Perhaps MIT / Transparent Cable prototypes :-)
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OK, so it's a little more complicated. It looks like there are 4 resistors, which I assume are in series with the coil.
Not sure what the switch will do exactly. It could bypass everything, or just the resistors, or just the coil.
Was this system using horns/pa type of setup? if so maybe the user was experimenting with the bass configuration.
It is probably very cabinet specific, and my guess is it was more of a hack/experiment.
I don't see any capacitors involved. Since there is only one in and one out, it's safe to say the entire circuit is in series. Nothing shunts to ground. Therefore the circiut is something like this:
with "vvv" representing a resistor and "uuu" representing a coil. "0" and ">" representing the input and outputs.
Somewhere around there the switch bypasses some or all of it.
Clearly someone was playing with a bass cabinet somehow.
I see at least one cap, barely seen at the top of the picture behind the 10 ohm resistor. There may be more behind the other 10 ohm resistors.
Are those 10 watt resistors?
Thanks @grannyring I see it now.
Ok, with more coffee and less fuzzy vision than I had yesterday (comes and goes) I can see most of the circuit.
It seems that all parts are in parallel. However, 2 of the resistors are switching in or out, changing the parallel resistance from 5 Ohms (10 Ohms / 2) to 2.5 Ohms (10 Ohms / 4). Lowering the parallel resistance reduces the effectiveness (depth) of the notch filter.
This makes it most likely a shunt-type notch filter. Impossible to tell what exactly it’s doing without full analysis of the driver as well as knowing the coil and cap values.
It could have been an experiment to remove ringing in a driver, with the switch allowing for different levels of suppression.
In any event, this is clearly a DIY hobbyist’s experiment which would only be useful for his particular speaker/experiment. No use at all for anyone else. If I purchased this (I wouldn’t) it would be for experimental parts only.
This could all be confirmed with an Ohm meter. If you want to understand more about this type of circuit (or whatever it ends up being) come over to the DIYAudio / multi-way forum where we can post pictures and discuss with a number of speaker builders. :)
Not exactly sure, but they look a lot like the low pass filters from Legacy Audio used for some of their late 80s early 90s loudspeakers. Classic, Focus......etc. Bill from Legacy would just give them to you if you asked, if you had a problem with too much bass in your room caused by standing waves. This is a few years before they came out with the Steradian.