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Old 04-28-2009, 04:47 PM   #1
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HOW-TO: Carputer IR crossover/linearization design (56K death)

Most of you known I run a car PC for my audio...
http://www.diymobileaudio.com/forum/...-complete.html

The last few days I've been taking measurements of the car speakers using my Berringer measurement mic...
Here it is 'in action'...







This how-to will focus strictly on using Acourate...with that said, I'm assuming you already have an idea on creating logsweeps and crossovers...and for that matter, using Audacity to play/record your sweeps.
Here is Audacity recording a driver response...



I'm going to be focusing on the high-pass crossover with this...low/sub use the same process....

Once you have your crossovers designed, go ahead and load up the highpass. You'll notice it's loaded in 'Active Curve 1'...more about curves later.
This show a 3rd order Neville-Theile crossover at 2500Hz...



From here, we want to convolute the logsweep, so we choose, aptly enough, LogSweep Convolution...





Load your highpass logsweep...
Note the file structure I'm using...everything has it's own folder! There are a lot of proccess and files generated. Until you become fluent with this software, I recommend keeping a comprehensive folder structure as well...



You must also select your 'inverse' sweep...
I made my sweeps ahead of time and seperated them in respective folders, i.e. HI and LOW folders. I used a sweep of 45 to 3500Hz for my drivers, and 2000 to 24000Hz for the tweeters.
Make sure you don't mix them up! Your hipass sweep MUST use the hipass inverse file. Acourate saves them all with default names, in a default directory, so if you create a new sweep, your old ones will get overwritten.



Once the Convolution has finished, you'll see your sweep in the bottom graph in the 'time domain' window...




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Old 04-28-2009, 04:48 PM   #2
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From here, you need to select the peak area...left-click to the left of the spike and right-click to the right of the spike...(see above pic).

Now we have to extract just the data we need, so we call up F4, Cut'n'Window...
Make sure Before peak in area...is selected, and enter 6000 in the 'Position/Count' window...this will get all relevant data...



Once that finishes, it'll load in the Amplitude Domain window...go ahead and select 'Amplt' in the top, and display this...



At this point, you can compare your tweeters output to the crossover...you can see where mine are a little weak from 7000 to 9000Hz...but from 2000 to 6000, it's a respectably flat response...
That's correct that!!

Now, we call up 'Phase Extraction', F2...
At this point, we just want to use 0Hz in both fields, and make sure minimum phase is selected...

Save the result to the next available series, in this case, series 4...



Now, so far, you may have noticed, we've used up 4 'Active Curves'...and we'll need a lot more! So now, we're going to save our work so far...
Save it in a seperate directory, i.e. 'Working'...



After you save, we want to 'Clear All Curves' with the double-trashcan icon...



You'll get confirmation dialogs for each curve you want to delete...
Confirm 'Yes' to all of them except Curve 1, our crossover we loaded back at the beginning...we want to keep this loaded for the work we do next.



Now select Curve 2 (because we don't want to replace Curve 1!), and reload the work we just saved...



Now we're back to where we were, but now with 4 available curves left...



From here, we call up 'Frequency Dependant Windowing', F3. This is just a fancy term for frequency smoothing. We want to smooth out the excess data and use just the 'profile' response of the logsweep. This makes the Impluse Response a LOT easier on CPU cycles...



Select 'Both Sides' and enter in this data in the Peaks fields. You can experiment here with different figures, depending on how accurate you want your results to be...

When that completes, you'll see the smoothed response (brown line)...

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Old 04-28-2009, 04:49 PM   #3
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With a smooth response to work with, we need to apply a 'difference' to the response...a 'mirror' response curve, which will be used to flatten the original tweeter response...so we call up Amplitute Difference...



'Difference' meaning subtraction, so we're going to select our crossover (XO3R48) and subtract that from the last procedure we did, which was the Windowing (FDW2)...save it to the next available Curve Series...



And the output of that procedure...(blue line)



So now we have an 'anti-response' of our tweeter to flatten out the frequencies, but it's still not utilizing the crossover we designed for it!

At this point, we want to elliminate any data outside of the crossover range, so again, we use the right and left mouse buttons to select an area inside the crossover domain...



Anything at -20 or -30dB isn't likely to be audible, so that's a good area to select. On the upper range, your likely not going to hear anything at 24000Hz, so 20 to 23KHz is workable...

Now we're going to run Phase Extraction again, F2, but this time, in the Hz dialog boxes, we want to enter the targeted range we selected...if you look at the bottom left side of the program window, you'll see the Hz data displayed for you...



Now it's convolute time! We're going to convolute, F5, our response to the crossover (in Curve 1)...So again, we select the crossover, and the last process we performed, which was the Phase Extraction (MinPhas4)...save it to Series 6...



You'll see the black line as the result...note how it's conforming the the crossover now...



From here, since we're out of Curves again, we're going to unload all (double-trash cans) Curves, EXCEPT the last one, Curve 6, and of course, our crossover, Curve 1



We're left with our crossover profile, and the convoluted response for our tweeter...



Because of all the data visible outside of the auditory range, we're going to run Cut'n'Window again, F4...
Note the settings...we want a count of 32768 before the peak. Save to Series 2.

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Old 04-28-2009, 04:49 PM   #4
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Because of how some of the response data is above 0dB, we want to normalize the response to prevent clipping. Normaize function is F8.
Make sure you select the previous saved Curve, and use 'Individual Gain' option...



The resulting window is now corrected to 0dB max...



Now the highpass cross over for that tweeter is complete! All that's left to do now is save it, and view it with your lowpass...



Remember to save it to a folder you know will be safe!

Once saved, go ahead and unload all the curves...



...and return to 'All' view...



Load up your completed low-pass response in Curve 1, and your high-pass response in Curve 2...



Adjust the scale on the left size of the program window to get a better view of your work...



For using Pristine Space, you need to save your work as a wav file...since Acourate can only save stereo wav files, you need data in both L and R channels, or in this case, Curve 1 (left) and Curve 2 (right)...



Since I've been using LEFT channel output for my lowpass and RIGHT channel data for my highpass since day 1, this output configuration works perfectly for my setup....

You'll note in that last pic, the output of the tweeter, generally, is quite a bit below the driver for most of it's range...
There is a technique with Acourate which allows you to do output level matching, basically by performing the same high/low sweep as you used before, but running it with these IR files loaded up.
Once that's done, you load the high/low sweep together, and normalize them together...
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Old 04-28-2009, 05:02 PM   #5
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awesome stuff...not sure if most people will understand what you just did....im a lil lost myself....love the mic though...i use speaker workshop and some white noise to measure frequency response with a home made mic setup and use my 3sixty.2 to help flatten the response
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Old 04-28-2009, 05:12 PM   #6
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Yeah, hopefully will be able to use this info, one heck of a write up
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Old 04-28-2009, 05:14 PM   #7
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awesome stuff...not sure if most people will understand what you just did....im a lil lost myself....love the mic though...i use speaker workshop and some white noise to measure frequency response with a home made mic setup and use my 3sixty.2 to help flatten the response
Nice! I might try some white noise from the listening position and see how it looks...
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Old 04-28-2009, 05:20 PM   #8
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i didnt read it all but it seams to me your calibrating for the best sound clarity, kinda like color calibrating a monitor??? very interesting
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Old 04-28-2009, 05:35 PM   #9
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Yeah, that's just about right! This was just a correction for the speakers (and enclosures) themselves...with crossovers.

Next, I'll take measurements from the listening position, and adjust for 'room' accoustics and time alignment...
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Old 04-28-2009, 06:35 PM   #10
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time alignment is the last thing i have to tackle...im still working on the response
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