal ) but it has everybody a bit jumpy about the sound in this new building, but just to say again the main goal would be to just have a clear useable sound, nothing too special

Here's as much details as i can get:

Location, Kilkenny, Ireland - the building is the ground floor of what was a furniture shop
Room Details: slightly convoluted - there are 3 sections, running side by side - the overall size is roughly square 12 * 12 M but the ceilings are a bit hard to describe so i made a diagram attached
Walls: The walls are mostly old so i dont think they could be square so hopefully no problems there ( although they are not that far out so i could be wrong )
Material: The Walls will end up mostly being gypsum with rockwool backing on wooden frames, ceiling will be the same, floor will either be carpet ( my choice becase i dont think we'll be able to get them to do ceiling damping unless there's a problem ) or Linoleum

Audio Style - at the moment it's just accoustic guitars, electic guitars bass and vocals but we expect to have some drums and keyboards and sax soon. Typcially there would be a good few people on stage. The service is roughly 50:50 music and speech. Volume levels are moderate, not loud anyway. PA system is a 16 ch 1500 watt ( i think ) with 2 dyncachord speakers ( some suggestions of adding a second set of speakers )

Threre will be aprox 200 seats and each will have a soft cushion like covering

Here are my questions:

1) My first question may seem a little odd. I have an idea about turning the stage itself into a bass trap. My plan would be to build the stage and instead of leaving it hollow i would fill or partially fill it with rockwool. I suppose i'd have to leave and opening(s) of specific size somehow - is this stupid idea and if not has anyone any advice for me ( probably not that high - maybe 2 feet - about big enough to hold a regular band - i suppose 5 * 8 metres)

2) is there some kind of guideline as to where to start regarding how much bass trapping i should have in a room of those dimensions - i hope this is not a vague question - the reason i want to know is becase i need somewhere to start whereby i'd have a good chance of getting it right at the construction phase and then add more later only if necessary - I would put traps in all the corners and then my stage trap above it if was worth doing - but maybe i should be telling my pastor that i'd probably need some more traps as well?? I see photos on the net of churches and the seem to have traps on the walls, some of them have tons of them, like nearly half the walls covered

3) I am not really thinking in terms of high/mid absorbtion or diffusion - am i wrong

4) does anyone have any advice for me about stage covering material - i was thinking that i'd want to avoid the hollow wood sound if someone walked over it at all costs - but i read somewhere that it's imperative to have a hard surface to get a natural sound from instruments ( although i dont know if we are at that level as i mentioned earlier )

[gullfo]

the stage should probably be wood on frame with a lot of absorption underneath to dampen and act as a bass trap. alternatively, constructing the stage with concrete then adding wood can reduce the possible resonance. you could build the speakers as soffit mounts into the proscenium and on the back, i'd put some bass traps on each corner with the desk in-between. you could do carpet on the floor although with the seats filled the carpet is unnecessary except on the walkways. you'll likely want something overhead. maybe some tectum tiles which can be painted and will add the necessary overhead absorption and still preserve the energy. same over the stage - maybe hang down the tectum tiles about 16" or so and the lighting below that. in the example shown, the front of the stage is about 1' high in the front and about 16" in the back to provide a very small slope. perhaps contact someone local who has experience building stages as they are really an art form (imho). if you need to extend seating all the way to the back, i'd put the bass traps up overhead in the entire back section but add panels on the bottom of them to preserve the energy levels.

[gullfo]

here's another approach. use the overhead in the "stage" area and the rear for bass trapping. use corner slats for trapping. use polys distributed around for diffusion and bass absorption.

[bobmurphy]

Thanks Glenn for your replies and images - really nice looking room both visually and i imagine it would sound good too.

