Garage studio in South African township

Some new things today - added another bass trap along the top of the back wall (will leave fully foiled & not yet put cloth over it for now so I can cut holes if needed) - got the fronts on the baffles - took the thin plastic off all the walls (it is still covering the ceiling for now) - put loads of the calico cloth up - put some thick plastic on some of the walls at the back that are neither first reflections nor going to be slatted - listening to music test is even better (tighter bass) and I listened to a few references and then listened to a test recording I did with a local singer - my test sounded terrible! So good to be able to see it under a microscope to see (hear!) what's really going on. Ideally I'd do a test for each change but I have other work to do while my carpenter beavers away so I can only test at the end of the day Here is the new REW test F with all these changes https://www.dropbox.com/s/kgzy7z50b7mi9 ... .mdat?dl=0 What I'm seeing in the graphs: - Comparing test C (previous best test) to F, the SBIR is 3db better at 100Hz & there's none of that funny stuff happening sub 30Hz. I did do 2 sweeps this time so presumably it was car noise and the average of 2 sweeps takes it away from the test results. It's often written that 6dB is a doubling of volume so I must admit I'm a bit worried about the SBIR dip - which is currently a 20dB difference between 40 and 100Hz. I do hope to get a parametric EQ at some point to adjust for the extra bass that flush mounting brings. Perhaps if the region of 40-80Hz is brought down it might help the 100Hz dip? - The waterfall shows a good improvement <1kHz - The RT60 is a tiny bit better - The spectrogram I have no idea what it means! But I think the disappearance of those blue blotches is good - though perhaps that's just the car noise already mentioned.

Today I got some thick plastic from the garden centre. It weighs in at 0.268 kg/m2, meaning F = 336Hz, even lower than the foil. I tried putting it up on the ceiling, over the thin plastic for now, covering the rear 2/3's of the ceiling - the area that isn't first reflections (and I actually bothered to do the mirror test rather than eyeballing it and realised the first reflection point was much further back in the room than I thought.) Test H (https://www.dropbox.com/s/kkp0wiu7n4kdd ... .mdat?dl=0) Here is the before and after SPL for both speakers. The main thing I see is the weird dip at 12k. This isn't present on either the Left or Right speaker tests. For the T30 graph (not sure which of the RT60 graphs is best to show), there is quite a bit of improvement in the 500-5000Hz range. But still my mids are well below what I'm aiming for. I noticed on the Bob Gold site that 100mm of 703 is actually more absorbent in the mids than the highs. And given that I started by covering my entire room pretty much in exactly that, that could be part of the problem. I can still add some more of the thick plastic to the bass traps and a couple of other areas, but I also wonder if I just need to take some of the fibreglass batts out of the room? I also checked again the Bob Gold calc (http://www.bobgolds.com/Mode/RoomModes.htm) and for my dimensions (4.02m L x 2.74m W x 2.53m H) it recommends around 300 sabins = 28 sq m of absorbtion. My rear wall plus left and right walls alone are 27. At the moment I have about 40 sq m of absorption. I had thought that people who did inside out walls did fill every section with 4" of fibreglass and then just use thick plastic and slats to deal with the too-many-sabins problem, but I'm not seeing the results (yet) on REW tests, plus it would have been cheaper to buy a few less fibreglass batts so I may have made a mistake here. Hopefully in the next few days I'll have all the slats I ordered up and see how that affects things. The calc also gives this to aim for "Recommended RT60 161ms, ±50ms from 200Hz to 4kHz = 111 to 211ms" which made me feel a bit better in that I'm not miles from that at the moment & am working to get everything above 111ms.

Did a test with more covering on the rear bass traps. https://www.dropbox.com/s/y4cy9vns5bvxo ... .mdat?dl=0 Test H is the "before" with just the foil Test I is around 30% cover with the 3mm ply veneer covering the traps (saw a thread where this was suggested)Test J is full cover over the foil with the thick plastic (therefore not a very fair test as I don't have enough 3mm ply lying around)Q - is it fine to do foil and plastic or best to take the foil off if I decide to keep it (fully or partially) I'm looking at the area below 111ms on the RT60 graph for improvement. There is quite a bit of improvement in both tests and the most with the full plastic cover. But the waterfall is a bit worse and the dip at 390Hz on the SPL is worse. What I don't quite understand is how with most of the ceiling and all of the back wall covered in thick plastic, my RT60 is still far too low. How do I ever get liveliness back into this room?! (Lots of slats are going up soon so we'll see what they do, but from what I've read it's more the highs than the mids that they'll help with in terms of reflection).

