Room Mode calculator - HTML only version

Post and discuss acoustic topics, Studio design, construction, and soundproofing here
Dan:

I guess my post was confusing.
I didn't mean that Everest said room modes or modal prediction or obliques were irrelivent.

As DJ said, Everest wrote "that tangential modes have only 1/2 the energy of of axials, and obliques only 1/4."

And Jeff said that they could be more powerful or less or equal or whatever.  Leo Beranek has an example where the tangentals and obliques are stronger than the axials.

My position is that it doesn't matter who's right. What is irrelevent is which is the stronger mode group: axial, tangential, oblique.
Because for example if you believe Everest and have a strong axial and a weak tangential that are within 1hz of each other, they're going to add to make something stronger than the axial alone (at some spots in the room?). So the fact that the tangental exists is still important, even if at half the strength. So it's important to know the frequency of all modes. A post-build measured resulting mode's strength will be determined by other things.

So when I say 'irrelivent' I mean it's irrelevant which mode group is strongest. (whether one is stronger or not is another argument which I'm not qualified to give an opinion on other than quoting others, but for the purposes of predicting the frequencies which is strongest is irrelivent)

Everest's actual quotes are, from page 333 of 4th of "Master handbook of acoustics"
All modes do not decay at the same rate. Mode decay depends, among other things, on the way absorbing material is distributed in the room. Carpet on the floor of the test room has no effect on the 1,0,0 or 0,1,0 axial modes involving only walls. Tangential and oblique modes, which involve more surfaces, would be expected to die away faster than axial modes that involve only two surfaces. On the other hand absorbtion is greater for the axial modes in which the sound impinges on the surfaces at right angles than for low angle of incidence common for tangential and oblique modes
Presumably he's talking about reasonably reflective surfaces like drywall/gypsum.

and from page 350
Tangentail modes have only half the energy of axial modes, yet their effect on room acoustics can be significant... oblique modes, having only one-fourth the energy of axial modes, are less prominent than the other two.

In other words, from what you wrote
I don't think  Everest says it is irrelevent, just lower in most cases.
Yes. Just lower in some cases.
I agree with Jeff at some point you will run into a strange room.
Yes, me too.
How close the modes are and if they are "stacking" is the more important part.
Yes.
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Bob nice work ...

DJ
1/2 energy only means -3dB
1/4 energy means -6 dB

The pictures here of the EW testlab show at least 2 tangential modes which are VERY dominant.
This theoretical - 3 dB really won't make a practical difference, when it shows as a problem.

Compare those numbers with dips they create to - 20 dB and more.

But one finds that in the FAQ. Look at that Room modes page

Important is how isolated do they appear.

The number of Tangentials and even more Obliques rize that fast that there aren't many isolated.
The ones that are and are excited correctly are or cann be from the practical point of view as important.

Bob,
You realy should block the order of the modes, an e.g. 0,20,1 mode really has no sense.

It should be good that rather than, or additional to your current input one can enter the max order of the mode.
If you don't want the user to enter that than calculate the max order of the longest axial and make that a variable in your from to loop.
It has no sense to go higher in order than the axials.

Something is wrong too with this color coding.
As you do it now your isolated modes are the safest and the denser the color (red) the more risky.
That's not the case at all.

The more isolated the more risky.
What Dan refers to is that it becomes more risky when isolated modes stack up, causing a more powerful isolated mode.

Your color code becomes denser red when things become healtier.
In principle this color coding as used now gives no useful information.
Not the short spacing is defining but the isolation of this modal energy which causes this troublesome modal behavior.

Could you make that link to vibration data accessible?

divinely-inspired
Eric.Desart
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Hi Eric:

You realy should block the order of the modes, an e.g. 0,20,1 mode really has no sense. ... It has no sense to go higher in order than the axials.
Could you explain that a bit?

It should be good that rather than, or additional to your current input one can enter the max order of the mode.

I used to have that in the first version of the page on day 1, but I replaced it with it calculating the max order based on the cutoff frequency and dimensions (simple algibra to work out the max n by inverting the equasion).
If you don't want the user to enter that than calculate the max order of the longest axial and make that a variable in your from to loop.
That is what  I'm doing now. Actually rather than one single number, it creates 3 of them, one for each dimension. If you push the Options button after you calculate you'll see the ranges it uses -- and they change whenever you change room dimensions or cutoff frequency. By doing it automatically it really reduces wasted computation time, which gets huge for large frequency cutoff and large rooms.
I can add an additional max integer again to further reduce that.

