Cabinets

[nikki1]

I'm building a pair of 612C cabinets. The guy who built our kitchen is cutting all the panels for me out of 3/4 cabinet grade ply faced with cherry and maple veneer depending on what shows to save $$$. Also edge banding all the edges which show with cherry veneer. All I have to do is assemble the parts etc and finish them.

I have extended the sides of the cabs to accomodate the horns ending up with one cabinet for all.

If anyone's interested I'm sure they'd be glad to make the same as a "kit" and ship it to you. Haven't got the cost yet but if you like I'll pass it along.

They do excellent work.

[Altec Best]

We just Love Pictures around Here ! What are you putting in them,604's maybe ?

GM told me that running full range they should be beveled.I have a pair of original 612C's w/604-8G's that are beveled from the factory.

[amandarae]

Yep! Same here. Beveled with 612C badge on the back and I bought it with 604-8G's and the matching network installed on them as well.

Abe

[nikki1]

What do you mean by beveled? Looking at your pics it looks as though the edge of the hole for the speaker has an outward flaring bevel around the edge of the opening. That what you mean? I thought of that but not shown that way in the plans. According to the plans I have the fronts, which mount the speakers are flat, set in 1 1/2" to allow for the cleats (3/4") and 3/4" wide grill cloth frames. Speakers are rear mounted. I'm putting in a pair of 416-8A's, 806/511 horns and 511B xovers. Just what the specs call for. The materials cost $180.00 per box, and when I'm done they'll be brand new 612C's with the horn enclosure as part of the cabinet. Bass box will be to Altec spec.

[Altec Best]

Yes the outside edge of driver opening 15" beveled opening.Well then your OK, LF drivers don't need the bevel as far as I know, just a 604,605,etc... Full range drivers. I think the bevel was added later on in the production of the 612C. But when the 612C was purchased from the factory with 604-8G's in them they came with this bevel.But I think they (Altec) just started cutting this bevel in all the 612C's just in case you ever want to mount a duplex.GM just said full range drivers,I don't know the reasoning behind it though. Your cabs look very nice indeed ! What I have found though is they sound much better when I lift them off the floor 12" or so.They really excelled when they were mounted up high near ceiling pointing down onto the listener !


PS.Maybe GM or any other guru will see this thread and can add something, my cabs have one?

[nikki1]

Maybe I'm wrong about rear mounting. Should my 416's be front or rear mounted? I know that if fronted there'll have to be a bevel due to the little reinforcement "webs" around the edge of the frames. Can't see anyother reason for it with the exception that if rear mounted maybe the flare from the bevel adds something to the low freq's. Wild guess though.

[GM]

GM just said full range drivers,I don't know the reasoning behind it though.

Eigenmodes (standing waves) develop between parallel surfaces and since the baffle cutout is circular it can create an infinite number in theory if excited, summing to a strong enough pulse that will modulate any output from a rear mounted driver that falls within this BW, so beveling it dramatically reduces its fundamental amplitude, ergo rolls off its harmonics faster.

If the driver is front mounted and the baffle thickness represents a tunnel WRT the driver frame construction such as occurs with many smaller 'full-range' drivers, then the mounting hole rear lip needs considerable flaring to ensure there's no reflections that can bounce off the rear of the driver, modulating it and/or create an acoustic choke.

Eigenmodes are half WL in nature, so have both even and odd harmonics. For example, a 13.25" dia cutout's fundamental will be around 13560"/sec/2/13.5" = ~502 Hz depending on the local ambient, so in theory even rear mount woofers need the front of the cutout beveled if XO'd above ~300-500 Hz depending on the slope order. I've never measured nor read of anyone measuring any strong enough to show up on a plot though or been able to perceive them Vs a free air comparison; so until someone can, I see no reason to do it for 15" woofers except for cosmetic reasons.

GM

[GM]

The guy who built our kitchen is cutting all the panels for me out of 3/4 cabinet grade ply ..........

Not trying to 'rain on your parade', but cabinet grade plywood isn't void free since it doesn't need to be and if any cab resonances excite them enough to be heard as background noise they are very hard to chase down, eliminate even with a mechanic's stethoscope.

GM