Understanding Room Mode Calculators

[hookiefree]

I have downloaded a bunch of Excel Spreadsheets and done analysis on my room and come up with a bunch of numbers and graphs but I have no idea what it all means or what to do with it all. I'm trying to find out how to treat my room. Do I need slat resonators or will just 703 panels do? If slat resonators, what should I tune them to and how big should they be?

Does anybody have a link to a spreadsheet with extensive documentation or a link to a site that breaks it all down in plain english?

 

[apl]

Read Ethan's articles on acoustics.

Your calculated room modes only cue you in to one problem, namely, that the room has modes. Since it has modes, lots and lots of them, there will be acoustic issues when you try to record and mix. For example, your room has modes and so does a guitar’s A string. If you were sitting at the 12th fret of your A string you would be unable to hear the harmonic one, two, or three… octaves above the open A. Conversely, if your one of your monitors was parked on the 12th fret you couldn’t get any of those harmonics into the room. The 12th fret on a guitar is the location of the null of a certain set of frequencies on that string and the existence of modes in your room tells you that you have nulls (also called nodes) that are dead at certain frequencies and anti-nodes that are unstable and very easily excited at certain frequencies. Some times the nodes and antinodes are only a few inches apart. Calculating the modes only shows you that there are too many to attack individually.

The easiest way to eliminate modes is with the use of broad band absorbers which make the room acoustically behave as if it were very large. The treatment also adds some damping to acoustics to cause sound to decay in a controlled way.

Slat absorbers tend to be of limited bandwidth and rigid fiberglass doesn’t do well at lower frequencies. That’s why bass traps are of special construction. The most compact bass trap is the membrane type. Some bass traps and treatment for higher frequencies will give you a great room, without you having to go through the calculations that will only tell you that you need bass traps and other absorption.

 

[Ethan Winer]

Hooks,

APL gave you some great advice. The main use of a mode calculator is to help you design a new room. Or determine new dimensions for an existing room if you're able to move walls or build new walls. But no matter what frequencies a mode calculator reports, you still need bass trapping at all low frequencies. Some peaks and nulls are related to room dimensions, but others are determined by the distance between you and the room boundaries. Therefore, the best approach is broadband absorption that works to as low a frequency as possible.

> Does anybody have a link to a spreadsheet with extensive documentation or a link to a site that breaks it all down in plain english? <

There's a good explanation in ModeCalc sidebar of my Acoustics FAQ:

www.ethanwiner.com/acoustics.html

--Ethan