Had to wait a long week while my carpenter was unavailable – he's the only guy round here I've found who understands what I'm talking about so I had to wait for him. I know I'm going quickly compared to some, but I find I'm so impatient to see it done. Gave me time to get the slats varnished and then he & his brother put them up. Slats! Slots! I feel I've joined some kind of club! (photos in next post as I've hit max attachments) REW test K with the slats up (https://www.dropbox.com/s/nwbza2awb093r ... .mdat?dl=0) Comparing back to test F as the tests after that were non-permanent (now using variable smoothing for the pics – hope that's ok, it seems to be similar to what you suggested Stuart though not quite as strict. Compared to 1/48 smoothing, it's not hiding any problems in lows or mids, but is tidying up the graph in the highs) - SPL is similar apart from >4k there's a dip and the SBIR at 100Hz is a tiny bit worse. - RT60 is a whole lot better - Waterfall is a bit smoother in the low end (also shows the same improvements in mids/highs that the RT60 graph shows.) - Listening is much more enjoyable, less fatiguing I then did a whole bunch of tests to hunt for more of the elusive liveliness that's still somewhat lacking. For test L (https://www.dropbox.com/s/qm2wfd59ioi7f ... .mdat?dl=0) I took out all of the ceiling fibreglass that wasn't in the first reflection point area (and tried a few small things that you can see in the file, but the main test I included in the next file so this can be safely skipped) For test M (https://www.dropbox.com/s/54brkn4lf726k ... .mdat?dl=0) I tried putting back some of the ceiling fibreglass, but 50mm (2”) this time to try to hit highs and not mids and I also tested putting some board directly under the speakers to extend the baffles to nearly the floor to see if that affected my SBIR. M.1 is with extended baffle, M.2 is without. There is also some testing with the listening position moved forward slightly to help with the SBIR dip. - SPL shows test L being much worse for the 100Hz SBIR dip, but putting back some of the ceiling 703 solved that in test M. Test M also solved the >4kHz problem, not quite sure why. The extended baffle didn't seem to help the 100Hz dip by more than a few dB. - RT60 greatly affected in test L by removal of ceiling absorption, but the highs have gone too high. Test M seems to be a good middle ground, it's the best I've seen the RT60 so far. (Incidentally, I've seen some debate as to whether RT60 means anything in a small room, but I've found it very useful in getting the deadness/liveliness balance right where for example you can make good decisions on reverb in a mix.) - I'm not really seeing much for or against the extended baffle - the low end on the waterfall is perhaps a little smoother, but it doesn't seem to be hear or there unless I'm missing something.

Some pics Testing the covering of the bass traps to try to reflect mids Slats!

WOW! that looks great with the slats up, suddenly like a studio! These graphs and explanations of your trial and error are really interesting so thanks for taking the time to share. I guess you're almost finished with this now? I wonder if there's anything that can be done to sort out that 100Hz, but I'm guessing you've got a 3.4m dimension somewhere in the room that's the mode for?? Nice work Gareth

Thanks Gareth. What's also great, it the slats really seem to make a difference to how people perceive the studio - like they actually believe in it. I must admit I've run out of ideas to deal with the 100Hz dip. The only thing left up my sleeve in the room is to use a parametric EQ to deal with the 6dB excess bass caused by the soffits. On my SPL graph at 50Hz, 200 Hz and 500Hz, it's pretty much spot on 6dB too high at 92dB (test ran at 86dB for both speakers). So my hope is by lowering that to 86dB, the relative drop between 50 and 100 Hz will be less. But that assumes the 100Hz won't just drop down 6dB (but then maybe I can boost it at 100Hz). My theory is that if it is destructive interference, then having less energy at that frequency in the room will mean less interference and less dip/smoother curve. But I did try running a REW test at 70dB to see how it affected the dip and it didn't reduce it relatively - the whole graph just moved down. So that's not a great sign, but I'm hoping anyway. I'm sure having done all I can with treatment I'll be able to get something out of EQ'ing. Anyway I hope Stuart will correct me if I'm talking nonsense.

