No compromises front loaded double 18” cab

Peter Morris said:
On paper the 9000 and 9601 look similar. Same power, Fs, similar Qt, slightly different Vas but the Voice Coil construction is quite different and I suspect the 9601 will behave better when you drive them hard.

Have you compared them in any detail?
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No hands on only theory :)~:-)~:smile:

If split winding technology of 18sound does the same as B&Cs SW technology , then yes this driver might be something, dont know if there is a Voice Coil mag test already.
The 9601 also has demodulation ring like both SWs from B&C, but the 9601 is the most expensive driver between the three ( at least for me ).

Another argument for B&C is, that they seem to get it right with the first attempt :)~:-)~:smile: .

Overall the better the motor the more useful are standard ( not LEAP 5 ) simulation programs IMO.


Uwe
 
Re: No compromises front loaded double 18” cab

" I did run the 18xl1600 and it created kind of a big bump at the bottom, I am not sure that I like this. I could play with the size of the box but I am growing attached to the size of the box I am looking at for logistical reasons. "

Interesting the 1600 looked better then the 115 when I did it. But my box is just under 12 cubic feet.
 
Re: No compromises front loaded double 18” cab

Luke Robinson said:
I did run the 18xl1600 and it created kind of a big bump at the bottom, I am not sure that I like this. I could play with the size of the box but I am growing attached to the size of the box I am looking at for logistical reasons. I did not look at the TBW but I suppose I should.

Power is another discussion. I am looking at amps now. Up until now I have been using mostly QSC. Short of running everything bridged (not my favorite way of doing things), It looks like I am going to have to take a look at other manufacturers to get the power that these beasts are going to demand. So it seems like either the Powersoft k20, or Lab Gruppen FP14000 are the contenders.

Does anyone have any opinions as to why one may be better than the other? I may find myself running either at 2 ohms from time to time. On Paper the K20 is the front runner, the power rating is higher, and it takes up half the rack space. My price on both is close enough that price is not a big factor.
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Before you can look at output power, you should look how much power you can get into the amps.

Here in Germany we have aproximately 4kW long term input power for single phase 230V/16A feed ( which I can get everywhere ).
My rule of thumb is to expect about 8kW short term output power for sub application ( still music, not welding ), if the amp is class D, has high efficiency and PFC.

For 2 Ohm operation ( if the amp supports this ) these 8kW are diminished, because efficiency goes down, and are distributed over 8 drivers ( 8 Ohm each ).
For me the conclusion was to buy amps optimized for 4 Ohm operation and at a prize, where I can buy two for the prize of one big boy amp.

As I understand the power distribution in USA presents you an even more difficult task

Uwe
 
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Re: No compromises front loaded double 18” cab

Luke Robinson said:
Interesting, I am glad that I came here, I am learning of much. :razz:

I am pretty sure that I am going to split the cab like this, In my prediction software we were looking at a 12" deep port so going this route I guess we are looking at making them 10" to start.
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The closest I've seen to any "rule of thumb" for estimating the length reduction was from a manufacturer specialising in car audio, they suggested to shorten by 1/2 of the height of the port - eg a 22" wide, 4" tall port would be shortened by 2". I suspect that may still be a little simplistic, though better than nothing.

Building a prototype with some facility to get in and cut the port progressively shorter and measuring impedance would be needed to be sure - given your "No Compromises" goal that would seem a worthwhile investment.

HTH,
David.
 
Re: No compromises front loaded double 18” cab

David Morison said:
Building a prototype with some facility to get in and cut the port progressively shorter and measuring impedance would be needed to be sure - given your "No Compromises" goal that would seem a worthwhile investment.

HTH,
David.
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I am definitely building a prototype before going into full production mode.

Here is where I am going to need a little knowledge. What is the process for taking measurements of impedance to optimize the port depth? If I am going to be able to adjust port depth i'll need some way to add or subtract port while keeping the box in tact. I think that I can figure that out, there are a few ideas swimming through my head as I am typing. but is some one can suggest, or link me to a description of the process of port optimization I would be be grateful.
 
Re: No compromises front loaded double 18” cab

Luke Robinson said:
I am definitely building a prototype before going into full production mode.

Here is where I am going to need a little knowledge. What is the process for taking measurements of impedance to optimize the port depth? If I am going to be able to adjust port depth i'll need some way to add or subtract port while keeping the box in tact. I think that I can figure that out, there are a few ideas swimming through my head as I am typing. but is some one can suggest, or link me to a description of the process of port optimization I would be be grateful.
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Just do an impedance curve. Make sure you don't have anything in front of the speaker blocking it ( 10' away should be fine) and try to not have any other noise going on during the measurement (even HVAC noise) Other noises will cause the speaker under test to act as a microphone and produce a voltage back into the impedance rig really screwing with your measurements.

In the "perfect world" the 2 peaks will be equal in height/value. But in reality this is not always achievable and when they get "kinda close" it will be fine.
 
Re: No compromises front loaded double 18” cab

Luke Robinson said:
I am definitely building a prototype before going into full production mode.

Here is where I am going to need a little knowledge. What is the process for taking measurements of impedance to optimize the port depth? If I am going to be able to adjust port depth i'll need some way to add or subtract port while keeping the box in tact. I think that I can figure that out, there are a few ideas swimming through my head as I am typing. but is some one can suggest, or link me to a description of the process of port optimization I would be be grateful.
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Dayton's "Woofer Tester 3" has been one of the more common tools for that, looks like it's been replaced by a slightly more advanced package now though: http://www.parts-express.com/dayton-audio-dats-v2-audio-test-system--390-806
 
Re: No compromises front loaded double 18” cab

Thanks for the diagrams David. Actually I was still suggesting something a little different but the diagrams help. Consider the divider between the upper and lower ports. I'm wondering if the presence of the lower port, and it's air movement, acts to essentially extend the divider outwards and forward of the cabinet for the upper port. And vice versa for the other port.

