Help with treating a temporary room

[WheresTheDug]

Hi Guys,

I haven't been around the forum for a long time. Long story short(ish).... a few years back I had the intention of building a studio at the foot of my current garden. I realised it was probably too big a job to try and figure out myself (even with the help from this group) so I commissioned Stuart to design it all for me. He did an epic job but unfortunately I never got to build it for a few reasons. Firstly we had to sack our architect because he messed up the measurements of the plot and the structure that he designed (and which Stuart went to a lot of bother to work within) was actually too big for the plot !!!!! Then we engaged another architect but my wife took seriously ill. We decided that the studio was a very low priority at that point in our lives. Fortunately, she is now well but the whole experience caused us to re examine our plans and our dreams for the future.

We decided that, as the kids were approaching school leaving age, that I would sell my business and "retire" or at least start a second career of some sort at some point.

We also decided to look for a plot in the country to build a new home including an outbuilding to function as a studio and a workshop for my guitar building projects. We found a 1 acre plot and are in the process of finalising plans etc. With any luck we should be wind and water tight by the end of this year or early next year. Final completion for the house is estimated as Q3 or Q4 2020 (barring any holdups with planning or building control). That's the good news.

The bad news (and the point of this thread) is that I will be stuck in my current room for another 12 - 18 months. Therefore, I fancy a little project to try and treat it as best I can. I have no expectations of it ever being a great room (not least because of the isolation problems) but I want to experiment with things like membrane traps, helmoholtz resonators etc to gain experience and understand the theoretical and practical aspects of treatment. I see this mainly as practice for when I get to work on the real rooms.


I have been reading Stuart's guide to making measurements to share on the site as well as reading the first 20 pages of Frank's build. Damn, that's impressive


A few years back I tried treating the room and I build a studio desk with build in speaker stands and a pull out shelf with a Roland electric piano on it. However, I now know that the desk was WAY too big, the speaker stands caused more problems than they solved, the space for rack gear wasn't necessary and the top is so flexible that it actually resonates like an acoustic guitar I will be trimming it down tomorrow and putting the speakers back on stands.

This is how it all looked until I emptied it today.

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Here is a rough plan of the layout.

Batcave Dimensions.skp

The dimensions are a bit wonky as they show fractions of a millimeter which I didn't intend but they are pretty much right. I will need to do a new Sketchup drawing of the room as it is a slightly unusual shape and nothing is actually square. The ceiling is 202cm high in the front left corner but only 199cm in the front right. Both rear corners are 208cm The length along the left wall is 458cm but the right wall is 460cm. However, i don't know what is behind the drywall. I suspect just studs and no insulation then the structural brickwork. The is no insulation in the ceiling and a wooden floor above my head so you can hear a spider run across the kitchen floor from the mix position


Start of today's project:

I spent today totally emptying my room (it was raining so everything had to go in a tent in the garden) to let me take new baseline measurements.

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It's amazing what you can fit in a tent

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To be honest there's also a fair bit in the house and the desk is outside with a tarpaulin over it

The empty room ready for measurements

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I didn't remove the Superchunks or the shelves and the Rockwool above the shelves in the little alcove - but other than that I gutted it.

Calibrated and ready to go

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Now I just need to figure out how to upload the REW files for analysis> I have saved all the measurements in one file but even when Zipped it is still 56mb. The webpage keeps crashing when I try to up load it. Should I put the file in dropbox and post a link or is there a particular way I need to upload?


What am I trying to achieve and what (specifically) do I need help with at the moment?

1. I want to nail down my listening position and speaker placement.

I have looked at various mode calculators etc and all the rules of thumb like 38% from the front wall etc. However, in my room the true back wall is only a small part of the rear surface of the room. The longest point in the room is a patio door which is 54 - 55cm beyond the actual wall.

What do I consider the dimensions of the room for any calculations?

Likewise, the room is slightly wider at the rear than the front. and slightly taller at the rear than the front. Can I just split the difference and take an average width and height?

How accurate does any average need to be?

2. I need to control some serious dips in the bass response and some modal ringing down there too.

What steps can I/should I take?

Should I just keep piling more rock wool in? I'm running out of space

Should I try and target specific modes with helmholtz devices or go for a wider range with panel absorbers?

3. What can I do about the back wall that isn't a wall?

The main entrance/exit and source of light is the windows/patio door that makes up most of the rear surface. I can't cover them with solid bass traps.

Glass is clearly very reflective. However, as double glazed doors aren't great acoustic insulators maybe this works to my advantage by letting a lot of the bass pass straight through like an open window.

Could I try moveable absorbers or some sort (I previously had a couple of broadband absorbers on legs making gobos but they were a pain for getting in and out. I also had a curtain across the full back wall but this contributed to making the room very dull and dark. Maybe some form of heavy but partially reflective curtain such as a MLV or something?

4. How can I stop the room being too dull?

The measurements I took before emptying the room had the RT60 down about 150ms and lower in the high frequencies than anywhere else. I probably still need more absorbtion but the room is already dull. I am wondering about adding some slatted walls to try and reflect some highs back. Is this worthwhile? If so where should I target these?


That's probably enough to keep me going just now

[Soundman2020]

Alan! Wow! Talk about a blast from the past!

It's SO good to hear from you again, and I'm really, REALLY happy that your wife recovered, and is doing well. I did send you an e-mail at one point, asking about that, but I guess you were way too involved to be answering.

