Investigating helper woofers

[Jakob]

Sitting with two spare 2216Nd and looking through some posts here regarding M2's with dual woofers got me thinking of building a pair of test cabs just for the fun of it.
Except having fun it would be nice if one could learn something on the way. I thought it could be wise to start taking a closer look at some of JBL's own design's with helper woofers; 4435 and the Everest DD66000. One thing that strikes me right away is that they seem to differ when it comes to having both woofers sharing the same cabinet volume (DD66000) or in separate chambers (4435).
What would be the pro's and cons of either design? Could letting them share the same chamber mean you get away using a smaller cabinet then if having the drivers in two separate chambers? Is that true regarding the Everest or is its internal volume twice the one suited for only one woofer?

Any info on this greatly appreciated!

[1audiohack]

Hi Jakob;

I don’t have definitive answers to all of this but here is some of what I think I know. :)

Two drivers in the same cabinet with no division need the same large volume as if they were in single or divided enclosures.

4350’s and 4355’s have undivided enclosures as also save for the small box for the 12”.

I can think of several reasons for dividing the box, the antics of one woofer wont have a direct affect the other driver. A better reason in my book is the smaller volumes drive the standing wave resonances higher, possibly out of the passband on at least the helper and it’s easier to build small enclosures rigid.

Why the DD65-66-6700’s don't have a divided enclosure is possibly the rigid as hell non box shape. They certainly would have a divided enclosure if it made any improvement.

I myself like the double wide 15” enclosures. They have a sonic signature that is much to my liking.

Integrating a woofer identical to the main speaker seems to be much easier (to me) than integrating a sub. Just put a two pole filter on it, preferably electronic with a knob and another amp channel and go at it.

I have discovered that I am a HiFiPA guy. :)

Barry.

[Jakob]

Hi Barry,

Thank you for your input and excuse my late reply!

Do you think the main reason for JBL to put the woofers beside each other instead of on top mainly is to get the mid and tweeter at the preferred height or are there other sonic reasons for this design?

I would really like to have a smaller footprint so I will need to go with the "on top of each other" design...

[1audiohack]

Hi Jakob;

I really don’t know if there is a solid reason for this. The side by side arrangement works well for seated listening in a domestic environment as used on the Sovereign and Everest DD series as well as the 4435 and 2350/55 when at home.

Large format monitors are usually sofit mounted though.

One benefit of a wide baffle (~44”-48”) is you get the baffle step down naturally into the mid-high 200Hz range where Olive and Timbers like to boost the bass response for home systems. The mutual coupling of two woofers in very close proximity works just about right to overcome the loss ~250-280Hz.

Two woofers can work vertically like the M9500 implementation. These I have never heard. :( I have one 9500 horn and driver and it is a stellar performer.

Barry.

[ivica]

Hi Barry,

Thank you for your input and excuse my late reply!

Do you think the main reason for JBL to put the woofers beside each other instead of on top mainly is to get the mid and tweeter at the preferred height or are there other sonic reasons for this design?

I would really like to have a smaller footprint so I will need to go with the "on top of each other" design...

HI Jakob,

I think that the placement of the 'helper driver' is not so important i using DD66k solution of its operation, cutting its FR near 100Hz.
So putting the 2216nd on top each other is ok solution, but the height of the hor is important.

regards
ivica

[turnitdown]

Height, particularly with monitors that are assumed in some locations to be soffit mounted, is probably the consideration for going side by side. As mentioned, it also favors sitting on a sofa while listening as it keeps the HF driver at ear level.

I'm about to build vertical 4435s and my (tape) measurements show that I can have the center of the 2344 at about 40" from the floor, just 3-4 inches above my ear and with 100x100 degree dispersion this works quite well.

I have been using one of my 2234s per side as helpers with an 18mH coil and the requisite resistance in parallel with the driver per the 4435 formula. It adds a wonderful "bigness" and a gentle but noticeable extension to the bass. Not 'night and day' difference, just more goodness.