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Author Topic: JBl 728 passive 2x18 sub  (Read 1665 times)

Mal Brown

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JBl 728 passive 2x18 sub
« on: September 29, 2021, 04:10:19 PM »

one of my least favorite vendors has some at $1150

 I know most of you hate on Kw-181.  We'll hate is a strong word but it isn't a real popular box here.   I own 4 of them and could move them tomorrow.  Very popular box in the local DJ community here...

So questions on the 728...

1. in comparison to a pair of 181's, how much power do I need to have on tap to drive the 728 to similar max levels.

2. can they go louder yet ? 

3. How well would a pair of these match up, with a DZR-315 ?

Given I have tools and some cabinet building skill - moderate, not expert.  Am I better off building Bennett's older design for the 18NW100 ?  not sure I want to bite off the double 18 and 21 inch box...

Thanks!

« Last Edit: September 30, 2021, 09:17:46 AM by Mal Brown »
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Mal Brown

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Re: JBl 728 passive 2x18 sub
« Reply #1 on: September 30, 2021, 09:18:58 AM »

based on inputs received via PM, maybe the 728 isn't such a step up...
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Tim McCulloch

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Re: JBl 728 passive 2x18 sub
« Reply #2 on: September 30, 2021, 05:10:28 PM »

based on inputs received via PM, maybe the 728 isn't such a step up...

1)  I'd venture they're closer than they are further.
2)  Possibly, or they'll play lower but not both.
3)  No idea, haven't heard the DZR box.

The KW-181 isn't a bad sub, the penalty is having to haul almost 35% more wood for the same acoustic result of a 2x18 box.

We have a dozen SRX728 (cardioid deployment) used with a VerTec 4889 rig.  With a 1:1 ratio of forward subs to top boxes I have to turn down the sub drive -6dB.  I haven't heard or used the QSC subs in a similar fashion.

The SRX728 hits a sweet spot of price/weight/performance that few others match, and greater performance comes with a bigger tab in all 3 criteria.  Is it a step up over pairs of KW181?  I can't say yes or no for your situation, but I doubt there is enough difference to switch brands.
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Scott Holtzman

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Re: JBl 728 passive 2x18 sub
« Reply #3 on: October 01, 2021, 12:48:39 AM »

1)  I'd venture they're closer than they are further.
2)  Possibly, or they'll play lower but not both.
3)  No idea, haven't heard the DZR box.

The KW-181 isn't a bad sub, the penalty is having to haul almost 35% more wood for the same acoustic result of a 2x18 box.

We have a dozen SRX728 (cardioid deployment) used with a VerTec 4889 rig.  With a 1:1 ratio of forward subs to top boxes I have to turn down the sub drive -6dB.  I haven't heard or used the QSC subs in a similar fashion.

The SRX728 hits a sweet spot of price/weight/performance that few others match, and greater performance comes with a bigger tab in all 3 criteria.  Is it a step up over pairs of KW181?  I can't say yes or no for your situation, but I doubt there is enough difference to switch brands.


I don't have SRX's but I do have STX's.  They are almost the same box, the STX's are a hair larger, a little better joinery and handles to make them "tour grade" and they dissipate heat a bit better so their short term power rating is 8000 watts. 


I also have a small pile of KW-181's, I used to have a bigger pile but we do less work that needs them and over the years they have been cannibalized for parts, traded for stuff etc.  At one point we have 18 I believe and the most I ever ran at one times was 12 of them.  I agree with Tim, it's not a chargeable difference.  Do you have clients come up to you and say, I want to pay for more low end at the next gig?  What is your exact end game for the upgrade? 


The biggest difference to me (and this includes the powered SRX's which we also have) is the built in amplification is optimized for the driver and is far more efficient that a rack full of amps.  I have powered the STX's with Yamaha P7000's, LG FP6400's and QSC PL236's.  I had to run two of the Yamaha's bridged per double 18 (one per driver) that drove them well, the FP6400's one 828 per channel was not enough, we were leaving a great deal of output on the table.  We generally take the Pl2's bridged.  I don't like bridged amps at 4 ohms but I don't feel I am leaving much on the table though. 


All of these options don't work well if all you have for the stacks is one 20 amp circuit a side. With the QSC's that will power two KW181's and a KW153 top.  That is the issue, I have to have twice the power to bring a pair of passive VRX932LA's and one 828 per side and that configuration just begs for 2, 828's a side so now I really need 50 amps just for the PA. 


I think the active are a much better configuration and you can pick up the SRX powered for about $800 more.  You are going to spend that much on the NL4's, amps, processing and racks if not a lot more.  You can get the ST828S's I have for $1200 each brand new but now you really need some power if you want to light them up. 


If you are anywhere near Cleveland OH and want to hear everything you have talked about at once and we can watch the power draw you are welcome to stop by any time.   


Shameless plug I have a pair of STX828S's for sale in the Marketplace for $1600 for the pair. 



