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  1. #571
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    Cool

    Hi Richard,

    Distortion is important but isnít the only criteria for an accurate monitor.

    The primary limitations of a dome midrange is itís not a uniform directivity driver on its own. Whereas a JBL image control waveguide using either a soft dome tweeter or a compression driver is. Eargleís text pre dates JBLís recent developments pioneered by Charles Sprinkle. A waveguide also improves distortion performance towards the lower end of the driverís bandwidth.

    Most modern recordings these days are monitored using two way near field monitors with distances of about one meter and reference levels of 85 db. The use of a dome tweeter is industry standard. At these levels a two way monitors can comfortably do the job.

    Only a few near field monitors feature three way designs using a midrange driver. Some are some mids, others cone mids.

    The larger Quested monitors featuring the ATC dome mid were used in large record company control rooms. This application is now far less common with the trend towards successful contract mixing engineers working from home these days. They all use two way near field monitors. The market for near field monitors has grown significantly in the last decade. But the market for dome mid range drivers is static or declining.

    Innovation has however occurred in the development of concentric mid/hf direct radiator drivers. Pioneer were one of the first to use a concentric mid/hf direct radiator driver. Charles Sprinkle has used this approach in the Kali brand of near field monitors.

    https://www.kaliaudio.com/independence

    Eargleís text is more of a reference or the evolution of monitoring systems. I have not made reference to diy loudspeakers because is a small niche.

  2. #572
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    Quote Originally Posted by RMC View Post
    Thank you for having posted the Crowe and JBL Tech Note texts relative to this issue, they're providing the context and perspective in order to tackle the problem. Moreover, indicating the JBL HF horn distortion data is actually much worst than Eargle's "best case" type numbers. The 25% and 40% measured are quite large, therefore clearly showing where a major improvememt is deeply needed.

    His theory is that you need a 15"/horn combo. That imperative offered only keeps users swimming in distortion, which btw they would never accept from another component! (e.g. amp), rather than trying helping them out of it or a notable reduction thereof.

    Then he tries to make a case with partial info, using a worst possible dome mid as if it had any relevance, since very few would purchase a mountain shape dome mid response curve. Quite theoretical gymnastics. Who builds speakers using as bad as possible drivers? Probably no one or so, then definitely not a typical case, can't be called serious work.

    For comparison with CD use he promotes, the maximum excursion of a typical JBL 4" compression driver is given at 0.55 mm (pic shown), and for the poor dome he chose to display "only has a 0.4mm of linear excursion" he wrote ( +/- he omitted). Calculating his way leads to a displacement capability difference between the two of only 0.15 (or 1/7th) of a single mm! Far from a biggie, and not very significant.

    In addition, he treats the ATC dome mid like an exception, it isn't. People looking for dome mids, including for the 93 to 97 db sensitivity range, should see for themselves the ones offered (i did). Likewise for high sensitivity dome tweeters. Excluding cheap low-quality units, there remains a number of them for both types, obviously he didn't check.

    Declaring/deciding the solution (need of 15"/horn) without having first established one's needs and goals, duty/use, db spl required, dispersion pattern needed, budget, etc. seems cavalier and sure doesn't help the DIY in making the best choices or decision for his own situation.

    Harping on about horns he missed the most important opportunity he had: providing DIY/users with solutions, even suggestions, leading to a significant reduction of high CD/horn distortion. But he's offered them no alternatives to the problem as if there were only horns. Therefore they'll remain in double digit distortion, for many cases, and passing on the hot potato in DIY/users hands.

    It should be more of a concern than he has shown. In view of his dome denial, plus distortion skepticism, its evident horn users and candidates for such are the ones that need to be rescued, not the junk dome he tried to convince with.l

    Reality and/or practicality is horns are mostly useful in PA/SR work, over about 110-115 db level and/or where a specific sound dispersion pattern is important. Such require horns, many others don't or less so. Moreover, there's the case of people who like/prefer horns for whatever reason, good or bad, its their right and money too. But that doesn't mean horns are necessary for the person's use, its rather a personal choice, the result of influence or imposed by a cloning project. Naturally, going the horn way does come with higher distortion to endure...

    In a lot of cases domes are an undeniable, practical and cost effective part of the solution to achieve lesser distortion.

    Between DB's more output and distortion reduction (switching CD): "It is JBL's contention that the reduced distortion is the greater of these two benefits," (From horn document he posted). Thanks.

