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Kay Pirinha
03-09-2019, 07:35 AM
Hi,

I have a set of JBL drawings that they published in the 1970ies for their then new K series. I'm quite sure that I've yet found them here some days ago, but cannot find them at the moment. The drawings show two vented enclosures of 3.75 cuft and 5.75 cuft, resp. The smaller one was for one 15" driver K130, K140, or K145, or two K120's. The baffle drawing contained a list of suitable port dimensions. E.g. the K140 requires two ports of 4" dia and 2" length.

Which port length will a 2225 require for smooth LF performance? And which for a 2205?

Best regards!

Mr. Widget
03-09-2019, 10:21 AM
The 2205 and 2225 use the same tuning. You should refer to this document from JBL.

http://www.jblpro.com/ProductAttachments/enclgde.pdf


Widget

RMC
03-09-2019, 08:17 PM
Hi Kay,

Could the following plan given with the 1979 JBL Enclosure Information Manual be the type of plan you were looking for? BTW, maybe I'm blind, but I don't recall seeing in the LH Library that 1979 version I have.

Both Bullock and Dickason, give the same vent length formula for a tube mounted flush with the outer front panel (i.e. one flanged end), being the following:

Lv = 1.463 x 10^7 x R^2 divided by Fb^2 x Vb, then subtract 1.463 x R

where Lv is vent length in inches, Fb is box tuning frequency, Vb is box volume in cubic inches and R is vent radius in inches. If I were you I would add a little to the length calculated just in case, considering its easier to shorten a vent if need be than to increase its length (i.e. having to replace it).

The box volume and tuning given in the Enclosure Guide (4 cu.ft/40hz) for the 2205, 2225 and others is more a general rule of thumb for that group, not a specifically taylored suggestion to each driver. In my view, the 40 hz tuning suggested is too low here for acceptable bass response in that enclosure, unless you had intended to use at least 2 boundaries box placement (e.g. floor/back wall).

I modeled quickly this 4 cu.ft. box in Winspeakerz, with the usual QL 7 and Half-space, for 2205 and 2225 drivers and you can see the results posted here for 40 and 50 hz tunings. The 40 hz Fb gives a downhill going type of bass response... The LF curves for both drivers look generally similar at both tunings. And this can be explained by the two box size influencers: Qts and Vas.

The 2205H has Qts of 0.21 and Vas of 297 L. The 2225H has Qts of 0.28 and Vas of 170 L. (the latter item close to half the 2205). In principle the 2225 should have done better response wise than 2205 in that 4 cu.ft. box based only on higher Qts. However, the 2225 low Vas number reduces the 2225's appropriate or ideal box size, similar to what low Qts does for the 2205 . (Alpha = Vas/Vb and Vb = Vas/Alpha, called the box volume ratio).

For both drivers, lower box tuning makes their LF performance more difficult, considering the lower you tune the more strain is put on the driver. These are PA/SR woofers, not subwoofer type material.

Clever JBL Engineering though: more on one hand (Qts) and less on the other hand (Vas), leading to about the same result for both 2205 and 2225 in the same box size... Regards,

Richard


83476834778347883479

Kay Pirinha
03-10-2019, 05:17 AM
No, sorry, the plans I have relate to the K series musical instrument speakers exlusively. A friedn of mine got them more than 40 years ago from Harman Germany, the local JBL distributor those days (now Audio Pro). I have only bad photocopies that I can't find at the moment, due to a move.

Thanks for your simulations, Richard ;)!

Best regards!

Kay Pirinha
03-26-2019, 03:21 AM
Just now I've found the enclosure plans I've been speaking of. Here's (http://www.lansingheritage.org/images/jbl/plans/1975-kit-plans/page12.jpg) the 3.75 cuft one, here's (http://www.lansingheritage.org/images/jbl/plans/1975-kit-plans/page13.jpg) the 5.75 cuft, and here's (http://www.lansingheritage.org/images/jbl/plans/1975-kit-plans/page10.jpg) the baffle drawing and porting table for the K series speakers.

Best regards!