John Sayers' Recording Studio Design Forum Archive

I am renting right now and will be for the next few years. It is not possible for me to go room-within-a-room at this time. So, I guess my question is this:

1. Is it possible to control just the mix position without being hermetically sealed from the rest of the shell? There is no need for isolation.
This is just a quick sketch. Nothing is scaled or thought through. It is for illustration purposes only. This is a mix room only. No acoustic tracking will ever take place on the property.

Front wall is at the top of the drawing. Back corners are unusable due to a fireplace and pass through. Pass through goes to the kitchen, we will continue to use it. (Although it can be smaller.) On the left wall is the door to the backyard. We will continue to use that too.

I can't bolt anything to the floor. Everything has to be freestanding though I can build darn close to the ceiling. I would like to keep points in the ceiling down to 16 or less.

The pink area at the back of the room is actually floor to ceiling cabinets 13" deep.

Pink = absorption. Brown = slots or solid wood. Yellow = hangers. (You know, for discussion's sake.)

2. Can it work? If so, will I then have two separate "rooms", each contributing their own modal character?

3. Will it be a refraction nightmare?

4. Can pressure devices work as freestanding devices? Or do they need to be connected to a boundary wall?

5. The dotted line running from front to back on the right of the room is near the 1/4 wavelength of the most evil mode at this time. Am I right to think that panels will do something at the velocity low point?

6. Would not having panels on the left side as well really throw off the symmetry inside the "mixing zone"?

(At this point I'm feeling kind of foolish if the answer to the primary question is NO!. So let me press on... )

7. If there are slat walls on the side, in their own frames of say, 3/4" and 5/8" MDF, will they create and increase problems in the exterior sections of the room that would affect the mixing zone?

8. Could they be used as say, an inside out double leaf that is not there for the intent of isolation, but instead to help stabilize what is happening inside the mixing zone?

9. What would be best usage of the areas outside of the mixing zone? In my first thoughts, the two front corner absorbers are slot absorbers. Would they be the best use of that space if the room is "broken" up so? Or is the room not broken up in any way and they will work as if the mix zone isn't there?

10. Am I completely off my rocker? (Keep in mind I am just now starting chapter 14 of MHoA. I haven't yet been introduced to enough ideas to allow me to start thinking about these things realistically.)

- Mark

Well, I still don't have an answer (Actually, I might be closer to an answer but can't be sure at this point.), but I learned something. I think.

It's possible that I have seen evidence of low frequency diffusion. I say possible because in everything I have read in the last 6 weeks, I have not read the REW manual. I really have no idea how to interpret the information I have gathered. I have some ideas of what's happening, I just assume 75% of them to be wrong.

So... Here is the data and a description of events if anyone is interested in sussing out the principles.

As far as my original question goes, I'm going for it. Details will be here http://www.johnlsayers.com/phpBB2/viewt ... =1&t=18419

In my efforts to decided whether to go the long way or the short way in this room I did some low frequency tests to see if one has better modal influence.

Length = 20', Width = 13' 4", Height = 7' 2".

Sub is in the corner for all of these tests. Mic is in the listening position if I were to build the room in the wide orientation. The ceiling is 6' 8" on the left side of the picture, 7' 8" on the right. The cabinet doors are 3/4" MDF. Upper doors are 10.4' square in area each, lower doors are 7.8' square each. Please disregard all the speakers, vacuums, and kitty blankets lying around.

CabinetDoors001 depicts the room with the cabinets closed and couch in place. I wanted to compare the REW measurements with various calculators based on average ceiling height. (Close enough to figure out which modes are what. I think.) REW File https://docs.google.com/file/d/0BxqCOj6 ... sp=sharing


CabinetDoors002. Because I wanted to see how the extra 14" of room 'depth' would effect my measurements, I opened just the top cabinets doors. REW File https://docs.google.com/file/d/0BxqCOj6 ... sp=sharing


CabinetDoors003. Seeing the difference, I moved the couch out of the way and opened all six doors. Very interesting indeed. REW File https://docs.google.com/file/d/0BxqCOj6 ... sp=sharing


CabinetDoors007. Finally, I had to buck up and take the doors off to see what the difference was. (I did take that last door off after the picture was taken and before the measurement.) REW File https://docs.google.com/file/d/0BxqCOj6 ... sp=sharing


North end of the room is the direction the camera is facing. These are the coordinates of the cabinets doors.

