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Thread: Altec 9844-8B

  1. #181
    Senior Member Skywave-Rider's Avatar
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    Thanks a lot for your interpretations and for posting the data, Zilch.
    I plan to go back and conduct the missing tests and re-evaluate the low freq performance of N-19Z. With and without helper.

    I wonder when the BMS units will appear....

    The helper woofer scheme makes the stock crossovers work much better.

  2. #182
    Senior Member Skywave-Rider's Avatar
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    Question about 2.5

    I have completed missing RTA from last test, and made additional with BMS 4552ND on N-800-F and M-19-Z in 2.0 and 2.5 woofer modes.

    Next I will do a listening shootout in mono between 902 HF on N-800-F and BMS on whatever x-over sounds best with that. Both 2.0 and 2.5 will be compared.

    All of it will be posted together.

    In the interim I have gotten fuzzy on the 2.0/2.5 modes which I was clear about last month.

    Do I understand this correctly: In 2.5 with 20mH in line with helper woofer, the crossover sees 16 Ohms down to the crossover region, when lower frequencies engage the helper and the inductor essentially allows both woofers to play in parallel, 8 Ohms.

    Looking at Zilch’s sims:


    Green and yellow are 8 Ohms. ERROR: PLEASE READ POSTS ABOVE!

    In helper mode, the crossover region in the low pass appears to be significantly boosted by maybe 8dB in the upper bass, really lower mids, whereas when 1 woofer is operating (16 Ohm), you'd have an 8 dB contour cut there. A boost lower down would occur when both woofers kick in.

    Do I have this right? ERROR: PLEASE READ POSTS ABOVE!

  3. #183
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Skywave-Rider View Post
    Green and yellow are 8 Ohms.

    In helper mode, the crossover region in the low pass appears to be significantly boosted by maybe 8dB in the upper bass, really lower mids, whereas when 1 woofer is operating (16 Ohm), you'd have an 8 dB contour cut there. A boost lower down would occur when both woofers kick in.

    Do I have this right?
    Nope, green and yellow are 16 Ohms:

    http://audioheritage.org/vbulletin/s...232#post197232

    In "Helper" mode, the impedance only changes below 200 Hz. You choose a lowpass filter which provides the crossover and response for the single woofer and the compression driver largely independent of what happens when the helper kicks in.

    Since your single woofer is 16 Ohms, in 2.5 mode, it's getting the green curve, i.e., boosted drive in the the crossover region. I think that's what you want, conceptually, since it's just one driver and not the acoustic summation of two drivers playing simultaneously in that region.

    That would also appear to be the reason Altec used this "16-Ohm" lowpass with the 8-Ohm parallel pair, i.e., to provide LESS drive to them in this region, the cyan curve, and that's why I suggest that the N800-F may be a better lowpass for use with the N19Z highpass in either case, though it may be necessary to adjust component values to achieve the optimum crossover frequency and slope.

    Recall that the N19Z lowpass is merely transcribed rote from Model 19 as a starting point, and provided primarily as an alternative for performance comparison....

  4. #184
    Senior Member Skywave-Rider's Avatar
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    Right!

    That makes sense now and correlates with the last listening test. No wonder I couldn't understand it. Thanks yet again for setting me straight Zilch. Please write a book....

    I assume voltage drives vis a vis horn/cabinet and specific real world characteristics translate to a frequency response x amplitude graph. Is that why voltage drives are used in sims? Because the data is more straightforward?

    When the helper woofer is not engaged, that is, in a simplistic hypothetical wherein the main is playing in 16 Ohm mode alone, is the diaphragm excursion of the helper "controlled" or damped by the amplifier? It seems as though it would be. Otherwise the helper is operating passively and doing "something." I don't exactly know what. Without an acoustic phase reversal chamber, if there is such a thing for speaker cabs, it would have to detract from the output of the main.

    Sorry, I'll look that up in Dickason.

    I realize this may be a moot point since in the real world, especially when listening to music, there is usually program content below 200Hz. And therefore the helper voice coil would be energized and operating to some extent most of the time and within its unique range.

    I've also realized that the impedance characteristics in this dual woofer system along with your 20mH helper scheme are fascinating!

