The Subaru SVX World Network   SVX Network Forums
Live Chat!
SVX or Subaru Links
Old Lockers
Photo Post
How-To Documents
Message Archive
SVX Shop Search
IRC users:

Go Back   The Subaru SVX World Network > SVX Main Forums > Not Exactly SVX

Reply
 
Thread Tools Rate Thread Display Modes
  #1  
Old 11-30-2004, 02:22 PM
Whoru465's Avatar
Whoru465 Whoru465 is offline
The name's...
 
Join Date: Jun 2004
Location: Boston, Ma
Posts: 356
Send a message via AIM to Whoru465
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
__________________
-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..."
Reply With Quote
  #2  
Old 11-30-2004, 03:12 PM
Mr. Pockets's Avatar
Mr. Pockets Mr. Pockets is offline
Moderator
 
Join Date: Apr 2001
Location: Champaign, IL
Posts: 6,916
Send a message via ICQ to Mr. Pockets
Registered SVX
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.
__________________


2005 RX-8 Grand Touring
2005 Outback
2002 Mercedes-Benz E320 wagon

END OF LINE
Reply With Quote
  #3  
Old 11-30-2004, 03:20 PM
lee lee is offline
Registered User
 
Join Date: Mar 2002
Location: Indialantic, Florida
Posts: 2,940
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).
Reply With Quote
  #4  
Old 11-30-2004, 04:55 PM
Whoru465's Avatar
Whoru465 Whoru465 is offline
The name's...
 
Join Date: Jun 2004
Location: Boston, Ma
Posts: 356
Send a message via AIM to Whoru465
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
__________________
-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..."
Reply With Quote
  #5  
Old 11-30-2004, 05:10 PM
lee lee is offline
Registered User
 
Join Date: Mar 2002
Location: Indialantic, Florida
Posts: 2,940
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.
Reply With Quote
  #6  
Old 11-30-2004, 11:07 PM
Shadow248 Shadow248 is offline
Rep from the outside world
 
Join Date: Oct 2001
Location: Allentown, PA
Posts: 1,209
Send a message via AIM to Shadow248
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.
Reply With Quote
  #7  
Old 12-01-2004, 02:57 AM
UberRoo's Avatar
UberRoo UberRoo is offline
SVX Appeal
 
Join Date: Feb 2004
Location: Puget Sound, Washington
Posts: 843
Quote:
Originally posted by Shadow248
...just as long as the magnet is not so tight against the back that the pole vent is sealed.
That's pretty much right. The safe rule of thumb is that the clearance behind the magnet should be at least as large as the diameter of the vent. (The hole in the center of the magnet.) You can get away with less than that, but as the distance approaches about 1/3 of the diameter [based on Pi] the vent will start behaving like a dampener, robbing you of response. One-half of the diameter is pretty much a bare minimum because even that can have a 'tuning' effect on the vent much like a speaker port, though admittedly small. Most ports are less than an inch, and that much clearance is almost always achievable without much complication. (Although I've seen people router out cavities in their enclosures to gain them an extra half inch.)

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.
__________________
1994 LSi, Laguna Blue SVX Appeal
1992 LS-L, Ebony Pearl SVX-Rated
UberLocker
Reply With Quote
  #8  
Old 12-03-2004, 03:36 PM
drivemusicnow's Avatar
drivemusicnow drivemusicnow is offline
Poor College Racer
 
Join Date: Sep 2002
Location: IL/MI
Posts: 1,522
Send a message via AIM to drivemusicnow
... 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.
__________________
Greg

97 Red SVX LSi clean
96 Black SVX LSi beater
90 Red Eclipse GSX track ho
99 Ford F250 work horse
My Locker
Reply With Quote
  #9  
Old 12-03-2004, 04:46 PM
Mr. Pockets's Avatar
Mr. Pockets Mr. Pockets is offline
Moderator
 
Join Date: Apr 2001
Location: Champaign, IL
Posts: 6,916
Send a message via ICQ to Mr. Pockets
Registered SVX
Quote:
Originally posted by Shadow248
...the chances of standing waves being an issue are so slim it's worthless to even mention.
Well, thanks. It'd be one thing if you had simply said that my point was just moot, but I can really appreciate the effort you put forth in making sure to call it 'worthless.'

Such care in posting is a very rare thing these days.

__________________


2005 RX-8 Grand Touring
2005 Outback
2002 Mercedes-Benz E320 wagon

END OF LINE
Reply With Quote
  #10  
Old 12-03-2004, 05:02 PM
Whoru465's Avatar
Whoru465 Whoru465 is offline
The name's...
 
Join Date: Jun 2004
Location: Boston, Ma
Posts: 356
Send a message via AIM to Whoru465
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..."
Reply With Quote
  #11  
Old 12-03-2004, 07:02 PM
Subafreak's Avatar
Subafreak Subafreak is offline
Superbeast
 
Join Date: Aug 2002
Location: Central Village Ct.
Posts: 4,330
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.
__________________
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!
Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 03:51 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
© 2001-2015 SVX World Network
(208)-906-1122