school music dept. fix

Hi, I am a mentor at a local school that has recently had some redevelopment work in the performing arts area. There are 5 practice rooms adjacent to the main music room and also a control room. The control room is shared and also has video editing gear and lighting dimmers and joins onto a green screen room. The windows are all double glazed but the doors are all single. The practice rooms have been treated with what looks like mdf with holes in it around the top 1100mm and the bottom 1200mm is mdf without holes. The middle section has fabric covered panelling. Basically all the rooms sound very boomy, long reverb time and quite uncomfortable acoustically. We have a budget to fix the rooms but will concentrate initially on the control room and practice room A. Anyway the plan is for me to find some ideas and advice and relay this to the architect. I hope the sketchup file is enough to start things off. Cheers, Scott

I'm trying to open your SKP model, but Sketchup is telling me: "This does not appear to be a SketchUp model". - Stuart -

Not sure what happened there. I've attached another version, bit rough but hopefully it will open.

Hi again, Not sure if the skp file works this time or not but thought I'd add a couple images of the rooms. My thoughts at the moment are that room "C" could be changed into 2 rooms for mixing and recording. The room is 4.7 x 7.7 x 3.1 Maybe not quite big enough? Here are a couple images of the rooms as they are. You can see the mdf on the top and bottom third of the walls. Thanks for any help with this, Cheers, Scott

Maybe you could explain a bit more about what it is that you are trying to do, what your goals are, etc. I would suggest that either "B" or "C" would be best for the control room. "A" appears to not be suitable for that at all, due to the location of that large white "box" in one corner, which I'm assuming is some type of structural support column and can't be moved. The doors and windows in that room also make it very problematic for use as a control room, even if that "box" can be removed. That room might make a decent live room, though,but I can't see it working out as a control room. So your options for control room are basically "B" or "C".

The practice rooms have been treated with what looks like mdf with holes in it around the top 1100mm

Perhaps an attempt to make a perforated panel device? Can you determine the thickness of the MDF, the depth of the air cavity behind it, and the diameter and percent coverage of the holes? We'd need to know that in order to calculate what it is supposed to be doing, but from what you say about the room being "boomy" it certainly doesn't seem to be working very well!

and the bottom 1200mm is mdf without holes.

Perhaps those are membrane traps? That would be unusual for a practice room: Once again, it would be very useful to know how thick that MDF is, and how deep is the air gap behind it, to figure out what frequency it is tuned to.

The middle section has fabric covered panelling.

What type of paneling? Some sort of acoustic panel? If so, how thick is that paneling? Also, what about the floor and ceiling? What is the floor made of (concrete, wood, etc), and is there any type of covering on top of it (carpet, laminate, etc.)?

Basically all the rooms sound very boomy, long reverb time and quite uncomfortable acoustically.

That isn't surprising, since there is no sign of any bass trapping in the photos, and bass trapping is critical for small rooms. But in order to find out just how bad it is, in objective terms, it would be useful if you could download the REW acoustic analyzer program from Home Theater Shack (it is free), run it on your room, and post the resulting data file here for us to analyze and take a look at. Just set up a good quality speaker in the typical location where you set up instruments for practice, and use a good quality mic in the location where a teacher would commonly be conducting / listening while the musicians are playing. It does not need to be very precise: This is just to get a rough idea of what is going on in that room. Do that for the worst-sounding room.

Anyway the plan is for me to find some ideas and advice and relay this to the architect.

To me, it looks like the basic idea would be to take out all of that exisiting "treatment" in the rooms, and install proper treatment, specifically designed to address the specific issues of each room, after measuring and analyzing the actual response. Some close-up photos of the existing "treatment", taken with a better quality camera, would also help to determine if that stuff is any use or not. - Stuart -

Thanks for your reply Stuart, looks like I have my work cut out for me. I am at school tomorrow and will get back to you ASAP with some more updated information and images. Thanks again, Scott

The main goal of this project is to create a learning area that will encourage students to focus on the sound. It’s a music education environment and I think the space should sound fantastic. It’s much more fun to learn an instrument and discover music in a place where it sounds great. It's just not happening here like it should. I’ve spent over 25 years playing music all over Australia and recorded in many great studios. My job here is to bring some of that experience back into the classroom. We have a great rock program here and always have 4 or 5 bands on the go as well as singer/songwriters wanting to record. There is also a drama/dance area adjoining the music area that comprises 2 rooms that can be opened into one and are roughly 25m x 25m each. One has a sprung dance floor and the other is carpet. They also have drapes all around, portable stage and in house pa. This area sounds great! We have recorded live rock bands here acoustic instruments and I’ve mixed at home with excellent results. This room is wired back to the current control room. Also room “B” and “C” are wired to the control room. This is also great for recording school choirs and concert bands. Still need somewhere to mix. Anyway back on track again, the best I can come out with is using room C as a control room. Also getting room B sounding good as a rock band practice/live room. I have attached a better image of the mdf paneling that is in all the rooms. Still not exactly sure what it is but I doubt it can be removed easily. The mdf is 25mm thick and there is no air gap. The fabric covered paneling hallway up the wall is like pin board. The floor is concrete covered with carpet and the ceiling I’m not too sure about. Lots of heaters and lights and things up there. I will update this asap with the results from the REW test. We’re getting a Behringer ECM8000. I have a macbook pro. Hopefully shouldn’t be too difficult. Cheers, Scott

