B&C 18SW100 - ported PA sub

DJSteve

Member
2016-04-06 8:31 pm
Does anyone have any experience with this driver, or general thoughts/guidance on using it as a replacement in a 6.0 cu ft (170 L) ported box? I plugged the T/S info into an old version of WinISD and it seems like a pretty good fit, however would appreciate hearing more experienced opinions before dropping $800 on a pair of drivers.

The box it's going into is a B-52 ACT-18s. They originally came loaded with Selenium 18SW2P but the driver B-52 has for replacement now is something different (I suspect proprietary made by Celestion). The drivers have caused some issues, mainly with glue failures, but the boxes themselves are well built and in good shape... we like the form factor of the trapezoid cabinet with tilt back wheels, so considering the possibility of upgrading the guts instead of replacing the entire cabinets.

The box appears to be currently tuned to about 36hz (three 4" diameter x 10" length port tubes). WinISD shows vent mach of 0.04 and they are flared on the outside end, but that seems to not use xmax in its calculation... I've been told going to the longer xmax B&C driver may really need bigger port area--any thoughts on that? Being a trapezoid box, corner ports are going to be somewhat difficult due to geometry, and I have somewhat limited space to increase diameter+length of what's there.
Selenium is 6.5mm Xmax / 21mm Xlim
B&C 18SW100 is 12.7mm Xmax / 28.5mm Xlim

We normally run a pair of these with a PLX3602 bridged mono... we're careful to avoid clipping but even so we're driving them fairly hard and I have some suspicion that may be a factor in the glue failures. It seemed like the 18sw100 would give us some additional output + low frequency extension and significantly better power handling than we have now without having to buy new or build from scratch... while also ending up with some pretty stout drivers to play with when/if I wanted to experiment with building new boxes.
 
Hi All,

FYI:Comparing Selenium 18SW2P versus B&C 18SW100.

b:)
 

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The PLX is a fine amp, but not very good with bass. When doing bridge with one 4 Ohm load attached, its driven very hard and will run out of steam. If you want to use this much power in bass, get another amp.

Port area: The more air you have to put through it in the same amount of time, the more area you need. Changing speakers to much more xmax will require bigger ports, unlesse they were very big from the beginning.

the 18SW100 is one of the finest driver for the money it costs and outperforms many other 18S with similar specs. You have to simulate if it will fit your cab.

I´d try to rent another amp and see what changes first.
 

DJSteve

Member
2016-04-06 8:31 pm
Thanks for running all that analysis and putting together the fancy report. Graphs all look pretty similar to what I was seeing but you show your work and I just trust what WinISD spits out. :)

Doing ports on the sides of the cabinet is an interesting idea, but probably not the most practical for the way we use them. We normally run these in sets of 2 or 4 side by side centered on the dance floor (for multiple reasons--acoustic coupling gains, acting more as a point source to avoid cancellation, and length/ease of running speaker cable) so if we put ports in the side at least one per cabinet would effectively be blocked off. If increasing port size, I think it would be easiest to do it on the front of the cabinet. The ports that are there now are 4" ID but have flares on the front--these could relatively easily be increased to 5"-6" ID. Probably can get up to about 16" length without major modifications, though depending on length/diameter may need some angle to keep from hitting the sides.

From a theoretical and/or practical standpoint, is there any reason all ports need to be the same diameter? If not, how do you decide on port length--figure total cross section area and cut all the same length? Or would length be a function of individual port diameter?

If there aren't reasons that make it a bad idea, a couple thoughts I had were to possibly upsize the center port while leaving the other two 4", and/or add additional smaller ports in the top corners. The secondary motivation for considering the top corners is air circulation, as it seems like having ports at the top would allow heat to escape more readily than the current setup. Not sure how much difference it would actually make, but something that occurred to me while looking at different speaker designs while having glue failure issues fresh in my mind...

