Graduate Reducing standing waves with phase randomization

[Jaryd Miles]

Will constantly randomizing the phase of an audio signal, say a speaker in the corner of a square room, reduce standing waves (i.e. room modes) in the room?

For example if you wanted to create a diffuse field in a small (i.e. no standing wave interference patterns) at low frequencies.

 

[sophiecentaur]

That would produce a frequency dependent amplitude modulation of the original programme. Could sound pretty unpleasant, I think.

 

[houlahound]

I doubt you get much interfetence of low frequency audio in a room that you couldn't fix with a mixer/equaliser.

 

[sophiecentaur]

I doubt you get any inte5frtrncr of low frequency audio in a room.

I was referring to the frequency of the random phase changes.
The problem, I thing, would be that any variation at any frequency will be audible and probably unpleasant.

 

[Jaryd Miles]

I was referring to the frequency of the random phase changes.
The problem, I thing, would be that any variation at any frequency will be audible and probably unpleasant.

Say the application is testing the sound insulation of a wall, where it is desired to have equal energy at all frequencies incident on the wall (to give a truer representation of the wall's performance). So 'audio quality' aside, would the random phase give a more even sound pressure level around the room or would the standing waves and the associated nodes/anti-nodes remain in the same position?

 

[sophiecentaur]

If you are trying to measure, rather than to listen, I should think that a swept frequency measurement would take you through peaks and troughs in the sound level, measured in the room, as the phase difference of direct and reflected wave change with frequency. That would give a good indication of the absorbency of the wall material. I remember, years before you could buy RF vector analysers at a decent price, we used a R&S instrument that worked on the same principle to what I'm suggesting and it would give you the equivalent to a swept Voltage Standing Wave Ratio, which would tell you how good the termination was, on a cable.
Now this method will not tell you 'sound insulation' because you need to measure levels on the other side of the wall BUT it will tell you the sound absorbency (but you don't know if the incident sound has gone through or been lost in the material of the wall.