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Thread: DEEPER BASS: D. B. KEELE/E-V's STEP-DOWN MODE

  1. #16
    Senior Member ivica's Avatar
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    Quote Originally Posted by RMC View Post
    A clarification note. In part 1, E-V, Post # 2, I must add the following in order to avoid any confusion.

    The paragraph where I quoted E-V concerning "With regards to Subpassband speaker protection...", this should be seen like a "by the way" note on out of LF passband filtering and how E-V suggests to determine such filter's frequency on low-frequency enclosures in general (i.e. 0.8 times Fb or box tuning frequency). This is NOT part of the Step-Down process, because the way the 6 db boost (and cut) filter is designed it already includes subpassband filtering at 12 db/oct., In addition to equalization. No requirement for redundancy then. I should have put that paragraph at the end of my E-V text as a BTW note.

    In a spec sheet's section on subpassband speaker protection, E-V mentions "The step-down equalization described in the Step-Down section provides the required protection."

    However, In part 3, Stepping-down with a regular equalizer, post # 4, the need for a subpassband filter remains relevant...

    Richard
    Hi RMC,

    Thank You for your explanations about the application of bass speakers in the smaller box and active EQ.
    Generally speaking, almost any speaker can be EQ in order to get the most from it, but I am not sure that the acoustical signature of the speakers with such EQ and the other without it that has 'native' better response would be the same. I am sure that almost any cheaper bass driver from say Asia that can be EQ would sound the same as say JBL 2269H , 2231A , 2245H, without EQ in the proper tuned box, especially if it would be used for the home listening conditions, where usually not more then 10W of power from the amp has to be 'delivered'.
    My experience with EQ-ed LF drivers would not produce the same feeling to me while listening the music, as not EQ-ed properly 'loaded' previously mentioned JBL bass drivers, but I can imagine that the other people would have opposite conclusion.

    regards
    ivica

  2. #17
    Senior Member RMC's Avatar
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    Hi Ivica,

    Your post is an interesting one. And I DON'T necessarily disagree with it. However, no time now since I'm writing another text on cone excursion in step-down mode that I would like to post tonight. But I will come back to your ideas in the near future. There is also a lot more info to come from me on "step-down" mode that I need to finish writing (e.g. real applications), including curious stuff or disagreements I may have. See you later.

    Richard

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    Hi Richard,

    Have you previously heard the EV interface A model with the 8 inch woofer and 12 inch Passive Radiator that used the step down equalisation?

    I recall it had un characteristically deep bass for a modest enclosure.

    EV were the forerunners in the application of T/L parameters in the 1970’s.

    In relation to your prior posts concerning EVs approach to assisted alignments l post a link here to the EV interface A Equaliser Owners Manual. The manual is quite comprehensive and covers topics including set up and placement and amplifier power recommendations. Moreover the manual provides insights to the peculiarities of implementing an assisted bass alignment for the consumer.


    .
    https://electrovoice.com/binary/Inte...s%20Manual.pdf

  4. #19
    Administrator Robh3606's Avatar
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    Hello Richard

    Thanks for the simulation in post # 11. A few things aren't clear to me.

    What are the boosting filter parameters you applied (frequency, amplitude, and Q or bandwidth) ?
    Any LF subpassband filtering applied ?
    The Bx-63 parameters, the software allows you options where you can duplicate what it does.

    On the bottom graph you have TWO response curves (orange and red). But on the top graph I see THREE cone excursion curves ! (two orange at Fb and one red). The orange curves are typical shape of cone travel in a vented box. However, the red excursion curve, looking like a pair of boobs, isn't typical for a vented box...
    Ignore the double orange curves I was doing a quick sim and forgot to add fill to the box. The bottom line is that is a typical curve for an unassisted reflex box. The red curve is the important one as there is no free lunch using EQ. You have to remember that the peak 6db of EQ is applied at resonance where the cone movement is minimal. So you have a 4X the power applied with the associated increase in cone displacement. So you have the minimum at resonance and humps on either side.

