GK Build-Your-Own-Combo : Porting Questions

[Super Turbo Deluxe Custom]

Also, is there any reason behind the rule to making your ports total half the size of the speakers? Like for a 212 cab, should I shoot for 12" total in ports?

I'm sure there is a formula, but I don't know if it's a rule because some cabs are sealed.

 

[whyachi]

Port options:

 

[Dan025]

Also, is there any reason behind the rule to making your ports total half the size of the speakers? Like for a 212 cab, should I shoot for 12" total in ports?

I'm sure there is a formula, but I don't know if it's a rule because some cabs are sealed.

the math is long and fairly complex and needs a lot of info on the driver. this info is known as thele-small parameters(my spelling may be off). ports are louder, sealed is good, open back is most forgiving in design.
once you have a design though a change in port design is easy, there needs to be a proportion of port cross section and length so if you double the diameter you must make the port 4 times longer if i remember right. bigger ports have lower velocities and therefore less turbulence. slots offer large cross section and are easy to build long lengths into the box.

 

[whyachi]

Also, is there any reason behind the rule to making your ports total half the size of the speakers? Like for a 212 cab, should I shoot for 12" total in ports?

I'm sure there is a formula, but I don't know if it's a rule because some cabs are sealed.

the math is long and fairly complex and needs a lot of info on the driver. this info is known as thele-small parameters(my spelling may be off). ports are louder, sealed is good, open back is most forgiving in design.
once you have a design though a change in port design is easy, there needs to be a proportion of port cross section and length so if you double the diameter you must make the port 4 times longer if i remember right. bigger ports have lower velocities and therefore less turbulence. slots offer large cross section and are easy to build long lengths into the box.

So ports need to be four times as long as the diameter? So a 3" port needs to be 12" long? That'll work on those designs, they're all about 22" deep counting the 2U rack.

 

[Dan025]

no
it is compicated

if you have a desghn that spesifies a 3in port and 12in long but you wanted a 6in port for looks or it has some noise assosiated with turbulence it would need to be 48in long. to get a starting point you need theile-small parameters of the driver or a blueprint of a cab that is designed for the driver. 

 

[whyachi]

no
it is compicated

if you have a desghn that spesifies a 3in port and 12in long but you wanted a 6in port for looks or it has some noise assosiated with turbulence it would need to be 48in long. to get a starting point you need theile-small parameters of the driver or a blueprint of a cab that is designed for the driver.  

My designs don't specify anything, honestly. I set out to design a 4Ohm 212 cab with a 2U rack unit on it and I could build myself. I have no other specifications. I didn't want a 6" port for looks or anything, the one with the round ports has four 3" ports with the amazing forethought that 212 = 24" of speaker, / 2 = 12" of port, / 4 corners = 3" ports.

Can you explain turbulence? I'm picturing my amp bouncing around like an airplane and I am fairly certain that is in correct.


Here's the info on the speakers I'm looking at, just by the frequency response. Those go down to 40hz, the best I've found besides that is 48hz.
http://professional.celestion.com/bass/pdf/BL12-200X8.pdf

 

[Dan025]

now it get's tricky i'd like to help and i know where to find the info but it is alot of explaining. a lot of physics and alot of math.

 

[whyachi]

now it get's tricky i'd like to help and i know where to find the info but it is alot of explaining. a lot of physics and alot of math.

Unless your physics involves calculating how much beer must be consumed to successfully jump a 4x4 quad over a pond using a picnic table and an empty keg as a ramp, you'd probably lose me with it.

I'm not an audiophile, I just want a cab with a rack built in that sounds halfway decent. Can you generalize a bit without me having to get Max to Photoshop up a pH.D so I can understand you?

 

[Dan025]

is there a comercially available amp or cab that uses this speaker?

 

[whyachi]

is there a comercially available amp or cab that uses this speaker?

Google and Talkbass says no, and actually besides Celestion's website I can find very little reference of that particular speaker.

 

[Dan025]

try these
http://image.ajdesigner.com/vc/ajbandpass.exe
http://www.ajdesigner.com/fl_subwoofer/subwoofer.php


just a note it is safer to go too low on tuning than too high. that is big box or longer ports. too high and you'll have a one note wonder that has a super sensitive response to a narrow frequency range. lower and you get lower notes but slightly less volume too.

 

[whyachi]

The first one is an .exe? I'm on a Mac, sorry.

I'm not entirely sure what the second link is, Vas and Qts and fs and whatever.

 

[Dan025]

a sealed box is safer, just go big on size and don't worry too much about the physics. most instrument speakers are suitable for free air and box volume is less important unless you go too small

 

[Dan025]

The first one is an .exe? I'm on a Mac, sorry.

I'm not entirely sure what the second link is, Vas and Qts and fs and whatever.

it is in the "small" parameters on the right of the speaker website

 

[whyachi]

it is in the "small" parameters on the right of the link to the speaker website

http://www.earcandycabs.com/products.php?req=read&product_id=47&PHPSESSID=f0f45290732e7c69935b342fa13d7346

That was my inspiration on the design, and the dimensions on that model are very similar to the BassBomb's. That cab also uses the same woofers. Found one!  :hello2:

 

[Dan025]

so i think you have what you need then

 

[whyachi]

All I can see is the placement of the port tubes on that cab, I have no idea how far in they go. That's what I was trying to figure out.

 

[Dan025]

that website calculator should tell you that, you need to know what the port diameter you want to use is
or are you doing a slot?

 

[whyachi]

I think I'm going four 3" round ports as I've read in a lot of places that the ports should equal about half the speaker area.

 

[Dan025]

are you using the bass bomb dimensions for the box? cuz that effects port length