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MJC
12-26-2004, 09:04 AM
Hi all happy holidays.
This month I had the pleasure of auditioning a pair of speakers that were designed by a local electrical enginneer. They are of the MTM type, that has a time aligned baffle. The tweeter is set back 3/4" from the mids.

But the main thing about these speakers is the crossovers. He calls it Group Delayed. Each driver has its own crossover board that is mounted right next to the driver. He spects all parts to tight tolerances. And all the leads and wires, including the wires running from the boards to the drivers are cut to precise lengths.
The result is a pair of speakers that image beautifully, better than my mirrored L212s, with very detailed highs and a quick mid-bass down to 45~40htz.
But its the depth of the soundstage that I've never encountered before. At least 10~15' deep.
He told me that one guy who has heard them said "that they sound better than his $22K speakers."
He had a local cabinet shop build 12 boxes, from his design, which are already sold. Even though he is still in the process of building the other 10 crossovers. He said that they are very time consumming. I forget the brand of the tweeter, but I think the 6" mids are Focal.

But this enginneer's main income is from designing analyzers for coffee roasting(among others), that he said all roasters use. I also tried his coffee(mohca expresso), every bit as good as his speakers.

The one thing I forgot to ask was how much he was selling them for. The next time I go over to his shop to buy some coffee, I'll take some of my cds and ask how much the speakers go for.

whej4312
12-28-2004, 01:33 PM
MTM designs have been around for years. It's just that Joe DiAppolito decided to patent his version. As far as Real Group delay designs, many of your european high-end manufacturers as well as American high-enders use very close tolerances in both driver topology and in the execution, placement and design of the network. Here in Colorado, Avalon Acoustics claim's that they can control off axis group delay and distortion nodes by A; physical placement of the Drive Units on the baffle plane. Augmenting the physical size of the baffle, controlling unwanted resonant points within the confines of the cabinet, and B; Controlling crossover and acoustic anomolies in the crossover with regards to the drivers inherant acoustical/electrical properties within the cabinet design. I have many friend's as well as myself that have experimented with wire types, wire lengths, coils, caps, and resistors to obtain a certain sound. Trust me, these things matter enormously. When you get a chance to hear these speakers again, one thing to look for is a lack of vertical dispersion. MTM's (Symmetrical Array) generally have stellar horizontal charictaristics but lack a true vertical soundstage.They sound closed-in and lack placement of the image vertically. In your L-212's case, driver placement on the baffle plane is a big problem. The baffle is much to wide to make the L-212's behave like a point source. Damping the face acoustically helps a ton. I have a few tricks on that idea. Finally, while we all know that JBL can and does build some of the most remarkable drivers out there, their overall cabinet designs and crossover execution leave a lot to be desired. In my opinion the closest JBL has ever gotten to a real world high-end worthy loudspeaker is, K-2, LSR28, and more importantly the Century Gold. But if you look at the networks or cabinet design in any of them, they still leave me wondering why. Why James B. Lansing Sound Inc. Can't build a speaker that would flatten the industry much like or beloved L-100 and 4310. As simple as they were, they did, to this day what no one has. Sell well, and sell often. Plus that patented, trademarked, and elusive WestCoast Sound we all love. Speed baby, It's that simple...

Ian Mackenzie
12-28-2004, 02:22 PM
[QUOTE=MJC]Hi all happy holidays.
But the main thing about these speakers is the crossovers. He calls it Group Delayed. Each driver has its own crossover board that is mounted right next to the driver. He spects all parts to tight tolerances. And all the leads and wires, including the wires running from the boards to the drivers are cut to precise lengths.

]

Sorry I think he's pulling you leg.

For the real facts do a search for Siegfried Linkwitz

whej4312
12-28-2004, 04:29 PM
[QUOTE=MJC]Hi all happy holidays.
But the main thing about these speakers is the crossovers. He calls it Group Delayed. Each driver has its own crossover board that is mounted right next to the driver. He spects all parts to tight tolerances. And all the leads and wires, including the wires running from the boards to the drivers are cut to precise lengths.