I must apologies - i think i was a little unclear - the drawing was actually an elevation not a plan - it's the roof that goes up and down like that - ( actually the plan is a 12 * 12 square with one of the walls in a sort of double l stagger
a bit like this ( edit : sorry actually this is not a great diagram but try to ingnore the white bits and if you like ill do a diagram )

--------------¬
---------------+------------

sorry ....
( o dear god this is a record 3rd edit - i think i read your post late last night and got the idea that you thought i had a plan instead of an elevation - from your diagram which i have now PROPERLY LOOKED AT ( big sorry ) it's clear that that's not the case ...... yes that diagram is inspiring too )


so it seems you dont think my stage bass trap is a silly one - i suppose i couldnt see anything wrong with it - i dont know what size openings to leave for the bass to get in though - i put a slot resonator in my studio and i left 5, 10 , 15 mm slots so maybe that ???


my studio is upstairs in my house but they actually screeded a 2in concrete over plywood and i find it pretty good as a solid foundation so i might do something like that maybe ( edit: sorry this reply is a bit all over the place ... i meant for the stage top - i might finish it in concrete .... also i forgot that i meant to say i doubt if there'll be anyone in the area with experience of stage building but im sure it IS an art - still i think i'll be designing it myself and getting my carpenter to build it - do you know of any good websites or books etc on this)



still wondering if it's possible to give a general percentage of a room like that that should be dedicated to bass traps... but from your pictures i can see that the people who built that room put a lot of treatment into it - is it a building you're familiar with ? do you know what it sound like ? .... ok i dont think i've every been this silly on a post i think i need some sleep or coffee i wasnt looking carefully enough at those photos - ( and the software really does make it look like a photo anyway ) thanks again though for your ideas - the room looks great that way - i might make a few changes i think we might need a wider stage with less steps and we might not be able to spare too much room unfortunatly for resonators and diffusers but we were going to do corner traps so i'll definitely get my measuring tape out

thanks again for the ideas

[gullfo]

Hi Bob, i got the elevation bit and created the design accordingly. that room is 100% virtual... but basically the corner traps go floor to ceiling and extend in from the corner 2' (600mm) but angle away from there so it shouldn't be a lot of lost floor space. the stages could be whatever configuration makes sense for your congregation. the polys all around actually should add a significant amount of bass trapping as well as diffusion. using the tectum panels as described will also moderate some of the mid-high frequency range. one of the important aspects of this room is intelligibility so people in the back can hear what is going on up front. you'd probably have to add some scattered absorption on the side walls to reduce the reflections there but not too much. possibly long heavy drapes which are decorative and serve the purpose of being able to change the room response slightly could be useful.

for the stage bass traps, i'd make them as open as possible to let the maximum amount of bass energy to enter and be absorbed.

[FLZapped]

First of all, build the stage to be stiff and massive to avoid resonances in the first place.
Second, small room acoustic principles cannot be directly applied to large rooms. Large room acoustics are not controlled by modes as much as small rooms are.

Finally:
Church acoustics are much different than any other room. You actually WANT a live room. People need to hear themselves in order to properly sing out during service. Therefore, you'll want the minimum amount of absorption as possible and what you do use, will be generally narrow band in nature. Diffusion is the way to go in a church sanctuary. Looking at the plans provided, I'd say there is too much absorption.

There are a couple places better suited to check:

http://www.jdbsound.com/cgi-bin/discus/discus.cgi

http://www.churchmedia.net/forums/acoustics/

[xSpace]

Better suited?

[gullfo]

thanks for joining in. the links are quite useful. i also find the prosoundweb church section to be quite a good read. http://www.prosoundweb.com/church

First of all, build the stage to be stiff and massive to avoid resonances in the first place.
Second, small room acoustic principles cannot be directly applied to large rooms. Large room acoustics are not controlled by modes as much as small rooms are.

my first suggestion was build the stage with concrete and second was to hire a stage building professional having worked in the theater for a number of years, there are various approaches to building stages depending on the desired results - sometimes a wooden stage is used, other times massive steel plates on hydraulics are the answer...

agreed on room size. however this isn't really that big a room (12m x 12m). and given the need to support seating room for 200 people, it will be tight. however those people do provide absorption so that is a consideration.

Church acoustics are much different than any other room. You actually WANT a live room. People need to hear themselves in order to properly sing out during service.

you want a room which preserves and directs the energy but intelligibility will be critical so balancing reverberation versus being able to hear spoken words is always a challenge. many times, using time aligned small monitors placed around the room with a little bit of reverberation meets the need for hearing what's going on up front, in others, more reverberation is desirable because the congregation enjoins in the singing. i'm generally a live space fan so either going with exposed concrete or using the tectum (or other cementitious wood panel products) will help.

