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Old 5th March 2003, 08:51 PM   #1
toenail is offline toenail  United States
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Default Newbie w/ sub ?'s

First let me say that as a newcomer I'm impressed with the collective knowledge of this forum. There's a ton of good info out there. I've been searching the archives for a while and came up with a few unanswered questions.

I'm trying to make use of some old left-over car-fi components in the home, namely a JL Audio 12w0 8ohm driver. I original stuffed it into a 1.39 ft3 box that was handy and have found that output really rolls off around 40hz. In the quest for flat response down to 20hz I used the WinISD program to find the optimum enclosure to build and came up with a ported 6.7 ft3 box utilizing a single 4.02"dia port that is 7.38" long. Tuning frequency is 22hz. Response is dead flat to 28hz, -3bd is 21hz, close enough for me.

Questions-

1) I like the sound quality/accuracy of the JL driver in the sealed box it's in now, will that be degraded in this application?

2) I've seen reference that subs with Qts of .4 or higher should really be used in sealed enclosures, this one is .42, how does his affect sound quality?

3) Phase Plot and Group Delay functions in the WinISD program are completely foreign to me. Is there a tutorial that explains these graphs?

Thanks in advance for any help you can offer. If you don't have time to explain something feel free to point me to links- I like to read and learn as well.
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Old 7th March 2003, 07:48 AM   #2
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1 possibly it mite sound slightly worse,but if the response is flat,then it wont sound much different

2 with a higher Q u may get some midbass peakyness..

winisd will show if this is evident or not bear in mind that most rooms have 40-60hz ish boom already so if ur driver booms a little there it mite sound realy crap.

Flat response is best.or even a slight dip in midbass is ok for som ppl

3 the group delay to me(correct me if im wrong),shows u how much out of phase the port is compared to the speaker ,the difference in the 2 waves meeting u..measured in milliseconds,the higher the worse but usualy with bass up to 30ms isnt tooo bad but stil..lower the better.

as For Phase plot i think it shows the point at which uve tuned the box i dont particulry understand what it means other than that/

the impedence one is more useful than phase i think.



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Old 8th March 2003, 02:10 PM   #3
toenail is offline toenail  United States
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Thanks for the reply. I'm thinking this sub will be x'd-over at 50hz or less and would be used mostly for entertainment- TV/movies/impress your pals etc. I'd just like for it to be as accurate as possible.

Your point about transfer function/room gain is a valid concern. Flat in an anechoic environment may not equal flat in my living room. I've downloaded some more software to simulate in-room response and will see where that leads me.
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