JBL Vintage 4646A LF Speaker Plans

[robmuso]

Hi Everyone,
I am trying to source drawings with all dimensions for building some JBL Vintage LF enclosures.
The model I wish to copy is a JBL 4646A. I will also need port dimensions.
http://www.jblpro.com/pub/obsolete/4646a.pdf

If that model is not available, can anyone offer any other drawings to suit the following LF Speaker.
Preferably a rectangular shape Cabinet. If the volume is slightly bigger eg: 2 cu ft, that will be ok.
The LF speaker used will be a JBL 2206H.

I've been a muso for over 40 years and I now basically need a nice compact system that I can use at my gigs as a keyboard player.
I want a modular system so that I can manage lifting it easier as I get older.
I'm now 63, but I love the sound quality from the JBL vintage products from the 80's.
For the HF, I will be using the 2426J Driver with a 2370A Horn Flare, but they are already made in separate boxes that will sit on the top of the LF speaker.

I hope someone can please help me with this as I will be most appreciative and respectful with those who offer their help.
Thank you.
Regards,
Rob muso

[RMC]

Hi Rob,

With all the info given on the first page of the 4646A data sheet you posted you can somewhat easily "reverse engineer" the box to make yourself a set of plans or sketches, and even a copy of the box.

You have material thickness, box outside dimensions, box volume, vent tuning frequency. For the vents diameter compare these to the dust cap of the 4 in. voice coil to get some idea, vents would seem 3" dia. or so, though the dustcap is a little more than 4 in. to cover the coil correctly.

But to be sure of vent dia./length you can model the box (with driver specs, box volume and tuning frequency given) in speaker design software, some of which are free such as Win ISD Pro 2016 edition.

The 2206H spec sheet doesn't give driver thickness number remaining outside the box when front mounting of the driver, contrary to many European woofer spec sheets. That number being useful to know the amount of the 4646A front panel recess here which is about that of the driver thickness outside the box in driver front mounting. I'd say recess looks like about 1/2" from the picture.

If you already have the 2206H measure that thickness and the front panel recess is about that number, or a bit more. Just for example, my 12" 2214H have 10-11 mm thick outside the box in front mounting.

As for the baffle cutout for woofer the 2206H spec sheet says 280 mm (11 1/16").

This box cloning is relatively easy compared to some other models where you don't necessarily have all the info. Here you have in the 2206H/4646A data sheets just about all you need, except a ready-made set of plans, but in this case it can be figured out with some work, without too much pain... Regards,

Richard

P.S. I can help but don't have the time to do the work in your place.

[robmuso]

Thank you RMC.
Much appreciated.
robmuso.

[dprice]

I happen to have a 4646A here next to the computer...

Ports are about 3" diameter x 5 7/8" long. I say about since there is a trim ring to make it look pretty that is closer to 2.75" diameter and about 7/8" long.

Good luck!

[robmuso]

Hi dprice,

Thank you so much for your help.
Could I please ask one more favour?

Could you please measure from the outside edge to the front baffle to see how far in the baffle is recessed in from that edge?

And could you please do the same for the back panel, and let me know those two dimensions?

I have the external dimensions of the box from the brochure.

My aim is to find out the box internal dimension from front to back.

One thing that I don't know is if the front baffle is 1" (25.4mm) or 3/4" (19mm) thick.

I don't expect anyone to dismantle anything, but even an approx measurement through the port to the back panel could help.

However, the acoustic wool could be in the way of that.

Any advice or help would be much appreciated.

Thank you so much.
Regards,
robmuso

[dprice]

The front and rear baffles are recessed a hair over 1/2". I would assume 1" for the front baffle because 3/4" leaves little to work with to support the beastly 2206 after being partially recessed...it could be 3/4" since these were designed for fixed installs rather than road duty.

Build with baltic-birch plywood rather than MDF. I would go 1/2" with extensive bracing and 1" for the front baffle to reduce weight (and look for a neo driver to really cut the weight).

[RMC]

Hi Rob,

The 4646A data sheet you posted SAYS the material thickness used is 3/4" (19mm)... So if you want a correct clone physically and acoustically you should follow the original dimensions given...If you don't go for the probably original 3/4" particle board (which I NEVER use) then I'd suggest 3/4" Fir plywood with the usual bracing, which is lighter and less expensive than baltic Birch.


Richard

[robmuso]

Thank you dprice & RMC (Richard),

Very decent of you both to help me with this.
That now gives me everything I need to know to build a pair of 4646A boxes for my gigs as a keyboard player / vocalist.

Much appreciated.
Kind regards,

robmuso (Rob)