    Richard

    J. Eargle, Loudspeaker Handbook, 2nd Ed., P. 178
    What and how you project your posts is entirely up to you.

    But dissecting and cross examination of a text book on the basis of validation of you own position is on the one hand taking the hobby a bit too seriously or are you taking a
    narcissistic approach to proving your right and the author is wrong?

    Who are you discussing the matter with?

  3. #573
    Senior Member RMC's Avatar
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    Following up on my previous dome/horn distortion post, this concern applies to most if not all CD/horns, not just to a selected few. The so called good horns aren't that many among all those used by audiophiles. It should at least provide proper uniform coverage re intended use (not automatic) and have pretty low distortion (one can't assume this).

    Preferably horn distortion improvements would take place in the higher range, where high percentages occur. Down in the CD/horn spectrum its somewhat lower using some models, the bulk of this issue being elsewhere.

    Seems more difficult to achieve up there considering second harmonic distortion increases two-fold per driving frequency doubling, for a given intensity. If there was an easy fix for this it would have been implemented long ago and possibly across the board too.

    There's far less frequencies influencing the data from about 500 hz to 1.5 khz (a frequent horn xo range), than there are frequencies from 1.5 khz to 16+ khz, actual distortion usually being mesured at numerous frequencies.

    Any device that's not improving distortion numbers of the higher range in a worthy manner is of little help if any towards a notable distortion reduction. It simply skips an important matter. To be helpful it should do the "magic" on a good chunk of the HF problem, instead of a very limited bandwidth.

    In my view its good common sense to tackle an important or critical issue, one also having a nice yield/improvement. Whether 15%, 25% or 40% distortion these are serious numbers, then its logical it would be a good place where to give attention.

    When given some thought, what's worth having the best low distortion electronics gear upstream when major output components downstream still generate a sizeable amount of signal alteration.

    The above is largely justified by the fact higher up in the spectrum, where most of the bandwidth often is, JBL and Eargle both show the distortion percentage goes up fairly, as frequency increases. For the dome driver this is a lesser concern.

    Richard
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  4. #574
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    From well-known British Loudspeaker Engineer Stan Kelly, described as a high efficiency guy, has a different and quite direct approach to CD/horn distortion: how much can one cope with and the driver/horn design is done accordingly (within limits). Kelly sees horn distortion as inherent, a basic design factor, in such process.

    The increased mass Kelly alluded to would likely be the one from a cone. There's still a mass (lighter one) and a resonance frequency involved with the compression driver's diaphragm.
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  5. #575
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    The main goal in CD/horn design is high efficiency for high output level. CD/horn engineering entails some compromises too, its a balancing act between various aspects. There's a number of compression driver parameters the Design Engineer has to juggle with, e.g. of such parameters: BL product, diaphragm-to-phasing plug spacing, moving system mass, spacing between phasing plug slits, etc.

    Moreover some engineer's choice(s) made will impact distortion level. The pic here shows one trade-off involved.

    Cost considerations are also part of the design process. Beryllium seems like a preferred diaphragm material, so does high saturation alloys in the magnet assembly. However, these two are expensive options according to Eargle, Loudspeaker Handbook, 2nd ed., P. 175
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  6. #576
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    Hi Richard,

    Have you investigated the co axial compression drivers from BMS

    Note with the curves raised 10 db the 2nd harmonic H2 is like -30 db with these drivers
    This equates to 0.1 % H2 distortion
    The H3 distortion is an order of magnitude lower.

    In that respect these are blameless compression drivers.



    https://www.bmsspeakers.com/fileadmi...ion_driver.pdf


    https://www.bmsspeakers.com/fileadmi...ta_2012-02.pdf

    Below is a single diaphragm HF driver


    https://www.bmsspeakers.com/fileadmi..._datasheet.pdf

  7. #577
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    Not wanting to impact or maybe rain on someone else's "parade" i chose to post the following here.

    Good news, i found late last night, the justifications for the UREI cab's actual operating mode. It looks to be what i had anticipated in another thread.

    Recall i mentioned over there things such as: it would "flirt" with a sealed box, mimic or so sealed cab operation/transient response when covering the vents with the foam plugs, if low density foam it would be seen as a resistive vent. That appears to be the case.

    UREI describes the cab as a quasi-closed box, probably with the standard port covers on. Most likely the vent would be a resistive one in my view. Without the port covers it might be called an overstuffed vented box depending on the amount of damping material applied at the factory.

