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DanDan
#31
16th November 2012
16th November 2012
#31
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,268

Oops

I misread your high point and low point to mean a flat ceiling, not an A one.
So ignore, reverse, my previous comment. As ever I recommend a minimum trap depth of 4 inches. The bigger the air gap the better in terms of LF, so I would be inclined to hang the cloud panels horizontal, parallel to the floor. This will deliver a nice big varied depth gap.
DD
Jens Eklund
#32
16th November 2012
16th November 2012
#32
Lives for gear

Joined: Oct 2009
Location: Stockholm
Posts: 4,574

Quote:
Originally Posted by kwow
Hi Jens

I just calculated the angle, and the angle at the top (right above my head) is about 156 degrees, and the sides are about 12 degrees each of the triangle.

Is this a sufficient slope?

Thanks
Keith
kwow
#33
16th November 2012
16th November 2012
#33
Gear nut

Joined: Dec 2003
Location: LA, CA
Posts: 80

Thank you DD and Jens.

I'm sorry if I didn't explain things well (or I should have posted a picture of the front wall) but yeah, it's an A type ceiling thing.

But I'm relieved since I made 2 panels specifically for clouds with a certain color fabric and all (haha).

So I guess I'll hang the two panels parallel to the floor with plenty of space behind them.

What about the orientation of these panels though as far as front to back? Should one of the panels literally be right above my head? Or should the panels be more towards the front wall?

Thanks again!

Keith
DanDan
#34
16th November 2012
16th November 2012
#34
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,268

Snooker

Take a look at Jens diagrams. It's like snooker or pool shots. HF can be considered to follow ray like paths. Your aim is to prevent EXTRA paths from tweeter to ceiling to ear other than the direct one of course. A mirror can be used to literally see these paths and thus block them. Get a friend to hold the mirror in place at the ceiling. If you can see the tweeter while seated at your mix position you have a path. Move the mirror about to define the 'envelope' of possible paths. Then extend that envelope because at lower frequencies the beams spread.

DD
kwow
#35
16th November 2012
16th November 2012
#35
Gear nut

Joined: Dec 2003
Location: LA, CA
Posts: 80

DanDan

OK, I'm starting to get it (at least a little bit).

Looking at Jens' diagram and you mentioning the mirror trick made me remember this Ethan/RealTraps page where it talks about FIRST REFLECTIONS: CEILING AND FLOOR.

So the point of hanging these panels would be:
1. To take care of the first reflection coming off of the ceiling.
and
2. At the same time controlling the low frequencies which are more wide-spread/non-directional with the thickness of the panels and the space behind the panels.
Correct?

I was understanding the concept of the first reflection off the side walls, but when it came to the ceiling, I was not able to think 3 dimensionally (haha).

I'm going to hang those 2 panels from the ceiling today.

Thanks so much!

Keith
DanDan
#36
17th November 2012
17th November 2012
#36
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,268

Yes

Yes to all of that. Two panels, unless they are big, seems very little.
I have a kinda 4 minimum thing.
The Mirror or ETC will locate your traps well. If you want to have a go at the Vertical modes, I suggest stimulating them with sine waves and go up there to find the hot spots. You may find peaks at the wall ceiling corner. Extra panels up there would have a go at both height and width modes.

DD
kwow
#37
19th November 2012
19th November 2012
#37
Gear nut

Joined: Dec 2003
Location: LA, CA
Posts: 80

DanDan

I went ahead and hung the two 4" panels that I made. I'm in the process of making two panels for the back of the room right now. Once I'm done with those, I'll take a measurement and see where I'm at.

One of the reasons that I wanted to go with two panels initially was that I was a bit nervous about hanging a lot of heavy stuff above my head. And also I have a beam going from front to back in the room so it was convenient to hang stuff from the beam. Another thought that I had was that I don't didn't want to make the room too dead.

I have a decent amount of R30 left from building the superchunks so I'm thinking using that to cover the front wall/ceiling corners for the bass response, and if I still have reflection problems then hanging panels on the side walls/ceiling corners as you mentioned.

