D140F Recommended cabinet volumes - help !!

[bassman133]

Hi Forum

Hope someone with some experience is out there. I have been advised to make this post by JBL Tech Support.

I have a couple of D140F's (16 ohm I believe) in a really small 2 x 15 cab which does not do low bass properly. I am sure that the cab is too small, but the questions is whether a reflex cab can be too big ?

I have seen the 1960's manual with the table at the following links:

http://www.lansingheritage.org/images/jbl/plans/1960s-manual/page11.jpg and

http://www.lansingheritage.org/images/jbl/plans/1960s-manual/page12.jpg

but neither the D140F (or the E140 for that matter) are represented in that table.

So does anyone have the above table info (or at least a part of it) for the D140F ?

Or even at the bare minimum, the speaker data sheets have minimum and maximum enclosure sizes in cu ft; does anyone have these figures for the D140F ?

Thanks v much !

[duaneage]

2 JBL E-140 in 1.24 cu ft

77.46 hz tuning frequency

Vent tuning will be a real bitch

[Zilch]

I don't have T/S parameters for D140(F), just E140.

BB6P says "Extended bass" vented, 3.637 cuft, tuned to 50 Hz, F3 = 107 Hz.

I cannot get usable bass below ~50 Hz out of a pair in the same box. :(

Same with a single in 2 cuft.

I can get to 37 Hz (-10 dB) in 4 cuft tuned to 40 Hz, but the curve is funky, and max power derates to 150 W for a single....

See lines 6 and 10 here:

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

[bassman133]

Thanks for the replies - I have already seen line 6 of the guide which shows a 4cuft box - what I'm wondering is if I can get a better low-end by increasing the size of the box for a single 15" unit to either 5.5 cuft or 6.7cuft - what will happen ? Will it give better low end ? Are there disadvantages (eg power handling, larger excursions, or other) to increasing the size - other than it's heaver and bigger ! :-)

Thanks !

[johnaec]

You say your existing box is really small - increasing the size will definitely improve the low end.

John

[Zilch]

Download WinISD for free and try your options.

It's a box modeling program....

[Tom Loizeaux]

Check out this chart from the JBL Library.
www.lansingheritage.org/html/jbl/plans/1970s-kit.htm

It shows port size for a varirty of enclosure sizes for the JBL K series drivers. The D140F has a softer surround then the K140, so I don't think the numbers will apply directly.

My experience with the K140s is that they require at least a 4 cu.ft. cabinet, tuned to 38Hz, in order to produce the fundamentals of the electric bass.

Hope this helps.

Tom