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Author Topic: Smaart Queries  (Read 9258 times)

Arthur Skudra

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Re: Smaart Queries
« Reply #10 on: January 26, 2011, 01:33:28 pm »

When I zoom into the impulse response I do get some very early reflections which could be affecting the readings that I am trying to take. I don't have access to a baffle but the floor is a good option. If I was to place the microphone on the floor how would I go about getting hi  frequencies to the mic other than by physically tilting the speakers?

Do you have any tips on how to interoperate the phase response that intact posted?
You could also use a large case lid or a sheet of plywood stretched across some chairs as a ground plane as well.  Size determines how low in frequency you can get a good measurement (think about the size of the wavelength you're dealing with).  For that matter, you can lean the microphone against a wall as well.  Tip should be touching the surface, maybe at an angle so that the HF is not shadowed by the microphone shell itself.  Essentially you're creating a PZM microphone here, where the reflection is so short that the first dip of the comb filter is so high in frequency that it does not adversely affect the frequencies of interest you're measuring in the system.  Not sure what you're asking for re: phase.
Does any one reading this have any idea about Smaart courses in the UK?
Training schedule can be found here (Edit: Mac beat me to it ;) ):
http://www.rationalacoustics.com/pages/Training_Schedule
Check regularly, new classes being posted often.  You could also contact Jim Cousins, perhaps he can be a help to you as well!
http://www.rationalacoustics.com/pages/Instructor-directory
« Last Edit: January 26, 2011, 01:35:28 pm by Arthur Skudra »
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Dave Gould

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Re: Smaart Queries
« Reply #11 on: January 27, 2011, 06:58:52 am »

Hey Arthur I have just checked the Rational Acoustics website and realised you are one of the Smaart instructors so I much appreciate you taking time to reply to my queries!

'Not sure what you're asking for re: phase.'

In the original post I asked if the crossover points in the screen shots that I posted happened to be 120degrees out of phase which was the cause of the null in the response? Or could this be the type of electronic x-over causing this?

Also I am getting really confused when it comes to reading the phase traces, when I capture a phase traces of L/R stacks together does this give me any clues to the phase interaction between speakers? Or do I need to capture each stack individually and compare the resulting traces in order to see the phase interaction, such as combing or cancellation?

I have checked the Rational Acoutics website for courses but there are none, are there any thrid party companies that offer training in the UK?

Once again, Thanks!
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Rasmus Rosenberg

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Re: Smaart Queries
« Reply #12 on: January 27, 2011, 03:40:39 pm »

Hey Dave,
The phase trace can be really hard to get your head around. Best to do (before getting a class) is to read Bob's book. And setup a small measurement setup and practice. Here are the youtube film about phase:

http://www.youtube.com/watch?v=A9098KMP_Q8&feature=channel

http://www.youtube.com/watch?v=C2PGZq5PEe8&feature=channel

Rational video about combfiltering:

http://www.youtube.com/watch?v=GJQKjcBC96c&feature=feedu

Bob about summation:
http://www.youtube.com/watch?v=5Ig_oRpz3_k

And Last but not least Josh Evans videos on sub alignment.
http://www.youtube.com/watch?v=J_Am7476Igo&playnext=1&list=PLCA6F46128BD3E840

My best advice, besides all thats said are; practice. Start slow and build on. Take a speaker on the floor, put it on a stick, put it on a sub. Measure an EQ, a delay line, a cross over, etc. One of the first things to learn are the "mechanics" of what different things look like on the screen.  A thing that help me a lot was to either remote control my computer/ have my measurement set up on a cart or building a long screen cable so I could use an external screen. What i would do was to put the mic in a position and then move it around to see what happens. Way to many people just put the mic up and go stare at the screen 15 mtr away and change things, with out hearing the change (or what the mic picks up). The ability to hear, measure and see things change on the screen is IMO really a helper to make the link between what we measure and what we hear. Smaart V 7 really helps IMO with the learning curve also, because you can see Impulse, Phase and magnitude response at once. Save up for the upgrade and a class.
Where are you located? In UK there are quite a lot of people that are good with Smaart, or other measurement platforms for that matter. I know that the top PA companies has people educated in Smaart ( I took a class with a lot of them :) Try to contact Rational, The distributor or them.
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Cummins Mebane

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Re: Smaart Queries
« Reply #13 on: January 27, 2011, 07:45:40 pm »

My SMAART7 came today. Looking forward to learning it and picking up the great tips found here. My needs are modest since my pro days were long ago. I am mostly a serious hobbyist these days.  :)
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Sidewinder Band
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Dave Gould

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Re: Smaart Queries
« Reply #14 on: January 28, 2011, 07:51:21 am »

Dude!!! Those videos are ace! Even though I am currently reading Bob's section about Summation through for the second time, I am still finding it difficult to get my head around the concept of phase and it's affiliates but these videos are helping for sure.

I have a pair of NS10's at home and a few pieces of outboard which I will test over the weekend to see their response. Hopefully this will give me a better understanding about how the readings as I am working to my own schedule and not be rushed. Also I noticed on Bob's video he unwrapped the phase response trace, is this an easier way to read the trace compared to the wrapped trace that I have posted?

Cheers!
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Arthur Skudra

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Re: Smaart Queries
« Reply #15 on: January 28, 2011, 02:33:46 pm »

Hi Dave,
Not sure if there are any third parties doing Smaart training, really any course on measurement from Meyer Sound, Systune, etc covers the same basic principles in FFT measurements, each having it's own unique twist.  I do suggest you contact the Rational Acoustics distributor for your area, and express interest in taking the next class being offered in your region, hopefully enough express interest to get another course happening in your area.

With regards to phase, the key is to look at the *slope* of the curve, they should be the same slope and within 120 degrees of each other in the region of overlap in order to get good summation happening.  When the phase curve is flat and parallel to the floor at a range of frequencies of interest, you know that the delay in Smaart is set for those particular frequencies.  Adjusting the time delay spinners will move this "flat" portion of the phase curve up or down in frequency.  This is why the phase curve is flat in the upper frequencies of that device after getting the time delay set correctly.  Another use of the phase display is to compare different captured traces of like devices, if one is parallel and separated from the other 180 degrees, you should check your system for a polarity reversal somewhere.

So in summary, for the most part you're looking at slope, and 180 degree differences with your phase trace when measuring sound reinforcement systems, that's all.  This is why having a wrapped 360 degree display is perfectly acceptable for our measurement purposes, unless you have a 40" laptop screen and can handle a huge unwrapped phase display with your computer!   :P

Arthur
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Re: Smaart Queries
« Reply #15 on: January 28, 2011, 02:33:46 pm »


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