I'll have to look into using ETC to locate the good spots for the panels, and using sine wave to find the hot spots. I don't know how to do either of those things. So if you have a link or something that would lead me to what I need to know, I'd appreciate it!

Thank you

Keith
DanDan
#38
19th November 2012
19th November 2012
#38
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,268

ETC

The ETC is very accurate but quite difficult to actually do. The Mirror technique will generally provide exactly the same result in practice.
It is simply. Sit at your mix spot. Have a friend slide a mirror along the side walls and ceiling. When you can see the speakers you obviously have a HF reflection path. Mark the areas where these reflections are visible, masking tape. Try to cover as much of these areas with absorption.
Your room will have three strong low modes, associated with L W B.
Here's a little app that calculates the modes and shows where to expect the high pressure zones.
hunecke.de | Room Eigenmodes Calculator
If you play a Sine wave at one of these frequencies the room will resonate very strongly. If you walk about you will find the hotspots. These are obviously the best place to locate LF traps.

DD
#39
19th November 2012
19th November 2012
#39
Lives for gear

Joined: Feb 2010
Posts: 1,307

Quote:
Originally Posted by DanDan
The ETC is very accurate but quite difficult to actually do. The Mirror technique will generally provide exactly the same result in practice.
1 - the ETC is only as "accurate" as the measuring setup (eg, no "operator error"). a measurement platform not taking into account hardware propagation delays is not technically "accurate".

2 - generating the ETC is not "quite difficult" for a novice, generating the ETC is no more difficult than measuring the frequency response.

3 - the mirror technique does NOT provide any information as to the time-arrival off-set, gain, nor spectral content of the indirect specular energies. nor does the "mirror" illuminate one to the fact that there may be a coupling issue, nor does the "mirror" clearly define edge diffraction sources.

but at least this time you have not erroneously recommended the ETC for modal issues,

Quote:
Originally Posted by DanDan
It is simply. Sit at your mix spot. Have a friend slide a mirror along the side walls and ceiling. When you can see the speakers you obviously have a HF reflection path.
sorry, but this again is not entirely accurate. just because you can "see" the speaker (read: acoustic center) in the mirror does not mean there is a source of high-gain early-arriving indirect specular reflection incident from that boundary. you can use the mirror to identify POSSIBLE reflection paths, but not ACTUAL destructive reflection paths. for that, we need measurement analysis to determine how the indirect energy impedes the listening position.

Quote:
Originally Posted by DanDan
Mark the areas where these reflections are visible, masking tape. Try to cover as much of these areas with absorption.
i may have missed it; did the OP specifically mention the total specular response he/she wishes to achieve? blanket coating the room with absorption at all of these POSSIBLE reflection points as discovered by the "mirror" can quickly lead to a dead room. were you explicit in stating this outcome?

Quote:
Originally Posted by DanDan
Your room will have three strong low modes, associated with L W B.
Here's a little app that calculates the modes and shows where to expect the high pressure zones.
hunecke.de | Room Eigenmodes Calculator
If you play a Sine wave at one of these frequencies the room will resonate very strongly. If you walk about you will find the hotspots. These are obviously the best place to locate LF traps.

DD
i disagree that walking around the room and finding the areas of high PRESSURE via your ear is "obviously the best place to locate LF traps". if using resonant, pressure-based absorbers - yes. if using porous-only velocity based absorbers, then no.

why would you place a velocity-based absorber (which are most effective when located in areas of high particle velocity for a given wavelength) at areas of high PRESSURE (= low particle velocity)?

Last edited by Tim Farrant; 19th November 2012 at 10:08 PM.. Reason: removing abusive comment
DanDan
#40
19th November 2012
19th November 2012
#40
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,268

Batman and Robin, The Return

localhost, pretty much everyone knows at this point that you disagree with pretty much every word from my fingertips. There is no value to such disagreement because it is blind to content. Wolf.

The OP has stated they have do not know how to generate or use an ETC.

A visible path, given a hard boundary behind, is always associated with a sonic path. It is also true that there are other paths which are not visible. But I have never found an absence of a high gain path when a visible one exists, nor found an invisible high gain one.

