Go Back   Cockos Incorporated Forums > REAPER Forums > Recording Technologies and Techniques

Reply
 
Thread Tools Display Modes
Old 02-21-2015, 11:02 PM   #1
SLHQC
Human being with feelings
 
Join Date: Jun 2014
Location: Wollongong, Australia
Posts: 5
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.
SLHQC is offline   Reply With Quote
Old 02-22-2015, 02:24 AM   #2
Arran
Human being with feelings
 
Join Date: Aug 2012
Location: Bolton, UK
Posts: 234
Default

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.
Arran is offline   Reply With Quote
Old 02-22-2015, 02:57 AM   #3
SLHQC
Human being with feelings
 
Join Date: Jun 2014
Location: Wollongong, Australia
Posts: 5
Default

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!
SLHQC is offline   Reply With Quote
Old 02-22-2015, 03:36 AM   #4
Arran
Human being with feelings
 
Join Date: Aug 2012
Location: Bolton, UK
Posts: 234
Default

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.
Arran is offline   Reply With Quote
Old 02-23-2015, 04:31 AM   #5
SLHQC
Human being with feelings
 
Join Date: Jun 2014
Location: Wollongong, Australia
Posts: 5
Default

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?
SLHQC is offline   Reply With Quote
Old 02-23-2015, 04:37 AM   #6
SLHQC
Human being with feelings
 
Join Date: Jun 2014
Location: Wollongong, Australia
Posts: 5
Default

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?
SLHQC is offline   Reply With Quote
Old 03-29-2017, 07:54 AM   #7
SymboliC
Human being with feelings
 
SymboliC's Avatar
 
Join Date: Dec 2013
Posts: 289
Default

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!
SymboliC is offline   Reply With Quote
Old 03-29-2017, 10:14 AM   #8
ashcat_lt
Human being with feelings
 
Join Date: Dec 2012
Posts: 7,272
Default

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.
ashcat_lt is offline   Reply With Quote
Old 03-29-2017, 10:50 AM   #9
grinder
Human being with feelings
 
grinder's Avatar
 
Join Date: Jan 2009
Location: New Zealand
Posts: 2,905
Default

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
grinder is offline   Reply With Quote
Old 03-31-2017, 06:50 AM   #10
drumphil
Human being with feelings
 
drumphil's Avatar
 
Join Date: Jun 2006
Location: Australia
Posts: 3,738
Default

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.
drumphil is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 08:28 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.