Simple cab design 1x12... your comments please

[billfitzmaurice]

I played a little with the bassboxpro and found that 4 x 3" ports would ask for a 12.25" long ports and the internal space with the recessed baffle is only 14.25" so there are just 2" between the back pannel and the end of the tubes.
Not enough to avoid turbulance?

Not enough to maintain the box tuning, it must be at least the diameter of the duct. Make them smaller or make the cab larger.

Interesting! the triangular corner ports would save bracing... My only concern is that the would be a little far from the driver

They're better off further away.

 

[LowGrowl]

Not enough to maintain the box tuning, it must be at least the diameter of the duct. Make them smaller or make the cab larger.

I just realized that the pipe goes through the 1" thick baffle. then a 12" long vent will insert only 11" into the cab and that gives me 3.25" of space. Just bit bigger to the 3" diameter vents...

For the Triangular ports I would need another tool I don't have to make the 45 degrees cuts...

SO!
I will go with the 4 x 3" round ports

Better to have this perfect. Is to have it done!
Ray

 

[bryanspkr]

Too much reliance on box programs here. When you finish, check your tuning by using the signal generator on your program and slowly sweep back and forth until the point of least excursion. Wear ear plugs for this! A flashlight may help too. Just only one example of how it is necessary to think of these programs as a rough guide.

 

[will33]

I just realized that the pipe goes through the 1" thick baffle. then a 12" long vent will insert only 11" into the cab and that gives me 3.25" of space. Just bit bigger to the 3" diameter vents...

For the Triangular ports I would need another tool I don't have to make the 45 degrees cuts...

SO!
I will go with the 4 x 3" round ports

Better to have this perfect. Is to have it done!
Ray

That's still cutting it close, don't want your lining stuffing up the end of the ports. 2-1/2" might be enough using 4 per driver. Plug that in your model and check air velocity at the highest power input the drivers can handle. Triangles may still be the better way here. Most any circle saw or jig saw I've seen you can adjust the foot for angles, yours might too. Or just rig up a guide to follow so you can run the whole saw at an angle if the blade has to stay straight.

 

[bryanspkr]

Get some Precision Ports if you can fit them. The same ones that the builder of DNA (former eden) is letting people think he designed. Definitely the best flare design I have found.

 

[BogeyBass]

I played a little with the bassboxpro and found that 4 x 3" ports would ask for a 12.25" long ports and the internal space with the recessed baffle is only 14.25" so there are just 2" between the back pannel and the end of the tubes.
Not enough to avoid turbulance?

not sure what your dimensions are but 12" seems long. Should be able to shorten that.I'm going over the math for my 21 x 18 x 16.5
remember that if you make your own port or use pre made plastic ones there is 1/2 inch depth to the baffle, so you can remove 1/2 from your length to calculate how close it is to a rear wall. Since the port would be mounted to the front and includes the depth of the baffle.

minus the front and rear baffle and a 1" set back = 14.5"
for the sides minus 1/2" inch for both sides.

so internal dimensions should be 20x17x14.5 for 2.853 cubic feet

the driver is .049 cubic feet

and assuming 4x3" round ports at 11inches would be .147

.049 driver + .176 port = .225

2.853 cubic feet - .225 = 2.628 cubic feet

so using 11 to 12 inch port should put you around 45 to 46hz Fb



thinking 11.5 inch port would be fine and with 14.5 inches of actual cabinet depth. There should be 3.5 inches of clearance.

Even if you went to a 10 inch length port you would still be around 44hz. and in general without sticking to a hard core perfect alignment we are looking to be 5 to 7Hz above Fs of the driver which is 37hz.

The design I showed could work for many 12" drivers

round ports just add to the cost because you need to buy the flared plastic inserts. Otherwise you just cut the openings and screw them in. They seem to be more complicated, but to me seem rather simple. And the performance out weighs the cost. I dont care to mud wrestle today.
But 4x flared round ports, placed symmetrical and closely to the driver will be the most accurate and best performing port you can build.

 

[dog1]

Your basic design looks good to me. And, that's a real nice woofer.

As long as you get good glue joints and don't have voids in bad places (like where the driver mouinting screws go), you should be in good shape with pine plywood. For minimizing weight, maybe use 1/2" plywood, and then double-thick the front baffle (which really won't be all that much heavier because the cut-outs will reduce its weight).

Yup. Internal bracing on small cabs with good, glued and screwed joints is a waste. But, a heavy baffle board is almost a must.

 

[BogeyBass]

Too much reliance on box programs here. When you finish, check your tuning by using the signal generator on your program and slowly sweep back and forth until the point of least excursion. Wear ear plugs for this! A flashlight may help too. Just only one example of how it is necessary to think of these programs as a rough guide.

I agree to a point. Box programs are not much more than spreed sheets with nice graphics. Just like any spreed sheet will save you a lot of time and painful math to get in the ballpark.
Which is why I will give myself a error factor. Say the program says 11.5 inches for the ports. I will subtract and add 1inch to that measurement to see where the range will fall.
Likewise with volume I will look at the enclosure minus and plus .5 cubic feet. and include the Minus and Plus 1inch port length to that too. Then make a quick graph including all those error factors. To get a real idea where the tuning will fall.
Likewise the only real way to know is to test with a Oscillator.
But depending on what type of test equipment you have ,if at all. So if you dont have test equipment, and you factor in a large error factor. The model will still show you and be close enough to guarantee you a good box.


So depending of course on cabinet volume, lower cone excursion is found by going 5 to 7hz above the drivers Fs and more cone excursion will be found by going 5 to 7hz below the Fs.

so in general I tend to be happy if i'm getting 5 to 7hz above Fs
when looking at error factors. Of course with the main goal and calculations being made for the actual wanted numbers.

