The Be version seems very well behaved in that regard.
The PEK surround, and the fairly ductile Be foil is good at damping resonances. That along with the lack of inductance control(impedance is more then double at 20k) in the drivers is what makes the top end drop as much as it does.
While the AL diaphragm has a "extended" ragged response due to high frequency breakup and seconday resonances, just as with any large format AL diaphragm.
You can see the difference easily in the 950pb, where the AL diaphragm has a long audible resonance ca at 9k.
While the Be diaphragm does not, the resonance is moved higher up due to the material. And the surround is well selected to kill it off, along with superior damping for Be foil.
Do notice that the Be foil is fairly soft/ductile, as you can see damaged Be drivers with domes that have deformed these days.
Whereas the Japanese Be in TAD/Pioneer exclusive, Yamaha etc.
Is much stiffer and lighter,so it is more fragile and will shatter instead of deforming.
So there is differences/teadeoff in the same materials.
Regardless of metal, different thickness, geometries, production tech and heat treatment will give different characteristics to the material.
The JA6681B is just simple to filter and well behaved through its useable band.
Also comes from a time and place where they put a lot of time and money into making drivers that was well behaved acoustically and easy to deal with.
Still you are on very subjective terms, about how people perceive the sound of theyre own diy projects. Everyone that does so has a strong confirmation bias.
Considering the effects of room acoustics and placement being to a larger degree determining then most of the details discussed here.
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This is also true for people who buy audio equipment, not only for diy people.
But that is also why it's extra important for diy people to measure their speakers to have objective data to counter that selfbias.
Someone tried that not sure how it turned out. I would just find 2450Sl or 2451 and not have to go through issues you would have to deal with.
Rob 🙂
Thanks for this great wealth of info.
Regarding SPL room interaction has major impact, of course. I can’t submit a sketch right now but please review: My room is only ~ 2405 cu ft. The north wall is 14 ft wide, 9 ft of which is trigonal, above which are three ~ 31” x 46” windows. No windows on the east wall. The south wall is 23 ft opposite the north wall and is 11 ft wide. There is no west wall. The one side of the south wall opens to a 27 ft x 3 hallway, across which is a 9 ft x 7 kitchen. Twelve feet of the hallway is open to the living room and past the kitchen is a 4 ft wide x 8 staircase that turns and descends. There is a triangular ceiling over everything which peaks at 11 ft.
Except for a 65” Sony OLED TV, a 4.5 ft x 27” open glass table, two small upholstered low back chairs and my subwoofers, the room is empty. There’s 28 year old thin pile carpeting over which are a few large and fairly new half inch pile remnants. The windows are covered with black out curtains which I only open once weekly to aerate the room.
I hope to be seated 12 to 13 ft away from the main speakers. My Altec midwoofers will play down to ~ 70Hz at 83db, below which I will use two of my four Rythmik F12 subs with a stereo DAC, or possibly more subs if advantageous and use a multichannel DAC, like this one. https://www.merging.com/products/interfaces/hapi-mkIII
With a room that small I’m certainly not wanting SPLs anywhere near hall levels-in fact, like all sane horn users I must endeavor to do everything possible to minimize risk of hearing loss.
The next consideration is choosing a horn and driver to ideally cross with my midwoofers.
https://josephcrowe.com/blogs/news/altec-416-8b-in-100l-sealed
Note that Troy Crowe says to cross them close to 500Hz, which will minimize third harmonic and IM distortion. And I want to main system impedance well above 4 ohms to minimize distortion with this amp.
https://www.stereophile.com/content/first-watt-j2-power-amplifier-measurements
Thus, would the JBL 2450J be the best choice for a two-way system, or would that SL model be required if it also wanted to avoid a tweeter? From what I think you said, the 2450J can reach towards 16kHz, which even though I can’t hear that high can perhaps best deliver the lower HF harmonics that makes recorded music sound natural. Marco's certainly much experienced with its sound and highly recommends this driver and perhaps Ro808 also, as the next best and affordable thing to those Sony and Yamamoto drivers he raved about.
OTOH, I wouldn’t be opposed to adding a tweeter if the 2450J gave superior lower midrange and is the overall best choice for the midwoofers but still needed a tweeter. However, IF it ends up that a horn like the AH425 would be the only good choice for my room, rather than a biradial, successful tweeter placement would likely be impossible.
Please advise.
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Hi @Robh3606 ,
So, if someone already has the 2450. . .
Kindest regards,
M
As much as I agree with you, was there not someone on the lansingheritage forum who reported success? Or am I confusing it with another forum?
So, if someone already has the 2450. . .
Kindest regards,
M
I just looked for it @ lansingheritage and found info which has made me think I don't want to go that route. I don't have them, I was offered a nice pair. Thank you and Robh3606.
Good memory! I thought there was a thread here too. The worst of it no 1/4 20 for horn mounting. This thread goes through the "agony".