    Finally, I notice on the red excursion curve that the right hand bump is at almost 8mm @35 hz, Xmax being 8.5 mm, and the left hand bump, around 20 hz, about 7+ mm, for the same input power but with even lower frequency! Effect of subpassband filtering ?
    Well that is where the 12 db slope comes in to "protect" the driver

    Rob
    "I could be arguing in my spare time"

  5. #20
    Senior Member RMC's Avatar
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    CONE EXCURSION

    Hi Robh,

    I think I found the explanation for the non-conventional looking, two mountain shape, red excursion curve compared to the conventional curve(s) with no EQ in Post # 11. And why the output at 35 hz reaches almost Xmax sooner than the output at 20 hz or so, which seems unusual since the deeper bass = the more cone travel normally.

    In the extensive E-V Step-Down documentation/applications I have, I don't recall ever seeing a cone excursion graph (same for JBL Kramer/Timbers 1983 article), though one can get some idea by looking at LF Maximum Acoustic Output graph (E-V) or table (Kramer/Timbers article) for different box/driver duo (spl vs frequency). Because LF drivers are thermally or excursion limited:

    "The curve which follows shows the system's low frequency maximum acoustic power output versus frequency. The maximum output is limited by either (1) the thermal power handling capacity of the speaker, or (2) the speaker's maximum linear cone excursion capabilities, whichever occurs first." ("TL 606 Builders plans Bass box" E-V document (form # 1545-846). Kramer/Timbers have a similar mention.

    If you recall in part 1 (post # 2) E-V mentioned: "In step down, the enclosure is tuned to a lower-than-normal frequency. This increases system output at the new tuning frequency and reduces output slightly in the region of original tuning."

    In part 2 (post # 3) Keele said "The net effect on the system response is one-half octave extention of low-frequency response with only about 3 db less maximum acoustic power output capability in the passband."

    Also, in the same "TL 606 Builders plans Bass box" document E-V writes: "Note that some 2 to 3 db of maximum output in the 60 to 90 hz range is sacrificed when the step-down mode is used." Naturally, in that specific case its at 60-90 hz while in other box/driver combinations it will vary...

    There's a trade-off in "step-down" mode. In order to get deeper lows, one has to sacrifice some LF output capability a little higher in the spectrum. Since E-V clearly indicates that step-down EQ has no effect on maximum output, then this capability "loss" has to be a side-effect of lower than normal box tuning, that boost EQ does not compensate for because its applied lower.

    Now, if one compares excursion curves at 35 hz or so, with and without EQ (orange VS red curves in Post 11) the trade-off or sacrifice could well explain why the higher cone travel on red vs orange curve (i.e. lower output capability in that region meaning increased cone travel).

    I do believe the left Xmax bump around 20 hz on the graph (which does not exist in a conventional LF alignment) is caused by the EQ boost, therefore normal in this application.

    The above sacrifice or trade-off would explain the right "mountain" approaching Xmax sooner on the red excursion curve, and I think the subpassband filtering and/or higher-order alignment dropping faster is the other reason for the left "mountain" being lower than the right one on that same red excursion curve.

    Makes sense to me. Regards,

    Richard

    NEXT TIME ON TO BX 63/A

    EDIT: Robh, I'm at post # 16 now so I have some catching-up to do tomorrow...

  6. #21
    Senior Member RMC's Avatar
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    Hi Ivica, RE POST # 16

    As I mentioned I don't necessarily disagree with what you wrote. But the name of the game here is smaller cabinet. The idea came to me from another thread were a fellow wanted smaller box with comparable LF performance. In order to have a smaller box,while keeping efficiency up and distortion down, there is not a whole lot of alternatives.

    Stepping-Down woofer/box tuning looks to me like an acceptable or good compromise. Its still a compromise but well worth trying. Why not perfect? Resulting response is roughly flat, there is a trade-off for lower bass in reduced output capability in the region of original box tuning, cone travel is higher in the region of original box tuning ... But at least one gets what he wanted: smaller, deeper bass box! In normal use the "penalties" are not a big deal.

