No compromises front loaded double 18” cab

Re: No compromises front loaded double 18” cab

David Morison said:
Forgive me if I'm missing something here, but you seem to have increased the port area quite a lot without any corresponding increase in length?
I'm sure there will be some extra effective length from having the ports built in along the box walls; will that be enough to keep the tuning the same do you think? If so, do you have any firm way of calculating that please? The closest I've seen seems to be more of a rough rule of thumb but I've yet to see anything more concrete. I'm not even sure how easily that rule of thumb could translate to triangular ports.

Many thanks,
David.
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The numbers on B&C graph are for one box - Here is their original suggested design for the 21SW150
 

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Re: No compromises front loaded double 18” cab

Evan Kirkendall said:
I got bored this week and started working on my own "no compromises" front loaded double 18. I've got some d&b B2's, but the price is just too much to justify the number of boxes I need. So, I got to work and finished the first prototype today. The raw response came out pretty nice- -6 @ 35hz completely unprocessed, and gobs of output. Guess I'll be spending some time in my shop making more sawdust soon! :)



Evan
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You have the right drivers to build a very close cousin to the D&B B2.
 
Re: No compromises front loaded double 18” cab

I whipped up Peter's design in Sketchup.

I made a few assumptions that I'm hoping can be confirmed.
- 18mm ply
- all dimensions are external measurements, with the exception of the noted port dimensions...

I also attached a design for a single 21SW152, 30"x24"x30", using round ports.

(If any mods feel we are straying too far, I can take this to another thread)
 

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Re: No compromises front loaded double 18” cab

Spenser Hamilton said:
I whipped up Peter's design in Sketchup.

I made a few assumptions that I'm hoping can be confirmed.
- 18mm ply
- all dimensions are external measurements, with the exception of the noted port dimensions...

I also attached a design for a single 21SW152, 30"x24"x30", using round ports.

(If any mods feel we are straying too far, I can take this to another thread)
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yes thats correct ... and best of all I can use your picture to give to my friend who is promising to build me this design to go with my DIY mid-hi

It does however need some extra bracking not shown on my quick ugly plan.

THANKS ,,, fantastic.

Back on topic - I have been wondering how Luke is going with his boxes ????
 
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Re: No compromises front loaded double 18” cab

Glad I can help. I'd recommend checking out the thread on Art's Dual Lab 12 cabinet, the port design could be a handy reference when figuring out how to attach a grill to your cabinet.

PM me your email address and I can send the sketchup file, very handy tool for visualizing different cab designs.

Also looking forward to a report from Luke.
 
Re: No compromises front loaded double 18” cab

As a casual reader of this I'd like to ask a question about having four ports - why? I'd assume it has something to do with larger volumes of air with the same tuning, right?

On my list of things to do is tear apart all the beat up old subs I can find as well as properly educate myself of loudspeaker design, but until then I'll have to ask silly questions like above.
 
Re: No compromises front loaded double 18” cab

Max Warasila said:
As a casual reader of this I'd like to ask a question about having four ports - why? I'd assume it has something to do with larger volumes of air with the same tuning, right?

On my list of things to do is tear apart all the beat up old subs I can find as well as properly educate myself of loudspeaker design, but until then I'll have to ask silly questions like above.
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In as laymen of terms as possible, modern drivers require cabinet porting that can sustain the large amount of air being moved. A lot of guys have stuck modern drivers in classic designs only to be disappointed by the marginal performance increase, the ports become the bottleneck in the cabinet performance.
 
Re: No compromises front loaded double 18” cab

Spenser Hamilton said:
In as laymen of terms as possible, modern drivers require cabinet porting that can sustain the large amount of air being moved. A lot of guys have stuck modern drivers in classic designs only to be disappointed by the marginal performance increase, the ports become the bottleneck in the cabinet performance.
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Thank you, Spenser. While it's on my mind, is there any reason why it might be advisable to choke the air flow in a port? I know I'm asking for simple answers to complex questions, which is the worst thing to do here, but I promise I'll learn the details someday.
 
Re: No compromises front loaded double 18” cab

Max Warasila said:
Thank you, Spenser. While it's on my mind, is there any reason why it might be advisable to choke the air flow in a port? I know I'm asking for simple answers to complex questions, which is the worst thing to do here, but I promise I'll learn the details someday.
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Just to add a bit more - in this case the 4 ports also brace the side walls and reduce losses due to the cabinet flexing. It also one of the few ways to get the port size need into a box with this frontal area.
 