It’s a music education environment and I think the space should sound fantastic. It’s much more fun to learn an instrument and discover music in a place where it sounds great.

Exactly! Yes!!! A man after my own heart. :)

It's just not happening here like it should.

with the latest data and photos you posted, I'm really not surprised. Those rooms must sound terrible! It must be agony to try to teach in there...

I have attached a better image of the mdf paneling that is in all the rooms. Still not exactly sure what it is but I doubt it can be removed easily. The mdf is 25mm thick and there is no air gap.

:shock: Then it is doing nothing at all! Very strange. Perf panel resonators work on the Helmholtz principle, which requires a sealer air cavity behind the panel. The air trapped in the perf panel holes acts as the "slug", vibrating in and out of the hole at the resonant frequency, and the air trapped in the sealed cavity behind acts as the spring. If there is no sealed air cavity, then there is no effect at all: there is no spring, and no way for the air "slugs" to move. So what you have there is just flat bits of wood on the wall with pretty decorative holes in them: they do nothing at all acoustically (except to reflect back all sound). Whoever put those in doesn't have a clue about what they are supposed to do: maybe they saw proper perf panel installed in a real studio somewhere, thought it looked cool, but had no idea how it works... and you ended up inheriting a "cool-looking" but totally useless red wooden "decoration"! To add insult to injury, it is in the worst possible place. Corners are very, very useful for bass trapping, but there is no bass trapping going on there: all that energy is just being reflected back into the room. Muddy "boooomy" sound comes to mind.

I doubt it can be removed easily.

No problem: Just cover it over with absorption. Maybe make yourself some simple panels of 4" OC-703 in wooden frames with cloth over the front and plastic between the cloth and 703. Make several of those, to cover all of the useless decorations. Since they are up near the ceiling, you should angle the panels diagonally across those wall/ceiling corners. The exact angle doesn't matter: 45° is optimum, but any angle that looks good will be fine. Do that all around all of the rooms, wherever that "perf" panel is. Cover it all, entirely. That alone should make a noticeable difference to the room sound. Should help eliminate some of the harsh "boomy" sound. You'll probably need to do more than just that to get the room sounding good, but that will at least take the edge off the ugly sound. Try that, and let us know how it sounds. But do try to measure the room using REW first, so you have an objective point of comparison. Measure both before and after, so you can see the difference, and based on that we can help you figure out what else needs doing.

I will update this asap with the results from the REW test. We’re getting a Behringer ECM8000. I have a macbook pro. Hopefully shouldn’t be too difficult.

You'll also need some type of good quality audio interface to connect the mic to the computer. The ECM8000 is a condenser mic and needs phantom power, so make sure your interface can provide that (most can). - Stuart -

Hi again, I have made some measurements using REW. Hopefully I have made them correctly. I used a ecm8000, A&H zed12, and a RCF322A. I have measured room B, the main rock practice room, room C, and also one of the small practice rooms. The files are located here. http://jetblack.com.au/files/roomB.mdat http://jetblack.com.au/files/roomC.mdat http://jetblack.com.au/files/small_practice_room.mdat Thanks again, Scott

I have made some measurements using REW. Hopefully I have made them correctly.

There's something major wrong with the way you took those readings: all three files are identical, and show nothing useful at all. The peaks are around 180 dB, and if that were the case your room would have collapsed and you'd be a puddle of mush on the floor! (OK, not quite, but that's dozens of times louder than the loudest rock concert ever recorded on plant Earth...). So please go over your procedure, find out what you are doing wrong, and try again. It seems that you are not measuring anything at all from the mic. - Stuart -

I've had another go at it. i hope this looks a little better. To be honest I'm struggling a little with the measuring and rew software. I have bought a sound level meter and measured a drum kit played moderately in room C from 2 meters and it peaked at 107db. Is this normal? The perforated mdf is stuck on with spongy/rubber stuff sort of like double sided tape about 6mm thick. Thanks again, Scott http://jetblack.com.au/files/roomB_2.mdat http://jetblack.com.au/files/roomC_2.mdat

I have bought a sound level meter and measured a drum kit played moderately in room C from 2 meters and it peaked at 107db. Is this normal?

