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Author Topic: Repair or replace insubordinate subwoofer? Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 04-16-2010 08:17 PM                        I don't have much experience with blown subwoofers, but the few I've seen have had noticeable damage. But maybe that's because they used paper drivers. Anyway, over the past few months or whatever I have not noticed any magnificent rumbles coming from our large giant screen auditorium. So I put my noise generator in the CP65, nothing. Disconnected the speaker lines from the amp and put my meter on 'em... wide open. Climbed up behind the screen, sub was still connected and looked in perfect condition. I disconnected it and put my meter on the terminals... wide open. Removed the cone and put my meter on that... wide open. I don't remember the model of the JBL sub itself, but the cone's model is 2242 HPL. Should I order a new one or is this something that I could fix myself? Keep in mind that this one sub powers ALL of the large giant screen auditorium, so it works pretty hard, but I've never heard it clip nor seen the amp clip during playback.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 04-16-2010 08:38 PM                     There are folks out there who can recone your blown sub (But my last price check had a recone so close to the cost of the whole driver it was a toss-up.) But, if that house is more than say 100 seats you need to have at least two subs and if it's over 300 seats 4 subs would be better. Back in the analog-only days you could get away with one sub but not with digital sound. Oh, and it is very easy to overdrive a sub and blow it out without clipping the amp.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-16-2010 08:40 PM                     only one sub you need more than that  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-16-2010 09:28 PM                     The 2242 is a phenomenal driver...it can handle 800-watts continuos pink noise....all day. As Gordon mentions...if you only have one for an auditorium, it is WAY under speced. Up until last month, the only system that used the 2242 was the 4645B or 4645C. Tell me how big your theatre is (distance from the screen to the back row of seats) and I'll tell you how many of those 4645Cs you SHOULD have. I suspect, the number will be around 4, not 1. I would definitely recone the driver...the cost of the recone will typically be half the price of a new 2242HPL or perhaps even less. JBL prohibits selling the recone kits to end users. Steve  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 04-16-2010 10:01 PM                     I have seen several JBL subs where the flexable wires going from the cone itself to the terminals have broken off. It was as if there was too much solder, and after many 'cycles', they broke off.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-16-2010 11:21 PM                     Too much solder can indeed be a problem. As can too little...it is quit tricky to get right. Sometimes, the bond where the v.c. lead to the tensile lead (the flexible wire John speaks of), also fails. But still...it would almost be impossible for one 4645C to be sufficient for most any sized theatre in a digital audio application. Steve  |  IP: Logged Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 04-16-2010 11:49 PM                        Those wired seemed fine to me. I really don't know how big the theater is, but it has 237 generously-spaced seats. I would guess the throw is somewhere between 60 and 70 feet maybe.  |  IP: Logged Bobby Henderson "Ask me about Trajan." Posts: 10973 From: Lawton, OK, USA Registered: Apr 2001 posted 04-17-2010 12:44 AM                     The two largest, originally designed for THX, houses in our local Carmike theater have 4 sub drivers each. These auditoriums have just under 200 seats each. They originally had a little over 200 when the seating was standard slope. The #3 and #6 houses flanking #4 and #5 have around 150 seats. They have 2 sub drivers each. The 4 smallest houses have 1 only sub driver; these are rooms with barely over 100 seats. Those subs were added in 2002 when the theater was upgraded to DTS on all 8 screens. That's arguably a conservative configuration for subs in an 8-plex. So only 1 sub driver for a room significantly bigger than anything in our local Carmike? From my perspective it seems grossly under-equipped. Gotta have at least 2 or more subs. Incidentally, what's the most sub drivers anyone has seen in a modest sized commercial movie theater auditorium? Private, pimped out screening rooms do not count.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-17-2010 07:22 AM                     Okay...lets split the difference...with 65-feet. Using the JBL 4645C's sensitivity of 97dB at 1W/1m...you need 6945-watts to play at digital spec. The 4645C only has 800-watts of continuous (pink noise, the figure you SHOULD use for subwoofer sizing due to how subwoofer tracks are played) power handing. Seems a bit impractical. Go up to two subs...you need 3481-watts but only 1600-watts of capability. 3 subs bring you down to 2300-watts needed with 2400-watts of capability. This is the tipping point for a 65-foot room with this subwoofer. You would need to use amplifiers with 800-watts/channel (20-20KHz power, not the stupid 1KHz power spec most amp companies throw about). Or use one with 1600-watts bridged into 4-Ohms and one bridged into 8-Ohms for the other 800-watts. A better design though is to get the 4th subwoofer. It brings you down to neading 1745-watts. Two 500-watt/channel amps or one big 900-watt/channel amp (into 4-Ohms). Something like the DCA-3022 by QSC will do it fine. Steve  |  IP: Logged Joe Redifer You need a beating today Posts: 12859 From: Denver, Colorado Registered: May 99 posted 04-17-2010 02:21 PM                        But ideally I'd need 9, right? No prob, I'll place the order Monday. I'll also call the electrician and have him install another breaker panel for all the amps we'll need. Let's see, I'll need another sound rack to install the amps. Actually I'll just order all new amps for every channel... the newer thin QSC DCA series and just throw the old fat QSCs away. That way they will fit into the existing rack. Might as well get a bunch of Monster Cable® to go with that, because without Monster Cable® everything sounds like crap.  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 04-17-2010 03:02 PM                  Joe...  |  IP: Logged John Hegel Expert Film Handler Posts: 166 From: Lake Mills, Iowa Registered: Sep 2000 posted 04-17-2010 04:43 PM                        Just curious what would be the disadvantages of using non cinema subs? yamaha 218v I have 5 of the yahaha 218v's on one of my live music stages/bar. We run playback music 24 hours a day and live shows 10 hours a week on these without any problems. In my opinion these offer a lot of bang for the buck. [ 04-18-2010, 01:57 AM: Message edited by: Adam Martin ]  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 04-17-2010 05:01 PM                     quote: Steve Guttag Up until last month, the only system that used the 2242 was the 4645B or 4645C Any news I am not aware of? Regarding the subject, Joe, reconing is definitely the right choice. But keep in mind that you will likely break it again in the future as Steve' math suggests.  |  IP: Logged Ian Parfrey Phenomenal Film Handler Posts: 1049 From: Imbil Australia 26 deg 27' 42.66" S 152 deg 42' 23.40" E Registered: Feb 2009 posted 04-17-2010 05:23 PM                     If Joe has only the one driver available for sub work, is there any way to horn load that one driver? This, if it is possible for sub 40Hz work, would surely make that driver far more efficient and negate the need for multiplying the number of direct radiating drivers. Granted, horn loading will give lumpy response, but would that be noticeable at these sub 40Hz frequencies?  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-18-2010 12:10 AM                     Gee...which do you think will cost more, a properly designed horn loaded cabinet or another subwoofer? JBL now has the 5749 LF system that features a pair of 2242HPLs mounted in the same cabinet that the 4642A uses (which only has 2241HPLs). The 2242 is a much better driver and will deliver a smoother response while handling more power. As for Joe's situation...ultimately, the only permanent solutions are to turn down the sub or to get enough subs and amps to handle the SPL requirement. 4 subs and suitable amps are not unreasonable for a theatre of that size. It is like sizing an A/C system. Too small and it never works properly and costs you a bundle of money doing it.  |  IP: Logged

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