Once again, fibrous absorption in prediction and impedance tubes absorbs most at locations of high particle velocity. However in real world tests by the BBC, traps located away from the boundaries achieved only 30% of the predicted hypothetical. Reality lies somewhere between Test and Textbook.

DD

Last edited by Tim Farrant; 19th November 2012 at 10:09 PM.. Reason: removing comments that lead to bickering
Jens Eklund
#41
19th November 2012
19th November 2012
#41
Lives for gear

Joined: Oct 2009
Location: Stockholm
Posts: 4,574

Quote:
Originally Posted by DanDan
localhost, pretty much everyone knows at this point that you disagree with pretty much every word from my fingertips. There is no value to such disagreement because it is blind to content. Wolf.

The OP has stated they have do not know how to generate or use an ETC.

Another one of your snide 'call yourself an acoustician' comments has been deleted by moderation elsewhere.

A visible path, given a hard boundary behind, is always associated with a sonic path. It is also true that there are other paths which are not visible. But I have never found an absence of a high gain path when a visible one exists, nor found an invisible high gain one.

Once again, fibrous absorption in prediction and impedance tubes absorbs most at locations of high particle velocity. However in real world tests by the BBC, traps located away from the boundaries achieved only 30% of the predicted hypothetical. Reality lies somewhere between Test and Textbook.

One of us here is an identified Acoustician, practicing in the real world.
The other is anonymous. From the writing, the anomymous one could be a mouthpiece for the banned SAC/foxfyr/demon.

These snide persistent attacks from an anonymous source are not acceptable. I am sure Tim has by now come to an understanding of your nature.
As ever you are welcome to take issue with me on any topic in PM in order not to pollute the public space.

DD
Are you trying to get this thread closed as well? If not; whatÂ´s up with all the accusations made here?

EDIT:
using REW Filtered IR to place absorbers in proper places
DanDan
#42
19th November 2012
19th November 2012
#42
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,268

Truth

In the media and in general, one cannot be sanctioned or deleted if speaking the truth. Every word I wrote is true and verifiable.
localhost's 'self proclaimed' and 'erroneously' snides, happen to be false.
That's what's up, as is obvious.
I trust moderation to act appropriately.

DD
Jens Eklund
#43
19th November 2012
19th November 2012
#43
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Joined: Oct 2009
Location: Stockholm
Posts: 4,574

Quote:
Originally Posted by DanDan
In the media and in general, one cannot be sanctioned or deleted if speaking the truth. Every word I wrote is true and verifiable.
localhost's 'self proclaimed' and 'erroneously' snides, happen to be false.
I trust moderation to act appropriately.

DD
Good luck with that.
#44
19th November 2012
19th November 2012
#44
Lives for gear

Joined: Feb 2010
Posts: 1,307

Quote:
Originally Posted by DanDan
localhost, pretty much everyone knows at this point that you disagree with pretty much every word from my fingertips. There is no value to such disagreement because it is blind to content.
i raised 3 issues with your above statements. care to refute them instead of the "scapegoat conspiracy" that you present that somehow everyone is after you and following you around disagreeing with what you say? if my 3 issues above are inaccurate, please refute them.

your earlier comments (for example) with regards to modal analysis within the ETC is going to result in you being "disagreed" with. period. especially coming from someone who not-too-long-ago went to great lengths to make attempt to show that the ETC is useless. now you're recommending the tool consistently. hmm.

Quote:
Originally Posted by DanDan
The OP has stated they have do not know how to generate or use an ETC.
My First Measurement. Am I doing it right?

"Here are the ETC, FR, Water Fall, and the IR file again."

Quote:
Originally Posted by DanDan
Another one of your snide 'call yourself an acoustician' comments has been deleted by moderation elsewhere.
Quote:
Originally Posted by DanDan
One of us here is an identified Acoustician, practicing in the real world.
it wasn't a snide comment it's a question. are you a true acoustician or a self-proclaimed acoustician? if you're going to call yourself an acoustician and use that as a form to imply your recommendations are somehow "more valid", then by all means i would like to know whether this is a self-applied label.