Re: No compromises front loaded double 18” cab

Almost 2 months later, and I'm coming down the home stretch! 16 cabinets didn't seem THAT bad on paper, but good lord I'm tired! Working on putting the grills on this week, finally have 4 finished! I'm very happy with the final results! They're getting powered with Lab Gruppen PLM20000's. Can't wait to get them all out on a gig! :)
 

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Re: No compromises front loaded double 18” cab

Bennett Prescott said:
Hey Luke,

.... if everything was true to simulation life would be a lot easier. The good designers are good because they have built a lot of bad cabinets and learned to modify expectations and simulations to meet reality.
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I don't know how this pearl got past me earlier.

However many lines of code in any given model it is always short. Throw in the emotional and intangible inputs of cosmetics and brand history and we have quite a stew.
 
Re: No compromises front loaded double 18” cab

I am very interested in what you gentlemen use for wire and insulation inside
Also grill fit and finish. .
 
Re: No compromises front loaded double 18” cab

John,

Generally bass reflex subs do not use insulation inside, as it cuts output level down, and since subs are low-passed, there are no upper frequencies coming out of the ports needing to be absorbed.

Wire should be stranded 14 AGW (or thicker) and tied to the speaker frame and stapled to the cabinet interior to avoid flex failure and rattling.

I prefer to use speaker cloth stretched over a plywood frame, Evan is using perforated steel with an expanded foam backing.

Art
 
Re: No compromises front loaded double 18” cab

Just my little diy tip.

A lot of people like to seam seal the inside with latex or silicone caulk. That be a bit of a bear after the cabinet is built. You don't always have good access inside to put a caulk gun into the corners.

I like to use latex house paint. I'll buy the "mess up" cans at the hardware store where they screwed up the color somehow. This is cheap, and often times it's some shade of grey anyway. I will then pour it into the cab about a cup at a time and position the cab so that the paint runs down the corners and fills every little nook and cranny. Pour some in, run it around the corners and let it dry. It works great and prevents air leaks.....
 
Re: No compromises front loaded double 18” cab

So nothing at all inside?
Odd but hey..just not used to it
Wire is wire at that volume I suppose
Grills are a stickler. .
 
Re: No compromises front loaded double 18” cab

I used perforated sheet metal and found a local supplier to powder coat it.Iit is a very tough finish and so far no chips on the gills. I got Undercover to make me covers for the subs, and decided to attach wheels to the back with quick release hardware from Penn-Elcom in the case that I need to remove the wheels for packing. The 12 subs are holding up well and have done their fair share of shows. so far all of the band engineers that have used them have been quite pleased. I am thinking of building some more over this winter.
 
Re: No compromises front loaded double 18” cab

Luke Robinson said:
I used perforated sheet metal and found a local supplier to powder coat it.Iit is a very tough finish and so far no chips on the gills. I got Undercover to make me covers for the subs, and decided to attach wheels to the back with quick release hardware from Penn-Elcom in the case that I need to remove the wheels for packing. The 12 subs are holding up well and have done their fair share of shows. so far all of the band engineers that have used them have been quite pleased. I am thinking of building some more over this winter.
Click to expand...

Never did get finished pics! :)

PS- My cabs have some internal stuffing.


Evan
 
Re: No compromises front loaded double 18” cab

Penn is the only ones up here that have grills.... they cut but not bend
Maybe I dont need them bent...good blocks and screws..

I always thought that a little non fiberglass insulation or dacron was always added to cabinets
I got 12 Precision Device PD186 coming around start of December.
Love the clair 218 look so I will go with that look.. (there same as you gents also)
I notice alot ocf the wheels used are the 3" blue ones....I was curious as they spec at less weight load and are 50% more....adds up when purchasing 50-75 of them..iwas going to mount them on the back..I was a little concered about rattling.
My boxes will be very inert as I believe in that!!
I have 6-10 double 18 And 6 single 24" to build plus 8-12 tops/monitors (15" & horn)
 
Re: No compromises front loaded double 18” cab

So I've been doing all sorts of math for this box today (since I'm building a variation on it to compliment the DIY Mid Hi) and I've been having a super difficult time determining why the standard math doesn't work for this box. Every calculator, program - hell even my own calculations by hand - say that two ports with an area of 43.5 square inches each should be 25" long for a 32Hz tuning. However, every design I've seen like this has a port length more along the lines of 10", which is what the calculations say would work correctly for a single port.

What gives? What magical formula lets the effective port length for boxes of this type to be around 10", despite all math and reason? Even if the math is done for a single port, the length is ridiculous - 28"! I'm sorely confused at this point.
 
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