I encountered an interesting issue when I “upgraded” my CB NAC62/HiCap/NAP140 system’s subwoofers, from a pair of REL T-5is to a pair of older, but beefier REL R-218s.
I had the T-5is high-level inputs connected independently to each loudspeaker, via the speaker terminals, as follows:
- Connection at the left speaker terminals: Left subwoofer’s speakon cable’s red & yellow to left speaker’s positive, and black to left speaker’s negative.
- Connection at the right speaker terminals: Right subwoofer’s speakon cable’s red & yellow to right speaker’s positive, and black to right speaker’s negative.
This is the official REL recommended way to connect dual, mono (left and right) subwoofers. I was using this set up for many months, and it worked perfectly.
Now I have swapped in the R-218s, and with both subwoofers connected, I’m hearing much higher frequencies than expected from the subwoofers. In other words, it sounds like the subwoofer’s crossover has been bypassed, which shouldn’t be possible via the REL’s high-level inputs (only via the low-level LFE input). Just to be clear, it’s not a subtle effect, and makes the system completely unlistenable.
If I disconnect the speakon cable from either the left or right subwoofer, the issue goes away, with the remaining connected subwoofer behaving as expected. Otherwise, I’d suspect that one of the R-218s was defective. And in that case, I would expect the problem to persist in just one (defective) subwoofer, whether one or two subwoofers were connected to the system.
Also, if I connect one subwoofer via the speakon’s cable red lead to speaker terminal positive, and yellow to speaker terminal negative (with the black speakon lead floating), things work fine (perhaps the yellow/red lead connected subwoofer needs a higher volume setting, but otherwise seems to behave correctly). However, I don’t consider this a solution, but rather just a data point.
Next, I swapped the T-5i’s back in, just in case I messed something up during the switch-over. But the T-5is worked perfectly like before. No issues at all.
By the way, R-218s have class D amplifiers vs class A-B amplifiers in the T-5is. I do know that the REL speakon cable’s black lead needs to be lifted when connecting to class D amplifiers. But I’ve never read of any special handling that’s required when the REL amplifiers themselves are class D.
So I’m really reaching here, but perhaps my unserviced 140’s negative output has some voltage leakage, which interacts with the dual R-218’s class D amplifiers somehow (if so not sure why only when two are connected)? And on the other hand, perhaps the T-5is are more resilient to voltage leakage?
Anyway, if anyone has any ideas, I’d like to understand the root cause of this behavior, and how I can go about fixing it. I will try REL support next week, but thought I would share here in the meantime.
Please don’t suggest that I switch to using low-level inputs. To each his own, and there’s nothing wrong with that, but I personally prefer REL’s recommended high-level connection method.