Measuring freq resp and RT60. How many measuring positions? how many source positions

[chickenfingers]

Hi

Does anybody know how many measuring positions and how many source positions should be used to measure RT60 and freq. response using the sweep sine signal method? I´m using an OMNI-DIRECTIONAL source in a room of around 6x6x4.
I know some may say RT60 is not valid for a room this size, but the standards say I have to measure it and so I will.

thanks for your input.

ps: I was going to post this on the "acoustics forum" website but can´t seem to find the subscribe to this forum button/link. Even though I´m already a registered user.

Sergio

 

[highfigh]

Hi

Does anybody know how many measuring positions and how many source positions should be used to measure RT60 and freq. response using the sweep sine signal method? I´m using an OMNI-DIRECTIONAL source in a room of around 6x6x4.
I know some may say RT60 is not valid for a room this size, but the standards say I have to measure it and so I will.

thanks for your input.

ps: I was going to post this on the "acoustics forum" website but can´t seem to find the subscribe to this forum button/link. Even though I´m already a registered user.

Sergio

That's 6x6x4 meters, right?

Try this link and go to their home page, to see how they test their panels. They have their mic on a boom that swivels.

http://www.atsacoustics.com/page--Free-Online-Room-Acoustics-Analysis--ora.html

Also, look online for a room mode calculator- you're going to have some standing waves that will need work.

 

[nibhaz]

Check this link

This link here starts to cover the RT60 basics. You can join and search the forum by following the register link located towards the top right hand portion of the page.

 

[Savant]

Sergio,

Didn't we already cover this? If you follow the guidelines in ISO 3382, you should be on the right track.

 

[chickenfingers]

Sergio,

Didn't we already cover this? If you follow the guidelines in ISO 3382, you should be on the right track.

I know Jeff, but I only have a brief summary of the ISO 3382 and they didn´t have a copy at the library. Besides, the situation now is slightly different... Could you give us some advice... again, please.

Did the following measurements:
3 Source positions (using OMNI source) - 6 Measurement positions and 3 measurements per Measurement position. All the position were chosen carefully ot cover the complete area of the rooms.

I´m not sure how to procede with the measured data. The 3 repeated measurements per measuring position were made as an insurance since it was my first time ever measuring RTs with a PC (instead of an I´ll do it all for you B&K sound level meter) and the REW software (hence sine sweep signal). I found out that these 3 measurement were almost identical confirming that the sine sweep signal is not nearly as random as measuring with say, pink noise.

The procedure I´m thinking of to derive the final RT60 is:

1) Average the 3 measurements per Measuring position. That gives me six RT60s (one per measuring position) per Source position. So 18 Measurements in total
(6 measurements x 3 source positions) . Here is where I get a little confused...

2) Should I calculate the average (or mean?) of each lot of "six RT60s" to get three RT60s (one per Source Position)?

3) And then repeat the procedure with the resultant three RT60s?

????

I have the above data for two classrooms. The first is 7mx6mx4m the second is a long useless room of 14mx6mx2.7m. I say useless because I don´t know what use can they give to such a large classroom in a school specially with that height. Not even the engineers and architect on site are sure what the purpose of the room is. May be for kids?. Anyway...

Did I over do the measurements for the small room?
Should I only use measured data for ONE source position in the small room?
For the large room, I´m pretty certain I have to use all the available data.

MOST IMPORTANT THING THOUGH, HOW SHOULD I GO ABOUT MANIPULATING THE MEASURED DATA? Are steps one two and three correct, should I get the mean or the average?.

I would really appreciate it if you can help me out on this one. And again thanks for all your previous answers.

Sergio


ps: I´m still trying to find out how to subscribe to the Discussion Forum at the "Acoustics Forum". I´m already registered but don´t have a clue how to subscribe to the Forum.

 

[Savant]

Sergio,

Hmm... I thought you were working from ISO 3382-2:2008. I got this impression from previous threads, particularly the one where you were asking about least-squares-fit.

Regardless, I would strongly encourage you to purchase a copy. All of the questions you have are addressed therein.

Beyond that, I would say that I don't think you overdid anything. Provided the source-mic distances and other distances are in accordance with the standard requirements, you should be able to simply take the average all the RTs. (Average and mean are the same, btw. You might be thinking of the median, which is not what you want in this case.)

Finally, I don't know what to tell you about the other forum. I've never had any trouble over there. Have you contacted the mod?

HTH.