Quote:
Originally Posted by DanDan
Once again, fibrous absorption in prediction and impedance tubes absorbs most at locations of high particle velocity. However in real world tests by the BBC, traps located away from the boundaries achieved only 30% of the predicted hypothetical. Reality lies somewhere between Test and Textbook.
and what does this have to do with your recommendation that velocity-based porous absorbers are "best placed" at areas of HIGH PRESSURE (as measured with the "ear" and sine sweeps, walking about the room).

"If you play a Sine wave at one of these frequencies the room will resonate very strongly. If you walk about you will find the hotspots. These are obviously the best place to locate LF traps. "

Quote:
Originally Posted by DanDan
These snide persistent attacks from an anonymous source are not acceptable. I am sure Tim has by now come to an understanding of your nature.
As ever you are welcome to take issue with me on any topic in PM in order not to pollute the public space.

DD

ill continue to call out what i disagree with regarding your commentary. feel free to refute as necessary. i personally do not mind the snide name-calling you continually put forth here - it's irrelevant to me as well as to the topics.
DanDan
#45
19th November 2012
19th November 2012
#45
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,268

Quote:
your earlier comments (for example) with regards to modal analysis within the ETC is going to result in you being "disagreed" with. period. especially coming from someone who not-too-long-ago went to great lengths to make attempt to show that the ETC is useless. now you're recommending the tool consistently. hmm.
Boundaries cause modes. The ETC, particularly filtered, can be used to identify which ones are strongly reflective at LF.

As I said , the OP has stated that he doesn't know how to use ETC.
Here's what he said.

Quote:
I'll have to look into using ETC to locate the good spots for the panels, and using sine wave to find the hot spots. I don't know how to do either of those things.
I am an Acoustician according to the Institute of Acoustics UK. To suggest otherwise or question the simple fact is mendacious. Look it up. I am also a Sound Engineer as evidenced by many successful records and membership of the Audio Engineering Society. I make no claims whatsoever, as actions and history are eloquent enough.
On the other hand localhost is anonymous and repeatedly troublesome. Why is such anonymous nuisance allowed to persist here?

As ever, I would very very much welcome some real Moderation Tightening. There is no post on topic or of value here past number 38.
I would be happy to see them all deleted, but will be compelled to riposte if professional slight continues.

DD
Jens Eklund
#46
19th November 2012
19th November 2012
#46
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Joined: Oct 2009
Location: Stockholm
Posts: 4,574

Quote:
Originally Posted by DanDan
Boundaries cause modes. The ETC, particularly filtered, can be used to identify which ones are strongly reflective at LF.
In a SAS (Small Acoustic Space; normal studio sized control room i o w)? How, show us please?

Small Room, Big Absorption, Strange Graph
19th November 2012
#47
Lives for gear

Joined: May 2009
Posts: 3,365

Quote:
Originally Posted by DanDan
On the other hand localhost is anonymous and repeatedly troublesome. Why is such anonymous nuisance allowed to persist here?
I've taken value from his posts. Is that good enough reason? And until GS forbids users from having anonymous handles, they are simply a fact of life here.

Quote:
Originally Posted by DanDan
As ever, I would very very much welcome some real Moderation Tightening. There is no post on topic or of value here past number 38. I would be happy to see them all deleted, but will be compelled to riposte if professional slight continues.
Disagreement and debate form the very heart and soul of science.

I see no reason that a forum user should instruct moderators on which posts should or should not be allowed to remain. That's the mod's job, but I'd rather see self-moderation.
Jens Eklund
#48
19th November 2012
19th November 2012
#48
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Joined: Oct 2009
Location: Stockholm
Posts: 4,574

Quote:
Originally Posted by Syncamorea
I've taken value from his posts. Is that good enough reason? And until GS forbids users from having anonymous handles, they are simply a fact of life here.

Disagreement and debate form the very heart and soul of science.