Thanks for the help so far! I guess one question that I didn't explicitly ask in my original post--are there other drivers I should be considering instead of the 18SW100 for this application? It seemed like the most natural fit of anything I modeled, however I didn't perform an exhaustive search.
 

DJSteve

Member
2016-04-06 8:31 pm
The PLX is a fine amp, but not very good with bass. When doing bridge with one 4 Ohm load attached, its driven very hard and will run out of steam. If you want to use this much power in bass, get another amp.

To perhaps clarify, the motivation for this upgrade is not really that we need/want more output as it is about longevity. We've had issues with glue between magnet and front plate failing so magnet/pole piece moves down and pinches voice coil, one where the fabric spider started to fail (crack/tear possibly just due to age) and one where the spider came loose from the cone/voice coil. So I'm mainly looking for a higher quality replacement driver... and if we can gain some output in the process that's not a bad bonus.

The biggest thing we've noticed about the PLX amps is it seems like they are quite sensitive to power input voltage. Running off a 50A 240V distro where the voltage never dips below 120 you can melt faces; the same system running off 120v outlets on the end of long extension cord or a building with crappy wiring and you wonder what's wrong. Perhaps we give up some performance compared to a transformer amp or a higher end switcher, but that's a compromise we're willing to make to be able to pick up an amp rack without throwing your back out or tying up a bunch more money.
 
1)From a theoretical and/or practical standpoint, is there any reason all ports need to be the same diameter?
2)If not, how do you decide on port length--figure total cross section area and cut all the same length?
3)Or would length be a function of individual port diameter?
4) I guess one question that I didn't explicitly ask in my original post--are there other drivers I should be considering instead of the 18SW100 for this application?
Steve,

1)No.
2)Yes. Remember to reduce port volume from box volume when estimating Fb.
3)No.
4)The B&C 18TBW100 would be a good alternative, cheaper, but heavier.

Art
 

DJSteve

Member
2016-04-06 8:31 pm
Thanks, Art. I think my plan will probably be to try it out as-is first, then enlarge the center port and/or add ports to the upper corners to increase the area.

As far as driver, it looks like the 18TBW100 is basically identical to the 18SW100 except the magnet / motor structure? Are there reasons to choose one over the other (either in this application or others) besides the cost/weight tradeoff? It looks like the TBW models slightly more gain but the SW specs 1db higher sensitivity... which in theory would still make the SW louder, but I'm guessing in the real world with other factors at play it's really about the same either way?
 
1)As far as driver, it looks like the 18TBW100 is basically identical to the 18SW100 except the magnet / motor structure?
2)Are there reasons to choose one over the other (either in this application or others) besides the cost/weight tradeoff?
3)It looks like the TBW models slightly more gain but the SW specs 1db higher sensitivity... which in theory would still make the SW louder, but I'm guessing in the real world with other factors at play it's really about the same either way?
1) Yes, neo vs ceramic magnet is the primary difference.
2) The TBW has a 2 Hz lower FS, and heavier cone. Heavier cones hold up to horn loading better, less distortion. In your BR application probably little difference, other than the heavier cone is a dB less sensitive.
3) Pretty much a financial/weight choice, audibly very little difference.

Going to the larger (15.5 cubic feet gross) Keystone tapped horn design would be more than 6 dB more efficient than the BR, from a financial standpoint that means only half the drivers and power amps required for the same output.

Art
 

DJSteve

Member
2016-04-06 8:31 pm
I just went ahead and pulled the trigger on a 18SW100. Figured for ~$45 I might as well save 10 lbs. Just got one for now--this way I can try it and see how it sounds before completely committing... and can also use another coupon code on the second one to save a bit of cash.

I've seen/read some stuff on the Keystone and am definitely intrigued. Unfortunately I don't really have time to tackle building cabinets from scratch right now, but may give it a shot once things slow down a bit. If I have a driver that can be used both ways, that obviously lowers the barriers to trying it out. :)

Thanks Art and everyone else for the help / input! I'll try to update once the speaker gets here and I'm able to try it out.