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Thread: New driver and horn for my 'speakers: JBL 2450J + Truextent BeX4016 + Arai horn

  1. #31
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    Quote Originally Posted by marco_gea View Post

    The Woofer will be the same one that I was previously using, i.e., the Fostex FW405N (http://www.fostex.jp/products/fw405n/)
    This Fostex has a Rated Input of 50w, that seems very weak to me for a bassdriver. Musical power is 150w, but again thatīs only half of that what the JBL 2235h is capable of.
    Does Fostex has different power-ratings or are these drivers just not intended for driving high levels?

    Besides that, all the other parameters look very temping.

  2. #32
    Senior Member gibber's Avatar
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    Quote Originally Posted by marco_gea View Post
    Hi Ralph,

    yes, there's a cute 2.5-yr old at home... ;-)
    I remember the time... Enjoy it despite the occasional drawback it entails


    Quote Originally Posted by marco_gea View Post
    ...using it as a tweeter crossed over lower (7kHz in my case), I found that its frequency response is a bit ragged in the stop band (which causes issues with the passive crossover), and then it slopes down beyond 10kHz, becoming approximately -5dB at 20kHz (the upper frequency limit that I can measure - but the Pioneer then goes on and on... till over 100kHz!)
    You have cheap 3D printing now, here's your solution to raggedness from the year of Quincy Jones "Thriller" with that flat-as-a-witches guest singer (Jones or any brass considered OTT today, poly-anything will do nicely)Name:  IMG_3338.jpg
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  3. #33
    Member marco_gea's Avatar
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    Quote Originally Posted by Dr.db View Post
    This Fostex has a Rated Input of 50w, that seems very weak to me for a bassdriver. Musical power is 150w, but again thatīs only half of that what the JBL 2235h is capable of.
    Does Fostex has different power-ratings or are these drivers just not intended for driving high levels?

    Besides that, all the other parameters look very temping.
    Yes, the Fostex woofer is not intended for PA-high levels. It is designed first and foremost as a top-notch home hi-fi transducer, which entails a different set of design trade-offs. It sounds wonderfully detailed even at very low listening levels, and can still comfortably reach 115dB peaks at 1m, which translates to almost 110dB for a stereo pair at a typical domestic listening distance. Plenty loud enough for listening at home at realistic levels, even with very dynamic (20dB crest factor) recordings.

  4. #34
    Member marco_gea's Avatar
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    Quote Originally Posted by gibber View Post
    You have cheap 3D printing now, here's your solution to raggedness from the year of Quincy Jones "Thriller" with that flat-as-a-witches guest singer (Jones or any brass considered OTT today, poly-anything will do nicely)
    Hi,

    I'm not entirely sure what I'm looking at there (nor what Q. Jones has to do with any of it!).
    Is that a 3D-printed replacement waveguide for the PT-Rx ribbon tweeters?

    Marco

  5. #35
    Senior Member ivica's Avatar
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    Quote Originally Posted by marco_gea View Post
    I'm starting this thread to document the journey I've embarked on, namely replacing the mid-range section of my current 3-way loudspeakers:
    http://www.homebuilthifi.com/project/9409

    Intrigued by a post that I read here a while back:

    An interesting JBL driver candidate for diaphragm replacement with Be would be the 2450. This driver was originally developed to accommodate a Be diaphragm as JBL was considering going head to head with TAD with that design. It was the reason for the development of the "Coherent Wave" phase plug. It allows for output from the diaphragm to be recombined in-phase at the driver throat in comparison to the out-of-phase output from a traditional phasing plug with variable length paths. According to JBL, it really only works with a Be diaphragm. The Al and Ti diaphragms are in breakup mode over most of their bandwidth, and as one designer said, are so "phasey" that there is limited benefit from the "Coherent Wave". However, a Be diaphragm, being pistonic for most of its bandwidth, would theoretically benefit the most.

    This theoretically in-phase output would be a unique driver attribute compared to the TAD drivers and even JBL's current Be drivers. It would be interesting to have feedback if this two decade old technology actually results in a superior driver with a Be diaphragm.

    I decided to purchase a pair of second-hand 2450J drivers and send them to Guido Behringer to have Truextent BeX4016 diaphragms installed in them.

