Acoustic Treatment in mixing and recording room.

[Tonato17]

Hi,

I have spent the last months reading the forum, watching videos about acoustics, reading books about acoustics, and understanding as much as I could about acoustics. I definitely understand a lot more than before, but I am awarethat I am starting this journey.

Before I continue with the thread, I would like to thank you guys for the invaluable help you provide!!

I am a musician and I live in London. I have sounpdroofed a room for the purposes of mixing and recording my music. This room is on a ground floor. My aim is to produce and record my music in here. I want to feel that I have no limitations apart from my own ability to produce/record/mix music to high quality standards., So my aim is to be able to produce, record and mix music professionally in this room. I hope I can achieve this with the acoustics of my room.

For the soundproofing, we built a room within a room: We added two layers of plasterboard to the original room, attaching 60 Kg m3 to the walls and ceiling. Then we built a wooden frame with an air gap, filled the frame with 60Kg m3 rockwool and closed it with two layers of plasterboard with Tecsound in between each layer. I must say that I am very pleased with the soundproofing, it works really good.

DIMENSIONS OF THE ROOM: As the room is not a perfect rectangule please see the diagram for a detail measurement of the room, but overall the room is:
Lenght of longer wall: 4.30 m
Lenght of shorter wall:3.60 m
Width:2.44 m
Ceiling: 2.20 m

I am now in the process of treating the room acoustically.
I have downloaded REW and I bought a behringer ECM8000 microphone. At the moment I am using an M-AUDIO Fast Track C600 for the measurements with REW

I have taken measurements of the room. I don't think I have correctly calibrated the sound card with REW and SPL meters. I don't have a sound level meter with me at the moment, I'm in the process of buying one (still researching which one to buy)
It might seem easy to do but I am stuck in the calibration process for the REW. I am uploading the measurements I did, hopefully they will help to understand the acoustics of my room and will show if the measurements were done correctly or they need to be re done/re calbirated.
The measurements I took were done in 3 different heights (low, middle and high part) following this diagram:
1 2 3
4 5 6
7 8 9

So for example M5 would be the middle of the room at listening height. The room is not fully empty. It would be very difficult to empty it, If I really have to do so, I want to know all the measurements are being taken correctly.

I have many questions, in particular how to calibrate the soundcard/microphone/spl meters to take trusty measurements with REW.
Any advice of which Sound level meter to buy would be great as I couldnt find RadioSack in London.

Many thanks and I look forward to hearing from you!
Toni

https://www.dropbox.com/s/ux4lv2v6tijny ... .mdat?dl=0

[Soundman2020]

Hi there Toni, And Welcome to the forum!

For the soundproofing, we built a room within a room: We added two layers of plasterboard to the original room, ...

How was the original room built? What materials / layers / sequence? Assuming that it already had typical stud-framed walls with drywall ("plasterboard") on both sides, what you did might have created a three-leaf system... Have you tested the isolation across the entire spectrum, down to low frequencies? 3-leaf systems provide good isolation for mid and high frequencies, but poor isolation for low frequencies, around the MSM resonance of the wall system and roughly an octave either side.

attaching 60 Kg m3 to the walls and ceiling.

I assume that you meant to say something like "... attaching 60 Kg m3 MINERAL WOOL INSULATION to the walls and ceiling....". Correct?

Lenght of longer wall: 4.30 m ... Lenght of shorter wall:3.60 m ... Width:2.44 m ... Ceiling: 2.20 m

I'm wondering why you chose those dimensions.... did you check that with a room mode calculator? You have a problem: the length is almost exactly twice the height (there's only 2% difference), so all your axial modes and tangential modes related to those two dimensions will line up almost perfectly at the same frequencies.

I don't have a sound level meter with me at the moment, I'm in the process of buying one (still researching which one to buy)

A decent one will cost you around US$ 100. Avoid the cheap Chinese junk toys that sell for under US$ 50: no use at all. Extech is a good brand. Galaxy is decent too. You need one that has both "A" and "C" weighting, and also both "Fast" and "Slow" integration settings.

I have taken measurements of the room. I don't think I have correctly calibrated the sound card with REW and SPL meters

Right! According to the data in your MDAT file, you did the tests at an average level of about 30 dBC. Most people would consider a level of 35 dBC to be "absolute silence", or at least "extremely quiet", "barely audible". I doubt that you actually did the tests at that level, so calibration must be the culprit.

And considering that the data set shows "No mic calibration" and "No soundcard calibration", it seems that you didn't calibrate correctly at all.

The measurements I took were done in 3 different heights (low, middle and high part) following this diagram:

There's no real need to do that. The only important location for room behavior is at the mix position, at the client couch, and perhaps in a couple of other spots. The variation in your measurements is much larger than I would expect, so I'm assuming you had the mic positions very widely separated, by at least a meter.

