# First Post. First reflections first?



## modusmongo (Jun 26, 2013)

Hi folks! I've been over at the REW forum for a week or so getting a somewhat accurate reading of my room, and now I'd like to talk to you about how to improve the sound.

I have a rectangular room ALL IN WOOD except for the ceiling which is plaster. 6.91m x 4.94m x 3.5m ceiling.

Here is a pic of the room from behind my comfy chair as well as a speaker placement plot:
















After using two different uncalibrated mics, and three different soundcards for connecting the system to the testing software, I am confident that the readings below are of good enough quality for me to start doing some room treatment based on the results. Here is the REW mdat file.
View attachment Acoustics forum.mdat


As you would imagine, the room is extremely live. Unfortunately, it is the only room I have, so it will have to do. While soft music sounds fabulous, anything with crashing cymbals or electric guitars turns into a ringing mess at volume. This will not do! While I can see that the bass needs treating, it is the mids that are making it hard for me to enjoy loud music, so i'd like to treat them first.

What I would like to do, pending your approval, is to start by reducing First Reflections. I imagine that I need to put dampening panels on the side and rear walls using the mirror method, then the ceiling as well. I'll get a good sized thick rug for the area between the speakers and my chair.

For the moment I'm only interested in treating for the sweet spot around my chair.

After getting T20 T30 readings down in the midrange, I'll reassess the room with calibrated equipment and go after the bass response holes, and probably create a minimal convolver file.

I can not buy the GIK stuff. Way out of budget for me ;-). I also live in France where compressed fiberglass does not exist. I need to go DIY with Rockwool (I assume). I also do not expect to achieve perfection; I'd like to tackle one thing at a time then go after the next thing that bugs me.

So my questions for you are:


Am I going about this all wrong?
Does anyone here have experience buying rockwool in France/Europe?
What brand and thickness rockwool should I use? 
What size panels?
Do I need to frame them in wood, or can I simply wrap them in tissue and hang them?
What kind of wrapping tissue?
Should I leave space between the wall and the panels based on my readings?

Thanks in advance for your time and experience!


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## AudiocRaver (Jun 6, 2012)

I definitely agree with the approach, get control of the midrange RT60 & early reflections! Have no experience with the materials. The local experts will have ideas. Good Luck!

What kind of speakers are they?


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## modusmongo (Jun 26, 2013)

Hi cRaver. Thanks for the reply. The speakers are French: BC Acoustique "Gange". Three-way non ported. Each driver in a separate enclosure. I like them very much, but I hope to like them more! See you around.


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## bpape (Sep 14, 2006)

I would do more broadband treatments. While a room that live will tolerate some small amount of mid/high absorption only, I think you'd get more bang for the buck with a more broadband approach. Think 75-100mm panels for side wall reflections - 150-200mm for the wall behind you, and then we will address the front corners.

We use ECOSE in our products as the core in Europe.

Bryan


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## AudiocRaver (Jun 6, 2012)

Thanks, Bryan, sounds like sage advice.


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## modusmongo (Jun 26, 2013)

Hi Bryan. Thanks for your response.

Would the panels you suggest still be placed in the typical "first reflection" positions? How big do you think they need to be?

I can not find anyone who sells Knauf Ecose boards in France (it _*is*_ the board and not the roll that I want, yes?). Of course, I may not be looking correctly; is there a model number I should be looking for? I can find rockwool "laine de roche" in panels for around 7€/m2 at 100mm thickness and rolls at 9€/m2 at 200mm, but I wonder if it is as compressed as I need - I am assuming that the boards are more compressed than the rolls. I know there are ecological considerations as well, but I don't know how much I can pay for them - that is surely the subject of MANY other threads. I suppose my bottom line question is "how much of the cheap stuff do I need in order to match the absorption of the good stuff?"

AND, I really do need to know how much I can expect to achieve with the room. I rent my apartment, so I can not make any drastic changes. Maybe I should be looking for a good set of headphones ;-)


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## modusmongo (Jun 26, 2013)

Hmmm. Just re-reading my last post. I hope it doesn't sound like I have an attitude problem. I did come here for advice and will take it as long as I can afford to. I would *LOVE* a Roomkit #4 from GIK, but it's out of the budget.

I'm really hoping (as suggested in this thread) that someone will read the .mdat file and point me in the right direction. I *am *a DIY kind of person; so building panels and traps will be fun for me.

A fine day to you all


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## chashint (Jan 12, 2011)

Sorry I cannot offer help with your room treatments, but just thought I would say your posts are not abrasive and do not make you appear to have an attitude.
Good luck with your room, it looks very nice.


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## bpape (Sep 14, 2006)

You can use the roll if it's at least 2lb/cu ft density. For the mineral wool, what is the density (probably in kg/m3) for what you found?