Set 1 from North = 5'5" = 209hz
Set 2 from North = 8'1" = 141hz
Set 3 from North = 13'8" = 82.7hz

Set 3 from South = 6'4" = 178.4hz
Set 2 from South = 11'11" = 94.8hz
Set 1 from South = 14'7" = 77.5hz

Distance between set 1 and 2 = 2'8" = 423.9hz
Distance between set 2 and 3 = 5'8" = 199.4hz
Distance between set 1 and 3 = 8'4" = 135.6hz

Table from Floor = 3'7" = 315.6hz
Table from Ceilling = 4'0" = 282.5hz

REW screenies are 40-105dB and 20hz - 250hz for SPL, Decay, and Waterfall. 900ms for IR. (Didn't think to change that.)

CabinetDoors001 = Upper Left - CabinetDoors002 = Upper Right
CabinetDoors003 = Lower Left - CabinetDoors007 = Lower Right
With the cabinet doors open there is an immediate 3dB reduction in the peaks at 56hz (2,0,0), 98hz (2,0,1). 123hz (3,1,1?) is down 7dB.

The dips at 77hz (0,0,1), 141hz (4,1,1), and especially 148hz (5,1,0) are relaxed significantly.

There are new peaks at 67hz (Which might be the (2,1,0) of the new room depth.), 88 and 90hz (0,1,1), 131 and 133hz (1,3,0), 146hz with the couch gone (Which would be the (5,1,0) of the new room depth.), and big peaks at 191 and 200hz (7,0,0) once the couch was gone.

There are new dips at 51hz (Which would be the (1,1,0) of the old depth) when the couch is gone. 128hz (0,3,0?) which is worse with the couch in place than when it's gone. 183hz without the couch which would coincide (pun intended) with the (3,1,2), (5,3,0), and (2,4,1) of the new dimension.

Which of this is modal and which is influenced by the panels and couch I have yet to suss. But there are certainly differences.
It is interesting that looking at these decay plots is like looking at a compressor in action. With all doors open the decays tend to be more uniform even though the peak response at the mic seems to be slightly flatter with the couch in place. Removing the doors from the room lets the decays get a bit wild again, but also shows that some of the influence was from the new room depth. It also shows that the doors had a significant impact in the 77hz, and 149hz ranges.
I am going to have to figure out where that 60hz is coming from. It is in most of the measurements but once in a while it disappears. I think the refrigerator might be a good place to start.
With the cabinet doors opened, the averaged decay rate is 60ms longer. (Am I reading that right?) It's also smoother.

Considering everything above, I feel like I am seeing the results of diffusion. Cool.

I'm seeing many other things too, not the least worrisome is that the cabinet doors and couch have so much influence over what is happening in the room. It seems to me that it would be very easy to place acoustical features incorrectly, or to design them just off enough to throw the whole thing out of whack.

I am very scared.

-Mark

Well, I took a look at all your REW files, but there's a major problem: they all cut off at 400 Hz! It looks like you only tested the sub by itself, which doesn't tell you much about the room.

I also don't see the changes you mentioned: what I see is that the mic was in a very different location for each of the tests, thus making them all invalid for comparison against each other. So you are not showing how the acoustics changed in the room each time, but rather you are showing the different acoustic responses at each of the locations where you had the mic. Several other things seem to have changed in the room between the first two and the last two: there's a large black object on the floor in the right rear corner of the room on the last two that was not there on the first two.

So I would suggest that you repeat the tests in reverse order, starting with a totally empty room then adding the sofa, the doors open, all doors open, only top open, only bottom open, all closed, and do each test full-range, first with just the left speaker, then just the right, then both together, then the sub by itself, then all three together, and do not move the mic at all between tests: it MUST be in the exact same location for every test, or else the results are not valid for comparison. They would still be valid individually, just not usable to compare against each other.

Also, do all the measurements in one single file, and label them. Makes it easier, only having to download one big file, instead of a dozen small ones...

- Stuart -

Soundman2020 wrote:Well, I took a look at all your REW files, but there's a major problem: they all cut off at 400 Hz! It looks like you only tested the sub by itself, which doesn't tell you much about the room.

Whoops. Yes. I was testing for sub location when I bumped into the cabinet door thing.

Soundman2020 wrote:I also don't see the changes you mentioned: what I see is that the mic was in a very different location for each of the tests, thus making them all invalid for comparison against each other. So you are not showing how the acoustics changed in the room each time, but rather you are showing the different acoustic responses at each of the locations where you had the mic.

I assure you, the mic did not change position. Once I noticed the differences I left the sub and mic in place and started opening and closing cabinet doors. The mic is spiked, bobbed, and measured from floor, walls and speakers. I checked it frequently. It was the same for all those tests and is now back within 1mm and 1 degree where it was. Which leads me to wonder what else changed.

