4688 TCB Monster Subwoofer

[Zilch]

Those'd be bigger sheets than we can get around here....

[loach71]

Those'd be bigger sheets than we can get around here....

Everything is BIGGER in BIG SKY COUNTRY...
Even California expats are moving here...

[jbl_man_uk]

I have come across lots of these 2x18 TCB subwoofers for sale over the past few years,mainly ex-club and install,and funny thing is,they are ALLWAYS either empty,or blown,or without the original drivers,which leads me to think that they are quite severe on drivers when pushed hard resulting in failures...they do go quite low,but have no bass punch at all.not one of JBL`s better designs.

[Zilch]

they do go quite low,but have no bass punch at all.

Punch's not their job, mon.

They just supposed to relocate stuff and make ears bleed.

Yeah, I'm sure they REALLY suck.

Lemme see if I can blow this one up.

[I wanna put 2242Hs in it, anyway.... ]

[loach71]

I've managed to construct two test versions (made of MDF) of the 2245H variant of the woofer described by el-Zilch-O in this article. The bass output is prodigious. It compares favorable with Greg Timber's ported monster (2245H loaded). It seems more efficient than the ported design - by about 6 dB in its passband. I think I will now start on the baltic birch- MDF laminated final versions of this sub -- it seems to move the earth on Dolby Digital / dts LFE tracks. Standing on end, a 30" footprint is not that intrusive...

Many thanks to el-Zilch-O for help with the BB6 Pro design -- maybe I should learn to read...

[Zilch]

I was HOPING you'd do a test box first before committing it to the full laminated construction, as 2245H is unexplored territory using this design.

Glad it's working for you....

[loach71]

The test 4688 loaded with 2245H drivers compares favorably with Greg Timbers' 2245H ported sub (12 cu ft extended bass shelf). My first impressions are the following:

* The 4688 is more efficient than the ported box. (about 6 dB overall in the passband mentioned below)
* The 4688 gives a drier, more analytical bass.
* The ported sub seems to give a little more extended bass on the low frequency end of the passband - which is probably due to the EQ Greg recommends. When I supply the same EQ on the 4688 clone, the low bass seems about the same.
* My 1/3 oct spectrum analyzer and calibrated mike (el-cheap-o DOD unit) doesn't see much difference in the response in the passband 20 Hz to 90 Hz, using 48 dB / octave high and low pass filters at the above frequencies.

Overall the 4688 seems the winner due to better efficiency and its 30" square footprint. I never got the 2245s in the 4688 clone to bottom out - even though I was using a bridged BGW 750C per woofer...

Now for the heavy work on the laminated enclosures... and lots of Jack Daniel's for the woman -- it is great WAF lubricant...

[OGHinz]

Is the JBL 4788 identical to the 4688?

[loach71]

Is the JBL 4788 identical to the 4688?

Never heard of that model. Seached the jblpro website and came up with nothing.

Now that spring is here in Big Sky Country, I am doing the finishing on the qty. 4 (yes Zilch -- FOUR) 4688 TCB subs. I am using Purple Heart veneer then followed by multiple coats of Tung Oil. Should be finished in a month. It has been a long journey - but the sonic results are quite pleasing. Thanks again for the BB6 Pro help.

[JBL 4645]

So that’s what looks like inside I do love a good peek show. I would like to own just one of those I did have its baby the JBL Control SB-5 (TCB) many years ago
The only time I heard and felt the (TCB) range was at the Odeon Leicester square Last Action Hero 70mm Dolby SR (1993) and they had two of those beasts behind the screen and even in a large auditorium they shock the seats when Slater, comes crashing though the wall in 4x4! There also THX approved!

“It’s a mean, mean mother from outer space.”

[Zilch]

Somebody over there across the pond recently posted that two of them were available empty, and they only wanted one.

May be your chance!

http://audioheritage.org/vbulletin/s...ad.php?t=15719

[discus96]

Following your suggestions and this thread I will start my "JBL 4688 Clone project"

I have just bought on e-bay two recently reconed 2240H and the "TCB Subwoofer system" looks just perfect for my HT and Music application.

Thanks to Zilch drawings, pictures and indications, I'll try to produce an exact copy of the 4688.

Dimensions are very well indicated in his BB6 pages, my doubts are regarding the ducts lenght and dia so I picked Zilch picture of the 4688 inerior and put few lines to see If I understood correctly.
Please check if this is OK.

Thank you

[Zilch]

The duct length is 14" to the outside, of course.

Where you have written "No Ducts" is the blind closed box shown on the drawings. While there are no ducts there in the conventional sense, that box in combination with the bracing (left tip of your port dimension arrow) serves to constrict the areas (volumes) just inside the ports such that they function as ducts.

The BB6P sims show the approximate equivalent effective duct length, which for the center chamber is modest in comparison to the outer chambers....

[4343]

Is the JBL 4788 identical to the 4688?

Found this at: http://forums.audioholics.com/forums...t=34477&page=2
Seems to be a cine version.

I started sawing scraps for the 2226 version, 2 short sides are 1" MDF, back and ends are 3/4" ply, baffles are 3/4" ply laminated to 5/8" MDF, removable panels are 5/8" MDF laminated to 3/4" ply. Not quite done with the removable side yet, but the rest of the pieces are cut and ready to glue up this week.

All I have to test with is 2205B's... Could the low chambers be tuned a little lower if I was to put 2235's in it?

[Thom]

It felt like someone fired up something like that over here last week. Fortunately it was for only a few seconds and at reduced volume. They kept it under a 6.0.