The MDAT plots you showed are OK but very hard to read. Try the frequency response just 30-400Hz and with the gradations on the left being 5db each. Log scale across the bottom. Waterfall is hard to read for the same reasons and has the same answer - though initially it looks like a need for more control below 100Hz, which is not at all unusual.

I opened the MDAT file - the above is just for clarification and ease of reading in the thread. Looks like you have a peak about 50Hz that's about 8Hz wide to address, another around 75, a dip around 150, and a general peak around 160-180. One other large null about 230Hz. Overall, the response could be MUCH worse.

Definitely the decay times below 100Hz need to be addressed.

Don't seem to have many reflections that are not at least 20db down in the first 20ms but that's more likely just the setup in the room. Reflection control can still be a benefit even outside those bounds. Whether it's absorption or diffusion will depend on the overall decay desired in the room as well as the off axis response of the speakers.

Bryan


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## modusmongo (Jun 26, 2013)

Hi Bryan. So somewhere in the area of 32kg/M3 right? I can get panels 1.35m x .6m. Densities are 26, 55 or 70 kg/M3. Thicknesses from 75 to 125. Which would be preferable? Is denser always better? If it is denser, do I need less thickness?

I was thinking of putting one panel each on the left and right walls at the mirror positions, two on the ceiling end to end (2.7m x .6m) and four on the back wall doubled for a 200mm thickness. But where on the back wall? Just off center where the reflections come back to me? Is this enough for a start, or should I double up? Thanks


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## sdurani (Oct 28, 2010)

modusmongo said:


> I've been over at the REW forum for a week or so getting a somewhat accurate reading of my room, and now I'd like to talk to you about how to improve the sound.


Can you move your speakers slightly closer to each other, so that the middle of their woofers are 2.47m apart, and re-measure the frequency response?


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## modusmongo (Jun 26, 2013)

Hi Sanjay. I had to move them away from eachother slightly (they were 220cm apart). I did the readkings left and right separately.
View attachment LandR.mdat


Left is GREEN. I hope these charts are easier to read than my last ones ;-)


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## bpape (Sep 14, 2006)

If I remember the conversions right you'd want the 55.

Back wall, centered behind the seating.

Density vs thickness is just the opposite - the thicker you get, the less density you need. Never a substitute for thickness.

Bryan


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## modusmongo (Jun 26, 2013)

So I went to the local HW store to look at the rockwool. Very unimpressed. It was 100mm thick, but I could squeeze it to 15mm easilly. HOWEVER, I did see that they have *hempwool*. It was thick and lovely and not expensive. A 100mm panel was really 100mm. I could squeeze it a little bit, but not very much. It was "substantial". It was also unadulterated, pure, no chemicals - I like that. Does anyone have an opinion on using it for my project instead of rockwool?


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## bpape (Sep 14, 2006)

It would again depend on the density. 

For example, 3lb/cu ft cotton can easily be compressed by squeezing it. 3lb/cu ft fiberglass like OC703, really doesn't compress and if it does, it stays compressed where the cotton will come back for the most part. 

Yet, they're both the same density and the cotton will actually perform slightly better.

Bryan


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## modusmongo (Jun 26, 2013)

This stuff is DENSE. In the 70kg/m3 range. Is hemp a good performer?


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## modusmongo (Jun 26, 2013)

Sorry, I exagerated. Calculation puts it at 48kg/m3

Which equals 3.02lb/ft3


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## bpape (Sep 14, 2006)

Hemp should be fine and the density is fine.


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## sdurani (Oct 28, 2010)

modusmongo said:


> Hi Sanjay. I had to move them away from eachother slightly (they were 220cm apart). I did the readkings left and right separately.


Thanks for trying that. One last request: can you make sure the centre of the woofers are 2.47m apart (1.235m in from the left and right walls) and measure both speakers together? 

The reason I say together is because most recordings have the low frequencies summed to mono, so both speakers will usually be playing the same bass at the same time, not individually. 

Also, those are the locations in your room where you will find nulls. If you can place the objects that generate sound pressure (your speakers) precisely where sound pressure is lowest (nulls), you could smoothen out the low frequency response.


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## modusmongo (Jun 26, 2013)

Hi again Sanjay. Will do. But are you not also concerned about the placement front to back? Do you want me to place the speakers so that the woofers are 1.73 meters from the back wall? One last question: the speakers are currently "toed in" (they converge at the center of the back wall). Should I change this?

Thanks for helping!


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## bpape (Sep 14, 2006)

Remember that when you change toe in, you're changing slightly distance to side and front wall also.

Bryan


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## bpape (Sep 14, 2006)

Remember that when you change toe in, you're changing slightly distance to side and front wall also.

Bryan


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## modusmongo (Jun 26, 2013)

I make the measurements from the center (left to right) of the bottom front edge of the tower - just under the woofer. That should keep things consistent, right?

