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Old 02-21-2015, 11:02 PM   #1
SLHQC
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Default TRS to XLR speaker cables result in much lower volume. Why is it so?

Hi

I have a situation that has left me scratching my head...

I have powered monitors (Fostex PM1) which have trs/xlr combo input jacks on them.

When I connect them to an interface using trs to trs (stereo jack) cables the output level of the speakers is significantly louder (more than twice the volume) than if I connect them using trs to xlr cables.

This is the case using two different interfaces (a Presonus StudioLive 16.0.2 and an Edirol FA-101), which both have balanced trs monitor outputs.

The trs to xlr cables are wired correctly. Checked with a multimeter.

Can anyone offer a suggestion as to why this may be the case?

Cheers and thanks in advance.
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Old 02-22-2015, 02:24 AM   #2
Arran
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I can't find the specs for these online, so at a guess I'd say that the jacks are calibrated for an unbalanced -10dBV consumer epuipment level signal, and the XLRs for +4dBu balanced.

Last edited by Arran; 02-22-2015 at 02:31 AM.
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Old 02-22-2015, 02:57 AM   #3
SLHQC
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Quote:
Originally Posted by Arran View Post
I can't find the specs for these online, so at a guess I'd say that the jacks are calibrated for an unbalanced -10dBV consumer epuipment level signal, and the XLRs for +4dBu balanced.
Ah yes! It seems you're right! I just did the comparison using a powered foldback wedge (FBT Jolly 8BA) and the level was the same with both cables.

Plus, I just found the Reference Manual for the speakers (which is a miracle in itself after all these years) and, sure enough, it says under XLR & TRS Combination Input:
"This input is an electronically balanced input and is compatible with both -10dBV and +4dbU signals."

In any case, the volume level difference is massive, so I think I'll be sticking with the trs-trs option...time to get a-solderin'...

Thanks so much for your help!
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Old 02-22-2015, 03:36 AM   #4
Arran
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Ok, I recommend that if your output is +4dBu, which it is with the Presonus, that you go in via XLR to avoid overdriving the input, you should be able to make up the volume difference with speaker volume pot.
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Old 02-23-2015, 04:31 AM   #5
SLHQC
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Thanks for the advice. Don't want to break anything!

Just checked the specs and it says

Main Outputs
Type XLR Male, balanced (stereo pair); ¼” TRS Female, balanced (stereo pair)
Rated Output Level +24 dBu
Output Impedance 100Ω
Aux Outputs
Type ¼” TRS Female, balanced (mono)
Rated Output Level +18 dBu
Output Impedance 100Ω
Monitor Outputs
Type ¼” TRS Female, balanced (stereo pair)
Rated Output Level z +18 dBu
Output Impedance 100Ω

See: http://www.presonus.com/products/Stu....0.2/techspecs

What do you make of that?

Wouldn't the +18dBu level mean the signal should be really hot, even using the xlr's?
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Old 02-23-2015, 04:37 AM   #6
SLHQC
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Actually I think I just answered my own question. The +18dBu figure would account for the trim pot on the monitor output, right?

Or am I totally confusing things?
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Old 03-29-2017, 07:54 AM   #7
SymboliC
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As this topic addresses pretty much the same issue that I'm having nowadays, I just wanted to bump it up when I came across this thread as a result of my Google search.

I also have Fostex active nearfield monitors and I exprienced a real drop/decrease in the overall output volume as I've started to use XLR to 1/4" instead of 1/4" to 1/4".

Is this a normal thing?

My audio interface is Roland DUO Capture EX.

My main question is, would it be misleading to monitor my projects if I choose to go again with 1/4 to 1/4? Is there a bare difference in signal quality or is it just the same except the volume level transmitted?

Thanks!
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Old 03-29-2017, 10:14 AM   #8
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Quote:
Originally Posted by SLHQC View Post
Wouldn't the +18dBu level mean the signal should be really hot, even using the xlr's?
That's going to be your maximum output level. 0dbFS = +18dbu on that output. That's only 14db above nominal on the +4dbu inputs, about 6db less that the main outs will give you. It leaves a little more headroom in the speakers.

You didn't post the rated max input for the speakers, but I'd hope they could handle +24dbu at least cause that's a pretty common spec. In that case the XLR ins will never give you everything the can from the Aux output, but the TRS is going to be like 14db more sensitive, so that you'll end up hitting almost +32dbu, and probably distorting all to hell. The trim knob can help with that, but that's never very precise and you'll kind of never know how close you are until you get there.
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Old 03-29-2017, 10:50 AM   #9
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Arran are you able to fill me in on how a "jack" is able to be "calibrated for an unbalanced -10dBV" I truly do not understand this as a normal jack is just a physical connection. Is there an included resister of something?

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Old 03-31-2017, 06:50 AM   #10
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Quote:
Originally Posted by grinder View Post
Arran are you able to fill me in on how a "jack" is able to be "calibrated for an unbalanced -10dBV" I truly do not understand this as a normal jack is just a physical connection. Is there an included resister of something?

Grinder
The physical plug isn't what's causing the difference in level. It's the electronics connected to each plug that cause the difference.

Here is an example. Imagine you have a mixing desk that accepts balanced line level TRS connections. Then you add XLR connectors for a mic, and you add an op amp that boosts the mic level signal up to line level when connected to the XLR plug, and then connects to the same wires as the line level input.

Now you get a different level depending on which plug you use, because the design assumes that TRS connections will have signal at line level, and XLR connections will have a mic connected to them that outputs mic level signals.
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