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Mal Brown

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Re: JBl 728 passive 2x18 sub
« Reply #4 on: October 01, 2021, 11:22:56 AM »

Interesting read Scot.  The places I go where my 4 181's are overmatched have 50 amps, 220v on either a range plug ot a CA style connector.  I use a construction spider to break that out to 20a 110v lines.  What let's me skate is that the LA400's I own are so efficient.  900 to 1000 watts per side at 4 ohms is all it takes...  same to the mid-bass / low mids drivers.  So the power requirements for what I'm doing are modest. I can see where going crazy on the sub front could actually run me out of power.
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Art Welter

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Re: JBl 728 passive 2x18 sub
« Reply #5 on: October 01, 2021, 03:03:03 PM »

Interesting read Scot.  The places I go where my 4 181's are overmatched have 50 amps, 220v on either a range plug ot a CA style connector.  I use a construction spider to break that out to 20a 110v lines.  What let's me skate is that the LA400's I own are so efficient.  900 to 1000 watts per side at 4 ohms is all it takes...  same to the mid-bass / low mids drivers.  So the power requirements for what I'm doing are modest. I can see where going crazy on the sub front could actually run me out of power.
Mal,

No experience with the QSC KW 181, but sounds from Tim and Scott, the SRX728 wouldn’t offer a whole lot more output, though would save a bit of weight.
A dual B&C 18NW100 bass reflex of similar size and Fb would have a bit more output potential than the SRX 728.

Since you mentioned DIY, if power and output is a concern, you might consider my Keystone Sub “tapped horn” (TH) design using the B&C 18SW115-4.
Dimensions are 45 inches tall, 26.5 wide, 22.5 deep.
Unlike many horn designs, the Keystone is not much more difficult to build than a bass reflex box.
Due to the TH advantage, sensitivity is nearly identical to the SRX 728, it’s smaller and lighter, and uses a single four ohm driver, so uses the same power as the SRX for the same output.
That said, because the 18SW115 has almost double the excursion potential of the JBL2268H (14mm Xmax, 16mm Xvar vs 8mm), the Keystone can put out quite a bit more SPL than the 728, as doubling excursion equates to a 6 dB level increase.

Plans are available in this thread:
https://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers.html

Art
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Scott Holtzman

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Re: JBl 728 passive 2x18 sub
« Reply #6 on: October 02, 2021, 04:34:50 AM »

Interesting read Scot.  The places I go where my 4 181's are overmatched have 50 amps, 220v on either a range plug ot a CA style connector.  I use a construction spider to break that out to 20a 110v lines.  What let's me skate is that the LA400's I own are so efficient.  900 to 1000 watts per side at 4 ohms is all it takes...  same to the mid-bass / low mids drivers.  So the power requirements for what I'm doing are modest. I can see where going crazy on the sub front could actually run me out of power.


It always surprises me when venues don't take into account power requirements. 
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Scott AKA "Skyking" Holtzman

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Mal Brown

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Re: JBl 728 passive 2x18 sub
« Reply #7 on: October 02, 2021, 05:29:23 PM »


It always surprises me when venues don't take into account power requirements. 

Well, as mentioned before.  I live out here in what isn't even secondary market...  The venues are muni parks, the events are small festivals and families in the parks.  I will occasionally see crowds of 2500 but more often 500 to 1000.  There isn't an actual commercial venue anywhere near me that has capacity over 500...  There are afew events I do that bring in MultiQuips with 100 amps on board.  Generally I get 50 of that and supplement with 110v shore power...
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Scott Holtzman

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Re: JBl 728 passive 2x18 sub
« Reply #8 on: October 02, 2021, 05:32:43 PM »

Well, as mentioned before.  I live out here in what isn't even secondary market...  The venues are muni parks, the events are small festivals and families in the parks.  I will occasionally see crowds of 2500 but more often 500 to 1000.  There isn't an actual commercial venue anywhere near me that has capacity over 500...  There are afew events I do that bring in MultiQuips with 100 amps on board.  Generally I get 50 of that and supplement with 110v shore power...


Let me be clear Mal, your venues with the range plugs are ahead of 90% of the cover band crowd lounges.  I noticed when I was in CA and Denver that even the dumpiest bar if they have a stage they generally have some time of aggregate power connection. 
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Scott AKA "Skyking" Holtzman

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Mal Brown

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Re: JBl 728 passive 2x18 sub
« Reply #9 on: October 16, 2021, 11:36:38 AM »


Let me be clear Mal, your venues with the range plugs are ahead of 90% of the cover band crowd lounges.  I noticed when I was in CA and Denver that even the dumpiest bar if they have a stage they generally have some time of aggregate power connection.

We'll probably as being private enterprise they also get inspected.  Muni parks?  The inspector is on the city or county payroll and hey it was good 15 years ago and I have other places to inspect ...  I mean, they meet code just aren't necessarily venues  thought out as alternatives to Red Rocks ;-)
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ProSoundWeb Community

Re: JBl 728 passive 2x18 sub
« Reply #9 on: October 16, 2021, 11:36:38 AM »


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