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[Bill Hornibrook]

Hi guys. This is a driver I've been interested in ever since it first came out. With my life almost completely shut down, now's the time to do something about it I guess.

I've built boxes in the past (most recently sub boxes for it's big brother 21SW152 - which came out very well) but mostly from plans. I'm not a designer.

B&C's recommended enclosure for this 18 is 3.53 cubic feet tuned to 40Hz. That I'm keeping. This is the reason I want to try this driver out.

They used that recommended box for their frequency response curve combined with a port 9 1/3 inches long and an area of 31 square inches. That gives a nice flat response at 1W/1m, but it's awfully small - and of course I'm going to be pushing it a lot harder than that. So I'm thinking that maybe I need a larger port? Here are the T/S parameters if any of you want to give this a go.

Resonance Frequency:                                       30hz
Re                                                                    5 ohms
Qes                                                                  .21
Qms                                                                 4.3
Qts                                                                     .2
Vas                                                                     5.93 cubic feet
Sd                                                                   187.55 cubic inches
No                                                                   2.2%
Xmax                                                               16.5mm
Xvar                                                                 14mm
Mms                                                                330g
BI                                                                   39Txm
Le                                                                   3.85mH
EBP                                                                 142Hz

If any of you have any curiosity about these drivers, I am building these - one way or another. And I'll let you know how they came out. I am in clubs every week, and their unique combination of size, power handling, and punch means they'll get used a lot. Here's a link to the driver:

https://www.bcspeakers.com/en/products/lf-driver/18-0/8/18ds115-8

And thanks to anyone who may want to help me out!

[Paul G. OBrien]

B&C's recommended enclosure for this 18 is 3.53 cubic feet tuned to 40Hz. That I'm keeping. This is the reason I want to try this driver out.

They used that recommended box for their frequency response curve, with a port 9 1/3 inches long with an area of 31 square inches. That gives a nice flat response at 1W/1m, but of course I'm going to be pushing it a lot harder than that. So I'm thinking that maybe I need a larger port?

Yes that size port is totally inappropriate for the amount of power this driver can handle. Doing a quick simulation in WinISD, at full power port air velocity goes right off the chart, to keep it anywhere close to an acceptable range at 30m/s port area must increase significantly.. my sim says 4"x9"x26" times 2 which will effectively increase total cabinet volume to about 5 cu ft. That is still a very small box with tons of output.

[Bill Hornibrook]

5 cu ft. is fine. Are you saying these ports need to be 26" long? Is there a compromise that gets me partially there? And thanks for your response Paul.

[Chris Grimshaw]

Longer port = lower tuning
Wider port = higher tuning, but also lower air velocity

Remember that you can safely fold the 26" long port. Along the bottom panel and up the back, for example, would be fine.

Chris

[Art Welter]

5 cu ft. is fine. Are you saying these ports need to be 26" long? Is there a compromise that gets me partially there?

Paul's suggested ports total around 1.1 cubic feet.

Increasing the net cabinet from 3.5 to 4.5 cubic feet would reduce the port length to around 17.5" with the same 40Hz Fb, reducing the port volume to .73 cubic feet, for a gross cabinet increase of only .77 cubic feet. LF output will increase slightly with the larger net size.

Although dual ports will chuff slightly more than a single of the same area, locating ports on diagonal corners creates a "chimney effect", as heat rises it escapes through the upper port, regardless of cabinet orientation.

Art

[Bill Hornibrook]

Yeah that 4.5 box looks really good Art - well within the size range I'm thinking about. Port chuff is not an issue in clubs - not at the levels I'm at anyway.

Although I'm a DJ, these will probably not get pushed really hard all that often - certainly not to the full potential of the drivers. For big gigs I have the B&C 21s. The cabs these new ones will be replacing are quite large and loaded with older B&C 18s- I believe a predecessor to the NW100s. They don't have quite the low end I'm comfortable with, and they're a bit of a pain to move by myself.

Power amp will be Peavey IPR27500 - which has served me well with the 21's for over five years now.

Thank you Art and Paul for your efforts on my behalf I'm going to start working up designs for that 4.5 box tonight.

[Paul G. OBrien]

Remember that you can safely fold the 26" long port. Along the bottom panel and up the back, for example, would be fine.

Yeah that was my thought when I ran the sim.

Bill.. Remember that these box and port volumes are internal and you have to factor in wood thickness to arrive at the correct panel sizes to maintain those volumes.

[Bill Hornibrook]

Well noted Paul. I'm working up a rough work-up adding in plywood thickness, driver displacement, and internal bracing. And of course the port. I'm planning on tying all walls together. There's bound to be enormous internal pressure in a box this small.

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