Something is wrong too with this color coding. As you do it now your isolated modes are the safest and the denser the color (red) the more risky. That's not the case at all.

You've described it backwards. The brighter within each colour band is more risky. There's a legend on the side under the piano.

The more isolated the more risky.
I thought when they overlapped they were more trouble.
What Dan refers to is that it becomes more risky when isolated modes stack up, causing a more powerful isolated mode. ... Not the short spacing is defining but the isolation of this modal energy which causes this troublesome modal behavior
Oh, you mean if there are two or more modes within 1% of each other (stack up), and no other modes within 10% of that frequency (isolated), that would be a bad thing, a really obvious hole.
Hmm. Everest may agreee with you "Master Handbook of Acoustics 4th pg 343" says "The spacing of the modal frequencies is the critically important factor. In the D region of figure 15-7, the modal frequencies of a small room are so close together that they tend to merge helpfully and harmlessly. In the B- and C- regions, below about 300hz, their separation is greater and it is in this region that problems can arise. ... Gilford states his opinion that an axial mode separated by more than 20hz from the next axial mode will tend to be isolated acoustically."

Your color code becomes denser red when things become healtier.
Yes. Now you've got it.

In principle this color coding as used now gives no useful information.
Hmm. What I thought I was doing was the Bonello 5% of frequency test. i.e. that it's disireable to have all modal frequencies at least 5% of their frequency apart. Anything wider than that shows up as light green in my chart, and gets bright yellow and bright redder as they get closer together.

So you'd like me to have a new column with red flags on any two or more modal frequencies that are within 2% of each other, but have no other mode within 20hz, for any mode between 10hz and 150hz ?

Hmm. The actual Bonello rule is "To meet Bonello's criterion, each 1/3 octave band below 200hz should have more modes than the preceding one, or at least the same number. Modal coincidences are not tolerated unless at least 5 modes are in that band." I can easily plot this as a graph, similar to Everest's figure 15-22 on page 349.

Could you make that link to vibration data accessible?
I was reading some of the copyright links you provided from studiotips, and one of them said that having a link that people can click on to another page could be a copyright violation especially if it's to page 3 in a sequence of html pages, but merely having unclickable text is clearly not a copyright violation.

BTW, I notice that your spreadsheet and my webpage differ a bit in the results. The predicted frequencies are different by about 0.28%.
For example, for a 16' 2" x 11' 6.5" x 8' room, yours say: 34.8, 48.8, 59.9, 69.7, 70.4
Mine says for a (16.166666666666666666666666666667, 11.541666666666666666666666666667, 8 feet) room: 34.9, 49.0, 60.1, 69.9, 70.6.
I remember yours did something with temperature or humidity or something. I wonder if that's it.
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Bob,

Unlike you I calculate Metric, so I convert from Imperial to Metric.
But your's and my conversion is with that much decimals that it doesn't matter.

The main reason is the Temperature in function of speed of sound.
If you accept this as an input (I'll do that in my future next version) than you can correct this speed of sound to Temperate (it's fun to check the effect, it allows to prevent this slight deviation versus others, and it's easy to implement)
Since you work Imperial use the ASTM C 423 formule to define speed of sound (is what is used in reverb rooms).

Write the formulas you use with ref to the standard:

ASTM C 423-00: section 11.13 Speed of sound:
The 00 refers to year 2000

c = 49.022 x sqrt(459.67 + T° F) ft/s
T° F = Temperature in Farenheit
In metric
c =20.047 x sqrt(273.15 + T°C) m/s
T°C = Temperature in degrees Celsius Americans call this Centigrade but not the Europeans who use it.
Both Metric and Imperial are given in the same topic of the standard

Usinf T as imput allows your constant soundspeed to be set as a variable.

Thinking metric I just used your numbers as meters, combined with 300 Hz this gives a stupid number of modes.

Therefore: What about integrating the Schroeder frequency as limit 1 times, 2 times etc.
This will by definition limit the return to sensible values were the roomresponse is dominated by modal behavior.

I even think it's better to use less colors.
Instinctively Red is a warning sign, NOT green (that's called communication stereotype in communication science)
Red should be the ones to look at. Green the safe one just there as info and something in-between.