    I intend to pair these with Yuichi Arai's A320FL radial horns, which were originally documented in the May 1992 issue of the Japanese magazine "MJ":

    Attachment 75630Attachment 75631

    This is an interesting design that adopts a Hypex expansion with a cut-off frequency Fc = 320Hz and T = 0.6, resulting in a very linear on-axis frequency response down to Fc when paired with JBL 2441 drivers, as well as good horizontal directivity control to approx. 10 kHz (I intend to use a supertweeter for the last octave or so):

    Attachment 75632

    I had the horns made out of baltic birch plywood by a French company specializing in bespoke audio designs:

    Attachment 75633

    Another interesting feature of this design is the fact that the throat adaptor operates a very smooth transition from the circular throat of the driver to the rectangular throat of the radial horn, while respecting the same throat exit angle of the "classic" JBL 2" drivers (244x and 2450) in the horizontal plane:

    Attachment 75634

    I will post again in the next few days/weeks as I proceed to make the first measurements using my set-up (calibrated Beyerdynamic MM1 microphone + HolmImpulse software)...

    Marco
    HI MARCO,

    As I know JBL Be diaphragm differs from The BeX4016, so the results would be different, especially over 10kHz, where phasing is important.
    On some old papers it has be mentioned that a lot of resonances can be established in the CD driver in the diaphragm and phase plug interaction, so I believe tha at JBL they have payed their attention on all of that when they have constructed their Be diphragm, may be BeX has applied the same results, but as BeX suspension is of different type then JBL, I would expect different interaction too.
    May be much cheaper (5 times) good results can be get with the JBL Tl SL diaphragms.

    Regards
    Ivica

  6. #36
    Senior Member gibber's Avatar
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    Quote Originally Posted by marco_gea View Post
    Hi,

    I'm not entirely sure what I'm looking at there (nor what Q. Jones has to do with any of it!).
    Is that a 3D-printed replacement waveguide for the PT-Rx ribbon tweeters?

    Marco
    You were looking at a PTR7/III. Had you never opened yours? 3D? -- no.
    It is brass from the year Quincy recorded that brass-laden killer of a track.
    Which might serve as a blueprint for your 3D printed version, if of interest to avoid what you called "rugged".

    All the best,
    Ralph


    N.B.: brass = non-magnetic, be sure to have no spoons, no screwdrivers, no coins, etc anywhere near if you haven't opened the thing before.

  7. #37
    Member marco_gea's Avatar
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    Quote Originally Posted by ivica View Post
    HI MARCO,

    As I know JBL Be diaphragm differs from The BeX4016, so the results would be different, especially over 10kHz, where phasing is important.
    On some old papers it has be mentioned that a lot of resonances can be established in the CD driver in the diaphragm and phase plug interaction, so I believe tha at JBL they have payed their attention on all of that when they have constructed their Be diphragm, may be BeX has applied the same results, but as BeX suspension is of different type then JBL, I would expect different interaction too.
    May be much cheaper (5 times) good results can be get with the JBL Tl SL diaphragms.

    Regards
    Ivica
    Hi Ivica,

    in reply to the points you made:

    - yes, of course the JBL and Truextent dias are different, especially in terms of the suspension used;

    - the 2450 driver has a "Coherent Wave" phase plug that was reportedly developed with the specific intention to use a Be diaphragm (alas, then the marketing guys decided against it), so I would tend to believe that it ought to be well-behaved in terms of phasing;

    - the 2450 driver also differs from the modern Be-equipped JBL drivers in that it has an internal conical throat - this one may regard as a good thing (it helps load the diaphragm to lower frequencies) or a bad thing (it causes beaming in the top octave);

    - yes, I'm sure the Ti SL dias as originally used in the 475Nd (K2 S9500 & K2 M9500 systems) are also a good option. Based on the FR for the 475Nd in the M9500 horn, though, it appears that they still exhibit some nasty ringing, which the Be dias don't (at least up to 20kHz).

    Regards,
    Marco

  8. #38
    Member marco_gea's Avatar
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    Quote Originally Posted by gibber View Post
    You were looking at a PTR7/III. Had you never opened yours? 3D? -- no.
    It is brass from the year Quincy recorded that brass-laden killer of a track.
    Which might serve as a blueprint for your 3D printed version, if of interest to avoid what you called "rugged".

    All the best,
    Ralph


    N.B.: brass = non-magnetic, be sure to have no spoons, no screwdrivers, no coins, etc anywhere near if you haven't opened the thing before.
    OK, cool thanks.
    But I don't think I'll embark on any such customization of the Pioneer tweeters any time soon.

    Marco

  9. #39
    Member marco_gea's Avatar
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    Smile New in-room measurements

    ...after a few minor tweaks to the passive crossover.

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    The general trend is now very similar to the one recommended in the JBL synthesis installation manual:

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    Sounds good ;-)

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