Therefore, you'll want the minimum amount of absorption as possible and what you do use, will be generally narrow band in nature. Diffusion is the way to go in a church sanctuary. Looking at the plans provided, I'd say there is too much absorption.

agreed on minimum absorption - which is why absorption was only placed in the corners (space and modes) and the rest is all poly based for diffusion and low end absorption which will keep things from getting muddy. the front wall provide broadband absorption and diffusion for the stage, and the back end walls provide termination of the reverberation with any back end liveliness support from the overhead polys and concrete/tectum panels

[bobmurphy]

Thanks for all the helpful replies and apologies for abandoning the post, but sound treatment had to be put on hold while i tried to keep up with the builders and electricians on other things - things have changed a bit since i was last here - for a start i have ended up doing a whole lot of other stuff on the project and to be honest it's gotten a bit ahead of itself i think - i am always several steps behind the project and there are tons of things that nobody thought of etc etc ........ i dont want to moan or anything i just want to explain that the sound treatment unfortunately looks like it will have to fight to get in the door at all let alone have proper time/money spent on it - ( i recently handed the pastor 10k worth of a budget that had never been considered and the budget was quite low to begin with )

..... with that in mind here are some questions and bits of information and i would really appreciate any comments

The main goal at the moment is to just get very quick estimate on roughly how much diffusion/absorption/trapping to put in because ultimately both real estate on the walls and ceiling and also budget are slightly problematic and i need to be telling the electrician on monday where we want the cables for the wall lights ( see below)

i initially posted here a question about bass traps but i am now wondering if bass traps are necessary in large rooms at all ( though i will probably use the stage as a trap as i cant hurt )?

the main question ( already debated here to a point ) is whether to absorb or to diffuse - i suppose this must depend to a degree on the type of church we are talking about - the church is not a traditional church ( eg congratulation and solo organist )- conversely it's more on the lines of hillong or matt redman (think slightly tamer u2 or crowded house if you're not familiar) and though the music is not incredibly loud i doubt that we want a particularly live room - one site recommended a rt60 at 2000hz of 1.0s for amplified church music and speech - i have calculated ours to be 1.7 unless i do some absorption - the main goal is intelligibility and control-ability of the sound -the last thing we want is people going home with headaches from the "noise" which happened in our last building - ( the current building we are in has a very low rt - i think it's about 0.5 - it's a room used for playing bridge and it suits us fine - carpet floor and acoustic tile suspended ceiling with concrete walls)

the ceiling has already been done and it's done in plasterboard ( in fact all the room is plasterboard except the floor which i am hoping to convince them to carpet) - also there are about 50 down-lighters in the ceiling

the real estate problem on the walls comes from two decisions one to put 3 large windows (right behind the desk ) and 2 large double glass doors in to let in light and also the plan to use wall lights( about 9 of them )

i wonder also about what to do behind the stage - i see the beautiful diffusers in the drawing but there are a few problems with this 1) we want to have a black backdrop behind the stage with white drapes illuminated with colored lights in front of that 2)we don't have the budget to do major carpentry work, certainly not high quality work and materials that would be an art-piece behind the stage 3)we need to conserve floor space because like everything the size needed for the stage was vastly underestimated - i was thinking about putting absorbtion or polys behind the backdrop

the polys seem quite interesting so i would probably use those anywhere i could except that again i will need to work out the balance beteeen diffusion and absorption

i have two large areas to the left and right of the stage with very little in so i can use these for quite a bit and i would like to know the best thing to do in these spaces - the finished product needs to look nice obviously not like i found a space to throw al lot of treatement and stuck it all there - but there;s prob no need to tell anyone here that - anyway the 2 walls left and right of the stage are composed of 2 sections each, an area of aprox 5m wide by 4m tall and then another area of 5m wide but this one slopes at the top from 4m high down to about 2.5m ( in one of these areas is a double patio door and in the other is a single wooden door and a window aprox 1200 by 900

sorry if this post is a bit all over the place any comments are greatly appreciated -i will try to attach my sketchup file to this or else some 2d exports - there are a couple of problems with it though - 1) the small door and window together near the stage are just estimated size and position 2) there are 2 more pillars closer to the stage

thanks again

edit: also meant to mention that i had a bit of time in the room to myself when it was semi slabbed with plasterboard and it sounded ok but there seemed to be a flutter between the tall area to the left of the main door ( as you go in ) and the opposing area near the patio door ( not sure which side or maybe above it ) so i am thinking of putting some kind of floor to ceiling diffuser on that wall ( next to the main door which is marked on the model) - was wondering about the possibility of building a low cost skyline diffuser

