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JBL sub recessed switch

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JBL sub recessed switch

Postby tallen55 » Wed Aug 28, 2019 1:09 am

I just got a pair of JBL818S subs. What is the recessed switch on back panel? It says +1/-1 or +2/-2. (I’m assuming its for different speaker cables) Thanks
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Re: JBL sub recessed switch

Postby AlecSp » Wed Aug 28, 2019 8:32 am

30 seconds of googling find the spec for the sub, which says:

Connectors: NL4 Input, NL4 Loop-thru (+/-1 or +/-2 Selectable)

So, it looks as if the switch determines which pair is used on the loop through, where you might connect on to other speakers - and is typically used to send separate sub & top signals down a single cascading 4 core NL4 cable.

If you're simply cabling into the input of the sub, you can ignore the switch.
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Re: JBL sub recessed switch

Postby Wonks » Wed Aug 28, 2019 8:45 am

Yes, it must be as AlexSP says. I couldn't find anywhere where it specifically states this (big black mark for JBL) and initially I had a much more complicated idea which didn't work at all.

So it allows for a 4-core cable to carry two amp signals to the sub, and then for a 2-core cable to carry the other signal on to some tops or another sub. As 2-core Speakon cables are normally wired between the +/-1 connections on a NL4 Speakon, for the 4-core amp to sub cable, you'd want to wire the pass-through signal on the +/-1 connections and the sub signal on the +/-2 connections. You'd then set the input selector switch to the +/-2 setting.

But if using a 2-core speaker cable direct from an amp to the sub, then this would normally be connected to the +/-1 contacts, so set the input selector switch to the +/-1 setting.

The two Speakons on the sub are simply wired in parallel, so the +/-1 and +/-2 connections are linked through.
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