Re-measured Atec 9844-8Bs with stock crossover and HF driver (902-8B) with Fuzzmeasure, 1 meter:
Compared to Zilch's measure of 902/811B w/M19 crossover, below:
Re-measured Atec 9844-8Bs with stock crossover and HF driver (902-8B) with Fuzzmeasure, 1 meter:
Compared to Zilch's measure of 902/811B w/M19 crossover, below:
Hi Skywave,
- Here's what I can achieve ( for HF ) with a "remagged" 802-8D body / holding a newer type 35480 diaphragm ( with loading-cap reinstalled ) on a Sammi exponential 800 hz horn ( Zilch had one and called it a P-Audio something biradial ).
- This is a single 17.5 uF cap into a HF contour circuit ( 8R & 6.8uF cap ) & a LCR "series-notch filter" at 7150 hz ( it's the wrong "Q" so I won't go into details ) .
- "Design" loss is @ 10 to 12 db ( all dependant on the resistors used & the preferred "slope" of Midrange to UHF ) / meaning / this could be used with a 93 to 96db, 8-ohm woofer ( also depending on the amount of HF one likes )
- My smoothing ( 1/24 octave ) represents a pretty critical "look-see" / as does the size of picture / along with the vertical scale allowing a good look .
>< cheers
Earl,
Considering you are using 1/24 octave smoothing, that looks real good. You're also running 5dB per major division, so even more so.
Are you considering LCR notch filters for the 9k and 12.5k (approx.) peaks? I don't know how they compare in amplitude to the one you're working on at 7150.
IIRC, you have more HF than the stock 802 usually gives on various Altec crossovers..
Are you using the loading cap because the 35480 diaphragm is "light" and prone to damage or does it give an improvement in frequency response?
I would like to see what those horns are.
Oh, plus you don't have that lousy 3k dip!
Seems we're not making it up, Skywave. The characteristic HF roller-coaster is apparent in the early CBS Labs measurements of Model 19, and my own with Gary's 802-8Gs as well.
Somebody needs to do polars and power response; the information is not forthcoming from the purveyors, apparently....
- No , up that high ( & particularly over 10K ), LCRs steal more energy ( from the total response ) than they are worth .Originally Posted by Skywave
- Loading caps ( which most people take off ) slightly bump-up the HF just before initiating a faster roll-off of the UHF ( the slope-rate increases ) .IIRC, you have more HF than the stock 802 usually gives on various Altec crossovers..
Are you using the loading cap because the 35480 diaphragm is "light" and prone to damage or does it give an improvement in frequency response?
- Zilch has a pair I believe.I would like to see what those horns are.
- I believe all aluminum diaphragms have some inherent peaks & dips / the circuit designer ( as well as the horn designer ) must work around them ( to minimize them / somewhat like I've done ).Oh, plus you don't have that lousy 3k dip!
>< cheers
- Either you or Widget have already done polars for this horn ( long , long ago ) .Somebody needs to do polars and power response; the information is not forthcoming from the purveyors, apparently....
- Apparently not .
>< cheers
Hi,
- Here's another collage of FR studies ( for the 9846 "Studio Monitor" ) . I made this from "official" Altec information ( published in 1971 ) .
- I made it because I was trying to identify the standard FR "holes" in the response ( at the time ) for Altecs' smaller drivers ( on 811s & 511s ) .
- This type of sleuthing is necessary because Altec was particularly miserly in publishing meaningfull response graphs for its' HF products ( drivers with the recommended horns ).
- BTW, sadly, GPA maintains this approach ( with a couple of exceptions ) / As is said in universities to those seeking tenure ; "Publish or Perish" .
- Pics like this are always an interesting study ( in themselves ) of human behavior ( & motives ).
- ie; which FR ( or both ) is one going to believe ( & then champion / or denigrate ) ?
- BTW. the 9846B had an integrated 2-channel amplifier built into it (the box was biamped ) / it is conceivable these amp channels also contained some electronic EQ .
>< cheers
- Just in case you think the little squiggles in the FR of the 802-8D ( that I show above ) are caused by the horn / I don't think they are .
- Look at this obsolete B&C product ( circa 1999 ) on the same horn ( different passive EQ of course ) .
EDIT: Oops! my bad, below is a picture of a different horn ( very small ) & the DE16 . The horn is about the size of what can fit into a typical Duplex situation ( this came from a different train of thought, that obviously got derailed)
FWIW:
- It's a DE-16 ( not a DE-25 as the pic may suggest / bad labelling on my part ).
>< cheers
At first, I thought it was the vanes in the sectoral horns, but I believe Skywave and I have both demonstrated that the HF "undulations" do not occur using BMS drivers. Next prime suspect, the radial tangerine phase plug.
I don't know how audible any of this is, but even with BMS drivers EQ'd flat, the sectorals exhibit a distinct coloration. Whether that's pleasant to particular listeners, I can't speculate, but they are certainly not "transparent."
Mr. Widget suggested that I try them, which I did, worked with them some, and moved on; the 811B was returned to its owner, and the 511A is under the workbench, now, pending chopping the throat to 1.5" for trials with JBL throatless large-format drivers.
