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Acoustic measurements

post #1 of 4
Thread Starter 

Hi guys, I came this bit of information from another site. For those who are well versed in acoustics, or measure rooms, take a look at this :

 

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.

 

Is this guy on crack or what? I assumed pink noise was pretty much standard across the board for measuring sound in rooms. Now we need to use guns? WTF?

post #2 of 4

I don't know anything about room acoustics, but the main point here is that an omnidirectional sound source should be used, which speakers are not.  I wouldn't think the spectrum of the noise is so important so long as you know what it is and if it covers the audio range.

 

That seems more thorough for determining the characteristics of a room.  If you just wanted to know how your own speakers interact with the room at a given listening point in the room, not sure of the utility of a more comprehensive measurement than just using the speakers; that said, very small changes in positioning from the test spot can greatly influence results, so knowing more about the room and correcting those things doesn't seem like a bad idea.  Anyway, depends on if you're interested in the speakers + room or just the room.

 

I'm sure somebody else will come along with much more useful and correct insight on this.

post #3 of 4
Quote:
Originally Posted by Yahzi View Post
Is this guy on crack or what?

 

Yes, he's on crack. This is the correct method:

 

Room Measuring Primer

 

--Ethan

post #4 of 4
Wow! There are some very complicated methods for a fairly simple process! I use ecotect and a bit of software developed by sheff uni! Never a gun redface.gif! Check out http://www.nagata.co.jp/e_index.html pretty much the best!
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