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Room measurements using pink noise
post Jan 15 2013, 11:54
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I was browsing around and found this bit of information which I don't quite understand, so anyone who is well versed in acoustics can perhaps set a few things straight :

Accurate room measurement is complex in that you need.
1: A way to record what is going on in a room.
2: Away to create the sound in a room that 1 will measure.

Currently 1 is reasonably easy and cost effective to achieve as there are a number of accurate (or accurate enough) systems available that do much of the number crunching in software.

The most common way to achieve 2 is to use the loudspeakers already in the room and this while convenient, leads to inaccuracies in measurements.

The reasons for this are as follows.

To accurately excite all the modes in a room you need a source that is broadband and truly omnidirectional.
While most decent speakers can be broadband -but often are a little deficient at low frequencies-, few if any are truly omnidirectional.
This means that when using a speaker as an audio source in room measurement, you are in reality only measuring the combined response of your speaker and the room. The in room measurement of Bi or Di polar speakers that had the same frequency response would be totally different.

Ideally you want a sound source that as already mentioned is truly omnidirectional as this will excite all room modes equally. Any one who hasever looked at polar plots of speakers will know that even the best claimed omni speakers rarely are truly omnidirectional.

A gun shot on the other offers typically a wide bandwidth, is omnidirectional and has the added benefit of being loud. Loud enough so that true reverberation time and modal measurements can be made.

It has even been suggested, for those that don't want to fire their magnums in their listening rooms, that something as simple as a hand drill could be used as a sound source. These are cheap, the results are repeatable and will certainly put a lot less stress on a system than trying to belt out Pink noise at high SPL.

I thought pink noise was the standard method of measuring speakers in a room. He seems to be saying that a gunshot rather than pink noise is preferable as the levels are higher, or at least that's what I think he's saying. Is this guy completely on crack or does he have a point?
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post Jan 16 2013, 19:19
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Hi Ethan. So measuring the room on it's own is really just pointless? Because we don't hear just the room?
Not always... If you are working on room acoustics it would be helpful to measure the room acoustics alone. If you are building a theater, concert hall, or "music room" you might be using it for live acoustic instruments.
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Ethan Winer
post Jan 16 2013, 19:29
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QUOTE (DVDdoug @ Jan 16 2013, 13:19) *
If you are building a theater, concert hall, or "music room" you might be using it for live acoustic instruments.

That's what I would have said if you didn't beat me to it. I deal with recording studio "live" rooms too, where the sounds are created by acoustic instruments and guitar amplifiers etc rather than playback speakers.


I believe in Truth, Justice, and the Scientific Method
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