    As for the LF sound of these filter-assisted boxes compared to regular vented I haven't had the opportunity to compare at the same time side by side with same program material comparable speakers.

    Regarding EQing responses, in the past in another thread I did mention an article discussing experiments by a bunch of Engineering guys at MIT published in High Fidelity Magazine in the late seventies from Mark F. Davis, "What's really important in loudspeaker performance". Frequency response was one of great of importance. The work of Floyd E. Toole on this matter is world-renonwed, in his book 2008 Focal press, Acoustics and Psychoacoustics..., some of his work is on Harman's Web site re subwoofer placement, in the JAES and numerous magazine articles, e.g. speaker measurements VS listener preferences, e.g. on-axis response and power response (off-axis) are important criteria. His landmark work is the reason why JBL hired him as Acoustical V. P., if my memory is right. Regards,

    Richard

    EDITED FOR CLARIFICATIONS PURPOSE

  7. #22
    Senior Member RMC's Avatar
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    RE iAN'S POSTS # 9 & 18

    Hi Ian,

    I do remember E-V's Interface A for which I probably have some stuff buried somewhere in my audio Library. Never owned it and don't remember hearing it, been way too long.

    Some of Ian's links in those two posts, though interesting by title, just don't want to open on my laptop for security reasons (security certificate not valid or inappropriate says Internet Explorer)... But I have most of it already anyway, since I own a pretty good E-V and JBL Library. BTW E-V's tech sheets up to the 90's (4 pages filled) are second to none, each giving a LOT of practical info not seen elsewhere. Too bad cost cutting has reduced them to only 2 pages...

    THE most interesting link in my view is the third one in post # 9 titled Scrib. This one opens but bugs on my laptop. It is the web version of the Pro Sound Facts document I have quoted from many times in the past and I have the original paper version of it from E-V. That one EVERYBODY around here should have a copy not only on their desk but also under their pillow... Its probably in itself a vented-box workings and construction course... Regards,

    Richard

  8. #23
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    Quote Originally Posted by RMC View Post

    Some of Ian's links in those two posts, though interesting by title, just don't want to open on my laptop for security reasons (security certificate not valid or inappropriate says Internet Explorer)...

    Richard
    Same with Firefox, mentionning that security is not properly implemented on this site.

  9. #24
    Senior Member RMC's Avatar
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    Bx 63 and related matters




    Hi Robh, (EDITED VERSION)

    I don't own nor use the BX 63, so in the absence of a nice data sheet, please forgive my Columbo's work.

    At least now I know why no detailed data sheet found: That's a JBL Consumer Products device, not Pro division, as written on the Technical Manual I have (Consumer tends to do more user manuals than technical data sheets). B380 Tech Manual also identifies JBL's Consumer Products Division, so again no detailed data sheet.

    The BX specifications mentioned in the Tech Manual (none re high-pass filtering/EQ boost), are said to be the same for both BX 63/BX 63A, except 63 has X-over at 63 hz only and 63A has X-over at 63 to 140 hz. Therefore, I assume both use the same LF HPF/EQ and the only peak boost frequencies with Q 2 filters are 20, 30, 40hz as shown in Post # 5. At least that's the case for the 5235.

    The original BX 63 (not A version) was made specifically for the Kramer/Timbers 2245H subwoofer project as mentioned in that article (see post # 1). Going through that article another time I pretty much found right and left what I was looking for re LF filter parameters. It is a 6 db peak boost underdamped (bumpy) filter, that has a Q of 2. I understand the BX 63 has three fixed-frequency filters with Q 2 as mentioned above.

    And there is subpassband protection according to Robh: "Well that is where the 12 db slope comes in to "protect" the driver" (Post # 19). Kramer/Timbers mention this:"The quasi-fifth-order aligment includes a subsonic roll-off to unwanted cone motion below 20 hz."