Soundman2020 wrote:Several other things seem to have changed in the room between the first two and the last two: there's a large black object on the floor in the right rear corner of the room on the last two that was not there on the first two.

Whoops again. That is a 17"x17"x20" end table made of 3/4" particle board. It has some mass. It was beside the couch in the first pictures. For whatever reason, I slid it out into the room by a couple of feet. The couch did not leave the room - I slid it haphazardly to the south side of the room, just under the camera. But it did not move for the duration of the tests. I can't remember moving anything else. But can't be 100% sure.

Soundman2020 wrote:So I would suggest that you repeat the tests in reverse order, starting with a totally empty room then adding the sofa, the doors open, all doors open, only top open, only bottom open, all closed, and do each test full-range, first with just the left speaker, then just the right, then both together, then the sub by itself, then all three together, and do not move the mic at all between tests: it MUST be in the exact same location for every test, or else the results are not valid for comparison. They would still be valid individually, just not usable to compare against each other.

I tried to recreate the first test. Much has moved in the room. I'm not really sure where the couch was. So I shoved it around a bit and this is as close as I could get. Sub is 1' from the corner facing in, sub only to 400hz, mic at the bob, couch in approx. the same position, end table in approx the same position. This is the new measurement compared to original with all 6 doors off. The black line is the original test and the green is my close as possible recreation. I then removed the end table to see what the influence was. Green line is my close as possible recreation, red line is the same without end table. Definitely different. Cabinets Revisited - https://docs.google.com/file/d/0BxqCOj6 ... sp=sharing


When I started redoing the tests I was still convinced that I am going to load the room on the short axis. So the test are incomplete because I only did the top 3 as the cabinet doors are 1" particle board, very heavy, and the screws will only go in and out so many more times. (I am renting and will need to remount them securely at some point.) The reason I thought I was going to load the room on the short axis is because of L/R symmetry being that the cieling will be higher on one side if I load it on the long axis. After seeing yesterdays test between L/R full range, well... I'm going to have to put those doors back on and measure the long axis anyway. So I will leave everything as is and complete the test.

That being said, here are the parameters for yesterday's test:
* Couch is located where it would be if I load the room on the short axis. Coffee and end tables in place.
* Only the top three doors were included in the test.
* Sub is in the best practical position assuming soffit and side slat walls. (It is no longer in the corner.)
* Mic is at the bob which is at speaker center height (38% from ceiling and where my ears will be when seated), at the listening position on the x/y axis, and pointing up about 30° (Right at the corner of the ceiling and front wall. Yoiks.)
* The shelves are not present. They did a lot to the width/height tangentials. I may put them back in tomorrow.
* All tests were authenticated with 5 or 6 takes. (I have always done at least 5 takes. If they are sufficiently alike I keep one of them and dump the rest. I did the same on the first CabinetDoors day. This is an example: https://docs.google.com/file/d/0BxqCOj6 ... sp=sharing

Here is what the room looks like from the vantage point of the speakers on their own axis. Left side of the picture is right speaker pointing towards back left corner. (WARNING! Children should be removed from the room before viewing this monstrosity.) I will be presenting minimal graphical evidence in this post because I really need to get moving on this room. It's going on three months since I wanted to start. I'm glad I started studying, but I really must move forward. I will add to this session tomorrow and post at least the mdat in this thread. Remember, this is only 3 doors at this point, and no shelves. The graphics are both speakers because the single speaker plots tell mostly the same story. (Although one interesting point is that the left speaker transfer function is affected more by the cabinet doors than the right or both.)

CabinetDoorsAgain - https://docs.google.com/file/d/0BxqCOj6 ... sp=sharing

Looking at the frequency response we can see that the cabinet doors when closed have a pretty big impact in the 100hz - 170hz range. When the doors are open or gone, things change dramatically in that region. We can also see some smoothing in the (1,0,0) when the doors are open that isn't as apparent when the doors are gone. One could almost guess that would happen just by looking at the doors in the room. Also, when the doors are either open or gone, I am being attacked by new (0,x,x) modes. The ceiling is much too low and has become my enemy. On the waterfalls I think I am seeing the transition range smoothing out some with the 3 doors in place. Easier to see in REW than these little screenies. The differences between the doors open and gone are few. Here I notice that the low end decay seems to be less consistent with the doors open. It's easy to see the size of the room change with the doors open or gone. Cool. In the end, with only 3 doors in play, the influence of the doors is small and the changes have more to do with the new room dimension. I'm happy to see that by moving an 8' x 3' section of wall back 13" it can have so much impact even though there is still the rest of the room doing it's thing. It gives me hope that I may be able to shape certain bit of sound within a selected portion of the space without actually having to change the shell of the space. Maybe I can manipulate the room in the way I first proposed in this thread.

