MOTU M2 balanced TRS output. -10dBV or +4dBu?

[Tupisac]

I have a pair of JBL 305p monitors, hooked up to MOTU M2 with balanced cables (TRS 2 TRS). I have my monitors set to -10dBV. Setting it to +4dBu makes them significantly quieter, requiring me to almost max out pots on speakers and interface to get to proper loudness.

And I was perfectly fine with that until I've decided to test them with unbalanced RCAs. I'm thinking about adding a sub and I was checking if I can run consumer subs lacking balanced connections. Turned out RCA output on -10dBV was audibly quieter, comparable to a level I've got from TRS output at +4dBu.

Was I using it wrong all the time?

Is it normal for balanced connection on +10dBV to give me so much more headroom? This basically rules home theater subs out...

Or maybe there is something else wrong? I've been using old, crappy RCA cables daisy chained with various converters, like TS->mini jack->RCA. Also, I've seen some reviews on this very forum stating that there is something wrong with M2 rca outputs...

 

[twsecrest]

Are you maxing out the volume controls on the source (computer) and MOTU, to send a strong signal to the JBLs?

-10bDV is for an un-balanced connection, +4dBu is for a balanced connection.
At least that what I remember from reading the manual, many years ago.

You might get a cable with one end being 1/4" TRS and the other end XLR.
Just in case there is an issue with the JBL's 1/4" jack.

Me, I would get the sub-woofer with balanced inputs and outputs.

 

[Tupisac]

-10bDV is for an un-balanced connection, +4dBu is for a balanced connection.

I remember reading that it's not always the case. For example, according to JBL manual, you should set JBL monitors to -10dBV while connected to LSR310S sub via balanced connections.

Anyway - I've fired REW generator, set it at 1 kHz sine at 0 dBFS, maxed out volumes in system, on motu and measured voltages with dmm:

TRS (between T and S) - 2,384 Vac
RCA - 2,212 Vac

Those differences don't look very significant.

Me, I would get the sub-woofer with balanced inputs and outputs.

The thing is that basically everybody recommended SVS solutions so far. Looking a the specs, basic SB-1000 goes way lower, it's smaller and apparently as flat as they get. Also, sealed, so technically it should be really responsive and quick.

 

[twsecrest]

Monoprice 10" sub-woofer.

Monoprice 10in Powered Studio Multimedia Subwoofer with 200W Class AB Amp and Composite Cone - Monoprice.com

Accurately mix and master your bass‑heavy music using this 10‑inch Powered Studio Reference Subwoofer from Monoprice™! This studio‑quality subwoofer designed

www.monoprice.com

 

[Tupisac]

Monoprice 10" sub-woofer.

Monoprice 10in Powered Studio Multimedia Subwoofer with 200W Class AB Amp and Composite Cone - Monoprice.com

Accurately mix and master your bass‑heavy music using this 10‑inch Powered Studio Reference Subwoofer from Monoprice™! This studio‑quality subwoofer designed

www.monoprice.com

Not available in my area...

 

[Tupisac]

Anyway - I've fired REW generator, set it at 1 kHz sine at 0 dBFS, maxed out volumes in system, on motu and measured voltages with dmm:

TRS (between T and S) - 2,384 Vac
RCA - 2,212 Vac

Those voltages don't make any sense..... https://en.wikipedia.org/wiki/Line_level

 

[staticV3]

@Tupisac to measure output voltage with a DMM, use a 60Hz sine wave. Not 1kHz.
Also make sure that in REW under Soundcard you're using either Java EXCL or ASIO output to avoid Windows messing with the signal.

According to Motu, the M2 is supposed to output 16dBu (=4.89Vrms) via the TRS Line out
...except that they also say "Maximum output voltage: 3.6V"
lol

The RCA Line out supposedly puts out 9.5dBu (=2.31Vrms)

When Amir tested the M2, he got at least 1.93Vrms via RCA and 4.89Vrms via TRS.

That you got almost identical voltage with 1/4" TRS and RCA makes me think that you measured the TRS voltage between Hot and GND or between Cold and GND, instead of between Hot and Cold.

Edit: ah yes that's exactly what happened.

TRS (between T and S) - 2,384 Vac

T is Hot, S is GND. So you measured half of the signal amplitude of the differential signal.
TRS between T and R will show 2.384*2=4.768Vrms. Maybe a bit higher if you use a 60Hz sine.

 

[Tupisac]

Thanks.
With 60 Hz it's 5,05 V between tip and the ring on TRS.
2,49 V on RCA.

Still - no idea how those voltages correspond to line levels from the wiki.

Also - should I set my JBL monitors to +4dBu then? What was actually happening while I was driving them via balanced TRS on -10 dBV?

 

[staticV3]

should I set my JBL monitors to +4dBu then?

Generally you will get the least amount of noise by setting your DAC to its max output and your Amp to the lowest volume.
So I would set the JBL to 4dBu.