For the real facts do a search for Siegfried Linkwitz
Time alignment is critical in any application. Ian do you remember the L300? Everest? Why were the faces of the cabinets back 5 to 15 degrees? Siegfreid Linkwitz essentially came up with a different way to document and change phase anomolies at the crossover points, hence Linkwitz-Riley 2nd, 3rd, and 4th order constant phase and null phase networks. I have never heard a very good Linkwitz passive design. I have indeed heard many successful Linkwitz odd and even order Electronic Crossovers though. Any old AES journals have tons of info on their work. While this guy claims group delay, I really wonder where the delay is. If the tweeter is physically stepped back, than what does that do to lobing at the x-over point. Sound's like this guy is playing at phase trickery to make his sound stage bloom!!:banghead:

Want bloom? Buy Toobes!!

Robh3606
12-28-2004, 05:24 PM
"Time alignment is critical in any application. Ian do you remember the L300? Everest? Why were the faces of the cabinets back 5 to 15 degrees?"

Take a look at the L300 brochure on the site. The 4333 and L300 both used a very long midrange horn. There is no way that an angled baffle would be able to compensate for the path length diferences between the woofer, compresion driver and the slot. The only reason I can see why was to help the 077 because of the limited vertical dispersion.

Rob:)

whej4312
12-28-2004, 07:41 PM
"The 4333 and L300 both used a very long midrange horn. There is no way that an angled baffle would be able to compensate for the path length diferences between the woofer, compresion driver and the slot. The only reason I can see why was to help the 077 because of the limited vertical dispersion.

Rob:)
Are you sure? I wonder what the polar pattern of the 300/4333 look's like at their crossover points? I agree that the 077 slottie might be one of the reasons, or it could be even simpler. Because who would put L300's on a pair of stands!! Maybe JBL just did it to aid in deep shag dispersion!! LOL!!:rotfl:

Robh3606
12-28-2004, 10:01 PM
Well take a look see what you think.

http://www.lansingheritage.org/images/jbl/specs/home-speakers/1975-l300/page3.jpg
Rob:)

Ian Mackenzie
12-29-2004, 02:09 AM
I think you may have your magnification turned up too high.

I was referring to the wires being cut the exact same length.

As to the rest of it I really do not have time to debate theoretical issues about Linkwitz crossover design or why JBL do and didn't do certain things with their products.

You can be assured however they are both classic examples of sound engineering practise with respect to real world considerations.

Ian

Ian Mackenzie
12-29-2004, 05:40 AM
[QUOTE=whej4312]Time alignment is critical in any application. Ian do you remember the L300? Everest? Why were the faces of the cabinets back 5 to 15 degrees?

QUOTE]

Pigs arse,

They (L300) were angled slightly back due to the limited vertical dispersion of the drivers.

Any idiot could tell you that.

There's no fancy theoretical rocket science with this stuff

If your gonna bullshit at least do it properly and check your references...that way won't notice so much.

Ian:o

Mr. Widget
12-29-2004, 10:36 AM
Ian, calm down boy. :)

Group Delay is a BS answer. I really don't doubt that the coffee engineer is putting some good practical design engineering into the mix and quite likely is designing a speaker that images better than most JBLs. Many people have.

As for precise wire length... other than to maintain specific resistance goals, there is no reason (that I know of) to jump through those hoops. In the design of microwave communications equipment wire length and even shape make a difference, but last time I checked we were listening to Hz-KHz not GHz.

Many designers will focus a bit too much in one area or another. In the halls of audio marketing they turn up the BS factor to 11, but I assume this guy is still a believer and not a snake oil salesman.

Please do find out what components he is using as well as crossover topology and price... a photo or two would also be nice.

I would love to see what he is up to.

Widget

BTW: I agree with whej4312. I think your imaging would improve dramatically if your baffles were treated or narrowed to 8", but I have mentioned this before.

4313B
12-29-2004, 10:49 AM
BTW: I agree with whej4312. I think your imaging would improve dramatically if your baffles were treated or narrowed to 8", but I have mentioned this before.Just build some mini-L250/250Ti pyramids for the 8-inch 3-ways. :)

boputnam
12-29-2004, 11:03 AM
Dammit, Giskard!! :bash:

Doods...

