Which horns for JBL 2451 Be drivers?

[Herman Chigrin]

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

[ivica]

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

[pos]

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.

[baldrick]

Haven’t 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.

[Herman Chigrin]

So far am leaning towards 2451be+2384 or Radial type horn.

Will I need a spacer between 2451 & 2384 horn combo?
What is the horn model no from JBL 4367? Is it the H9800?

Herman

[Ian Mackenzie]

Guys how big is the 2384? Not sure about the Waf?

I assume a Tad 4003 would work

[pos]

Hello Herman,

This is a great driver choice!

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...

[pos]

You're welcome

This was touched on in the third post of that thread:

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.

16 or 32 ohms compression drivers will even let you use some top headphones amplifiers that no speaker amplifier can touch in term of residual noise and distortion: https://www.massdrop.com/buy/massdro...near-amplifier

Another peculiar benefit of using a 16 ohms compression driver compared to an 8 one is that you will be able to use a smaller and cheaper protection cap

[Dr.db]

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!

Can you share any measurements regarding this 1,5"-yuichi horn?

I was told simply scaling down a horn doesn´t really work, it rather has to be redesigned and the proportions adjusted...
So I´m really interested if this horn performs as good as the full-size yuichi a290

[ivica]

Can you share any measurements regarding this 1,5"-yuichi horn?

I was told simply scaling down a horn doesn´t really work, it rather has to be redesigned and the proportions adjusted...
So I´m really interested if this horn performs as good as the full-size yuichi a290

Hi Dr.db,

I do not think that 3/4 scaling down would be the best solution. As You know that all JBL 2-inc CD drivers has (almost conical or exponential) horn that 'convert' 1.5inch phase plug opening to 2inch driver mouth. Such horn length is about 6cm to 7cm, so such "transition small horn" can be made if You want A290 to connect with JBL 1.5inch driver.
Other solution can be done using Dr.Yuichi recalculation procedure but starting with 1.5inch driver mouth instead of 2inch. I do not think that it would differ much then previously mentioned adding small 'transition' horn.

I think that EQ 2451Be (if it is Trex-Be) would be greater problem, but if You are using JBL Be (476) diaphragm, then I believe that there would be no problem about EQ it.


regards
ivica

[Herman Chigrin]

I think that EQ 2451Be (if it is Trex-Be) would be greater problem, but if You are using JBL Be (476) diaphragm, then I believe that there would be no problem about EQ it.

regards
ivica

Ivica,

what is the problem with putting EQ on 2451Be (Trex-Be), as opposed to JBL Be (476)?

Herman

[ivica]

Ivica,

what is the problem with putting EQ on 2451Be (Trex-Be), as opposed to JBL Be (476)?

Herman

HI Herman,

I would expect that 4" Trex-Be would have large dropout over 10kHz compared to JBL 476-Be diaphragm, as 2440 vs 2441 diaphragms have.

regards
ivica

[johanwholst]

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

[Mitchco]

+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

[johanwholst]

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

+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