duct length confusion

[sdaniel]

I can't find a definitive answer, and know one of you will be able to straighten me out. (At least on this issue.) The JBL guide linked below is not clear to me, and I'm sure someone here can answer the quandary off the top of their head.



2205 driver

5.5 cubic feet

Free air 30Hz?

Two 4" ports.



On this chart: http://www.jblpro.com/pub/manuals/enclgde.pdf I feel line # 8 is the most appropriate. I also went to www psp-inc.com, and entered the data, specifying two 4" ports, and got 10.76", which is comfortingly close enough to JBL's 11".



The question that I cant resolve is if I need both ducts to be 10.76 inches each, or each to be half that, for a total combined length of 10.76?



I have had the speakers for some time, and the ducts are about 5" each. They don't sound bad, but since I am going to have them apart for refinishing, now is a great time to resolve this nagging issue.



Thanks so much,



SDaniel

[Zilch]

The recommended ports are 11" long, but that's tuning for the foam-surround extended bass drivers. Look to line #6 for 2205.

BB6P indicates your box is too big and your tuning too low (it says two 4" ducts at 9.55") for 2205 (Orchid). You're cone excursion limited at 90 Hz at relatively low power (150 Watts).

Instead, it suggests:

High Fidelity: 1.9 cuft tuned to 48 Hz with one 4" port 5" long (Red).
Extended Bass: 3.1 cuft tuned to 38.8 Hz with one 4" port 4" long (Blue).

Your existing box with 2226 in it instead, with two 4" ports 6.39" long (34.25 Hz) will easily handle 450 Watts and have better bass (1.5 dB+ worth,) too (Black).

Don't know what you're using it for, but the high end may be better, as well....

[Would somebody check my BB6P work here, please? It'd be good if I was gettin' it right.... ]

[sdaniel]

So, I was glad to read that it would be two at 11” each. Then all your good work confused me. 1.9 to 3.1 cubic feet just seems too small for a 15 inch driver.



I hope we can just talk about what I have, which is the 2205 in a 5.5 cu” box, as I don’t want to change too much and don’t want to have you kind people do a lot of extra work!



A little background might help to understand where I come from. I built my boxes from a JBL enclosure guide and the info in a K series booklet in 1979, roughly. Back then I was using borrowed LE15A’s, and did not know that things needed to be so exacting. So, like the on line calculator I found at this site, pretty much figured 15 inch woofers were similar. Right or wrong, that’s why I have what I do! If my memory serves, I was given a range of box sizes and corresponding porting data, and I chose the volume based on the component layout, amount of wood needed, and aesthetics. They will be used for home hi-fi and theatre. They are bi-amped, work with K110’s and 2405’s. A DC300a powers the woofers. Having used them for years, they can’t be that far off, or I just have easy to please ears!



In the end, I can change duct length, and could reduce the box size, or both. If I absolutely had to, entirely new boxes could be made, but only after I build a new dining room table for my sweet wife! (And at that point I’d consider finding cosmetically awful 4345’s or similar, and putting the components into new, hand made enclosures. What fun that would be!)



Thank you all for your guidance,



SDaniel

[Zilch]

BassBox 6 Pro tells me your box is too big and tuned too low for 2205

Line 6 is the proper size and tuning for that woofer.

Tuning to Line 8 makes your present design worse. It plays lower, but you lose power handling capacity (already poor) AND bass response.

Line 8 is for extended bass woofers like the LE15A's you originally had.

Your situation is much improved by replacing your 2205's with 2226's.

Orchid: Your box with present 5" ducts, 2205. It's tuned to 36.67 Hz.

Black: Your box with present 5" ducts, 2226. It'd be tuned to 36.54 Hz.

Blue: Your box with 11" ducts, 2205. You'd be retuning to 29.1 Hz. Bad idea.

Download WinISD and play with tunings yourself.

If you switch to 2226's, you can make it better by using 6.39" long ports, as shown above.

If you want REAL bass, you should consider 2235's and tuning per line 8 with 11" ducts (Red).

I think you're using the wrong bass driver for Hi-Fi and theater, and retuning your boxes as you propose isn't going to fix it.

Again, it'd be good is someone confirmed my findings here before you actually do anything....

[Miss Orchid]

Orchid:

Yes?







Just teasing.

[Zilch]

Heh, heh....

[Zilch]

1.9 to 3.1 cubic feet just seems too small for a 15 inch driver.

Yeah, well, WinISD says even smaller is optimum for 2205, at least for maximally flat tuning. I don't think I'd build that, tho, except maybe as a stage monitor; there's not much in the way of bass available:

[sdaniel]

Thanks. Nobody is presenting anything different, and what you say makes sense.

Whoever sold me the 2205's as a replacement for le15a's goofed a bit!

Seems like the best thing is to 'trade' what I have, or my k140's, for a pair of 2235's, and make only minor modifications to my ducts.

Now to get that program and play some.

SD