Congrats on retiring, too! And on getting a plot of land away from it all. That bodes well for a great studio... hopefully one that will actually get built this time!

Anyway, on your current temporary place: Just upload the MDAT file to a file sharing service, such as DropBox, and share the link here: or send it to me by e-mail: I'll be happy to take a look.

This is so great to have you back on the forum again, and back in "studio mode"!


- Stuart -

[WheresTheDug]

Thanks Stuart it's great to hear from you again too. I don't remember seeing the email or I would have replied, sorry.

Yes, everything is very exciting at the moment. As well as building a house I start college next month (at age 50) to do a 2 year full time course on stringed instrument making. Maybe I will manage to turn that into a second career.

I've put them on drop box here

https://bit.ly/2GhgboC

I have tried to follow your calibration and test instructions to the letter but if things don't look right just let me know.

Your insight will be much appreciated

I hope to be able to get you involved properly on the new project when the time comes.

[Soundman2020]

Got the file OK, and the data looks fine. You seem to have done the tests right.

Just glancing through initially, but the first thing that sticks out, is the imbalance between your left and right channels. Some of it seems to be room symmetry (I noted the "kink" at the rear), because it changes as you add more treatment to the room, but some does not change at all, so that is most likely the signal path itself: Speakers with different settings? Speakers and/or mix position not set up symmetrically in the room? The biggest issue there is a 5 dB peak centered at around 5 kHz., but covering 2k to 12k, roughly. Not sure what that is...

Second, there's no low end. I'm assuming that's just the speakers themselves: The response rolls of steeply below about 45 Hz, and by 40 Hz it's already 12 dB down. If you want to use your setup for serious contemporary music (bass heavy), then you might want to consider getting a sub... or even a pair of subs. Subs are good not just to fill in the low end, but they can also deal with some of the acoustic problems in your room.

For example, you have a fairly major dip between about 115 Hz and 170 Hz. Some of that is probably modal, some is SBIR, some is floor bounce... but all of that could be greatly improved with a pair of subs set up as a plane wave array. We are in the process of doing that right now for a room in New Orleans... (results coming in the next few days, hopefully). I'd suggest that you get a pair of good subs, that you can then re-use for the new studio.

If you compare all of your REW FR graphs at once (see below), you can clearly see the dip I'm talking about:

Alan--tempCR--REW--FR-20-500--all--low-dip.png

You can see the large dip centered around 145 Hz. And you can see that it hardly changes at all with treatment... so my guess is SBIR and floor bounce: the dip is in the region where both of those would be in your room. If you can give me the exact locations of where you had the speakers and mic, then I can figure it more accurately. But anyway, a pair of subs set up for plane wave can have a big impact on your entire low end. The AX7's are nice, but they don't go very low. Mate those with good subs, tweak and tune, and you have a really nice setup.

On that same graph (above) you can see that there's a general lack of bass trapping in your room. Your rear traps are having some effect on the 100 Hz issue and the 178Hz issue, and even smooths out the 80 Hz region a bit, but below about 75 Hz, nothing budges. The 62 Hz monster is standing his ground, not yielding an inch! So your traps are not deep enough, or not placed correctly, or the insulation you are using isn't suitable. Or maybe a tuned trap would be a better bet. But do be warned! Tuning traps is not as easy as the text books make it look...

So, I'd suggest more bass trapping... but the problem is that the place where it needs to go, is all glass! Most of your wall is windows... I'm afraid that some of those are going to need covering up. Maybe bass traps in wheels?

Anyway, on to some comments about your first post:

I fancy a little project to try and treat it as best I can. I have no expectations of it ever being a great room (not least because of the isolation problems)

... and the low ceiling. Oh, and the ceiling is also a bit low. Plus, the ceiling isn0t very high. Not sure if I mentioned that the ceiling elevation is an issue? But perhaps not as a big an issue as the lack of ceiling height...

However, I now know that the desk was WAY too big,

Ummm... Yup! I won't argue with that! Not in the least!

the speaker stands caused more problems than they solved, the space for rack gear wasn't necessary and the top is so flexible that it actually resonates like an acoustic guitar I will be trimming it down tomorrow

Ummm... Rather than just trimming it down, I'd suggest building a whole new desk: low profile, open, suitably angled surfaces... I could modify one of my desk designs for you. Build it nicely, and you can re-use it for the new studio as well.... But the big question is: are you planning to keep the Mackie 8-bus? That's a pretty big console (looks like the 24.8, if I'm not wrong, but it might be the 32.. If you want to keep that for now and the future, then the desk needs to be fairly wide. But if you are planning on going with something smaller, or even fully ITB; then the desk can be shrunk too.

Your video screens are too high as well, and need to come down lower.

Also, are you planning to keep the Adam A7X's? They are pretty good speakers, so no problems there. Just asking.

I have looked at various mode calculators etc and all the rules of thumb like 38% from the front wall etc. However, in my room the true back wall is only a small part of the rear surface of the room. The longest point in the room is a patio door which is 54 - 55cm beyond the actual wall.

Ah yes! My favorite subject! Control room layout. The first rule here is to forget the rules... Well, not all of them, but most of them. Forge the equilateral triangle rule, and the 38% rule, for example. Those do work... sort of... in most rooms... but they are not necessarily optimal for any room.

