Studio Retrofit in Central Coast California

[vince.cimo]

Hi all. I'm in the process of renovating a mix space and could use a bit of help with the treatment. Our overall room dimensions are 18' 9" x 15' 2" x 10' (see attached drawings and model). The back and side exterior walls are made of 8" thick cement block (which I believe to be mostly hollow), whereas the interior wall, dividing our mix and live room is of single stud construction, with two layers of drywall on one side, and drywall + green glue + mdf on the other. We have a small window (as seen in the model) which is about 4' long by 16" tall, mounted at a slight angle (dual pane, 3/8" laminated glass). On the far end of the room, there is a 2' wide shelving unit.

My thinking was to situate the mix position about 6'-8' away from the center of the wall containing the shelving unit, and modifying the shelving unit so that we can 'soffit mount' the speakers flush with it's front face. (I could really use some advice on how to achieve this). Below the speakers and in all of the corners, I was going to build 1'-2' thick pink fiberglass columns, covered with muslin. On the opposing wall, I was planning on building a light frame to house about a foot wide of pink insulation, spanning the entire length of the wall and going up about 7'-9' to act as a large bass trap. I was then planning on hanging a cloud and making broadband absorption panels from some 2" rockwool, placed in any reflection path of the speakers. After the absorption, I was going to add some diffusive grating throughout the room to add back a bit of life.

This studio is in a rented space and is being funded by myself, a recent college grad with only about $700 to spend on the treatment. We do, however have a bunch of reclaimed materials at our disposal, including a bolt of 96" wide felt, 30 or so 2x4's, 8 4x8 homasote panels and 12 hollow core doors.

First off, I'm wondering if my thinking is correct in overall room treatment direction and if so, would like to hone in on the actual dimensions of the absorption and diffusion panels.
Secondly, I have no idea how to soffit mount the speakers in this existing shelf. I've looked at the Genelec guide as well as the this design (http://johnlsayers.com/phpBB2/viewtopic.php?f=12&t=718), but I'm not sure how I could integrate these principles into an existing shelf.

Anyway, hope this all makes sense! I'm attaching a 3d model I put together ( I use Rhino 3d, and would highly recommend it, but I have a .3dm and .skp export I'll include), and some photos of the space. Thanks for your help guys!

Model files posted here: https://www.dropbox.com/sh/4dkfklvwjaw8 ... pAvsa?dl=0
Video Walkthrough Posted Here: https://www.dropbox.com/s/f20c0ovejru46 ... 0.mp4?dl=0

[vince.cimo]

No takers?

[Soundman2020]

I don't know how I managed to miss this thread, Vince! Sorry about that. I saw your other ones, but this one slipped by. It's usually a better idea to keep all your questions about your build, together in one single thread, so you yourself can keep track of them, and also so that the rest of us don't get confused, thinking there are a bunch of different builds by different people!

Anyway, better late than never!

My thinking was to situate the mix position about 6'-8' away from the center of the wall containing the shelving unit,

You didn't say what the dimensions of THIS room are, by itself, so its hard to say if that is the tight spot or not! You only mentioned the size of the entire space...

and modifying the shelving unit so that we can 'soffit mount' the speakers flush with it's front face. (I could really use some advice on how to achieve this).

It's great that you want to soffit mount your speakers, since that's the best thing you can do to improve the overall acoustics of the room, but that shelf unit is the wrong shape and size, and seems to be way to flimsy to be usable as a proper soffit. I would suggest ripping it out completely, and using the same materials to build it the right way.

Below the speakers and in all of the corners, I was going to build 1'-2' thick pink fiberglass columns, covered with muslin.

Why? For what purpose? Why not just build a conventional floor-to-ceiling soffit, such as John's design?

I was planning on building a light frame to house about a foot wide of pink insulation, spanning the entire length of the wall and going up about 7'-9' to act as a large bass trap.

