3 Questions about sub box design
Thread Starter
0 Watt CAFz'r
Joined: Oct 2005
Posts: 35
I have 3 questions about designing then building a sub box for 2 x 12 inch subs.
1. Assuming the interior cubic feet would be correct/ideal for each sub, does the actual shape of the box change the performance? eg. square box, rectangle box, trapazoid, or circle shaped box.
2. When building this box, is there any difference or advantage in keeping each sub separated with a dividing sealed wall? Are there any pros/cons to not having a separating wall inside the interior of the box with 2 subs?
and lastly...
3. If a person is designing a correctly sized ported box with ideal sub specs, (incuding tube length and tube diameter) does it matter on which side or sub box wall the port tube is placed?
Any help appreciated! And this is a great forum! [img]graemlins/thumb.gif[/img]
1. Assuming the interior cubic feet would be correct/ideal for each sub, does the actual shape of the box change the performance? eg. square box, rectangle box, trapazoid, or circle shaped box.
2. When building this box, is there any difference or advantage in keeping each sub separated with a dividing sealed wall? Are there any pros/cons to not having a separating wall inside the interior of the box with 2 subs?
and lastly...
3. If a person is designing a correctly sized ported box with ideal sub specs, (incuding tube length and tube diameter) does it matter on which side or sub box wall the port tube is placed?
Any help appreciated! And this is a great forum! [img]graemlins/thumb.gif[/img]
50 Watt CAFz'r
Joined: Oct 2003
Posts: 200
I'll take a stab at this one...
No, at least not audibly. Airspace is airspace, for all intents and purposes. There was discussion that a box with all parallel sides (i.e. a perfect cube) would be subject to standing waves inside the box, but the actual wavelengths of bass frequencies make it a non-issue in most cases, unless we're talking about rediculously huge boxes.
AFAIK, the only advantage to having two or more subs share airspace is that the overall internal volume is usually less than if each sub had its own chamber. I don't even fully understand why this is (maybe someone could clarify). Other than that, best practice is normally to have each sub in its own chamber. It's not good to have subs "depending" on each other mainly because if one blows, or even just gets accidentally disconnected, it will adversely affect the other sub, often causing it to over-excurt and possibly cause damage.
Usually best practice is to put the ports on the same side that the sub is mounted on to keep everything relatively in-phase, but this can depend heavily on the application, box placement, type and design of car, and your overall goals for the system. Sometimes the design of the box doesn't allow for the ports to be on the same side as the sub, especially if you're using round ports. Sometimes slot ports can help get around this, but in the end if you have to put the ports on a different side, then so be it.
Hope this helps!
1. Assuming the interior cubic feet would be correct/ideal for each sub, does the actual shape of the box change the performance? eg. square box, rectangle box, trapazoid, or circle shaped box.
2. When building this box, is there any difference or advantage in keeping each sub separated with a dividing sealed wall? Are there any pros/cons to not having a separating wall inside the interior of the box with 2 subs?
3. If a person is designing a correctly sized ported box with ideal sub specs, (incuding tube length and tube diameter) does it matter on which side or sub box wall the port tube is placed?
Hope this helps!
Guest
Posts: n/a
1. IMO the shape of the box wont change the output audibly unless it is something very extreme. But rounding internal edges or making them 45 degree angles can never hurt.
2. having the subs in seperate enclosures will prevent any possible issues with changing box parameters if one sub malfunctions. If one sub stops working the box space doubles for the other one and it may over-excurt. Putting in a divider also doubles as an internal brace for the box.
At the same time running them in one common chamber is easier to build and also gives you the ability to run one central port which might be better asthetically for some people.
3. where the port is placed in relation to the sub itself is a matter of trial and error in a lot of applications. In hatchbacks and SUVs sub up port back generally works well. In a truck car both firing back provided me good results as did firing both forward with the box at the very front of the trunk and the back seat folded down. For both firing forward i also sealed the box from the rest of the trunk with expanding foam.
2. having the subs in seperate enclosures will prevent any possible issues with changing box parameters if one sub malfunctions. If one sub stops working the box space doubles for the other one and it may over-excurt. Putting in a divider also doubles as an internal brace for the box.
At the same time running them in one common chamber is easier to build and also gives you the ability to run one central port which might be better asthetically for some people.
3. where the port is placed in relation to the sub itself is a matter of trial and error in a lot of applications. In hatchbacks and SUVs sub up port back generally works well. In a truck car both firing back provided me good results as did firing both forward with the box at the very front of the trunk and the back seat folded down. For both firing forward i also sealed the box from the rest of the trunk with expanding foam.
50 Watt CAFz'r
Joined: May 2004
Posts: 467
1 - Doesn't overly matter... just try to avoid a parallel front and back this is where the sound waves go directly back and then bounce off the wall and resonate forward.
