Room modes, calculated versus measured

Posted: Thu Mar 17, 2005 4:21 pm

Sources for Mode Calculators (in no particular order):

1. Acoustic-X: Program no longer available.
2. Whealy: Link no longer available.
3. Auralex: http://forum.studiotips.com/viewtopic.php?t=497
4. JBL: http://www.harman.com/wp/index.jsp?articleId=131
5. Desart: http://forum.studiotips.com/viewtopic.php?t=1414
6. THX: http://www.kwaudio.com/Resources/THX%20Room%20Mode%20Calculator%20V%201.2%20092501.xls
7. WSDG: http://www.wsdg.com/resources/resour.php?SL=te&BL=5
8. Winer: http://www.ethanwiner.com/MODECALC.EXE

A graph that compares the results from the above can be downloaded here.

I had written a bunch of commentary on this, but I don't think it will help.

I will say that Acoustic-X was developed by Pilchner-Schoustal, a leading studio design firm in business since 1986. You can still buy a copy, but it probably won't run on Windows XP machines.

Besides Acoustic-X, all are free downloads. Perhaps someone has an updated link for the Chris Whealy spreadsheet?

JBL's calculator was developed by Floyd Toole.

The THX calculator is useless.

The WSDG calculator also appears a bit dodgy.

The top five listed above all agree with each other for the 12'x10'x8' model input into all eight.

The eighth one does agree with the first five for the nine axial modes it calculated in the range graphed (up to 220 Hz since that's as high as some of the calculators go).

Regardless of all of that, seven of the eight calculators appear to consider tangentials and obliques worth calculating - whether or not they're actually calculating them correctly.

My $0.02. (Hopefully my last for this thread!!! Confused

)

Posted: Thu Mar 17, 2005 4:37 pm

Chris Whealy
http://www.rmmpnet.org/members/ChrisW/index.html
Only this site is often out.

We'll ask Chris to upload them in the calculation tools section as backup.

Posted: Thu Mar 17, 2005 4:41 pm

Jeff:

Quote:

Perhaps someone has an updated link for the Chris Whealy spreadsheet?

As of March 7th, his ISP's webserver was dead.
For comments to that effect please see the bottom quarter of this post, starting at 'Bob'.

BTW, the MODESv2p.xls at http://forum.studiotips.com/viewtopic.php?t=497 (as noted above) written by -- oh boy, I hadn't noticed -- Jeff D. Szymanski is neat because it gives a text list of modes rather than just a graph.

Posted: Thu Mar 17, 2005 4:43 pm

Eric,

Hopefully Chris can update us as that link appears to be dead.

I did have another thought for Ethan:

I've reviewed this entire thread and couldn't find anywhere you actually attempted to correlate the response you measured with a predicted response. (I.e., not just measured versus modes, but measured versus modal response based on your loudspeaker/mic setup.) Have you done so? If so, can you post it? It sure would help your argument if it shows what you're talking about.

(Edited for clarity.)

Posted: Thu Mar 17, 2005 5:05 pm

Jeff,

> Sources for Mode Calculators <

Awesome, thanks for doing that. Thumbs Up

I noticed two things:

1. For axial modes, anyway, my ModeCalc program gives the same results as all the others. Very Happy

2. My program is the only one that doesn't require the user to own Excel.

> My $0.02. (Hopefully my last for this thread!!! Confused

) <

Hey man, your input is always highly valued by me.

--Ethan

Posted: Thu Mar 17, 2005 5:08 pm

Ethan Winer wrote:

1. For axial modes, anyway, my ModeCalc program gives the same results as all the others. Very Happy

Which I mentioned.

Quote:

2. My program is the only one that doesn't require the user to own Excel.

Not true. Acoustic-X is a stand-alone program. Also, I only gave eight examples. There are at least two others I did not list, both stand-alone. One is proprietary (not free and not yet released for sale) and the other is old (DOS) software that I couldn't find a link to anywhere on the 'net.

Posted: Thu Mar 17, 2005 5:15 pm

Jeff,

> I've reviewed this entire thread and couldn't find anywhere you actually attempted to correlate the response you measured with a predicted response. <

Look at my very first post to this thread where I showed the predicted response from Eric's spreadsheet, and compared that to what I actually measured with ETF.

> not just measured versus modes, but measured versus modal response based on your loudspeaker/mic setup. <

I documented most of the test setup, but I failed to measure or report the exact placement of the speakers in relation to the boundaries. This is why earlier I asked Eric what he thinks I should try next.

My "lab" is an ideal test room for further investigation because it's a perfect rectangle, with standard sheet rock on all sides and the ceiling. This room is used regularly by one of our employees as a working project studio, and all treatment is on stands or otherwise easily removed. Even the couch (not shown in the photos) is on wheels!

--Ethan

Posted: Thu Mar 17, 2005 5:23 pm

Ethan Winer wrote:

Look at my very first post to this thread where I showed the predicted response from Eric's spreadsheet, and compared that to what I actually measured with ETF.

