# PN vs Sweep



## proper88 (Dec 20, 2015)

I measured my 2-way active system in my car wit REW 5.14
.) 3 different positions measured with sweep(averaging to one frequency response)
.) With perodic Pink Noise and mic movement from the left to the right ear. Use RTA with option <Adjust RTA levels>

Why i get so much differents results ?


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## jtalden (Mar 12, 2009)

Welcome to HTS!
I haven't any experience in a car, but the results should track very closely in my experience.
The difference is probably due to the settings you selected for the measurement processes. The major factors are:

Sweep Averaging:
> Randomly position the mic at locations within the target area and take a sweep. 
> Collect a minimum of 10 sweeps - more is better. 
> Use the 'Average the Responses' button for the average.

RTA: 
PinkPN
> RTA 1/48 Octave
> 'FFT Length 'should match the 'Sequence length' of the signal generator.
> 'Forever' averages.
> Start the measurement and immediately (or ASAP) start moving the mic around the target area. 
> Cover the area in maybe about 10 seconds and stop the measurement.

The results should be very similar. 

If this is how it was done then more info is needed on your entire process to understand the issue.


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## JohnM (Apr 11, 2006)

Also need to make sure the RTA window is set to Rectangular. I'd start by checking sweep vs RTA for one position to make sure they give consistent results, at the moment you are comparing different measuring methods and different averaging processes.


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## subterFUSE (May 10, 2014)

In my car, the RTA with pink noise shows more rolloff in the high frequencies than do a series of averaged sweeps from the same mic location. Your measurements seem to show the same thing.

I don't use the RTA method for that reason. I have had better results with taking a number of sweeps from different microphone positions around the listener's head location, and then averaging them together. I have a microphone stand with 4 mic clips which makes it faster to move the mic around between measurements.

It would be fantastic if REW allowed for multiple microphones simultaneously, because I do own 4 Dayton EMM6 mics. The time saved by taking 4 mic location measurements from a single sweep would be really helpful.


See pics below...


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## proper88 (Dec 20, 2015)

JohnM said:


> Also need to make sure the RTA window is set to Rectangular. I'd start by checking sweep vs RTA for one position to make sure they give consistent results, at the moment you are comparing different measuring methods and different averaging processes.


First i have to say that REW is a very good software, with many nice features(EQ is my favorite) and easy to use. I also use ARTA, but interface and handling is not so good.

The strange thing is the faster rolloff in high frequencies.
I will start tomorrow to make more measurements

Here are my settings; maybe the mode is not correct ???

Thank you for your support JohnM !


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## JohnM (Apr 11, 2006)

You need RTA 1/48 octave instead of spectrum. When you want to average as you move the mic you will also need to have averaging, as mentioned above.


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## jtalden (Mar 12, 2009)

If we are measuring more than one channel at a time using Moving Microphone Method (MMM) there may be significant rolloff in the high frequencies due to phase cancelations between the tweeters. MMM is not suitable for that situation.

MMM should agree closely to averaged sweeps when measuring one channel at a time as is normally done for EQ purposes. 

Below is the variability of 7 Sweep measurements when the mic is moved around a vertical window about 36"x18". The LP in this case is about 14ft from the speaker so this is a small angular difference. We can see that any EQ done using a sweep at a single mic location must consider that a short distance away there is significant variability. There is no assurance that the LP is a good average of the nearby locations. That said, I also now often use a single location. I now understand the variability I see around my LP and have found that good enough EQ results can be obtained without using MMM if appropriate care is used in choosing filters. 









Below is the repeatability of 6 MMM measurements. we can see that there is very high repeatability so if several successive EQ sessions are done to fine tune the EQ filters and adjust a house curve there is no chance that measurement variability will confusing the process.









Below is the average of the 7 sweep measurements Vs one of the MMM measurements. More sweep averages would provide better agreement between the 2 curves. The MMM will always be smoother at the same smoothing and thus helps to prevent excessive EQ filtering. MMM can also be a little higher in the higher frequencies. That is, it will rolloff less. To get the same sound at the LP the house curve we choose will thus rolloff a little differently as a result.









Good results can be obtained using different methods. 

If the objective is average the listening area and provide highly repeatable measurements as the house curve is refined then MMM is a good option.


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## proper88 (Dec 20, 2015)

With changing mode from <spectrum> to <RTA 1/48> and tipps froum the user hear i get nearly the same results.
I must say it again, a perfect piece of software, fast support and all is free, amazing !!!
Thank you :T


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## jtalden (Mar 12, 2009)

Yes, That looks correct.

If the 'RTA' trace was shifted up a little (~2dB?) so the bass and MR are overlaying the 'sweep average' then the high frequency of the RTA trace would fall a little above the 'sweep average'; an expected difference.

The RTA is a little smoother in the higher frequencies; also an expected difference.

It all looks as expected.


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## lkwrnflknf4lk (May 15, 2019)

would you guys use sweeps or PN for a amateur PA setup in a small open air venue?


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