    That seems quite similar to JBL's 5235 Robh referred me to and to E-V's own thing. Now I got some stuff to work with.

    in post # 11 you wrote re B380 it had 4.5 cu. ft. and tuning at 26 hz. Moreover, in post # 14 you mentioned using 2235's as B380's and added "Use the DSP in a crown amp to simulate a BX-63 so same idea..." Finally, in Post # 19 you said "You have to remember that the peak 6db of EQ is applied at resonance where the cone movement is minimal." I do know that, but.... Reading again this & above paragraphs one may notice something doesn't seem right.

    (Said here with all due respect and NO intention here to show any "fault" on your part nor any insult from me, but simply to illustrate below some misconceptions about approximate B6 alignments and peak boost frequency). Moreover, I also know very well that boost at Fb is not always the case, far from it you'll see!

    With a stock BX described above (boost @ 20, 30, 40 hz) or even 5235, how can one apply the boost at the 26 hz tuning frequency of a B380 or B460 for example? 30 hz is near but still a little higher than 26 hz. However, the graphs in your post # 5 show a nice 25 hz to me, middle of the road between 20 and 30 hz. Which of these two do you then choose? Looks to me JBL offered a ready-made no question solution, whereas with Keele/E-V its more choose and/or design your own.

    I will come back later with numerous examples and some possible explanations on peak boost frequencies. E-V's peak boost frequencies are "all over the map" by the way, and I still believe that E-V Engineers are as smart as others.

    In your particular case, if the Crown amp's DSP allows, you may determine precisely 26 hz as peak boost frequency, not with a BX? In the Kramer/Timbers article they do mention on P. 4, for their 8 cu. ft. B460, "With 6 db of boost added at 26 hz, ...", then regarding their B380 "...requires the same equalization..." (as B460) and conclude "... maximum EQ boost occurs at vent resonance, ..." (last page). So, how could they say that in view of "...Model BX 63 which was chosen for this application because it was designed specifically for the present combination of driver and enclosure." (P. 4). For these Kramer/Timbers quotes, the only explanation I may see is CUSTOM MADE BX?: "We would also like to thank D. B. Keele Jr. (JBL) for his kind assistance with the computer. His efforts made the special voltage drive of the BX 63 a reality." Unless at vent resonance isn't really "at vent resonance", but a little higher as I've seen many times on Keele/E-V stuff. (BTW, no wonder they used Keele for this considering the work he did at E-V on this matter). EDIT: Or the 30 hz BX boosting filter is in reality a 25-6 hz filter? Or if the 30 hz setting for example is really a 26 hz setting then why call it 30 hz ? Or that filter's tolerance is such that it "drifts" to 25-6 hz ? Tough question. Could be a marketing thing for wider user acceptance with common numbers such as 20, 30, 40 hz... In Post # 2 E-V said peak boost frequency within 5% tolerance provides no significant performance compromise. 26hz vs 30 hz = 4 hz, and 4hz/26hz = 15% or 4hz/30hz = 13%, and to stay in the 5% tolerance of the "advertised" filter frequency would mean 5% of 30 hz = 1.5 hz ! 0r 28.5 hz not 25-6 hz...

    In the Kramer/Timbers article they say: "The equalization necessary to flatten the response ..." (P. 4) This implies response isn't flat to begin with probably due to lower than normal box tuning applied. {BTW, in the B380 Technical Manual frequency response is quoted as being: "24 hz to 70 hz (- 6 db), Thru BX 63A Crossover"}.

