crossover boxes

[thinking]

I've been getting the parts together for a set of Jeff's crossovers, and here's my question. It would seem that putting all these inductors inside a sheetmetal box would tend to mess with their inductances, putting an iron core inside them certainly does, but the original Altec crossovers were in metal boxes, what gives here. Does it really not cause much of an effect on them? If not, I was thinking that a couple of these old pc power supply boxes were about the size of the factory box that came with the later units that had the mid-frequency correction set-up, and the price is real good.

[donaldpatten]

thinking
I have used plexiglass sheets 0.180 inches thick.
Just drill holes PCB style and solder the coil & cap lead
wires on the back side , Lay the coils on the plexi ( cookie sheet style ) and tie them down with cable ties.
No worries about magnetics or insulation problems;
and it is strong.
Don

[armandh]

or non ferrous metal such as aluminum

[Audio_by_Goodwill]

Originally posted by thinking:
I've been getting the parts together for a set of Jeff's crossovers, and here's my question. It would seem that putting all these inductors inside a sheetmetal box would tend to mess with their inductances, putting an iron core inside them certainly does, but the original Altec crossovers were in metal boxes, what gives here. Does it really not cause much of an effect on them? If not, I was thinking that a couple of these old pc power supply boxes were about the size of the factory box that came with the later units that had the mid-frequency correction set-up, and the price is real good.

<font size="2" face="Verdana, Helvetica, sans-serif">I'm not 100% sure, but I don't think you have anything to worry about. Inductance is based on the geometry of the coil.

L (inductance) = u (mu naught) n (number of turns) PI r^2 (radius squared).

Mu naught is the permitivity constant, and is symbolized with a greek letter that I can't type.

Pi is 3.14159...... also a letter I can't type.

Audio_by_Goodwill
Michigan, USA

[thinking]

The plexiglass is a good idea, I've worked with it in the past. The aluminum comment also got me thinking, so I checked a couple of factory units to be sure. The 604E and the 904 units both responded to my magnet, although the 904 does have the aluminum faceplate.

[donaldpatten]

Thinking
The N1600 for 605's has a 1mH IRON CORE coil in a steel box: no problem, in effect the iron core shields the coil.
If you have air core coils they will change inductance ( mH's ) in a steel box but not in an aluminun box,( or Plexliglas sheet ) .
Don

[thinking]

Ah, that's probably what was making it not make sense. I'm sure the 604 crossover had iron core, probably the others as well. And after another thought, I actually stuck one of the air cores in a steel box and checked it, and yes, as expected it does change the inductance. Guess I'll go with the plexiglass. Back in college I built an exotic crystal radio in a plexiglass box, really looked cool. It had so much output I almost had to put a volume control on the earplugs.

[thinking]

I have a handheld inductance/capacitance meter from circuitspecialists.com Enter 6243 in the search box. Nothing fancy, but it gets a number to work with.

[thinking]

I should add, the inductance doesn't change a huge amount, particularly if you keep it away from the sides. It's probably in the range of 1 to 2 percent, but after carefully changing the number of turns on the coil to get just the right number, and using an air core to reduce distortion, it just seems to be a step in the wrong direction. Most likely wouldn't produce an audible difference, most caps aren't any closer than several percent tolerance, and we live with them, but yes, if you put your inductor next to a steel box, it will affect it so some measurable degree.

[donaldpatten]

Thinking
What type Super Duplex ( 604/5 ABC ? ) do you have ?
Are you near Chicago ?
Don