I hope you meant to say "a foot deep", not "a foot wide"!

The idea of treating the entire rear wall is excellent, and very necessary, but for good acoustics in that room, the corners will need superchunk bass traps (floor to ceiling). The wall in between those can be done as you suggest.

I was then planning on hanging a cloud and making broadband absorption panels from some 2" rockwool, placed in any reflection path of the speakers.

Yup!

After the absorption, I was going to add some diffusive grating throughout the room to add back a bit of life.

What do you mean by "diffusive grating"? Are you talking about space couplers? Also, be careful with diffusion: numeric based diffusers cannot be used well in small rooms, due to the lobing artifacts they create in both time and frequency (and therefore phase as well). You need at least ten feet between the diffuser and your ears, and probably more if the diffuser is tuned low. There is still scattering going on down to at least an octave below the low cut-off frequency of the diffuser, so take that into account. You didn't say how long the room is, but I get the impression that it is too small for diffusion.

This studio is in a rented space and is being funded by myself, a recent college grad with only about $700 to spend on the treatment.

Ummm... I'd would seriously consider taking another look at your budget! That won't go very far at all...

We do, however have a bunch of reclaimed materials at our disposal, including a bolt of 96" wide felt,

What type of felt? That doesn't sound like it will be useful for anything, but if you can provide the details, I can look into possible uses.

30 or so 2x4's, 8 4x8 homasote panels

Those are good!

12 hollow core doors.

... and those aren't. At least, I can't think of much use for them off hand...

Secondly, I have no idea how to soffit mount the speakers...

Just use John's design. It's a tried and proven design that works.


- Stuart -

[vince.cimo]

Hi Stuart! Thanks a lot for the reply. To clarify, the room dimensions I provided before (18' 9" x 15' 2" x 10') were for the mixing room in question (the room being treated). Does that change the decision to avoid diffusion?

I took your advice and ripped out the shelf. I found a sketch up model of a small studio that John Sayers designed and am more or less copying the detail, with a bottom bass trapping cabinet full of acoustic hangers, and the top filled with insulation. Based on reviews and posts, I have decided to soffit mount the NS1000's, which also have the advantage of having a remote amplifier, which eliminates the need for any complicated ventilation .

I just have a few questions left before I go and build this thing.

1. Do I want my soffit wall decoupled from the rest of the mixing room wall system?

2. In order to make the NS1000's point at my mixing position (roughly 35% into the long throw of the room), I had to break the equilateral triangle rule, the speakers themselves are 10' 6" apart from cone to cone, but only 6' 10" from the sweet spot. Is this going to screw up my stereo imaging?

3. Because the soffits are built into a corner, the hangers get pretty small. Any recommendations for orientation? Should I just orient the hangers as to maximize the number of them in the space?

4. The wall joining the two soffit walls is going to be filled completely with 2" 703. Should that wall be covered with a hard surface or just covered with cloth? Keep in mind, I'm going to have my genelecs and a mono ns10 in front of that wall on speaker stands.

5. How big of a cloud do I need in a space like this? I was planning on doing a hard backed cloud aimed down at the mixing position (10-15 degrees) that was faced with 2" 703. Is there a recommended size or just as big as I can get.

6. What role should diffusion play in my treatment solution?

[Soundman2020]

(18' 9" x 15' 2" x 10') were for the mixing room in question ... Does that change the decision to avoid diffusion?

As long as you can get at least ten feet between the diffusers and the ears of people who are doing critical listening in the room, then you should be fine. BUt do not the phrase "... ears of people who are doing critical listening ..."! Do you plan to have a client couch at the back of the room?

If so, then you'll be hard pressed to get sufficient distance for those diffusers. You might be able to do it if you raise them up high enough...

