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

  1. #61
    Senior Member RMC's Avatar
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    E-v peak boost frequency comments




    The span of peak-boost frequencies seen in the data goes from - 3 hz below Fb to + 7 hz above Fb, which represents a sizable 10 hz spread! The reason for that may very well be woofer capability related. This also tends to demonstrate there is some possible fiddle with this peak-boost frequency. However, then one may not get 100% possible LF extension (when going more + hz than normal), but may still reap acceptable benefits from it.

    Also, remember the speaker builder is allowed a 5% tolerance of the recommended peak-boost frequency in order "to provide no significant performance compromise." (E-V)

    Interestingly, double-woofer boxes have less issues compared to some single woofer ones since E-V DID NOT use the usual "double driver/double internal volume/double vent area/vent length unchanged" rule-of-thumb, to model them in duo when they had trouble singly. A few singles with abusively large boxes/low tuning show driver "running out of steam": e.g. 1 X 18", Qts 0.27, 20.4 cu.ft., Fb 18 hz = begging for trouble VS same 2 X 18", 19.9 cu.ft., Fb 25 hz = making more sense and improved driver performance. So they did use smaller cabinets than rule-of-thumb for some two-driver boxes, with little higher bass F3, but did so mostly for higher output level capability in my view.

    BTW, JBL also has some questionable normal mode recommended box volumes for some drivers, such as 2205H, 2220H, etc., even well after T/S science was known, like E-V does.

    Box size and tuning VS driver ability have to make sense to begin with, regardless of manufacturer name. The best way to insure that is to model it appropriately in speaker design software, then look at spl vs Xmax. Suits you?

    Nevertheless, boxes with less than twice Vb for double-woofer could still be an option to consider when lowest bass possible isn't the main criterion, but rather a reasonable box size having more LF SPL with less excursion penalty, or when a single bass cabinet with two woofers, reasonable size and logical step-down would do the job.

    In reviewing a dozen + E-V woofers before writing this thread I noted Qts is generally < 0.30. I also found yet another driver, this time with a Qts of 0.36, which also shows a little bump in LF on step-down with filter Q 2 but a bit more peaky than the driver with Qts 0.34 mentioned in an earlier post (# 53).

    In that review, more often than not, E-V drivers tend to have somewhat less cone travel capability than "equivalent" or so JBL drivers. The data is no surprise to me as I've understood long ago that JBL targets more the Premium audio market, whereas E-V seems to be more Middle audio market oriented on woofers, when considering the technological advances implicated and the important price points issues. More Xmax is usually better (if its ever going to be used) for very high level LF reproduction. LF capability also makes some JBL drivers good candidates for Step-Down mode, as well as some other brand names.

    Again, It all depends on what level of LF output one is expecting for home use (usually much less than PA work) and budget. A step-down LF output level (e.g. 116 db @35 hz or 118 db @ 30 hz), or even less than that, is more than adequate for most audiophiles, those who have neighbors, no hearing loss or don't try to impress the gallery. I tend to agree, for normal everyday use, with Ivica's mention In post # 16 "... used for the home listening conditions, where usually not more then 10W of power from the amp has to be 'delivered'." When one considers a conservative 93-95 db/W/M, then 10 watts means 103-105 db already, which is pretty loud.

    Other E-V speakers of interest that are/were commercially available will be covered later, some individually or in groups when convenient, also with probable explanations. Naturally, I've kept a few "rounds of ammunition" in the holster for later use.

    Richard

  2. #62
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    http://www.behringer-electric.de/fil...bl_english.pdf

    Go to page 24

    It’s an interesting account of JBL LF driver evolution

  3. #63
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    For those interested in this topic l contacted the author of the paper below requesting clarity on the EV step down implementation.

    The author kindly responded with the explanation below.

    There are 3 steps:

    Step 1
    You just tune your vented box with two identical ports which tunes the box to a conventional 4th-order HP Butterworth alignment.

    Step 2
    You then cover one of the ports which drops box tuning down about one-half octave ( x 0.707 fB).

