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Building a room - need help with ratios Modular Synthesizers
Old 23rd March 2014
  #31
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jhbrandt's Avatar
Al,

Post or link your .skp (SketchUp) file and I'll have a look.

Cheers,
John
Old 23rd March 2014
  #32
Gear Head
 

That´d be awesome! There you go!

Index of /studiodesign

Old 23rd March 2014
  #33
Gear Guru
Mystery

A couple of people have been asking what it was that formed my view on mode calculations. One example is hardly conclusive in any sense but the following has caused me not to trust or depend on them.
This was a concrete new build. I was on board to promote acoustics, to steer choices beneficially. Ultimately though this was designed for appearance and multi function. Concrete walls and floor. Double plasterboard vaulted ceiling, average height shown. The whole span of heights were run through the calc.
I spent a long time using ModeWiz to achieve prediction nirvana.
The planning limit was 25 sq metres. The final dimensions chosen got close to that and passed all four criteria. All four.
Building a room - need help with ratios-6.2-room-report-copy.png
Bob Golds calc showed nothing scary.
Building a room - need help with ratios-bob-g.jpg
And bingo.....
Building a room - need help with ratios-rib.jpg
DD
Old 26th March 2014
  #34
Gear Head
 

Thats very interesting DanDan! Could it be that some of the frequencies near and next to the obvious roommodes have some sort of amplifying effect on them? Some sort of physical phenomenon related to sound and air as medium? Or maybe the inner shell dimensions and the rooms boundaries some how interact. Whats your hypothesis?
Old 26th March 2014
  #35
Gear Guru
Mystery

That's the trouble Al. The factors you refer ARE room modes, there are no other X factors. There was no inner shell, this was close to the hypothetical concrete rectangle.
The only possible factors were:-
Windows, quite a few.
An A vaulted ceiling of double plasterboard. Should be pretty solid and reflective at LF. It was certainly not resonating. Note the full span of heights was calculated and recalculated.
The floor is suspect. It is concrete but the builder went the extra mile and installed underfloor insulation. I think he even had rebar in there, this was a really well laid floor, but jumping on it causes a massive boom. I cannot tell if this is compression effect setting off those modes, or if the floor itself participates in the resonance. The former seems most likely.

Other things seem to be quite certain though. A GS had a massive isolated 40Hz in his live room recently. He installed 50cm of light fibre on one of the walls. Sorted.

DD
Old 26th March 2014
  #36
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avare's Avatar
 

Quote:
Originally Posted by DanDan View Post
A couple of people have been asking what it was that formed my view on mode calculations. One example is hardly conclusive in any sense but the following has caused me not to trust or depend on them.
Thank you Dandan.

Andre
Old 26th March 2014
  #37
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jim1961's Avatar
 

Quote:
Originally Posted by DanDan View Post
A couple of people have been asking what it was that formed my view on mode calculations. One example is hardly conclusive in any sense but the following has caused me not to trust or depend on them.
This was a concrete new build. I was on board to promote acoustics, to steer choices beneficially. Ultimately though this was designed for appearance and multi function. Concrete walls and floor. Double plasterboard vaulted ceiling, average height shown. The whole span of heights were run through the calc.
I spent a long time using ModeWiz to achieve prediction nirvana.
The planning limit was 25 sq metres. The final dimensions chosen got close to that and passed all four criteria. All four.
Attachment 390900
Bob Golds calc showed nothing scary.
Attachment 390901
And bingo.....
Attachment 390903
DD
I take it things didn't sound so swift?

That is a pretty awful waterfall.
Old 26th March 2014
  #38
Gear Guru
Bad

Yes awful. My early directive to keep corners open for large traps fell by the wayside so massive corner trapping was not possible. Overall an early lesson in how being only partly involved can go wrong. They work around the problem though, in nulls, and are actually very happy. Perhaps the sea views have something to do with that.....
DD
Old 26th March 2014
  #39
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jim1961's Avatar
 

Quote:
Originally Posted by DanDan View Post
Yes awful. My early directive to keep corners open for large traps fell by the wayside so massive corner trapping was not possible. Overall an early lesson in how being only partly involved can go wrong. They work around the problem though, in nulls, and are actually very happy. Perhaps the sea views have something to do with that.....
DD
This is speculation on my part and nothing new. But in my space, the walls are thin, there are multiple openings to adjoining spaces, its a pier house so no cement floor.... I said all that to say that my space is the opposite of the space you described. In other words, there are lots of ways for the bass to leak out. Consequently, my mode problems are minimal.