Just came from the HW store with 12 panels of hepmwool. 120 x 60 x 10cm. Now to the sewing machine!


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## bpape (Sep 14, 2006)

Sure - that will work. Just saying to consider it when moving things around. Some people set up to a measurement and then change the toe in.

Bryan


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## sdurani (Oct 28, 2010)

modusmongo said:


> But are you not also concerned about the placement front to back? Do you want me to place the speakers so that the woofers are 1.73 meters from the back wall?


Not at the moment; not for this one measurement. One change at a time so we can measure whether it makes an improvement or not.


modusmongo said:


> One last question: the speakers are currently "toed in" (they converge at the center of the back wall). Should I change this?


For this one measurement, toe in doesn't matter, since we're trying to improve the bass. However, as Bryan pointed out, toeing in your speakers could change the distance between woofers. 

So, IF you do decided to toe in your speakers for this one measurement, then make sure you pivot your speakers on the woofers (move the back of the speaker while keeping the front in the same location). 

Whether you toe them in or not, just make sure that the middle of the woofers are 1.235m in from the side walls before you measure. Thanx.


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## modusmongo (Jun 26, 2013)

Well... I need to post a little update. This afternoon, I put 3lb/ft3 hemp wool panels into light cloth covers and made the following absorption panels:


4' x 4' x 4" on the left and right side walls at the first reflection points
2' x 8' x 4" overhead ceiling reflection zone - will get this to 8' x 4' as soon as I tackle some upside-down engineering tactics 
4' x 4' x 8" bass trap(?) at the center of the back of the room

FWIW, these are all sitting on the floor (except for the ceiling panel, of course) and so go from the floor to 4 feet up.

It was late when I finished so I could only listen to a few recordings, but my initial reactions are:


WOW!
Sound stage has improved, not immensely, but appreciably. By that I mean that the stereo image is more detailed. I hear things moving from one side to the other that I did not hear before. Placement is less "right, left OR center" and more dispersed in the 120 or so degrees of my listening arc.
The sound is clearer. I am hearing details in the music which I never heard before.
The bass is deeper. I don't know if it has more "punch" because that was not a problem before, but when I got out of my chair to hear the sound outside of the "sweet spot", the first thing I noticed when I got back in was the immediate warmth of the lower bass frequencies.

So I'm a happy guy. Thanks, all of you, for your help.

Of course, there is more work to do. I have a feeling that the sound stage can get considerably better.

Sanjay: sorry this was not well timed with our experiments :nerd: I'll definitely be doing testing Sunday to get some objective feedback. Would you like me to do the mono test we were talking about earlier without the panels? It's no problem. Otherwise, I have left the speakers in the position you recommended and will do REW readings with the panels in place. Thanks for your help ;-)


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## sdurani (Oct 28, 2010)

modusmongo said:


> Would you like me to do the mono test we were talking about earlier without the panels?


Up to you.


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## modusmongo (Jun 26, 2013)

I guess what I'd like to know is: will doing the measurements without the panels have a benefit in terms of placing the speakers (or some other benefit)? If so, I'm all for it! Thanks.


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## sdurani (Oct 28, 2010)

modusmongo said:


> I guess what I'd like to know is: will doing the measurements without the panels have a benefit in terms of placing the speakers (or some other benefit)?


It will show whether the improvement is due to placement. Once you measure the difference, you can bring the panels back into the room and measure what their improvement is. Separate measurements will allow you to guage the effectiveness of each step.


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## modusmongo (Jun 26, 2013)

Hi folks. Here is the latest mdat:
View attachment After panels 1.mdat


Sanjay, here is a comparison freq response graph done without the new panels.

Red is the reading from my first post, and blue is today's reading in mono based on the speaker positioning you suggested.









Here is a comparison of waterfall from the "Sanjay" position (in BLUE) followed by the same speaker position , but with the panels in place:

















And finally the RT60 comparison. Again, the Sanjay speaker position without, then with the panels:

















I can see that some gains are being made with the panels, but the T20 and T30 times are still way too high, yes?

Sanjay, the readings in this position (without panels) are worse, right? What would you suggest I do now?

Peter


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## bpape (Sep 14, 2006)

Start with panels in your original. For some reason, the position he suggested is actually worse if i'm reading it right. Decay below 100Hz still needs some work which is to be expected. 

On some of these, you may want to wrap them with a membrane of some sort to not overdo the upper mid/high absorption while allowing more bass control to be done in the room.

Most likley doing the front corners VERY thick would be good for FR and for decay times.

Bryan


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## modusmongo (Jun 26, 2013)

Hi Bryan. Thanks for chiming in. I put the speakers back in the original position and did a quick read. The chart below is; Original Reading in PINK, Sanjay position w/ panels in GREEN, and the New Reading (original position w/ panels) in BROWN. Waterfall and RT60 of the new read after.