    I've seen no box tuning frequency mentioned in all the docs i have, nor any impedance curve that might show this. Seems like a taboo subject or proprietary info. Its possible there's an Fb involved, but i tend to think the effectiveness of such on reducing LF cone travel, in this case, might not be as good as in a normal vented cab?

    A couple of pics with highlighting show where the meat is. File size seems to dictate one pic be posted alone.

    Richard
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  8. #578
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  9. #579
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    UREI WOOFERS

    Apart from woofers specific to UREI use (U800 series), there aren't many from JBL which effectively fullfilled this task or could do so acceptably i guess: JBL's 2215H/J in the 813C and 815C respectively. I'm adding here the 2234H used in the lesser known UREI 813BX (consumer version, pic attached). No other JBL mentioned in the JBL/UREI documents. I'll propose yet another below.

    The above (and below) might give users some indication about driver suitability in the UREI cab, in case a replacement is needed. So many things get discontinued that you'd better have more potential options.

    I did look at the T/S for a few on and off the list but i figured the applications Engineers must have had reasons to put or not a driver on that list, or maybe limited the choice to the preferred one, excluding other possible candidates by the same token?

    Even with the help of JBL's transducer substitution documentation on-hand there's limited hope for other JBL LF option(s). A potential one that comes to mind is the LE15 said to be practically the same as 2215 (T/S data).

    Digging deeper JBL indicates the LE15 has no equivalent on the Pro side, although it has other things than T/S in common with the 2215. In fact JBL suggests to replace the LE15 by the 2234 (acoustic equivalent), as a last resort. As for replacing the 2215 JBL suggests again to use the 2234 (acoustic equivalent), also as last resort. However even if they might be little different the substitute is the same for both (one might say for lack of a better option).

    In addition, in terms of recone kit JBL suggests, for the LE15, to use the C16R2215. They could easily have said none is applicable in this case, in view of the above "no Pro equivalent", but they nevertheless referred to the 2215 kit (no mention of last resort here). (I'm aware LE15A/B and 2215A/B are "unique" recone wise (along with others), while the LE15H and 2215H should be reconed separately).

    Btw with regards to EBP both 2215 and LE15 are at 90, and the 2234 at 92. No real difference here too.

    I think there's elements showing enough common ground between the LE15 and 2215 that are hard to ignore. I don't pretend they are perfect twins, probably brothers though, not that much apart after all.

    Therefore i see two more potential woofers as replacement for the UREI cab: 2234 and LE15. The former was in fact used in UREI plus its been designated in some cases (last resort). The latter is as close to a 2215 than one comes across according to JBL's info.

    It doesn't prevent the LE15 and 2215 may still sound a little different, that's based on the Design Engineer's recipe.

    The K/E145, for example, isn't part of the select few here, not my choice. But one seldom sees, from a major manufacturer, an MI driver for control monitor duty.

    Richard
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  10. #580
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    https://www.mixonline.com/technology...onitors-383665

    Hi Richard this link refers to an Eminence helper woofer.

    When Urie became JBL itís conceivable that JBL tooled a variant of one of their drivers for the helper woofer. They did this sometimes to fit out a particular finished product.

  11. #581
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    UREI ADDENDUM

    The original woofers used in UREI didn't have typical model numbers such as those from JBL (except for 2215, 2234 and LE15 i mentioned previously). The UREI's looked like e.g. 800W and 802W.

    Note i use here for identification purpose "woofer" for the LF only and "coax" for those with double duty (LF/HF).

    These UREI specific woofer and coax drivers are U800 Series identified. The woofers were likely made by Eminence (not the JBLs above). As for the coax they were initially Altec 604 (various), however when Altec got in quality and money problems UREI switched to PAS Speakers to provide the coax drivers.

    So one might have an original pair with Eminence/Altec while another guy could own a Eminence/PAS duo. No clue if one is actually better than the other.

    I have most of the UREI info available, a number of scematics as well. Basically all the "physical" info, like enclosures number, cab volumes, woofers and coax model and/or part number, networks number, horns number, same for grilles, for each model. Also recone and diaphragm kits number. Standard specs too, etc.

    However, curious that i haven't seen yet a single set of T/S parameters for the UREI specific woofers. There seems to be a little mystery surrounding that component in particular. For the coax one could possibly search in the parameters from the Altec 604 data base for the coax used. For the PAS models good luck i guess.

