B&C Sub designs

K

Kip Conner

Junior
Mar 13, 2011
370
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Athens, GA
I'm going to be auditioning some of the B&C designs from their website with a carpenter/audio engineer buddy of mine. This guy is great with all things wood and is very knowledgable about lumber sources. I told him the plans called for 3/4" (18mm) Birch Ply. He tells me that there are several grades to choose from and that they numbered or lettered that show their level of quality.

What are you guys using?

I'm going to be starting with a modified version of the S18BN Single 18" cabinet. The real mod will be to loose the bottom angle cuts where the castors go and build some dollies for transport. We're also going to add some battons to some of the edges to increase the strength. Essentially where we gain volume, we are going to lose with the extra bracing.

i currently have the drivers in some OAP LF118 boxes and I'm getting some port choking so I need to try to something else.
 
Re: B&C Sub designs

Kip,

The baltic birch plywood grades refer to the presentability of the surface veneer layer. It does not reflect upon the structural integrity of the product. The grade should be essentially irrelevant for building pro sound subwoofers that will presumably be coated with something thick and black.

As far as trying that design to get away from port choking that you see in your current cabinets loaded with SW115 drivers, I would be a little circumspect. The port area in that design is around 265 sq cm. The Sd of an 18" driver is around 1200 sq cm. Additionally the port is not flared in any way. Finally the SW115 is a monster of a driver capable of a real serious amount of excursion (xvar is 16mm). I know only a little about this subject (having learned some from being around the forums here) but would bet that an 18SW115 driven hard in a cabinet with a port area around 21% of the driver Sd will suffer from significant port compression to the extent that if you were driving a great driver like that with enough power to approach its limits you will have enough port compression that your performance will be closer to that of a sealed box. With a lesser driver it would be less of an issue but with a top notch driver like that I think you will find you are wasting a fair bit of it's performance advantage due to port compression.

Port area up to 80% of driver Sd has been recommended and you might be in decent shape at 40% to 50% of Sd especially if the port is flared. But a straight profile port with only 21% of the area of Sd using that driver isn't going to give you the results you are looking for. I would refer you to Phil Graham's article on subwoofer port behavior here PASSBAND, llc | Articles which is essentially my only source of knowledge on this subject (along with getting some help from Phil in the past on designing a reflex enclosure to help minimize port compression problems). Phil or others please chime in and correct me where I might be wrong since I am certainly no expert.

Best luck,
Loren Jones

Kip Conner said:
I'm going to be auditioning some of the B&C designs from their website with a carpenter/audio engineer buddy of mine. This guy is great with all things wood and is very knowledgable about lumber sources. I told him the plans called for 3/4" (18mm) Birch Ply. He tells me that there are several grades to choose from and that they numbered or lettered that show their level of quality.

What are you guys using?

I'm going to be starting with a modified version of the S18BN Single 18" cabinet. The real mod will be to loose the bottom angle cuts where the castors go and build some dollies for transport. We're also going to add some battons to some of the edges to increase the strength. Essentially where we gain volume, we are going to lose with the extra bracing.

i currently have the drivers in some OAP LF118 boxes and I'm getting some port choking so I need to try to something else.
Click to expand...
 
Re: B&C Sub designs

The drivers that I actually have on hand are TBW100, that is what we loaded into the LF118 cabs. I consulted with Bennett (he's the B&C rep and board moderator) and while there are no other plans specific to these drivers the closest seems to be the SW115 in a cabinet design. I'm not 100% sold on the design, I just haven't found another that yet to try. The TBW100 is a brand new driver on the B&C line and I'm sending roughly 1600 of it's available 3000 watts.

Thanks for the tip on the grade. My guy did mention something in regards to smooth sides and what not. I plan to do a sanding and paint so the grade isn't as important as long the sides are true.

This is my introduction into cabinet building so I have a lot to figure out. If there were pre-made cabs out there, I would probably just buy them pre-built! It's a project born out of necessity... not because I want the challenge :)
 
Re: B&C Sub designs

Kip,

Well hopefully some others with more knowledge than I will chime in. The TBW100 is a great driver too with performanc pretty close to SW115 but for a lot less $$. I am pretty sure it would find port compression problems at high output levels as well. I am sure that enclosure on the B&C site will perform well, but on the other hand it isn't hard to keep the net Vb the same and keep Fb the same while designing it with a port area twice as large. The only problem becomes whether the cabinet is then deep enough to accomodate said port.

Loren
 
Re: B&C Sub designs

Kip Conner said:
The drivers that I actually have on hand are TBW100, that is what we loaded into the LF118 cabs. I consulted with Bennett (he's the B&C rep and board moderator) and while there are no other plans specific to these drivers the closest seems to be the SW115 in a cabinet design. I'm not 100% sold on the design, I just haven't found another that yet to try. The TBW100 is a brand new driver on the B&C line and I'm sending roughly 1600 of it's available 3000 watts.