So first you need to set up your room correctly, with the speakers and mix position in the correct locations, angles and orientations for that room, then you need to set the gain structure correctly on your entire system, from end to end, such that it produces 80 dBC from each speaker by itself when playing the REW full-spectrum pink noise signal, which implies that you will automatically get 86 dBC with both speakers on. Then you need to set up your measurement mic exactly at the mix position, with the tip of the mid in the middle of the spot where your head will be, and the mic facing forwards but angled upwards at an angle of about 60°. Then you need to calibrate REW with that setup, including both soundcard calibration and mic calibration, as well as actual SPL calibration, then you need to run three tests: one with just the left speaker on, one with just the right speaker on, and one with both speakers on.

I have many questions, in particular how to calibrate the soundcard/microphone/spl meters to take trusty measurements with REW.

The procedure for calibrating the soundcard is explained in the REW manual. You will need to get the mic calibration file from the manufacturer of your mic. And the rest of the REW calibration procedure is something I can send you if you are interested: PM me.

One other thing: the bookcase shown at the back of your room will have to come out: that's where you'll need your bass trapping.

- Stuart -

[Tonato17]

Many thanks Stuart!! I'm sorry it took me a while to reply, I couldn’t come much to the studio last week, been very busy with work. But I got an SPL meter (Extech 407730), calibrated the sound card properly and took some measurements. Before going through that, I will answer the questions regarding the soundproofing.

How was the original room built? What materials / layers / sequence? Assuming that it already had typical stud-framed walls with drywall ("plasterboard") on both sides, what you did might have created a three-leaf system... Have you tested the isolation across the entire spectrum, down to low frequencies? 3-leaf systems provide good isolation for mid and high frequencies, but poor isolation for low frequencies, around the MSM resonance of the wall system and roughly an octave either side.

The room is on the ground floor in a complex of industrial units. Originally, there was just a layer of plywood (around 30mm thick) for each wall, apart from the front wall (where the mixing desk will be, opposite the door) which is a brick wall and leads to the street. (Attached are pictures of the process and a diagram explaining what is next to each wall of the room.)

The plan was to build a two leaf, double wall system with layers of acoustic plasterboards (15mm) on each leaf. Mass – air – mass

The first part consisted in sealing all gaps and perimeters of the room with acoustic sealant. Then to add three layers of plasterboard to each wall/ceiling. We used green glue for each layer and tecsound 50 in the left and back walls. For the back wall (thick brickwall that leads to the street) we left it as it was. Then we added rock wool 60 kg m3 to the whole perimeter...each wall and ceiling, including brickwall.

Next we built a wooden frame around the room, with an air gap of 25mm from current boundaries, not touching it in any position. That 25mm is the air gap between walls and ceiling. The framework was filled with rock wool 60 Kg m3 and covered with two layers of plasterboard.

For the doors a friend gave me two professional music studio doors, very heavy and thick. We used those two doors...plus the original door! I think maybe that was a mistake. Maybe we should have used one of the doors as the outer door (which would have involved cutting one of the heavy doors to match the size of the original door and replace the original. That would have also involved reinforcing the door frame to handle the weight of the heavy door) and use the second door for the inner room.
Instead we added mass to the original door (Thick layers of plywood and Tecsound and we also used the two studio doors. The frame for each of both doors had to be very strong and thick to handle the weight. Those two doors with its frames are the 70 mm that comes inside the studio at the left.

Lenght of longer wall: 4.30 m ... Lenght of shorter wall:3.60 m ... Width:2.44 m ... Ceiling: 2.20 m. I'm wondering why you chose those dimensions.... did you check that with a room mode calculator? You have a problem: the length is almost exactly twice the height (there's only 2% difference), so all your axial modes and tangential modes related to those two dimensions will line up almost perfectly at the same frequencies.

I didn’t check much at that moment to be honest. I didn't know much about it and I was so concerned about maximising the balance between soundproofing/isolation and space that didn’t check much.

One other thing: the bookcase shown at the back of your room will have to come out: that's where you'll need your bass trapping.

I was thinking that, the 70 cm corner could be a big bass trap. I want to prioritise the sound quality of the room and then build the rest of the room according to that.

So first you need to set up your room correctly, with the speakers and mix position in the correct locations, angles and orientations for that room, then you need to set the gain structure correctly on your entire system, from end to end, such that it produces 80 dBC from each speaker by itself when playing the REW full-spectrum pink noise signal, which implies that you will automatically get 86 dBC with both speakers on. Then you need to set up your measurement mic exactly at the mix position, with the tip of the mid in the middle of the spot where your head will be, and the mic facing forwards but angled upwards at an angle of about 60°. Then you need to calibrate REW with that setup, including both soundcard calibration and mic calibration, as well as actual SPL calibration, then you need to run three tests: one with just the left speaker on, one with just the right speaker on, and one with both speakers on.

I calibrated the sound card and SPL meter with the Extech SPL meter. For the microphone I downloaded a calibration file.

What I think I didn’t set correctly is the listening spot, the distance between the speakers and walls, and speakers and microphone, which I believe is crucial as that is the the exact point to be considered. I wasn’t sure on how to place the speakers and the microphone correctly, and also, where to consider the measuring point on the speakers. The room wasn’t empty, that bookshelf has some books and there’s some stuff in that corner at the back.