  5. #185
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Skywave-Rider View Post
    I assume voltage drives vis a vis horn/cabinet and specific real world characteristics translate to a frequency response x amplitude graph. Is that why voltage drives are used in sims? Because the data is more straightforward?
    Yes, it's objectification of how the filter behaves electrically. How that transtlates through the other variables you mention to become the acoustic performance is indicated by what you are doing, the actual measurements. Bottom line, it's the acoustic crossover that matters, but understanding and controlling how the system gets there is essential to the design process.

    These sims just show how the filter behaves with resistive loads, and thus merely provide a rough indication of what's going on with them. They can be refined more by using electrical models of the actual drivers, instead, and even better, that combined with the frequency response of each in the desired alignment, as is done with crossover optimization software such as LEAP, in which case the acoustic performance can be predicted quite accurately. Some of that may be done with your RTA, actually.

    Regarding the "Helper" behaving as a passive radiator outside its passband, I agree that something is going on, but frankly, in detail, I don't know what. Considering the variety of designs incorporating this approach successfully, it's hard to conclude anything, since it's done both in common and separate volumes. Clearly, action as passive radiator in the conventional sense is not an issue, as the frequency is too high for resonance with the cabinet volume to occur.

    Does an active driver give a whit about an open duct or port above resonance frequency? Does it care about a conventional passive radiator up there, either? That's also why, when the issue was raised about the cabinet tuning being different for one versus two drivers, I deemed it moot; at the frequencies of interest, both drivers are operative, and above that, the tuning does not affect the performance.

    That's my analysis, and those are my assumptions. Others may know different and better, and hopefully, they'll step up to the plate and smack this around a bit here....

    Quote Originally Posted by Skywave-Rider View Post
    I've also realized that the impedance characteristics in this dual woofer system along with your 20mH helper scheme are fascinating!
    Another element not yet considered here is that when the impedance drops from the second driver kicking in, the amp will deliver more power, as well, providing more boost. That's less a factor with tubes, but I'll have to think through the implications....

  6. #186
    Senior Member Skywave-Rider's Avatar
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    LATEST MEASUREMENTS

    Listening report to follow shortly.
    Please hold your fire.
    Attached Images Attached Images   

  7. #187
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    MEASUREMENT MIC COMPARO

    I borrowed another ECM 8000 measurement mic and made a comparo as shown below. These measurements were not made in the same room I have been using for RTA; this is where I have done listening tests. (Note LF HVAC rumble, haha.) [RTA is 1 meter in this case, 4552ND/M19Z crossover for reference.]
    Attached Images Attached Images  

  8. #188
    RIP 2011 Zilch's Avatar
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    You'll have to explain your legends.

    I'm going to verify that those are actually Altec diaphragms in your 902s.

    Holding fire....

  9. #189
    Senior Member Skywave-Rider's Avatar
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    LISTENING SESSION

    Listening was done in the same room used previously and with 9844-8Bs placed as before, determined by the room mode calculator.

    Program material was mono or stereo summed and panned to one monitor or the other. I made no stereo listening test.

    In the previous comparison between N-800-F and M-19-Z, both with Altec 902s on the 811B horn, the N-800-F was preferable, though the M-19-Z had excellent UHF (see post #176.)

    In that session I switched between conventional 2 way (2.0) and helper woofer (2.5) mode, and generally found 2.5 mode to be better balanced for most program material on either crossover. (This time I switched, but not as much, because 2.5 mostly sounds better, though at times it can provide some boom.)

    Since I was able to get BMS 4552NDs in a group buy, I decided to pit those against the 902s, each on whichever crossover sounded best overall.

    Prior to changeover, I balanced each crossover/driver combination with pink noise and RTA. I used no additional compensation for the BMS drivers (the FR curves indicate none required!) Since the BMS is hot, I placed an L-pad ahead of the driver to get into the proper adjustment range for the L-Pads on M19Z and the stock attenuator on N800. No 19kHz notch filter was employed for the BMS.

    4552ND on N800F and M-19Z:

    The 4552/N800 pair sounds smooth on vox/ mids.

    The M-19 makes them forward and honk as was heard in the previous listening session with 902s.

    The LF is clearer on the N800, same impression as I had previously. In 2.5 mode, this crossover will sometimes boom.

    I did not notice boom on the M19 in 2.5 mode. The upper bass/lower mids however are not defined and that contributes to the lack of clarity in the low end.

