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Thread: Altec 9844-8B

  1. #16
    Senior Member Skywave-Rider's Avatar
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    It does get worse...

    Thanks again to all.

    I am reading and puzzling and hopefully not blundering. Too much.
    News: I took the plunge and ordered a set of APT-200s.
    http://www.partsexpress.com/pe/showd...number=290-536
    If they don't do the job, they can go back. (I realized the k-77s are not adequate.) I hope to try it all out next week. Kind of exciting.

    Wishing for a RTA and oscilloscope.

    Meanwhile, Rod's speakers are (were) awesome. Are those double 12" like my 9844s, or 15" woofers? They seem to be placed right on the floor, or nearly -- at least for the ad. That should help the bass. I will try that at some point.

    Enjoy the rest of the weekend.

  2. #17
    Senior Member Skywave-Rider's Avatar
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    Problems, problems...

    Tweeters are in transit.
    In the meantime sorting out the loading cap/diaphragm question. Trying to find out if I have symbiotic diaphragms or all aluminum. The covers from my supposed 902 drivers are not there, so it's hard to tell what's what. I have determined for sure though that I do have loading caps.
    If you can help, I have pics at this thread:
    http://www.audioheritage.org/vbullet...ad.php?t=19156
    Thanks!

  3. #18
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    Trying to find out if I have symbiotic diaphragms or all aluminum.


    - Your diaphragms are definately all aluminum ( not symbiotic ) .
    - As was pointed out in the other thread, talk to Bill at GPA about buying the proper, bigger back-caps that have a felt liner ( & then retire these "reduced volume" loading caps ) .


  4. #19
    Senior Member Skywave-Rider's Avatar
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    Thanks Earl K!
    Precisely the affirmation I was looking for. U made my day.

  5. #20
    Senior Member Skywave-Rider's Avatar
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    Got APT 200 tweeters rigged up onto the mounts I made for the k77s; very good results. I was able to listen only about 20 mins, but the insane imaging of the k77s is gone and it's become tight and precise. I was thrilled to discover that a lot of the severe phasing and comb filtering seems to have gone away. I did notice issues with smeared transients and experimented with positioning the tweeter fore and aft. I found forward such that both horn bells are in line to be the best (so far.) I would have imagined that lining up the diaphragms would be the way to go, but I have a lot to learn. Preliminary results: pretty happy.

    I ordered a Behringer DEQ2496 to look at some RTA; and hope to try it next week. Received 902 driver covers and felts today from Great Plaines Audio, so also looking forward to disposing of those loading caps.

    Let you know when I can get all this done and give a longer listen.
    Last edited by Skywave-Rider; 12-15-2007 at 10:43 AM. Reason: spellcheck isn't all that.

  6. #21
    Senior Member Skywave-Rider's Avatar
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    I've gone through 2 Behringer DEQ 2496 RTA/EQs, both have been defective and returned. Going for a third today from a different vendor, if in stock. I have a feeling there is a bad bunch of units out there.

    On another front, removed the loading caps and installed GPA covers successfully. Happy to report I did not run a screwdriver through any diaphragms.

    When/if I get the RTA I'll post images.

  7. #22
    Senior Member Skywave-Rider's Avatar
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    Behringer

    Got my 3rd DEQ2496 and reporting it is in continuous operation for 24 hrs with no known issues. So I think this one works. I see the production code on it is about 8mos newer (from Musician's Friend) than the previous one I got from B&H. Since the Altecs are not in my apt., I have not RTA'd them yet. I did check my Heresies and to my surprise, they are flatter than I thought they would be. (Note that I have Bob Crites tweeters installed, which are Eminence APT 50s on custom horns to fit the Klipsch.) Tried "AutoEQ" function on them and hated the sound. Sounds "plasticky." Frankly, I think the Heresies have no major issues in my current placement, and since they are horn speakers as well, have less problems with room reflections in the mid and upper octaves compared to:

    My EV Sentry 100s,

    Also in my apt..
    I just refurbished these and will be using them for mixing on my ProTools rig. I RTA'd and "AutoEQ'd" these and I will say in this application, this DEQ2496 worked well. Evened the frequency response. Showed me where alternate placements would be better, and makes the bass work from these monitors -- flatter. The sound of the Behringer unit is still there, but I can work with that. The Sentrys are for working, and a representative freq. response is more important to me when using them. For listening while not working, which is when I use the Heresies more, I won't use the EQ, or have it in line at all.

    I use digital EQ all the time in ProTools, and can't live without the Waves stuff, so it's not like I'm against DEQ. But when it's not necessary to do D to A/A to D, or vice versa, I'd rather not.

    At home I use an old Technics SU 8600 ss amp on the Sentrys and currently a Magnavox 88 02 00 6v6 pp amp on the Heresies. For the Altecs at my job, I have a recently acquired Crown PS 200.

    I intend to have some RTA of the Atec 9844s in the next few days. I know I will need expert advice from you guys, but I will try not to draw this out unnecessarily.