Thanks for the tip on the grade. My guy did mention something in regards to smooth sides and what not. I plan to do a sanding and paint so the grade isn't as important as long the sides are true.

This is my introduction into cabinet building so I have a lot to figure out. If there were pre-made cabs out there, I would probably just buy them pre-built! It's a project born out of necessity... not because I want the challenge :)
Click to expand...

Hi Kip,
I just ordered these exact same drivers for a project. I accidently ordered the 8 ohm version, so I'm hoping to swap them out for 4 ohm before getting started. I plan to build one of Art Welter's Keystone subs (Keystone Sub Using 18,15,&12 Inch Speakers - diyAudio) which he says should compare favorably to Danley TH118. I'm going to try 1 or 2 other designs as well before settling.

As for plywood, Baltic Birch is decidedly best, as you found. Art mentions using Arauco plywood (AraucoPly, MORE THAN JUST A PRETTY FACE - ARAUCO). I've seen this stuff in Menards, and though it's not hardwood, it looks to be void free or close to it. $40/ sheet for 3/4". It's what my first boxes will be made of.

Check out Art's last post in the thread I linked. The SW115 driver will take a lot more than rated power, and the same may be true of the 18TBW100.

Grant
 
Re: B&C Sub designs

Thanks Grant. I too, wanted the 4 ohm version that way I could drive my amps a little harder. The first batch of 4 Ohm TBW100 were much lower than 4 because they were specifically designed for a european audio manufacturer. It's my understanding that those drivers that made it into the U.S. got returned and that another shipment of 4 ohms won't be available until October. My long term plan is to take the four 8 ohm speakers that I have and move those into a double 18 box and just parallel the drivers and have four of the single 4 ohm boxes.
 
Re: B&C Sub designs

I've been reading through that thread over at DIY and that design might not be right for me with the drivers that I currently have on hand. It looks like I would need to get the 4 ohm version of the TBW100 to really get the maximum power out of that airspace. Or rob a bank to purchase a PL380 super amp that would push 5000w at 8ohm... and then roll back the input gain. :)
 
Re: B&C Sub designs

Kip Conner said:
Thanks Grant. I too, wanted the 4 ohm version that way I could drive my amps a little harder. The first batch of 4 Ohm TBW100 were much lower than 4 because they were specifically designed for a european audio manufacturer. It's my understanding that those drivers that made it into the U.S. got returned and that another shipment of 4 ohms won't be available until October. My long term plan is to take the four 8 ohm speakers that I have and move those into a double 18 box and just parallel the drivers and have four of the single 4 ohm boxes.
Click to expand...

I really have no experience with the subs you've picked out, but I will say this.

Build your double 18's with a bit of extra height, so that they are exactly the same as 2 of you singles when stacked. This way you can do 2 single's right next to a double and have a flat surface to put your tops on.

I don't think I've ever seen a home-built, or even a pro manufacturer do this with their single vs dual boxes. It would make a lot of sense, though. I know a bunch of people that own SRX728's and 718's but can't use them together like this, because of the height difference.
 
Re: B&C Sub designs

Yep, my guy and I talked about that scenario. The stacking height was also discussed in terms of times when the top boxes had to be stacked and ratcheted down.
 
Re: B&C Sub designs

Grant Conklin said:
Art mentions using Arauco plywood (AraucoPly, MORE THAN JUST A PRETTY FACE - ARAUCO). I've seen this stuff in Menards, and though it's not hardwood, it looks to be void free or close to it. $40/ sheet for 3/4". It's what my first boxes will be made of.
Click to expand...

+1 on this stuff if you can find it. It is surprisingly good for the price. BB is better, but if you want to save a few $$ or are experimenting, Arauco is not bad at all.
 
Re: B&C Sub designs

Apparently their US office is about 30 min from me in the Atlanta Area, so I would think that it wouldn't be too hard. After some phone calls...

AraucoPly referred me to DixiePly, about 15 min away

DixiePly referred me to Cofer Bros, about 5 min away

Do I dare call them and find out my neighbor has a stack in his garage? :)
 
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Re: B&C Sub designs

Kip Conner said:
I've been reading through that thread over at DIY and that design might not be right for me with the drivers that I currently have on hand. It looks like I would need to get the 4 ohm version of the TBW100 to really get the maximum power out of that airspace. Or rob a bank to purchase a PL380 super amp that would push 5000w at 8ohm... and then roll back the input gain. :)
Click to expand...

Interesting. What about the 8ohm TBW100 makes the keystone design less suitable (I assume you are saying that if you had the 4 ohm version you would find the keystone design would meet your needs better)? Just trying to learn for my own edification. Or said another way, what makes the 8ohm TBW100 in a vented enclosure more tolerable vs 4ohm version of same than the same drivers in the keystone?
 