I would suggest starting out with your speakers 110cm from the side walls, 122cm above the floor, and with a 10cm gap between the rear corner of the speaker and the front wall. You will later insert a 10cm thick absorption panel in that gap. The first two numbers refer to the acoustic axis of the speaker, NOT the top or bottom of the cabinet, NOT the center of the front panel, and NOT the center of the tweeter (more mythical "rules" debunked). To estimate where the acoustic axis is on your speakers: draw an imaginary line from the center of the woofer to the center of the tweeter: the acoustic axis is located about midway along that imaginary line, and extends out perpendicular to the front face of the speaker. That's the reference point for all speaker measurements.

Then set up your mic so the tip is 187 cm from the front wall, on the room center line, and 120 cm above the floor, angled upwards at around 70° or so. That marks the center of where your head will be. Now set up a vertical pole of some type, such as a mic stand, so that the pole is about 30cm behind your head, on the room center line, and perfectly vertical. Aim both of your speakers at that pole. An easy way is to temporarily tape a laser pointer onto the top of the speaker, directly above the acoustic axis, and making sure that it is set exactly at right angles to the front face of the speaker. Then it's easy to rotate each speaker on its stand so the laser hits the pole, while keeping the side-wall-to-axis distance correct, and the rear-corner-to-front-wall distance correct. When both laser dots hit the middle of the pole in the same spot, and the distances are correct, then you have the correct INITIAL layout, for doing a set of REW tests that I have developed, to help you locate an even better spot... I'll send you the instructions for that privately. Not for public consumption!

What do I consider the dimensions of the room for any calculations?

Average. So take the widest width and the narrowest width (ignoring the bookshelf alcove), and average them: that's your width. Ditto for the height. Same for the rear wall, but just use the glass, as that's most of the rear wall, with just small sections on each side. Bare in mid that the wavelengths we are worried about here are many, many meters long, so high precision is not necessary.

Can I just split the difference and take an average width and height?

Yup!

How accurate does any average need to be?

A few cm is fine. Your modal issues are mainly around 100 Hz (give or take a hundred...). The wavelength at 100 Hz is 344cm, so if your measurement is off by 5cm (about 2"), that's only a bit more than 1%. Not a big deal, at this stage.

2. I need to control some serious dips in the bass response and some modal ringing down there too.

See above: Subs is the answer. Two of them, carefully set up and tuned in a plane wave bass array.

Should I just keep piling more rock wool in? I'm running out of space

You do need more bass trapping, yes, and it needs to go on the rear wall... or should I say, rear window...

Should I try and target specific modes with helmholtz devices or go for a wider range with panel absorbers?

You can tune either type either broad (low Q) or narrow (high Q). There's pro's and con's either way, but before deciding what to to, get your subs in: there's probably other monsters lurking down there in the mud that you haven't seen yet, but that you might need to treat. Your lowest axial mode at about 34 Hz is slightly visible, whimpering softly, but put some subs in there and it will probably roar... Then we'll need fiddle with the subs a bit to get that roar back down to a groan, and perhaps treat it with some tuned devices.

3. What can I do about the back wall that isn't a wall?

Put bass trapping on there!

I can't cover them with solid bass traps.

Then you can't get good acoustics in that room! Plain and simple answer, but not the one you wanted. The rear wall of any small room is always the biggest issue, and always needs the most treatment. Take a look here: thread about Steve's high-end control room in New Orleans There's over 50cm depth of treatment across the entire back wall, and 90cm depth in the corners. You've seen the corner control room thread, and that has nearly 80cm depth into the corner, plus more on the side walls. Rear walls are ugly acoustic killers, and they need treatment. I would suggest building "treatment on wheels", sort of like gobos, that you can wheel into place in front of the windows when you need to do critical listening, then wheel out of the way when you want light.

as double glazed doors aren't great acoustic insulators maybe this works to my advantage by letting a lot of the bass pass straight through like an open window.

In theory, that's nice... but you can see that it isn't actually working for you in practice. Your first three lengthwise modes are theoretically 1.0.0= 33.97 Hz. 2.0.0= 67.94 Hz. 3.0.0= 101.9 Hz. Take a look around those spots on your REW waterfalls, and you can see all three of those monsters roaring and yelling... So that theory is out the window for your room! The modes are there, and very active. They are not going out through the glass, sad to say.

Could I try moveable absorbers or some sort (I previously had a couple of broadband absorbers on legs making gobos but they were a pain for getting in and out. I also had a curtain across the full back wall but this contributed to making the room very dull and dark. Maybe some form of heavy but partially reflective curtain such as a MLV or something?

Movable, yes, but not tiny little thin ineffective things like curtains and MLV. Think BIG. No, BIGGER! I mean REALLY B-I-G! The wavelength for your 68 Hz problem is 5.05m. It will just laugh at curtains and limp MLV. In fact, it won't even bother looking at them. To get useful damping, you'd need low density insulation about 1/16 wavelength, so about 31cm thick. And floor to ceiling. And at least one third of the room width on each side.

Tuned traps, such as slats, perf panel, rigid membrane, or limp membrane can be shallower, yes, but they still need to be big... because you have several issues, and each trap can only deal with one issue, so you need several traps... and they have to be large enough to take a serious bite out of the problem: if you make them matchbox size, they won't do anything. Neither show-box size. More like '70"-flat-screen-TV-box' size...

4. How can I stop the room being too dull?

By tuning it! Use thick plastic across the front faces of those traps that only treat bass or high mids, thinner plastic across traps that treat up higher, slats across traps the treat down lower. There are simple equations for figuring out the thickness of the plastic vs. frequency, and the dimensions and spacing of the slats too.

