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Author Topic: Sub Woofer Cracking Noise Don Furr Jedi Master Film Handler Posts: 509 From: Sun City, Ca USA Registered: Nov 2002 posted 11-27-2010 05:39 PM                     The sub in my screening room is a JBL 4645B. I'm feeding it with a 400 watt amp and as of late I'm hearing a cracking sound coming from the speaker. Of course it's in the louder passages in action movies such as Iron Man 2. (Blu Ray) I've never heard the noise while running Dolby Digital on film..just from the Blu Ray player. Questions: How old is the 4645B speaker? Could it need replacing (dry rot)? The processor is a CP500. Thanks...  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-27-2010 05:58 PM                     Check the surround edge of the cone and gently press straight in and see if the voice coil is rubbing. Usually one sub isn't enough.  |  IP: Logged Don Furr Jedi Master Film Handler Posts: 509 From: Sun City, Ca USA Registered: Nov 2002 posted 11-27-2010 06:03 PM                     I'll try that Mark...thanks. BTW the room is only 15X20 feet. Don  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 11-27-2010 06:22 PM                     Well if I'm not mistaken my excel sheet says 770W for a 4645B. You're powering it using a 400W amp: do you see it clipping during loudest passages? One of my 4645B was a bit noisy during louder scenes, despite the amp was not clipping nor overpowering it. The cone didn't have any apparent defect and the other 4645B I have was not doing it. Eventually I had to recone it.  |  IP: Logged Don Furr Jedi Master Film Handler Posts: 509 From: Sun City, Ca USA Registered: Nov 2002 posted 11-27-2010 06:27 PM                     Marco I haven't noticed any clipping either. I can't see any defect in the cone so I'm wondering if it's just time for a replacement speaker? Does anyone know the first year JBL made the 4645B's? This might be a really old speaker. Don  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-27-2010 06:30 PM                     Presuming it is 20-feet long and you have one 4645B...then you need 656-watts. The speaker can handle 800-watts so it is your amplifier that is deficient. Note, with two 4645Bs (4645Cs or a mix of the two) your amp needs drop to 330-watts total and you have a 4-ohm load which likely your amp can handle. The 4645B uses the 2242 driver which has a pleated damped cloth surround...as such, unless it has cracked/ripped it shouldn't have failed due to age (it is a good idea to periodically rotate a driver to prevent sagging). Checking the cone for rubbing is a good idea, as Mark suggested. It is also possible that the tensile leads might be rubbing the basket of the frame...including when the driver is moving at extremes...if they touch the frame it will give a staticy sound. It can also be as simple as a loose connection at the cabinet terminals and at the driver terminals. Lastly, since it is a 4645B...I would check the port tubes for tightness...I've seen many just fall into the cabinet. They are built rather flimsy and are angled at about 45-degrees in the cabinet. They are not well supported. -Steve  |  IP: Logged Don Furr Jedi Master Film Handler Posts: 509 From: Sun City, Ca USA Registered: Nov 2002 posted 11-27-2010 06:36 PM                     Thanks Steve. I'll get busy checking things. Don  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 11-27-2010 06:48 PM                     Don I second Steve. My two 4645B were BOTH squeaking when I got them second hand. I found that the reflex tubes and some woodden parts were loose. A good quantity of glue solved the issue. Anyway, my noisy cone was perfectly fine, couldn't see any issue with it. I couldn't feel any resistance pressing it with my hand. Steve why we have that slightly difference in result? I used 97dB sensitivity and 113dB SPL, 2/3 of 20 feet. The result I have is 770.7W for a single speaker.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-27-2010 07:09 PM                     I dunno...perhaps having grown up with Lucas Electric in cars, you are used to over compensating to minimize inherent problems? I've use the same spread sheet for many years now to calculate my power requirements and it has never failed me yet. I did a quick glance at my formula in the cell and I didn't see anything amiss. Perhaps you mis-keyed the feet/meter conversion? Mine is only to four sig-figs (.3048 feet/meter). -Steve  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 11-27-2010 09:53 PM                        I'm voting for the "bad surround" 4645b. Foam fails after a number of years. Can be reconed or replaced with another design, with slightly different results. Louis  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 11-27-2010 10:18 PM                     i think the issue off he foam has been discussed it is a non isue jbl does not use that one the subs  |  IP: Logged Don Furr Jedi Master Film Handler Posts: 509 From: Sun City, Ca USA Registered: Nov 2002 posted 11-27-2010 11:27 PM                     Update: Running my finger around the outer ring of the speaker, there is a soft spot about 6-7 inches long. When you run your finger around that area there is a noticeable cracking sound. The cone is flatted out in that area. I've got to assume the speaker is "shot". Where can I purchase a replacement speaker for this 4645B? Thanks for all the help. Don  |  IP: Logged Jeremy Weigel Phenomenal Film Handler Posts: 1062 From: Edmond, OK, USA Registered: Mar 2007 posted 11-28-2010 02:29 AM                     It will be cheaper to just have it re-coned (it's about 1/2 the cost of new). You can find authorized JBL centers here or Steve can also do them. I recently found this out the hard way with subs I inadvertently over drove.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 11-28-2010 08:34 AM                     Steve Yes, feet/meters conversion mistake thanks!  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 11-28-2010 11:26 AM                     Damn...I was thinking it was the Lucas "prince of darkness" electric thing.  |  IP: Logged

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