    Step 3
    You then EQ the response with a second-order HP filter with a Q of 2 (boost of +6 dB) at the lowered resonance. This changes the tuning to a 6th-order HP with the lowered f3 about one-half octave below the original fB.
    The paper explains all this. See Figs. 2, 3, and 4.


    http://www.xlrtechs.com/dbkeele.com/...Alignments.pdf

  4. #64
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    For those interested in this topic l contacted the author of the paper below requesting clarity on the EV step down implementation.

    The author kindly responded with the explanation below.

    There are 3 steps:

    Step 1
    You just tune your vented box with two identical ports which tunes the box to a conventional 4th-order HP Butterworth alignment.

    Step 2
    You then cover one of the ports which drops box tuning down about one-half octave ( x 0.707 fB).

    Step 3
    You then EQ the response with a second-order HP filter with a Q of 2 (boost of +6 dB) at the lowered resonance. This changes the tuning to a 6th-order HP with the lowered f3 about one-half octave below the original fB.
    The paper explains all this. See Figs. 2, 3, and 4.


    http://www.xlrtechs.com/dbkeele.com/...Alignments.pdf
    Thanks. This is the interesting stuff. ;-)

  5. #65
    Administrator Robh3606's Avatar
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    Hello Ian

    Thanks contacting him and posting his response! Great stuff!

    Rob
    "I could be arguing in my spare time"

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    No worries.

    Don Keele was helpful and friendly.

    For a practical example go to appendix 11 that covers application of a sealed, QB3 vented and the B6 alignment with a common woofer. Cross reference to equations 7 & 8 for Fb and Vb.

    The far right column in Table 1 gives the ratio of Fpk /fs where Fpk is the boost frequency.

    The comments concerning over volume are no biggie (box losses) and something you would have to do in the absence of modern simulation software back then.

  7. #67
    Senior Member ivica's Avatar
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    Very helpful explanation for bass tuning and EQ

    Quote Originally Posted by Ian Mackenzie View Post
    For those interested in this topic l contacted the author of the paper below requesting clarity on the EV step down implementation.

    The author kindly responded with the explanation below.

    There are 3 steps:

    Step 1
    You just tune your vented box with two identical ports which tunes the box to a conventional 4th-order HP Butterworth alignment.

    Step 2
    You then cover one of the ports which drops box tuning down about one-half octave ( x 0.707 fB).

    Step 3
    You then EQ the response with a second-order HP filter with a Q of 2 (boost of +6 dB) at the lowered resonance. This changes the tuning to a 6th-order HP with the lowered f3 about one-half octave below the original fB.
    The paper explains all this. See Figs. 2, 3, and 4.


    http://www.xlrtechs.com/dbkeele.com/...Alignments.pdf
    Hi Ian,

    Many thanks for this very short and useful explanations from Mr. D.B. Keele

    "Interestingly", that some amount of posts on this thread have disappeared from the Forum,
    but fortunately such Ian mentioned are present.

    regards
    ivica

  8. #68
    Senior Member RMC's Avatar
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    RE "Interestingly", that some amount of posts on this thread have disappeared from the Forum,

    I sure don't have the authority, capability nor will to remove posts here, even more so when it appears like one-sided censorship. If you remember or look at what was removed and kept its pretty evident who did it, and for what reasons... I'll leave it at that for the time being, and continue my work.

  9. #69
    Administrator Robh3606's Avatar
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    If you remember or look at what was removed and kept its pretty evident who did it, and for what reasons... I'll leave it at that for the time being, and continue my work.
    Actually to solve the mystery I removed them and in particular the blatant personal attack that started the string.

    Rob
    "I could be arguing in my spare time"

  10. #70
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    Curiosity from the past, e-v's 30 w woofer/tl series box




    Something maybe more "entertaining" than really practical follows. I was reading recently a Web page on E-V's history, where it was mentioned this 30" woofer was introduced in 1959. I've seen documentation on this a long time ago and was impressed by its huge size. I seem to remember reading elsewhere E-V describing it as the largest viable woofer in the world, or something like that.

    The interesting aspect here is that E-V modeled and sold that huge size driver/TL series box, also for step-down mode use, even if a 30" woofer might not really need boosting filter assistance... This E-V application of the concept being with a quite unusual driver. JBL too did that with their largest 2245H woofer (Fs 20hz), In the Kramer/Timbers article: out of three 2245 boxes they modeled, two were boosting filter assisted. Plus the fourth box for which they gave info, was also filter assisted using 2235H.