    The very short UREI history is that Edward M. Long presented his Time Aligned crossover to the AES convention in 1976 and UREI went in production in 1977 (model 813). In 1983 UREI was sold to Harman, JBL took over the business (UREI became a division of JBL). From 01/1984 JBL drivers were used with the release of the C Series.

    The crossover is effectively trade marked, and it appears to be patented as well, likely to prevent copy.

    Based on JBL listings i have the last UREIs made were 809A and 813C, both ended in 1994. They might have been the most popular models. Therefore any other can only be older than this...

    Richard
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  12. #582
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    Why yes, I am UREI fanatic through and through now, but I see no rain on my "parade" here. I think this information should go within the UREI thread, it's good stuff. The title of this thread is very misleading.

    PS, the UREI 813BX must be very rare. In all my scouring of everything UREI, this is the first time I've heard about them.

    A word about distortion from a laymen's perspective: I think what's considered acceptable is largely due to whatever the market-wank-a-teerers sell to us. Admittedly, that's where my standards come from. I then try and compare component A with competing component B. If I can, I'll actually have a show-down between the things in question. So yeah, a compression driver has a lot of distortion, but I wonder if similar drivers have similar distortion characteristics or ranges much like amplifiers. So from that, perhaps we can speculate as to what's acceptable vs what isn't? In the end, it all comes down to sound/satisfaction. As I've learned, give everything a shot before condemning it. I almost bailed from making the trip to see those monster UREI 813C's. One, because I never heard of them and two, because horns were supposed to be so awful. Oh yeah, I also thought my XPL200's were my "it" speaker system. Boy was I wrong. They now reside at my dad's and the UREI fleet continues to grow. To each their own, but my ears are convinced that there is something magical about the UREI's. Perhaps I shouldn't say that, why drive the demand up?

  13. #583
    Senior Member RMC's Avatar
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    Hi Derek,

    RE I think this information should go within the UREI thread, it's good stuff.

    Since the mid 70's i've accumulated a LOT of audio info from many manufacturers and other sources, not only JBL material but numerous others. For years on paper, have a ton of that (catalogs, brochures, spec sheets, etc). In more recent times on the computer.

    Sorry but i don't have time to spend on scanning and/or transferring e-files left and right. There's simply too many. Then someone else may want my Altec, McCauley, E-V, Vega, Turbosound, Fane Acoustics, Peerless, Vifa, etc. info. I have not only for speakers but for electronics also, this could become quite a task. When there's a specific request i try to provide relevant info.

    If you have a specific UREI question i'll try to answer it based on the info i have, but i cannot commit to transferring all my data for one or more brands. Its not located in a single place but rather in a number. Unfortunately too much work.

    RE PS, the UREI 813BX must be very rare. In all my scouring of everything UREI, this is the first time I've heard about them.

    As for the 813BX, i found on the web better pics than what my small camera allows since you're a fan of UREI.

    Richard
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  14. #584
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    Of course once I stab in 813BX, all kinds of information pops up.. Interesting that the seller states those were made in 1986. I thought the 813C debuted in 1985 with all JBL drivers? Interesting to see this 813BX with the PAS(?) coax and a 2234, knowing that. Although you mentioned a 2234 could be substituted for a 2215. In that same listing there is a gallery of photos with studios whom have 813's all soffit mounted. Very cool.

    Understandable about not having the time to upload stuff or move it. However, if you find time here and there and are up to it, I'd love to see everything you've got on the 8xx product line, most interested in the 813C of course. But the evolution of the product line is also fascinating. Also interested in the UREI 6500 amplifier. I'd like to own one someday just so I can say I've got one. Collect the whole set, right? LoL.

  15. #585
    Senior Member RMC's Avatar
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    Derek,

    RE Although you mentioned a 2234 could be substituted for a 2215.

    Yes, JBL themselves have used the 2234 in a UREI cab i.e. the 813BX so i figure they knew what they're doing, plus they are the ones suggesting the 2234 use as acoustic equivalent (last resort). No crime comitted here.

    To make a driver suitability determination the applications or design Engineer has access to a driver's whole pedigree. I'd call this the internal info vs the external we see (the one we're made aware of).

    Don't forget JBL has more driver(s) data in their computers than what we're actually shown (whether partial engineering specs, measurements made, tests they done, distortion figures, destructive testing, etc.). They know many things that we don't and Marketing releases in spec sheets the info they choose. Competition requires...

    Richard
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