    The UHF range is preferable on the M19, which is what I found when using the 902 driver on this crossover as well. (By ear, this is 12-14kHz and up.)

    HF is preferable on the N800, however.

    Conclusion: 4552ND sounds best on N-800-F.

    4552ND on N800F vs. 902 on N-800-F:

    When switching back and forth between the two drivers, it’s pretty easy to hear the HF roller coaster or undulating, non linear response of the 902. Some notes are peaky - I presume from the hills you see in the FR graph.

    The 902 will deliver more sibilance (4.5kHz-6.5kHz for males/5kHz-8kHz for females.) Sibilance is not necessarily bad. It’s some times realistic. But an overabundance is distracting. My judgment is that the 902 is not excessively sibilant; if the recording has sibilance problems, well; then watch out, it will be overbearing.

    The 4552 is very smooth throughout its range. Esses are subdued in comparison. The BMS compliments the 414 mids, they blend, and produce a mellow characteristic.

    The 902s are more dynamic, dramatic. I think this driver (and presumably its predecessors) does the greater share of providing a live performance reproduction, or as I hear others describe, the “Altec sound,” in the loudspeaker system.

    In comparison, the BMS sounds as though it flattens transients. Perhaps “flatten” is a poor choice of words. Because it does not sound like clipping of course, maybe “compression of transients” is a more apt phrase. I think it would be interesting to try impulse tests on both of these drivers. Perhaps the 902 exaggerates transients; if that is possible.

    Cymbal pings are often less prominent or in a few instances lost on the BMS. I don’t know if this is part of the “transient compression.” It may also be attributable to the 902 exaggerating the ping on an uphill of its undulating response.

    Generally the 902 has more air. The 4552 is drier.

    I had a female listener in attendance. Unprompted and without coaching, she tried to articulate some sort of issue in the BMS HF that was not present in the Altec driver. She stated she heard this on rides, tambourine, mostly metallic percussive sounds. As she is not a sound engineer, nor an audiophile, it was not easy to zero in on this without leading the witness. The best I can determine is she hears a sound in the HF associated with metallic percussion which stands out and is not normal or typical.

    I did not hear this during the listening session. However, since I’m aware of the 19kHz spike in the FR of the BMS, I might suggest it has something to do with it. Not empirical, I know.

    [As a sidebar, I have 4550s at home in an active setup. Prior to inserting Zich’s 19 kHz notch filter, I felt the presence of subtle “noise,” or irritation, gone after the filter was inserted. I am aware this could be a psychological expectation, but I don’t think so. BTW, I think that biamped system sounds great.]

    Conclusions: At very low listening levels, I would prefer the 902s. Better transient response (jumping to a conclusion, there) makes them more sparkly above 6 kHz which in terms of equal loudness, plays better at low volume.

    At mid to high levels, I would prefer the 4552s.

    4552s on N-800-F win, though I won’t sell the 902s.

    Crossover:

    This is the hard part.

    Perhaps I should do a recap of or rebuild the N-800-F. (See my initial query way down at #1, LOL.) If so, should I dig out the original Altec iron and wire wound?

    It might be cool to add the UHF circuitry and adjustability of the M-19-Z to the N-800.

    2.5 mode is a keeper. I don’t know if the bump at 250 can or should be dealt with. I would leave it switchable 2.0/2.5. It’s amazing how much more LF you hear, but it’s not as obvious on the FR graph as it sounds. It does cut lower mids/upper bass too, which is helpful.

    The rise at 1k and the dip (with BMS) at approx. 2k: Big issue? How does it look? I tried to pad the “floor bounce” area a lot. But I don’t know. I’d love to hear from those with experience.

    Somewhere I have the calculation for port tubes done. But I don’t know if that plays into the crossover LF mode issue.

    Zilch, I’m very curious to see what you think of and measure from the 902s.

  10. #190
    Senior Member Skywave-Rider's Avatar
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    Legend for RTA

    Quote Originally Posted by Zilch View Post
    You'll have to explain your legends.

    I'm going to verify that those are actually Altec diaphragms in your 902s.

    Holding fire....
    My apology for not being clear. I tried to edit this into yesterday's RTA post, but I can't. Is there a time limit on editing?