Where were you guys?? When I read the original post I just shrugged it off and decided I hadn't sufficient time. Plus, unless we can post directly with Mr. Grounds, debating what was heard and seen would be fairly unproductive.

It would be nice to get some photos and descriptions from Mr. Grounds himself, so that he can explain his design.

'nuff said. :slink:

Oldmics
12-29-2004, 11:17 AM
Thats too funny.

Perhaps a Columbian connection.

Oldmics

Zilch
12-29-2004, 12:03 PM
Why were the faces of the cabinets back 5 to 15 degrees?Because it looked cool, most likely. It also matched the profile of the new Bob's Big Boy counter that had just opened down the street, where everybody ate lunch daily.

I'm certainly not ABOUT to argue that L200 or B460 are "Time aligned," either, nope.

Or that we all love the "West Coast" sound.... :cool:

Mr. Widget
12-29-2004, 12:03 PM
But its the depth of the soundstage that I've never encountered before. At least 10~15' deep.

Electronics and source material has a lot to do with this too. Most CDs are rather flat and most moderately priced amps, preamps etc. tend to flatten the image as well.

What type of source material and electronics was "Mr. Grounds" :hmm: using?

Widget

Mr. Widget
12-29-2004, 12:06 PM
It also matched the profile of the new Bob's Big Boy counter that had just opened down the street, where everybody had lunch.
I thought that was a closely guarded JBL secret.:rotfl:

I think, " Because it looked cool, most likely." gets the nod.

Widget

4313B
12-29-2004, 12:10 PM
Dammit, Giskard!! :bash:Do it now! - your Gov's inflection.

Mr. Widget
12-29-2004, 05:30 PM
Do it now! - your Gov's inflection.
I guess I don't spend much time thinking about the Governator. It took me until now to figure that one out. :banghead:

Widget

Ian Mackenzie
12-29-2004, 06:33 PM
"But this enginneer's main income is from designing analyzers for coffee roasting(among others), that he said all roasters use. I also tried his coffee(mohca expresso), every bit as good as his speakers."

Well most Hi Fi inventors have some sort of pre market entry occupation like Duntech and lesser knowns like Metaxas who are shall we say known cons who lure wealthy people into parting with lots of money for an illusion they lust after.

On reading early literature by Duntech, he refers to things other than physical time domain for imaging and stage depth. Moreover impulse response step function was the main feature of his designs, all 6th order minimal phase crossovers. The drivers were almost exclusively Dynaudio or Scanspeak, noted for transient attack and the alignment of the coincident sources combined to offer true 3D imaging. The thing was his speakers came with full test reports backing up his claims, no snake oil, audio mythology required here. And yes I have owned a set of Dutechs which I reluctantly sold when one time when I relocated.

Review on the Sovereign in Electronics Australia - January 93

"What most audiophiles regard as the best loudspeaker system in the world; the almost legendary Duntech Sovereign.

"I have not heard any loudspeaker system which could out-perform the Sovereigns in terms of spatial localisation..this is as close as you will get to a live recording at home.

"Without hearing them, you will never appreciate just how outstanding these speakers are...sounds that are about as true-to-life as you could hope or want to achieve in a residential situation."

Harry Pearson reviews the Sovereign in The Absolute Sound - September/October 1991

"What it does have, aside from an unusually life-like ability to deploy an orchestra across the expanse of your living room, is the most uncanny ability to suggest...the sound of real bass instruments playing individually or en masse and doing so with the kind of authority you will find chilling..."
http://www.duntech.com.au/images/products/classic/sovereign-diagram.gif

Ian Mackenzie
12-29-2004, 06:43 PM
This may seem like information overload but I found the answers to specific questions most interesting:

Q4.1 A lot of hype is used to describe loudspeakers and I do not understand any of it. Is any of this stuff useful or is it all advertising techno-babble?

Answer: To a loudspeaker designer who lives and breathes loudspeakers the terms phase, amplitude, nyquist plot, and waterfall are as familiar as sky, tree and car to a normal person. So lets back up and take a fresh look at loudspeaker measurement. In my answer to this question I have restricted myself to the on-axis response, that is, what does the loudspeaker sound like when it is pointing at you.