2 - The advantage is (as noted above) it acts as a brace as well as if by chance one sub malfunctions or a wire comes loose for what ever reason it's a whole lot easier to see which one isn't working (shared chamber the one that is working will use the other as a passive radiator and will move it as it's moving the interior air of the box).
3 - I would say you would want them on the same side because there is an off chance of some cancelation if they are on opposite sides. (I'll be honest, haven't had all that much experience building boxes so I'm sure there are more people here that can answer this better than me)
2 - The advantage is (as noted above) it acts as a brace as well as if by chance one sub malfunctions or a wire comes loose for what ever reason it's a whole lot easier to see which one isn't working (shared chamber the one that is working will use the other as a passive radiator and will move it as it's moving the interior air of the box).
3 - I would say you would want them on the same side because there is an off chance of some cancelation if they are on opposite sides. (I'll be honest, haven't had all that much experience building boxes so I'm sure there are more people here that can answer this better than me)
500 Watt CAFz'r
Joined: Oct 2004
Posts: 870
1)Standing waves may be an issue with parallel walled boxes. Minimize by keeping the dimensions NOT even multiples of each other if possible.
If the back wall is close to the woofer, then adding some baffles (pieces of ABS cut in half lengthwise work well) of gluing some foam, or polyfill to the wall will help.
2) Agree with the above, but is there an audible difference? Not sure.
3) I would think placing the port on the same plane would usually be best, but I'll difer to those with actual experience trying it other ways.
There is a phase shift/delay between the port, and woofer anyways, so if you make a "mistake" in the right direction, it could be beneficial.
If the back wall is close to the woofer, then adding some baffles (pieces of ABS cut in half lengthwise work well) of gluing some foam, or polyfill to the wall will help.
2) Agree with the above, but is there an audible difference? Not sure.
3) I would think placing the port on the same plane would usually be best, but I'll difer to those with actual experience trying it other ways.
There is a phase shift/delay between the port, and woofer anyways, so if you make a "mistake" in the right direction, it could be beneficial.
500 Watt CAFz'r
Joined: Dec 2000
Posts: 952
Hmmmm
I beg to differ on some aspects;
I have found that keeping a cabinet asymetrical does work better, I also found that mounting the driver in such a way as to use the length of the box, works best. (with proper insulation.)
If you have the time and resources, try building two differntly shaped cabinets, with the same air space, cut a hole for a speaker, and by speaking into the chamber, you will get an idea of it's tonal characteristics, before you put the driver in it.
Idealy a spherecal cabinet is best, but,..
As for porting, idealy the port should be on the same plane(side) as the driver, and spaced half the diameter of the cone, away from the driver, and any cabinet walls.(this is the "ideal" situation scenario, a car is not an ideal place for stereo)For more on Cabinet porting see Dukk, I can only tell you about bottled ports.
BTW, a woofer should be as far away from a back wall, to prevent "doubling", and allow the Voice coil to cool better.
As for two woofers scenario, I found it is better to have two chambers in one cabinet. The devision will act as a brace, and reduce cabinet resonance considerably, as to effect a gain in output, because of lower cancellation from the cabinet. When porting both, try to put the ports close to each other. Allow sufficient space between the woofers&ports from any surface(like the back of a rear seat).
In theory a speaker needs a tapering cone shaped cabinet.
I beg to differ on some aspects;
I have found that keeping a cabinet asymetrical does work better, I also found that mounting the driver in such a way as to use the length of the box, works best. (with proper insulation.)
If you have the time and resources, try building two differntly shaped cabinets, with the same air space, cut a hole for a speaker, and by speaking into the chamber, you will get an idea of it's tonal characteristics, before you put the driver in it.
Idealy a spherecal cabinet is best, but,..
As for porting, idealy the port should be on the same plane(side) as the driver, and spaced half the diameter of the cone, away from the driver, and any cabinet walls.(this is the "ideal" situation scenario, a car is not an ideal place for stereo)For more on Cabinet porting see Dukk, I can only tell you about bottled ports.
BTW, a woofer should be as far away from a back wall, to prevent "doubling", and allow the Voice coil to cool better.
As for two woofers scenario, I found it is better to have two chambers in one cabinet. The devision will act as a brace, and reduce cabinet resonance considerably, as to effect a gain in output, because of lower cancellation from the cabinet. When porting both, try to put the ports close to each other. Allow sufficient space between the woofers&ports from any surface(like the back of a rear seat).
In theory a speaker needs a tapering cone shaped cabinet.
1. Box shape dosen't really matter
2. seperate chambers add bracing/loose volume
3. dosen't matter much unless the distance the sounds has to travil from the port to the front of the box is more then 1/4 of the tuned wavelength away. Ie about 9feet for 30hz. There are however some other variables to consider and port placement might still affect loading...
2. seperate chambers add bracing/loose volume
3. dosen't matter much unless the distance the sounds has to travil from the port to the front of the box is more then 1/4 of the tuned wavelength away. Ie about 9feet for 30hz. There are however some other variables to consider and port placement might still affect loading...
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