Does this cause damage?Originally Posted by Dr.db
Does this cause damage?
http://www.audioheritage.org/vbullet...p/t-20681.html
4313B
04-08-2008, 04:38 AM
A 2235H used as a sub can easily be overdriven and destroyed.
?????The mass controlling ring as used in the 2235H has fallen out of favor due to the limiting of xMax (This doesn't mean that people with a B380 and BX63 or BX63A should immediately start modifying that particular system design). Current thought is that the 2234H along with a few dB of EQ to fill in the resulting loss of VLF extension is a better solution. The Velodyne SMS-1 Mr. Widget recommends fills the bill. However, the Velodyne SMS-1 probably warrants a more modern transducer design such as the 1500 SUB or W1500H as Mr. Widget also states. Both of these transducers are significantly more robust and designed to handle the stress of small sealed enclosures. They are designed to handle EQ on the bottom end. Very small sealed box plus EQ. JBL has also used them in slightly larger vented boxes as well.
If one doesn't have the kind of funds required to run these modern subs one can go with something like the W15GTi mentioned by toddalin above. This driver has a higher Q and shouldn't require any EQ. It will dump a ton of bass tones into a room. It is specifically designed to sweep the field of competition in automotive applications but everyone is allowed to use any transducer any way they want regardless of design or intended application.
Anyone else slapping around the mass rings and if so on what DVD's??Quite common and it started when CD's hit the market. It was a source of warranty repair.
With both 4344 in 5 cubic ftDoesn't really count.
and now a B380 I have yet to ring the bell using 2235's.Shouldn't happen very often in the B380 with the BX63 due to the bump filter.
I have been able to get 121A to clank but only in a sealed box at high SPL levels.A 20 Hz filter should take care of that. They took a real beating when CD's first came out.
Back in the day, in cinema, I used to see people put 2235s in place of other 15" drivers to get more bass out of a double-15 sub. On several occasions, I had to recone said drivers because the mass rings punched out circular holes in the dust domes. The 2235 can do what it can do but not an ounce (or watt) more. It has a severe penalty for being overdriven and you don't get to do it but once. That said, my biggest recone job (quantity) was the 2245H that would often be driven out of the gap. Again, it was being overdriven, not that it failed of its own accord (except for foam rot but that was due to age, not due to how the customer used it). We used to stock the 2245 already reconed so techs could take ours on the way to the job and drop the failed one off on the way back rather than having to make the trip twice.
Hi Sguttag,
RE: "That said, my biggest recone job (quantity) was the 2245H that would often be driven out of the gap. Again, it was being overdriven,..."
Quite interesting and revealing post in the context of 2235. Even the 2245 "King of bass" was overdriven! This tends to show the 2235 wasn't the only one being abused, i.e. used beyond what driver is designed to do and can support. Not really a "manufacturing defect". More an operator issue in my book... Regards,
Richard
P.S. Also shows High-pass filtering is always a good idea in low-frequency sound reproduction...
The 2245 has a 24mm VC but misapplication can cause damage.
It’s interesting to note Jbl switched to the 2242 for commercial sub woofer applications.
Set up with the bx63 l think you’d have to be going out of your way to damage a 2245H. As l mentioned earlier clipping of the power amp cannot be underestimated as a cause of failure. I have witnessed a 300 watt amp shut down to avoid thermal self destruction with a 2245 / Bx63.
If you have averaged program power of 200 Watts a +3 dB peak is 400 Watts. Back in the 80’s unless you were bridging a power amp there weren’t many 400 watt power amps. I used a Phase Linesr 700B and later a Clair Bros 700B (clipping at 450 watts into 8 ohms) without collateral failure or reliability issues. Those amps had incredible control over a driver. I did use an 18 dB high pass filter @30 hertz which in most situations was inaudible. If l needed more output l ran 2x 2235’s a side. Problem solved.
Note, I did qualify it as in cinema use. This is dramatically different than home or even commercial music reproduction. The ONLY operative figure for cinema subwoofer application is continuous pink noise power. In cinema, we don't need to just handle the down-beat of music but a continuous effects signal that may go on for some time and is often generated by none naturally occurring sounds. Take, for instance, the rocket take off in "Apollo 13". That one scene significantly increased our recone business as it occured about the time that digital audio was taking hold in cinema as well. This put significant new demands on the subwoofer channel (note, it is its own dedicated channel in cinema and not merely a bass-extension to a main channel so it often, if not always has its own information and no bottom end of what other speakers may be playing). A typical speaker back in the day that had a 2245H in it was the JBL 4645 (no suffix, 4618 cabinet, for those keeping score at home). It is a system with a 95dB 1W/1m efficiency. In a theatre with say a 70-foot screen to rear wall depth, if you run the numbers on it, it would need to handle over 10,000 watts. While yes, no amp in use then (or probably now) could achieve that into 8-Ohms, its meger 300-watt power handling (a power EASILY achieved via bridging an amp back then) would have tried to explode the speaker. In truth often there were two in a cinema but that drives the power requirement down to just over 5000-watts and a power handling of 600-watts which, again, was/is easy to exceed using multiple amps and bridging larger amps, even back then. Even putting four of them in a theatre of that size, you need over 2500-watts but still only have 1200-watts of power handling. You'd have to get 6 of them into a cinema of that size before you have enough power handling to not drive them out of the gap.
The sub that replaced it was the 4645B (briefly, to be replaced by the 4645C) which did switch to the 2242 driver and increased cabinet efficiency to 97dB. Theatre sizes also grew shorter so that 60-65 foot deep theatres became more common. So, just three 4645B/C systems would be sufficient and that is if the theatre is played at reference. Most are played at 3-8dB below, which is why many cinemas get away with playing with just 2-systems. It has been my experience that the 2242 is a more forgiving driver than the 2245. Most cinemas that use JBL subwoofers now use the 4642A which uses two 2241 drivers. The system efficiency is 100dB 1W/1m and in typical cinema sizes of today, 1-2 are sufficient. Note, they don't play as deep as the original 4645 with the 2245 but they certainly hold up better and don't suffer from foam rot.
sguttag,
Thanks for that overview. I have two 4645C and two S1SEX subs in combo for my Synthesis system in a much smaller venue than even the smallest commercial cinema. They move substantial amounts of pant leg flapping air, driven by bridged S800 amps. Given proper calibration, they’re effective to sub 20Hz levels, but they probably don’t dig as deep as some more recent subs might if I were willing to spend additional $$$$.
At my advancing age, tactile impression is a significant part of my enjoyment of cinematic sound. While I’ve toyed with the idea of using two W15GTi transducers that I own to really get that Uber tactile bottom end, I’m not yet motivated enough to actually do it.
Out.
I suppose I should add that I have a couple of stereo systems using LE14H-3 subs, and I’ve not had a single issue with them, including bottoming out, despite some utilization that could be seen as abusive by some.
Out.
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