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Quote:
Originally Posted by LTD02 /forum/post/19249410


i've been thinking about this for a while...a long while. what if we take the other side of the argument and say that ssc is a gimmick that has little to no effect on imaging or anything else. as a result, this is a region where you can "season to taste" as you say without impacting performance. most cd's poop out around 16khz anyways and most imaging cues peak around 4khz or so and span the region from about 1khz to 8khz.

You're asking the right questions here, and I just don't know the answers yet, not having run the 30° curves this time around. I'm certainly not seeing the on-axis peak with this XO like I did last time using whatever I did back then, Altec Model 19 HF comp, probably. I'll have to check; I may still have those earlier 2452H-SLs and BMS 4555s around. I know I have a pair of 2452H-SLs that'll play flatter up top there, and they may well be them. See attached image below from other recent work here.


Into this mix, we also throw Stgdz's measurement of his QSC center (no screen) evidencing a significant peak up top, which I view as them doing on-axis boost, at least. Key is knowing what's happening at 30°. If it's there, also, then with no screen, the answer is easy -- EQ it out. From Seymour AT's study, same would be valid for woven screens. I've never had a sample of mirco-perfed vinyl to test, but would do that if somebody stepped up with a suitably sized piece of it. I have requested two different SheerWeave samples from the manufacturer.


From my previous experiments, we know Screen Array rolls off the top end off-axis, and in theory, at least, if woven screens do not exhibit the screen spread phenomenon, then its directivity must be normalized via other means; EQ won't get it. Like you, however, in the context of large- or small-room X-curve equalization, the whole deal may be academic for HT, though I can see how it might still be a significant issue in a large theater. If it's all a ruse, it's a mighty clever one. That's part of why I'm so focused on the standard incorporated in HT media, which is apparently not available in public domain. X-curve itself isn't, even, rather, "trade secret...."



Edit: Found 2452H-SL #8 and re-ran the curves. I'm surprised these work so well on the 4722N crossover with no adjustments, not even SPL level, 2432H vs. 2452H-SL. Conclusion's the same, just less about which to equivocate:









 

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granted the 2452 is superior to the 2432...


[pause for a zilch applause session for the measurements]


[ok, that's enough love, the show may now continue]


i'm not sure that answers my question. i was kind of honing in on the question of how important (or not) ssc is to imaging and overall quality of sound. my guess, and that is all that it is but based on way too much reading :), is that frequency response above about 10k is kind of meaningless for the kind of imaging cues we ascribe to horns--controlled directivity, off axis linearity, etc. and instead kind of stands on its own as on-axis are you there or not type response. exceptions may include the supertweeter in the k2 and everest...ummm...perhaps they shoot a hole through heart of my theory. ;-)


some of my posts i put in the "just thinking out loud" camp. this is one of them.
 

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z., i posted 983 before reading 982. sorry if any wires got crossed there.


982 is worthy of sleeping on before i reply. give me a little time to digest what you have said, as you have said a lot in a very few words in that post. great stuff.
 

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Quote:
Originally Posted by LTD02 /forum/post/19249546


i'm not sure that answers my question. i was kind of honing in on the question of how important (or not) ssc is to imaging and overall quality of sound. my guess, and that is all that it is but based on way too much reading :), is that frequency response above about 10k is kind of meaningless for the kind of imaging cues we ascribe to horns--controlled directivity, off axis linearity, etc. and instead kind of stands on its own as on-axis are you there or not type response.

If it's not about imaging, then it's about spectral balance. Unless you toe them in, this will in detail vary mains vs. center. How much it matters in typical HT, I just don't know. All I can do is measure to determine if it is real.


Quote:
Originally Posted by LTD02 /forum/post/19249546


granted the 2452 is superior to the 2432...

It also argues in favor of installing SL diaphragms in 2445/6, those using them. I can say the impulse response is significantly "cleaner."


[Unless they're willing to spring for berylliums, instead....
]
 

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Discussion Starter #987
So it is the CD. I did not know you could swap CD's, but they have to fit so I am assuming that they are the same size?
 

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From what I gather, the suggestion was to use the diaphragm of the 2452SL on the 2445/6. Now can you also use that diaphragm on the 2432H without a hitch?
 

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MK, If you are swapping CDs, I would not mind picking up your old ones!
 

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Quote:
Originally Posted by MKtheater /forum/post/19250620


What are SL diaphragms?
http://www.avsforum.com/avs-vb/showt...4#post19224594

Quote:
Originally Posted by gpmbc /forum/post/19250674


The CD referenced is the JBL 2452 SL in comparison to the 2432H on the same horn.

