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Thread: Which horns for JBL 2451 Be drivers?

  1. #1
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    Which horns for JBL 2451 Be drivers?

    Hello,

    I now have some 2451h drivers with original diaphragms. My plan is to load them with Be diaphrams and try to make a nice 2-way monitor. 3-way is an option but I will barely manage making a 2-way. So here goes:


    1. How do I chose between the 8ohm and 16ohm Be diaphragms (http://reconingspeakers.com)?


    2. Which 1.5 horns would you recommend for 2451 with Be diaphragms?


    Some options that I found:
    Multi-cell horns like this: http://stereo-lab.de/produkt/klug-horn/
    M2 waveguide
    2384 waveguide
    JBL 4367 horns -- are these even available?
    Wooden radial a la TAD style (I think the TH4003 is 1.5" throat)


    Just tryin to get the best perfomance (music only no movies) out of these 2451. Thanks in advance!!


    Herman

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    Senior Member ivica's Avatar
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    Quote Originally Posted by Herman Chigrin View Post
    Hello,

    I now have some 2451h drivers with original diaphragms. My plan is to load them with Be diaphrams and try to make a nice 2-way monitor. 3-way is an option but I will barely manage making a 2-way. So here goes:


    1. How do I chose between the 8ohm and 16ohm Be diaphragms (http://reconingspeakers.com)?


    2. Which 1.5 horns would you recommend for 2451 with Be diaphragms?


    Some options that I found:
    Multi-cell horns like this: http://stereo-lab.de/produkt/klug-horn/
    M2 waveguide
    2384 waveguide
    JBL 4367 horns -- are these even available?
    Wooden radial a la TAD style (I think the TH4003 is 1.5" throat)


    Just tryin to get the best perfomance (music only no movies) out of these 2451. Thanks in advance!!


    Herman

    Hi Hernan,

    I think If You want 2-way system, I would suggest to use D16R2441 JBL AL diaphragm or may be even D16R2445. With Be(Trx) UHF driver would be "a must".
    Concerning the 2-way system and FH dispersion I think that M2 horn would be the best, or may be You can make a 1.5-inc Yuichi large horn WITH FINS.
    LF driver would be a 'problem' may be ?

    regards
    ivica

  3. #3
    Senior Member pos's Avatar
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    Hello Herman,

    This is a great driver choice!

    Quote Originally Posted by Herman Chigrin View Post
    1. How do I chose between the 8ohm and 16ohm Be diaphragms (http://reconingspeakers.com)?
    Depends on your amp.
    Noise (hiss) is the biggest issue with high sensitivity devices in an active system.
    16 ohms will give you a 3dB advantage there, and also reduce amplifier distortion, but at the cost of 3dB reduction in max SPL capabilities (if the amp is the limiting factor).
    That said some low power amplifiers with very low residual noise might be more at ease with a 8 ohms load, like the LPUHP amps, but this is a rare case.

    IMHO 16 ohms nominal is generally the better choice there.
    JBL even went to 32 ohms nominal with the D2 (dual 16 ohms coils in series), and only wire them as 8 ohms (coils in parallel) in passive PA speakers.

    2. Which 1.5 horns would you recommend for 2451 with Be diaphragms?
    I suppose you will not be using a tweeter, so constant directivity up high might be an interesting asset, leaving out tractrix horns
    On the other end of the spctrum the size and low frequency cutoff that you should target will depend on the woofer and crossover frequency choices.
    The come the issue of the throat size and bolt pattern.


    Multi-cell horns like this: http://stereo-lab.de/produkt/klug-horn/
    No experience with these, but multicell horns generally need a tweeter up high where each cell starts to beam.
    Stereolab does adapt to any existing throat size and bolt pattern in there resin tractrix horns, but I don't know is that is the case with those wooden horns.

    M2 waveguide
    very good choice, but you will need the adapter sebackman designed in order to plug the 2451 on it.

    2384 waveguide
    no experience with that one, but it is said to be very good and it looks like it has both new (2435/2450SL/D2) and old (2451) bolt patterns.
    Is it sturdy enough to handle a 2451 without specific bracing?

    JBL 4367 horns -- are these even available?
    I think these can be obtained, but you might again have to use a specific adapter as these are designed for the D2 form factor.

    Wooden radial a la TAD style (I think the TH4003 is 1.5" throat)
    Memebr Woody designed a 1.5" version (3/4 scaled down) of the Arai 290 horns, and they seem to measure and sound pretty good!
    TH4003 is not a good choice here: almost impossible to find and clones might not be accurate, narrow directivity up high, 39mm throat vs 38mm for the JBL...

    Another candidate you should consider is the H9800.
    I think Guido still does clones (in Germany), and can provide a 1.5" version with an adapter plate suitable for a 2451 driver.
    I also know someone in France who might sell some in the near future.

