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#1
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Sub Question...
My 17 year old cousin asked me to design a box to mount his subs and amp in for his Jeep Wrangler. I have no problems coming up with the design and have made a scale model out of cardboard (thats what Industrial Design training will do to you ), but I need to know one thing. What kind of clearance is needed behind the speakers? Do I just need enough room to clear the cone and magnet assembly, or does there need to be a large cavity in order for the accoustics to work? I have never done car audio stuff before so any help would be appreciated Thanks
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-Mike '92 Pearl LS-L (sans Spoiler) #0993 Mfg. 5/91 "It says here, 'Breakfast any time'... That's right... In that case, I'll have the pancakes in the Age of Enlightenment..." |
#2
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I took an audio course in college, and I remember there was something about preventing standing waves in an enclosure. But beyond some dense foam rubber, I don't remember anything else - just that there's more to consider besides physical dimensions.
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2005 RX-8 Grand Touring 2005 Outback 2002 Mercedes-Benz E320 wagon END OF LINE |
#3
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you need to know the thiele-small (T/S) parameters for the sub to know what size & type of box to build (usually given by the manufacturer). There are a variety of modeling programs to help, the most famous of the freeware programs is probably WinIsd (do a search).
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#4
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Thanks Lee, but I don't think I will go through so much trouble...This is a favor And it will be a while before he can buy the components so I'm not too worried. I was thinking just leaving the back open, or using mesh to enclose it, and not worry. The kid just wants it loud....Damn kids
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-Mike '92 Pearl LS-L (sans Spoiler) #0993 Mfg. 5/91 "It says here, 'Breakfast any time'... That's right... In that case, I'll have the pancakes in the Age of Enlightenment..." |
#5
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OK, but to maximize loudness the two enclosures are ported and bandpass, and both of them are very sensitive to the size of the enclosure and the size of the port to the outside of the box. Leaving the back open and pumping in big numbers from an amp will overextend the voice coil - wave bye-bye to the pretty woofer
I have several design programs, if you tell me the brand model, there's a good chance I could tell you a solution. |
#6
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I always favor sealed enclosures for their inherent accuracy. A good sub in a sealed box should be loud enough for any sane person. About clearance in the back - from my experience it's not an issue, just as long as the magnet is not so tight against the back that the pole vent is sealed. That's not good. So just as long as there is some space, you should be fine. Also, unless you have a very advanced modeling program, it would be nearly impossible to determine the wave reflection properties of your enclosure. Besides, you are only dealing with a very small part of the overall frequency band when designing a sub enclosure, so the chances of standing waves being an issue are so slim it's worthless to even mention.
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#7
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Quote:
Things not regarding the vent: Mr. Pockets is right about enclosure dynamics. Even the experts have great difficulty controlling these problems. Usually it's just the luck of the draw. The problem is quite rare, but if you end up with horrible problems, adding a strategically-placed baffle inside the enclosure will cure it. Box design is almost as much a black magic as it is a science, and there's always a bit of art mixed in. Using the thiele-small parameters is your best bet. Speaker designs vary tremendously, and the enclosures must be built to match. When they're designed for each other, the results can be fantastic. When they're not, the results are rarely better than mediocre. A buddy of mine was tuning the display boxes at a stereo shop to have an enormous sweet spot right at 47Hz (as I recall.) Their sales tactic was to let the customer watch their display cabinet vibrate it's way across the showroom floor. Even with a cheap sub and tiny amplifier, one 12" sub pretty much dismantles their showroom. Boxes fall off shelves, windows rattle, magazines slide of tables, dust falls from the ceiling. If you like rap, that box is for you. The point is that good design is important. |
#8
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... you really don't have to worry about "standing waves" too much unless the box is purely square/rectangular, and even then its rare. the wave length of tones that subs produce are very very rarely anywhere shorter than 7 feet... (figure a 150hz tone has a wavelength of approx 7.5 ft... )
you're doing this as a favor, so just go the the manufacturers website... find the specs for size of a ported box, or a diagram/drawing of their recommended ported box, and build it.. it should be pretty simple, and if it fits, sound great.
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Greg 97 Red SVX LSi clean 96 Black SVX LSi beater 90 Red Eclipse GSX track ho 99 Ford F250 work horse My Locker |
#9
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Quote:
Such care in posting is a very rare thing these days.
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2005 RX-8 Grand Touring 2005 Outback 2002 Mercedes-Benz E320 wagon END OF LINE |
#10
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Now take it easy fellas, lets not get to fisticuffs Thanks for all the info, I will put it to good use, have a good weekend. Thanks again.
__________________
-Mike '92 Pearl LS-L (sans Spoiler) #0993 Mfg. 5/91 "It says here, 'Breakfast any time'... That's right... In that case, I'll have the pancakes in the Age of Enlightenment..." |
#11
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It's funny, looking back I've built some really crappy speaker boxes. With some really crappy speakers. I had a set of Urban 12"s in my BRAT that you could hear from a mile away. (Maybe it was the cap?) I remember hooking them up to an 80x80 Legacy amp as soon as I left the store (Ames) and using the cardboard box they came in as my speaker box. I was such a NOOB.
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92 SVX #772 140k 6speed, ECU Tune stage II, Koni/Ground control, 3,270lbs. 91 Legacy Turbo 5spd. FMIC, crappy stock turbo, ACT clutch. 78 BRAT (New toy) (Soon to be EJ22T powered) 90 240 SX. RB25 powered!! DRIFT!!!111!!! (GF's car) To many cars to spend time on teh web! |
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