    No mention by JBL or Robh of a normal mode Fb, then a step-down mode Fb, for the B380/B460. Kramer/Timbers modeled the B380/B460 equivalents only in step-down mode in their article. Had there been a given Fb for a usual or straight vented box, I think that Fb would have been around 30-35 hz range (likely 33-35 hz? after some simulations I've done. Otherwise, what would be the interest or real gain in taking a normal mode Fb of say 30 hz and down-tune it to 26 hz?). If that is the case, and I think its possible, then this is good news for my previous cone excursion explanation (post # 20) regarding the right hand excursion bump shown in red in Post # 11, in view of "... and reduces output slightly in the region of original tuning." (2-3 db according to E-V/Keele). EDIT: I think Robh realizes that when he wrote in Post # 19 "The red curve is the important one as there is no free lunch using EQ"

    Richard

  10. #25
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    Hi Richard,

    Please find below a consolidation of information relevant to Jbl which will fill some of the gaps as pointed put in your posts.

    The link to Harman and LH below is the bx63/a schematic and manual posted in a prior thread for your examination.

    http://manuals.harman.com/JBL/HOM/Te.../BX63%20ts.pdf
    http://www.audioheritage.org/vbullet...Answers-Needed

    (It’s worth pointing out that most members here who have been around a while are quite familiar with the Bx63/a and the functionality of the B460 and B380. So there is no need for me to further elaborate or a dissection of that.

    Concerning your prior post the summary below is taken on full review of the article and the manuals. This should also help you join the dots.

    For continuity here is a link to the article .

    http://www.lansingheritage.org/image...subs/page3.jpg

    http://www.lansingheritage.org/html/.../1983-subs.htm


    In summary the article was about 2 Quasi 5th order assisted designs using the JBL Pro 2245H and the JBL 2235H extended-bass woofers.

    The article discussed 3 designs:

    *B6 12 cu ft 20 hz assisted - boost 20 hz f3 21 hz (2245H)
    *Quasi 5th order 8 cu ft 26 hz assisted - boost 26 hz f3 26 hz (2245H)
    *Quasi 5th order 4.5 cu ft 26 hz assisted - boost 26 hz (2235H) f3 - see text in article

    *Fb =boost frequency in all 3 designs

    *Bx 63/a was used for both Quasi 5th
    order assisted designs

    *Relative response of the 26 hz tuning is -2.9 DB -37.5 hz (refer to chart in article)

    *QL=7 per computer table in article

    *Reference in the article was also made to an 12 cu ft unassisted design (2245H) tuned to 25 hz that is comparable to
    the Quasi 5th order 8 cu ft assisted design. The trade off being box size versus amplifier power

    *D.B Keele Jnr provided computer design of all 3 Quasi 5th order designs

    * The article references Hoge W.J.J, Keele D.B Jnr and Small R.H


    *In reference to your question of the unassisted tuning please refer to the Jbl enclosure guide in the link below.

    https://www.jblpro.com/pub/manuals/enclgde.pdf

    We look forward to your future posts

  11. #26
    Administrator Robh3606's Avatar
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    The plans

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  12. #27
    Administrator Robh3606's Avatar
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    BX-63 Manual

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  13. #28
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    Hi Rob,

    The 2369H looks an interesting candidate with Vas 234L , Xmax a stupid large 19mm, Qts 0.36, Fs 28

    If you have time can you run the numbers in BassBox Pro?

  14. #29
    Administrator Robh3606's Avatar
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    Hello Ian

    Yeah it's a great driver! Here it is same box with and without EQ. Fb 26hZ and electrical filter 26Hz Q 1.5 power input limited to 600 watts. Power limiting makes it damn near indestructible as you won't exceed thermal limits or X-Max using the EQ. So you get 3Db more output F3 shifts down to 25Hz all in a smaller 9 Cu Ft box. Not bad!!



    Rob
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  15. #30
    Senior Member RMC's Avatar
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    Hi Ian, (RE POST # 25)

    RE "Please find below a consolidation of information relevant to Jbl which will fill some of the gaps as pointed put in your posts." Sorry, but that info, which I already had AND CONSULTED before writing Post # 24, does not fill any gaps pointed in my post regarding JBL's BX 63/A story. Please read post # 24 again, and where I mentioned "That {re BX 63 filter} seems quite similar to JBL's 5235 Robh referred me to and to E-V's own thing. Now I got some stuff to work with." However, your material may be useful for members less familiar with the matter.