For the speakers and microphone distances I aimed for an equilateral triangle, placing the speakers very close to the back walls, and at around 30 cm from the left and right walls and 120 cm from the floor. Which gave me 90 cm between speakers and speaker to microphone.

Something in reference to the SPL calibration. I used the pink noise speaker calibration signal. The Extech was set to C and slow. It measures 84 DB for both speakers when each of them measured 80 DB separately. I think it must be related to an incorrect placement of the speakers and microphone.

I took those three measurements. I think they are much more accurate than the first ones, in terms of REW calibrations and mic placement.
Emptying the room would mean a whole day job, as it would also mean re filling it, and moving heavy gear. I could do it if needed (I am happy to do it if that will give a more accurate and transparent response on the room) but before doing it I want to be sure I am measuring everything correctly, to do it only once.

The speaker stands are generic stands, not heavy by any means.

Attached are the new REW file with the new measurements.

Once more, many thanks for all the incredible help and advice!! I feel I am moving in the right direction with the info and advice I have read and received from this forum.

I want to complete the job to the highest possible standard. If that means doing the panels myself, or taking it a little bit longer just to do it right, I am up for that.


https://dl.dropboxusercontent.com/u/702 ... ATION.mdat
https://dl.dropboxusercontent.com/u/702 ... nsions.skp

[Soundman2020]

Originally, there was just a layer of plywood (around 30mm thick) for each wall,

OK, great, but what is beyond that? What's the entire sequence, from the rooms on the other side of your walls? You say that there was already plywood on there, implying that there is some structure behind that which holds the plywood up! What is that structure? Wood framing? Metal framing? Magical incantations? Assuming it is some type of framing, that also implies there is something else attached to the other side of the framing: Drywall (plasterboard)? Plywood? MDF? OSB? Stucco? The cast-off shells of gnomes, fairies, pixies and elves?

I'm assuming here, but if you have a stud framed wall with drywall on the far side and plywood on your side, then you already have a two leaf wall! Anything additional you put in front of that will make it either a three-leaf wall, with the resulting potential penalty in low frequency isolation, or even worse, a four-leaf wall, with the even larger reduction in isolation.

The plan was to build a two leaf, double wall system with layers of acoustic plasterboards (15mm) on each leaf. Mass – air – mass

Not if you already have two leaves in place! In that case, adding two MORE leaves, will result in a four-leaf system: Mass - Air - Mass - Air - Mass - Air - Mass.

In simple, visual terms, you started out with the situation on the left or second-from-left in the diagram below:

2-leaf-3-leaf-classic-walls-diagram-MSM-walls.gif

In either case, you had a typical house wall, with roughly 30 dB of isolation (Yeah, the labels are in STC numbers, not dB, unfortunately, so they are not an accurate indicator of isolation, but they still serve admirably for this purpose).

So let's say you starter out with the second situation: A stud framed wall with sheathing on each side. You then built a second stud-framed wall next to that, also with sheathing on both sides, expecting that you would get a massive boost in isolation. But since you created a four-leaf system, with the notoriously poor low-frequency isolation that it provides, all that you got was the situation in the third diagram, labeled "STC-40". In real, world terms, your isolation in creased by maybe 3 to 6 dB: You get STC-40, instead of the STC-36 that you already had. A lot of work, and money, for very little return.

If you would have built your new wall with only ONE leaf on it, instead of the two you have, then you would have gotten the situation depicted in the fourth diagram: an increase of 14 STC points, instead of just 4! That's huge. Probably around 10 to 16 dB, in real-world terms. In other words, you would have produces a three-leaf system, which is still not good, but still far better than a four-leaf. By doing that you would be leaving out one quarter of the mass, and getting an improvement of about double the isolation, subjectively. This is not intuitive at all, but it is, in fact, the way sound behaves in resonant systems.

And if you would have first taken off the plywood from the existing wall before building the new wall, then you would have the situation in the fifth diagram, labeled STC-57, which is a true two-leaf system, thus providing optimal isolation for the least use of materials, and the least cost. That one shows a 21 point jump in STC rating, with respect to the original wall, instead of the 4 you actually get with the third diagram. In real world terms, that's probably around 18 to 23 dB increase in isolation. In other words, that wall is about four times better, subjectively than a four leaf wall, even though it only has half the mass! Not intuitive, not "logical", but a clear demonstration of the power of resonant systems. 50% reduction in mass, produces a 200% increase in isolation.

Finally, if you would have used the layers of mass that you took out of those other two leaves, to beef up the only two leaves that you need, then the result would have been yet another jump in isolation: Probably about 6 dB, give or take. For a total increase of around 25 to 30 dB, with respect to the original wall. Instead of 3 or 4.

The first part consisted in sealing all gaps and perimeters of the room with acoustic sealant.

Then to add three layers of plasterboard to each wall/ceiling. We used green glue for each layer

That sounds suspiciously like you used the Green Glue as though it were an adhesive? Is that it? Or did you also nail through the drywall into the studs, in the normal way?

We used green glue for each layer and tecsound 50 in the left and back walls.