Also, that "ten foot rule" (which comes directly from Cox and D'Antonio, the guys that wrote the book on numeric based diffusion) comes with a caveat: It is "ten feet minimum, or the distance needed to get three full wavelengths of the lowest frequency sound that is affected by the device". So if your diffusers are tuned low enough that three full wavelengths is longer than ten feet, then you need to use the "3 waves" distance, not the 10 foot distance. ANd don't forget to take into account that there is still significant scattering going on to about an octave below the tuned cut-off frequency of the device....

So if you can meet the distance requirements and tuning requirements for the diffusers, then by all means use them!

I have decided to soffit mount the NS1000's, which also have the advantage of having a remote amplifier, which eliminates the need for any complicated ventilation

Depending on how hard you drive them and how long you use them at high level, you might still need ventilation. To find out for sure, wrap one in several layers of blankets, then pile some pillows around it, leaving only the front exposed, then play music at typical studio levels for a few hours, and stick your hand down the side every now and then to see if the speaker is getting warm. If so, then it needs ventilation.

1. Do I want my soffit wall decoupled from the rest of the mixing room wall system?

Not necessary, no.

2. In order to make the NS1000's point at my mixing position (roughly 35% into the long throw of the room), I had to break the equilateral triangle rule, the speakers themselves are 10' 6" apart from cone to cone, but only 6' 10" from the sweet spot. Is this going to screw up my stereo imaging?

Changing the toe-in angle of the speakers is allowed, if needed. It does change imaging a bit, but it makes it wider, which can be a good thing as it gives yo a bit more "definition" in where instruments are placed. In other words, it makes the sound stage seem wider. However!! Note the phrase "if needed", then read on below....

3. Because the soffits are built into a corner,

Well, there's your problem! They should NOT be "in the corner". That's bad, for many reasons. For a room with your dimensions, your speakers should be roughly 52" from the side walls, which places them about 78" apart (all measurements are "center to center") of the front panel of the speakers. You would then set up your listening position at about 7' from the front wall, then angle the speakers (toe-in) so that they are both pointing at a spot about 8' to 9' from the front wall, which means about 1' to 2' behind your head. Whatever angle that turns out to be for the speakers is about right! As long as it's not less than about 25° or more than about 40°, then you should be good. If it is outside that range, then you can tweak and twiddle the dimensions above to get it within that range. The speakers must also be set up such that the height of the acoustic axis is about 47-1/2" above the floor.

If you really want to get it as good as it can be, then do a test with REW with that exact setup, with the mic located exactly where your head will be, then do several additional tests, where each one moves the mic by 3" increments forwards from that location, and also 3" increments back from that location. Then look at the data and analyze it carefully to see if there might be a better location for the mix position a few inches further forward or backward. For each reading, do three tests: one with just the left speaker on, one with just the right speaker on, and the third test with both speakers on. If you calibrate REW correctly before you start, then each of the individual speakers should show an average level of about 80 dB(C), then both together should automatically be at 86 dB.

And finally, just use your ears! Curves on a screen can tell you a lot about the technical situation, but your ears will tell you if it actually sounds good! So move your head back and forth a a few inches around the spot that shows up as best on the REW graphs, to make sure it really is a good location.

3. Because the soffits are built into a corner, the hangers get pretty small. Any recommendations for orientation? Should I just orient the hangers as to maximize the number of them in the space?

Yes, but first to the above to make sure that your speakers and soffits are positioned correctly: I think you'll find that the hanger space inside the soffits will end up quite a bit larger than it is now.

4. The wall joining the two soffit walls is going to be filled completely with 2" 703. Should that wall be covered with a hard surface or just covered with cloth? Keep in mind, I'm going to have my genelecs and a mono ns10 in front of that wall on speaker stands.

I would make it deeper than just 2", and yes, I would cover it with cloth: no hard surfaces there.

5. How big of a cloud do I need in a space like this? I was planning on doing a hard backed cloud aimed down at the mixing position (10-15 degrees) that was faced with 2" 703. Is there a recommended size or just as big as I can get.