In the early days of hi-fi, when two loudspeakers which "measured the same" sounded entirely different, the popular notion (even amongst early designers) was that loudspeaker measurements were completely meaningless. What they were measuring was the first and most simple characteristic of how loud it plays, which we call "amplitude". The amplitude is how loud the speaker is at different points on the musical scale. If a pianist plays every note at the same volume, then they should also sound the same volume through a loudspeaker. But that is only the first paragraph of a long story.

It was not until the late Richard Heyser wrote penetrating and lucid AES (http://www.duntech.com.au/www.aes.org/index.htm) papers about the time behavior of loudspeakers, that it was even possible; in principle; to measure loudspeakers meaningfully. His great breakthroughs related to the effects of phase upon the sound of a loudspeaker. Basically his insight (in this specific area) was that the apparent position of a loudspeaker had something to do with its phase.

*footnote: Phase is the measure of whether one thing is in step with another. To illustrate this, imagine that the Salvation Army band is marching by in a parade. If you look at their feet, you will notice that the right foot of every man moves forward at the same instant. The feet in this band are in phase with each other. Contrast this with a crowd on a city street; there is no relationship between the feet - they are completely out of phase.

If the phase and the magnitude of a loudspeaker were not locked together in an intricate dance called "minimum phase", then the speaker would appear to be at several places in the room at once, stretched out in a line from the listener, through the speaker, and out to infinity. In order to prove this hypothesis, he designed equipment which could measure phase. The problem was, that measuring phase this way was about as easy as balancing three eggs one on top of each other. Partly to solve this problem, he devised "time delay spectrometry". I won't go into TDS here, but suffice it to say that this was a revolution in loudspeaker measurement. With TDS you could also see the time response of the speaker.

This brings us to the next important loudspeaker measurement which is called the Waterfall plot (or Cumulative Spectral Decay to scientists and engineers). This plot displays how loud the speaker is at all frequencies (called the Magnitude response by the same people) at each instant in time. These plots are shown one after each other, like cards in a deck. The effect is like looking at a cliff face. The steeper the cliff the better.

As time passed, the Maximum Length Sequence system was perfected and offered by DRA Labs in their MLSSA package. This allowed engineers to process their measurements in all sorts of interesting ways. One plot, which shows a huge amount in once glance, is the Nyquist plot. In this plot, the loudness and the phase are displayed like the hands on a clock. The longer the hand, the louder the speaker and the hour the hand is pointing to is the phase. In this system, 3 o'clock is zero degrees, 12 o'clock is 90 degrees, and so forth. As the frequency rises the hand traces out a line on the clock face and this is the plot you get. A ideal loudspeaker would show a straight line going from the centre out to some distance and then squiggling around in a tight little bunch for all frequencies (So far as we know the only conventional loudspeaker which does this is the Duntech Prince).

So in summary if the manufacturers had the nerve all they would need to show you is the waterfall plotm and the Nyquist plot and you could tell virtually everything you need to know about on axis response.


<TABLE cellSpacing=0 cellPadding=0 width=500 border=0><TBODY><TR><TD>Q3.1 What makes a good loudspeaker?

Answer: A good loudspeaker creates the illusion of being at a musical performance and lets you hear the emotional message that the performer has woven into the music.

At first this might seem to be the wrong answer, particularly if you are of a technical bent. Some designers might say, "The magnitude and phase should be so and so." or "The cumulative spectral decay must exhibit x dB of clean decay in the first y milliseconds". For Duntech, there are a myriad of measurements and assessments which must be performed before the loudspeaker is approved for shipping. Above and beyond all the measurements, the final decision on each pair of speakers is always made after intense listening sessions.

Q3.2 Can you tell anything by looking at a speaker?

You can actually tell a lot just by looking at the speaker. If certain features are not attended to you will not get very close to the sound you are looking for. When you look at the speaker, does it use more than one driver of each type? Two drivers sharing the load will not go into overload as easily as one and will be more dynamic and more natural sounding than one.

Does the speaker have time collimation of the drivers? If the drivers are not arranged so that all sounds arrive at the listener at the same time, then the music will be scrambled. The reason why most speakers have flat front baffles is because it is cheaper to build them that way, not because it sounds better.

