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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Subwoofer Forum => Topic started by: Jacob Shaw on July 23, 2015, 11:58:50 am

Title: Response and impedance
Post by: Jacob Shaw on July 23, 2015, 11:58:50 am
What is the best way to measure the responce of a loaded bass bin, also is there a way to measure the actual excursion or impiedance at various frequencies?  I want to compare data from the real world results to modeling.  I just got a moth traveler, and I have a good fluke meter.
Title: Re: Response and impedance
Post by: Art Welter on July 23, 2015, 01:18:50 pm
What is the best way to measure the responce of a loaded bass bin, also is there a way to measure the actual excursion or impiedance at various frequencies?  I want to compare data from the real world results to modeling.  I just got a moth traveler, and I have a good fluke meter.
Jacob,

Frequency response can be measured with a dual FFT program like Smaart or the free REW. Best results are outdoors, well away from any buildings, bass response is generally tested with the mic on the ground at two or more meters from the front of the cabinet.

Excursion can be measured by eye, simply put a white dot on the cone and use sine waves and a ruler. Divide the two way travel by 2 to get the excursion at any given frequency. Make the sine wave tests quick to avoid burnout, best to have all the info typed up first.
Impedance can be tested with this:
http://www.parts-express.com/dayton-audio-wt3-woofer-tester--390-804

You can also measure impedance using a resistor and a VOM, but it requires different calibrations for different frequencies, the process took so long I have not attempted it since.

Art
Title: Re: Response and impedance
Post by: Ivan Beaver on July 23, 2015, 01:22:39 pm
What is the best way to measure the responce of a loaded bass bin, also is there a way to measure the actual excursion or impiedance at various frequencies?  I want to compare data from the real world results to modeling.  I just got a moth traveler, and I have a good fluke meter.
Do you best-or cheapest or easiest or most accurate?

Those are often VERY different things with different results.

Just saying you ?measured something" does not mean that what/how you measured it is actually accurate.

Very often people "measure" things, and because they don't understand how to use the measurement system and therefore get inaccurate results.

There are two aspects when measuring something.  One is understand the system, and the other is to understand the measurement-no matter what the system.
Title: Re: Response and impedance
Post by: Jeff Bankston on July 23, 2015, 05:22:41 pm
in the the middle of a large backyard with no wind. and up off and away from the ground.
Title: Re: Response and impedance
Post by: Ivan Beaver on July 23, 2015, 07:10:29 pm
in the the middle of a large backyard with no wind. and up off and away from the ground.
And away from reflections.
Title: Re: Response and impedance
Post by: duane massey on July 23, 2015, 09:09:25 pm
Yep, stay away from mirrors......
Title: Re: Response and impedance
Post by: Jacob Shaw on July 24, 2015, 07:16:59 am
I am fimilliar with mic placement, and I'm good at research.  I understand that there will be a learning curve.  What are some opinions of REW?  I do like freeware.
Title: Re: Response and impedance
Post by: Art Welter on July 24, 2015, 12:19:02 pm
The results using REW look OK. If I were not already using and familiar with Smaart, I'd be using REW.
I will be using it eventually, as it has features not available in the version of Smaart I have now.