Hi Random question, what dimensions did your silencer boxes end up? I'm still trying to sort mine out and we have similar sized rooms. Do you need to run that fan on high speed at all or is it OK on low speed? Thanks! Gareth

garethmetcalf wrote:

Hi Random question, what dimensions did your silencer boxes end up? I'm still trying to sort mine out and we have similar sized rooms. Do you need to run that fan on high speed at all or is it OK on low speed? Thanks! Gareth

Mine are 100cm x 59cm x 26cm and made from 18mm chipboard with 25mm liner. My external one is letting in a bit of sound, but I can see daylight through the join from the room so they didn't seal it right - it should be better once I've finished that. But I can see why Stuart likes two rather than one for the in and out. I know a lot of people would maybe double up the board and maybe add green glue but I was keeping my costs down. The fan I run on low and I feel like even that is much more than I need, so I wish I had got a variable one, but it wasn't easy finding anything round here. When I had it blowing into the room from outside I could hear a lot of the fan noise in the room and when I have it blowing out I still hear a little (Stuart also posted about this earlier in thread). I think part of my problem is I have no duct at all - just fan plugged into silencer which is on the external wall with a hole through to the room. I think more ducting would give a chance for the fan noise and turbulence to get absorbed.

We are now off the to the UK for 6 weeks and I've basically finished the room bar a few cover strips that will cover the staples, and the registers/vent covers (Gareth did you find any in UK? any links? I'd love some with built in air filters that are washable). Could also use a small sofa if I can get one. REW tests Test N: https://www.dropbox.com/s/0b3xnftd4xy2h ... .mdat?dl=0 Test N.1 is putting the lower baffles permanently under the speakers Test N.2 is testing covering some of the bass traps with 3mm ply to help boost the lower-mids in the RT60 Test P (I skipped O): https://www.dropbox.com/s/f0mu0i80qu5y5 ... .mdat?dl=0 (80MB includes test N.1) Test P.1 is with the door now covered with 50mm insulation to match the wall opposite it & the back bass traps now permanently covered in 3mm ply in two patches Test P.2 is bringing in the dreaded desk - which made the SBIR dip worse at 100Hz but better at 400Hz Test P.3. (only done at +20cm) is trying the desk at a 6 degree angle (spoiler - it didn't bring the magic I'd hoped for) Test P.4. (only done at +20cm) is trying some cushions on the desk first reflection points to see what they were doing Also included K,L,M,N for comparison (note for REW newbies, in REW you can use alt-up/down arrow to quickly switch between measurements to see the change) What I'm seeing in these tests is that there's pro's and con's for moving the listening position between 0cm and 20cm (having done Stuart's walking mic test I zoomed in on this area) - moving forward helps the SBIR dip but worsens the 40Hz mode. The highs also dip at some positions. Also my waterfall was better a few tests ago than it is now! Maybe I still need to try some things when we come back, like taking off the rear 3mm ply or taking out the lower baffles. I'm very happy with the improvements in my RT60 from the start though. It is now within +- 50ms albeit a bit low overall. And overall, what the graphs don't show is that I'm hearing my reference tracks like I am in the studio with them. It feels like cheating! So happy with how it sounds and looks.

Thanks for the reply. I'm going to start with one silencer on each path too and can always add an outside one if needed. I've not looked for registers yet but there's loads on eBay I have the following small sofa from ikea - cheap and comfortable enough for an hour http://www.ikea.com/gb/en/products/sofa ... -20340541/ Looking great!! I'm hoping I can get mine started soon. Gareth

It's getting better and better, Nick. Your "big dipper" is very likely a floor bounce issue. You could test that by dropping a large, thick panel of insulation on the floor, in between the speakers and the desk. I'm downloading your library of MDAT tests at present, to take a look at them, but it's taking a little while! :shock: :!: - Stuart -

I may have overdone it with the REW tests - I wanted to record the changes between anything 2 things I changed in the room. But you can just look at the final test P if you want - it has most of the main previous tests in it as well for comparison.

