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ncc74656

Measurment microphone for RTA/FFT

10 posts in this topic

I am looking to use my laptop in cars to do RTA measurements and perhaps FFT later on as i play around with things. From what i have been reading the phantom power is required for many of these XLR connections. I have seen some battery operated flat response mics but the price jumps quite a bit.   i am intending to buy the trueRTA application and perhaps the LEAP software or some derivative there of. 

 

I am looking for some guidance on what microphone and accompaning hardware is needed to accomplish this. am i able to use my onboard sound card or should i buy a USB card with higher performance. 

 

anyone ever used a PC for this type of work and have a setup that works well?

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I've used my computer's soundcard -> Tascam US-122mkii -> Dayton Audio EMM-6 mic. 

This setup worked very well. I was also able to create a feedback loop with the Tascam to measure impulse response. Impulse response measurement is crucial if you want to accurately set your T/A. The differences in soundstage depth, width and coherency is drastic when T/A is setup based on impulse response. 

I personally found that tuning for a flat response sounds terrible. You'll be happier if you tune with your ears. The only purpose that I would continue to use RTA software in car audio is for impulse response measurement. 

 

 

I wrote a basic tuning guide for a 2-way front stagea couple years ago, no RTA required. BTW This could easily apply to a 3-way front stage. I attached it to this post.

 

 

Two-way front stage tune.docx

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The only audio card I can recommend for this sort of measurement is a DAL card.  Last I checked they required a desktop and were $300.

That being said, the whole goal isn't a good one.  Really the only use for a mic in car audio is to find acoustic aberrations that you want to eq out with either physical changes or of course electronic filters.  Trying to achieve a target frequency response is not something that is trivial, nor logical.  If you are unsure the difference between octave analysis, 1/3 octave, and narrow band and the anomalies you will find in amplitude you are in over your head trying to use an "RTA".  Even in just narrow band FFT analysis window block length has a huge influence.

In general your ear hears in 1/3 octaves, but they are TERRIBLE for tuning.  Remember the goal of filtering and eq is to remove crap.  Fixing the response should be done with speaker choice, installation, mounting and so on.

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yes i am looking to use a 1/24 octave rta for comb filter analysis, i would also like to use this laptop with some of the LEAP style software with FFT's. im fine with buying a 300.00 card if it allows me to accomplish my goal, that said i would like to buy this equipment once instead of doing trial and error with it. i have the USB-C port on this so i can adapt any PCI-E desktop card into this laptop IF required BUT id much rather have a more self contained measurement apparatus.

 

over the last year i have studied much of vance dickason's work, he has many how-to's and setups that have worked for him but most of it is pre 08 and thus many of the products are not in production anymore. im basically trying to recreate some of the setups he recommends in books such as the LDC.

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What is your goal?  ie, what are you trying to accomplish?

A real measurement mic is $1000.  You can surely use the non-calibrated Dayton, but you should also understand the differences and corrections required when using it in different sound fields and depending on your goals that may change what you need completely.

If you just want to measure relative 1/24 octaves just use the onboard mic and whatever free ware.  Make a change and see the relative difference.  Just don't expect absolute values, but in reality absolute values will just cause you to do dumb things if you are measuring for the reasons I think you are...tell us though and I can give you better guidance.

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for the basic day to day the relative differences would work fine for me i think.  secondarily I want to be able to play around with off axis db/spl graphs to better understand speaker placement and lobbing. finally i intend to follow some of the design suggestions in the LDC and try my hand in building myself a home stereo with my own passive crossovers, so i would be using this mic and software for room analysis and general speaker response planning.  im fine with spending extra money to be able to have a quality product i can rely on.

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Don't waste your money. Start with a usb Mic or your laptop and then when you don't understand the data ask.  After you then find the weakness of the so cheapo Mic you can shop for a better one.  The one you linked is garbage for the money.  

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Don't.  Spend less and learn it will NOT help you do anything to buy that.  Seriously a $5 usb Mic can a do everything you highlighted and until you realise what it doesn't spending more is stupid.

I made measurements today with 120 measurement mics and enlightened a ton of people.  Sure it was a few hundred thousand dollars worth of year but it was chosen for a particular purpose.  Yours is child's play and a real Mic will be a waste of cash until you learn how to use it.

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