OK, that should give you some food for thought! Personally, my tow major suggestions here would be to get a pair of good subs and a controller, and to add more bass trapping, but tuned it to not suck up the highs and mids. Watch out for killing the 200-500 Hz range: it's very easy to over-damp that. There's already some signs you are doing that around 350 Hz...

- Stuart -

[WheresTheDug]

WOW, another short generic response

Glad to see we only have to deal with the back window and buy some subs. At least the ceiling isn't an issue

OK, there is a lot in your reply to digest but I thought I would start by answering some questions and giving you some more details about what has been done so far and my thinking at the time (garbled though it may have been).

he first thing that sticks out, is the imbalance between your left and right channels

I think that is most likely poor speaker placement on my part. The mic was dead center and 160cm from the front wall and 132cm high and angled roughly 60 degrees. I placed it touching a plumbline from a mark on the ceiling to make accurate repositioning possible. I will apply the same process in future for the mic but obviously from a more appropriate place. I chose 160cm based on the length of the room to the walls NOT the window/door. Learning point No1 checked

Positioning the speakers is harder because of the superchunks which get in the road of the measuring tape and the soffit that runs round the floor. I will figure out some way to make more accurate measurements going forward. Your speaker positioning instructions would be very much appreciated

The A7x apparently go down to 42hz so that is probably consistent with your observation about the bass being steeply rolled off by 40hz.

Also, are you planning to keep the Adam A7X's? They are pretty good speakers, so no problems there. Just asking.

Yes. I do plan to mate them with a sub or pair of subs in the new studio but would rather not go there at the moment. I still haven't built the house and studio structure so I could end up divorced if I start using the budget to buy a pair of Sub10 at this stage There is a kitchen to pay for first. The other reason is that I currently play very quietly in this room as structural transmission to the rest of the house is really bad so adding subs will only cause me even more problems in the domestic department.

you have a fairly major dip between about 115 Hz and 170 Hz.

Yep, even I managed to spot that one

If you can give me the exact locations of where you had the speakers and mic, then I can figure it more accurately.

Mic - see above

Speakers- If I interpret the accoustic axis properly it is about the top og rubber suspension on the woofer (about 6cm up from the center of the woofer). On that basis the measurements were taken at 125cm high. I can probably get them very close to 122cm just by removing the spikes from the speaker stands.

Left Speaker is 22cm from real wall to inside rear corner and 78cm from side wall to outside front corner.

Right Speaker is 22cm from rear wall to inside rear corner but between 80 and 81cm from the side wall to the outside front corner.

EDIT - [I have now re-read your response several times and think I have mixed up a couple of things about positioning. I initially thought you were measuring from front and back corners but I now see your are talking about Acoustic Axis in 2 dimensions and only referring to the speaker corner for distance from the rear wall - DOH) However, I am still struggling a little with figuting out exactly where the Acoustic Axis really is for measuring purposes. Any chance you could knock up a reall rough diagram on an image of an A7x or something so that I am sure I am measuring to the right place.]

Why are they so far forward? Three reasons.

1) I have 20cm of Rockwool RW45 in the absorbers behind them and this is hanging 1cm from the wall.

2) The last 1cm is down to the IEC connector and audio cables on the back of the speakers which stick out a bit. I was thinking about trying to make up some right angled XLR cables and getting a couple of right angled IEC power cables to get closer to the wall.

3) I have 21cm Soffit at floor level that restricts the ability to get other things such as speaker stands hard against the front wall.

Why 20cm of RW45 instead of 10cm?

Because I read Rod Gervais book, and two Alton Everest books (including Masters Hand Book of acoustics) as well as many posts on here that said thicker panels absorb lower frequencies. I thought might as well use the space with as much RW45 as possible given the soffit issue. Eventually I then got to the chapters about SBIR and tried to position the speakers as close to the front wall as possible given the absorbers that were already in place.

I have been thinking about making that full front wall RW45floor to ceiling. I could re orientate some of 20cm panels for top and bottom (maybe even angling the top row to make them more like corner traps). I could then run 10cm across behind the speakers. Is that worth trying?

Then set up your mic so the tip is 187 cm from the front wall, on the room center line, and 120 cm above the floor, angled upwards at around 70° or so. That marks the center of where your head will be

The lowest I can go on my chair is 130cm but even then I usually sit much higher for playing guitar. Are you assuming that my head is lower because I'm also leaning forward? If so does that mean that in my theoretical listening position my chair would actually be further back than 187cm?

So your traps are not deep enough, or not placed correctly, or the insulation you are using isn't suitable. Or maybe a tuned trap would be a better bet.

The current traps are as follows:

Superchunks - 1200 x 600 sheets of RW45 cut in half then cut diagonally to get four triangles out of each sheet. Which should make them 45cm deep ceiling to 21cm off floor due that bloody soffit again. I could probably build a few more panels of 1200 x 600 and run these diagonally in front of the existing triangles. Is that worth doing? I already have a lot of RW45 in the room. I can add more if necessary (I know IT IS!) but obviously I would start by reusing the existing stuff more effectively if that will make a significant difference.


Front Wall - 1200 x 600 x 200m RW45 panels times 3. The two outer panels are 1cm from the wall. The middle is angled from 10cm out at ceiling to 1cm at the base. Again, my rookie thinking was that adding some extra air space would help increase efficiency slightly without adding extra material.

