Rather than applying logic on the measurements versus calculated modes, you can test those assumptions.
You know about the coupling with the mode.
You know the pattern of the mode.
When you do such tests, you can alter some of the parameters knowing what the theoretic effect should be.
This certainly works for the isolated phenomena.
For the other ones there can and will be interaction between those modes, but also with early reflections.
It's a matter of checking by deduction then.
Of course you can also put them in simulation models which gives you already an idea how more complicated patterns will look.
But at a certain moment this all becomes to complex, AND senseless.
Here I certainly second Brian's comments as well.
One isn't going to a PhD study for one little room which then is valid for that room with those specific parameters.
And even when you should have such a model, only finding the variables to put in the model should be nonsense.
So the simple and logical manner is:
You measure: Some will be clear, some leave question marks.
For the question marks adjust the parameters of your measurement to confirm or disprove your possible assumption.
If I'm sure that something should be a tangential based on theoretical assumptions, then it MUST be possible for me to find the traverse null lines as well. I can work with 2 speakers from which I reverse polarity. In one case I will cancel the mode in the other I have a perfect coupling.
What I mean is. You see something, you're not sure, then check your hypothesis. For the isolated phenomena it's nothing more than understanding the consequences of your own assumption.
And when too difficult when too many interacting phenomena occur, then forget it.
You can't expect a room mode calculator to substitute FEM simulation software calculating for hours and hours on CPU's with gigabyte speed, and still then the result will never be better than one's input.
And this 10 to whatever % at the lowest mode is maybe fun to play with. But I only see it as play and diversion.
It's easy enough to check in real live if this is the first order axial or not.
And if Toole from Hartman, only registers the phenomena without explanation, showing it as a question mark that's enough for me.
And if for 60 years top mathematicians and acousticians worked out their theories which they tested in practice and standard theory and examples confirm this logic that's enough for me.
At a certain moment this becomes a bit talk for the talk.
Are you going to be busy for days before mounting corner absorption because you can't model it exactly?
If I see in fact nothing is questioned here based on arguments.
It's just a collection of questions.
Well it's good that they exist, but do nothing to disprove whatever, nor cause the need to prove whatever.
There are simple manners to check if assumptions are confirmed or disproved.
And 10% questions are diversions.
Such modeling must be extremely complicated AND senseless, and certainly not meant for studio groups but for end works in college.
_________________ Best Regards - Eric Desart
Also or Non Respected Past RO Acoustics & Design Moderator?
Last edited by eric_desart on Wed Mar 23, 2005 3:27 pm; edited 4 times in total
avare Recording Org Pro Audio Forums
Joined: Feb 12, 2004
Posts: 339
Location: Hamilton, Ontario, Canada
Please stop being so agressive, okay? I'm not here to fight with you or anyone else, and I will not participate if you won't behave like a human being. At John Sayers' site you promised Steve that you would try to be civil, so please knock if off, okay?
--Ethan
This must be the thread that you are referring to at RSD.
> This must be the thread that you are referring to at RSD. <
The very fact that you bring it up here shows clearly your intent to continue making trouble. If you have nothing useful to contribute to the science of acoustics, why are you even posting?
Andre,....
.......If you have nothing useful to contribute to the science of acoustics, why are you even posting?
Maybe because most like him to contribute and he knows the CONCEPT science?
Edited:
Andre I read the referred thread now.
I should say: as to be expected. And your comments were 10^20 correct and rightfully entered in the interest of many.
_________________ Best Regards - Eric Desart
Also or Non Respected Past RO Acoustics & Design Moderator?
Looking up references to answer a question posed over at Ethan's EQ forum, I happened to take a fresh look at Gilford's 1979 AES paper, The Acoustic Design of Talks Studios and Listening Room. (This paper was originally presented for the Radio and Telecommunication Section of the IEEE.) I wanted to quote a few sections that have relevance here:
Gilford wrote:
There will be room modes...in all parts of the audible spectrum, but whether or not they will be appreciable as colorations depends on the following factors:
(1) the bandwidth of the mode
(2) the degree of excitation of the mode
(3) its separation from neighboring strongly excited modes
(4) the positions of the sound source and microphone with respect to standing-wave systems
(5) the frequency content of the source.
What's interesting is that the above was detailed in Section 2.1, Formation of Simple Modes in Small Rooms, that discussed only axial modes.
He goes on (from Section 2.3 The Relative Importance of Axial, Tangential, and Oblique Modes):
Gilford wrote:
For the case of a typical small studio...calculation shows that no frequency is likely to become prominent unless it (has) a high early intensity and a long decay. This condition* is satisfied only by the axial modes, which are therefore the only ones likely to become individually significant. An exception to this rule is that a few tangential or oblique modes of low frequency may possibly be audible, owing to their high initial intensities or wide spacings.
Emphasis on the last sentence was added by me.
{*Gilford is explaining an image-source method of calculation. I omitted references to it to keep things simple here.}
Finally, I believe I may have discovered another alternative for Ethan to consider for his axial mode calculator:
Gilford (context: from Section 3.4 Design Precautions for Avoidance of Colorations) wrote:
A simple calculation...enables a list of all the axial modes for all three dimensions to be written down in order of frequency. It will be unnecessary to continue the list beyond, say, 350 Hz because...the axial modes in a well-designed talks studio will not be prominent above that frequency. The list must next be examined to find modes, or groups of modes with almost the same frequency, which are separated from their nearest neighbors on either side by intervals appreciably larger than their bandwidths. In practice the minimum separation for audibility appears to be about 20 Hz.
Modes or groups separated from their neighbors by greater intervals than this should be noted, and...attempts should be made to alter the groupings by changes in the proposed room dimensions.
