MTM with jBL LE14H-4?

[dubkarma]

I was all ready to start working out a cabinet to house two LE14H-4 drivers and a 2450SL/2332 in an MTM configuration. My ancient version of BassBox (5.1), which I am just learning to use, suggests that a 4 cf volume tuned to 31-32 Hz for each driver would yield an f3 of 32 Hz.

But then I seemed to recall, though I could not locate, a discussion on these forums warning against using any of the LE14H-x drivers in an MTM configuration.

Could anyone point me to that discussion or refresh my memory of why LE14H-4s are best not used in an MTM design. . .?

Thanks,

Joel.

[Robh3606]

Hello Joel

??

http://www.lansingheritage.org/html/jbl/specs/home-speakers/1990-k2-s9500.htm

Rob:)

[Earl K]

Joel,

I mention the following so that you are encouraged to experiment with your own MTM approaches.

One of my MTM channels ( in my asymmetrical 2-chnl setup ) uses a JBL LE10H over LE14H ( no suffix ).
- There's an Altec 288-8K driving an Emilar EH500 radial horn in between the two "M" parts.

Tonality, this is a great setup with the le10H nicely complimenting the le14 ( & filling in for any deficiencies that it may have over 400hz ).
- The le10H works in a sealed .7cu' enclosure.

Real world impedance differences ( ie; 8 vs 6 ohms ) ends up level matching these 2 types of woofers ( plus the fact that that the le10H is closer to ones ears also helps a smidge ).

Granted this is best used as a small-to-mid sized room setup but I mention it because these parts are still around on the used market ( while the le14-4 is hard to impossible to get > as far as I understand ).

The other channel is twin 15's ( JBL ME150H ) also using an Altec 288-8K on the EH500 radial .

Another worthwhile asymmetrical setup could be a 12" over a newer tech ( JBL ) 15" ( run the 12" in a sealed enclosure ) .

Based on my experience I can see the 2204/6H on top of the newer 2216nd being successful ( mid-you, those JBL PRO twelves might benefit from an application of "Hill-Billy" aquaplas ) .

You'll want to find a horn that you can force to a 750-850hz crossover point for any of this to really gel properly.


:)

[speakerdave]

I was all ready to start working out a cabinet to house two LE14H-4 drivers and a 2450SL/2332 in an MTM configuration. My ancient version of BassBox (5.1), which I am just learning to use, suggests that a 4 cf volume tuned to 31-32 Hz for each driver would yield an f3 of 32 Hz.

But then I seemed to recall, though I could not locate, a discussion on these forums warning against using any of the LE14H-x drivers in an MTM configuration.

Could anyone point me to that discussion or refresh my memory of why LE14H-4s are best not used in an MTM design. . .?

Thanks,

Joel.

You may be recalling a discussion about linear vs nonlinear woofers for mtm setups. Notice first that using a pair of 14's or 15's to a horn and calling it mtm abuses the language and glosses over significant differences between midranges and woofers, direct drive tweeters and horns. The issue of linearity in mtm first came to my attention during the early planning on Project May. At the time the JBL statement speaker was the S9800, but the M/S9500 were still prominent in that role, and the Project May team thought to emulate that configuration using 2235's. Our mentor told us those woofers are too linear for that layout. Subsequently the project was generously gifted with four 1500Al's. No one said explicitly, but I gather the issue is that a woofer that reaches into the VLF alone will get fat on the bottom when used in pairs because of the additive effects of acoustic coupling over a certain frequency range based on the distance between the woofer centers. Many like the rumble/roar of 2230/31/35's in pairs in the 4350/55; part of that success is the crossover at 300Hz. JBL came to consider the doubled less linear 2234's, with only one playing to 1000Hz, in the 4435 a better overall balance and more natural bass.

All the woofers of the LE14 series are linear woofers that reach into the VLF. LE means linear efficiency. The LE10/14/15 woofers were JBL's response to the transition from monaural to stereo sound in the late fifties which called for woofers that would produce bass in smaller ported enclosures. The page linked by Robb considers the WHW arrangement of the 14's in the M/S9500. Those 14's, the 1400ND (and the 1401ND and 1400ND pro), are not linear woofers like the 2235 and the LE14 series. In pairs they reach most excellently into the high twenties in the M9500, but singly, no. They were designed for speakers like the DMS-1 and the S/M9500. I used the 1400ND for years and experimented with them in different setups. They work very well in pairs, and do not work well singly. The S7500 should not be considered an exception to this, since it was meant for the Japanese market where the taste for lean bass and the cavity gain in smaller rooms would allow for the use of a single 1400ND per speaker.

If you have access to four LE14H-4's (lucky you!) and want to use them in a pair of speakers, I would suggest a side-by side arrangement and a crossover in the 300Hz area to a cone midrange below the horn, ala 4355. In truth, though, it is usually best to be guided by the way JBL uses its drivers. It is especially important when deciding on a low frequency system to emulate a design that has already been engineered. One LE14H-4 in each speaker is meant to be plenty for domestic use, and they do that most excellently. If you want to go louder, consider using 15's.

[Ian Mackenzie]

MTM is a layout of two identical drivers with a high frequency driver in between the woofers.

MTM to some also relates to D’applito (MTM). This is a particular design with geometry relating to the distances between both woofers and that of the horn. Particular crossover slopes are also employed.

The challenge with large drivers is the distance between the woofer centres results in a crossover point that is not practical for most horn types that will fit between the woofers.

If you were considering the LE14 you would need to find a suitable horn that did similar things as like the M9500. Not diy easy.