So I guess the lesson with looking at mode calcs is to realize that the more dense and rigid the surfaces, the more impactful the modes will be.
Old 26th March 2014
  #40
Gear Head
 

My previous room was a basement with 60cm thick brickwalls and with the dimensions had over 20db massive boost at 41.5Hz (in modecalc and in reality) and i fixed it with bales of fluffy glasswool in the corners.

But back to the task at hand.
I would really love to have the listening against the angled wall because of the windows so i am wondering if building these soffitstyle walls (30/60degree) with huge fluffy glasswool behind as basstraps work?
The 80 degree corner would be a truly massive trap.
What do you think?



Old 26th March 2014
  #41
Gear Guru
Limp

Yes, Newell refers to light boundary spaces as Limp Bags. This includes a metal skinned recording truck. Concrete bounded spaces, should and one has to assume normally do, have modes pretty much exactly as predicted. This should be an advantage. By choosing optimum dimensions the spread of modes should be excellent to begin with before treatment. One could optimistically call it 'modal support' rather than considering them as enemies.
I do think would be helpful to include fudge factors for known lighter boundaries. Ditto the 1.2 slower speed of sound factor for known large amounts of fibre unless they are equal everywhere in which case the whole thing should scale down.

An often forgotten point is that these ratios do NOT scale over a wide range. Afaik most of the favourable ones were determined for quite large rooms, and cannot be expected to hold true in Small Acoustic Spaces. Cox -
Quote:
it can be shown that there are very few room ratios (about 20 clustered around 1:2.19:3) that can be applied to a range of room volumes (50 - 200 m3). This is because room ratios are generally not scaleable.
EDIT, Al was simulposting..... Interesting idea Al. The massive trap is very welcome, the other one looks a bit thin. If I may throw a couple more into the pot. How about making those corner walls actually solid and soffit mounting the speakers? You could probably include a place to silence your computer in the left one. Another thought, how about placing the speakers at the opposite wall? This would allow creation of a massive fibre trap on the angled boundary. The lack of symmetry would be of no consequence in that scenario IMO.

DD
Old 26th March 2014
  #42
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jim1961's Avatar
 

Quote:
Originally Posted by DanDan View Post
Yes, Newell refers to light boundary spaces as Limp Bags. This includes a metal skinned recording truck. Concrete bounded spaces, should and one has to assume normally do, have modes pretty much exactly as predicted. This should be an advantage. By choosing optimum dimensions the spread of modes should be excellent to begin with before treatment. One could optimistically call it 'modal support' rather than considering them as enemies.
I do think would be helpful to include fudge factors for known lighter boundaries. Ditto the 1.2 slower speed of sound factor for known large amounts of fibre unless they are equal everywhere in which case the whole thing should scale down.

An often forgotten point is that these ratios do NOT scale over a wide range. Afaik most of the favourable ones were determined for quite large rooms, and cannot be expected to hold true in Small Acoustic Spaces.

DD
I agree there maybe an advantage in terms of predictability. But it seems the modes themselves are much nastier, requiring much more aggressive treatment, than in limp bag (or mass) type rooms.
Old 27th March 2014
  #43
Gear Head
 

soffit before the speakers?

Quote:
Originally Posted by DanDan View Post

EDIT, Al was simulposting..... Interesting idea Al. The massive trap is very welcome, the other one looks a bit thin. If I may throw a couple more into the pot. How about making those corner walls actually solid and soffit mounting the speakers? You could probably include a place to silence your computer in the left one. Another thought, how about placing the speakers at the opposite wall? This would allow creation of a massive fibre trap on the angled boundary. The lack of symmetry would be of no consequence in that scenario IMO.

DD
I currently have Dynaudios BM6as which I really like but because the bassport is behind the speakers the soffit mounting could cause problems. Someone has probably done it though so Ill consider it and maybe I could even upgrade my speakers.

Actually wouldn´t it be a good idea to build the structure so that there is the slots to later soffit mount some better suited speakers?
The place for a computer is a good idea and the cooling shouldn´t be a problem either. Small compartment with a small door maybe...

