Rehearsal/recording space project-design solutions?(updated)

Edit: I needed to simplify this post a lot and change the content as well. Basically we have a very challenging rehearsal space in the context of acoustics, and I'm looking for ideas to improve the sound quality within it. First I thought of going down the RWAR (room within a room) route, but that idea got shot down rather completely on another forum, so I guess it's back to square one (again :lol: ). The current problem exists on a very wide frequency range, with sound bouncing of from the various hard surfaces making the sonic quality extremely poor. So here are some sketchup pics I did in order to demonstrate the room: Some additional info: - The walls are concrete between 15cm-48cm in thickness, the brick wall is 13cm thick. - The seemingly random measurement of 70cm from the ceiling marks the position of the lowest lighting, but they're adjustable. - There's quite a bit of piping above the lighting, lowest being about 50cm from the ceiling - A pathway must be preserved to the doorways - The ''balcony'' is some kind of metal and cannot be disassembled - The upper ''box'' behind and left of the stairs marks a very small entry space, with a heavy metal door to another set of stairs (the space is quite deep to the ground). The lower ''box'' underneath is simply a little space. The objective At first I dreamed of dropping some decibels, since there's a sauna section located in the same building and some of the sauna goers get distracted by the noise, but apparently that's a very time & money consuming process. The walls are of thick concrete, so either it's the piping or impact transmission- or both- that bleeds the sound to the sauna section located above and to the side of the brick wall. So in case soundproofing is a complete bust, then the only thing I'm looking to achieve is a pleasant sound in the room. The frequency response doesn't need to be ''studio flat'', since the space won't be used for mixing (at least not according to current plan), but you know, recordable and nice nonetheless. The problem areas - The ceiling and it's height. I've mulled over hangers and suspended ceiling and whatnot, but frankly I don't what would be the best solution. Also the height of corner traps would prove to be problematic, but I guess there's no harm in assembling eg. two on top of each other? - The metal balcony. First of all I must admit my ignorance in asking whether it's even significant in the context of acoustic? There's quite a bit of space left under and above it, and I feel like something should be done about it. I have this mental image of sound waves bouncing of from the wall under the balcony to the floor and to the bottom of the balcony until eternity. :lol: Budget I've thought of using something in the range of €400-€500, but it's a balancing act between the benefit and the cost. So it's not set in stone, but if the figure gets close to €1000 or something, then it'd be out of question (unless it'd get me something mind blowing :P ). I already have 20m2 of 100mm thick rockwool and ~17 meters of cloth. All suggestions, advice and ideas are extremely welcome, so fire away in case you got some. :D

I know bumping is not a welcome action on a forum, but I think the updated situation justifies it. :P

The room dimensions suggest standing waves at under 30 Hz, only the ceiling-floor mode is higher. So I would start treating the ceiling and turn it into a bass trap. I wouldn't bother about the lower modes as you use the room as a rehearsal space. And of course you have to do some treatment of the walls to tame reflections. The balcony could turn out to be a problem, but I would have to see measurements to pin point that. I could imagine experimenting with placement of sound sources and player positions makes this a useful room for practicing.

bert Stoltenborg wrote:

The room dimensions suggest standing waves at under 30 Hz, only the ceiling-floor mode is higher. So I would start treating the ceiling and turn it into a bass trap. I wouldn't bother about the lower modes as you use the room as a rehearsal space. And of course you have to do some treatment of the walls to tame reflections. The balcony could turn out to be a problem, but I would have to see measurements to pin point that. I could imagine experimenting with placement of sound sources and player positions makes this a useful room for practicing.

First of all, thanks a lot for the advice, and here's the measurements of the balcony: 1,21m in ''depth'' or width if you will, the longer side is 7,32m and the shorter one 6,01m. It's about 1,5cm thick (this is from memory, I probably should find out an accurate measurement?). The side facing to the ''inside'' of the room has this kind of a narrow front (in search of a better word) that exceeds the thickness of the material in general. The height from floor to the balcony's bottom is generally 1,6m, but where the front is, it's 1,47m. ''The front'' is only about 0,5cm thick.

I'm sorry for not being clear. With measurements I mean acoustic measurements, to see how the room responds on the balcony :mrgreen: It's faily hard to predict these kind of situations as everything is strongly dependent on placement.

^^ Ah, I did think it was a fairly odd thing to ask! :mrgreen: But there's a plan in my head, and I was wondering what you people think about it: a) Hanging DIY acoustic panels from the ceiling in a way that's reminiscent of a suspended ceiling. The idea would be to hang them to the level of the top end of the balcony- covering the area left between the balcony and the two other walls. If this is something you'd recommend, how thick of a layer of rockwool I should use? Is there a danger of making the sound too ''dead'' with this treatment alone? The easiest measures of thickness to achieve would be in the increments of 100mm, since that's the thickness of a single slab of wool I already have + plan to get more. The air resistivity of the wool is 8333 Pa*s/m2. Ps. Though if a different mineral wool is recommended for this, I could use the existing wool for the superchunks & such, and buy a specific kind for the ceiling panels. b) To treat the reflections I've been mulling between molton and acoustic panels. With molton it would be easy and relatively cost effective to cover large areas of wall, but the absorbing qualities are rather poor. However, with the ceiling treatment I have in mind, would acoustic panels be an overkill? Or perhaps few of them just enough? c) Superchunks to the corners. As in the corners formed by the new ''ceiling'' and the area left inside it.

