Questions about an ABC box
06-03-2006, 10:58 AM
#1
0 Watt CAFz'r
Thread Starter
Join Date: Mar 2006
Posts: 11
Questions about an ABC box
Hey guys,
been lurking in the shadows for long enough...
I have 2x Audiobahn 1251t subs, and im trying to design an ABC enclosure to mount them in for my 90 Jetta. Size of the box is going to be 32" wide, 16.5" tall so that it will fit into the space between the shock towers if i need to pack stuff in the trunk.
This image is NOT to scale, just a quick MS paint to show my thoughts on the layout.
The lower chamber will be 2 cubic feet, the upper one 1 cubic foot. The red line will be bracing for the enclosure, and build material is going to be 3/4" MDF.
The slot ports will be 3/4" wide, 15" tall, and have a length of about 18-19" depending on the final tuning of the box, each of the openings are sticking into the box volume 1 1/2". The horizontal peices in front of the ports are bracing, but also to prevent the subs from directly driving the port.
I am using WinISD Pro to find the port length for a 3 cf box two ports, so all the lengths are based on the output from there. Currently I am tuning it for around 30hz.
so, now the questions.....
I have read a few long articles on the design of these boxes, and I am under the assumption that the specific frequency to tune the box to doesn't matter, as long as the sub can handle the box volume and what not? This box (based on 3cf) is within the "suggested" box sizes for a ported enclosure on the audiobahn website, so i think its ok, or am i mistaken?
In previous boxes, I have always been told for quality of sound, keep the port one diameter from any wall, and dont put it in the direct line of sight of the woofer to pervent it from pushing air directly into the port, is this true? Its the reason the two boards are in the way of the port openings, as well as why the openings are sticking into the box interiour.
and finaly, this is the first slot loaded sub I have built, is 3/4 too thing of a slot? I think from my reading that its the port volume, not the specific sizes that matter for the ressonance?
If the general idea of the box seems sound to you guys, ill do the calculations and draw up a scale version to see how it looks. I just want to get some idea if its feasible before doing all the damned math =)
thanks
been lurking in the shadows for long enough...
I have 2x Audiobahn 1251t subs, and im trying to design an ABC enclosure to mount them in for my 90 Jetta. Size of the box is going to be 32" wide, 16.5" tall so that it will fit into the space between the shock towers if i need to pack stuff in the trunk.
This image is NOT to scale, just a quick MS paint to show my thoughts on the layout.
The lower chamber will be 2 cubic feet, the upper one 1 cubic foot. The red line will be bracing for the enclosure, and build material is going to be 3/4" MDF.
The slot ports will be 3/4" wide, 15" tall, and have a length of about 18-19" depending on the final tuning of the box, each of the openings are sticking into the box volume 1 1/2". The horizontal peices in front of the ports are bracing, but also to prevent the subs from directly driving the port.
I am using WinISD Pro to find the port length for a 3 cf box two ports, so all the lengths are based on the output from there. Currently I am tuning it for around 30hz.
so, now the questions.....
I have read a few long articles on the design of these boxes, and I am under the assumption that the specific frequency to tune the box to doesn't matter, as long as the sub can handle the box volume and what not? This box (based on 3cf) is within the "suggested" box sizes for a ported enclosure on the audiobahn website, so i think its ok, or am i mistaken?
In previous boxes, I have always been told for quality of sound, keep the port one diameter from any wall, and dont put it in the direct line of sight of the woofer to pervent it from pushing air directly into the port, is this true? Its the reason the two boards are in the way of the port openings, as well as why the openings are sticking into the box interiour.
and finaly, this is the first slot loaded sub I have built, is 3/4 too thing of a slot? I think from my reading that its the port volume, not the specific sizes that matter for the ressonance?
If the general idea of the box seems sound to you guys, ill do the calculations and draw up a scale version to see how it looks. I just want to get some idea if its feasible before doing all the damned math =)
thanks
06-03-2006, 01:18 PM
#3
0 Watt CAFz'r
Thread Starter
Join Date: Mar 2006
Posts: 11
I dont think so, the port on the far left enters the rear/small chamber, the center port goes from the front/large chamber to the rear/small chamber, and the one on the far right enters the front/large chamber.
the red lines do not indicate a wall in the sub, its where im planning on putting a brace in, there will be mostly open space through it
the red lines do not indicate a wall in the sub, its where im planning on putting a brace in, there will be mostly open space through it
06-04-2006, 10:39 AM
#6
Administrator
Join Date: Feb 2006
Posts: 16,855
A couple of thoughts..
1) That's a lot of wood and corners. The design appears technically feasible but IMO is needlessly complicated.
2) You have a pair of 12s right? And you only have 11.25" of vent area. That's less than a single 4" diameter port. Double the area you have..at least
3) Yes 3/4" of slot width is IMO to narrow. The above should fix that though..
1) That's a lot of wood and corners. The design appears technically feasible but IMO is needlessly complicated.
2) You have a pair of 12s right? And you only have 11.25" of vent area. That's less than a single 4" diameter port. Double the area you have..at least
3) Yes 3/4" of slot width is IMO to narrow. The above should fix that though..
06-04-2006, 02:03 PM
#7
0 Watt CAFz'r
Thread Starter
Join Date: Mar 2006
Posts: 11
Thanks for the input Dukk.
If i had more room to play with, I would have arranged it differently, but im comprimising to get it in the trunk and at least be able to get a weeks worth of groceries in as well =)
if i double the size of the ports, they are going to be much more complicated in shape to fit into the size constraints i have in mind.
Will I be better off running 6 4" tubes instead of 3 slots then? I might have better luck fitting them in...
If i had more room to play with, I would have arranged it differently, but im comprimising to get it in the trunk and at least be able to get a weeks worth of groceries in as well =)
if i double the size of the ports, they are going to be much more complicated in shape to fit into the size constraints i have in mind.
Will I be better off running 6 4" tubes instead of 3 slots then? I might have better luck fitting them in...
06-06-2006, 11:14 PM
#8
500 Watt CAFz'r
Join Date: Nov 2004
Posts: 779
where to start.......
the design you posted would be almost inpossable to build even for an experienced builder. you still missing a few ports.and as dukk already mentiond you are definalty going to need more port area.and yes that will casue you port lenghts to become alot longer. imo if you want to save a bit of space and still use the abc design. stick the subs in a common chamber and make the box only have 3 ports. i would go with at least 25 sq" of port (per port). make the ports u shaped .( very similar to what i have in my avaitar). by placing like this they take up the least amount of space. by using only 3 ports you will end up with a wider port. as a rule of thumb port hight to width ratios are kept at about 1:9.
the design you posted would be almost inpossable to build even for an experienced builder. you still missing a few ports.and as dukk already mentiond you are definalty going to need more port area.and yes that will casue you port lenghts to become alot longer. imo if you want to save a bit of space and still use the abc design. stick the subs in a common chamber and make the box only have 3 ports. i would go with at least 25 sq" of port (per port). make the ports u shaped .( very similar to what i have in my avaitar). by placing like this they take up the least amount of space. by using only 3 ports you will end up with a wider port. as a rule of thumb port hight to width ratios are kept at about 1:9.