    In the long view, if I find myself living in a larger place, the Altecs will be my room mates, and will probably (maybe) be powered by one of my little tube amps.

    Side note: A few weeks ago I used the 9844s at a video/film screening with the APT 200 tweeter and the Crown amp. It sounded very good -- but they are certainly bass shy -- as they were with the original crossover.
    Last edited by Skywave-Rider; 01-02-2008 at 11:20 PM. Reason: Brain lock, and model numbers.

  8. #23
    Senior Member Skywave-Rider's Avatar
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    OK, be brutal, what do you think? PART 1

    This is one of my 9844-8Bs pictured with a Genelec 1031 (boo,) and a Westlake BBSM-8 (yay!) behind. Please no comments on the ill-placed Sonex foam you will see scattered about, it is not my doing as this is not my control room or studio. I donít own the other speakers either. In fact I did own Genelecs and happily sold them last Summer. If I can get the Altecs running satisfactorily, I will try some mixing with them in this place to hear how the result translates.


    Inside one cab showing new GPA covers over the 902 drivers:


    Inside the other cab shows one 414 appearing different, though it is stamped 414-16. Does this seem correct?


    Close up of renegade woofer:


    Compared to its room mate:


    As you can see the previous owner had port tubes which I pulled off. Once I get things sorted out, I might want to try that to help the low end.

    I measured and aligned the rear of the voice coils for the 902s and the Eminence APT200s. The tweeterís setback position will cause bad reflections off of the cab:


    So I went ugly and put on a sound blanket:


    I made the next several unscientific measurements using my new DEQ2496/companion mic, from a 3 foot distance with the mic height exactly between both horns. Kind of aimed at the blanket. The room is a studio which has non parallel walls, though the ceiling and floor are. I used a Sonex gobo to help kill reflections from the close wall:


    Continues in next post....

  9. #24
    Senior Member Skywave-Rider's Avatar
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    OK, be brutal, what do you think? PART 2

    Continued from previous post.....

    This is the result with both L-pads turned to minimum output:


    The 902 brought in:


    And the APT 200 brought in:


    Since I don’t really know what the hell I am doing, I tried to get levels across the spectrum as even as possible, but I was looking from the other side of the room and should have done better. Here are the L-Pad settings:

    Left pot is 902.

    I then rolled the whole mess into a typical rectangular room with the idea of giving a listen. I also took some readings there as well. The room (a classroom) has hf absorptive panels on the left wall -- which you can’t see -- so I brought in the Sonex gobo for the right side against the blackboard:


    For the next two readings, I can’t remember what the mic placement was...
    I think it was about the distance between the speakers; first with 902s in “normal” phase, which is reverse polarity:


    And now with 902 leads reversed so that they are actually in phase now:


    Now for some potentially bad news. I decided to do a close check in this room for each speaker, which I did not do in the studio room (don’t know why.) So I went back to the 3 ft placement as shown previously, but stayed in the classroom. Left speaker:


    Right Speaker:


    Looks like the left 902 is 5 dB down at about 2.5k. And generally the curves are not as similar in that range as I would expect. But I have not done this before, so I don’t know how significant that actually is, given room placement differences. I did not roll each speaker into a single location. I simply measured them positioned as they were in the classroom image. Here’s the approximate L-Pad settings:


    Right now I’d like to hear your opinions. After digesting what you guys say, I will see what I can do to make the 3way as good as I am able. I may also try the cascade filter modification suggested by Art J. Then I will definitely compare one three way to one 2way. And for this I don’t know if I should modify one of my existing crossovers or do you think I should build a copy of the original network?



    I now see an attractive benefit of going active --- being able to change things on the fly.

    Thanks for all the help!
    Last edited by Skywave-Rider; 01-07-2008 at 04:41 PM. Reason: Added caption.

  10. #25
    RIP 2011 Zilch's Avatar
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    You want to measure on tweeter axis. There's a rationale for this, but I'll have to look it up. Those tweets should be putting out much higher VHF than you're showing.

    Forget the tweeter time alignment for now. Move them to the front and compensate with phase inversion, if required. I believe you'll find the top of the cabinet and the pad are messing you up.

    It looks like something's up with phase in the left speaker between the mid and tweet making the notch at 6K3 Hz. Measure each driver in each system individually (running on their respective filters) to see how well they match.

    That'll also show whether the filters are operating as expected. Then, it should be easy to see the effect of inverting the phase of each in the display, woofers plus mid, mid plus tweeter when you run those together.

    The bass response certainly changed when you switched rooms. No matter, you're going to have to measure that nearfield to get any reasonable idea of what's going on down there. Your first curves are more what I'd expect to see, typical, in this respect.

    Make notes in a notebook what you do with pic numbers. It quickly becomes difficult to remember what's what without that when you're trying to figure out what's going on and changing stuff....

