604 back mounting questions

[rogerh113]

Hello,

I just got a pair of 604-8g, and am starting to think about cabinets and build details. One thing that I think I would prefer to do (or I am pretty sure my wife would prefer me to do) is to rear mount the 604s. I have seen little info on this, and hopefully someone can provide some perspective and insight from actual experience.

I was thinking of using 8 of the steel threaded inserts on the back of the front baffle to secure the driver. Probably add a bit of glue to them when installing to assure they are secure.

Is there any particular issue with back mounting the driver and is there a limit to the mounting board thickness? I think I saw somewhere, perhaps on the '1974 Altec Enclosure' manual, that the baffle should be 1/2" max. Not sure if I interpreted that properly or if it meant something else.

Any insight would be appreciated. There are probably some issues I need to take into account that I have not thought of.......

regards -- Roger

[Altec Best]

Hi Roger, Welcome to the Board ! The baffle should be very stiff 1/2" is too thin and would flex.... Use 3/4" or thicker for best performance.

[rogerh113]

Thanks. I was planning to use 3/4 inch, and probably braced unless that causes a problem. On page 12 of the Altec 1974 Enclosure Manual, it says on footnote 1 - "Use mounting baffle no greater than 1/2". I could not locate what footnote 1 referred to, and thought maybe it was just a general statement to prevent the builder from creating sort of a horn by having the baffle too thick. I also cannot imagine mounting this beast on a 1/2 inch thick board.

regards -- Roger

[VolvoHeretic]

I can't really answer your questions, but you could, depending on how much room the screw-in inserts leave you, round-over the speaker cut-out with a 3/4" or 1/2" router bit, or front mount with the speaker recessed flush and have a rim piece of 1/8" copper or aluminum water jet cut to cover the gasket and screws painted or clear coated to preference.

This is what I would like to build.

[rogerh113]

Thanks for the idea on the round over, and I will add that to the design if the threaded inserts allow. At a minimum I should be able to do a generous easing of the cut out edge, which should be sufficient.

Impressive layout. I think you may want to add another chair or two !!

regards -- Roger

[mah]

Roger, that is what I did, including the glue. I used flat-head(Allen) machine screws to avoid screwdriver slip. Used 4-bolt mounting - I consider that adequate.

I also rounded the cut-out front edge with a 3/8" radius round-over router bit. Plenty of clearance to the screw(bolt) heads.

My cut-outs are 13 3/4 inch diameter.

Cheers.

[rogerh113]

Thanks very much - sounds like a good solution then. The 13 3/4 opening would certainly provide a bit more clearance to the bolt holes, and every little bit helps.

You don't think the 4 bolts leads to more vibration of the speaker frame against the baffle? Since the bolts are in shear, I figured 4 would hold the beast up, but it might be a bit more likely to vibrate. Plus given the limited thickness of the baffle (3/4') and any depth losses due to the threaded inserts, those attachment bolts will be none too long. Certainly 4 bolts would simplify things a bit.

regards -- Roger

[mah]

It's a matter of personal choice. Some say 8 bolts are better for even clamping pressure and the option of less bolt tension. Alternatively it can be argued that the mounting points are vibration nodes and 4 are preferred to 8.

- - - Updated - - -

Roger, The 13 3/4" cut-out mates well with the inner gasket surface, on my baffles. It requires care in getting the driver centred when marking the bolt hole centres.

[rogerh113]

Thanks for the information. I have not done a speaker enclosure (or open baffle) before, so I am learning as I go. If nothing else I am very careful when I lay out and cut stuff like this. A very minor mistake can destroy hours of work and many $ in material, so best avoided. It is really useful for me to go through and resolve the whole build in my mind before I start - that way I have already sort of done it, and actually building it is the second time around.

regards -- Roger

[GM]

Hello,

I just got a pair of 604-8g, and am starting to think about cabinets and build details.

Greets!


Something like this or .......? http://www.diyaudio.com/forums/multi-way/259659-gpa-604-8h-iii-build.html


Using a double baffle, you have the option to 'blindly' use the 12-24 T-nuts/black machine screws like Altec use to provide with each driver as well as provide a better 'roundover', even better than what he did, which is mostly cosmetic.


The 1/2" baffle thickness limit refers to the small front mounted 405 driver, which would need a >45 deg chamfer on the rear if any thicker one to keep reflections from it comb filtering/modulating the diaphragm.


That said, a 1/4" thick BB ply baffle would be sufficient for the 604s if made not much bigger and ideally we want a motor support/mass loading cab brace, further reducing front support requirements. Where cosmetics isn't an issue I advocate using small baffle 'inserts' with rear mounts for ease of periodically rotating these old tech gooped surround drivers, etc., to ensure the cab can be made very rigid, massive.


GM