Yes, that is typical. For loud sounds like that, it is best to set your meter to "C" weighting and slow response, to get a more realistic reading. 107 dB is about right for drums played softly to moderately. You'll probably see 115 dB or more for drums played hard. Drums are the loudest instruments of all, and are the hardest to isolate.

To be honest I'm struggling a little with the measuring and rew software.

There's still something wrong. One file shows practically flat response, and is probably the result of calibrating your sound card, while the other file (roomB) shows what looks like major comb-filtering, such as you might get from placing the mic really close to a speaker with a reflective surface next to them both. How are you doing the readings? Connect the mic to your interface, and make sure you select the correct input device on the "Preferences" menu, under the "Soundcard" tab. Then go to "File -> Measure", and make sure you see the bars on the meter jumping up and down as you speak near the mic, while not ,oving at all when you don't speak. If that's not what you see happening on the meters, then something is wrong with your setup. Check it over again. If you do see the meter behaving correctly, then click "check levels". You should hear loud pink noise coming from your speakers: if not, then once again something is wrong with your setup. Check it again. As you hear the pink noise, the meter on the left should show the output level being sent to your speakers, and the two meters on the right (or at least one of them) should show the input level being picked up by your mic. If the level is too low or too high, REW will warn you so that you can adjust it. If you only see results on one meter, then make sure that that is the channel you have selected for input on the "preferences" menu. If everything checks out OK, then click "Star measure", and you'll here a sine wave tone that sweeps up the entire spectrum, rapidly increases in frequency. The progress bar will also advance as the test progresses. If everything works out, then REW will show you the response, or it might also give you a warning if it found an issue with the measurement. Is that how you are doing it? Do you hear the pink noise and sine sweep? - Stuart -

Trying again... http://jetblack.com.au/files/RoomB_3.mdat http://jetblack.com.au/files/RoomC_3.mdat

Sorry to have to bump this but summer break is nearly over and I'm yet to make much headway...it's been busy. I wonder if I have made the measurements correctly this time? My only hope at this point is to have at least one good sounding room. That would be room B. I have had thoughts of making portable bass traps. This get me around a few regulations and could also be handy in the future. Any advice is greatly appreciated. Scott

Hey Scott, sorry about the lack of response! Looks like your post slipped though the cracks... Anyway, the good news is that you took the readings correctly this time: that is all good and valid data, for both rooms. The bad news is that room "C" is a mess! That's going to need a lot of treatment to make it usable. The good news is that room "B" is much better, and I think it can be tamed without too much hassle. This is a bit surprising, as I was expecting "C" to be better, but REW doesn't lie! I'm really busy right now on a couple of other projects, but I'll try to take a more detailed look at this later, and see what I can come up with, in terms of recommendations on how to treat it. Meanwhile, have there been any changes to the rooms since you posted those photos? Also, do you have more photos and accurate dimensions of both rooms, including positions and heights of doors, windows, electrical outlets, lights, etc? Maybe you could update the SKP that you posted before, and confirm all those dimensions? - Stuart -

Thanks Stuart, I have attached a new skp although basically the same as before. Thanks for your time with this. Cheers, Scott

Rough idea for room "B" as a rehearsal room: Combination of easy-to-build absorbers and poly-diffusers. Should keep the room bright but still controlled and balanced. The devices can all be built very simply and inexpensively, with common building materials: 2x4 (or even 1x4), 4" OC-703 panels, plywood. Screwed and glued. Fabric finish for the absorbers (stapled). If there's a carpentry shop at the school, they could easily build those in a few hours. Dimensions are not critical, so you can adjust those an inch or two as needed, but placement in the room is important. I would also do a couple of clouds on the ceiling, like the absorbers but bigger, and hung from chains, at angles. That should make the room somewhat better for what you want! :) You could do something similar for room "C", if that is also going to be a rehearsal space. But it would be different of you want to use that as a control room. Hope that helps! - Stuart -

Thanks so much Stuart! This looks great and I'm looking forward to showing the staff tomorrow. I have made absorbers before but I'm not sure of the construction of the poly diffusers. Are there plans anywhere online? I've had a look and can't find any. Once again thanks. I'm looking forward to hearing the results. Cheers, Scott

Poly's are very simple to make: it is basically just a sheet of something flexible, such as plywood, bent to a natural curved shape and nailed to a backing of some type, such as another sheet of plywood, or a wooden frame. I'll see if I can fins something on that. - Stuart -

OK, I found some stuff on poly's, including how to make them: http://forum.studiotips.com/viewtopic.php?p=45486 http://www.gearslutz.com/board/bass-tra ... polys.html http://gikacoustics.com/diffusion-by-jeff-hedback/ http://www.gearslutz.com/board/attachme ... -28-1-.jpg http://www.gearslutz.com/board/attachme ... l-test.jpg :) - Stuart -