subwoofer box construction
06-25-2003, 05:27 AM
#1
50 Watt CAFz'r
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Join Date: Nov 2002
Posts: 295
subwoofer box construction
Hey,
I am trying to help a friend make a box. He wants the box to take as little space as possible. The sub needs about 1cub ft of internal box space and it will be a sealed box.
Here is the question:
- does it make a diff is the box is square or is it good if we make is just as deep so that the sub can fit and then make it long and tall ?
I am trying to help a friend make a box. He wants the box to take as little space as possible. The sub needs about 1cub ft of internal box space and it will be a sealed box.
Here is the question:
- does it make a diff is the box is square or is it good if we make is just as deep so that the sub can fit and then make it long and tall ?
06-25-2003, 09:01 AM
#3
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Join Date: May 2003
Posts: 30
well, actualy, it is more prefferable to have a non square box, because the sound waves comming from the back of the speaker and reflecting off the back of the box can cancell eachother out and it could possibly cause a drop in Db at certian frequencies, so, build it with a slant on one side (polygon) or if it has to be square, build it a little bigger with some internal braceing, this will help to relieve or atleast reduce the possible problem of standing waves
06-25-2003, 09:12 AM
#4
Originally posted by ThA NexT BiG ThinG:
well, actualy, it is more prefferable to have a non square box, because the sound waves comming from the back of the speaker and reflecting off the back of the box can cancell eachother out and it could possibly cause a drop in Db at certian frequencies, so, build it with a slant on one side (polygon) or if it has to be square, build it a little bigger with some internal braceing, this will help to relieve or atleast reduce the possible problem of standing waves
well, actualy, it is more prefferable to have a non square box, because the sound waves comming from the back of the speaker and reflecting off the back of the box can cancell eachother out and it could possibly cause a drop in Db at certian frequencies, so, build it with a slant on one side (polygon) or if it has to be square, build it a little bigger with some internal braceing, this will help to relieve or atleast reduce the possible problem of standing waves
06-25-2003, 02:09 PM
#6
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Join Date: May 2003
Posts: 30
http://www.jlaudio.com/tutorials/boxdesign/index.html
Enclosure Shape, Bracing and Strength, Sealing the Box
Enclosure Shape
While it is always a pretty good idea to stay away from perfect cubes, they don't necessarily have to be avoided like The Plague. Due to the very small dimensions of most mobile subwoofer enclosures, there is little chance of generating standing waves in the enclosure (standing waves cause nasty response fluctuations). For a standing wave to exist, the distance between parallel boundaries must be 1/2 the wavelength of the frequency at which the standing wave exists. Considering that sub-bass waves vary from 56.4 feet (20 Hz) to 11.28 feet (100 Hz), the generation of a standing wave is going to be impossible....after all, the enclosures we're speaking of have to fit in the average sedan or hatchback!
Any standing waves that might be generated by upper ordered harmonics (caused by distortion) in the enclosure can be readily absorbed with the addition of damping material such as polyfill (available at your local cloth store--it is used to stuff pillows and quilts) or Fiberglastm (the pink stuff) and/or they can be broken up with strategically placed bracing within the enclosure.
In short, don't worry too much about shape. Make the box to fit the space you can allot to the enclosure and forget about it--there are more important things to worry about...like bracing.
BTW: this is an excerpt from a link that "somebody" posted from another link (see 8" boxes?)
after its all said and done, wouldn't a 1/4 or an 1/8 have a standing wave as well? i thought just for reflection directly back into the speaker was bad enough to do some funny things, and it was always beter to have non paralell surfaces?
[ June 25, 2003, 03:17 PM: Message edited by: ThA NexT BiG ThinG ]
Enclosure Shape, Bracing and Strength, Sealing the Box
Enclosure Shape
While it is always a pretty good idea to stay away from perfect cubes, they don't necessarily have to be avoided like The Plague. Due to the very small dimensions of most mobile subwoofer enclosures, there is little chance of generating standing waves in the enclosure (standing waves cause nasty response fluctuations). For a standing wave to exist, the distance between parallel boundaries must be 1/2 the wavelength of the frequency at which the standing wave exists. Considering that sub-bass waves vary from 56.4 feet (20 Hz) to 11.28 feet (100 Hz), the generation of a standing wave is going to be impossible....after all, the enclosures we're speaking of have to fit in the average sedan or hatchback!