    When Bob Carver introduced in the seventies his high-power Phase Linear power amps, models 700 and 400 with their large VU meters, things started to change forever. The power race was on for both amps and speakers, plus it never ceased...

    However, the 30W woofer remained for some time before becoming "NLA/obsolete" in the eighties I think (its certainly not on my 1991 EV price list). It was something special. For comparison purposes, the well-known JBL 2245H has a diaphragm area of 201 sq. in. In addition, a number of manufacturers like B&C, Beyma, 18 Sound and RCF still make 21" woofers, one of which is described by an authorized dealer as "features a massive 260 square inches of diaphragm surface area—nearly 40% more than an 18" driver" (Re B&C 21SW152-4 21"). Rather 30% more based on my calculation regarding the above two contenders. Still nice though.

    The 30W had over 500 sq. in. of cone area according to E-V data sheet, which is almost DOUBLE that of the 21"size! This IS REALLY massive... Sure the "old dog" can't match the more recent power ratings, the ear splitting SPL's and probably not cone travel capabilities of modern drivers. As for the latter, it don't necessarily need to. Since air moving to reproduce low frequencies can be done mostly by cone size or cone travel, or a mix of both, its pretty evident the 30W does it primarily with cone size.

    This driver was used mostly in E-V's Patrician home speaker system. Nonetheless, a Pro Sound TL series vented box was also made for it and the relevant specs summary gives enough info for our purpose. The two data sheets I found for the 30W (one from E-V and one from University Sound (see note 1) which was kind of E-V's commercial/installed sound division the 30W was later transfered into) do not give detailed T/S parameters, presumably because its an old woofer.

    Though, I'm pretty sure E-V did measure the T/S at one point because that driver was also used in the 28 cu.ft. (800 L., 125 Kg) 1983 Patrician II loudspeaker system (a special Swiss-made! anniversary edition for... Japan market, naturally) and the brochure for this indicates "The uncompromising application of the Thiele/Small principles..." and further adds on the specs page "Type, bass reflex after Thiele/Small". Can't design one of those boxes without knowing driver T/S parameters. Not published by E-V though, as far as I could see.

    Swiss-made? I assume its because E-V and Mark IV Audio (EV's owners at the time) had their European division in Switzerland, where E-V was also the main equipment sponsor for the well-known Montreux Jazz Festival held in that country. Any better IMAGE OR PERCEPTION of quality craftsmanship and precision than Swiss-made to sell it on Japanese market? I think this explains Swiss manufacturing in that particular case.

    Other E-V available info of interest includes: polystyrene foam cone, Fs 15 hz, 8 ohms (surprising, in the old days many were 16 ohms), power rating 60W RMS/150W pulsed, conversion efficiency 10%, EIA sensitivity 54 db (equivalent to 101.68 db/w/m using Eargle's formula and nomograph- see note 2), no Xmax given but they say "Even at full power input, cone motion is within the linear range." Finally, the driver may have been modified over time since recommended enclosures were sealed (and ported boxes said to be neither necessary nor desirable!), and the TL 303 and Patrician II are vented boxes...

    TL 303 box in the next post.

    Richard

  11. #71
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    Tl 303 box for 30w woofer




    The dimensions and weight of the TL 303 box make this a one-time or so placement adventure at 76 cu.ft gross internal volume (85.3 cu.ft. ext.), 8-foot high, 4-foot wide, 32 inches deep (ext.), and a net weight of 550 lb... That box was designed with ONE driver. The normal/step-down mode info follows, as well as some other, and comments.

    Normal mode F3: 26 hz, step-down mode (with EQ) F3: 17.5 hz (a bit below hearing threshold). Kramer/Timbers, 12 cu.ft. assisted box, 2245H, "... resulting in a system F3 of about 21 hz."

