room modes

[shagoofa]

Hello everyone,
Iam presently working on finding room modes in an room. By finding room modes i mean automatically detection of room modes from its impulse response. Does anyone has an idea as how to do it

help me please

 

[shagoofa]

shagoofa

hi shagoofa

 

[bpape]

Um - impulse response shows where you're getting early reflections. Room modes are a function of room dimensions. Which room modes you encounter are a function of what the room generates PLUS where you sit.

Here is a nice spreadsheet from Linkwitz Labs that calculates all of the room modes - not just the axial ones and also does some comparisons of your ratios to other theoretical parameters.

http://www.linkwitzlab.com/modes1.xls

 

[Ethan Winer]

Shag,

> Iam presently working on finding room modes in an room. <

Believe it or not, knowing the modes for a room that's already built is not particularly useful. No matter what you calculate or measure, the solution is always the same: Broadband absorption that works well to as low a frequency as possible, placed in as many corners as you can manage.

--Ethan

 

[Savant]

shagoofa,

You can get a frequency response measurement by performing an FFT on an impulse response measurement. The size of the FFT will dictate the frequency resolution. Whether or not low frequency peaks/nulls are caused by modes can be determined from comparing the measured frequency response to a predicted frequency response for the loudspeaker and microphone positions you are using to make the measurement. Software available that can reliably predict this for you are RPG's Room Optimizer and CARA 2.1.

Alternatively, you can use something like the Linkwitz Labs file bpape linked to as a guide when looking for modal effects in a frequency response measurement.

To do either of the above, I recommend using only one loudspeaker source with various - 4 or more if you can - microphone positions. To get an idea of what each loudspeaker in a multi-channel setup might contribute to the overall response, move the test loudspeaker around to the different locations and make different measurements.

Of course, you should also prepare yourself for the typical end result of lots of measurements: more questions than answers!!!