Anyway, I need to consider the long room option more carefully. So... the cabinet doors must all go back on. May as well do the shelves too. See you in 12 hours or so...

Soundman2020 wrote:Also, do all the measurements in one single file, and label them. Makes it easier, only having to download one big file, instead of a dozen small ones...

- Stuart -

Nice feature. Thanks.

-Mark

OK Stuart. I am starting to catch up a little. I see your point now about how to measure effectively.

We must gather enough data to demonstrate what is causing what. That means collecting data that represents each individual element, and that means carefully considering what we wish to know. Only then can the measurements be used against each other to glean the information we are looking for.

I know that sounds really basic. But I hadn't yet had my mind around using REW as a measurement tool. I still don't really. For instance I have yet to figure out how windowing affects an impulse response. The more I search, the more confused I become. That being said, I am finding out more about REW and what each display means each day.

So, with that in mind, and since I was changing the room again for new measurements which (hopefully) will help me make a decision and actually start work, I did another set of tests on the cabinet doors that is very consistent and tells a lot of the story. Unfortunately, I missed an opportunity to measure with the doors completely off. But there is still a lot of good information there. If I end up going back to a place where I need to take the doors off again, it will be easy to replicate this test and fill in the last 3 sweeps.

1. Room was empty except for the coffee table which holds the computer and my cup of coffee and was pushed off to the side and spiked and measured. I emptied the room to try to get the greatest wealth of room resonances and reflections.
2. Mic and speakers are in what would be the best location if the room were set up to mix on the short axis. Same as last tests.

Cabinet Doors Again 2 https://docs.google.com/file/d/0BxqCOj6 ... sp=sharing

This is actually really fun to look at. I can't get into it now, as I must move forward. I will study it again though, in the future. I will know more about acoustics and the measurement tools. I look forward to finding out what I find out.

[EDIT] Just wanted to say, the results are pretty dramatic. It's worth looking at the REW session if you are interested in what the cabinet doors are doing.

-Mark

I hadn't yet had my mind around using REW as a measurement tool.

Well, that's normal! Acoustics is a huge subject, and you can't expect to understand it in a few minutes. REW is also a very complete analysis tool, which also needs a bit of time to figure out fully.

I still don't really. For instance I have yet to figure out how windowing affects an impulse response.

Windowing doesn't affect the IR directly: it affects your view of it. it's just a way of looking at different sections of the response, sort of like a magnifying glass that focuses in on certain parts, but it also filters out other parts. For example, if you keep the window short enough, then you can look at just the part of the sound that arrived at the mic before the room reverberation gets there. Etc.

I did another set of tests on the cabinet doors that is very consistent and tells a lot of the story.

Great! And it is very evident that the effect of those doors is basically only happening in the upper end of the lows, and the bottom end of the mid range, between about 60 Hz and 600 Hz, roughly. Below 60 the effect is not very significant, and above 600 it is mostly just just slightly increased or decreased overall levels. So any treatment you propose to put in those cabinets should be aimed at that frequency range.

It's also clear that the room is suffering a sever lack of bass trapping!




- Stuart -

Soundman2020 wrote:Windowing doesn't affect the IR directly: it affects your view of it. it's just a way of looking at different sections of the response, sort of like a magnifying glass that focuses in on certain parts, but it also filters out other parts. For example, if you keep the window short enough, then you can look at just the part of the sound that arrived at the mic before the room reverberation gets there. Etc.

Very good. Thank you. I was leaning towards that description in my head. But every search I have done leads me to some physics department as some university and articles seem to be written by mathematicians who's primary focus is light waves.

Soundman2020 wrote:Great! And it is very evident that the effect of those doors is basically only happening in the upper end of the lows, and the bottom end of the mid range, between about 60 Hz and 600 Hz, roughly. Below 60 the effect is not very significant, and above 600 it is mostly just just slightly increased or decreased overall levels. So any treatment you propose to put in those cabinets should be aimed at that frequency range.

It's also clear that the room is suffering a sever lack of bass trapping!

Well, cabinets are closed for good. I am loading the room on the long axis so that wall will be covered with angled slat walls.

I'll be building the first corner slat in a couple of weeks. I would be honored if you would look in on this thread. When I get back from vacation I'm moving forward at an accelerated pace. I expect I will be making a lot of mistakes... o.O

http://www.johnlsayers.com/phpBB2/viewt ... 19#p129234

-Mark