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

  1. #46
    Senior Member RMC's Avatar
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    Answer makes sense. Trying to think why Kramer/Timbers, Keele and E-V never mentioned this issue as I recall. Maybe related specifically to driver or driver category used (e.g.2269)?

    Richard

  2. #47
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    After reading the EV XEQ-2 Manual and the Keele paper below l think careful attention needs to be paid to use of the table 1 Fpk/Fs ratio (6 dB Q=2) for boost frequency and the formulas 7 & 8 for Fb and Vb respectively.


    As an example interpolation of values of Qt for the Jbl 2269 (0.36) from Table 1 and equations 7&8 yields

    Fb = 23.3 hertz
    Vb = 125L plus 20% for box losses = 150L (fill =none)
    Fpk/Fs = 25 hertz (6 dB Q=2)
    QL=7 (note overvolume added)

    These are the theoretical values.
    Practical implementation would suggest checking the driver T/S after Break in before design of Fb and Vb.
    The ports have considerable length and will increase the overall gross volume overall as will substantial bracing and driver Vd.


    For a continuum of values Keele refers to equations 4&6. This could be conveniently arranged in Excel.

    What this means is an accurate implementation of the classic B6 alignment with your woofer at home will require some home work before making saw dust.

    I would also stress the importance of Xmax of your driver, power handing and a high pass filter before getting too excited. As we know recone kits are in limited supply.

    Most vintage Jbl woofers have a relatively small Xmax of 4-7 mm compared to the 19 mm of the 2269.

    Back to the Jbl 2269 l estimate the gross internal volume to be in the order of 190-200 L or 7 cu ft3. No free lunch here if you were hoping for a compact Sub.

    As a preliminary exercise l created an boost at 25 hertz in Bassbox 5.1 using the manual acoustic environment that can be added to the box curve. Note l did not incorporate the high pass filter. The curve is below. The trade off being amplifier powerversus box size versus bass extension

    The total acoustic power output is impressive being a frightening 132 dB at thermal power limit.

    The curve is small signal parameters and it would be interesting to evaluate the power power compression at a maximum power.

    I don’t doubt BassBox Pro will provide a more accurate simulation


    http://www.xlrtechs.com/dbkeele.com/...Alignments.pdf
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  3. #48
    Administrator Robh3606's Avatar
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    Hello Ian

    You bring up a very good point on the older vintage drivers, attached is a sim with the 2231 vs 2235 in extended bass response alignment. If you look at the box size Fb it's remarkably similar except for Excursion and power handling. These older drivers with limited X max are poor candidates for any kind of boost. The 2231 runs into trouble with 100 watts input in a large reflex box. Forget about adding any additional power.

    Rob
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    "I could be arguing in my spare time"

  4. #49
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by Robh3606 View Post
    Hello Ian

    You bring up a very good point on the older vintage drivers, attached is a sim with the 2231 vs 2235 in extended bass response alignment. If you look at the box size Fb it's remarkably similar except for Excursion and power handling. These older drivers with limited X max are poor candidates for any kind of boost. The 2231 runs into trouble with 100 watts input in a large reflex box. Forget about adding any additional power.

    Rob
    I indeed highlighted the problem with excursion in my initial reply when using a Linkwitz Q transformer. ;-)

  5. #50
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    As a matter of relevance that leaves the more recent soa drivers for those who have them like the 2216, 1500AL ect?

    No doubt for HT diy subs it has merit but only with large excursion drivers like the 2245, 2242, 2266 or 2269

  6. #51
    Senior Member Lee in Montreal's Avatar
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    A 2245 has ample bottom octave presence. I don't think it needs a Q transformer. ;-)

  7. #52
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    Correct,

    I think the standout virtue of the 2245 is its linearity.

    The authority makes the music sound real.

    The question remains is there a relevant b6 application for Lansing forum members?

    The 12 inch systems have Xmax limitations.

    A number of people have the 4345 and the b460 as a sub and some have the 2242 as a sub.

  8. #53
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    Hi Robh,

    I looked around quickly to try to understand what may be the cause of the Q 2 filter generating a too peaky LF response when you modeled the 2269 driver.

    I've noticed that JBL 226x series woofers tend to have higher Qts than most older generation JBL drivers in the 22 series (except a few, e.g. 2241). The 2269H/G in particular has a Qts of 0.36/0.39 which may be part of the explanation regarding response curve being too peaky in step-down mode with filter Q 2.

    Also, I've found a couple of JBL boxes using the 2269: ASB 7118 and MD7. The first one has some interest being a vented-box, whereas the second one has less since its a horn-loaded Disco enclosure.

    No net ASB 7118 box size or tuning frequency is given in the spec sheet, so I'm walking on thin ice. From box outside dimensions I calculated 8.79 cu. ft., naturally less than that for a real Vb. Interestingly though, in half-space loading and even for full space loading(!) the frequency response shows a bumped curve of about 2-3 db in the 45-50 hz range. Either the box was really designed to bump (?) or its a driver effect.