    RE "The link to Harman and LH below is the bx63/a schematic and manual posted in a prior thread for your examination." That Harman link refers to the BX 63's Technical Manual I had and quoted from in Post # 24 and other... As for the "Answers-Needed" 2012 thread link, well Robh posted here (in Post # 5) the same BX63 curves than he did in the 2012 post (also post # 5), nothing wrong with that, but no new info. As for the other attachement Robh provided in the 2012 thread (in post # 7) "JBL Low Frequency Systems Instruction Manual", I already had the Brochure for that (i.e. "JBL Low frequency Systems B460 B380 BX 63"), and after a quick look today at that Instruction Manual (for which I thank Robh and Ian) I note its the same specs pages I already had in the Brochure, but with a lot more wording on connections, etc. Again, there's really nothing new in there about the "Step-Down" process, nor filling any gaps past or present (e.g. Boost/Cut EQ filter detailed parameters). On the latter I wrote in Post # 24 "Going through that article another time I pretty much found right and left what I was looking for re LF filter parameters."

    RE "(It’s worth pointing out that most members here who have been around a while are quite familiar with the Bx63/a and the functionality of the B460 and B380. So there is no need for me to further elaborate or a dissection of that." I'd be tempted to say this one is the most amusing, since the above thread doesn't help your own cause! In the 2012 thread link, member Parisphoto says "Answers Needed", then member Rusty Jefferson requests from Robh a complete scan of the BX 63 owners manual, Robh posts the scan, Grumpy thanks Robh for the manual, Titanium Dome says "Finally, a post of the "missing manual", Parisphoto tanks Rob so much for posting the manual, Robh says "I never realized that we didn't have one somewhere on the site", Hjames adds "The missing Manual"! Thanks so much for this..." And some of these are quite senior members (2003, 2004, 2005)... So, If its as well-known as Ian implies, why this then??? I think he should have read the Thread before writing that pretention or linking to that Thread...

    The cruel reality is that JBL has given no detailed specs, in its BX 63/A related information documents, on the most important part of the device, the peaking boost/cut high-pass filter, except for some left and right in the Kramer/Timbers article... As if this was a secret, contrary to E-V giving so much info its almost overwhelming!

    RE "Concerning your prior post the summary below is taken on full review of the article and the manuals. This should also help you join the dots. For continuity here is a link to the article" I've had the original Kramer/Timbers article since it was published in Audio Magazine in august 1983. As mentioned previously, I have read it again recently and also checked again some things in it before writing my last post (# 24) in which I quoted many times from it, however I refered to it as the Krame/Timbers article since these are the two authors. As I said here before, I did find in it most of boost/cut filter parameters, but it DOES NOT help "join the dots" as you say. So, your summary of that article may be more helpful to others than me.

    RE "*In reference to your question of the unassisted tuning please refer to the Jbl enclosure guide in the link below." This issue was not really a question if you look at it, but more a tentative answer to an unknown fact (i.e. a possible normal mode Fb for B380 enclosure). The "JBL Pro Enclosure Guide" I've had in my laptop for quite a few years and did check it for the 2235H before writing post # 24. The example didn't appear optimal to me. That's why I made some quick simulations of my own as reported in post # 24. The proposed boxes in the Enclosure Guide are more "quick suggestions" or "rule-of-thumb boxes" to help novice speaker builders. They're not necessarily best, optimal or made-to-measure to each driver. This can easily be assessed by looking at the groupings or driver categories and more importantly what's in each of those with their own T/S. More like a "fit the driver in a box size group", instead of an optimal design or "made-to-measure box" considering each driver's particular parameters. In that specific 2235H case, the 5 cu. ft./ 30 hz tuning box suggested not only didn't match the B380, but also it didn't appear to match with the right hand bump in Robh's excursion curve (post # 5). "One size (doesn't) fits all" in my book.

    As you probably know already, I tend to do my homework before posting. Even during and after...

    Richard

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