[gullfo]

the drapes behind the stage are actually ok because then the treatments can be somewhat ugly but effective. while it's true that big rooms tend to have less LF modal issues, they can also be problematic to balance the reverberation across the frequency range. i'd at least plan on bass trapping behind the stage to get the front end of the room tight and use scattered absorption all around the room to try to get the reverberation under control and keep some diffusion. the polys are an option and can be used over the stage and in the back ceiling plus some mounted on the ceiling. i'd include the scattered absorbers as well to get some balance.

some photos of the space would be helpful.

[bobmurphy]

so would absorption and bass trapping around and over the stage and diffusion throughout the rest of the room be an idea ?

does anyone have a comment as regards the ideal rt60 for the room ? - i have heard varying opinions on that and i am concerned that we get the right level of reverb in the room - i think i've said that the room we're in at the moment has a very low reverb time and that we're happy BUT actually i noticed today in church that the room is pretty dead and i am seeing the point about getting the room live enough so that people feel like they are hearing some reverb when they sing .... however there could be some loud rock style music in the room ( we dont have very loud or rock based worship at the moment but we have a lot of teenagers who are expressing interest in the worship team and we also might guest rock groups ) and so we want to have a room that we can do that kind of thing in too

could anybody suggest whether it's better to go for diffusion or absorption to take care of the flutter echo ?

glen - do you have a link to anywhere that shows construction of large slat diffusers like the ones you drew in case i get to use them anywhere - or even polys i seem to be able to find tons of stuff on absorption and traps but very little on diffusers

[gullfo]

you can use a combination of absorption scattered around to create a diffusive space but it sounds like you already have a reasonably dead space which is not ideal.

in general, an RT60 of 600-750ms would likely be a good target range for your size space but is likely hard to hit due to the low ceiling and the people absorption, carpeting, and the fabric seats. there is also the need for the music and choir / singing to mix well and the speech portions of the service to be clear. this will require a mixture of absorption and diffusion which absorbs a lot at speech levels (frequency) but preserves the wider range for singing and music. you will need a distributed sound system to truly meet your needs but assuming that is a future enhancement, we should focus on the room as much as possible.

do you have the detailed measurements of the space? including the stage and other areas, the doors, windows, lighting, etc so we can work out a reasonable plan.

[bobmurphy]

thanks for the reply but i am sorry i think i may have confused things - the *new* building will be anything but dead rt60 of about 2.6 i think if i dont do anything with it (at the moment it's gypsum nearly everywhere and what's left is concrete and an increasing amount of glass) - when i was talking about noticing the room being dead today i was saying that i see why i wouldnt want to deaden the new room too much because the room we are currently in is very dead and i think it might be discouraging people from singing

the attached sketchup model is based on accurate measurements ( is that ok ) or else i can post something else

i will post some photos of the building tomorrow

[gullfo]

gotcha. for some reason i interpreted you a saying the new room was dead. in that case i'd start with the trapping in the corners (slats perhaps) and polys over the tallest locations and scattered absorption to bring it down to 1000ms or less. I'll take a look at the SU you provided and assume it is accurate.

[bobmurphy]

here's the latest sketup model -


( sorry i couldnt upload it - too big - it's in here https://www.dropbox.com/home/Public "final model2")

it's all pretty accurate except for the 2 door and window scenarios stage right and also the stage and engineer platform is not necessarily going to be exactly like that - also the areas where the 3 roof sections meet is a little more complicated there is a sort of boxing around the steel joists that are there
and finally the ceiling lighting and front of stage lighting is not put in ( ceiling lighting is about 50 down lighters ) everywhere except directly over the stage and the stage lighting has another bar with 4 spots right where the 2 roof sections meet - ( there are also projectors in the ceiling here )

there are some pretty awful features in the room ( ie the 3 colums have to stay and there is lots of glass even behind the engineer's head - i am thinking of making a small shield which would be right behind his head possibly using diffusion or absorption )

i will try to upload photos tomorrow