1kHz suck out from 2206H in SR4722X cabinet, ideas?

[sebackman]

Hi,

I just realised that I newer reported back on this thread. At the end of the day I ended up with making a mounting ring to move the 2206 out from the cabinets and to cover the sides in the box with foam. This made a real difference when listening on axis. Less so off axis.

Attached are some pictures to show the results.

Kind regards

//RoB

[sebackman]

And the finished speaker loks like this

[Horn Fanatic]

Half a wavelength at 1000 Hz is only 17 cm. Could be reflections from the floor if cabinet is situated directly on the floor.

It could also be the horn working as a kind of helmholz. Try stuffing it with rags.

It is impossible for a horn to act as a "kind of Helmholtz". There is no such thing as a "kind of Helmholtz". Either it is, or it isn't. If stuffing the horn with rags cures the problem, doing so would render the horn useless under normal operation. The suck out could be caused by a number of factors, beginning with the room dimensions. It could also be caused by phase cancellation due to the box dimensions, or inadequate bracing. Perhaps the culprit is the lousy crossover networks JBL uses, or a standing wave occurring inside the enclosure. Perhaps the horn is resonating due to the cheap material it is constructed from. Try damping the back of the horn with that gooey black material with the adhesive back. I think it can be found at Parts Express. Even if it doesn't solve the problem, it couldn't hurt. The frequency response for the 2206 is virtually flat from 100 Hz to 2KHz, which makes it an awesome driver to reproduce the vocal range. I'll suggest the suck out could be caused by a design flaw with the enclosure. I'll even go as far to suggest the tuning could be improved. Even a box which has no parallel surfaces, will resonate, not just from the material, but standing waves as well. That pearl was imparted to me by an acoustical engineer who worked in the acoustics division at Boeing.

H.F.

BTW - In my 40+ years of speaker manufacturing and design, I have never found one legitimate book, document, or article that advocated the use of foam inside an enclosure. I suspect those who began the use of it many years ago were DIY types who knew nothing of loud speaker enclosure design.

[sebackman]

Hi Horn Fanatic,

-Totally agree with all of you suggestions.

The horns are really made of cast aluminium and not too shabby. These are also dampened as you suggest.
http://www.audioheritage.org/vbullet...ighlight=baked

“Great minds think alike” 

The cabinets are internally extra braced and the shape is trapezoid so I don’t think the internals would create the dip. At least not at the level I use to measure. There are no passive filters in the box as I use active XO.

I think it comes down a “design flaw” in the cabinet where the sides on each site of the 2206 cone produces a standing wave that cancels the direct sound at 1kHz- ish on axis. If I move off axis the dip reduces.

These are original JBL SR4722X cabinets made for the 2206 that I had lying around but they were made for PA and not HiFi. I guess that a flat front cabinet had not produced these curves. The ports are changed to reflect HiFi use.

So maybe “design flaw” is a bit harsh as the reassessed baffle is there to protect the drivers when transporting a PA speaker.

Anyway, by introducing the spacers and putting foam on the cabinet sides the dip was reduced significantly. The acoustic foam is applied on the outside of the cabinet, please see the pictures. Internal dampening is normal material.

The 2450SL/2332 measures just like text book. No problems there what so ever.

Well, now they are “good enough”. …Maybe a 077 can find its way in later, who knows.

Thank you
//RoB

[subwoof]

That cabinet ( 4722 ) and all of it's variants just didn't work for any project no matter the woofer / horn / driver combo.

Impossible to get any decent bass and yes - the "suck" happens with any model 12 ( and I have many )...

The Vb is just too small and the cabinet ( as you discovered ) is too shallow.

I gave up and used the carpeted ones for the cat's perches in the office.

meow