Any standing waves that might be generated by upper ordered harmonics (caused by distortion) in the enclosure can be readily absorbed with the addition of damping material such as polyfill (available at your local cloth store--it is used to stuff pillows and quilts) or Fiberglastm (the pink stuff) and/or they can be broken up with strategically placed bracing within the enclosure.
In short, don't worry too much about shape. Make the box to fit the space you can allot to the enclosure and forget about it--there are more important things to worry about...like bracing.
BTW: this is an excerpt from a link that "somebody" posted from another link (see 8" boxes?)
after its all said and done, wouldn't a 1/4 or an 1/8 have a standing wave as well? i thought just for reflection directly back into the speaker was bad enough to do some funny things, and it was always beter to have non paralell surfaces?
[ June 25, 2003, 03:17 PM: Message edited by: ThA NexT BiG ThinG ]
06-26-2003, 01:19 PM
#7
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Posts: n/a
A 1/4 wave will reflect and cause cancellations between two solid surfaces. An 1/8wave is not developed enough to reflect. JL made a mistake it appears 
Personally I DO always try to line at least one wall in the enclosure with some sort of sound absorbing material. While the low frequencies generated by the woofer will not cause problems, all the out of band resonances and noises ARE high enough in the spectrum to cause funny noises as they reflect around in there and eventually eminate through the cone.
Of course that's just me
Personally I DO always try to line at least one wall in the enclosure with some sort of sound absorbing material. While the low frequencies generated by the woofer will not cause problems, all the out of band resonances and noises ARE high enough in the spectrum to cause funny noises as they reflect around in there and eventually eminate through the cone.
Of course that's just me
06-27-2003, 10:49 AM
#10
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Join Date: May 2003
Posts: 30
there are mant tains of thought on port placement, JL audio probobly has some info on where to place them, those florida guys have done tonnes of r&d on ported boxes, the same basic shape rules aply.
GENERALY it is best to not have the port and the voice coil line-up (or be paralel) but for the port to be horizontal and the woofer to be vertical, or vice-versa, the reason for this is that you want to avoid the reflected sound waves from bouncing directly back and exiting the port. What you want is for them to almost become traped, ALMOST, (I gotta be sooo careful!) The port is like annother speaker, this is why its so important to have the right port length. Bassically a port is like a pipe organ, and the length of the tube resonates at a certain frequency. and if the sound waves bounce and shoot right out the port, well, then the design isn't working to its maximum potential, or at all. This is why I said in another post that very generaly, a ported box has a more of a peaked response curve, rater than (generally[for Dukk]) a sealed box usualy has a more flat response curve, but then, it also has to do with how well you design these two enclosure styles. For years companies like JL, and BOSE (no highs no lows) have had massive succes with their ported and bandpass designs. If you dont have the propper calculations, a ported box can be very difficult to design, and very hard to have function properly, compared to thr relative ease of a sealed design. You can go to www.jlAudio.com to learn more
GENERALY it is best to not have the port and the voice coil line-up (or be paralel) but for the port to be horizontal and the woofer to be vertical, or vice-versa, the reason for this is that you want to avoid the reflected sound waves from bouncing directly back and exiting the port. What you want is for them to almost become traped, ALMOST, (I gotta be sooo careful!) The port is like annother speaker, this is why its so important to have the right port length. Bassically a port is like a pipe organ, and the length of the tube resonates at a certain frequency. and if the sound waves bounce and shoot right out the port, well, then the design isn't working to its maximum potential, or at all. This is why I said in another post that very generaly, a ported box has a more of a peaked response curve, rater than (generally[for Dukk]) a sealed box usualy has a more flat response curve, but then, it also has to do with how well you design these two enclosure styles. For years companies like JL, and BOSE (no highs no lows) have had massive succes with their ported and bandpass designs. If you dont have the propper calculations, a ported box can be very difficult to design, and very hard to have function properly, compared to thr relative ease of a sealed design. You can go to www.jlAudio.com to learn more