So I am very happy with the sound of my studio and the sound isolation. However, it's uncomfortable for me to work in, especially when my sinuses are playing up like now, when it's really unpleasant. I think it is too much absorption, though I have considered the pressure might be high in there as I am pumping in air quite hard and my outbound silencer might not be able to keep up. That gives me one idea though to test, which is to have the air pumping out instead of in. I wish I had got a pump with a variable dial as my lowest setting is more than I need when it's just me. But given that I filled every nook and cranny of the inside out walls with absorption, I do think that in hindsight was a mistake. Mr Sabin probably knew what he was talking about. So I plan to take some of it out or cover it fully rather than with slots as I have now. My graph shows my RT60 (if you believe in a small room one can trust such a number) at it's lowest at 79ms at 250Hz - just where my slats are doing their job. I did really want a lot of slats in my room, but I might have overdone it! I do also like the idea of a 1D diffusor on the back wall, even though my studio isn't really big enough for it. Anything that might make it more of a room to enjoy being in. I am considering either a QRD calculated via QRDude (http://www.subwoofer-builder.com/qrdude.htm) or the Arqen design (http://arqen.com/sound-diffusers/).

However, it's uncomfortable for me to work in,

"Uncomfortable" in what sense? Please describe exactly what physical sensation you are experiencing.

I am pumping in air quite hard

What speed? What flow rate? Did you do the math properly when you designed that system? Are you SURE you are not overdoing the flow velocity (which should not exceed 300 fps EVER in a studio). Are you sure you are not exceeding the correct flow rate for your room? DO you have suitable filters on your air system, to ensure that you are not circulating dust, pollen, and similar stuff? Also, are you sure you used suitable insulation, and that the parts that can cause problems are suitably covered?

But given that I filled every nook and cranny of the inside out walls with absorption, I do think that in hindsight was a mistake.

I can't agree with that. It's not a mistake, if done correctly.

Mr Sabin probably knew what he was talking about.

Actually, later research showed that he was wrong in some aspects. Close, but not exact.

So I plan to take some of it out or cover it fully rather than with slots as I have now.

Taking it out would damage the acoustics. Covering it would be the right thing to do, but that leads to the question: Why is it not covered?

My graph shows my RT60 (if you believe in a small room one can trust such a number) at it's lowest at 79ms at 250Hz

That's way too dry, even for a small room such as yours.

at 250Hz - just where my slats are doing their job.

Are you sure about that? And if so, why did you tune them so low? But taking out the slats is NOT going to fix your room: it will likely make things worse, not better.

