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Old 10th February 2007, 10:27 PM   #1
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Default TL lookover..

Even though this is for car audio purposes, this forum is more knowledgeable in TL designs than car audio forums. Im making a TL for a single Ascendant Audio Assassin 8 for my car. I modeled it using a dos program that I found here, but im still not 100 percent sure if I did it correctly. Line length is 87 inches including all the turns. This gives the enclosure a tuning of ~39HZ. Any suggestions are welcome and will be highly appreciated.

Cheers

-Sergio
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Old 10th February 2007, 10:32 PM   #2
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Straight pipes (constant CSA) result in nasty higher harmonics that are incredibly hard to tame. Stuffing and a xo can take care of some of it, but think 30+ db peaks followed by 30+ db dips in the higher response. A bit of taper either way (positive or negative) will help tame the resonances.
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Old 10th February 2007, 10:46 PM   #3
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Well I dont need anything above 50 HZ, Im guessing thats where he nastiness will be. It will be crossed over at 50HZ anyway as my front stage will take care of everything from 50 and up. Im just looking for output from 30-50HZ (20 would be even better, and probably very possible with cabin gain) BTW I forgot to attach the parameters to save some time. They are found here http://www.ascendantaudio.com/assassin8specs.html
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Old 10th February 2007, 11:33 PM   #4
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Well my math is not so good, but from the pic you posted, I assume the CSA is a constant 50 square inches, or 322 square centimeters. I used 2.2 meters as the length of the line.

From the graphs below, you can see that the higher resonances are out of control and it will be hard to control. A regular amount of stuffing and your average 12 db/oct active xo is not going to make a flat response above 50 hz, and even up higher than the xo point I think you will still hear those nasty peaks audibly. You can also see in the second picture that below tuning excursion goes through the roof, so 20 hz even with cabin gain is going to be a bit of a stretch.

In my opinion, this line is too short, should be tapered and can be a good bit thinner.
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Old 10th February 2007, 11:35 PM   #5
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Picture 2. Driver excursion.
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Old 10th February 2007, 11:51 PM   #6
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Hmmm I got a slightly different graph using the same program, can you take a picture of all the parameters that you used? I may have something off...If you notice though all of the craziness is well beyond the range that the driver will be used for. I do agree that it has to be a good bit thiner. I used MJK's alighment tables and got an Sl of 127.44 square centimeters and a line length of 72 inches or 1.833 M.. Can you graph that for me so that i can compare both of our graphs? Something must be wrong in my part...

Thanks
-Sergio
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Old 11th February 2007, 12:02 AM   #7
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Input parameters as graphed above.
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Old 11th February 2007, 12:11 AM   #8
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This is 1.83 m line with 127.4 cm CSA. I don't really like this one either, as the driver is nowhere near excursion at full rated power until it gets down to below tuning where excursion spikes hard. Getting closer, but still not there, as far as I'm concerned.
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Old 11th February 2007, 12:18 AM   #9
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Yeah Im getting the same graphs as you are now. What do you suggest i do? Im not very good at the whole design process. But by the looks of it looks like its going to be tough to find a suitable enclosure for this driver. Do you or anyone have any suggestions for line length, S0, and taper? As stated before, I am looking for a good response from 30-50HZ...
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Old 11th February 2007, 12:39 AM   #10
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This program is not suitable for the design process, in my opinion. You need MJK's software for better sims. Then you can play with stuffing and driver position as well.

I am no expert but I know what kind of FR curve I like to hear. I usually design for stronger bass down low than most people.

I'd tune that line closer to 30 hz if I were you, and play a bit with positive and negative tapers while keeping a close eye on the excursion graph.

See what you can come up with and remember you will probably need to use a rumble filter at 25 hz or so.
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