Front Ceiling - 1200 x 600 x 100mm panels times 2. The front one is hangin with a slight angle ranging from 50mm to 80mm (no real reason). the rear one is hanging with a 50mm air gap.

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First reflection points - 1200 x 600 x 100mm of RW45 hanging with a 100mm air gap behind each.

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Rear sides - 1200 x 600 x 50cm of RW45 on each wall with no air gap.

Rear ceiling - 200 x 600 x 50cm of RW45 on each wall with 50mm air gap.

The "everything test was done with two unopened bales of RW45 against the rear windows at floor level. plus two extra 1200 x 600 RW45 panels that had previously been gobos (one 200 deep and one 100 deep) just for good measure.

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The back corner above the book shelves is also stuffed with RW45

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Now to the elephant in the room. Well to be fair an elephant would probably take up less space and be easier to carry

The desk is (WAS) enormous. I spent a long time trying to design it in sketchup to accommodate everything I needed including the Video Screens, Mackie desk (it is a 32:8 by the way so it is BIG), space for my computer keyboard and mouse, some extra storage and (the bit that caused all the problems) a pull out shelf with a keyboard. Th big problem was trying to get the height sufficient to get my knees under the keyboard AND still be able to see the Mackie plus put the speakers at the right height. In retrospect it was a cock up; or as I prefer to call it - a valuable learning experience

I cut it down today in between chucking tarpaulin over it every time a rain shower started.

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It needs to be that wide to fit in the Roland piano. It only needs to be that deep to accommodate the Mackie and leave enough space for the keyboard and mouse. Which brings us to the Mackie. Do I intended to have a mixer in the new studio? I don't know yet but probably not. I think ITB is more likely. The only advantage I can see to the desk is lots of mic pres for recording drums. The truth is I don't really use it much just now at all. All EQ is literally bypassed and I just use it as a big patchbay so that I don't need to keep plugging and unplugging different guitar solutions like Kemper or Two Notes Torpedo or Mic on a Mesa etc.

I like the idea of building a purpose built desk as you suggested. I had assumed that the desk design for my real studio would be specific to the rest of the control room that I end up with. However, if a relatively generic desk can be built now that can be used in the new studio then I'm probably up for a project

Thanks again for all your input already.

Alan

[DanDan]

Your speakers are quite a distance from the Front Wall. This causes an SBIR dip, which can gang up with mid height and distance to side wall BIRs.
I would remove the traps behind the speakers to somewhere else. Corners are best. Try the speakers almost touching the Front Wall.
You will gain free Bass.
DD

[WheresTheDug]

Thanks DanDan

Your comments obviously echo one of the things Stuart said so I would be mad to ignore it

I have been thinking about the speaker placement issue and need for more trapping since Sturat's post and think I have a cunning plan that Baldrick would be proud of

Step 1

Take the current vertically orientated 200mm deep absorbers and turn them though 90 degrees to make them horizontally orientated. This will retain the maximum amount of trapping on the front wall but leave the tops of the panels just below the base of the speakers allowing me to slide the speakers back towards the wall.

Take the existing 200mm deep middle panel and rotate it through 90 degrees and place it in in the top left corner of the front wall. Build a new 200mm deep panel and place this in the top right corner if the front wall. This would either be against the wall or could easily be brought forward to create an air gap if better.

This would result in the whole front wall being trapped except for a band in the middle about the same height as the speakers. Therefore, the speakers could be placed against the wall if necessary.

Then fill as much of the space between the speakers as possible in that middle band with 200mm of RW45.

Does this sound like a viable plan so far?

This leaves me with a few further questions:

1 - should I put nothing directly behind the speakers or leave enough space for 50 or 100mm of RW45?

2 - the floor plinth (I've been calling it a soffit until now but plinth seems like a better description) impedes me from getting the current speakers stands or any other traditional stands in a position to adequately support the speakers that close to the wall. How should I hold the speakers in place? I am thinking about some bricks or breeze blocks to build my own stands or should I build a solid wooden stand fron 2x4 or 4x4 to the exact size?


Step 2

Remove the current side wall absorbers. Build some framing along almost the entire length of each wall and fill this with plinth to ceiling 100mm deep RW45.

This leaves another question -

The left wall has a radiator on it which I can't cover with RW45. Should I only take both walls to the same point or should I stop before the radiator on the left wall but run all the way to the book selves in the rear corner of the right wall? This wouldn't be symetrical but the difference would be fr behind the listening position so shouldn't affect imaging.


Step 3

Place a 200m deep RW45 panel on the rear wall directly nect to the book selve alcove. This will cover most of that wall.


Step 4

Place a 100mm deep panel diagonally across the left rear corner next to the radiator, This would sit on the plinth so would leave around 50cm empty in the upper corner unfortunately but there is also an alarm sensor in that corner which I can't cover up.


Step 5

Build a moveable RW45 absorber f400mm deep from floor to ceiling in the right corner of alcove at the rear window/door.

Build a similar moveable absorber in the left corner but with a gap part way up to allow access to the light switch on that wall.


Step 6

Build a further 3 200mm deep moveable gobos on wheels that would completely cover the rear wall in fron of those to new trap in Step 5.

In this case could I build both of the 400mm deep traps to fill floor and ceiling but leave a gap in between that could be used for storage shelving?


I expect I would still need to do some more work on the ceiling, maybe four 100mm deep hanging panels above the mix position instead of the current 2 and some additional 50mm panels further back.