 

[billfitzmaurice]

Yup. Internal bracing on small cabs with good, glued and screwed joints is a waste. But, a heavy baffle board is almost a must.

I never use thicker than 1/2" unless it's with a 20 plus pound driver. And then it's only so that there's enough material there to hold screws. High mass is for hi-fi cabs that never have to be moved.

 

[LowGrowl]

not sure what your dimensions are but 12" seems long. Should be able to shorten that.I'm going over the math for my 21 x 18 x 16.5
remember that if you make your own port or use pre made plastic ones there is 1/2 inch depth to the baffle, so you can remove 1/2 from your length to calculate how close it is to a rear wall. Since the port would be mounted to the front and includes the depth of the baffle.

minus the front and rear baffle and a 1" set back = 14.5"
for the sides minus 1/2" inch for both sides.

so internal dimensions should be 20x17x14.5 for 2.853 cubic feet

the driver is .049 cubic feet

and assuming 4x3" round ports at 11inches would be .147

.049 driver + .176 port = .225

2.853 cubic feet - .225 = 2.628 cubic feet

so using 11 to 12 inch port should put you around 45 to 46hz Fb



thinking 11.5 inch port would be fine and with 14.5 inches of actual cabinet depth. There should be 3.5 inches of clearance.

Even if you went to a 10 inch length port you would still be around 44hz. and in general without sticking to a hard core perfect alignment we are looking to be 5 to 7Hz above Fs of the driver which is 37hz.

The design I showed could work for many 12" drivers

round ports just add to the cost because you need to buy the flared plastic inserts. Otherwise you just cut the openings and screw them in. They seem to be more complicated, but to me seem rather simple. And the performance out weighs the cost. I dont care to mud wrestle today.
But 4x flared round ports, placed symmetrical and closely to the driver will be the most accurate and best performing port you can build.

Thank you bogey... very close to what the program is coming with. 2.5cuft internal volume and 42hz tunning in this case.

 

[LowGrowl]

I agree to a point. Box programs are not much more than spreed sheets with nice graphics. Just like any spreed sheet will save you a lot of time and painful math to get in the ballpark.
Which is why I will give myself a error factor. Say the program says 11.5 inches for the ports. I will subtract and add 1inch to that measurement to see where the range will fall.
Likewise with volume I will look at the enclosure minus and plus .5 cubic feet. and include the Minus and Plus 1inch port length to that too. Then make a quick graph including all those error factors. To get a real idea where the tuning will fall.
Likewise the only real way to know is to test with a Oscillator.
But depending on what type of test equipment you have ,if at all. So if you dont have test equipment, and you factor in a large error factor. The model will still show you and be close enough to guarantee you a good box.


So depending of course on cabinet volume, lower cone excursion is found by going 5 to 7hz above the drivers Fs and more cone excursion will be found by going 5 to 7hz below the Fs.

so in general I tend to be happy if i'm getting 5 to 7hz above Fs
when looking at error factors. Of course with the main goal and calculations being made for the actual wanted numbers.

Agree! I will build the cab to this point with almost all of your recos... Then i will have something to test!

 

[LowGrowl]

Ok Taking Bassbox pro as a reference (is the only reference I have cause this is my firts build) :

With the same box dimensions (2.5cuft) the suggested fb is 40.7Hz for an F3 of 53.4Hz with 4x3" vents (in this case 71mm is what i found in my local home depot). The vents lenght would be 12.3"
Now.. Increasing the fb to 44hz led to a f3 of 53.1 hz with 9.7" long vents

I think we have a winner!

Also the graphs look all the same between both designs

Ray

 

[will33]

The 44hz tuning will work just fine in that design. Unless somebody notices any other glitches, I'd say it's ok to make with the sawdust.

 

[will33]

You gonna build a mid subchamber into one of the cabs? If so, allow for the volume occupied by that and build that cab slightly taller so your woofers end up in equal space. Doing a separate topbox for one is fine too. The crossover for it should be designed specific to the driver used....that's the most complicated part for most of us. You coukd do that as a later add-on and run your 12's full range 'til then.

 

[LowGrowl]

You gonna build a mid subchamber into one of the cabs? If so, allow for the volume occupied by that and build that cab slightly taller so your woofers end up in equal space. Doing a separate topbox for one is fine too. The crossover for it should be designed specific to the driver used....that's the most complicated part for most of us. You coukd do that as a later add-on and run your 12's full range 'til then.

That sub-chamber is a possibility, other could be to use a colsed back driver... I'll get into that later....

 

[LowGrowl]

OK... here a few looks of the first cab

Just a box with some bracing

Front Pannel ready...

View of the baffle...

More to come...

 

[BogeyBass]

holy ####!! you dont waste much time do you!

are you still going to do the strips for the false front?

 

[LowGrowl]

holy ####!! you dont waste much time do you!

are you still going to do the strips for the false front?

I think I dont have room for that. In order to make the internal volume slightly bigger i moved the baffle to the front. So i only have 3/4" for a frame or grill or whatever I can found to protect the speaker.

Duratex coating has arrived also. I may have this ready to try at a gig this saturday

Ray

 

[billfitzmaurice]

The panels could vibrate a lot. IME if you must use spline braces they should be at least 3 inches deep to adequately stiffen panels of that size. And IME only use spline braces where cross braces can't be.

 

[will33]

Ya, I'd run a stick of crossbrace top to bottom and side to side. There really isn't room for front to back sticks thst wouldn't be fairly close to the corners, so I'd add a couple more splines to the back wall. This would only amount to a few cubic inches and wouldn't throw off your design enough to notice, the stiff box will be worth it. If you're concerned about shrinking it too much, swiss-cheese the splines.