Eric's spreadsheet does not predict a modal response. None of the tools I reviewed above predict the modal response. They just predict the modes. I can do that comparison myself. What I'm asking is if you used any tool to predict the response. Since I'm assuming that's a no, I move for a mistrial. If you don't have the loudspeaker/mic setup documented, then this entire thread is moot. If you really want to argue the relevance of any mode's contribution, I'm sorry to say you'll have to "do-over" and (please) document things a little better next time. If you cannot predict the modal response yourself, find a tool or a person who can. Only then can we start to talk about what is and isn't important. Thumbs Up

Until then...

Posted: Thu Mar 17, 2005 6:25 pm

Ethan Winer wrote:

2. My program is the only one that doesn't require the user to own Excel.

And I would be completely remiss if I didn't mention:

RPG's Room Sizer and Room Optimizer programs: www.rpginc.com

and

CARA: www.cara.de

Compared to the above calculators, none of these provides a list or graph of modes. But both predict low frequency responses. (Relevant to another part of this thread, no doubt!)

The Room Optimizer program will give a bonafide modal response prediction and an SBIR prediction based on listener and loudspeaker(s) locations.

The CARA program gives a predicted LF response, but I am completely unaware of how it does that. Terry Montlick and I have speculated elsewhere (at AVS). From the little I've played with it, CARA appears to be doing something similar to Room Optimizer. But I haven't delved in deep enough to know for sure.

So there you have it folks: 7 (possibly more?) free tools; 4 you can buy; at least 2 that will give predictions of modal response.*

*Room Sizer gives a response, but assumes a corner/corner loudspeaker/mic setup. It's more for designing the room size (duh.) than figuring out what you've already got - which is what Room Optimizer is useful for.

I will, of course, add more thoughts if anything else comes to me! Very Happy

Posted: Thu Mar 17, 2005 7:14 pm

Jeff,

Great link where these mode thingies are compared.

For the CARA thing I would like you to take a good look at their forum,

http://www.rhintek.com/cgi-bin/yabb/YaBB.pl?board=Tech_Support

or something, a guy we both now has some serious problems with the way CARA works.

Thumbs Up

Bert

Edited by Rod to correct link only.

Posted: Thu Mar 17, 2005 7:19 pm

CARA Forum

Wink

Posted: Fri Mar 18, 2005 4:14 am

Hey David,

Thanks!

I'm a bit lazy.... Wink

Posted: Fri Mar 18, 2005 6:35 am

Ethan Winer wrote:

....... Eric, you have to remember that most of the people who read my FAQ and download my ModeCalc program are beginners. They have no idea how to interpret the data your calculator outputs. If you want to think of my program as "dumbed down" a little for the masses, I have no problem with that.
--Ethan

It's just because it ARE beginners that they can easily be mislead.
Experts KNOW it's strongly incomplete. Beginners DON'T.

This is NOT a simplification, it can lead to WRONG interpretation, and only experts know that.
And you even refused (continuously) to mention this limitation.
You present it as a complete room mode calculator, NOT a dumbded down version with limitations.
And only experts know, never beginners who trust this to be A room mode calculator AS IS.

They argue exactly like you did yourself, in that thread with the by you deleted message clearly stating it were tangential modes.
It's not shown in this calculator so it has to be something else, something non-modal. You even explicit stated it couldn't be modes because you calculated them.

You conclude, based on your OWN calculator there are no dominant non-axial modes in YOUR OWN ROOM.
Well there are, AND THEY ARE DOMINANT.
You clearly told at SOS, that you searched, more than once, and never could find any non-axial modes, and you standard shift the proof to others telling otherwise, questioning any related suggestion and reference to whoever and whatever.
Here you get 4 example cases with dominant or significant non-axials.
And you're supposed to be the expert.

And somewhere here at RO the real reason is entered by yourself.
You couldn't find somebody to program a good Room mode calculator calculating all modes for you.
And that's why, and only why, your users only see axial modes.
And that's also why those endless discussions restart over and over again.
Because referring to another guy's calculator must be the biggest sin on earth.
You rather delete a related message, disprove the existence or possible importance of non-axials, and all literature related to it (even without knowing it).

Posted: Fri Mar 18, 2005 9:40 am

Jeff,

Good points as always. But...

> Eric's spreadsheet does not predict a modal response. None of the tools I reviewed above predict the modal response. <

Then what use are they? Why would anyone use a "mere" mode calculator when it won't predict anything useful or give some idea of the response you'll actually get once the room is complete?

> I'm sorry to say you'll have to "do-over" <

Not a problem. Do you think I should put the speaker and test mike in opposite corners as Bob suggested? Or should I do what I did the last time but measure and document all of the positions?

> Acoustic-X is a stand-alone program <

Wow, tough crowd.

You said that program is no longer available, so why mention it now? Pardon me for not being more clear: Of all the programs that you listed or that are free mine is the only one that doesn't require the user to own Excel.

--Ethan

Posted: Fri Mar 18, 2005 9:45 am

Eric,

> And you're supposed to be the expert ... You rather delete a related message ... <

It's a waste of my time to continue this sort of discussion with you, so I won't. When you're ready to discuss acoustics without relying on insults, and are prepared to address even half of the points I make, I'll be glad to continue.

--Ethan

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