Does the cabinet use diffraction control? The best way to control diffraction is to use felt. The felt must be cut into all sorts of shapes to work best where they are placed. The second best way is to use a curved or sculpted baffle. We have built speakers with curved enclosures (spherical even!) and the listening tests confirm what the measurements say: felt is the only way to go.

Q3.3 My friend says that the "rap test" is a sure fire way to pick a good speaker, what do you think?

If you rap on the side of a speaker with your knuckle and it produces no sound or a dull tuneless thud then it is adequately braced. If the speaker sounds like a tympani then it will colour the sound. There is more to this than meets the ear though. Some manufacturers have gone to huge lengths to control cabinet resonance and then ignored the matters of diffraction, crossover design and driver selection. It is as if someone has built a house with a safe door from a bank for the front door, and put a flimsy screen door with the hinges hanging off on the back door.

Q3.4 What is pulse coherence?

Answer: Pulse coherence is the name we give to the package of properties which makes a Duntech loudspeaker what it is from a measurement standpoint. A pulse coherent loudspeaker produces a sound which is "in step with itself" and is not muddied by diffraction from the cabinet. Technically, the sound is in step with itself when the summed response of all drivers working together preserves the original electrical waveform which was fed into the speaker. If you were to look at the input voltage waveform on an oscilloscope and then the measured sound using a microphone placed at 3.5 metres you would see exactly the same shape. Amazingly, very few loudspeakers actually do this. Pulse coherence is part of the Duntech design philosophy.

John, I trust your still with us, Hopefully this will help purify what you think you know rather than rely too much forum chat waffle from those all over or parts unknown.



</TD></TR></TBODY></TABLE>

Don McRitchie
12-29-2004, 07:44 PM
The "Dun" in Duntech stands for John Dunlavy, the company's founder. In the early 90's, John sold Duntech and moved back to the States to found DAL (Dunlavy Audio Labs). DAL was very highly regarded, but became a victim of the Asian financial crisis that saw their major market disappear. They closed their doors in 2002. Duntech continues on and the philosophy espoused in the above posts comes directly from John Dunlavy.

In 1998, I had the privilege of meeting John and spending around 5 hours with him at his plant in Colorado Springs. I listened extensively to their systems, including their equivalent to the Duntech Sovereign. To this day, I would say these systems were the most accurate, holographic speakers I have ever heard. They made me a believer in phase and time alignment. However, like all speakers, they are not perfect. Achieving time and phase alignment dictates that cross-overs must be 1st order with 6db slopes. This means that the drivers have to cover a very wide frequency band and this limits their power handling. The drivers themselves lack the power compression defeating technologies that are the hallmark of JBL so that they are not linear with power.

Nonetheless, my dream would be to own both a TOTL Dunlavy and a TOTL JBL (like Project May :)). Each excels in their own domains.

BTW, a very good combination of these approaches is the 250Ti. This is one of the few JBL's that is both phase and time aligned.
<SUP></SUP>

Ian Mackenzie
12-29-2004, 08:11 PM
Thanks Don,

I just called the web page contact Ph in Aust and was advised the company that was in Aust has been acquired by Orpheus Loudspeakers.

There is a limited part of the original Classic range being made at the moment and there will be a new range released later in 2005.

http://www.duntech.com.au/images/all.html

<TABLE id=table6 cellSpacing=0 cellPadding=8 width=560 border=0><TBODY><TR><TD class=heading vAlign=top align=left width=560>Company Profile<!-- end include --></TD></TR><TR><TD vAlign=top align=left width=560><!-- start include -->Orpheus has been in the business of designing and manufacturing high fidelity audio speakers for 20 years. The company has a solid base in Australia with two separate facilities in Sydney; one for design and testing, the other for warehousing and distribution.

The company’s commitment to excellence along with its years of experience in designing high quality and high performance audio equipment has led to the growth of a substantial following in Australia. This is true for the consumer range as well as for the company’s commercial studio and reference equipment. Orpheus Audio professional users in Australia include ABC Radio and TV, Studio 301 (formerly EMI Studios, Sydney), Channel 10 and Channel 7 TV Studios. Orpheus also sells through a very select dealer network in Australia comprising 20 of the best hi-fi stores in the country.

