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B&C 21" sub build project (B&C 21SW152)


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This is almost OT for this forum because these cabs will never have live music through them. These days I'm a DJ/karaoke host five nights a week and that's what these subs are for. I DJ for millenials playing contemporary pop, rap and hiphop at high SPLs and nauseating amounts of low end.
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The idea behind building these subs was to get the rough equivalent of my four 18 cabs out of two cabs of similar size so I can get everything in my van and not have to use my F250. I noticed that there were a couple of online places that were heavily discounting these B&Cs, so after taking a nervous gulp I ordered a couple of them from Crispdeals - an outfit based out of Brooklyn that I had never dealt with before - for $535 apiece. Six days later they were on my front doorstep. I'll use these guys again.

If you have never seen these drivers, let me tell you ... they literally take your breath away the first time you lay eyes on then. They're just absolutely the most gorgeous drivers I've ever owned.

OK I'm going to lose at least half of this forum right here. What you see in the next shots are all the tools I used to make these cabs.
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The plywood is 3/4" five ply flooring that I picked up at Home Depot for $22 a sheet.

OK I just lost the other half of the forum. I guess I'll just talk to myself from now on biggrin.gif

B&C's recommended enclosure volume for this driver (their exact wording) is 6.71 cu' coupled to a port with an area of 75 sq" and a length of 19". That's not only what I built, it's why I built. I would not have made them if they were any bigger. I need to be able to move this stuff around by myself.

Although 6.71 cu' is not much, once you start adding things up these cabs get a lot bigger. The driver itself displaces .56 cu'. The port is unusually long. I had to recess the front baffle 2" so the cone wouldn't hit the grille. The cab is also heavily braced. The cab's final dimensions came out to be 31"x26"x23". I really thought I could keep the weight at around 110 pounds but when I was all done they weighed out at 125 pounds apiece! Now I can still handle them, but that's about all I would ever want to move around these days.

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You guys can laugh all you want, but these are really solid cabs.

Carpet hides a multitude of sins biggrin.gif

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Here we are on my deck where I was testing them before taking them out to the club.

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I'm sure some of you (if any are left) may be curious as to cost. Total cost per cab including driver was around $750 before the casters and heavy duty refrigerator feet that I put on the bottoms. I think with that last trip to Home Depot we're up to around $800.

I'm absolutely thrilled with the sound of these guys but I need more power. I'll put more up tomorrow if anyone is interested at all. The real test won't be until this weekend though. That's when I'll need everything they've got.

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$800 per box is a little pricey but if you like the sound and they do the job you need them to do then thumbs up!
Half the fun is in the building and knowing they are exactly what you want. The down size is should you try to sell them they may be a hard sell.
Go easy on your back. Loading them like that may strain yours someday. Think ramps....
Thanks for sharing.
Dookietwo

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Just my jigsaw - very carefully. It's not as pretty as the pic suggests.

I would like better grilles. These are very flimsy - just generic Parts Express. If anyone has any suggestions along those lines I'd really appreciate it.

Oh yeah - this is my last build. I haven't done this in years and I forgot how much time it consumes. I thought I'd be able to knock these cabs off in a couple of days. It's been a month.

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i have the dayton grills from PE and they are very thick, although i do think they are soft metal. the bent edges make them firm. i'm not sure what would be better for you, my subs have a plastic mesh and its been fine.

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The actual distance between the cone and the grille is about 1 1/4" so I think I'm OK. But that was a design mistake. I was originally going to recess the grille but ended up mounting it flush across the whole front of the cab.

The driver is rated at 60mm peak to peak (about 2 3/8") before damage. Power rating is 4000 watts continuous. I don't have an amp anywhere close to that, but I did bridge my Yamaha P7000s and ran just one cab to see what I've got with some sine waves down to 32hz. These are 4 ohm drivers, and that amp must have been putting out close to 2000 watts RMS. At 32hz the driver was cruising right along with no signs of distortion or distress (audibly it was just a pure sine wave!) but I had to discontinue the test because the amp started to smoke.

