How to read these room mode values?

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Kalle Rantaaho
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2013/08/22 08:36:41 (permalink)

How to read these room mode values?

I fed in my room measurements to this calculator
 
http://www.mcsquared.com/metricmodes.htm
 
When I lined up the given Hz-values on a straight graph the results were:
 
Axial-modes: From 22 Hz up almost evenly (about 15 Hz variation max) spread except for a bunch of three at 172-174 Hz.
Tangential modes: first one at 40 Hz, a group of three between 80-100 Hz, one at 125 Hz and again
group of three at 170-185 Hz. From 250 Hz upwards almost evenly.
Oblique-modes: Spread evenly 95-195-285-380 etc. up to 855 Hz.
 
What does this actually tell me??
 
 

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    The Maillard Reaction
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    Re: How to read these room mode values? 2013/08/22 09:02:08 (permalink)
    Most explanations I have read indicate that the axial mode is the one to focus on because the other modes are happening at much lower energy levels. Furthermore the energy level of the first instance of the axial mode is usually the one with the greatest level and so they should be accorded the most concern and or treatment.
     
    I know you mentioned it elsewhere, but if you can remind us of your room dimensions it might be fun to go see the complete results at the calculator you used.
     
    The other thing to consider is that these predictions are describing some instantaneous or steady state in an empty room, where as in practice you will be experiencing an environment where the levels of the peaks and nulls are undulating in seemingly random cycles. I like to think of what I observe on a RTA as rhythmic cycles that are overlapping in such a way as to seem random. If you watch it carefully you may begin to imagine patterns of repetition.
     
    best regards,
    mike
     
     


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    The Maillard Reaction
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    Re: How to read these room mode values? 2013/08/22 09:19:22 (permalink)
    FWIW, I've enjoyed this calculator in the past:
     
    http://www.bobgolds.com/Mode/RoomModes.htm
     
    It comes with a pretty good set of explanations:
     
    http://www.bobgolds.com/Mode/RoomModeExplanationReferences.htm


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    wst3
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    Re: How to read these room mode values? 2013/08/22 12:10:57 (permalink)
    Thanks for that link Mike- that is a very cool calculator!

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    Kalle Rantaaho
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    Re: How to read these room mode values? 2013/08/22 13:49:26 (permalink)
    mike_mccue
     
     I know you mentioned it elsewhere, but if you can remind us of your room dimensions it might be fun to go see the complete results at the calculator you used.
     
    best regards,
    mike
     



    The total measurements are H 2.02 m, W 5m, L 7m. Half of that will be used as "studio", but as the wall separating the other half is rather thin and porous with an open (with curtain) doorway, I figured the low frequencies behave as if the whole room was used.
     
    EDIT: At the moment, when the room is still a mess with stored stuff everywhere, it sounds about dead.
     
     
    post edited by Kalle Rantaaho - 2013/08/22 13:53:18

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    bitflipper
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    Re: How to read these room mode values? 2013/08/26 13:34:02 (permalink)
    Kalle Rantaaho
    Axial-modes: From 22 Hz up almost evenly (about 15 Hz variation max) spread except for a bunch of three at 172-174 Hz.
    Tangential modes: first one at 40 Hz, a group of three between 80-100 Hz, one at 125 Hz and again
    group of three at 170-185 Hz. From 250 Hz upwards almost evenly.
    Oblique-modes: Spread evenly 95-195-285-380 etc. up to 855 Hz.
     
    What does this actually tell me??

    It tells you that your room is most likely to mess with your head at around 174Hz, so any time you apply EQ to a track or bus around that frequency you'll do well to double-check with headphones.
     


    All else is in doubt, so this is the truth I cling to. 

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    The Maillard Reaction
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    Re: How to read these room mode values? 2013/08/27 11:32:29 (permalink)
    I had to take a few days to digest the info provided at the Bob Gold site and all the referenced links.
     
    The results of the room mode calculator don't tell you all that much, mainly because they don't reconcile what you will actually experience at the listening position.
     
    The results can suggest where you should look for issues.
     
    The reference material led me to read differing opinions regarding the proximity of the standing waves along the frequency spectrum.
     
    Some posited that the the waves that occurred distinctly, at a frequency that was clearly separate from other standing waves, would be the most likely to be noticed while listening. The calculator does not, however, predict if you will hear a peak or a null because your listening position needs to be known for this to be considered.
     
    As a corollary the standing waves that are bunched up, the ones Bitflipper mentioned at 170-185Hz, might sum to be a huge problem or they may sum in such a way as to have minimal effect. So, some people assumed and argued that the bunching would exasperate problems while other folks predicted that the bunching increased the likely hood that the effects would probably offset each other. The actual results are, once again, very much dependent on the listening position.
     
    It took me several reads and some reading between the lines to garner the conclusion I just shared.
     
    The point that I think seems to describe the *conclusion* of my reading of the references, the linked explanations, and the forum discussions at the acoustic design forums, is that a room mode calculator identifies areas of special interest.
     
    Once you have established and tested at a listening position the calculations may explain why you are observing certain peaking or nullification.
     
    I hope that makes sense... if it doesn't I invite you to go read all that stuff too... I'd like it seem simpler. :-)
     
    all the best,
    mike
     
     
     
     
    post edited by mike_mccue - 2013/08/27 13:27:34


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    bitflipper
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    Re: How to read these room mode values? 2013/08/28 10:44:49 (permalink)
    You can think of resonant modes as peaking filters in a parametric equalizer. Imagine an acoustical EQ with many bands, each of which has the same parameters as an electronic equalizer: center frequency, gain and - most important - Q, or bandwidth.
     
    At any given gain amount, high-Q filters are more apparent than low-Q. And just as you can stack filters in your favorite parametric equalizer to achieve steep slopes, so too do closely-overlapping narrow acoustical resonances reinforce the effect, narrowing the Q and increasing the amount of gain (positive or negative).
     
    The ideal room has broad (low-Q) overlapping modes spread evenly across the spectrum. This almost never exists in the real world. But if you know which frequencies your room is lying about, you'll know when to be confident and when to be susp icious about what you're hearing/fixing/tweaking.


    All else is in doubt, so this is the truth I cling to. 

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