Dual 18" 2242H Cabinet Design

[Serge]

I know this is an easy one for some of you guys but I am a newbee so I need some expert advise to avoid wasting time and money.

I am building a dual 18" cabinet based on the SR7419x cabinet. I love the sound of this cabinet but I want to take it up a notch and put some 2242s inside of it and retune the ports. I will be building something from scratch so that I dont have to mess around with the origional cabinet.

I am also doing someting different though. I am using the shorter dimension of the cabinet as the baffle and the width of the SR as the depth of the cabinet. The box will have internal dimensions approx. (24"W x 48"H x 30"D). That's about 10ft^3 per woffer.

If I have a (6"x18") rectagular port (similar to the SR), what would be the ideal port length to provide a frequency responce down in the 30s?

Anyone have any experience building something like this or could point me in the right direction, I would appreciate it.

[Loren42]

I know this is an easy one for some of you guys but I am a newbee so I need some expert advise to avoid wasting time and money.

I am building a dual 18" cabinet based on the SR7419x cabinet. I love the sound of this cabinet but I want to take it up a notch and put some 2242s inside of it and retune the ports. I will be building something from scratch so that I dont have to mess around with the origional cabinet.

I am also doing someting different though. I am using the shorter dimension of the cabinet as the baffle and the width of the SR as the depth of the cabinet. The box will have internal dimensions approx. (24"W x 48"H x 30"D). That's about 10ft^3 per woffer.

If I have a (6"x18") rectangular port (similar to the SR), what would be the ideal port length to provide a frequency responce down in the 30s?

Anyone have any experience building something like this or could point me in the right direction, I would appreciate it.

To get the box tuned to the desired frequency I need to know the exact internal volume after you subtract the displacement of all internal braces and the displacement of the woofer.

JBL should give you the driver's displacement on their specification sheet, which I can look up as well, but I have no clue on the amount of bracing you plan to add. Can you calculate that volume for me?

The port displacement also needs to be known, but that is just an iterative approach to get that. My software does that automagically.

Without the data I am requesting I can only give you a guesstimate.

Also, why do you want to use a rectangular port? Round ports are easier to make, easier to tune, and there is no sonic benefit to a rectangular port.

All that assumes that there is room for a round port on your baffle.

[SMKSoundPro]

There is much info here! Everyone will add their own ideas. Read them and heed them. They do know what they are doing!

Scotty.

[Allanvh5150]

Hi Serge,

Just running the numbers that you have given, with the cabinet tuned to 32Hz the port length will be somewhere in the region of 5.25"

Allan.

[Loud & Clear]

Man! I need two of those!!!

[Loren42]

Man! I need two of those!!!

I want to know how he gets it out of the basement!

[Mike Caldwell]

Don't forget about internal bracing, side to side front to back, stringers along the cabinet walls ect. Within reason the more the better. As noted before you need to subtract that from the cabinets overall volume.

Mike Caldwell

[4313B]

To get the box tuned to the desired frequency I need to know the exact internal volume after you subtract the displacement of all internal braces and the displacement of the woofer.

JBL should give you the driver's displacement on their specification sheet, which I can look up as well, but I have no clue on the amount of bracing you plan to add. Can you calculate that volume for me?

The port displacement also needs to be known, but that is just an iterative approach to get that. My software does that automagically.

Without the data I am requesting I can only give you a guesstimate.

Also, why do you want to use a rectangular port? Round ports are easier to make, easier to tune, and there is no sonic benefit to a rectangular port.

All that assumes that there is room for a round port on your baffle.

Don't forget about internal bracing, side to side front to back, stringers along the cabinet walls ect. Within reason the more the better. As noted before you need to subtract that from the cabinets overall volume.

If one uses good old fiberglass insulation then it becomes a bit more complex. Basically 1" to 2" fiberglass is going to negate the volume displacement of most drivers, ports and any reasonable amount of bracing. This is where prototyping comes in where everything is dialed in pretty tight and total system loses are documented.

It's fairly easy to end up with a larger than optimal net effective volume tuned too low.

[SMKSoundPro]

Don't forget about internal bracing, side to side front to back, stringers along the cabinet walls ect. Within reason the more the better. As noted before you need to subtract that from the cabinets overall volume.

Mike Caldwell

Note the bracing.