Placing the listening on the other side of the room I would have to have an absorber or a diffuser infront of the window. Hmm. If I build the angled side I can have the windows as they are. They are kind of my sea view :D

EDIT: With the soffit walls how much should i bring the wall in to the room? Now in the picture there is the soundproofing wall built first and then i would build the soffitstyle construction in front of it. Does this make sense? Does a stud structure and two gypsum layers constitute a solid wall in this scenario?
Old 27th March 2014
  #44
Gear Guru
Pondering

You are right to mull this over for a while.

Placing the speakers at the neighbours wall will probably greatly increase the soundproofing problem.

I don't think the ports would be a problem. In fact they may well be best corked. Afaik the smaller ATC's, often soffit mounted, are fully sealed. Fast bass.

Yes many people build a little generic cubicle and do a custom surround for the current speaker choice.

A silent CR makes a great vocal and other source recording space.

I think a double sheetrock wall is soffit enough.

DD
Old 30th March 2014
  #45
Gear Head
 

Quote:
Originally Posted by DanDan View Post
You are right to mull this over for a while.

Placing the speakers at the neighbours wall will probably greatly increase the soundproofing problem.

I don't think the ports would be a problem. In fact they may well be best corked. Afaik the smaller ATC's, often soffit mounted, are fully sealed. Fast bass.

Yes many people build a little generic cubicle and do a custom surround for the current speaker choice.

A silent CR makes a great vocal and other source recording space.

I think a double sheetrock wall is soffit enough.

DD
Delved into flush mounting the speakers and decided to do it. I´ll use the plans on the John Sayers forum and modify them to work with the angled side of my room. Have to get some sleep first and then start doing the sketch up.
Old 31st March 2014
  #46
Gear Head
 

simple flush mounting

Here the first sketchup









So this would be the most simple 60 degree flush mount exept for the 90 degree angled wings(?) on the sides to make the RFZ even better (not really sure if that helps since the absorption in the first reflections is going to be installed anyways ) . The sketch doesn´t have the structure like it would be built yet. And I could have the ceiling angled towards the soffit to have further help to create a goor RFZ. There is going to be a cloud built as well but this really is just a sketch.

I would of course build it according to John Sayers advise, having the lower part as a trap with either hanged frigid slabs or fluffy glasswool bales and having a 15cm opening / port just above to the floor covered with fabric. I would then have the corners filled with fluffy glasswool as well as casings above the speakerlevel aswell and behind the frontwall. Maybe a diffuser in the front wall in front of the workstation if needed. Theres going to be traps in the backwall corners and a QRD diffuser behind the listening in the backwall.

I´m going to remove my Dynaudio BM6a´s backplates to be installed under the speakers so that I have connections available plus I don´t have to worry about ventilation which would be a problem since the BM6a`s are active speakers and have the heatsinks in the backpanel.

I would actually love to angle the wall above the normal speaker height and have the speakers positioned higher so that I could have my acoustic research AR18´s as reference speakers in my speaker stands behind the workstation. This means a more complicated structure to be built so I don´t know if its really worth it.

The listening postition in the sketch is postitioned according to the 38% "rule" if the 38% is measured from the soffit wall. Of course the real boundary is the angled wall behind it but I intend to trap it good to get the bass under control so it shouldn´t be a problem.

Any suggestions / comments?
Old 31st March 2014
  #47
Gear Head
 

Here a sketch for having angled flush mount. Maybe I´ll build this just to be able to upgrade the speakers and having all the speakers flush mounted. Dynaudio AIR 25s would be a nice upgrade ' . Hmm. This is probably a total overkill though...




Heres an alternative:
Old 31st March 2014
  #48
Gear Head
 



Here is the backpanel of the Dynaudio BM6a´s. There is -4db-0db for LF and HF so It should be possible to flush mount these, right?

As I understand the LF boost when flush mounting could be as high as +6 db so I hope the -4db is enough to deal with the possible boost.

EDIT: the -4 db probably won´t be enough so i guess I need to get into electrics again :D

Here is what the owners manuals says about the eq:

Old 6th April 2014
  #49
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jhbrandt's Avatar
I really don't recommend flushing this monitor. Save it for near-fields.

Cheers,
John
Old 6th April 2014
  #50
Gear Guru
Curve

One way of achieving exactly whatever curve you want is using something like Dirac Live. This will give you much more sophisticated control than the Eq on the speaker, and over the whole spectrum.
DD
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