In other words the air moving in and out of a port acts as a boundary for the adjacent port; assuming both upper and lower drivers are fed the same signal and the port air movement is the same.

Conversely if we take the same diagram, and move the two ports to the top and bottom, they don't act on each other or affect each other, at the port exit, since they are not immediately adjacent.

David Morison said:
Art, I think what Michael is suggesting is that the air in the region in red below acts as part of the port air mass, whereas without the central divider, the actual port walls would need extended back to the end of the red region to achieve the same tuning. (If you can excuse the rather basic diagram & description...)
That would be consistent with your first sentence above I think.
Regards,
David.
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Re: No compromises front loaded double 18” cab

Michael Smithers said:
Thanks for the diagrams David. Actually I was still suggesting something a little different but the diagrams help. Consider the divider between the upper and lower ports. I'm wondering if the presence of the lower port, and it's air movement, acts to essentially extend the divider outwards and forward of the cabinet for the upper port. And vice versa for the other port.

In other words the air moving in and out of a port acts as a boundary for the adjacent port; assuming both upper and lower drivers are fed the same signal and the port air movement is the same.

Conversely if we take the same diagram, and move the two ports to the top and bottom, they don't act on each other or affect each other, at the port exit, since they are not immediately adjacent.
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Ah, that's a subtlety I'd missed first time round, sorry.
I honestly don't know, & I'm not sure there's much point guessing.
Put a gun to my head to make me try, I'd imagine that moving air forms less of a boundary than an actual cabinet wall, so any "extra" length from that would be marginal, but that really is just a gut instinct.
Cheers,
David.
 
Re: No compromises front loaded double 18” cab

Time to get to work! I am going to start the prototype today.

I spent some time getting dimensions together and making a cultist, trying to maximize plywood, I should be able to get 2 subs for every 5 sheets of 5x5 Baltic birch here are my cut lists. A few others have expressed interest in the project so hopefully this helps. I am modifying the eighteen sound design with a center divider like some have been discussing here, the front baffle that supports the woofers has been split into two pieces since it will be separated by the center divider anyway. then center divider will com almost all the way to the front to support the grill in the center of the box.

218-Cut-Sheet.jpg218-Cutsheet.jpg
 
Re: No compromises front loaded double 18” cab

Looks similar to something I drew up back in the spring.

45" Width 24" Height 32" Depth

Two separate 6cu.ft. chambers tuned to 35Hz, central triangle ports, designed around the 18TBW100 but would probably work with others in the same class.

I spent a lot of time trying to maximize port area while maintaining reasonable port length.

Dual18TBW100BR.JPG
 
Re: No compromises front loaded double 18” cab

Hey Luke,

Is your plan to divide the cabinet into two enclosures or just extend the center port divider all the way to the back panel? If so, I wonder what that one extended wall does to the port tuning. Based on other posts, seems like it would lengthen it slightly. What's your plan for tuning the port length?

When I have made cabinets in the past, I've routed channels in the mating panels so everything slots into place. A small nail gun tacks the panels in place until the glue dries. Makes for quick and easy assembly without clamps.

Have your simulations given you any sense for how efficient these subs will be?

Ciao
Simon
 
Re: No compromises front loaded double 18” cab

Progress has been made! I cut out everything and have dry fitted the box together, It looks pretty nice, All I have left to do is ports, witch I am trying to figure out how I will be able to adjust the depth on until I Know what I need, I may just make the 10" ports to start and assemble the box entirely with glue, but only screw in the ports in so that I can get in and remove them to adjust length.

Simon, I am dividing the box in two with the center divider that is between the ports. I am not too sure about efficiency, but that was not the greatest concern to me. I did the simulation on a friends PC. I need to get a cheap used laptop so that I can go back to it, and to use the Dayton testing device that came in the mail a few days ago. I am all Mac and Paralells was not running the software too well....

Here are some pics of day one of construction

I found it easiest for my baffle design to cut some blanks out of cardboard to lay them out on the plywood, I roughed them out with a saber saw, and then made a jig for the table saw to cut the angles. The last shot just shows the lap joints that are used all over the box for a better seal.

218 sub1.jpg218 sub2.jpg218 sub3.jpg218 sub4.jpg218 sub5.jpg
 
Re: No compromises front loaded double 18” cab

Nice build. Glad to see things moving smoothly for the most part.

You also might want to call & check availability of recone kits for your current driver contenders - for just-in-case reasons.

Cheers,
Justin
 
Re: No compromises front loaded double 18” cab

Hey Luke,

Nice work on the build.

I'm curious about the port design. Based on the link posted earlier in this thread that related aerodynamic theory and especially boundary layer friction to high power port design, your port with the different cross sections top, middle and bottom may not behave consistently. Since the boundary layer is going to affect the narrow center section of the port much more so than the top and bottom, I wonder if the ports effective tuning is going to shift upwards with power. Probably all ports exhibit a change in effective tuning at different air velocities, but this design may exaggerate that behavior.

I'm curious what your testing reveals, but a pencil sketch on napkin application of the theory indicates the best port cross section for a high power application is a circle, as it has the least surface area for a given internal area.

In either case, nice woodworking. Let us know how they perform.

Ciao
Simon
 
Re: No compromises front loaded double 18” cab

Thanks,

I have one glued up now, and I cut out the port pieces, one set of test drivers arrived today, and I am waiting on the other. IIhave been bombarded with work this week, but I hope to have some time next week to play with drivers and tuning.

I will certainly update when I make more progress.
 


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