What are Room modes?

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satrne

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What are they? I know they deal with frequencies and room dimensions, but how do they apply to recording??

Also, How are they measured/altered ??

Thanks !

Justin
 
They don't apply to recording as such - they apply to monitoring... if you don't properly hear what you're trying to record, your tracking will be off... if you make sonic decisions in a room with bad acoustics, your mix will be "off", or may simply sound wierd (except in the room you're in)....

There are charts for room nodes based on dimensions.... proper room analysis requires a tech with sensitive analyzers (not a Radio shack and spectrum analyzer s/w, or worse, those silly graphic EQs with built-in SAs!!!)
 
Actually, Bear, they apply to recording too. If you have a tracking room with modal problems, it's a lot harder to place both instruments AND mics for best sound.

Satrne, what modes are is the resonant frequencies caused by pairs of parallel walls in a room. Each room will have 3 primary modes, caused by length, width, and height. The formula for figuring this out is Frequency= 1130/x, where x is the dimension of either the length, width or height. If you take your dimensions and apply this formula, then take each freq. and multiply it by 2,3,4,5, etc, until the answers are greater than 300 hZ, you will have a listing of all the primary, or Axial, modes of the room. The ideal for a rectangular room is no two frequencies closer than 5-6 hZ, and no gaps greater than about 20 hZ up to about 300 hZ. This is almost impossible to achieve, but you can get close. The closer you get, the less bandaids you will need to make the room sound right. Oh, and you change modes by moving walls...

Try searching this section for "mode", there is a link somewhere for an Excel spreadsheet I wrote that will figure that out for you and chart it. It's called roomtune. (duh, maybe I should have just told you to search for roomtune...) HTH, Steve
 
knightfly said:
The ideal for a rectangular room is no two frequencies closer than 5-6 hZ, and no gaps greater than about 20 hZ up to about 300 hZ.
Click to expand...

I've been reading up on this lately becuase I am moving soon but that's the first I've heard that part. I was under the impression that once you figure out where the room modes are you then create absorbers and diffusers to handle that feq range. I never noticed any mention of certain modes being acceptable and preferred modal spacing. What is wrong with large gaps? Does that creat too uneven of a response?

I looked through the SAE stuff and maybe I missed it but is there a practical walk through of analyzing and a treating a room? Once I find my room modes what is the next step? How do you determine how much absorbtion in that range is necessary to get a flatter response?
 
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