And you understood the principle:
Bad is poorly spread, isolated, or stacked and isolated.  were modes come close together they embed one another neutralizing the destructive effect (this is called modal overlap on which Schroeder's frequency is based).

You use a picture for which you didn't ask permisssion.
A picture even with a link does NOT necessarily constitutes fair use. Certainly not when published on a page.
Respect is that users can directly go to the source you used it from.
With a book it's not possible (but one needs to ask permission to the publisher).
Here it is easy possible to link.  Overtyping a link is not easy and no respect for the reader nor the Author.

If you think that that US is strict in Copyright, I can assure you it is not. Some countries are much stricter than US law.

For you this is bargening between finding the boundary between what can at the edge, to bind people to your page.
That's the same with your examples of absorbers.
You give the name of several of the ones who made them without link to the source itself.  Well that constitutes breach of Copyright.  That name alone is poor respect of Copyright and does not constitute Fair Use.
That's this edge thing which is caused by binding people, making them dependent of you.
Well collecting all those things together is a huge and nice work, That's added value by transformation.
That does not allow you to hide the source.

This all does NOT mean that I shouldn't respect you.  I do and you make nice work.

Chris Whealy's spreadsheets are an example of respect
Last edited by Eric.Desart on Sat Mar 26, 2005 12:51 am, edited 3 times in total.

divinely-inspired
Eric.Desart
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One last thing Bob.

It should be very helpful if you could make it as such that one could select and copy only the first 2 columns.
That way people could simply copy the results and enter them in a spreadsheet or a text file.

That makes it a clear winner over other HTML calculators were those numbers appear in seperate boxes forcing one to copy them peace by peace.

For now it also selects this colors row and that causes trouble (my browser gets completely blocked on it when trying to copy.

divinely-inspired
Eric.Desart
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Bob,

The reason, and the only one that I link easily to your site and even asked Scott to put it in the FAQ is at least you search a way to handle copyright.

Lot's of people don't care at all.
They assume it is invented for others and in as far applicable Copyright is written to protect their personal rights.
I should NEVER link to such a site (if I'm aware) I don't care how valuable it is.

So don't think I'm attacking here. I'm not. It's respect for your search causing this.

divinely-inspired
Eric.Desart
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Eric:

One last thing Bob.
It should be very helpful if you could make it as such that one could select and copy only the first 2 columns.
That way people could simply copy the results and enter them in a spreadsheet or a text file.
That makes it a clear winner over other HTML calculators were those numbers appear in seperate boxes forcing one to copy them peace by peace.
For now it also selects this colors row and that causes trouble (my browser gets completely blocked on it when trying to copy.

Hmm. With Interenet Explorer it works very well. I just drag the mouse over the whole table including colours, and I can paste the whole table into notepad and it shows up without the colours. For example:
45.3 hz (1,0,0 Axial)
49.5 hz (0,1,0 Axial)
67.1 hz (1,1,0 Tangential)
71.5 hz (0,0,1 Axial)
84.7 hz (1,0,1 Tangential)
87.0 hz (0,1,1 Tangential)
90.7 hz (2,0,0 Axial)
98.1 hz (1,1,1 Oblique)
98.9 hz (0,2,0 Axial)
103.3 hz (2,1,0 Tangential)
108.8 hz (1,2,0 Tangential

I guess I'll have to add a non-table TextArea field at the end with the same data so it can be cut-pasted in other browsers.
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Eric:
Just in case you're worried -- that background picture I made myself in visio and paint.
The lowest octive frequencies I computed myself (lower than the piano keyboard's lowest key).
You can compare the two different pictures
http://www.vibrationdata.com/piano.htm
and
http://www.bobgolds.com/Mode/RoomModes.htm
I only mentioned where I got the frequencies from due to the recent fun you had with incorrect equasions being copied from place to place -- I wanted to show that if I had them wrong then they came from somewhere, rather than I was in agreement.
I don't think the concept of a picture of a piano is copyright. I don't think that A is 440 hz is copyright.
Last edited by Bob on Mon Mar 21, 2005 10:54 am, edited 1 time in total.
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Joined: Sun Feb 08, 2004 4:37 am

I work with IE but I had serious trouble.

I agree I used longer tables.

But if you could do it somehow by splitting this table (you're the specialist) to make copy and paste easy you made the most powerful calculator on the net.

