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PostPosted: Tue Jun 06, 2017 10:19 pm 
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Posts: 55
Location: Derbyshire, England
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

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PostPosted: Tue Jun 27, 2017 12:04 pm 
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Location: Santiago, Chile
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: :!:


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PostPosted: Thu Jun 29, 2017 11:56 pm 
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Location: Manenberg, Cape Town, South Africa
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.


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PostPosted: Wed Nov 01, 2017 6:05 pm 
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Location: Manenberg, Cape Town, South Africa
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/).


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PostPosted: Thu Nov 02, 2017 1:37 am 
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Location: Santiago, Chile
Quote:
However, it's uncomfortable for me to work in,
"Uncomfortable" in what sense? Please describe exactly what physical sensation you are experiencing.


Quote:
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?

Quote:
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.

Quote:
Mr Sabin probably knew what he was talking about.
Actually, later research showed that he was wrong in some aspects. Close, but not exact.

Quote:
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?

Quote:
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.

Quote:
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.


Quote:
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:

Attachment:
QRD-Diffusion-lobing--pattern-graph-SML-ENH.PNG


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...

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PostPosted: Tue Nov 07, 2017 1:09 am 
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Joined: Mon Jan 23, 2017 2:59 am
Posts: 48
Location: Manenberg, Cape Town, South Africa
Hi Staurt

Thanks for your replies.

Soundman2020 wrote:
Quote:
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:
Quote:
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:
Quote:
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:
Quote:
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:
Quote:
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).

Attachment:
R1.jpg


Soundman2020 wrote:
Quote:
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:
Quote:
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.


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