Correct. 2452H-SL is the true large-format (4" diaphragm) compression driver used in the TOTL 573x Screen Arrays:

http://www.jblpro.com/catalog/genera...x?FId=91&MId=1

Quote:
Originally Posted by gpmbc /forum/post/19250981


From what I gather, the suggestion was to use the diaphragm of the 2452SL on the 2445/6. Now can you also use that diaphragm on the 2432H without a hitch?

Well, almost. The 2452H-SL diaphragm has a different (through the back cap) terminal configuration, but factory 4" SL (Aquaplas-damped) diaphragms are available that will likely fit and improve the performance of the earlier large-format driver series in terms of both measured and perceived smoothness. Aftermarket beryllium diaphragms are also available from TruExtent at a substantial premium:

http://www.electrofusionproducts.com...mDiaphragm.pdf


2432H is a recent (with the last year or so) entry-level addition to the 3" diaphragm (originally termed "medium format") 243x series of JBL compression drivers. Variants are available with aluminum (two types), titanium, and beryllium diaphragms, the latter allegedly being pistonic to 18 kHz. 2432H is different in design from the others, having an extended throat. Whether there are other differences that might preclude installation of these alternative diaphragms, I have not determined. This is the realm of tweakers -- generally, I assume JBL engineers know what they are doing, and go with the program; that alone is complex enough to fathom.


JBL consumer uses 243x drivers with Aquaplas damped diaphragms in their TOTL Synthesis (and some other) products, as well as an additional new magnesium-alloy variant. These are not offered by JBL pro, and are difficult to acquire.


Screen Array waveguides are available in both 1" and 1.5" throats. Both 243x and 2452 drivers have 1.5" exits and bolt up to the larger throat. MK originally had the 1" variant waveguide and drivers in his 3622s. 2430H was the former entry-level 1.5" exit driver used in 4622. 2431H produces more extended VHF with a thinner aluminum diaphragm, 2432H uses titanium, and 2535HPL, beryllium. The consumer variants have different but similar part numbers with a suffix designating the diaphragm material.


We're also talking about $$$ here. 2452H-SL (and 2435HPL) MSRPs are fully $1K per each higher than 2432H. Generally, it's a mistake to assume that swapping drivers and/or diaphragms is trivial, and the consequences must be verified both via measurements and listening. In the case of 2452H-SL, my odds were improved by the knowledge that JBL uses them in their TOTL Screen Arrays, but still, I was surprised to discover that MK's 4722N passive crossovers worked so seamlessly with both, at least insofar as VHF response is concerned.


Yes, 2452H-SL is audibly "better" than 2432H. If prior experience applies, 2432H performance might well be improved, relatively, via Aquaplas damping, but this falls within the purview of tweakers, as well, and nobody has done it with 2432H thus far, to the best of my knowledge.


[Don't be askin' me how BMS 4555 sounds on the Screen Array waveguide, now; I leave that for others to discover....
]
 

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"Don't be askin' me how BMS 4555 sounds on the Screen Array waveguide, now..."


could you be persuaded to bolt it up just as an experiment to see if the passive crossover in the 4722 works with that driver? ;-) if you happen to hear them playing by accident and happen to report your thoughts, well...it'd all be good. ;-)
 

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Maybe; let's see how Monday goes.


It's 4722 crossovers, actually. MK had 3622s prior to starting this 3731 build project. Long gone, presumably.


They're different crossovers for different drivers.
 

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Discussion Starter #996
Hey Zilchlabs, I have to correct you about my history.


I went from

Klipsch THX ultra II KL-650's to

M&K S-5000's

JTR triple 8's

JBL pro 3622N's(they had a different network than the ones you have now)

JBL pro 3731's(kind of)

Jbl pro 4675C hybrid of some sort.


I only name these as this is where the high performance HT started and eventually took off.
 

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And for those following along I now have the correct 1200hz passive xovers that were made for the 3731s. MK's horns came with the 4722 xovers which I sent off to Zilch for research and development. Seems everyone is benefitting here which is great. I'm still awaiting my last 2) TD15Xs which I'll be using for midbass (2 per speaker) then gotta build boxes and a little room construction to accomodate these behemoths.
 

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"I'm still awaiting my last 2) TD15Xs which I'll be using for midbass (2 per speaker)"


that sounds...serious. :) something about seeing all these big driver systems warms the cockles of my heart (even though i have no idea what cockles are).
 

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4555 requires drilling additional driver mounting holes in the Screen Array waveguide flange.


What are y'all thinkin', big boy HF for under $600/pair?

http://www.usspeaker.com/bms%204555-1.htm


[You want me to dial it in better now, right...?
]


 
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