In 2004, Orpheus Audio acquired Duntech Audio Australia Pty Ltd – a very highly respected name in the audio industry worldwide. Duntech loudspeakers have been acclaimed by many highly respected and widely read international audiophile magazines, including Audio, Australian Hi-Fi, Digital Audio, Gramophone, HI-FI Choice and Stereophile.

Orpheus Audio – now bolstered by its Duntech resources and expertise - has an ongoing research and development program to refine and improve its technologies and performance across its entire range of products.

</TD></TR></TBODY></TABLE>


<DT>DUNTECH AUDIO </DT>

<DT>12A Lime Kiln Road, Lugarno. N.S.W. 2210 </DT>

<DT>Telephone: 61 2 9584-0743
Fax: 61 2 9584-1708 </DT>

Ian Mackenzie
12-29-2004, 08:31 PM
Here is a link to other Aust speaker manuacturers, notable are Krix Loudspeakers, Whatmough Monitors, Legend Acoustics, VAF Reseach and Whise Precision Audiohttp://home.vicnet.net.au/~macinc/

hector.murray
12-30-2004, 07:33 PM
Any News from "Mr Grounds" or has MJC gone silent?

Robh3606
12-31-2004, 09:44 AM
Hey Ian


Thanks for the link! There is some real nice stuff on the site.

Rob:)

Robh3606
12-31-2004, 09:47 AM
Hello Don

Have you ever read the Stereophille review on the L250's?? I would love to scan and post it to get owner reactions. Let's just say it has a few twists and is not that favorable.

Rob:)

4313B
12-31-2004, 10:33 AM
I did a review of Stereophile once.
I found the pages to be too rough to wipe with - which means it has virtually no redeeming value whatsoever.

hector.murray
12-31-2004, 11:51 AM
ROFLMFAO:p

MJC
12-31-2004, 11:59 AM
Any News from "Mr Grounds" or has MJC gone silent?
I haven't been on this site since I started this thread. And have been too busy to get back to Carl Staub, the engineer of the speakers I was referring to.

whej4312 quote
In your L-212's case, driver placement on the baffle plane is a big problem. The baffle is much to wide to make the L-212's behave like a point source. Damping the face acoustically helps a ton.

If you paid attention to my Avatar you would see that my main pair of L212s are mirror imaged, and DO act as a point source. They image better than most speakers I've heard of late. They DO give me a better soundstage than my original L212s. I do have another pair of L212s that are treated with foam stuck to the inside of the grille that I bought on Labor Day weekend. But right now they are used as back channel speakers. Maybe this weekend I'll put them side by side my mirror imaged to do a comparision.

Being I haven't heard my L212s side by side with Carl's speakers I can't really tell how much better the soundstage is, if at all, other than his soundstage seemed to be much deeper.

4313B
12-31-2004, 12:16 PM
If you paid attention to my Avatar you would see that my main pair of L212s are mirror imagedYour avatar does look pretty neat MJC. It appears you did a great job reworking your L212's. :yes:

Don McRitchie
12-31-2004, 02:34 PM
Hello Don

Have you ever read the Stereophille review on the L250's?? I would love to scan and post it to get owner reactions. Let's just say it has a few twists and is not that favorable.

Rob:)
I never have. I would love to get the chance.

Don

Ian Mackenzie
12-31-2004, 03:07 PM
John,

Great pickup.

Glad to see you are enjoying your revived JBL's.

Would be nice if you can post us a closer look.


Ian

MJC
01-01-2005, 08:30 AM
John,

Great pickup.

Glad to see you are enjoying your revived JBL's.

Would be nice if you can post us a closer look.