Rob 🙂
https://www.audioheritage.org/vbull...an-I-turn-2450-into-2451&highlight=2450+snout
Hi @Robh3606 ,
Kindest regards,
M
Perhaps a good memory, but clearly poor searching skills. This is the second time, when you have supplemented my "good memory" with finding the subject matter.
Kindest regards,
M
Not too easy, and you would probably need to fabricate an adapter plate for most horn throats, unless you tappe new holes (not advisable..)
https://www.audioheritage.org/vbulletin/showthread.php?12214-Can-I-turn-2450-into-2451
The HP filter (low cut) is what minimizes harmonic and IM distortion in the woofer.
In the 100-1000 range your Altec woofer probably has less distortion than a compression driver at the low SPL you will listen at.
Recorded music sounds most natural (non-artificial) without adding harmonic distortion.
Adding harmonic distortion may make source material sound more euphonic, but that addition generally already has been done (or overdone..) in the recording stage.
https://www.proaudiodesign.com/pages/technical-services Their website says they do restorations, though they never replied to my request for a quote to restore a pair of JBL 2450J. I'll phone them next week about it. If they won't do the job maybe will get a useful referral, if needed, unless I opt for other driver alternatives.
But are you saying that Troy Crowe's recommended 500Hz crossover point is uncommonly low for my 15" midwoofers? https://josephcrowe.com/blogs/news/altec-416-8b-in-100l-sealed But is 500Hz the wrong choice despite my intention to cross with my subwoofers at ~ 70Hz,80db likely and given the 100 liter sealed cabinets rather than the large reflex cabinets those drivers were designed for and for minimizing IM and 3rd harmonic distortion?
https://greatplainsacoustics.com/pr...Ix_45k7dErBP0jDGJzmzw0gzjQutdQXpwlttSewcxVvNk and
Troy Crowe wrote the Altec 416-8B would do well crossed over up to 1800Hz, and it's "ultra low IMD" is even less when there is no stimulus tones below 100Hz.
Driven to 95dB (one meter) it's IMD reaches it's peak ~700 Hz, so if you were crossing over based on IMD levels that are similar to the noise your refrigerator makes, you might "ideally" cross below the point where the 15" IMD rises.
Ideally, you would also unplug your refridgerator whenever you are listening for IMD..
IMD will increase with SPL, the dispersion of woofers and tweeters does not change with level.
Most designers and listeners prefer crossover frequencies near the point where the woofer and horn's -6dB dispersion is similar, or "matching".
Arez wrote 600Hz is unusually low for a 15/16" woofer when it comes to matching it to the dispersion of a horn.
Troy's test did not include dispersion tests.
Altec Lansing's beam width charts indicate the 416-8B -6dB point is ~150 degree at 600Hz, dropping to ~70 degrees at 1250Hz, 50 at 2000Hz.
The deeper cone of the 416-8B makes it's upper dispersion a few degrees more narrow than a shallower cone like the JBL 2220B.
Art
I found this discussion very interesting, particularly Steve B's last post.
https://forum.speakerplans.com/radial-vs-constant-directivity_topic44930.html
https://forum.speakerplans.com/radial-vs-constant-directivity_topic44930.html
I went from 45° conicals, to exponential (on midbass) / Tractrix, to Le Cléach (where practical) and then back again to 50° / soon to be 60° conicals (Multi Entry Horns).
The latter are by far the most natural, uniform and right sounding horns I've made or heard.
A lot of that is to do with the single point/linear phase synergy effect, I believe.
The latter are by far the most natural, uniform and right sounding horns I've made or heard.
A lot of that is to do with the single point/linear phase synergy effect, I believe.
You mean from here http://www.romythecat.com/Site_Images/HornwiithScraches.jpg and then back?
Any experience with what Bjorn briefly mentioned here, diffraction horns?
https://www.audiosciencereview.com/...peakers-is-it-me-or.9633/page-45#post-2274682
Or anything like these?
https://audiohorn.net/x-shape-horn/
https://audiohorn.net/next-gen-bi-radial-horn/
No doubt yours is bigger than my ~23 ft x 14 room. It's mostly six figure income tier who gets that size listening room real estate here on overpopulated Schiit Island. https://en.wikipedia.org/wiki/Nassau_County,_New_York
For me it will probably be AH425 or TH4001 horns atop my midwoofers.
Unless you can recommend a commercially available diffraction horn compatible with my midwoofers.
https://josephcrowe.com/blogs/news/altec-416-8b-in-100l-sealed and my Rythmik F12 subs.
For me it will probably be AH425 or TH4001 horns atop my midwoofers.
Unless you can recommend a commercially available diffraction horn compatible with my midwoofers.
https://josephcrowe.com/blogs/news/altec-416-8b-in-100l-sealed and my Rythmik F12 subs.