JBL sub pass through, crossover, and sound quality

[txbdan]

This is probably irrational, but I seek reassurance. I just got a bad ass RME ADI-2 DAC FS to go along with my Genelec 8030Cs and JBL LSR310S sub. I'm using all balanced XLR cables to connect the DAC to the sub, using sub's HPF, then from sub to the Genelecs. The great mystery of what's in the sub and what its doing to my beautiful signal is giving me heartburn. Is it noisy in there? How does it retain the balance signals as I think they'd have to go back to single ended to be filtered? Is the filter active? What's it doing to my signal levels?

I need a beer.

 

[Jmudrick]

This is probably irrational, but I seek reassurance. I just got a bad ass RME ADI-2 DAC FS to go along with my Genelec 8030Cs and JBL LSR310S sub. I'm using all balanced XLR cables to connect the DAC to the sub, using sub's HPF, then from sub to the Genelecs. The great mystery of what's in the sub and what its doing to my beautiful signal is giving me heartburn. Is it noisy in there? How does it retain the balance signals as I think they'd have to go back to single ended to be filtered? Is the filter active? What's it doing to my signal levels?

I need a beer.

Maybe you do. Listen to music and don't worry about it. I have the RME with two 310s subs , Buckeye amp and Technics C700 standmounts. Works.

 

[DVDdoug]

You're not hearing noise, are you? Or not more noise than when the sub isn't used?

How does it retain the balance signals as I think they'd have to go back to single ended to be filtered? Is the filter active? What's it doing to my signal levels?

It's possible to make a fully-balanced filter but it's unlikely that it's built that way.

Usually, with balanced inputs & outputs there is a differential amplifier on the input that puts-out an unbalanced signal to be used internally, and then another circuit on the output converts it to balanced again. That's not a problem because there are no internal ground loops and the circuitry is isolated & shielded from electromagnetic noise.

In the old days, there were transformers on the input & output to convert between balanced & unbalanced but with op-amps and other modern solid state electronics it can be done better & cheaper without transformers.

 

[txbdan]

Hrmm that gave me an idea. I have a MOTU M4 with balanced ins and outs and decent specs. Maybe I can run a loop through the JBL and see what the total round trip looks like. I think I can do that with REW. Could do a loop measurement to see the M4 baseline. Best case, it could show the JBL distortion/noise is no worse than the M4 outs + M4 ins.

 

[txbdan]

Here's a quick go at it using a 6" TRS-TRS cable to loop the M4's output to input. That's all default settings using REW's tone generator. I'll have to read up more on how to optimize things. The meters on the interface show the input signal is a little bit less than the output signal. Not sure why that is. I have the generator set to -1dBFS. Tomorrow I'll dig out some more cables and loop around the JBL.

 

[Blumlein 88]

So worst harmonic is at -112 db. Does not look too bad.

 

[dasdoing]

the time alignment is what would worry me

 

[txbdan]

the time alignment is what would worry me

What do yo mean?

 

[dasdoing]

What do yo mean?

in order to integrate a subwoofer properly, most of the time a delay has to be set between the mains and the sub.

 

[Matthias McCready]

For the speakers and sub to achieve summation, ie a nice smooth hand off, rather than a hole in the frequency response, you want the phase traces to match up in the crossover region.

As suggested by Dasdoing this usually has to do with timing.

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Timing is about placement of the speakers relative to each other, listening position (timing can only be perfect in one place in a room), and any digital processing differences.

While analog transmission of sound is close to instant at these distances, digital conversions and processing do take time.

 

[txbdan]

So I suppose there are two things to test.
1. Is the JBL in bypass mode with the crossovers disabled.
2. Is the JBL with crossover engaged. This implements a 80Hz LPF for the sub and 80Hz HPF for the mains pass-through.

What's the best way to measure delay with REW? I think there is some kind of impulse response measurement I can do. I'll check later after work.

But ultimately, I can't imagine any delay introduced by the filters or the pass through itself is significant as this is how its designed to operate. Genelec does this with their subs as well.

 

[Matthias McCready]

So I suppose there are two things to test.
1. Is the JBL in bypass mode with the crossovers disabled.
2. Is the JBL with crossover engaged. This implements a 80Hz LPF for the sub and 80Hz HPF for the mains pass-through.

What's the best way to measure delay with REW? I think there is some kind of impulse response measurement I can do. I'll check later after work.

But ultimately, I can't imagine any delay introduced by the filters or the pass through itself is significant as this is how its designed to operate. Genelec does this with their subs as well.

If the filters are analog, there should not be any introduced delay.

I was mentioning the possibility in an overall sense, rather than your situation. For example the main speakers I have, due to digital processing, have a 20ms delay between the top section and the subs.

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As far as placement affects delay timing, it would probably be a few ms at most. This is more of a consideration in large rooms and spaces, where there can be significant timing issues (read: PA's).