I see no reason that a forum user should instruct moderators on which posts should or should not be allowed to remain. That's the mod's job, but I'd rather see self-moderation.
+1
#49
19th November 2012
19th November 2012
#49
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Joined: Feb 2010
Posts: 1,307

Quote:
Originally Posted by Syncamorea
I've taken value from his posts. Is that good enough reason? And until GS forbids users from having anonymous handles, they are simply a fact of life here.
maybe if i were here to court future customers (business) or sell vendor products would i use my real name. until then, it's a distraction. if he is simply unable to refute my commentary on the topic of acoustics, then allow him to make distractions. (eg, what does my real name have any relevancy to the subject of acoustics). simple distractions as one is not willing to address the points raised.
Icecube1
#50
20th November 2012
20th November 2012
#50

Joined: Feb 2011
Location: Norwich, UK
Posts: 309

Quote:
Originally Posted by Syncamorea
Disagreement and debate form the very heart and soul of science.

I see no reason that a forum user should instruct moderators on which posts should or should not be allowed to remain. That's the mod's job, but I'd rather see self-moderation.
+1

However, there is no need to belittle other users views. There are pleasant, sober ways of debating academic detail that probably would assist in persuading others to accept a new approach? IMHO
Icecube1
#51
20th November 2012
20th November 2012
#51

Joined: Feb 2011
Location: Norwich, UK
Posts: 309

Quote:
Originally Posted by localhost127
why would you place a velocity-based absorber (which are most effective when located in areas of high particle velocity for a given wavelength) at areas of high PRESSURE (= low particle velocity)?
True! Despite this, many professional (..meaning they earn a living doing it) "acousticians" do indeed utilise porous absorption close (ie with small air-gap with respect to wavelength of frequency of interest) to a boundary? Are we to say they are all wrong if ultimately they achieve the result they set out to achieve?

I would like to know how you determine, practically, the best place in the room for placing any porous absorption (depending of course on the specific requirement)?

How do you find relevant areas of high particle velocity?

Or maybe you never use porous absorption?

Thanks
20th November 2012
#52
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Joined: May 2009
Posts: 3,365

Quote:
Originally Posted by Icecube1
+1

However, there is no need to belittle other users views. There are pleasant, sober ways of debating academic detail that probably would assist in persuading others to accept a new approach? IMHO
Absolutely correct. If you feel I have belittled anyone, feel free to point out where that occurred. Self-moderation is a community process and I have huge respect for the expert contributors here. I have intended no belittling of others.
Icecube1
#53
20th November 2012
20th November 2012
#53

Joined: Feb 2011
Location: Norwich, UK
Posts: 309

No no Syncamorea, that was not related to you!! Sorry, for the misunderstanding.

I gave your initial comment a thumbs up, I just wanted to add that, "sometimes", when passions get aroused I have seen comments that appear to mock(belittle) other points of view, that's all.
20th November 2012
#54
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Joined: May 2009
Posts: 3,365

Quote:
Originally Posted by Icecube1
I would like to know how you determine, practically, the best place in the room for placing any porous absorption (depending of course on the specific requirement)?

How do you find relevant areas of high particle velocity?
I'm not trying to speak for localhost and the classes I took in acoustics happened so long ago, I may make errors since my old text books are at home and I'm not. However, my non-professional mentality hinges on a perhaps faulty memory of the pressure and velocity being 90 degrees out of phase and that room mode pressure is maximum at a boundary. So if you do a room mode simulation and get an idea of what modes should exist and where they should be, you can do the 1/4 wavelength math and bingo, your Vmax is located.

My gut instinct has always been that the most efficient porous absorber wouldn't have it's inner surface positioned at Vmax, but instead its thickness would be centered at Vmax. But if you carry out this process as a function of room size while assuming proper room proportions, you get to the point that the smaller studio/control/mix rooms would have excessive bass trap volume compared to usable volume.

Regardless, plot frequency versus the 1/4 wavelength dimension and think in 3D about the space those modes are occupying and the general location of trapping follows the typical bass trapping advice we've seen countless times - start with the tri-corners, trap as many wall-to-wall, wall to ceiling and wall to floor intersections as possible, then move on to areas at half wall dimensions, etc. In the big picture, I don't see the pressure max and velocity max as telling me to look at hugley different placements to trap with porous absorption because the required volume for adequate porous traps is so large, particularly relative to small/mid room total volume.

And once all of the modeling is done, and its lead is followed, you're still going to have to use the measurements made during the process and your own critical listening perceptions to get to the final result.

