> I'd guess your speakers were about 5.8' apart, but I wasn't able to devine enough information from their placement to guess about wavelength to effect. <
I meant the distance between the microphone and a boundary more so than SBIR, but I agree that the speaker distance can affect this too.
> I thought the rule was that if it sustains for a bit after the speakers stop then it's probably a mode. <
Good point there too. In fact, I thought of that just the other day, and I plan to do some more testing at different places near the rear wall to see how easy it is to distinguish modal versus non-modal peaks.
> Random microphone positions in the room will give random evidence of modes. <
Man, you're batting 1000.
The test I did moved the microphone along a diagonal line outward from one of the rear corners.
Can we please be a little more professional here and stick to the science? This is about modes, not about Ethan. Thanks for your cooperation.
> That's why you "Forgot" to correct your own info too, to the questioner? <
There's nothing to correct. I have that thread in front of me, and the poster said "around 125 Hz" with no indication of whether he measured, or how he measured, or if he was just guessing, or anything else that confirms he even knew what frequency was the problem. You are blowing all out of proportion one vague post from someone who neither of us is sure even understands what he reported. He also suggested it could be his walls vibrating. In that case modes have nothing to do with it.
Re your graph.
I'd been focusing so much on the peaks, I'd forgotten about the valleys. There's a couple of strong dips that correspond to tangental and oblique there.
I know Z,
You're 100% right.
There are more.
The reason I did't sum them up here, is that one first must calculate the effect of early reflections, to be 100% sure.
There are several tangential effects in this picture and some dominant.
But since Ethan like to prove himself right by proving me wrong, and there is nothing for me to check and only those deviating, not clear described measurements to go on I left it like that.
But you noticed correctly. also when the mic is in the node it can refer to a very dominant mode.
That's what such waterfalls hide. Such a watefall can hide as dominant modes as it can show. All odd y-axis modes and all other non-axial modes were y is odd are hidden + (others of course, depending on mode order versus x-axis + z-axis)
But i described that also in the original Studiotips thread.
But also important is how are they excited?
when the speakers are along the y axis and in phase, and you exite an x-axis mode your coupling is perfect.
With the same speakers and phase the y-axis mode will be cancelled.
Those things are easy to check by playing with reversing phase, playing with one and two speakers, and scanning the pattern of the mode that should be there.
But Bob, you've seen VERY well.
What you're doing now is finding a logic, which is ONLY possible by seeing ALL modes.
This helps you to identify the modes.
An axial alone calculator gives a false picture of this room.
E.g. This waterfall double peak at ca 100 Hz are probably not the 2 axials but an axial and a tangential.
This 85 Hz dip, if not an early reflection effect then that's a very dominant tangential one.
But one can make some logical assumptions and then test them.
Because such logical assumptions also tell you what to find at other spots or other coupling with the mode.
Last edited by eric_desart on Thu Mar 17, 2005 6:46 pm; edited 6 times in total
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!!! )
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eric_desart Recording Org Pro Audio Forums
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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.
Last edited by z60611 on Thu Mar 17, 2005 4:45 pm; edited 2 times in total
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.)
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Ethan Winer Respected Past Moderator
Joined: Mar 19, 2001
Posts: 3209
Location: New Milford, CT USA
1. For axial modes, anyway, my ModeCalc program gives the same results as all the others.
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.
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Ethan Winer Respected Past Moderator
Joined: Mar 19, 2001
Posts: 3209
Location: New Milford, CT USA
> 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!
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.
Until then...
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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!
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