IanWill do.
I had a thought the other day, while listening to just the mirrored pair and the 2 sub1500s, that I have another pair of boxes I built two years ago, not being used. Reworking the boxes by leaving the 8" driver holes where they are, on the wide face, pluging up the holes for the 066s and le5-9s and cutting out new holes on one end, at the same elevation as the pluged holes.
This configuation would simular to the Infinity Preludes, speakers that I auditioned in 2000, and thought were every bit as neutral sounding as the L212s. Just to see(hear) what improvement, if any, would take place.
Of coarse the Preludes come with a heathy price tag of over $12k for 5.2 system.

whej4312
btw, have you ever noticed that the size of the baffle of the Performance Series towers and driver placement is about identical to the L212s? And in the brochure for the L212 it sez that "the width of the cabinet is designed to create a front baffle surface that is effectively infinite for the high frequency radiator."
Although off setting the drivers two inches in has produced an even better soundstage, a better "center channel" in stereo playback.

So I guess at JBL, what goes around, comes around. Because here we are a quarter of a century later, 1977~2002 (the years that these two speaker systems were debuted) and the biggest difference in the L212 and Performance Series is what the drivers are made from, with the PS being Titanium.

Ian Mackenzie
01-01-2005, 10:33 AM
Nice work John,

Would be interesting to hear your impressions with the spare box

I wish I had some spare JBL drivers to tee up a L212. Eventually I plan to built a ''good'' 4 way electronic crossover to play around with these concepts.

Ian

Ian Mackenzie
01-01-2005, 10:38 AM
.

whej4312

So I guess at JBL, what goes around, comes around. Because here we are a quarter of a century later, 1977~2002 (the years that these two speaker systems were debuted) and the biggest difference in the L212 and Performance Series is what the drivers are made from, with the PS being Titanium.
Yes it does, Beautifully put.

MJC
01-01-2005, 11:17 AM
Nice work John,

Would be interesting to hear your impressions with the spare box

I wish I had some spare JBL drivers to tee up a L212. Eventually I plan to built a ''good'' 4 way electronic crossover to play around with these concepts.

Ian
Thanks, finding the 066s and the le5-9/2105 are easy, its the 112A that took most of 2 years to get 4 of them, being they were only used in the L212.
I still haven't gotten around to buying some .005uF polystyrene caps to use as bypass caps for the 066s, but I did install polyproplene bypass caps for the 2105 and 112A.

moparfan
10-30-2010, 12:32 PM
I am interested in your high regard for the LSR28. I would like to see if anyone else here has a similarly high opinion of the LSR28 or LSR6328. I don't have the reference point of all those other JBLs to compare them to. Yes, I know this is an old post...


MTM designs have been around for years. It's just that Joe DiAppolito decided to patent his version. As far as Real Group delay designs, many of your european high-end manufacturers as well as American high-enders use very close tolerances in both driver topology and in the execution, placement and design of the network. Here in Colorado, Avalon Acoustics claim's that they can control off axis group delay and distortion nodes by A; physical placement of the Drive Units on the baffle plane. Augmenting the physical size of the baffle, controlling unwanted resonant points within the confines of the cabinet, and B; Controlling crossover and acoustic anomolies in the crossover with regards to the drivers inherant acoustical/electrical properties within the cabinet design. I have many friend's as well as myself that have experimented with wire types, wire lengths, coils, caps, and resistors to obtain a certain sound. Trust me, these things matter enormously. When you get a chance to hear these speakers again, one thing to look for is a lack of vertical dispersion. MTM's (Symmetrical Array) generally have stellar horizontal charictaristics but lack a true vertical soundstage.They sound closed-in and lack placement of the image vertically. In your L-212's case, driver placement on the baffle plane is a big problem. The baffle is much to wide to make the L-212's behave like a point source. Damping the face acoustically helps a ton. I have a few tricks on that idea. Finally, while we all know that JBL can and does build some of the most remarkable drivers out there, their overall cabinet designs and crossover execution leave a lot to be desired. In my opinion the closest JBL has ever gotten to a real world high-end worthy loudspeaker is, K-2, LSR28, and more importantly the Century Gold. But if you look at the networks or cabinet design in any of them, they still leave me wondering why. Why James B. Lansing Sound Inc. Can't build a speaker that would flatten the industry much like or beloved L-100 and 4310. As simple as they were, they did, to this day what no one has. Sell well, and sell often. Plus that patented, trademarked, and elusive WestCoast Sound we all love. Speed baby, It's that simple...