LE14h-3

[Dr.db]

Does anyone know the excursion capabilities of the LE14H-3 woofers?
How much is x-max and x-mech?
I´ve read the technical reference´s from Techbot but couldn´t find anything...

Btw, has the older LE14H the same specs concerning excursion?


Thanks a lot,
Olaf

[RMC]

Hi Olaf,

I didn't have more success than you when looking at all the LE 14 info that I have.

I know we are missing part of the equation but as a general guideline only consider the following:

LE 14 H, VC length .630 in., Xmax 8.38 mm

LE 14 H-1, VC length .750 in., Xmax 8.5 mm

LE 14 H-3, VC length .780 in., Xmax ?

LE 14 H-4, VC length .780 in., Xmax ?

To play it safe I would tend to stay within the 8.5 mm Xmax number for the LE 14 H-1

This logic is based on the general woofer excursion formula for Xmax = (length of coil - height of gap) / 2. Again, I know we are missing height of gap, so as they say we have to play this by ear... Hoping this may be of some help to you.

Regards,

Richard

[Dr.db]

Hi Richard,

thanks a lot for your great info´s!

I´m just wondering how much x-mech could be?
The surround doesn´t look like it supports exessive excursion... And I expect the LE14H-3 to "bottom out" like the 2235h when driven hard because there isn´t much clearance after linear x-max...

Regards,
Olaf

[Ian Mackenzie]

The LE14-3 spec sheet is located in the transducer data forum in reference section
Gap 0.28 inch

[Dr.db]

The LE14-3 spec sheet is located in the transducer data forum in reference section
Gap 0.28 inch

I´m sorry, but please tell me what´s the conclusion of that? I´m not familiar with the technical backround...

Can you tell what´s the maximum excursion before damage?


@Richard: On some drivers it really differs a lot.

[Ian Mackenzie]

We don’t know that but attempting to use the driver beyond the Xmax is not recommended.

The longevity of the suspension components will be reduced.

You need to look at either more drivers or a different driver if you are thinking in those terms. l am unsure why you are asking this type of information if your not at all familiar with the technical background?

This is why there are numerous different woofers available on the planet ��!

[sguttag]

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.

[Titanium Dome]

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.

[RMC]

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...

[Ian Mackenzie]

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.

[sguttag]

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.

[RMC]

Hi Olaf,

RE: "I´m just wondering how much x-mech could be?" and "there isn´t much clearance after linear x-max..."

Over the years i've seen, read and kept a hell of a lot of woofer data sheets, and keep looking at some more these days from Eminence, among others from Europe and US manufacturers. This has showed me the difference between the Xmax number and the Xmech (or Xlim) number can be anywhere on the map...

Sometimes there is a large difference between those two numbers and sometimes the difference is small. The clearance after linear excursion varies so much from one driver to another that I would not even make a guess on it.

This is to say it is just too risky for me to attempt an Xmech or Xlim number or even a "rule of thumb" here. Since I'm looking at some Eminence woofers now here's a few examples of those Xmax/Xlim differences: 4/8 mm; 6.7/15.5; 4.2/8; 3.2/10.9; 7.2/16; 8.52/15.7; 9.1/14.5. And this is NOT a scientific sample but just a few of those I have in my laptop.

As can be seen from the above, sometimes Xlim is double or so Xmax, sometime triple or so, sometime just about 50% more. And I have seen proportions of less than these... Xlim is usually more than Xmax, however by how much is anyone's guess I assume.

Finally, many manufacturers provide an Xmax number, but not necessarily an Xlim figure...

Regards,

Richard

[RMC]

Hi Olaf,

RE: "And I expect the LE14H-3 to "bottom out" like the 2235h when driven hard because there isn´t much clearance after linear x-max..."

Your indication above regarding 2235H seems to be right according to the document attached (Xmax 8.5 mm and Xmech 11 mm) which isn't a lot of loose between the two numbers. This also confirms what I wrote in post # 5 about the difference that can be large (as in my previous post) or can be quite small (as in 2235H), plus that numbers can be anywhere on the map... If my memory is correct, I'm 90% sure that attached document is from Giskard and I did take it on this site but can't remember from which thread.

As for your expectation that LE 14H-3 would bottom out like 2235H I cannot say about that.

RE: 0.28 GAP With regards to the Gap mentioned in post #4, I plugged that number in the traditional Xmax equation mentioned in post # 2: .780 - .28 = .5 /2 = .25 inch or 6.35 mm, which doesn't appear consistent with the other versions of LE14 (excl. A) for which we have an official number: LE14H 8.38 mm and LE14H-1 8.5 mm.

On the other hand, I have a May 1988 JBL doc. about gap gauge service procedure (see attached on 2nd page) where .057 is the number given for "all low frequency transducers with 4-inch voice coils". For the sake of it, I plugged that number in the Xmax equation to see what it would give: .780 - .057 = .723 / 2 = .3615 in. or 9.18 mm, which is a closer number to the 8.5 mm mentioned above for H-1. The H-3 version's voice coil is a bit longer (.780) than version H-1 (.750) so could that explain the former's bit higher Xmax here (< 1 mm) naturally if the gap height remains the same?

The above-mentioned 1988 doc. covers for sure at least three versions of LE14, the A, H (1979) and H-1 (1982). The H-3 and H-4 versions were issued in 2000 and 2007, so after the document. Could it still be applicable? The case remains open i guess...

RE: @Richard: On some drivers it really differs a lot.

Yes, it does and its difficult to predict since the Xlim number differences from Xmax are all over the map...

For my part, I indicated right from the start I had no more success than you in finding a definitive Xlim answer. However, I've been trying hard to find peripheral info that MAY get us there or be of some help to you... Regards,

Richard

P.S. Problem attaching files I will re-try later.

[RMC]

JBL Gap Gauge Service Procedure and Usage Guide (1988)[1].pdf

[Dr.db]

@Ian:
Actually it´s very simple why I came up with this question. I have owned 2235h´s in the past and 99% of the time everything was under control, but once a year a certain track caused the 2235 to bottom at the same level. That´s why I changed to TAD 1603, it has about the same linear xmax but a much higher xmech (maximum excursion before damage). The TAD has never bottomed out!
JBL 2235H: 8,5mm (xmax) and 11,0mm (xmech)
TAD 1603: 8,0mm (xmax) and 18,0mm (xmech)

I´m absolutly not purposing to run the LE14h-3 beyond xmax on a daily basis, why should I?
But it could happen eventually... And it would be nice to know if the woofer would bottom out or have a enough clearance in such a situation.


@RMC:
I believe we have to wait until someone with specific backround informations shimes in, but thanks so far!