Room dip...

[Okatvius]

Hey)

Perhaps you could help me to answer some questions i didn´t find a answer for.

Is it possible that a dip in a room frequency response is based on a standing wave(modal, pressure hole) instead of a wall reflection.

Is always on both sides of a room resonance a pressure maximum by the first, second, third... mode...??

thx so much for your help

[Chrisc_o]

Originally Posted by Okatvius

Hey)
Is it possible that a dip in a room frequency response is based on a standing wave(modal, pressure hole) instead of a wall reflection.

If I understand standing waves correctly, they are caused by reflections in the room, so a pressure hole, as you put it, is caused by the wall reflection.

[Okatvius]

To explain a bit more detailed: If i sit in a modal pressure zone i´ll get a rise in response and modal ringing....but what is if i sit not in a pressure zone?

Is there also modal ringing and a dip or is there a flat response and nothing happens? On an anlyzer i see different holes at the sweet spot. Are these than only reflection from nearby walls (1/4wavelenght) or could it be likewise a standing wave.

[Okatvius]

@chrisc: yes you are right. but i there is a difference between a cancelation by a nearby wall and a room mode (which only develops by some exact frequencies). The cancelation from a nearby wall is only dependently from their distance to that wall.

[Ethan Winer]

Originally Posted by Okatvius

but i there is a difference between a cancelation by a nearby wall and a room mode (which only develops by some exact frequencies). The cancelation from a nearby wall is only dependently from their distance to that wall.

These are one and the same. Room modes are a special case of comb filtering peaks and nulls. The only thing special is that the waves fit exactly between opposing boundaries, so they are reinforced and bounce repeatedly, decaying over time. Other than that, the relationship between boundary spacing and frequency is the same for modal and non-modal peaks and nulls. I've written a lot about this:

RealTraps - A New Approach to Small Room Acoustics
RealTraps - Room Modes
RealTraps - Frequency/Distance Calculator
RealTraps - Recording Spaces
Why We Believe

--Ethan