I estimate this would probably need another 5 or 6 pack of RW435 1200 x 600 x 100mm x 4 per pack. Total cost about £90. Plus some cheap wood for framing say £50.


Does this sound like a decent starting point guys?

[Soundman2020]

WOW, another short generic response

Well, yeah, I do try to keep it brief and not too specific, so as to not bore people with long convoluted explanations.... Hmmm... But maybe I SHOULD write longer posts, with more specific details? I don't want people to think I'm just throwing out short, cheap, simple answers, ya know?

I think that is most likely poor speaker placement on my part.

It could be placement, or it could be adjustments, or it could be room symmetry... or it could be a combination of all 3.

Positioning the speakers is harder because of the superchunks which get in the road of the measuring tape and the soffit that runs round the floor. I will figure out some way to make more accurate measurements going forward

Have you tried using a laser measure? You can place it on top of the speaker and aim it at the walls, where the soffit won't be in the way, and it should be easier to find symmetrical spots on both sides, away from the superchunks, to get good readings. Plus, it's more accurate, as you don't have the problem of a physical tape sagging and twisting.

Your speaker positioning instructions would be very much appreciated

Sure! Here's what I'd suggest for the first approximation:

Alan-speaker-pos-V1-S0360001.jpg

Alan-speaker-pos-V1-S0360002.jpg

Alan-speaker-pos-V1-S0360003.jpg

Alan-speaker-pos-V1-S0360004.jpg

Alan-speaker-pos-V1-S0360005.jpg

Alan-speaker-pos-V1-S0360006.jpg

The green "stick" behind the mix guy's head is a the vertical pole that marks the post where the speaker axes will intercept. Use a mic stand set up vertically for that, or any other pole that you can get to stand up vertically. The rest is self explanatory, I think.

The A7x apparently go down to 42hz so that is probably consistent with your observation about the bass being steeply rolled off by 40hz.

Right! Which is one of the reasons why you need a sub... I'm pretty sure I saw a few bass guitars on your rack, and they go down below 40...

Yes. I do plan to mate them with a sub or pair of subs in the new studio but would rather not go there at the moment.

See above...

I could end up divorced if I start using the budget to buy a pair of Sub10 at this stage

I wouldn't go with the Sub10. There's nothing wrong with it, but the KH805 is pretty darn amazing at a similar price. I've had good success with those in a few studios. The specs they quote are actually conservative, and the real performance is BETTER than what they claim, which is unusual for a speaker manufacturer...

I now see your are talking about Acoustic Axis in 2 dimensions and only referring to the speaker corner for distance from the rear wall

Correct! The images above should make the measurement process a bit more clear, I think.

I am still struggling a little with figuting out exactly where the Acoustic Axis really is for measuring purposes. Any chance you could knock up a reall rough diagram on an image of an A7x or something so that I am sure I am measuring to the right place.

I've never seen them publish that, so I just use generic "rules" for typical 2-way speakers to estimate it, so take it with a grain of salt, but it won't be too far off:

Adam-A7X-axis-estimate.png

It might be a bit lower, if you take the ports into account, but it's close enough for government work, as the saying goes...

1) I have 20cm of Rockwool RW45 in the absorbers behind them and this is hanging 1cm from the wall.

That might be a bit too much, as it pushes your SBIR dip down rather low, but if you wanted to try that as well, then here's the alternate setup:

Alan-speaker-pos-V1-S03-alternate-top.png

Alan-speaker-pos-V1-S03-alternate-side.png

You could also do one more test, as Dan suggested, with no panels and the speakers up against the wall:

Alan-speaker-pos-V1-S03-alternate-3-top.png

Why 20cm of RW45 instead of 10cm?

Because I read Rod Gervais book, and two Alton Everest books (including Masters Hand Book of acoustics) as well as many posts on here that said thicker panels absorb lower frequencies.

Right, but you are missing the issue of SBIR: it's related to the distance between the speaker and the front wall: the further away from the wall you are, the lower down the spectrum it goes... into regions where it can't be treated so effectively, and where it is more obviously noticeable...! The closer you get your speaker to the front wall, the higher it goes, into the lower mid range where it won't be so objectionable anyway, and there's a better chance of treating it. With 20cm + 1, and the depth of the A7Xs at that angle, your front wall SBIR is around 170 Hz. Make it 10cm, and it's up to nearly 220 Hz. So, as with all things in studio design, it's a balancing act... always trading off one thing against another. But do try both: 170 isn't that terrible, and is still with the range of RW45. You might get lucky, and have better performance like that. Supposedly, RW45 has 0.56 coefficient at 160 Hz, so it should knock a couple of dB of your SBIR. For 250 Hz, the coefficient is 0.85, which is substantially better... (above coefficient specs are for 7.5cm, I think, so it would be a bit higher for 10 or 20, but it still gives you an idea of the relative differences).

The lowest I can go on my chair is 130cm

That's a pretty tall chair! Either that, or you are taller than most people. Typical chairs with typical people put ear height at 120 cm. That's the reason why it's the "standard" for speaker height: because most people seated on most chairs average out around there. 130cm is more like the top of the head for most people, seated. If I raise my chair to get my ears up to 130 cm, it's uncomfortable for my legs. We can try 130 if you want. Do another test with the speaker axis and mic position raised to 130 cm, instead of the 124 I show above.

If so does that mean that in my theoretical listening position my chair would actually be further back than 187cm?