If the unstated question is: "why do porous absorbers work well when placed at areas of high mode pressure?", I think part of the answer is that the pressure max is not that far from the velocity max and porous traps require significant volume to provide adequate absorption, so they overlap into the high velocity zone due to simple geometry.

Experts, feel free to shred all of my errors and mis-perceptions.
20th November 2012
#55
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Joined: May 2009
Posts: 3,365

Quote:
Originally Posted by Icecube1
No no Syncamorea, that was not related to you!! Sorry, for the misunderstanding.

I gave your initial comment a thumbs up, I just wanted to add that, "sometimes", when passions get aroused I have seen comments that appear to mock(belittle) other points of view, that's all.
Thanks for the reply. I assumed as much but, having been accused of being a "typical" INTJ, am aware that my style is not appreciated by all.
Icecube1
#56
20th November 2012
20th November 2012
#56

Joined: Feb 2011
Location: Norwich, UK
Posts: 309

Quote:
Originally Posted by localhost127
i disagree that walking around the room and finding the areas of high PRESSURE via your ear is "obviously the best place to locate LF traps". if using resonant, pressure-based absorbers - yes. if using porous-only velocity based absorbers, then no.

why would you place a velocity-based absorber (which are most effective when located in areas of high particle velocity for a given wavelength) at areas of high PRESSURE (= low particle velocity)?
I should have perhaps left the paragraph before as part of the quote.

For Localhost127:-
If not using high pressure points to find the best place to locate LF porous-only traps, then how?
Jens Eklund
#57
20th November 2012
20th November 2012
#57
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Joined: Oct 2009
Location: Stockholm
Posts: 4,574

Quote:
Originally Posted by Syncamorea
I'm not trying to speak for localhost and the classes I took in acoustics happened so long ago, I may make errors since my old text books are at home and I'm not. However, my non-professional mentality hinges on a perhaps faulty memory of the pressure and velocity being 90 degrees out of phase and that room mode pressure is maximum at a boundary. So if you do a room mode simulation and get an idea of what modes should exist and where they should be, you can do the 1/4 wavelength math and bingo, your Vmax is located.

My gut instinct has always been that the most efficient porous absorber wouldn't have it's inner surface positioned at Vmax, but instead its thickness would be centered at Vmax. But if you carry out this process as a function of room size while assuming proper room proportions, you get to the point that the smaller studio/control/mix rooms would have excessive bass trap volume compared to usable volume.

Regardless, plot frequency versus the 1/4 wavelength dimension and think in 3D about the space those modes are occupying and the general location of trapping follows the typical bass trapping advice we've seen countless times - start with the tri-corners, trap as many wall-to-wall, wall to ceiling and wall to floor intersections as possible, then move on to areas at half wall dimensions, etc. In the big picture, I don't see the pressure max and velocity max as telling me to look at hugley different placements to trap with porous absorption because the required volume for adequate porous traps is so large, particularly relative to small/mid room total volume.

And once all of the modeling is done, and its lead is followed, you're still going to have to use the measurements made during the process and your own critical listening perceptions to get to the final result.

If the unstated question is: "why do porous absorbers work well when placed at areas of high mode pressure?", I think part of the answer is that the pressure max is not that far from the velocity max and porous traps require significant volume to provide adequate absorption, so they overlap into the high velocity zone due to simple geometry.

Experts, feel free to shred all of my errors and mis-perceptions.
+1

using REW Filtered IR to place absorbers in proper places

Icecube1
#58
20th November 2012
20th November 2012
#58

Joined: Feb 2011
Location: Norwich, UK
Posts: 309

Quote:
Originally Posted by Syncamorea
I'm not trying to speak for localhost and the classes I took in acoustics happened so long ago, I may make errors since my old text books are at home and I'm not. However, my non-professional mentality hinges on a perhaps faulty memory of the pressure and velocity being 90 degrees out of phase and that room mode pressure is maximum at a boundary. So if you do a room mode simulation and get an idea of what modes should exist and where they should be, you can do the 1/4 wavelength math and bingo, your Vmax is located.