I do also like the idea of a 1D diffusor on the back wall,

Why? What is the ACOUSTIC reason you have for that? ANd how do you plan to tune the center frequency of such a diffuser to 250 Hz, which is what you say you need? In other words, to hit 250 Hz well, you'd need to build one that has a low cut-off of maybe 150 Hz and a high cut-off at around 500 Hz. Do the math (Using QRDude), and see just how big that monster would have to be... your room is probably not big enough to even fit it in. Also, using the Cox and D'Antonio equations, you would have to have that device at least 11 meters away from your head, in order to be out of the lobing patterns... the wavelength for 150 Hz (low cut-off) is 2.3 meters.... times 5 is 11.5 meters.... :shock: By all means put a diffuser on your rear wall, but do be prepared to lose the clarity and directionality of your sound stage, since this is what it will do: Considering the low tuning of the device you would need, and the size of your room, your head would be around the fourth or fifth red band up from the face of the diffuser. That's the type of lobing you could expect from such a device, in your room. A lean fractal might work, as it does get a generally smoother response, but the room is still very small for any type of diffuser. You also do need some diffusion up higher, but not much! A full height lean-fuser would be too much. I'd go for a much smaller one (not very tall), centered around ear height. Your decay time dip around 200 Hz to 500 Hz is typical of small rooms, and is not something that can be fixed easily. There's a basic principle in acoustics: sound waves are only affected by objects that are similar in size to the wavelength, or larger. At 250 Hz, the wavelength is roughly 1.4 meters, so any device you build that is smaller than about 1.4 m high or wide, is not going to have much effect on 250 Hz. Waves that are larger (lower frequency) than the dimensions of the object tend to wrap around it, and perhaps be diffracted or refracted by it, but not reflected nor diffused. Only waves that are smaller (higher frequency) will be reflected or diffused. So whatever it is you build to treat your 250 Hz problem, will need to be very large. You can make your slot walls appear to be larger, acoustically, by plugging some of the gaps between the slats. Use strips of cardboard about the same size as the gap, just to test if this would have any effect on your room response, but I'm betting the effect would not be large, if any. I very much doubt that your slot walls are having a major effect at 250 Hz. At least, not from being individually tuned to that frequency. There might be some "percent coverage" effect, or just plain absorption, but it's unlikely that you are seeing a tuned response at 250 Hz. It is FAR more likely that your 250 Hz problem is related to room dimensions, and room geometry: perhaps SBIR, perhaps modal, perhaps phase cancellation. But I would not blame it on slot walls, or over-use of insulation. Do you still have your original REW data, from the empty room, without any treatment at all in it? I'd really like to see that: I'm betting the underlying problem is probably visible in that... - Stuart -

Hi Staurt Thanks for your replies.

Soundman2020 wrote:

However, it's uncomfortable for me to work in,

"Uncomfortable" in what sense? Please describe exactly what physical sensation you are experiencing.

I feel like after a day in there, or less really, it’s like my ears are tired. Like they’ve been exercised too hard. I even notice it as I am working, and my levels are not loud – I feel like my ears are a little sore almost. Plus I have experienced tinnitus since starting with having a studio – it’s not too bad, but what bothers me is not knowing if I’m making it worse.

Soundman2020 wrote:

I am pumping in air quite hard

What speed? What flow rate? Did you do the math properly when you designed that system? Are you SURE you are not overdoing the flow velocity (which should not exceed 300 fps EVER in a studio). Are you sure you are not exceeding the correct flow rate for your room? DO you have suitable filters on your air system, to ensure that you are not circulating dust, pollen, and similar stuff? Also, are you sure you used suitable insulation, and that the parts that can cause problems are suitably covered?

I’m totally sure, but I don’t think these are the main issues. For example, I am experimenting with turning off the fan for a short time (and opening the doors frequently) – and it doesn’t solve the issue. I might have slightly too powerful a fan and try to get a lower flow rate, but I don’t think that’s make or break.

Soundman2020 wrote:

But given that I filled every nook and cranny of the inside out walls with absorption, I do think that in hindsight was a mistake.

I can't agree with that. It's not a mistake, if done correctly.

Yes, I can see what you’re saying – in that either I can completely cover the absorbtion (in which case it is extra sound isolation) or I can somewhat cover it with wood – either way I’m sure it’s possible to get the decay times up – though it might cost more than having put less insulation in.

Soundman2020 wrote:

So I plan to take some of it out or cover it fully rather than with slots as I have now.

Taking it out would damage the acoustics. Covering it would be the right thing to do, but that leads to the question: Why is it not covered?

I mean cover it with slats. It is covered with cloth already.

Soundman2020 wrote:

My graph shows my RT60 (if you believe in a small room one can trust such a number) at it's lowest at 79ms at 250Hz

That's way too dry, even for a small room such as yours.

This I think is my main problem. I have read in various places of it being draining on your ears to have too little decay in a room, so that’s for me at least one place to start. There is also mention of diffusion helping too, though there are issues in small rooms. I am quite drawn to the Myroom method (Mark I http://www.myroom-acoustics.com/hosted/ ... _paper.pdf Mark II http://www.myroom-acoustics.com/hosted/ ... 0x1.2m.pdf) which combines absorbtion and diffusion – basically like John’s slats, but turning them into the room. The designer speaks a lot about bringing life back into the room. One other possible thing is that I have yet to use my parametric EQ (FBQ2496) as I was waiting to do everything in the room first. But this does mean I have been listening every day with 6dB too much bass. I have tried a basic set of filters from REW into it to at least work with for now (I can still bypass it for further REW tests). It does change the sounds significantly and sounds more even across the spectrum, if less impressive (I guess more bass is always impressive even if it's not helpful for hearing accurately).