    Bullock (1) did cover the issue of driver Qts VS frequency response, box size and transient response. He mentions "relative box size increases with total Q"(Qts), "Responses are either flat ... and correspond to low Qt values, or non flat ... and call for a large Qt value." He adds that because of this driver will almost always determine if response is flat or not. In summarizing driver choice, he states when choosing low Qt driver one can get flat alignment and best transient response, while high Qt driver may allow realization of a very low cut-off frequency (which appears to be the case with the 2269). But he mentioned many times that transient response deteriorates with increasing Qt.

    I also checked Qts number for a sample of 10 E-V LF drivers used in step-down boxes and ALL had Qts of 0.16 to 0.28, except one at 0.34 which showed a predicted LF response with a very slight "bump" in typical enclosure. It seems to me there's some correlation between a normal/lower Qts number and flat bass, whereas higher Qts drivers tend to show ripple in response (peak or dip). Driver bass accent plus Q 2 boosting filter might well explain the "too much of a peak"?.

    In my book, the above looks like a feasible explanation for the above-mentioned issue. If so, it would be something to watch for when doing step-down with higher Qts drivers. Newer generation "Super Woofers" may render usage of traditional LF boosting tools having fixed Q 2 filter (e.g. BX 63/5234A/5235, etc.) more "touchy" to use with these specific drivers. Only a proper modeling in each case will tell for sure. Regards,

    Richard

    (1) Robert M. Bullock, Bullock on boxes, 1991. Of particular interest on these issues are: P. 19 center col., P. 31 right col., P. 34 left col.; See also P. 5 center col., P. 6 center col. and P. 7 left col.


    EDIT for clarification purposes: The 10 E-V LF drivers used in step-down boxes are in fact 11. And they include 12"/15"/18" Pro drivers. The 11th one has a Qts of 0.297 and its predicted LF response in typical enclosure also shows no frequency response bump in step-down mode with Q 2 filter.

    Even more Interesting, is the fact the eleven drivers have an Xmax number in the range of 3.3 mm to 6.4 mm (more for Xlim), according to their data sheet... This shows step-down/peak boost may also be used in a beneficial way, even with somewhat limited Xmax drivers. Especially considering the boost is applied at or near the new tuning frequency where vent help is important and cone excursion reduced, plus the 12 db/oct. roll-off at high-pass end of the filter, combined with the box natural roll-off below Fb, protect the woofer from too early overexcursion (up to a point). It all depends on what one is expecting from the speaker in terms of maximum LF acoustical level, particularly in a normal home set-up.

  9. #54
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    Hi Rob

    I also found the Q=2 way too much in your simulation with 8.6 cuft3.

    It caused peaking regardless of fb at the volume.

    However, if one follows and understands the Keeles paper that box volume is simply too large.

    In bassbox extended alignment Box volume is 6.9 cu ft3, Fb is 26.3 and F3. 31.4 hertz
    Adding Q=2 at 26 hertz caused peaking

    In other words that selection of Vb and Fn does not require boost

    The maximal flat QB3 alignments only requires 4.8 cu ft3 where FB is 29.5 F3 is 35.5
    Adding Q=2 at 26 hertz caused peaking

    Fb is too high.

    However reducing the Fb to 23.3 hertz , Vb to 5.3 cuft3 and boost at 25 hertz per my prior posted b6 alignment caused only +.2 dB positive ripple where F3 is 24.8 hertz (following Keeles equations and Fpk/Fs ratio in Table 1.

    There’s no guess work required.

    Back to the question of relevance new Jbl sub build would seem the only application



    Keeles paper explains the relationship of compliance and Qt

  10. #55
    Administrator Robh3606's Avatar
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    Hello Ian

    I also found the Q=2 way too much in your simulation with 8.6 cuft3.
    Are you talking the 2269? I saw the peak in the sim and dropped the Q to 1.5 also that was what the program came up with using the extended bass tuning. I didn't try to modify it. Do you get a different box size and tuning using that option??

    Rob
    "I could be arguing in my spare time"

  11. #56
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    Yes 2269H

    It said 6.9 cu ft in extended bass tuning (bassbox v 5.1) (no fill QL=7)
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  12. #57
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    I think (7.00am-too early) l worked it out.

    It could be you left the box the same volume after the 2245 sim so you adjusted the Q of the boost to 1.5.

    (Could be my data is invalid?)

    Similar result but the overall box size is bigger than need be.

    I think the “thinking “ behind Keeles formula is a trade off of amplifier power versus box size.

  13. #58
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    Quote Originally Posted by Robh3606 View Post
    Hello Ian

    You bring up a very good point on the older vintage drivers, attached is a sim with the 2231 vs 2235 in extended bass response alignment. If you look at the box size Fb it's remarkably similar except for Excursion and power handling. These older drivers with limited X max are poor candidates for any kind of boost. The 2231 runs into trouble with 100 watts input in a large reflex box. Forget about adding any additional power.