    Normal Fb: 23 hz, step-down Fb: 18 hz (same JBL box as above, step-down Fb 20 hz)

    6 db peak-boost frequency: 19 hz (same JBL box as above, boost applied at 20 hz)

    Efficiency half-space: 5% (in TL 303 box); 2245H: 2.10%

    Usable lower limit frequency: normal 20 hz, step-down 18 hz ("System can generate one-half acoustic watt or more down to this frequency")

    Usable upper limit frequency: 600 hz ("System is reasonably flat...")

    Maximum SPL at 10 feet, full power: 112 db (equivalent to 121.68 db at 1m using Eargle's formula and nomograph)

    There isn't a whole lot of deeper bass to gain (8.5 hz compared to normal mode) when dealing with already low numbers and mammoth size cabinet, or when compared to 2245H 12 cu.ft. assisted box (3.5hz). More for the fanatics or the show I guess. And the trade-off of smaller box with deeper bass but with 4 times power requirement isn't here, only deeper bass is. That box is definitely a curiosity from the past. I wonder how many of these they really sold VS the many fellows who built their own. The 28 cu.ft of the Patrician II (a 4-way system) makes about 50% more sense at half the weight, 67"X36"X20.7", 10 hz higher F3, but nothing indicates it can be used in step-down mode.

    Richard

    (1) I've used only the E-V data sheet and info here. Some University Sound spec sheet numbers are curious e.g. sensitivity rating averaged 500-5000 hz and frequency response to 1khz. Whereas E-V states rec. x-over 100 hz (as in Patrician II), and usable upper limit 600 hz.

    (2) The EIA (1mw at 30 feet) sensitivity conversion to db/w/m would have given 103 db/w/m here when adding 30 db for one watt plus 19 db for one meter. The 1.3 db difference isn't a large one, but would also need to be considered in max. spl output with that method. I used the more conservative number.

  12. #72
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    FWIW: I have a friend with a pair of Patricians in his living room. Trust me, those suckers move a lot of air with very little power!

  13. #73
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    Hi Chas,

    Thanks for the input. I do believe you. For the Patrician II the specs in the brochure I have indicate a minimum required input of... 1 watt! And the suggested amplifier power is 1.5-600 watts! I checked twice that suggested 1.5 w amp power and it IS 1.5 w. I mistakenly read initially a more usual 15 watts...

    When using EIA sensitivity number and method to convert to 103 db/w/m no wonder it moves a lot of air with very little power as you say. And that makes no say of horn loading.

    Lucky friend you have. There's a group of followers for that huge driver/box, many of which I've seen on the Web with their own speaker builder boxes, including some with multiple 30W drivers! Dear god help us, as they say (from the neighbors).

    BTW I just found the phrase EV used to describe it (I wasn't sure of the exact wording at the beginning of my post): "the largest successful driver ever produced."

    Regards,

    Richard

  14. #74
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    Some issues re step-down mode

    I've changed the order of presentation a little since some data stuff is not ready yet, whereas some other material is. Therefore things are presented when they are "fit to print".

    A) TRADE-OFFS

    There are two trade-offs when going the step-down/peak-boost way. The first one is 4 times required power for the 6 db boost in exchange for smaller cabinet with one half-octave or so deeper bass. "or so" because sometimes its a bit more or less depending on the step-down Fb and where the boost (Faux) is applied. We've seen in a previous post E-V Home built examples where this auxiliary filter frequency can vary a lot, Faux was from -3hz to +7hz compared to Fb, probably related to driver LF capabilities and box size (some too large or small, others OK).

    The second trade-off is a relatively small loss of maximum acoustic output capability in the region of original box tuning frequency, in exchange for more output deeper in the bass range. In one of his "B6" examples Keele mentioned about 3 db capability loss in the passband (this was compared to a B4 alignment). In a few of it's own documents, E-V mentioned some 2 to 3 db of maximum output is sacrificed. So, to gain some output on the left side of a response curve one has to let go a little on the right side (a bit higher).

    Up to now, I've seen one case only where that second trade-off yielded up to 7 db maximum acoustic output loss, likely because the driver was overstretched in the boxe's size, with too low step-down Fb of 24hz, and/or driver Xmax of 5.6 mm. Faux was applied at 29hz (+5hz compared to Fb, to compensate It seems). But it could still produce a worst case 113 db @ 33 hz and 115 db @ 28hz, which is pretty loud. Again, a matter of needs and budget.