And I thought you could bridge a P7000s into 4 ohms frown.gif You learn something every day...

So now I'm looking online for power amps. I'm going to get two (one for each cab) so I can run them off of separate circuits. The P7000s is still working and I've been using it. I'm hoping it hangs in there for a few more nights. But these drivers really want to see more than it's 1100 watts per channel anyway. They're just getting started when this amp starts to clip.

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Quote Originally Posted by mrcpro View Post
Power rating is 4000 watts continuous.
No, it's 4000 watts PROGRAM, 2000 watts continuous. I'd stick with a pair of RMX2450's bridged. About $300 each used.

BTW the Yammy P7000 is rated to power a 4 ohm bridged load for 20 milliseconds freak.gif .
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Yeah that's kind of what I'm looking at, among other things. Something that is capable of around 2000 watts RMS bridged at 4 ohms and won't blow up if I run them that way.

The actual phrasing on the B&C spec sheet is continuous power handling 4000 watts, nominal power handling (AES) 2000 watts. I understand what you're saying though wink.gif

Thanks everyone on your suggestions for more robust speaker grilles. I'm going to look into that as soon as I get this power amp situation resolved. I want grilles that are as stiff as the ones on my sets of Yorkville Elites. If they matched that would be even better smile.gif

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Learn what the spec's really mean. 2000 watts is about as much as I would put into that driver, even though it's a 6" VC and double-spider there's still the fatigue factor.

It's more or less 2000 watts "RMS", though even that may be a bit optimistic if you run it into limiters hard. If you don't high pass it, the rating is closer to 1000 watts RMS for mechanical reasons.

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Quote Originally Posted by Harmonycat View Post
So just how much do the finished subs weigh, considering that the woofers weigh just under 41lbs each?
125 pounds. I put 6 fairly heavy spring loaded handles on each, as well as casters. And as I said before, these cabs are heavily braced. But the elephant in the room (literally!) is that 41 pound driver.

Around 2000 watts is what I'm looking at per cab for all kinds of reasons. I've always been careful with my subs, and to this day have only blown one driver in the last 10 years.

Knock on wood.

I just got off work. If you're playing back contemporary dance tracks you can get addicted to what these drivers do really fast. My humble homemade cabs aren't the stars here - it's those B&Cs.
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If you don't high pass it, the rating is closer to 1000 watts RMS for mechanical reasons.

If he doesn't HPF them running 2000w into them he pretty much deserves what happens next, eh? :lol:

 

I assume he'll at least use the 30Hz HPF typically available on the RMX and other amps.

 

To the OP> If you can find them a couple used RMX1850HD's would be ideal as they are designed for continuous heavy loads such as bridged into a 4 ohm sub. It's the same amp as an RMX2450 with the voltage turned down a bit. I suppose bridged RMX4050HD's (turned down RMX5050's) would be "interesting" too for the minute or two the drivers would last :freak: .

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Oh, and BTW a pair of Danley TH118's would BURY those. A single one would have about twice the output of your pair on half the power.

 

 

So would just one McCauley M421 I'm sure. But that's not the point of this whole project. I need to be able to not only *ahem* afford it, but get it around. That was the reason I didn't spring for the Yorkville LS2104. The only thing I was actually considering purchasing if I didn't build these was a pair of SRX 718s.

 

I haven't been highpassing them this week but I haven't been pushing them either. I'll brickwall them at 40hz this weekend in order to get the most I can out of them with that P7000s. 30hz is where I'm looking at long term.

 

These DJ rooms are not big - 150 seating is typical. I'll take some pics this weekend. I'm confident that these two cabs will get me where I want to be without being literally pushed to their limits.

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I been thinking about building two dual 21in 2x4x4 trapesoy shape. but yeah those speaker are expensive, and power hungry ( ihave an itech6000)

i wonder how your cabines sound... you should had used 5/8 baltic birtch is what top manufactors use.. very stiff and consider water proof.. i build a pair of dual 15s with that staff and the cabinets thum hard on the front, had left them out on rain too many times and still together.

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