    If you plan on using a small woofer (12" max) or maybe include a midwoofer (10" would be ideal) then you can also consider the smaller JBL PT waveguides...

  4. #4
    Senior Member pos's Avatar
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    Quote Originally Posted by ivica View Post
    With Be(Trx) UHF driver would be "a must".
    Hi ivica,
    Not in an active system IMHO, as the HF rolloff is relatively gentle and very well behaved.
    That said in a passive system Ti SL diaphragms are easier to handle.

  5. #5
    Senior Member baldrick's Avatar
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    Havenít tried myself but several have compared 2384 to M2 and prefered 2384, I guess 2384 can also be used at lower freq.

    I use 2451be in M2 and sounds good enough for me but lacks a litlte at the top Even with EQ.

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    For a two way system you cannot beat 2384 or M2
    2384 is sturdy enough for 2451. Build quality is horrible, but they are readily available, cheap and sound great crossed at 700-800. Can easily be sanded down and painted and should definately be damped with bitumen or equivalent stuff. maintains directivity control beyond 10k with Be but I ended up with a tweeter

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    +1 to what @johanwholst said.

    I use a JBL 2453h-SL CD on the 2384 waveguide, biamped JBL 4722 2-way. User notnyt on the AVSForum has many CD measures on this waveguide between pages 121 and 146 starting at: http://www.avsforum.com/forum/89-spe...akers-121.html including a Be. I really like the sound of the 2453h-SL, but might consider Be...

    I use a steep digital XO at 630Hz as recommended by JBL for this system and sounds excellent. I tried at higher frequency, like 750Hz and 800Hz with the steep XO and it shifted the image up more towards the waveguide. At 630 Hz it the two sections blend seamlessly.

    Finally, if you use the 2384, you may have to shape the top a bit (10 to 20 kHz) due to increasing directivity because of its screen spreading compensation - i.e. designed for being behind a screen. See Zilch's measurements to get an idea: http://www.audioheritage.org/vbullet...l=1#post236160

    Personally, I have been very happy with the waveguide - very smooth response and directivity. It is a 90 x 50 pattern, whereas the M2 waveguide has a wider pattern both vertical and horizontal.

    Kind regards, Mitch

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    Guys, thanks for the excellent responces! I'm really amazed by the thoughtfulness and amount of good information to digest.


    My first surprise, Ivica, is that the Be Trx 4" diaphram will need an UHF driver. This is the opposite of what I imagined, from my understanding that Be is the strongest material and I assumed it will play more highs than other materials and increase the breakup freq.
    The stock diaphrams in my 2451 are ribbed titanium. They don't sound very pleasant. But from what I gather the 2451 Be is a good combo.


    When you say UHF would be a must, is it because the Be lacks quantity or quality of highs? I'm NOT seeking to get flat to 20khz extension.


    As far as LF driver, I do not know yet but my thoughts are light, hard, vintage sound drivers with low xmax that focus on mids and midbass. Maybe pair of 12" or pair of 15", like Tesla or Supravox.


    The goal is to cross around 700hz to a fast, dynamic and tonally rich woofer(s). A sub may be an option later down the road but the key for me is a CD on a horn that does not have nastiness. That and a good midrange midbass woofer. No subass needed for now. Music only.

  9. #9
    Senior Member ivica's Avatar
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    Quote Originally Posted by Herman Chigrin View Post
    Guys, thanks for the excellent responces! I'm really amazed by the thoughtfulness and amount of good information to digest.


    My first surprise, Ivica, is that the Be Trx 4" diaphram will need an UHF driver. This is the opposite of what I imagined, from my understanding that Be is the strongest material and I assumed it will play more highs than other materials and increase the breakup freq.
    The stock diaphrams in my 2451 are ribbed titanium. They don't sound very pleasant. But from what I gather the 2451 Be is a good combo.


    When you say UHF would be a must, is it because the Be lacks quantity or quality of highs? I'm NOT seeking to get flat to 20khz extension.


    As far as LF driver, I do not know yet but my thoughts are light, hard, vintage sound drivers with low xmax that focus on mids and midbass. Maybe pair of 12" or pair of 15", like Tesla or Supravox.


    The goal is to cross around 700hz to a fast, dynamic and tonally rich woofer(s). A sub may be an option later down the road but the key for me is a CD on a horn that does not have nastiness. That and a good midrange midbass woofer. No subass needed for now. Music only.