In my view, their primary feature of merit is imaginary gonadotrophic effect, but I have plenty of bigger horns that also play better....
- I don't know if that will be of any use / you'd still be trying to coax more low-mid from a driver that's now operating below it's natural Fs ( the 243X series ) . The larger 4" diaphragms of the 245x series will naturally be better in this regard .
- I love the look of 511(s) / so who cares about the sound ?In my view, their primary feature of merit is imaginary gonadotrophic effect, but I have plenty of bigger horns that also play better..... They're just too large for my place here .
- Still, I'll eventually buy a pair when the opportunity presents itself ( locally ) .
- Could be the radial phase-plug / though my 288(s) are generally more linear than any of my smaller 1" Altecs ( apart from the 802 that I just displayed a FR for) . OTOH, it's original diaphragm ( the 21597 ) was just brutal to look at ( FR wise ) .At first, I thought it was the vanes in the sectoral horns, but I believe Skywave and I have both demonstrated that the HF "undulations" do not occur using BMS drivers. Next prime suspect, the radial tangerine phase plug.
- A good 50% of my drivers ( all makes & brands ) need diaphragm rejigging of some sorts. If ( & when ) I buy a new pair of any make at least one will be a struggle to get correct FR out of.
- ( Hence my buried comments about Canada being a dumping ground for second rate QC product / heck, even Hector offers better "factory-rejects" direct from JBL / than what is typically obtained around here for full retail ).
Anyways;
- The worst culprits are the so-called self-centering types of diaphragms / I have a few B&Cs here that need the back-cap ( only ) partially screwed down ( what a pain this all is to implement ) .
- B&C uses the method of "captured-diaphragm" that was pioneered by Emilar . ( The "Back-Cap" holds it all in place instead of the older method that uses dedicated diaphragm mounting screws .
>< cheers
The experience you guys have accumulated boggles the mind and is well respected.
As an aside, last week I dragged out the 9844s and used them in a playback system for a documentary production class.
2.5 mode, small Teac receiver, student work coming out of a laptop with Tascam US144 interface.
One student had a stereo location recording of Indian music with a lot of percussion. Those speakers can still deliver dynamics. The "youngsters" always look surprised when hearing reproduction like this. And the Gonadotrophic Effect adds visual bewilderment to startled ears.
Hi Skywave,
- Here's another "look-see" of my second 35480 diaphragm / placed within the other "remagged" 802D body .
- The same vertical scale, picture size and 1/24 smoothing was used .
- This combo looks a bit nicer . I left out the 7.3K LCR notch-filter so one can get a better idea of the basic response .
- There's a bit more padding here / & the approach to HF contouring was different .
- This pad consists of; a 5 ohm conjugate ( parallel ) resistor with an 8 ohm "buildout" ( series ) resistor in front .
- The HF "bypass" cap ( paralleled "across" the 8 ohm buildout resistor ) is @ 2.2 uF .
- There's a 10 uF cap "amp-side" of all this / acting as a single-pole HP . I never got around to adding a coil to make it a 2-pole ( 12 db electrical ) hipass .
- I'm going to keep these diaphragms mounted to these 802 bodies for future projects ( like surrounds , etc. ) / I don't yet know what's up with the 902 bodies ( they have never measured this good ) .
>< cheers
BTW, the loading-cap is in place , on top of the diaphragm / like the other example which I've shown above .
Dr. Earl,
Looks good 1.2 to 16k +/- 4 dB without the notch. I'd think a lot of 802 users might want to try this.
When you rig them into a box sooner or later, I'd be interested to know how the sibilance range sounds without the notch. As you said earlier, graphs are open to interpretation, and to my eye, given your stringent display mode, the notch may not be needed. I guess you'll have to put your ear on it.
Your explanation of the circuit is much appreciated. Thanks!
Don't know if you guys are seeing it, but the roller-coaster resonances are standing out in high relief in Earl's burst decay waterfall.
This is non-tangerine 802, right...? :dont-know
- Yes, it's a non-tangerine phase-plug . I only own these 802-8Ds, ( of the alnico varietal ).
- My bad, for not making it clearer as to what I was working with, sorry. If I had 802G tangerine bodies I'd see what sort of FR I could get out of them .
- ( Like yourself ) I'm suspecting more & more that the tangerine phase plug is the source of the response undulations that you've previously catalogued ( & speculated about ) .
- These 802D bodies have locating diaphragm pins built into them / making diaphragm centering a literal "snap in" deal / even if it's ; "only one-attempt allowed to get it right" .
- Happily, the locating pins are obviously accurate for centering diaphragms / even with the newer type of diaphragm that I installed .
- First I'll need to review some of the above FRs (of yours) to try to matchup the resonances ( a significant drawback to ARTAs' CSD display page is that a cursor cannot be used to identify anything / everything needs to be "eye-balled' which I have found to be quite unreliable due to the builtin "skew" of the display ).
- "High Relief" could be a bit of an overstatement, in my experience ( if you're implying "audibility" with what I've displayed ) .
- FWIW, this CSD pic is showing a 30 db vertical scale .
>< cheers
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