Soundman2020 wrote:

at 250Hz - just where my slats are doing their job.

Are you sure about that? And if so, why did you tune them so low? But taking out the slats is NOT going to fix your room: it will likely make things worse, not better.

I am still lacking unstanding in the area of slats, and specifically the Helmholtz resonator type I am using. When we talk of the resonance being in the region 250-450Hz, which I have, is that the same thing as saying they absorb in that frequency? i.e. that it would lower the decay time in that frequency? And how does it affect the SPL graph? Looking back at my REW tests before and after slats, I did have a runaway peak on my waterfall at 215 Hz that the slats completely took away. And they didn’t seem to lower the T30 either. So yes, I can see that slats themselves are not my problem. However, I might try using the slats in the Myroom method as at least something to try.

Soundman2020 wrote:

I do also like the idea of a 1D diffusor on the back wall,

Why? What is the ACOUSTIC reason you have for that? ANd how do you plan to tune the center frequency of such a diffuser to 250 Hz, which is what you say you need? In other words, to hit 250 Hz well, you'd need to build one that has a low cut-off of maybe 150 Hz and a high cut-off at around 500 Hz. Do the math (Using QRDude), and see just how big that monster would have to be... your room is probably not big enough to even fit it in. Also, using the Cox and D'Antonio equations, you would have to have that device at least 11 meters away from your head, in order to be out of the lobing patterns... the wavelength for 150 Hz (low cut-off) is 2.3 meters.... times 5 is 11.5 meters.... :shock:

The reason I am after diffusion is firstly that it is at least something to try – what I do know for sure is that I am not comfortable in my room. And the Myroom designer has reported using it to good affect. However, I do understand that in my small room I am not going to be able to diffuse in that sub 1kHz range with the limitations of the diffuisor size and the minimum distance from listener to diffusor.

Soundman2020 wrote:

A lean fractal might work, as it does get a generally smoother response, but the room is still very small for any type of diffuser. You also do need some diffusion up higher, but not much! A full height lean-fuser would be too much. I'd go for a much smaller one (not very tall), centered around ear height.

This is also a good option I might try.

Soundman2020 wrote:

Your decay time dip around 200 Hz to 500 Hz is typical of small rooms, and is not something that can be fixed easily. There's a basic principle in acoustics: sound waves are only affected by objects that are similar in size to the wavelength, or larger. At 250 Hz, the wavelength is roughly 1.4 meters, so any device you build that is smaller than about 1.4 m high or wide, is not going to have much effect on 250 Hz. Waves that are larger (lower frequency) than the dimensions of the object tend to wrap around it, and perhaps be diffracted or refracted by it, but not reflected nor diffused. Only waves that are smaller (higher frequency) will be reflected or diffused. So whatever it is you build to treat your 250 Hz problem, will need to be very large. You can make your slot walls appear to be larger, acoustically, by plugging some of the gaps between the slats. Use strips of cardboard about the same size as the gap, just to test if this would have any effect on your room response, but I'm betting the effect would not be large, if any. I very much doubt that your slot walls are having a major effect at 250 Hz. At least, not from being individually tuned to that frequency. There might be some "percent coverage" effect, or just plain absorption, but it's unlikely that you are seeing a tuned response at 250 Hz. It is FAR more likely that your 250 Hz problem is related to room dimensions, and room geometry: perhaps SBIR, perhaps modal, perhaps phase cancellation. But I would not blame it on slot walls, or over-use of insulation.

Ok good to know.

Soundman2020 wrote:

Do you still have your original REW data, from the empty room, without any treatment at all in it? I'd really like to see that: I'm betting the underlying problem is probably visible in that...

Unfortunately that was my first and biggest mistake - I never took a REW measurement in the empty room because I didn't have the equipment at that stage and I had a limited window of time with my building crew. Hopefully at least anyone who reads this thread for research can learn from my mistake.