The cloud needs to be mostly over the desk and listening position, but it can be bigger if you want, or if the room needs it. Basically "as big as you can make it" is a good rule! But start out with something that covers most of the the area between your ears and the speakers. Leave a gap around the edges, more for aesthetics than for acoustics. You can also put concealed lights above the cloud for a nice visual effect.

Try with that one cloud initially, then you can add a second or third behind it, as needed, after you test the room with REW to see if it would be beneficial.

6. What role should diffusion play in my treatment solution?

It might be needed. But first get your absorption in order, then analyze the room with REW to see if diffusion would be beneficial.

One other point: For a room that size, I'd make the superchunks in eh rear corner quite a bit bigger. You could also tilt or "stack" the absorption on the rear wall, so that it is thicker at the top, up near the ceiling. In other words, tilt the top of the panels away from the wall, and/or move the upper panels more from the wall than the lower panels, and/or stack the panels two-deep at the top with only one-deep down lower.

It's looking good though! You have the right basic idea: now it just needs refining and tweaking to make it as good as it can be.



- Stuart -

[vince.cimo]

Hi guys. Stuart, great advice. I think I have enough of an understanding of this system to go for it. I'll be ordering about 50 2'x4'x4" Rockwool panels, building soffits with hangers, corner traps, a front and back absorptive wall, ceiling high first reflection absorption panels and a hard backed cloud. Phew, a lot of work. I did some initial testing with a set of HS80's (I don't quite have the power amp set up for the NS1000's yet), and am amazed by how different my frequency response is depending on slight position changes. Holy crap, like 20db of changes in some spots....that ain't no good. As far as I can tell, I have some pretty nasty modal ringing around 57hz, 114hz, 145hz, 183hz, 250hz and so on. Not surprisingly, this is more or less confirmed by Bob Golds room mode calculator (http://www.bobgolds.com/Mode/RoomModes.htm) [Dimensions: L- 18' 9.75", W- 15' 1.25", H- 9' 10"].


Do these MDAT's look accurate? I'm going to do another set when I get my NS1000's up and running. Also, just out of curiosity, should I go with those NS1000's or get something completely new (like a pair of A7's); it's going to cost my $800 or so anyway to get a decent amp for the NS1000's.

Thanks again guys!

MDATS: https://www.dropbox.com/s/2je8krd30su3e ... s.zip?dl=0

[Soundman2020]

and am amazed by how different my frequency response is depending on slight position changes. .... like 20db of changes in some spots....that ain't no good.

Yup! It's surprising, isn't it? That's the power of phase cancellation, either due to modes or due to SBIR.

some pretty nasty modal ringing around 57hz, 114hz, 145hz, 183hz, 250hz and so on. Not surprisingly, this is more or less confirmed by Bob Golds room mode calculator

Yes, but they might not all be modal. Bob's calculator only predicts modal issues, not SBIR issue (which depend on speaker and listener position, not room dimensions). But they can all be treated, in one way or another....

Also, just out of curiosity, should I go with those NS1000's or get something completely new (like a pair of A7's);

That's like asking "should I continue eating my same old hamburger meat, or should I get something like prime grade-A Fillet Mignon, done medium-rare, with sauteed mushrooms and a fine Chilean cabernet sauvignon ?" I think you see where I'm going... I have nothing against NS1000's, but if it were my room, I'd spring for a nice pair of A8x for that room. Perhaps even add a Sub-10, if you really want to blow the socks of your clients and friends.

MDATS

I downloaded your files, cleaned them up a bit, and did some analysis: First, you need to be more careful in calibrating when you switch from one set of speakers to the other. There's a difference of about 22 dB between the Genelec tests and the HS80 tests, which means that it's not really valid to compare the two. The Genelecs seem to have a much smoother overall response, even though they don't go down as low as the HS80s, but that might just be artifacts of having tested them at very different levels. I really would expect the Genelecs to perform better, but I can't be sure that that's what I'm really seeing on the graphs, though.