    Its important to note that E-V mentions in another document "Maximum acoustic output is theoretically reduced by the amount of equalization." Then adds, if the highest possible SPL is needed for an application then the normal mode configuration is recommended. (E-V, SEQ Step-Down Kit for Sentry 500 System, data sheet, P.2). E-V calls the resulting output a "Theoretical Low Frequency Maximum Acoustic Output", meaning its not an actual measurement, presumably as modeled by computer software, so a likely ballpark number.

    More to come.

    Richard

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    Some issues re step-down mode




    B1) KEELE

    Even though Keele mentions in his paper that his new alignments have coincident ("occurring together in space or time") F3, Fb and boost (Faux) frequencies, in his three modelings of "B6" alignments the boost frequency was 2-3 hz higher than Fb. I guess this is part of what makes them pseudo, or approximate B6 as E-V calls them. By Keele's own formula of EQ boosting "at 1.07 times the cutoff frquency", and elsewhere mentioning 1.07 times Fb, then Faux is destined to be a little higher than Fb. Though E-V did have some precisely at Fb, others higher/lower... Its normal for a B4 alignment to have F3 = Fb, for a QB3 it isn't.

    After discussing the suitability of woofers for use in sixth-order alignments (quote in post # 3), Keele ends that paragraph with the following regarding driver Qts: "If a hump of up to 3 db is acceptable, Qt values up to 0.85 would be usable." (P. 356) In my view this confirms what I wrote in Posts # 53 and 61 regarding higher Qts drivers used in step-down mode. These will continue to perform as they do, meaning their inherent tendency to bump in LF won't suddently disappear simply because they're being used in a pseudo B6 alignment. As stated earlier, most of the drivers E-V used in step-down had Qts < 0.30, one at 0.34 and another at 0.36, as seen up to now.

    In his applications (P. 356...), Keele indicates his sixth-order alignments "... are very useful when applied to two widely different classes of drivers:" "The class 1 driver used in a vented-box system is found to fit [ later he writes "roughly fit" P. 358] the quasi third-order Butterworth alignments of Thiele (QB3, alignments 1 - 4)." One of the most common btw. The class 2 driver is described as "the low-compliance short-throw high-resonance high-Qt driver that one normally associates with moderately inexpensive drivers."

    Interestingly, Keele modeled three pseudo B6 alignments with three different drivers: 15", Fs 40hz, Qts 0.38 (B4), Xmax 4.3 mm, 50W; 12", Fs 22hz, Qts 0.25, Xmax 6.4 mm, 40W; 8", Fs 90hz, Qts 0.7, Xmax 1.8 mm, 15W. Its pretty evident these are not super woofers. Will they produce 120+ db bass? Certainly not, this isn't the point at all by the way, but rather that sixth-order configuration "... allows the designer to "milk" more usable low-frequency output out of this type of driver than any other system configuration." (P. 356)

    Keele adds that even though the class 2 driver is handicapped by "high resonance and low displacement capabilities", "Appendix II describes a sixth-order system design using a typical class 2 driver which has usable response down to an octave below the driver's free-air resonance."

    His conclusion for the "B6" 15" driver is: "This modification somewhat reduces the maximum acoustic output capabilities of the system in the 35-70 hz range, but greatly increases the maximum output below 35 hz ..."; For the 12" woofer, in QB3 box, F3 39hz, thermally limited > 27hz, but in the "B6" box F3 26hz, thermally limited down to 21hz!; For the 8" driver in C4, F3 55hz, in C6 F3 38hz (from Fig. 7) and "... thermal limit extension down to less than 40hz." (P. 359) These are considerable gains for "old dog" type woofers.

    Here I have looked at vented VS vented B6 box, not sealed VS vented B6 (also included by DBK) which I think isn't really fair because of quite different system type, but these comparisons have shown even more dramatic improvements.

    This shows that less performing older woofers CAN greatly benefit from step-down mode, contrary to some belief governed only by LF highest maximum db SPL . We'll see later that some super woofers appear to benefit much less from step-down...

    More to come.

    Richard

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