Not sure I understand? Why would you use both, and how would you even do that? If you already used "green glue for each layer", then where would you put the Tecsound 50 membrane? And why would you even do that? Do you have accesses to some study done in a reputable acoustic laboratory that shows how such a "sandwich" performs?¡ How can two products that essentially do the same thing (constrained layer damping) work together, when neither is being used as designed? Personally, I would expect that combining a visco-elastc polymer that never hardens with a with visco-elastic membrane, would not do anything useful, and would likely degrade the performance...

For the back wall (thick brickwall that leads to the street) we left it as it was.

You DID paint it with a masonry sealant, right? Brick and mortar are very porous. Without that sealant, you lose a lot of isolation...

... built a wooden frame around the room, with an air gap of 25mm from current boundaries. That 25mm is the air gap between walls and ceiling.

No it is not: Assuming you used standard 2x4 wood framing, then your air gap is 114mm. THe depth of standard studs is 89mm, plus the distance from the face of that framing to the face of the final layer of drywall that you added to the original wall (25mm). So you have an air gap of 114 mm.

The framework was filled with rock wool 60 Kg m3

Just checking: So you have filled the entire air cavity with mineral wool, to a total thickness of 114 mm? In other words, the 89mm between the framing members, plus the 25mm up against the drywall that you put in the original wall?

We used those two doors...plus the original door! I think maybe that was a mistake.

OK, now this is a myster, for sure! How on earth can you open the middle door???? And what on earth did you attach it to???? You have one door on the original outer leaf, firmly attached to the outer-leaf framing, that door opens outwards (away form the studio). Then you have your second door on the inner-leaf, firmly attached to the inner-leaf framing, and that one opens inwards (into the studio). So how did you manage to get a third door in between those, and how can it possibly even open? I'm intrigued....

(and yes, assuming that you did managed to do that in some magical way, it was a mistake, since it creates a three-leaf system...)

Instead we added mass to the original door

"Original door"???? What "original door"???? You didn't mention that. So now you have FOUR doors in there? Another four-leaf system? And once again: what did you attach the other two doors to, and how in heaven's name could you even open them! Pictures please! Either you are not explaining at all well what you really did, or you have worked construction magic by hanging doors in places where they cannot possibly fit, and maing them open into spaces that are much smaller than the size of the door... Maybe your studio is called the Tardis, and the doorways are "bigger on the inside"?

I didn’t check much at that moment to be honest. I didn't know much about it and I was so concerned about maximising the balance between soundproofing/isolation and space that didn’t check much.

So you built a studio without first checking if it can even work as a studio? Ummm.... You should probably read up on room modes, standing waves, SBIR, comb filtering, flutter echo, reflections, reverberation, and such-like BEFORE you start treating the room, because you WILL need to take those into account for the treatment, seeing that you did not do so for the original design!

I was thinking that, the 70 cm corner could be a big bass trap.

Yes it can be, but it cannot also be a bookcase! Either it cam be a bookcase, or it can be a bass trap, but it cannot be both. If you want it to be a bass trap, then the bookcase has to come out.

I want to prioritise the sound quality of the room and then build the rest of the room according to that

. Start by downloading a copy of the ITU document BS.1116-2, and read through that, to understand what your final goals must be for the room acoustics, in terms of layout, frequency response, modal response, decay rates, etc. Then read "Master Handbook of Acoustics" by F. Alton Everest (that's sort of the Bible for acoustics) to find out how the theory behind how to do all of that.

What I think I didn’t set correctly is the listening spot, the distance between the speakers and walls, and speakers and microphone, which I believe is crucial as that is the the exact point to be considered. I wasn’t sure on how to place the speakers and the microphone correctly, and also, where to consider the measuring point on the speakers

Speakers go on stands: Very heavy, massive stands, behind the desk, tight up against the front wall, except for a gap of 100mm, where you will need to insert a panel of OC-703. The height of the stands much be such that the acoustic axis of your speakers is 120cm above the floor (or perhaps a little higher, under certain circumstances. Check with the manufacturer of your speakers to find out where the acoustic axis is located on the front baffle. For a 2-way speaker, it will be on the imaginary line joining the center of the woofer to the center of the tweeter, and much closer to the tweeter, but NOT at the center of the tweeter.

Your speakers in your room need be positioned 67cm from the side walls (meaning they will be 110 cm apart. Your mix position (location of your ears, and therefore also of your mic) will be about 155 cm from the front wall. Set up the speakers so they are aimed at a point 30cm behind your ears, in other words 185 cm from the front wall. Adjust the angles of the speakers such that the acoustic axis of both is aimed at that point. Set up a vertical pole (eg, mic stand) at that spot, and aim both speakers at it.

That's the theoretical optimal layout, but it should be possible to improve on it, with careful adjustments.

Now set up your measurement mic so that it is in the center of where your head will be, pointing forwards (between the speakers) but tilted up at an angle of about 60°. Calibrate REW like that, at 80 dBC for each individual speaker by itself, which implies that the level will automatically be 86 dBC with both speakers on. Do three REW tests like that: One with just the Left speaker, one with just the Right speaker, and one with both. Do not adjust anything in between tests. Leave the room when you run the tests (use "Star delay".