One thing I did notice is that there's a very, very big difference between the graphs for the left and right speakers, which indicates that there is a major problem with symmetry in the room, or that the speakers and mic were not set up accurately. Or both! The speakers MUST be set up very accurately around the center-line of the room, and the listening position (mic) must be perfectly on that line. In other words, if the left speaker is 125.7 cm form the left wall, then the right speaker must also be exactly 125.7 cm from the right wall (for example). And the same applies to distance from the front wall. Plus they must be both set up to have their acoustic centers at 1.2m above the floor, and the toe-in angles must be exactly the same. This is very important.

It is also very important to make note of exactly where the measurement mic is, very precisely, so that you can get it back to the same identical position for each test. So measure the distance of the tip of the mic from all four walls, and the ceiling, and the floor, such that you can always get it back to that point, accurate to within a few mm. If you don't do that, then you cannot validly compare different REW tests.


However, despite all of the above, all of the graphs show that the room isn't too bad at all! Surprisingly good, considering that there's no treatment in there yet. Once it is treated, I think it can be quite good.


- Stuart -

[vince.cimo]

Well, I chose the hamburger* meat (* meatless, I'm a vegetarian). The NS1000's don't sound especially good, but they are a damn good 'going to translate if it sounds good on these' speaker. I'm planning on getting my mix detailing on the nearfields and then check everything on the soffits, so I think they're going to work out. The soffit is half built! I'll post some pics. Our design is interesting....hoping it will work; we made sealed, sand filled panels (sandwiched between 2 sheets of OSB) and have them attached to a rigid frame. One last question. We are doing hangers for our lower cavity, but for the top cavity, is it important what it's stuffed with? Does it need to be insulation or can it be something like carpet scraps.
Are we going for mass or bass-trapping in that main cavity?

[Soundman2020]

I'm planning on getting my mix detailing on the nearfields and then check everything on the soffits,

Normally, people do it the other way around! Since the soffited speakers give the most accurate response, clearest sound, best stereo image, best sound stage, etc. those are the ones you should mix on, then check the mix once it is done using whatever other speakers you have in the room. That way, you are certain that any changes you hear when you switch to the non-soffited speakers are due to the speakers themselves, or their interaction with the room, rather than to problems with your mix. If you mixed on the non-soffited speakers, you'd never know if what you are hearing is accurate or not.

The soffit is half built! I'll post some pics.

That was quick! it usually takes me days to design a soffit, then days more to build it....

I'd love to see those pics, and also the design! Please post them when you can.

Our design is interesting....hoping it will work;

"Hoping it will work" is not usually a good way of building a studio!

we made sealed, sand filled panels (sandwiched between 2 sheets of OSB) and have them attached to a rigid frame.

An interesting concept, certainly, and it should work in theory... but there's always "Murphy's law"!

for the top cavity, is it important what it's stuffed with? Does it need to be insulation or can it be something like carpet scraps.

You could put carpet scraps in there too, but I'd also put in a lot of insulation scraps. It's not too critical, as that basically serves to damp internal resonances, but carpet isn't much good acoustically at all (that's why you don't see much carpet in pro studios!), so it won't do the job by itself. You'd want more than half of the volume filled with insulation scraps, and the rest can be carpet. You could even use the carpet to shape the ventilation chimney, if you wanted.

Are we going for mass or bass-trapping in that main cavity?

Neither! It is mostly damping for internal resonance within the cavity. The soffit basically acts like an over-sized speaker cabinet, and just like any enclosed cavity (speakers included) it will have several different ways in which it can resonate. The insulation is there mostly to damp out those resonances. So the insulation in there is not really part of the room treatment: it is part of the speaker acoustics.