    Rob
    Hi Rob,

    Attached is a data cut sheet on the EV TL 3512.

    This document clearly illustrates your point with curves that highlight small versus large signal output and maximum output in "normal" and "step down mode."

    A picture speaks a thousand words.

    The idea is neat with a small signal but when compared to the large signal in step down mode there is a significant differential in output below 100 hertz.

    The output below 100 hertz is very much dependant on the Xmax of the driver and we reiterate that with the older vintage JBL drivers with Xmax 4-7mm (particularly 12 inch or smaller ) step down is not appropriate. Your driver may be a high sensitivity type or a woofer in a bookshelf system - the same issue still applies.

    If you seek loud deep bass consider a dedicated JBL (or 3rd party) brand subwoofer.

    The attachments are purely to illustrate the point and mean no adverse criticism of the TH3512 system.
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  14. #59
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    Here is a fitting bit of trivia that was attributable to D. Broadus "Don" Keele, Jr.

    https://en.m.wikipedia.org/wiki/Sensurround

    Scroll down to development

    “pseudorandom noise generator, designed by D. Broadus "Don" Keele, Jr.

    There’s no doubt D.B Keele is an innovator when it comes to loudspeakers.

    I initially thought it was EV but no it was Cerwin-Vega woofers

    They would have been an interesting driver.

  15. #60
    Senior Member RMC's Avatar
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    E-v peak boost frequency examples



    As promised in an earlier post, here is the first part of some E-V real life Step-Down tuning applications. This shows, AMONG OTHER THINGS, how much this can vary in approximate B6 alignments as E-V says, contrary to classic B6.

    In the relevant Pro Sound Facts 19 page Bulletin, E-V mentions having modeled, in both normal and step-down modes, 34 single driver systems and 28 dual-driver systems for the speaker builder (though I counted only 23 in the dual-driver category). Sort of "modeled many for every taste", though some are questionable.

    Considering the large number (57) of box/driver combinations, in this speaker builder group, I will limit this presentation to the ones of interest (i.e. in step-down mode only) and use statistical presentation here to show the results since that still leaves 28 driver/box duos: 17 for single woofer and 11 for dual-driver enclosures. These do include 12"/15"/18" drivers. Probable explanations are given for "unusual" data, since none are given by E-V.

    SPEAKER BUILDER BOXES DESIGNED BY E-V

    BOOST FREQUENCY (Faux) COMPARED TO BOX TUNING (Fb)

    SINGLE WOOFER (17 boxes)

    * - 3 hz, 1 box, 12" wooder, box smaller than typical, Xmax 4.1 mm; < Fb more risky, must know what you do

    * + or - 0 hz (Fb), 6 boxes, similar to classic B6

    * + 1 hz, 1 box, same box size/Fb as + 3 hz below, but with different more capable LF driver

    * + 2 hz, 6 boxes, similar to Keele's step-down examples at + 2 hz above Fb

    * + 3 hz, 1 box, box larger (14.3 cu.ft.) than typically recommended for driver

    * + 5 hz, 1 box, very low Qts 0.16 driver, box larger than typical rec., low 25 hz Fb, driver overstretched?

    * + 7 hz, 1 box, box much larger (20.4 cu.ft!) than recommended & tuning too low (18 hz!) re driver capability

    DOUBLE WOOFER (11 boxes)

    * - 3 hz, 1 box, similar to above -3hz box except larger Vb, same comments as above apply here

    * + or - 0 hz (Fb), 4 boxes, larger box, same comment as above applies here

    * + 2 hz, 6 boxes, larger box, same comment as above applies here

    * Note 1: the above +3hz single box now in dual version shows 1hz closer boost to Fb in a 13.9 cu.ft. box, F3 up by 8hz

    * Note 2: the above +5hz single box now in dual version shows closer (+2hz) boost to Fb in larger 1.4 X box Vb, F3 up by 1 hz

    * Note 3: the above +7hz single box now in dual version shows much closer (+2hz) boost to Fb, 19.9 cu.ft. box, F3 up by 3 hz

    As can be seen, the majority of peak-boost frequencies are at Fb or a little higher (+2hz) in both single (12/17) and in double (10/11) woofer boxes.

    BTW the average down-tuned Fb for all boxes (single and double) is 32 hz. And the average step-down F3 for the same group is 33.7 hz.

    E-V appears to be adjusting or compensating on Faux when driver isn't a natural best fit for the box size/Fb.

    In a number of cases the peak-boost frequency (Faux) is higher than usual (Fb or +2hz) either to minimize the trade-off (maximum output loss in the vicinity of cabinet's original Fb), or to reduce driver excursion getting closer to Xmax... My comments follow in the next post.

    Richard

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