For the speakers and microphone distances I aimed for an equilateral triangle,

That setup is still perpetuated all over the place, but is incorrect. It has the speakers aimed at your eyeballs, bit your ears.... It only works for people who have had their ears swapped with their eyes, surgically...

around 30 cm from the left and right walls and 120 cm from the floor. Which gave me 90 cm between speakers

That makes no sense! You say the room is 244 cm wide, but your numbers add up to 150 cm! LEFT WALL - 30 cm - LEFT SPEAKER - 90 cm - RIGHT SPEAKER - 30 cm - RIGHT WALL = 150 cm. So what happened to the other 94 cm???? Either the room is not actually 244 wide (in which case all of the layout figures I gave you above are no use), or there's an error in your numbers.

It measures 84 DB for both speakers when each of them measured 80 DB separately. I think it must be related to an incorrect placement of the speakers and microphone.

There's something wrong there. If you have coherent sound playing through two sound sources, then both of them together will give you exactly 86 dBC if each of them individually is giving 80 dBC. The only reasons that you'd get less than 86 is due to setup problems, speaker problems (not in phase), or signal chain problems (EQ, phase, dynamics, delay, etc. applied when they should not be).

Attachments

I just noticed that there's a pole in front of the bookcase... What is that? It will have to be removed, along with the bookcase.

Attached are the new REW file with the new measurements.

You have two "L+R" measurements in there, but they are different. What happened in between? What did you change?

There's also a very large difference between the individual L and R measurements, implying that the room is not symmetrical. That's sort of understandable for the low end, but there's also large differences in the mids and even the highs. Something very asymmetrical about that room...


- Stuart -

[Tonato17]

Hi Stuart, many thanks for your response! As I said before, it is great to know you are there listening and giving me information and advice. I am taking it quite slowly as I am very busy with work lately, but I want to do it right and I fully trust your knowledge and the info I find in this forum. So, once more, thank you!

Originally, there was just a layer of plywood (around 30mm thick) for each wall,

OK, great, but what is beyond that? What's the entire sequence, from the rooms on the other side of your walls? You say that there was already plywood on there, implying that there is some structure behind that which holds the plywood up! What is that structure? Wood framing? Metal framing? Magical incantations? Assuming it is some type of framing, that also implies there is something else attached to the other side of the framing: Drywall (plasterboard)? Plywood? MDF? OSB? Stucco? The cast-off shells of gnomes, fairies, pixies and elves?

I'm assuming here, but if you have a stud framed wall with drywall on the far side and plywood on your side, then you already have a two leaf wall! Anything additional you put in front of that will make it either a three-leaf wall, with the resulting potential penalty in low frequency isolation, or even worse, a four-leaf wall, with the even larger reduction in isolation.

Originally there was just one layer of plywood for each wall (apart of the back wall which is a brickwall) There was only 1 plywood, with a wooden frame in the middle to keep it in place. This was an industrial unit, so it only had this plywood for each wall. Only 1, I could see it was the same from both sides. We added 3 layers of plasterboard to the plywood. We used green glue and of course we also used screws. Before beginning the project I I read "Build it like the pros" by Rod Gervais a couple of times at least. Because we did three layers, for two of the layers we used green glue and for the third one we used Tecsound instead. Green glue was used as a sandwich between plasterboards only, and the same with tecsound. We didn't use green glue and tecsound at the same time in a sandwich. Then we built the wooden frame with the air gap. The plan was to achieve the STC 63 by Mass - air - Mass, avoiding three-leaf walls. The only wall where I believe we ended up with three leafs is the left wall next to the rehearsing band as they also have a room within a room.

... built a wooden frame around the room, with an air gap of 25mm from current boundaries. That 25mm is the air gap between walls and ceiling.

No it is not: Assuming you used standard 2x4 wood framing, then your air gap is 114mm. THe depth of standard studs is 89mm, plus the distance from the face of that framing to the face of the final layer of drywall that you added to the original wall (25mm). So you have an air gap of 114 mm.

Yes it's true, I didn't consider the wooden frame as part of the air gap, but it does make sense as it is not acting like a sound barrier.

The framework was filled with rock wool 60 Kg m3

Just checking: So you have filled the entire air cavity with mineral wool, to a total thickness of 114 mm? In other words, the 89mm between the framing members, plus the 25mm up against the drywall that you put in the original wall?

Hmm.. We didn't fill the entire cavity with roockwool. We left the 25 mm without rockwool, just air and then we filled the wooden frame with rockwool.

We used those two doors...plus the original door! I think maybe that was a mistake.

OK, now this is a myster, for sure! How on earth can you open the middle door???? And what on earth did you attach it to???? You have one door on the original outer leaf, firmly attached to the outer-leaf framing, that door opens outwards (away form the studio). Then you have your second door on the inner-leaf, firmly attached to the inner-leaf framing, and that one opens inwards (into the studio). So how did you manage to get a third door in between those, and how can it possibly even open? I'm intrigued....
(and yes, assuming that you did managed to do that in some magical way, it was a mistake, since it creates a three-leaf system...)