Those individual return value boxes are annoying to copy.

Should be even nicer if you have a copy button to bring it as an array in a uses computer (don't know if this is possible).

divinely-inspired
Eric.Desart
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Eric
Thinking metric I just used your numbers as meters, combined with 300 Hz this gives a stupid number of modes.

Oh yea. That would be a huge room, and yea lots of modes below 300hz, probably thousands.

I even think it's better to use less colors.
Instinctively Red is a warning sign, NOT green (that's called communication stereotype in communication science)
Red should be the ones to look at. Green the safe one just there as info and something in-between.

I'm familiar with communication stereotypes. I tried to use a trafic light as the standard here. As you wrote, green is safe on my page, and red is things to look at.
I'll think about your suggestion to use fewer colours. I don't like the transition between yellow and red either, but I tried more shades of red and that was worse.

Therefore: What about integrating the Schroeder frequency as limit 1 times, 2 times etc.
This will by definition limit the return to sensible values were the room response is dominated by modal behavior.

Schroeder frequency: 2000 * square-root of (T / V)
where T is reverberation time, and V is volume in cubic meters.
Where am I going to get reverberation time from ?

And you understood the principle:
Bad is poorly spread, isolated, or stacked and isolated.  were modes come close together they embed one another neutralizing the destructive effect (this is called modal overlap on which Schroeder's frequency is based).

"Bad is poorly spread, isolated, or stacked and isolated" -- I'll think about how to flag that. Thanks
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Eric

Should be even nicer if you have a copy button to bring it as an array in a uses computer (don't know if this is possible).

I can make it a tab separated list, so it should paste into excel just fine. Or a comma separated list which can be imported into excel just fine.

(Actually I could make an ActiveX control which would run excel, and then populate the squares -- I've done this in C and other languages before -- but that violates my impression of what a well behaved website should do.)

With a real .jsp server I could generate an excel file and transfer the user to there and it would show up in the excel browser plugin that's automatically installed with Microsoft Office, but this is just an html page and it won't do that.
Regards
Bob Golds
"The only thing we regret in life is the love we failed to give."
"Be a rapturist -- the backward of a terrorist. Commit random acts of senseless kindness, whenever possible" - Jake Stonebender
Bob

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Bob,

I'm not bargaining.
You showed that link because that's were you got the idea.
As easily you can do it otherwise.

I give a typical example which indeed bothers me.

That Helmholtz formula.
http://forum.studiotips.com/viewtopic.php?t=94
You refer to this message which I DOOOOOOOOO respect.
I entered it in 4 to 5 groups at the time.

While I don't need a single soul for every line of text in it.
I calculated Helmholtz resonators long before I knew the word Internet.

A  guy in the science group which is very attentive find this mistake.
I'm convinced of the impact of this error in studio groups, so I make an extensive message, which goes even further and explains the how and why's.
I refer to ALL pertinent sources and give credit to all of them, including the ones checking the different editions of the books which I didn't had.

My job was transformation.
Putting this error in context, giving credit to anyone.

This makes it scientifically valuable and it gets credibility.

How often is linked to this original message giving credit to anyone involved?
One can as easily link to this message itself, than doing if it's their find.

This is literally breach of Copyright.

Secondly this original message links to Pro acousticians and put the problem in context.
If one should link to this message when telling those sites with wrong calculators, chance is VERY large that related comments ARE taken serious.

And their is NOT one line in this message which I needed others for.
Those books are official things. I could look if I could find them in a Univ lab or wherever.
Helmholtz formulas I knew and used decades before.

It's simple: A clever attentive guy noticed it. He's the one deserving credit
And I'm the one deserving credit to make sure I went more in-depth, put it in context.
But ANYONE who helped is mentioned giving proper credit.

Everest doesn't need a single soul to write a book.
Yet his and any other valuable book, articles, papers are full of references.

I once compressed pictures for a Java tree menu system.  For me an hour or two fun.
Thousands of people could have done the same
I still get credit on the net.  Even from people and organizations I don't know.

I released an idea to use the old Excel language to solve a problem that VBA can't solve in Excel programs.
It was just somewhere one lost message between thousands.
Well I'm mentioned with credit for the idea on the site of one of world's best Excel programmer.
This guy is thousand times better than I am, and does not need me for anything.