- Stuart -

[vince.cimo]

Hey Stuart. Other than the sand panel thing, we didn't really do anything weird in terms of the soffit design. Basically, our lower chamber is filled with hangers, the top partition dividing the two chambers serves as the bottom of our speaker box and the front baffle is a sand panel. The speaker sits flush with the front of the baffle. The bottom baffle is mounted on the back of the frame so we can do the panel of rockwool to dampen desk reflections. Your advice on placement was invaluable, we did some stereo imaging testing and found that your recommended placement was pretty much the best sounding for us as well.

The frame itself is attached to our slab with concrete anchors and connected to the adjoining walls and ceiling.

I've talked to a few different engineers whom I trust that have recommended I keep the NS1000's so I'm going to go for it; I think they're going to suit our needs, although they may not blow up the skirt of every pretty lady that comes in the studio.

I'll send some pics shortly, don't have them on hand at the moment.

A few notes about the drawings:
1. They're missing the hangers
2. We've increased the thickness of the front panel to add more mass

[vince.cimo]

Here are some pics guys. One last question. In theory, the top chamber should be 100% sealed off, with joints caulked if possible, correct?

Thanks for all your help! I'll keep posting during the build.

[vince.cimo]

Hey guys. Just thought I'd make a quick update. Walls are up. Geez, that was a lot of work. Those sand filled panels ended up weighing about 400 lbs a piece and required a material lift to get on the wall (plus like 6 burly dudes). They are up, secured and reinforced. If I did this again, I would probably just go for 3 or 4 layers of drywall or plywood. The sand is simply back breaking. Now that it's all up though, I'm looking forward to hearing how this thing sounds. In theory, we should be good with such a massive front baffle. I'll post pictures soon. Stuart, you disappeared! Still around?

[Soundman2020]

From the photo, it looks like your sand-filled panels are made from 1/2" OSB (plywood?) with 1/2" battens for spacing: Are you SURE that can handle the stress and tension? You'll have a few feet of head inside, and since sand basically acts like a liquid, there'll be a ton of pressure at the bottom edge, trying to force the panels apart. I suspect they will bulge and eventually fail due to that pressure, especially when you take into account any vibration from the speakers that would be tending to both "liquify" and compact the sand. Did you have an engineer calculate the stresses and confirm that you are OK?

Also, from your sketchup image "soffit2.jpg", the layout is not good. The speaker is way too close to the bottom edge and the inner edge of the front baffle. The idea of the baffle is to extend the front panel of the speaker as far as possible in all directions, with the goal being to make it act like an "infinite baffle". By only extending it an inch or so in those two directions, you are not even getting close to that goal. I'd suggest re-designing those soffits such that there is a much larger area around the speaker. Ideally, the speaker should be centered at about 2/5 of the width of the panel, not less than 1/5, but also not in the exact center either.

Your advice on placement was invaluable, we did some stereo imaging testing and found that your recommended placement was pretty much the best sounding for us as well.

Great! Glad it worked out for you. It's always good when practical implementation matches theoretical prediction...

One last question. In theory, the top chamber should be 100% sealed off, with joints caulked if possible, correct?

Not necessary. Since the cooling flow channel that runs behind the speaker is vented both to the cavity below and out to the front, it's not a sealed system at all. So since you need that anyway, there's not point in spending time sealing up the rest of the box.

Stuart, you disappeared! Still around?

Yup, still around! Just got a lot of stuff going on right now...


- Stuart -

[vince.cimo]

Stuart, we ended up using 2x4's and a lot of glue and screws to hold things together. The sand panels are up and seem quite sturdy. As far as our placement goes, we are past the point of no return so we have to live with inefficiencies in the design. I am aware that the speaker placement is not ideal, but outside of bringing the speaker further into the room, there's not much we can do if we wanted to maintain our stereo image distance. All said and done, the speakers sound extremely clear and accurate, and the bass response is phenomenal. Honestly, clearest bass I've ever heard; each note is the same volume with an even decay. Yay. We still need to finish some of the early reflection treatment but we're getting close. I'll post some REQ results soon.