Yes, this was such a bad mistake. Not only we created a three leaf system, but also the size and shape of the studio was affected by this. It would have made a difference to have a square instead. But it is done now and there isn't much I can do. Unless I tear off the second door and re do it again, which to be honest it is not the idea at the moment.

When I said original door, I meant the door that was already there, in the "outer room" To that door I added mass with tecsound in between. Because I had these 2 great doors, I thought it would be better to use them in front of that original door. So that is where the shape of the room changes, doing that L shape. We built a door frame to support both doors. There is like a 40 CM distance between both doors, which open inwards. So when I open the middle door, that one pushes the third door and that is how I get into the studio. I will attach specific pictures for you to see. I really wish we hadn't done it that way, but I feel that soundproofing is working and wouldn't want to spend a lot of money and time to amend that, even if it is something that bothers me significantly.

I was thinking that, the 70 cm corner could be a big bass trap.

Yes it can be, but it cannot also be a bookcase! Either it cam be a bookcase, or it can be a bass trap, but it cannot be both. If you want it to be a bass trap, then the bookcase has to come out.

Yes that is not a problem. I am happy to move things around, change things, put new furniture or get rid of the current furniture if needed. What I can't do is move that pole at the back, as it is a part of the infrastructure of the building.

Start by downloading a copy of the ITU document BS.1116-2, and read through that, to understand what your final goals must be for the room acoustics, in terms of layout, frequency response, modal response, decay rates, etc. Then read "Master Handbook of Acoustics" by F. Alton Everest (that's sort of the Bible for acoustics) to find out how the theory behind how to do all of that.

I have the Master Handbook of Acoustics, great book, I've been reading it these last few weeks. At the moment I don't have much time. My question is, can I achieve very good results by buying the acoustic panels/basstraps etc, once I really know what I need to buy, or would it be much better if I make them myself?

Your speakers in your room need be positioned 67cm from the side walls (meaning they will be 110 cm apart. Your mix position (location of your ears, and therefore also of your mic) will be about 155 cm from the front wall. Set up the speakers so they are aimed at a point 30cm behind your ears, in other words 185 cm from the front wall. Adjust the angles of the speakers such that the acoustic axis of both is aimed at that point. Set up a vertical pole (eg, mic stand) at that spot, and aim both speakers at it.

That's the theoretical optimal layout, but it should be possible to improve on it, with careful adjustments.

Now set up your measurement mic so that it is in the center of where your head will be, pointing forwards (between the speakers) but tilted up at an angle of about 60°. Calibrate REW like that, at 80 dBC for each individual speaker by itself, which implies that the level will automatically be 86 dBC with both speakers on. Do three REW tests like that: One with just the Left speaker, one with just the Right speaker, and one with both. Do not adjust anything in between tests. Leave the room when you run the tests (use "Star delay".

Great, I did that and took the measurements, which are attached.

Thanks, It still gave me 84Db together when each of them was 80Db. Maybe it's a problem with my speakers or the SPL meter...or the placement, but I followed your directions carefully.

I just noticed that there's a pole in front of the bookcase... What is that? It will have to be removed, along with the bookcase.

That is the pole that can't be removed, because it's a part of the building.


I am attaching the new REW measurements, with the setup of the speakers/microphone they way you describe.

I am also attaching some pictures of the room to give a more clear/accurate idea of it.

MANY THANKS!!
Toni

https://dl.dropboxusercontent.com/u/702 ... ments.mdat

[Soundman2020]

Thanks, It still gave me 84Db together when each of them was 80Db. Maybe it's a problem with my speakers or the SPL meter...or the placement, but I followed your directions carefully.

Ummmm... it does not look like you did! ...

170db-peak-FR-HIGHLIGHT.jpg

170.4 dBC? that would place you among the loudest sound sources on the planet! Louder even than this speaker:

HUGE-speaker-was3000-2small.jpg

That one produces up to 165 dB, and is used to simulate the massive explosions and other huge sounds of a major battlefield, for military training. It is rated at 30,000 watts.... And according to your REW data, your speakers are even louder.... Roughly twice as powerful...



In other words, you did not calibrate REW.


- Stuart -

[Tonato17]

Thanks Stuart!

Haha, definitely it wasn't properly calibrated! Louder than that speaker! Ha!
I'll see if I can take another measurement today. It is taking me ages to just take a measurement! Anyway, I'll post the new measurements today. The sound card was calibrated so I assume it must be the calibration of the SPL meter. I'll do both calibrations again anyway.

But with these measurements, are you somehow getting an idea of what are the main problems of the room and how to treat them?

Many thanks!
Toni

[Tonato17]

HI Stuart,

Here are the new measurements! Hope this time is ok. The SPL meter wasn't properly calibrated before! MANY THANKS!

Toni

https://dl.dropboxusercontent.com/u/702 ... ments.mdat

[Tonato17]

Hi Stuart,

Are you still there? Your help was massively appreciated and I'm looking forward to hear your thoughts about the last (hopefully well taken!) measurements to know how to begin treating the room. I am waiting to get in touch with you to buy and put panels into the room.

