Running self powered cabs with mic input, not line.

[Grant Bunter]

It turns out I've had a switch set to mike input (rather than line) on some JBL PRX615M's.
(Unless the switch is actually working incorrectly lol)

http://www.jblpro.com/ProductAttachment ... eet_v7.pdf

These are in use for FOH at a venue where I settle in new or returning artists as they change over.
One artist talked to friends, who pointed out the switch being set to mike input.
The friends say I am damaging the cabs running it this way.

I was asked to try using line instead of mike at next changeover, and see what the difference was.
Without making any change to channel strip EQ, in line mode, sound was weak and thin, lacking balls in the mids and bottom end, so to speak, until all faders (and master volume on the cab(s) was raised to 100%) were raised quite a bit, approaching unity.

Switching back to mike reintroduced more significant bottom end/mids at lower fader levels.

My initial though about this "issue" was that in mike mode I was running the mike preamp.
A far as I can tell from the block diagram in the manual, the mike/line switch simply changes sensitivity in the preamp for both mike and line.
So I can't be "damaging" anything as far as I can see.

Help me out on this one please...

[CoronaOperator]

In line mode the speaker would be expecting a balanced line in. By the weak bass, mids, and level it sounds like you are feeding it an unbalanced signal. Either only ts or 2 pins of the xlr cable instead of trs or balanced xlr. Or possibly a ground lift is engaged somewhere.

[byacey]

The input should be balanced regardless of mic level or line level input signal. You have to realize we're talking about a potential gain difference of up to 60 db or so, depending where the gain control is set.

Human nature often will pick the louder level as better sounding.

[Grant Bunter]

The cabs are fed from the mixer (A&H ZED12FX) L & R main outs with balanced XLR's, which tested fine when I got the system up and running and again at this attempt to change.
There is no ground lift facility in the cabs or on the mixer.

For roughly equivalent volumes:
In "mike" mode I have the gain on the cabs set to about +4dB (slightly past 12 o'clock). Master faders about -5dB
In line mode I needed gain control at 100% on the cabs to get anything other than very quiet (almost inaudible) out of the cabs. Master faders on mixer at unity. Channel strip fader pretty much at unity started to get richer bass on recorded music.

The artist wanted me to change back to mike input, he thought it sounded better, as in warmer and fuller.
It was sounding great for the other artist, who comes back in tomorrow.

Just want my ducks in a row when doing the changeover.
Despite a significant gain difference, can I cause any damage?

[Bill Fitzmaurice]

A mic input is intended to accept the lower voltage and lower impedance of a mic. It also may have pre-shaping. That's why it sounds different from the line input.

One artist talked to friends, who pointed out the switch being set to mike input.
The friends say I am damaging the cabs running it this way.

The friends are clueless.

[Grant Bunter]

Thanks for your input Bill,

This has been mentioned a number of times by the particular artist.
It would be improper of me to name the person(s), but they have a high enough profile here in Oz and, as always, they rely on rep.
Having said that, they are astounded someone out here can get the sound they are getting and readily admit there is no way they could have got there themselves.

I had tried to previously explain that the only difference would be impedance and a lower voltage.
I hadn't gone back to the block diagram prior to today though, nor considered pre shaping. Great point thank you.

I'm much more at ease about it all noting the switch selection is simply altering preamp sensitivity.
I know already which settings sound better. At least to my ears, the audiences ears, and the artist's ears. So that's a no brainer...

[NukePooch]

I've got the smaller brother of your mixer, the ZED10FX, and I always have run it through LINE inputs on powered speakers, specifically the QSC K-series and EV ELX-series. Maybe somewhere around 12 o'clock on speaker gains (on LINE), mixer just pushing into the yellow (+3).

I can get good sound running the speakers in MIC input, but the speaker gain controls are almost completely off. Any higher and it's instant distortion...

Just curious, are you running any processing between mixer and amp that is knocking a whole bunch of gain out of the signal?

[Hackomatic]

In line mode I needed gain control at 100% on the cabs to get anything other than very quiet (almost inaudible) out of the cabs. Master faders on mixer at unity. Channel strip fader pretty much at unity started to get richer bass on recorded music.

Something seems outta kilter. You should be able to crack craniums with those settings.

[Bruce Weldy]

Looking at the link....there is also a Main/Monitor button. That should be pushed in to the Main position. The Monitor position changes the EQ curve on the bottom end.

[byacey]

The various powered speakers I have worked on, this switch is strictly a 20 or 30 db pad on a transistor differential input mic preamp. It doesn't change the EQ in any way and it maintains the input impedance that the signal source sees somewhere around 10K on each leg.

The only thing I can think is the client is a victim of "louder sound is better" syndrome.

[Ryan Sober]

IIRC, those mixers have a "+4"/"mic" selector switch on the main output.
If OP has "mic" selected on the mixer and speakers, then no issue.
I personally prefer to send +4 down an XLR whenever possible.

[Grant Bunter]

I'm "just the sound guy" at this venue. None of it is my PA.

No, there's no processing between mixer and cabs.

Yes, Mains/monitor button is set to mains.

No, there is no +4 switching on the mixer.

The venue is outdoors, and is for a combined dinner and show (with mostly older clientelle), so it's not being run overly loud
I've had to keep on reminding all artists it's not just a show.