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