Speaker polarity Ampeg SVR-212
Hi folks, decided to sign up after lurking for a while. I recently got an Ampeg SVR-212. The previous owner had taken it apart to see what was inside but wasn't completely sure whether he had reconnected the woofers with their correct polarity.
It's a small job to open it up and my gut feeling tells me to wire the front woofer and the tweeter with normal polarity and the rear facing one with reversed polarity.
Anyone that can shed some light on this?
The tweeter may have the polarity reversed, this depends on the phase of the woofer and tweeter's around the crossover point.
Mmmm confusing! My gut tells me that if i connect the woofers both in phase while one is facing front and the other is facing rear (ie the two magnets back to back) they will work against each other. Both cones will move inside at the same time so they push and compress the air inside. When the cones move out again they wil create a 'vacuum' in the enclosure.
If i reverse the phase they will work together, one moves out as the other moves in creating a sort of large piston. Better explained here: http://en.wikipedia.org/wiki/Isobaric_loudspeaker
Any explanation on why you would wire them in phase?
As far as I can see the SVR-212 is just a regular 212 with another 12 on the back. Both need to be wired in-phase else there will be zero bass coming from that cabinet...... Both cones NEED to move inward/outward at the same time(di-pole) else the soundwaves created by one woofer will be out-off-phase with the other one. The principles are the same as when the two woofers were both mounted on the front.
Do the battery test. The woofer cones both need to move in the same direction.
I've just tried the battery test, when standing in front of the cab the front and rear speaker move towards me. This tells me about the current configuration, but i am 100% sure the person who connected it like this did not pay attention when hooking them up. So it's a 50/50 chance this is the way it should be :)
Red and black go to the front speaker. Blue and white go to the rear speaker (the darker colors are neg-).
Both speaker cones should move out when doing the battery test.
This is not an Isobaric (clamshell) situation.
There is a much larger chance of it being wired wrong then 50/50 as there are six terminals and six leads (counting the horn). :)
The distinction between the front and back speaker leads is important because the front speaker is meant to be full range -while the rear speaker is crossed over @ 150 Hz so it only produces the omni-directional low frequencies.
I think these cabs are great btw. I have put many miles on an SVR-215 over the past decade or so.
Good luck with yours.
1993 Ampeg catalog excerpt:
Wow thanks for the scan! I love old ads :-)
The cones both need to push out at the same time when you do the battery test. It isn't about moving in the same direction it's about them working in unison to compress or rarefy the air in the room by moving outwards together or inwards together respectively. If they both move to the front (i.e. front woofer outwards, back woofer inwards) then you will lose almost all your true lows and probably blow the woofers if you gig them like this.
Just listen to it. If it sounds bad, hook it up the other way.
I had some major GAS for one of these when they were new. I haven't seen one in a long time.
Just finished checking it out: all front wires were connected OK, but the rear white and blue were reversed. I swapped them so blue now connects to neg and white to pos and after closing it up i gave it a workout! It sounds great, there's a lot of volume coming from that small cab!
Thanks to all of you for helping me figuring out this babys wiring!
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