    Hi Herman,

    As You can see from the other member experience Be diaphragms would produce clear sound but over 10~12kHz UHV driver is needed, even EQ applied.
    I believe that is because of the mambrane suspension as it is not made of Be, but a kind of plastic , If You can get JBL Be original diaphragm (for 476 driver) then may be it would be a different story, but AL (JBL d16r2441 may be would be a solution for the home listening ) or even d16r2445. each of them have a kind of unpleasant response over 12kHz, but not so large as d16r2446. some experiments can be made with d16r2451SL diaphragm, but I believe that the result would be the same as Be(Trx) applied.)
    As You can see, some members are satisfied with 2384 horn too. May be 2381 or PT-H95HF, or PT-F95HF or STX825 are candidates too. Latter two are vary similar I think, but have to be used , I believe over 1.5kHz.

    https://www.jblpro.com/ProductAttachments/tn_v1n31.pdf

    some more results
    http://www.audioheritage.org/vbullet...l=1#post375519


    regards
    ivica

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    Senior Member baldrick's Avatar
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    From What Iíve heard Truextent is the manufactur of JBL BE and My guess is that 476be are quite similar as the once being sold from Truextent. The 476 is a bit different than 2451 and is probably the reason for them producing more UHF than 2451!?

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    Ari and I tried 2450sl with TE and 476be in M2. The sensitivity in the uhf is practically identical with a slight nod to the 476be.
    They also sound quite similar when eqed but 476be a tad more relaxed

    Regarding beryllium, cd horns and uhf:
    Implementing a tweeter is not easy!
    There are a lot of advantages dropping it.
    Added expense, comb filtering, loss of point source etc
    2384 handles 16k superb alone.
    I added tweeters, but ended up with costly 045be's
    Tested 2404 and 077, but they were a terrible match...

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    Thanks for the inspiration for a lower xo with 2384
    Dropped from 750 to 650 last night, and as you mentioned; it blends better with the midbasses even some additional distortion may be introduced

    Quote Originally Posted by Mitchco View Post
    +1 to what @johanwholst said.

    I use a JBL 2453h-SL CD on the 2384 waveguide, biamped JBL 4722 2-way. User notnyt on the AVSForum has many CD measures on this waveguide between pages 121 and 146 starting at: http://www.avsforum.com/forum/89-spe...akers-121.html including a Be. I really like the sound of the 2453h-SL, but might consider Be...

    I use a steep digital XO at 630Hz as recommended by JBL for this system and sounds excellent. I tried at higher frequency, like 750Hz and 800Hz with the steep XO and it shifted the image up more towards the waveguide. At 630 Hz it the two sections blend seamlessly.

    Finally, if you use the 2384, you may have to shape the top a bit (10 to 20 kHz) due to increasing directivity because of its screen spreading compensation - i.e. designed for being behind a screen. See Zilch's measurements to get an idea: http://www.audioheritage.org/vbullet...l=1#post236160

    Personally, I have been very happy with the waveguide - very smooth response and directivity. It is a 90 x 50 pattern, whereas the M2 waveguide has a wider pattern both vertical and horizontal.

    Kind regards, Mitch

  13. #13
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    Quote Originally Posted by johanwholst View Post
    Ari and I tried 2450sl with TE and 476be in M2. The sensitivity in the uhf is practically identical with a slight nod to the 476be.
    They also sound quite similar when eqed but 476be a tad more relaxed

    Regarding beryllium, cd horns and uhf:
    Implementing a tweeter is not easy!
    There are a lot of advantages dropping it.
    Added expense, comb filtering, loss of point source etc
    2384 handles 16k superb alone.
    I added tweeters, but ended up with costly 045be's
    Tested 2404 and 077, but they were a terrible match...
    Agree 100%, in my experience pouring over graphs will only take you so far and you have to trust your ears. Iíve got both SAM1ís with 2435be and H9800 with 2452/be in both cases I decided I didnít miss/ need any uhf and with some gentle eq just let both roll off gently above 14khz.i als use Tannoy HPDís that have similar roll off characteristics.

  14. #14
    Senior Member ivica's Avatar
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    Quote Originally Posted by baldrick View Post
    From What Iíve heard Truextent is the manufacture of JBL BE and My guess is that 476be are quite similar as the once being sold from Truextent. The 476 is a bit different than 2451 and is probably the reason for them producing more UHF than 2451!?
    Hi baldrick,

    May be I AM WRONG, but I think that 476 JBL Be diaphragm has metal (Be) so called 'diamond-shape' suspension, while Truextent Be diaphragm suspension is made of polyester or some other 'synthetic' material, so a kind of UHF frequency emphasize is diminished.

    http://www.audioheritage.org/vbullet...1&d=1354807911

    I think that in 476 driver, a kind of short copper ring is mounted in the magnetic circuit, but I am not sure.

    regards
    ivica
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    Senior Member Ian Mackenzie's Avatar
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    My comments is the limit (width) of the diffraction slot in the horn is possibly the issue . I

    This can result in a pencil beam at frequency = or higher width of the slot
    Btw l must re measure my Tad 4003s

    If l lost sleep on it l might by a Scan BE tweeter and cross it over actively with a small Pass Aleph amp @20000 hz

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