  11. #26
    Senior Member Skywave-Rider's Avatar
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    Thanks, Zilch.
    When I made the crossovers I checked and re-checked and checked the wiring some more because I know I am prone to these errors if I get distracted. I will check it again

    I will also check the connections to the 902 diaphragms for verification. The APT200s have a factory red dot, which is hard to screw up.

    When I do this again I'll go back to the studio, stick with the 3ft distance and roll each speaker into the same location for the checks. I'll align the bells of the horns and measure at tweeter height. I'll also use the same output of the PS 200.

    When checking individual drivers is it OK to disconnect as opposed to cranking down the L-pad(s)? And for the woofers, which are somewhat less directional, should I move the mic down? Sorry for the basic questions.

    Thanks for the notepad tip.
    I can't tell you how many hours it took me to do what I did -- but it's fun.

  12. #27
    RIP 2011 Zilch's Avatar
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    Key to understanding what's going on is parsing the system into its individual elements, and then looking for the expected behavior when you "assemble" them in measurements. If that doesn't happen, ask yourself the appropriate question: "HUH, what's up with THAT?"

    Example: Right and Left look similar except at 6K3. Why? Well, first look at the tweeters alone and the mids alone. Are their responses the same? Why aren't they summing in the Left one?

    Turning down the L-Pads is a good way to isolate the drivers, actually. The load stays in place, being provided by the L-Pad alone instead of the driver or a combination of the two.

    If you're not biamped, put an 8-Ohm resistor in place of the woofers as dummy load when you disconnect them to measure the mids and/or highs. OR, if the filter sections are separate, just disconnect the LF filter at its input.

    The bass is being made by both the woofers and the ports, and the best way is to measure each at a very close range, like 1/4". You then do a calculation to sum the relative contributions to the total response at each frequency within the range of interest, weighting each source according to its diameter. The volume of the pink noise must be turned down considerably for this, of course.

    If you want just one reading, find a location that's central to the woofers and ports, and back maybe 3 - 6". That won't be as accurate, but it will provide an indication of the LF response better than from 1M or more away, which is likely to incude additional room effects.

  13. #28
    Senior Member CONVERGENCE's Avatar
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    Nice looking set up you got there. THe 414 are 16 ohms connected in parallel = 8 ohms.

    Quote from your post"Inside the other cab shows one 414 appearing different, though it is stamped 414-16. Does this seem correct? " YES It could be a Z series they din't bother with the lid on some series that were
    sold with cabinets.

    Keep us informed this is interesting.

    ...............

  14. #29
    Senior Member Skywave-Rider's Avatar
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    REDUX

    Iíve redone all my measurements in a more systematic way as Zilch suggested. Thank you for all your guidance on this Zilch, your expertise has been invaluable and is greatly appreciated.

    I returned to the Studio room, and added more sound blankets. I also kept the pink noise levels consistent excepting for the woofer/port close micing. I was extremely careful about the speaker/mic positions. All tests were done at tweeter on axis from a distance of 3ft from the front of the cabinet (except for close woofer test.) I used only one side of the amp. The last session gave me a lovely few days of ear ringing, so I grabbed my range muffs. Best Idea I had all week

    I used dummy loads when removing drivers from the tests because I found there was always some output even at minimum settings. Additionally, as Zilch suggested, this was needed for taking the woofer out of the equation, since there is no L-pad for that.

    The tweeters are moved forward such that both horn bells are aligned. Although this should mean phase problems due to time alignment, the whole rig sounds much better this way. No more blankets on the top.

    Hereís the setup:

    Dummy loads are 8 Ohm, non inductive, L pads remained at this setting.

    I found after I did all the image cutting and pasting, that there are no big discrepancies between the drivers in both speakers and I think the response is very similar.

    I donít know what I can realistically expect from the crossover. But I would like to improve it as much as is possible. I donít know how good or bad the curves appear to you guys. I want to learn and am open to your suggestions.

    Here are the curves:
    Attached Images Attached Images  

  15. #30
    RIP 2011 Zilch's Avatar
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    Well, there it is. The mid phase is correct, but, with the tweeter in this position, you need to reverse its phase. Do you see that?

    And also that reversing the phase of the woofer produces the same notch between it and the mid as reversing the mid?

    That's occuring at 630 Hz, it looks like, and I'm surprised the mids are playing so strongly down at 400 Hz. Your crossover designer may recommend a change to that particular filter.

    The woofers are indeed rolled off below 50 Hz. As you have reported, there's no extended bass to be had here; need subs for that. You might achieve better balance with what's there by dialing down the mids and tweets more. It's looking somewhat "forward" overall.

    The notch at 3.55 kHz is in your mid/horn combo, apparently. Do your new rear caps have felt or foam damping in them?

    I don't normally run RTA pink noise so loud as to require muffs, though that certainly gives good signal to noise performance.

    You should be able to observe the notch between the mid and tweeter increase and decrease as you move it back and forth from the front. It'll repeat in multiples of the wavelength at crossover.

    Your results are certainly much better, and I would say also more reliable, now that you have the variables under control....

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