IMO, the above gives Ethan the option of adding some sort of mode spacing evaluator. Spacings wider than 20 Hz can be called to the attention of the user and steps can be taken then to change the "proposed room dimensions" to give a better spread of axial modes.
The science makes sense. And it takes the "need" for calculating "non-axials" out of the picture.
Whaddyathink, Ethan?
{Note: Posting same message in other thread.}
_________________ ---lovecow---
"You've got to be very careful if you don't know where you're going, because you might not get there." - Yogi Berra
> This must be the thread that you are referring to at RSD. <
The very fact that you bring it up here shows clearly your intent to continue making trouble. If you have nothing useful to contribute to the science of acoustics, why are you even posting?
--Ethan
Ethan:
You are wrong!
Andre linked that thread here, because, contrary to your claims, it quite clearly shows Steve getting annoyed at you for posting in your typical defensive and agressive style. He may have asked eveyrone to cool it, but it was you who started the fire there.
You must be on auto-pilot, as it only takes an ounce of rational to realise it's pointless posting claims that can so easily be disproved.
Andre was just putting the record straight. I don't blame him when he's been wrongly accused.
You are always accusing people of causing trouble, so I can only assume your blind to the fact that those people are only trying to put the record straight, after you started the trouble in the first place.
It's a bit like a burglar accusing a homeowner of starting trouble when he defends himself.
I offered an Olive branch to try and sensibly talk about this, and hopefully calm things down, and eventually end this stupid feud.
Paul
NOTE: this post is NOT an attack, but an observation.
In the "Master Handbook Of Acoustics 4th" pg 343, it says "Gilford states his opinion that an axial mode separated by more than 20hz from the next axial mode will tend to be isolated acoustically. It will tend not to be excited through coupling due to overlapping skirts but will tend to act independantly. In this isolated state it can respohnd to a component of the signal near its own frequency and give this component its proportional resonant boost."
The reference/bibliography says that is from what looks like the same place you found, except ultimately it was from an earlier print, namely: Gilford, C.L.S. "The Acoustic Design of Talks Studios and Listening Rooms", Proc. Inst. Elect. Engs., 106, Part B, 27 (May 1959) 245-258. Reprinted in J. Audio Eng. Soc., 27, 1/2 (1979) 17-31
But what concerns me is the last part of Gilford's
Quote:
In practice the minimum separation for audibility appears to be about 20 Hz.
If I play three notes together (25.5hz, 32.7hz, 41.2hz) what I hear is a chord (A major I think). Each of those three has a separation well less than 20hz.
And looking at a modal calc for a few rooms (e.g. 12.46, 11.42, 7.90ft), there are no two frequencies separated by 20hz. I don't think that Girlford meant that there are no rooms with modal problems.
So I'm thinking that Gilford's 20hz might be taken in context of his mentioning 350hz.
Again, on a piano, F @ 349hz, the next semitone down is E @ 330hz, which is roughly 20hz difference. In other words, the "separation for audibility" is a semitone.
I think it's an axium that people can hear the difference in tone of any two different semitones.
A semitone, by interesting coincidence, is roughly about as Bonello's rule of 5% of their frequency apart. i.e. 349hz/330hz = 1.0575757 or a difference of about 5%.
Perhaps people can hear differnces less than a semitone as well.
Here is an interesting summary of how the ear works
but more to the point is this experiment in how close two frequencies can be heard. Based on the forumula there, and assuming 7 cents (cent = 1/1200 octave) is the minimum audible frequency sparation, for a 1hz difference that works out to 250hz vs 251hz is a 7 cent difference. I won't bother with the 3.5 cent and 5 cent differences mentioned in the conclusion for no particularly good reason of mine, simply because obviously differences this small are no where near the order of magnitude larger scale that Gilford and Bonello are talking about, so I'll try with the 5% rule for my calcs, i.e. frequencies within 5% and separated by 5% from others, may be bad modally.
5% = 85 cents = 0.0708 of an octave.
Quote:
IMO, the above gives Ethan the option of adding some sort of mode spacing evaluator
It's been my plan to do that with my little webpage. I just have to find the time...
proudtower Recording Org Pro Audio Forums
Joined: Mar 14, 2005
Posts: 145
Location: achterhoek, netherlands
If I understand what you mean, this reffers to Ethans reply on my comment that human sound perception in the low frequencies is more lineair, and in higher frequencies (above 200 Hz, I think) is logaritmic.
(I probably should come up with a reference, but I have to search).
Ethan says that rearranging the frets on his bass does make a difference. I agree with him, but that is not the point.
The 20 Hz seperation doesn't mean you cannot hear other seperations or scales, but that spacings more than 20 Hz apart are annoying. And modes spaced some distance on the freq scale in practice can/will have larger level differences than in theory, where they are equal or differ only 3 or 6 dB.
Personally I don't care to much about modes (Jeezzz, what am I saying now!).
When you have a not to big room you cannot sacrifice space to make the room dimension ratio perfect. You have to do with what you have. Meaning that experimenting with damping and speaker/listening position has to do the trick, and it almost always will.
Bert
eric_desart Recording Org Pro Audio Forums
Joined: May 23, 2003
Posts: 816
Location: Belgium Antwerp
But I also believe Bert, that you're more busy with listening spaces than recording spaces.
Our brain solves a lot.
Recording spaces implies more accuracy.
But of course experience can solve a lot to. But you also have a trained instinct well aware of the concept modes and interference.
_________________ Best Regards - Eric Desart
Also or Non Respected Past RO Acoustics & Design Moderator?
proudtower Recording Org Pro Audio Forums
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