Not really. Ear height doesn't affect the distance from the front wall much.

Superchunks - 1200 x 600 sheets of RW45 cut in half then cut diagonally to get four triangles out of each sheet. Which should make them 45cm deep

Not very deep, then. I usually go for at least 60cm, and preferably 90 cm. Now, given the small size of the room, that would make them extend too far across the front wall, but you could still make them 60 to 90 cm down the SIDE walls and less across the front.

I could probably build a few more panels of 1200 x 600 and run these diagonally in front of the existing triangles. Is that worth doing?

You could add "wings" on the side walls, yes, plus some more depth over the main body.

Again, my rookie thinking was that adding some extra air space would help increase efficiency slightly without adding extra material.

It's not the air space per sé that changes the frequency: it's the total depth from the front face of the panel, up to the wall. That's what sets frequency. So you could have a 10cm panel 40cm from the wall, or a 50cm thick panel, or a 25cm panel 25cm form the wall, and they would all work down to the same frequency. The difference would be that the thicker ones would be more effective, and provide smoother coverage across the spectrum, while the thinner ones with air could provide a higher peak, but uneven "comb filtered" absorption from that point all the way up. Here's a simple simulation I did a few days ago for someone else who had a similar question:

Porous-absorption-graph--6-inch-various-combinations.png

All of those have the front face 6" from the wall, but with varying combinations of panels and depths behind that. It's fairly clear, I think.

Sorry about the delay in replying, but I've got several projects in progress right now, keeping me pretty busy!


- Stuart -

[WheresTheDug]

Thanks again for another excellent response Stuart.

Have you tried using a laser measure?

On my way to buy one after I finish this post

Sure! Here's what I'd suggest for the first approximation:

Thanks. Message received and understood.

I've never seen them publish that, so I just use generic "rules" for typical 2-way speakers to estimate it, so take it with a grain of salt, but it won't be too far off:

That's pretty much where I had it. The bit I didn't understand from a previous comment was about the acoustic axis "extending out perpendicular to the face". I thought you meant the actual axis was floating somewhere a little in front of the speaker but you just meant that sound transmits on a line directly from the axis on the face of the speaker.

There's nothing wrong with it, but the KH805 is pretty darn amazing at a similar price.

I ain't going to get away with that just now but hope to use something similar when I finally build the new studio. Could I get away with just one HS8S or T10S for the time being or do I really need a pair?

Remember that I monitor extremely quietly at the moment and have terrible structural transmission to the family areas of the house (hence the need for a new EXTERNAL Studio )

Quote:
1) I have 20cm of Rockwool RW45 in the absorbers behind them and this is hanging 1cm from the wall.

That might be a bit too much, as it pushes your SBIR dip down rather low, but if you wanted to try that as well, then here's the alternate setup:

My current plan is to stick with your advice and move the speakers back towards the wall. I plan to build a new front wall with 200mm RWA45 covering the whole wall EXCEPT an area behind the speakers themselves. I will recess them slightly into the space created but the face of the speaker will still be in front on the 200mm panels. I can push the speakers back to allow for either 50mm or 100m RW45 behind them.

You could also do one more test, as Dan suggested, with no panels and the speakers up against the wall:

I'll try all three but based on your other comments about SBIR I think I will end up 100mm or less.


Does this sound like a reasonable plan?

Assuming I go ahead with this strategy I will end up with the center of gravity of the speakers too far back for the current stands to support due to the little plinth on the ground obstructing the base of the stands.

Any suggestions for mounting the speakers?

I also still have your drawings for the previous studio design. Could I amend the soffit design slightly and build it for this room as a dry run for the real thing?

That's a pretty tall chair!

Yep it is

I use a Hag Caprisco

https://www.back2.co.uk/blog/hag-capisco-8106-review/

I have been known to sit in the same chair playing guitar for 6 - 8 hours at a time. Over the years this has contributed to serious back, shoulder and neck pain. I now play with the guitar on a strap and a chair that is high enough to let my legs drop out of the way. It has done wonders for my back!

I am about to start a 2 year luthiery course and one of the things I want to focus on is designing ergonomic guitars specifically for playing seated without the usual back problems of sitting twisted and hunched over or having to cross legs. This may eventually let me go back to a lower seat but at the moment I sit pretty high. When I want to mix I drop the seat down but even at the lowest level it is still a little higher than most office chairs (around 50cm floor to seat).

If I raise my chair to get my ears up to 130 cm, it's uncomfortable for my legs.

That's why the seat I use has the part behind the thighs largely removed as it stops the circulation being cut off.

Quote:
Superchunks - 1200 x 600 sheets of RW45 cut in half then cut diagonally to get four triangles out of each sheet. Which should make them 45cm deep
Not very deep, then. I usually go for at least 60cm, and preferably 90 cm. Now, given the small size of the room, that would make them extend too far across the front wall, but you could still make them 60 to 90 cm down the SIDE walls and less across the front.

Quote:
I could probably build a few more panels of 1200 x 600 and run these diagonally in front of the existing triangles. Is that worth doing?
You could add "wings" on the side walls, yes, plus some more depth over the main body.

Excuse the poor Sketchup skills but I am thinking along these lines at the moment for the sides and corners. The front wall isn't shown yet. I will also add treatment to the rear wall/window as instructed. I have some ideas for the gobos.

batcave-dimensions.jpg

All of those have the front face 6" from the wall, but with varying combinations of panels and depths behind that. It's fairly clear, I think.