If programmers in Excel groups write a couple of lines of code, others who are much better, and reacted as: "He, good idea" continue referring to this guy when using this 2 lines of code.

Do you know where I e.g. can't find my name or hardly.
In studio groups were I spend hundreds of times more time than in the rest.
Do you know when was referred to me in studio groups?
In the beginning when I introduced the triple leaf idea and related risks, and anybody felt unsure to cover their ass.
I even don't know if the notion triple leaf existed as such. I've searched the net back then because I didn't knew how to express this in English. Back then a google for "triple leaf" didn't return a thing in the sense I used it.

I could give you more formulas: I know I wittingly withheld things here for the very reason of respect for Copyright.
And the reason you won’t see many pro's entering calculation models is for the VERY same reason.

This are just general ideas.
I know I will not share solutions I worked on for months with this STANDARD attitude in studio groups.

I can't stop people to find a million reasons not to give credit to others.
So if you see this personally rather than me trying to take you serious IN RESPECT, than that's your approach.

I help people in function of how I feel about how they handle this.

divinely-inspired
Eric.Desart
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Schroeder freq: Just use the standard control room absorption (AES formula) or since room modes assume a reflective room adjust the parameter and show how you come to this value, or let the user enter it, giving a predefined standard in function of room size yourself.

This are just ideas.
I should have stayed awake myself too, knowing that those measures in meters were huge to calculate to 300 Hz.

At the other hand using the Schroeder is a nice and sensible addition.

Can you enter hidden inaccessible formulas???

FOR THAT COPY THING:
Don't make special things. You don't like exe programs, others don't like and block activeX things.
Just allow easy copy/paste for users. Then they can enter as they like where they like.
If you can store (copy it) it indeed as comma or fixed space or whatever seperated text file that should be perfect.
And you do with your nice method of programming.
That alone makes your's already better than others.

divinely-inspired
Eric.Desart
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mornin Bob,

you're onto something here, and IF you are willing to tolerate the bandwidth usage, and IF you are feeling ambitious, i'd be happy to give you all the functions i've ever written for calculating various TL-related things.  like dBA reduction or STC or even the equal loudness things, although those (eq loud) are really messy in their current excel form, and you'd probably want to impale me on a lance if you saw them all.  lol

but please don't take that as a request, just an offer, i'm sure you're as busy as the rest of us kids

Brian
Content posted by me is copyright 2004, 2005, 2006  Brian Ravnaas, but may be reproduced without permission for any non-commercial purpose so long as the intent is preserved.  NRC Canada data is copyright them and used with permission, www.nrc.ca
Brian Dayton

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Brian:
although those (eq loud) are really messy in their current excel form, and you'd probably want to impale me on a lance if you saw them all.  lol

The guy is really to modest!  :mrgreen:
bert stoltenborg

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the graphs are ok, but the functions that generate them really are a mess, lol
Content posted by me is copyright 2004, 2005, 2006  Brian Ravnaas, but may be reproduced without permission for any non-commercial purpose so long as the intent is preserved.  NRC Canada data is copyright them and used with permission, www.nrc.ca
Brian Dayton

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OK... it runs on Netscape, but not on Explorer. Nice. Simple enough for boobs like meself.....  I like the piano overlay.

sf
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last time i checked it, it ran on IE just fine
Content posted by me is copyright 2004, 2005, 2006  Brian Ravnaas, but may be reproduced without permission for any non-commercial purpose so long as the intent is preserved.  NRC Canada data is copyright them and used with permission, www.nrc.ca
Brian Dayton

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Bob,

Another thought.

If you add as an additional column your colors also in corresponding numbers (how to for you), when people copy the list they still have the flags as you intended them.

And to make it complete.

Also add a title section were you retake all relevant data, which is than copied with it.
Measures room,
Floorspace
Total boundary surface
Volume.

How to do it elegant is for the expert (you).
And it are just thoughts to make it the most practical net version.
I've no idea what it means for you.

divinely-inspired
Eric.Desart
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Bob the new parts added with the colors does not work on all browsers.  I have only seen it work in IE on XP so far.  It does not work on firefox on xp, or any of the mac browsers that I checked before I left to work.  I would test it on  Firefox and then IE if works on both of those chances are it works on most browsers and OS's.  If want to use a mac for testing I could set up something to allow you to access one remotely.

Dan
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