Konsta wrote:

^^ Ah, I did think it was a fairly odd thing to ask! :mrgreen: But there's a plan in my head, and I was wondering what you people think about it: a) Hanging DIY acoustic panels from the ceiling in a way that's reminiscent of a suspended ceiling. The idea would be to hang them to the level of the top end of the balcony- covering the area left between the balcony and the two other walls. If this is something you'd recommend, how thick of a layer of rockwool I should use? Is there a danger of making the sound too ''dead'' with this treatment alone? The easiest measures of thickness to achieve would be in the increments of 100mm, since that's the thickness of a single slab of wool I already have + plan to get more. The air resistivity of the wool is 8333 Pa*s/m2. Ps. Though if a different mineral wool is recommended for this, I could use the existing wool for the superchunks & such, and buy a specific kind for the ceiling panels. b) To treat the reflections I've been mulling between molton and acoustic panels. With molton it would be easy and relatively cost effective to cover large areas of wall, but the absorbing qualities are rather poor. However, with the ceiling treatment I have in mind, would acoustic panels be an overkill? Or perhaps few of them just enough? c) Superchunks to the corners. As in the corners formed by the new ''ceiling'' and the area left inside it.

A good ceiling treatment is about 40 cm thick. If you're using clouds, don't hang 'm to low, or they don't behave like you want. How heavy is your wool? Is it glass- or Rockwool? I wouldn't worry about chunks, in your case. The ceiling is a bass trap, and the other dimensions are so large they probably don't need traps. You can place 'm later anyways. You don't make things to dead, and even if you did this can easely be cured with some reflective materials being placed over the absorption. Panels for reflection control are about 10 cm thick. Molton works not very broadbanded, risking non-linearity in the traetment. I would always go for wool.

Clouds should be 400mm thick?! Seriously? Oh wow, I've got a lot to learn. :shock: And how low is too low approx? The wool I'm using is rockwool. I tend not to pay attention to the density, or weight if you will, since thickness + air resistivity (though density has a loose correlation to air resistivity, but it's non-linear so I don't trust that) gets such an accurate results via the paradigm by Delany, Bazley & Miki when compared to actual acoustic measuring results. It's generally not exactly the same as the actual measurement, but very very close, so thus the air resistivity instead of density. I can try to find out the density though, if you think it's necessary. :) Ah, adding reflective material. So simple, yet so effective. How did I not think of that? I'll go with wool for the walls too. Thank you very much again!

I am aiming at ceiling treatment that will act as a bass trap. A cloud to tame reflections can be thinner, like the panels on a wall. If you have limited space, you use corners for bass traps because this is most effective. (In fact wool is an absorber working best in a velocity maximum of air particles, but in the middle of a room wool is a bit annoying :mrgreen:. Absorption working on pressure max (when the air stands still) like Helmholz and 1/4 wavelength devices are best on boundaries). In your case a total treated ceiling (like they do in offices) is even better than only corner traps, IMHO. For Rockwool there is a regression formula relating density and air resistivity.

The ceiling treatment acting as a bass trap... How low is too low for it's position? I did some calculations, and they'd seem to suggest that an air gap up to 80cm is acceptable if the wool (the one I have, 8333 pa*s/m2) is 30cm or more in thickness. But I'm not sure how much empirical data there is for such a big air gap, and whether the formula can be trusted in under such circumstances. Anyhow, here's graphs on 30cm and 40cm thick rockwool + 80cm air gap: Does that look correct to you? And is it good enough for the ceiling treatment?

How do you come up with this?

bert Stoltenborg wrote:

How do you come up with this?

I like to use the revised model by Miki, based on the work of Delany & Bazley. The other one that gets accurate results compared to actual, tested results, is the Allard & Champoux model. I've been comparing results published by manufacturers & other studies to the predicted results by the two formulae, and they're surprisingly accurate. However, since the formula is largely based on empirical data, it's not that surprising. Edit: Vast majority of data published by manufacturers only has value down to about 120Hz, so I haven't been able to compare values under that frequency. I can't see a reason why the formula wouldn't work properly under 120Hz, though. If you're interested in further reading about the formulae and their differences, I'd start here: http://apmr.matelys.com/PropagationModels/MotionlessSkeleton/DelanyBazleyModel.html And here's a browser version of the formulae, in form of a calculator (instead of the excel based one): http://www.stanleyhallstudios.co.uk/pacalc/ As you can see, there's not too many variables, eg. fiber diameter is missing, but it works as a very good guideline IMO. However, if the trap is angled, then it's not very accurate. Luckily that's not the case here. :mrgreen:

I know these models. I like measurement data. You're right there is not much data about frequencies below 125 Hz. But if you look here http://www.bobgolds.com/AbsorptionCoefficients.htm you see 15 cm of wool already provides beter absorption then your way thicker sample. Extrapolating these data suggest more absorption than your models shows.

bert Stoltenborg wrote:

I know these models. I like measurement data. You're right there is not much data about frequencies below 125 Hz. But if you look here http://www.bobgolds.com/AbsorptionCoefficients.htm you see 15 cm of wool already provides beter absorption then your way thicker sample. Extrapolating these data suggest more absorption than your models shows.

But there's no data for 15cm of rockwool there? I also think the air gap might explain the difference, since at least according to the model, the 80cm air gap causes a dip in absorption between 100Hz and 200Hz, but the absorption is quite a bit better from ~70Hz downwards: And this is test data provided by the manufacturer: It's not exactly the same wool as I have, but it's from the same manufacturer and the air flow resisitivity is very close. Do you think that's good enough to use as ceiling bass trap material? Edit: Oops, there's a typo in the graph! The air gap isn't 800m, it's 800mm. :mrgreen:

I know in Finland you have more space than we here in Holland, but 800 meters seemed a bit large :mrgreen: I think you're fine with this wool. Glaswool vs Rockwool doesn't make a world of a difference.

Thank you very much for the advice! I was really at lost what to do with the space, but now I'm far more confident in starting the acoustic treatment. I'll start with the ceiling bass trap(s), and proceed to taming the reflections after that. :D