Yes, message received and point well made as always.


I have ordered another 24 slabs of 1200,600,100 RWA45 and some 3x2 CLS timber so will start making some progress next week with any luck.

Does my basic 6 step plan look sensible in addition to fixing the speaker position?

Sorry about the delay in replying, but I've got several projects in progress right now, keeping me pretty busy!

Tut tut..... I can't believe you would prioritise actual paying customers over helping me out for free

Seriously, no problem I very much appreciate all the help so far.

Alan

[WheresTheDug]

img_7773.jpg

So............

some materials arrived today

Still no work done on building actual partitions to hold this stuff but I think the back wall is about to meet it's match Gonna need more lights in here now though!

I have now doe a VERY UNSCIENTIFIC quick and dirty test on the impact of all this RWA45 on the back wall and the speaker placement. I simply pulled up the Test Oscilator on logic and slowly manually swept a sine wave. With the speakers in Stuart's draft suggestion but still on stands around 200mm from the front wall. The RWA 45 did help the dip a little but there was still a substantial drop between around 100 and 150.

I then moved the speakers back so that the rear inside corners almost touch the front all (albeit that they are no just perched on top of a 122 x 600, 200 panel on its side on top of the MDF plinth rather than solid stands) and the dip is MASSIVELY reduced. I wouldn't say it is gone completely but it is now negligible and certainly gives some hope for when I start making panels and taking proper measurements.

[WheresTheDug]

Stuart,

I've spent a bit of time tonight trying to put down my ideas more clearly.

Here are a few images of the proposed treatment (some of which is over the top of the existing eg the Super Chunks in the front corners) some is replacing existing and some is totally new.

The orange panels at the rear will be on wheels to allow access to the door.

Does this look like I'm heading in the right direction?

proposed-treatment--.jpg

proposed-treament-2.jpg

proposed-treatment-3.jpg

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

Is there a more efficient way to use the materials. For example, instead of building corner frames for the windoe alcove and tuffing these with RWA45. Would I get better results for less material by adopting a hanger type trap there?

I have updated the model in Dropbox too so you can take a closer look if if you have time.

Cheers.

[Soundman2020]

With the speakers in Stuart's draft suggestion but still on stands around 200mm from the front wall. The RWA 45 did help the dip a little but there was still a substantial drop between around 100 and 150.

Yup. Exactly where I would expect it. SBIR is a bitch.

I then moved the speakers back so that the rear inside corners almost touch the front all ... and the dip is MASSIVELY reduced. I wouldn't say it is gone completely but it is now negligible and certainly gives some hope for when I start making panels and taking proper measurements.

Don't you just love it when theory turns out to be right in practice?

I've spent a bit of time tonight trying to put down my ideas more clearly.

Nice work, Alan! I see your SketchUp skills have not declined...

The rear wall looks about right, but I would suggest filling the entire "bookshelf" alcove with insulation if you can. You will probably need some wood slats or thick plastic strips over some of that, in order to not kill the highs too much. Polys might be a good idea. Or a combination of both

There's probably too much absorption overall in the room: overkill. I suspect that you'd end up with a "hole" in the decay times for the 200Hz - 500 Hz region like that. I would eliminate two of the three side wall panels, leaving just one at the first reflection points. See how that goes, and if necessary, add another panel on each side. You don't want to kill the room entirely, and you do want to keep the decay times as even as possible. Broad wood slats above and below ear height might be an option there too.... and curving those into a shallow poly shape would be even better. Or spacing slats pseudo-exponentially with different sizes, to avoid to much lobing. Or doing both, with polys and slats in various place. That would be the best.

For the front wall, you are sort of doing an almost soffit, so why not go all the way and do an ACTUAL soffit mount for your speakers? It doesn't need to be the full deal, since this is just a temporary room, but a simple, basic one could still do good stuff for the room.

One other thing: any chance you can move that alarm sensor, so you can continue the superchunk up to the ceiling in that corner? Worth doing if you can.

Here's a very rough-and-dirty concept of what I would suggest:

Batcave layout--V3-S010001.jpg

Batcave layout--V3-S010002.jpg

Batcave layout--V3-S010003.jpg

Batcave layout--V3-S010004.jpg

Batcave layout--V3-S010005.jpg

I uploaded the actual SKP to your old directory on my server, so you can download and play around with it.

It's just a very rough concept, though! Don't take that as Gospel truth. Just some ideas to get you on the right track....

- Stuart -

[WheresTheDug]

That's awesome Stuart!!!

I'll get to work on the rear wall and gobos first as that seem pretty much non contentious. I actually have a couple of Oak newall posts of 1500x90x90mm lying in my workshop that I haven't had a use for. I'm going to rip them down the middle. Lop them off at 1m and use them to make legs for 2 gobos

The front wall will be stage 2. I like the idea of trying a soffit mount just as a trial run. How would I go about building it or modifying the one you sent me previously?

Is there any point in taking out the current front super chunks and reusing the materials as hanger instead?

The side walls will be last as I suppose they will be influenced by what I do with the front corners. I can always just re hang a couple of the existing panels that I have rather than take them apart and build a new frame to fill.

I'm not inclined to fully fill the book shelves at the moment unless it becomes absolutely necessary as I need storage space somewhere and don't really have any other space.

Happy to add wood slats and polys as required. I'll get the insulation in place first and then ask you for more guidance based on how the measurements look.