As for the bass that a whole deal on its own and requires a lot of experimentation. What was done in the M9500 was the result of a lot of trial and error and specifically engineered drivers. If you have a DBX drive rack and enough time you can shoe horn a reasonable result with PEQ. In the case of Jbl consumer offerings they did not have that flexibility and so more elegant design solutions were utilised. You won’t be able to do that without exactly the same drivers and horn.

These are complicated systems with less than predicable outcomes.

If you have 4 x LE14 and you to use them in a diy friendly way then Earl’s options are going to have predictable outcomes. Put a 2123H 10 inch mid above the dual LE14 woofers @300 hertz and you have a number of choices as far as horns are concerned.

[pos]

By running the numbers in a simulation tool it appears the LE14H-4 is to the LE14H-3 (or any other LE14H variant) what the 2234H is to the 2235H.
The lighter cone increases its midrange efficiency, making it the perfect candidate for a 2.5 way approach similar to the 4435.

curves here: http://www.audioheritage.org/vbulletin/showthread.php?21660-E2-clone&p=215472&viewfull=1#post215472
(wow, that was more than 10 years ago, time flies :))

[Ian Mackenzie]

(wow, that was more than 10 years ago, time flies :))

Ah that project is booked for the retirement party like in another ten years....

[dubkarma]

Gentlemen, Thank you all for your observations and suggestions! Much appreciated. . .I now have a much better sense of the challenge I have taken on!

I had originally thought to use the 2450SL driver/2332 horn in between the two LE14H-4 without a separate mid-range driver.

In fact, not so long ago I sold four 2123 drivers! But perhaps the other 10" JBL drivers I have—the 2251J—will serve as well. . .they were crossed over at 300 Hz and 1000 Hz in one of JBL's 4-way monitor designs the model number of which I can't recall just now.

On a somewhat tangential note, regarding the availability of the LE14H-4—I simply called up The Speaker Exchange in Tampa, Florida and asked if I could order some. They said, "No problem. It'll take us 10 days to get them to our shop."

Having said all that, I think I'll set aside this particular project for now and concentrate on my other JBL project. Some time ago I combined the 2216Nd-1 woofer with the D2430K driver on the STX825 horn and have been very pleased with the results. So much so, that I've gone out on a limb—or whatever the audio equivalent is—and acquired (also from The Speaker Exchange) the M2 horns and mounting plates. Time to see what kind of system I can put together using the M2 horn with its much broader dispersion.

Then, in the spring I'll reread this thread and see what I can come up for the LE14H-4. . .

Thanks again!
Joel

[dubkarma]

By running the numbers in a simulation tool it appears the LE14H-4 is to the LE14H-3 (or any other LE14H variant) what the 2234H is to the 2235H.
The lighter cone increases its midrange efficiency, making it the perfect candidate for a 2.5 way approach similar to the 4435.

curves here: http://www.audioheritage.org/vbulletin/showthread.php?21660-E2-clone&p=215472&viewfull=1#post215472
(wow, that was more than 10 years ago, time flies :))

Pos's observation got me looking at more spec sheets. I couldn't help noticing that the T/S parameters of the LE14H-4—or at least some of the most important ones—are near-identical to the 1400Nd, which in turn are/may be identical to the 1401Nd used in the DMS-1.

Below are some major T/S parameters for the 1400Nd alongside those of the LE14H-4:

1400Nd LE14H-4
Fs - 24 Hz Fs - 24.7 Hz
Vas - 7.5 cubic feet Vas - 204.8 L (7.23 cu. ft.)
Qts - .22 Qts - .23
Qes - .23 Qes - .24
Qms - 8.8 Qms - 6.73
Re - 4.6 ohms Re - 6.07 ohms
Mms - 120 grams Mms - 124.3 grams
Sensitivity - 92 dB (?) Sensitivity - 93.8 dB


That makes me wonder if, after all, the LE14H-4 are indeed a good candidate for the configuration used in the DMS-1 as well as the two different approaches taken, respectively, in the 4435 and the K2 M9500.

[badman]

The center to center spacing is a challenge, as is a horn small enough but with a big enough driver to keep the XO low. One alternative is to use dual woofers above and below the horn but with some side-by-side midranges added in, which will keep horizontal directivity relatively constant.

Here's one example https://www.diysoundgroup.com/home-theater-speaker-kits/home-theater-series/impressives/elusive-1099.html

[speakerdave]

Acoustic coupling begins when the distance between driver centers is one-half wave length and is full on when it's a quarter wave length. Work out your spacing, do some calculation and see if that gives you what you want when combined with the acoustic output of the drivers in an anechoic environment. If it doesn't you will need to work out EQ settings.

[speakerdave]

The center to center spacing is a challenge, as is a horn small enough but with a big enough driver to keep the XO low. One alternative is to use dual woofers above and below the horn but with some side-by-side midranges added in, which will keep horizontal directivity relatively constant.

Here's one example https://www.diysoundgroup.com/home-theater-speaker-kits/home-theater-series/impressives/elusive-1099.html


Right, the very idea of an MTM, like the idea of a coaxial horn, is geometrically challenged.

[badman]

Right, the very idea of an MTM, like the idea of a coaxial horn, is geometrically challenged.

Certainly. There are some executions with small-flange domes that work with smaller midwoofs, but it takes a solid neo-motored, high-output dome and they're less common than one might think. Why everyone seems to want 4" for a 1" dome I have no idea!

That said, I'd rather have a horn proper or some other more capable tweeter, I feel like domes almost always let me down in terms of bandwidth/dynamics/output.