Interesting that the freq response is clearly better in the latest reading, but the T20 T30 times and waterfall look better in the Sanjay position.

























How thick is VERY thick? I could make some 4' x 1' x 16" or 4' x 2' x 16" panels for the front corners. I suggest these sizes because the panels are roughly 4' x 2' x 4"; but I see your corner traps are triangular...


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## sdurani (Oct 28, 2010)

modusmongo said:


> Interesting that the freq response is clearly better in the latest reading, but the T20 T30 times and waterfall look better in the Sanjay position.


Thanx for trying. I was looking to see if placement could cancel some of the low frequency resonances, thereby minimizing a couple of dips in the bass range (peaks can be addressed with EQ). While decay time did improve, I was hoping for similar gains in frequency response. 

The reason I prefer to try whatever is possible using placement is because it isn't a lossy method of addressing bass problems. By lossy I mean getting enough amp power to get strong bass in the room only to absorb much of it away. Which is why on my system I used absorbtion only for problems I couldn't address with placement. Looks like you're at that point as well.


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## bpape (Sep 14, 2006)

The theory is good. 

That said, you will always need to have bass absorbtion in a room - purely to address decay time even if the frequency response is +/-1db.

Still have work to do below 100Hz on the waterfall. Look to get the tails down to the the floor by 300ms. Set the floor to be 40db down from the average level at 0ms


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## modusmongo (Jun 26, 2013)

Thanks Sanjay. It was worth the effort.

Bryan, what would you suggest for the front corners? Can I use the same hempwool? You said VERY thick. Like a foot thick, or more?


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## bpape (Sep 14, 2006)

The hemp seems to be doing a good job so no problem using it on the front corners. 2x4x16" would be awesome in the front corners. You can also use less material and do 17x17x24" triangles and take up less space.

Thick panels ont eh rear wall - 6-8" minimum, thicker if you can swing it.

bryan


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## modusmongo (Jun 26, 2013)

Hi Bryan,



bpape said:


> 2x4x16" would be awesome in the front corners.


For the front corners, I have a little problem. 2' wide will cover about 10" of the right side window.

Would 1' x 8' x 16" do as well as 2' x 4' x 16"?



bpape said:


> Thick panels on the rear wall - 6-8" minimum, thicker if you can swing it.


For the rear wall, I already have a 4' x 4' x 8" panel in the center of the wall. Were you you talking about the corners?

Also, all of these panels are currently sitting on the floor (leaning against the wall). When I finalize the installation, should they come up a bit? A lot?

Peter


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## bpape (Sep 14, 2006)

Good on the rear wall. Do what you can in the front corners.

Bryan


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## modusmongo (Jun 26, 2013)

Bryan,

For the front corners, would you please explain the difference between a 2' x 4' 16" panel, and a 1' x 8'tall 16" panel? If the 2 x 4 will really be that much better, I'll go that way, but it will block my right side window.

Thanks,
Peter


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## bpape (Sep 14, 2006)

While it is the same surface area, the leading edge is not as far out of the corner - though likely still OK. The other thing to the advantage of the 1x8 is that you are getting the full corner covered vs just 1/2 of it.

Bryan


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## modusmongo (Jun 26, 2013)

bpape said:


> While it is the same surface area, the leading edge is not as far out of the corner - though likely still OK. The other thing to the advantage of the 1x8 is that you are getting the full corner covered vs just 1/2 of it.


Actually just 1/3 in my case: 12' ceiling.

I'm curious about the height and placement VERTICALLY of the panels. To this point, I have everything on the floor because the speakers (and I) are on the floor, and it's the first reflections that needed taking care of, so all my panels go from the floor up to 4'.

But the upper 2/3 of the room remain untreated (except for the 2' x 8' x 4" overhead panel). So I'm trying to get my head around the idea of the sound that gets bounced off the ceiling to the back wall, then off the floor, etc. Sure, the listening area "sweet spot" is protected from first reflections, but there remain all these other ambient reflections. I suppose that they are good in a way, that too dead of a room would not sound good. What is your take on this?

Can I put the 1' x 8' x 16" corner panels from 3' to 11'? or do they need to be on the floor?

Last thing ;-) do the corner panels play in to the random reflections I was mentioning above? Does the sound tend to get corralled into the corners, and thus absorption there helps out?

Thanks so much for all your help. It already sounds much better :clap:


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## bpape (Sep 14, 2006)

Well, you also have all your furniture, etc. down low in teh room. Up high, there is nothing except hard flat parallel surface that needs some attention.

Corners do not need to be on the floor nor does anything else. Start pretty much everything 2' off the floor.

Sound goes everywhere. Doesn't go in a straight line only, really radiates more like a 3D sphere. Sound builds up at any boundary (wall, ceiling, floor, large desktop, etc.) Corners are just worse since they're at the end of 2 or 3 boundaries.

Bryan


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