I got in touch with GIK and they gave me an idea of how to put and where... Do you know the company? Would you recommend their panels?

As I said before, your advice is greatly appreciated and I am looking forward to hearing from you.

Many thanks,
Toni

[Soundman2020]

Hi Toni,

Sorry, I must have missed your update! I just tried to download your MDAT, but all I got is a message saying the file is not there any more. Please upload it again, and I'll take a look.

Yes I do know GIK Acoustics. Glen is a member here on the forum, and use to post frequently (although I have not seem him in a while... I assume he still works at GIK!). They make good products, as do several other companies that offer similar products and services. Where I disagree with them is not their products, but rather there "package deal" "solution-in-a-box" that you can buy, install, and supposedly obtain fantastic acoustics. In my experience, tuning a room is a lot more complicated than hanging a dozen panels at fixed points. Once again, I should make it clear that I have no doubt that there "packages" actually do work, and the acoustic response does improve. My point is that you will only ever get "decent" acoustics like this, but it won't give you "excellent" acoustics, much less "superb" acoustics. That said, if you need a low budget solution that will get your room workable, then those packages are a good option. But if you need the best possible acoustic response you can get from your room ( such as was achieved in this room: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471 ), then you won't get it from one of those packages.

- Stuart -

[Tonato17]

Hey Stuart,

Due to personal circumstances I had to be away for a while. Apologies for the really slow response. I hope you are still there!

Attached is the last measurements I took (quite a long time from now) I also got in touch with GIK and they advised me some panels in certain positions of the room. It is good to know that they are a good company that provide good products. Being realistic, I wont have time to learn how to make panels and make them myself, so it is a relief to know I can buy good quality ones.

By the way, I've seen you live in Chile. I am from Argentina (but live in London), so I speak Spanish : -) I've been there the last weeks and it was very nice to be back in Buenos Aires and meet friends and family.

Many thanks for your help!

Best,
Toni

https://www.dropbox.com/s/cdvsi9uqsfc8p ... .mdat?dl=0

[Soundman2020]

Attached is the last measurements I took

Great! That data looks valid, and I could download it without any trouble.

The first thing I noticed is the huge difference between your Left and Right channels:

tonato-LR-DIF--17H..20k--2.jpg

That's ENORMOUS! Here's what it should look like, for good speakers in a good room:

RDMOUS-final-lr-compare-151.jpg

In both of those graphs, the top curve (purple) is the combined frequency response of both speakers, and the bottom curve (light green) is the difference between the left and right speakers. (Sort of like taking the sound of both speakers and subtracting one from the other). I'm not too worried about the purple curve in your graph (since the room is not yet treated), but the green graph is another thing entirely...

In the case of the "good" room, you can see that there are practically zero differences between the left and right speakers. If you zoom in real close on that graph, you can see some very tiny differences, which is inevitable in a real room, but they are less than +/-1 dB. But in your room, the differences are much, much, MUCH greater, with wild swings of +/-22 dB. That means there are some frequencies where your left speaker is putting out more than 100 times the intensity of the right speaker, and at other frequencies your right speaker is putting out more than 100 times the intensity of the left speaker. Overall, you have differences of more than ten thousand times the intensity (44 dB). That's bad.

So first of all, before you do anything else, you have to find out why you have such a major discrepancy. Maybe one of your speakers is faulty, or your room is grossly asymmetrical, or there's a problem in your signal path (perhaps one channel on your console is bad), or your speakers were not set up right, or there were differences in the mic location / calibration between the two measurements.... . But clearly there's something really, really big wrong there.

Next: clearly you have no treatment in the room yet. It is empty. Which is good! The response on those graphs clearly shows many of the problems with the room: the modal activity stands out very obviously:

tonato-WF-17..500.jpg

You have modal stuff at around 42, 65, 74, 86, 102, 139, 163, 179, 200 and q few more. So you will need a LOT of bass trapping in your room. I would suggest "Superchunks" in all of your vertical room corners.

I wont have time to learn how to make panels and make them myself,

Wow! Then how will you have enough time to unbox, unwrap and install the ones you buy? It takes about the same amount of time... Here's how you make superchunks: http://www.johnlsayers.com/phpBB2/viewt ... 843#p51843 Fast and easy. And cheap...

I also got in touch with GIK and they advised me some panels in certain positions of the room.

Did you send them the REW data? Did they analyze it? Did they make the recommendations based on that? If not, then I can only conclude that a lot of "guesstimating" went on....

I would suggest that your first order of business (after you solve the asymmetry problem) is to build your bass traps, then run some more REW tests, to see how you are doing.

I've seen you live in Chile. I am from Argentina ... in Buenos Aires

Hola, che! Tenemos un Porteño en medio nuestro! Qué bueno. Muchos saludos del otro lado del continente (el lado bueno, obvio... )


- Stuart -

[Tonato17]

Hi Stuart, Many thanks for your response! It's been a long time since I don't post.... I haven't done much progress, but been reading about bass traps quite intensively for the last couple of days, and on and off since I wrote my last post. I have this entire week off and my priority is to at least have a clear plan of action of what I need to do by the end of it. I really want to tackle this this week!
Really cool to know about the superchunks!