Re: B&C Sub designs

Although I'm in the middle of a Lab-sub project, I feel a desire for building a sub based on a B&C 21".
For some reason I've had that desire for a couple of years. Totally irrational and unexplainable.

Some day.....

Anybody know of a good design for a B&C 21" that I could drool at?
 
Re: B&C Sub designs

It was mostly based on Art's suggestion on the power behind the speaker in the cabinet. With the 8 ohm version I would only be sending 1600w to each cabinet and it appeared that he suggested that they will handle more. It's a complicated build (for me) and I would hate to not be able to work them to their potential. With the 4 Ohm version by output increases to 3000+ watts per driver as opposed to the 1600 that I have available to send now. As it being less suitable, I would venture to say that's not less suitable. Looks like a fine cabinet design. For me, with the correct box I'm only limited by my power on hand.

After looking at the Keystone Sub Plans I would would have to modify the depth of the box a little to make room for the magnet since the design is factored around a Neo and the TBW100 are ceramic. The TBW100 might fit in there, not sure. Either way I don't want to get into re-engineering that design. Re-working the B&C design makes that one easier to pull off since I'm loosing some of the angled cuts.

For my first attempt at building something, I think the simpler build is for me. I just don't have the real world experience yet.
 
Re: B&C Sub designs

I can't speak to the power issues, but I do agree that having something with simple right angles for a first build makes things a lot more realistic. Best of luck with it either way.
 
Re: B&C Sub designs

Kip, Loren,

Loren Jones said:
As far as trying that design to get away from port choking that you see in your current cabinets loaded with SW115 drivers, I would be a little circumspect. The port area in that design is around 265 sq cm. The Sd of an 18" driver is around 1200 sq cm. Additionally the port is not flared in any way. Finally the SW115 is a monster of a driver capable of a real serious amount of excursion (xvar is 16mm). I know only a little about this subject (having learned some from being around the forums here) but would bet that an 18SW115 driven hard in a cabinet with a port area around 21% of the driver Sd will suffer from significant port compression to the extent that if you were driving a great driver like that with enough power to approach its limits you will have enough port compression that your performance will be closer to that of a sealed box. With a lesser driver it would be less of an issue but with a top notch driver like that I think you will find you are wasting a fair bit of it's performance advantage due to port compression.
Click to expand...

Yes to what Loren says about driver SD vs port area. It should be mentioned that flared porting is its own can of worms, and doesn't change the fundamental Reynolds number issues. It can help shape the vortex effects the port ends. Certain gradual flare profiles popular with the hifi crowd can be detrimental to port behavior at the higher Re in professional audio.

Port area up to 80% of driver Sd has been recommended and you might be in decent shape at 40% to 50% of Sd especially if the port is flared. But a straight profile port with only 21% of the area of Sd using that driver isn't going to give you the results you are looking for. I would refer you to Phil Graham's article on subwoofer port behavior here PASSBAND, llc | Articles which is essentially my only source of knowledge on this subject (along with getting some help from Phil in the past on designing a reflex enclosure to help minimize port compression problems). Phil or others please chime in and correct me where I might be wrong since I am certainly no expert.
Click to expand...

I think the phrase used was "an honest look at the simulations" followed by an immediate caveat that no one would build an 80% of SD port.
 
Re: B&C Sub designs

Also, if you give me the external dimensions of the box your using, along with wood thickness, port size I can tell you whats going on with your current setup. If the faceplate is recessed on your box I need that depth measurement, not the overall depth.


What amp do you have on them right now?
 
Re: B&C Sub designs

Wow, Alan that would be great. Any input on this project would be amazing!

I took the OAP white page and altered it with the internal dimensions and posted an actual pic that shows the port. From the white pages it looks like three ports, but as you can see in the pic those two pieces are really just braces for the face of the box.

I like the outer height of the box since it allows me to stack two of them if I needed to elevate the mid hi boxes. However, the reason for going with single boxes is I like to set the subs up in a cardioid arrangement with one sub behind the other. With the current box size it only takes a little over 6 inches to get the quarter wavelength spacing correct (32 1/4 total distance minus the cabinet depth). I was going to lower the frequency that I am basing my quarter wavelength on and get a little more spacing between the cabinets but the total won't be more than 8"

That being said, going deeper is probably not the thing to do. That leaves going wider with the box which should be no problem.

One thought: is it possible that if I remove that fiberglass batting on the inside it make an improve-able difference? The original design was built around a low powered PAS HL2880c 500w @ 8 driver. They then started putting in a 1200w @ 8 B&C driver (exact model unsure) but did not change anything about the cabinet design.

OAP LF118 with Internals.jpg
 
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