My gut instinct has always been that the most efficient porous absorber wouldn't have it's inner surface positioned at Vmax, but instead its thickness would be centered at Vmax. But if you carry out this process as a function of room size while assuming proper room proportions, you get to the point that the smaller studio/control/mix rooms would have excessive bass trap volume compared to usable volume.

Regardless, plot frequency versus the 1/4 wavelength dimension and think in 3D about the space those modes are occupying and the general location of trapping follows the typical bass trapping advice we've seen countless times - start with the tri-corners, trap as many wall-to-wall, wall to ceiling and wall to floor intersections as possible, then move on to areas at half wall dimensions, etc. In the big picture, I don't see the pressure max and velocity max as telling me to look at hugley different placements to trap with porous absorption because the required volume for adequate porous traps is so large, particularly relative to small/mid room total volume.

And once all of the modeling is done, and its lead is followed, you're still going to have to use the measurements made during the process and your own critical listening perceptions to get to the final result.
This seems reasonable to me.

There also seems to be consensus that pressure based absorbers are more efficient at a boundary and velocity(porous) absorbers are only efficient out from a tenth to a quarter wavelength, depending on whether you are in the lambda over 10 camp or the lambda over 4 camp!!! (...please don't go into detail about the meaning of efficient, I think this has been done to death on other threads, you know what I mean.)

So, bearing in mind there is a view that using points of pressure max at the boundary is not a good way to decide where to put velocity based traps. Then, yes, my "unstated" question is how do you decide?
20th November 2012
#59
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Joined: May 2009
Posts: 3,365

What I did is took my current room project and did the mode math, guesstimated the 1/10 and 1/4 volume requirements and hand-drew 3d perspectives of what would be needed where. The overlap between P and V for the volume of porous was so great, it simply didn't matter, because the room is small (10.3 x 11.6 x8'). My bottom line is that I need to make pressure absorbers and learn what they can do for the room and use porous to try to make up the difference.

As room size increases, I can see your concerns rising, but on the other hand, when I've treated larger rooms, I was more willing to give up space for treatments, so making large traps out at 1/4 wavelength was no problem. But I value function over form and have been accused of overkill on more than one occasion. Example: placing over 400 cubic feet of HH absorbers in a 3000 cubic foot control room, along with extensive porous traps.
DanDan
#60
20th November 2012
20th November 2012
#60
Gear Guru

Joined: Aug 2003
Location: Cork Ireland
Posts: 10,268

True

Quote:
If the unstated question is: "why do porous absorbers work well when placed at areas of high mode pressure?", I think part of the answer is that the pressure max is not that far from the velocity max and porous traps require significant volume to provide adequate absorption, so they overlap into the high velocity zone due to simple geometry.
+1. Absolutely. What is near? One wonders if the transition from one zone to another is gradual, linear, or logarithmic? How thin is this zone of highest pressure and how soon does velocity become significant?
1/10 lambda springs to mind.
Plus- corner effects (prime LF locations) are not often lab measured or included in predictions.
Plus- surface area has something to say here.
One trap, a quarter wavelength from a boundary will hardly do much....

Context and perspective will turn any of these seemingly contradictory views into reality. In other words, two 4x2 foot panels are best placed in tricorners. But a full wall of fibre say 200cm thick will very likely function brilliantly at a particular frequency if placed at a velocity peak spaced away from the boundary. Obviously a 1-2 Metre fibre wall even at the boundary will absorb a lot.

Pedantically it may of course be ultimately correct to suggest that there may be velocity zones at viable locations for absorptive trapping. Nobody has suggested how to find them. Or even predict them.
EDIT exactly as Icecube said....
Quote:
Then, yes, my "unstated" question is how do you decide?
I think we can leave that one aside until we have commonly available velocity meters. (I have had my eye on Intensity Probes for some time now, waiting for a serious price drop).

To be frank, corners and the difference between LF hard or soft boundaries are blatantly visible to the eye.
I have suggested Sine Waves for two reasons. They will help chose trap locations from the viable options. e.g. Chose between the Front and Back corners. But more importantly the experience of walking through that null and into those high pressure zones is extremely useful when one is encouraging clients to go for it.

DD

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