The first thing I noticed is the huge difference between your Left and Right channels: That's ENORMOUS!
In both of those graphs, the top curve (purple) is the combined frequency response of both speakers, and the bottom curve (light green) is the difference between the left and right speakers. (Sort of like taking the sound of both speakers and subtracting one from the other). I'm not too worried about the purple curve in your graph (since the room is not yet treated), but the green graph is another thing entirely...

In the case of the "good" room, you can see that there are practically zero differences between the left and right speakers. If you zoom in real close on that graph, you can see some very tiny differences, which is inevitable in a real room, but they are less than +/-1 dB. But in your room, the differences are much, much, MUCH greater, with wild swings of +/-22 dB. That means there are some frequencies where your left speaker is putting out more than 100 times the intensity of the right speaker, and at other frequencies your right speaker is putting out more than 100 times the intensity of the left speaker. Overall, you have differences of more than ten thousand times the intensity (44 dB). That's bad.

So first of all, before you do anything else, you have to find out why you have such a major discrepancy. Maybe one of your speakers is faulty, or your room is grossly asymmetrical, or there's a problem in your signal path (perhaps one channel on your console is bad), or your speakers were not set up right, or there were differences in the mic location / calibration between the two measurements.... . But clearly there's something really, really big wrong there.

Thanks. for the way you describe the issue it makes me think there was a problem on the setup when I took the measurements, rather than the problem laying on the room shape (I hope so!) Maybe gain, maybe sound card, maybe speakers...

Next: clearly you have no treatment in the room yet. It is empty. Which is good! The response on those graphs clearly shows many of the problems with the room: the modal activity stands out very obviously:

The room is not completely empty. There are keyboards a bookshelf, a 24 channel mixing desk, guitars and some other gear on corners. At the moment is a mess. There are a couple of pictures of it on a previous post.
I wonder if the L shape at the back of the room and the equipment stored in the corner made that difference between both speakers...

I will take new measurements and upload them. I will also try changing the speakers at different measurements (put the left to the right and vice versa)
I couldn't find how to look at this difference between measurements/speakers on REW. How do I do it? It would be good to know so I can check this before submitting the results.

Then how will you have enough time to unbox, unwrap and install the ones you buy? It takes about the same amount of time... Here's how you make superchunks: http://www.johnlsayers.com/phpBB2/viewt ... 843#p51843 Fast and easy. And cheap... I would suggest that your first order of business (after you solve the asymmetry problem) is to build your bass traps, then run some more REW tests, to see how you are doing.

Great, so that is my next step after the measurements are 100% accurate. I do want to have clear measurements before treating the room so I can always compare how it is evolving/improving from the original untreated room.

I have some questions on how to implement the superchunks:

In terms of materials.... I've been reading quite a lot about it. Some people seem to recommend the pink fluffy fiberglass which is less dense (I think it's also called R30) and others OC 705, or rockwool. After reading lots of opinions, my opinion is that it depends on the size of the trap.... For the superchunks I would be building, I read (http://ethanwiner.com/density.html) that The 705 or 6lb per Cubic Ft would be better. and It would perform even better in the bass range if I use FRK facing the room as it would absorb more bass and reject some high frequencies. Shall I build them this way then?

I could do 60cm x 40cm x 40 cm. I am going to build a desk for my mixing desk, so if it's better maybe I could have bigger traps and adjust the shape of the table to fit/take less space in the corners.

Questions in regard of positioning.... Please do take a look at the shape of my room again, attached (It's been ages and you might not remember it)

I will place two superchunks on the front floor to ceiling corners... But for the back walls I thought I could build a movable bass trap in front of the bookshelf and leave that space for the bookshelf and "guitars storage"
Would that work?

I could also build superchunks in all ceiling to wall corners as well.. Should I? Any different specification to the floor to ceiling ones? Maybe those ones without (or with) FRK and maybe smaller.

Finally, this is what GIK sent me when I got in touch with them.... As far as I am concerned, they didn't pay much attention to my REW measurements (for example they didn't address any of the inconsistencies you mentioned). They said I should treat the room with general bass broadband absorbers before getting into the details of modes and specifics frequency issues.

Many thanks for all your help and I look forward to hearing from you.
Toni


https://www.dropbox.com/s/56z6fnpknqw39 ... 0.skp?dl=0

[Tonato17]

Hey Stuart,

I just spoke with a carpenter friend of mine, who can give me a hand to build the panels. That is good news because I don't have many tools (which I would have to buy otherwise) and I am not very good at DIY (willing to learn tho!) He will only have a couple of days off to do it at his workshop and then bring them over... That means I'd like to plan in advance all the bass traps/panels I need to make the most of his help while he is available.

If you could help me to make a specific plan of what panels I need and where to place them that would be amazing. (The more the better so I can ask my friend to help me now he is available!). ... I have some time off these days and committed to this 100%. I am getting anxious and a bit frustrated as well.. I feel I need to move forward.

Your help is massively appreciated, once more, Many thanks!

Regards
Toni