    Anyway:
    • -"2.5" the 20mH is in line.
    • -"2.0" the 20mH is bypassed.
    • -"helper shorted/16 Ohm" means the helper is disconnected and shorted, the crossover sees one 16 ohm main.
    • -"main/helper shorted/8 Ohm/2.0" means the helper is disconnected and shorted, and a 16 Ohm dummy is inserted in parallel with main, no 20 mH.
    • -"main/helper shorted/8 Ohm/2.5" means the helper is disconnected and shorted, and a 16 Ohm dummy is inserted in parallel with main, plus 20mH in series with dummy helper.
    • -"helper/main shorted/8Ohm/2.0" means the main is disconnected and shorted and a 16 Ohm dummy is inserted in parallel with helper, no 20 mH.
    • -"helper/main shorted/8Ohm/2.5" means the main is disconnected and shorted, and a 16 Ohm dummy is inserted in parallel with main, plus 20mH in series with helper.
    Let me know if there are other inscrutables.

  11. #191
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    Could you draw a schematic diagram with the final cross. network?Thx.

  12. #192
    Senior Member Skywave-Rider's Avatar
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    schematics

    The M-19-Z is in post 118.
    The N-800-F is here:
    http://audioheritage.org/vbulletin/s...&postcount=484
    I do not yet know what my final configuration will be. Do you have 9844s?
    What is your setup?

  13. #193
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    I'm still working up an analysis of the latest measurements, but I'm popping in with an observation that we don't yet know for certain what the highpass filter is in Skywave's N800Fs, though I'm not certain we care, particularly, if it is not to be part of the final design.

    In another forum, we have found two versions of N800F using significantly different values for the highpass capacitor. One provides some compensation for the excessive midrange of the HF driver, and it's indeterminate which Altec actually used in this 8-Ohm application....

  14. #194
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    Quote Originally Posted by Skywave-Rider View Post
    The M-19-Z is in post 118.
    The N-800-F is here:
    http://audioheritage.org/vbulletin/s...&postcount=484
    I do not yet know what my final configuration will be. Do you have 9844s?
    What is your setup?

    I have only woofers 4x414-16B and 2x806A+811horns,also the N800-F crossovers.
    I read your experiments on 9844 speakers.First I was thinking to make the same enclosures.
    Also I'm thinking to use them into another setup configuration/enclosures.... ....more like K2 9500/5500 series design to give more impact on the bottom.I know ...probabily I loose some spl.Do you think your M-19-Z could fit to 806A drivers?
    What do you think?
    The 806A's could'nt touch more than 14-15khz max.;so I'm thinking to attach a supertweter like Fostex T90A.


    Zilch
    I can look inside on my N800-F,if you are interested.

  15. #195
    Senior Member Skywave-Rider's Avatar
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    Quote Originally Posted by felixx View Post
    Do you think your M-19-Z could fit to 806A drivers?
    What do you think?
    The 806A's could'nt touch more than 14-15khz max.;so I'm thinking to attach a supertweter like Fostex T90A.


    Zilch
    I can look inside on my N800-F,if you are interested.
    The Model 19 used 802s, which might have a similar top end limit compared to 806s.
    http://audioheritage.org/vbulletin/s...802#post208190
    I'm sorry, a lot my documentation went into the ether by way of a recent computer disaster. Double check that. The crossover Zilch designed (M-19-Z) is derived from the Model 19.

    I suppose you've read my personal folly in trying to integrate a tweeter into this system. I'm not saying you won't make it work, but many swap the HF driver for one having an extended frequency response, the BMS4552ND I'm using is one example of such a driver. The Altec 902, of course, is the stock driver which is the other one under evaluation here.

    There's also this thread:
    http://audioheritage.org/vbulletin/s...=14690&page=58
    which everyone should read for the shear drama of tweeter integration.

    Quote Originally Posted by Zilch View Post
    I'm still working up an analysis of the latest measurements, but I'm popping in with an observation that we don't yet know for certain what the highpass filter is in Skywave's N800Fs, though I'm not certain we care, particularly, if it is not to be part of the final design.

    In another forum, we have found two versions of N800F using significantly different values for the highpass capacitor. One provides some compensation for the excessive midrange of the HF driver, and it's indeterminate which Altec actually used in this 8-Ohm application....
    I somehow expected I'd have to dig into the glop. Steve O, over at AudioKarma, kindly detailed his procedure for me.
    It would be interesting to find out exactly what's in there, though.

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