What was actually happening while I was driving them via balanced TRS on -10 dBV?

Turned out RCA output on -10dBV was audibly quieter, comparable to a level I've got from TRS output at +4dBu

Going from -10dBV to +4dBu input sensitivity will reduce volume by 12dB.
Going from RCA to TRS will increase volume by 6dB.

Edit: here's a sheet:

 

[twsecrest]

@Tupisac to measure output voltage with a DMM, use a 60Hz sine wave. Not 1kHz.
Also make sure that in REW under Soundcard you're using either Java EXCL or ASIO output to avoid Windows messing with the signal.

According to Motu, the M2 is supposed to output 16dBu (=4.89Vrms) via the TRS Line out
...except that they also say "Maximum output voltage: 3.6V"
lol
View attachment 246853
The RCA Line out supposedly puts out 9.5dBu (=2.31Vrms)

When Amir tested the M2, he got at least 1.93Vrms via RCA and 4.89Vrms via TRS.

That you got almost identical voltage with 1/4" TRS and RCA makes me think that you measured the TRS voltage between Hot and GND or between Cold and GND, instead of between Hot and Cold.

Edit: ah yes that's exactly what happened.

T is Hot, S is GND. So you measured half of the signal amplitude of the differential signal.
TRS between T and R will show 2.384*2=4.768Vrms. Maybe a bit higher if you use a 60Hz sine.

I learned a few things today

 

[Tupisac]

Generally you will get the least amount of noise by setting your DAC to its max output and your Amp to the lowest volume.
So I would set the JBL to 4dBu.

Edit: here's a sheet:

Thanks! That's exactly what I was trying to figure out. By the way, where did you get that sheet? Haven't seen it in the manual.

Theoretically I'll loose more headroom by switching to +4dBu on TRS (like I'm supposed to) then by moving to unbalanced RCAs. Huh. Didn't expect that. But reference is reference and it looks like my headroom gain is just an illusion from over-driving my amps.

So, SVS is still in the game. Back to square one. Damn :/

 

[staticV3]

By the way, where did you get that sheet? Haven't seen it in the manual.

I made it for you

 

[Tupisac]

Oh, ok. Nice

But is this 0dB an actual reference according to JBL or is it just for this topic?

 

[staticV3]

I chose RCA in, -10dBV as an arbitrary 0dB reference to compare the other configs against. There's no deeper meaning to it.
"dBr" means dB relative to some reference.

The numbers also assume that TRS voltage is 2x RCA voltage. This is usually the case (like with your Motu), but is not guaranteed.

 

[sarumbear]

I have a pair of JBL 305p monitors, hooked up to MOTU M2 with balanced cables (TRS 2 TRS). I have my monitors set to -10dBV. Setting it to +4dBu makes them significantly quieter, requiring me to almost max out pots on speakers and interface to get to proper loudness.

And I was perfectly fine with that until I've decided to test them with unbalanced RCAs. I'm thinking about adding a sub and I was checking if I can run consumer subs lacking balanced connections. Turned out RCA output on -10dBV was audibly quieter, comparable to a level I've got from TRS output at +4dBu.

Was I using it wrong all the time?

Is it normal for balanced connection on +10dBV to give me so much more headroom? This basically rules home theater subs out...

Or maybe there is something else wrong? I've been using old, crappy RCA cables daisy chained with various converters, like TS->mini jack->RCA. Also, I've seen some reviews on this very forum stating that there is something wrong with M2 rca outputs...

INPUT SENSITIVITY SWITCH – Set this switch to +4dBu to protect from overload when connecting to professional equipment and sources with high output level capabilities. Set this switch to -10dBV when connecting to lower-level consumer-grade audio equipment or to the LSR310S subwoofer.

https://jblpro.com/en-US/site_elements/3-series-mkii-owner-s-manual-english

Line Out
Connector Type 1/4” Female, TRS Balanced, tip hot
Max Level Out +16 dBu
RCA Out (M2 and M4 only)
Max Level Out +9.5 dBu

https://cdn-data.motu.com/manuals/usb-c-audio/M_Series_User_Guide.pdf

Switch to +4dBu when connected via Line Out (balanced). Switch to -10dBV when connecting via RCA Out (unbalanced). In general, balanced is +4dBu and RCA is a nominal -10dBV connection.

Having to turn up the volume pot is not a deficiency of a system.

 

[Tupisac]

Having to turn up the volume pot is not a deficiency of a system.

I know, but louder is always better, amirite? -12 dB seems like a lot. That's why I'm curious what is an actual, nominal input according to manufacturer - for example when you test for max SPL. Or where I put 1 V from the known generator and I know that the speaker amp interprets it as 1 V.

 

[sarumbear]

I know, but louder is always better, amirite? -12 dB seems like a lot. That's why I'm curious what is an actual, nominal input according to manufacturer - for example when you test for max SPL.

Louder is not related to what you see on the display.

I wish manufacturers had specified correctly but alas they don't.