What's powering passive sub-woofer on a 5.1 or 7.1 AVR setup?

[jcarys]

Have you tried taking that 20-25 cable out of your setup, and checking the same sub with a short cable? That would be the first item I would want to test for hum. It's possible you just need a better shielded cable.

 

[Redacted]

A tube- or transistor-based analog power amp. No controls/processing.
Class-D power amps begin to introduce some but still negligible latencies.

Sure - but do you have the measured figures for an amp we may know of? It's interesting to some of us!

 

[Everett T]

For the OP:s ground loop start here

'Ground Loops 101' https://www.audiosciencereview.com/forum/index.php?threads/ground-loops-101.7162/

As for the amp needed, and as mentioned, a single channel (mono) or a multichannel amp, if you will be using more than one subwoofer, will be your options since the DSP is built into the passive sub itself.

 

[Kal Rubinson]

Sure - but do you have the measured figures for an amp we may know of? It's interesting to some of us!

I do not because it is rare that anyone is concerned with it.

 

[john61ct]

I am also confuses by the OP's imprecise writing.

OP, which exact component models do you already own?

Do you really not care to fix your ground loop hum? That might not cost much or even zero.

Which exact models are you considering adding?

The fact that the sub output is at line level rather than amplified does not matter to the signal processing, you just need to add an appropriate monoblock power amp.

At 1000W RMS a good one will be more expensive, so you need to give details to determine how much power you actually need so as to not waste money.

Now, does your Denon have DSP controlling the line level sub out?

Or does your unpowered sub have DSP controls included?

If both, then we can figure out which to choose, don't use both.

 

[Kal Rubinson]

Or does your unpowered sub have DSP controls included?

It does have some controls but, imho, they are minimal.

 

[john61ct]

So OP should likely disable them and let the Denon handle all the bass management.

 

[happy hopping]

Have you tried taking that 20-25 cable out of your setup, and checking the same sub with a short cable? That would be the first item I would want to test for hum. It's possible you just need a better shielded cable.

that's an excellent idea. I did use a 2nd cable since, it's also a long cable, and it's the same result. But I can dig out a simple 6 ft. cable and see if there is any difference.

the way I avoid the issue is: for movies / tv series that its just talk, for e.g., I'm watching Star Trek: Centre Seat right now, and it's just talk. So I don't need the sub-woofer. So the vol. is turn to 0. If I'm watching mission impossible, then the turn the dial to 1/3 and I do need to unplug the sub-woofer signal cable once or twice in a 2 hr. movie when the humming sound occurs

On the other hand, there can be as much as 2+ days, when there is no AVR turn on, no movies, and the sub-woofer is set at 1/3, and I forget to turn it back to zero, and the then 2 days later, when I was in the other room, or downstair, the humming sound occurs.

 

[happy hopping]

I am also confuses by the OP's imprecise writing.

OP, which exact component models do you already own?

Do you really not care to fix your ground loop hum? That might not cost much or even zero.

Which exact models are you considering adding?

The fact that the sub output is at line level rather than amplified does not matter to the signal processing, you just need to add an appropriate monoblock power amp.

At 1000W RMS a good one will be more expensive, so you need to give details to determine how much power you actually need so as to not waste money.

Now, does your Denon have DSP controlling the line level sub out?

Or does your unpowered sub have DSP controls included?

If both, then we can figure out which to choose, don't use both.

1) currently, I just own an old Yamaha AVR. I got it at least 7+ yr. ago. Prior to that, is a Sony AVR ES series, that unit dies after 19 year.

2) no budget for new passive sub-woofer yet. I bring out that link, as Focal is saying their highest end model, they choose passive over active. Now, I don't have $ for that Focal model, but I am curious as to that little box that they label as "Power supply" on the left, on page 16 of their manual, is that what Focal say as to what we need? because that doesn't look like a mono block. It looks like Focal said you need "a power supply". Is that all we need to power a passive sub-woofer instead of a monoblock?

3) room is only 120 sq. ft., so I don't need a lot of power.

4) When I bought my first Klipsch powered sub-woofer (not the current one). I have the same problem. The dealership gave me an orange plug that changes a regular + ve/ -ve + ground 3 Prong plug to just +ve / -ve plug, and that SOLVES the issue of humming. But about 7 yr. ago, I sold that Klipsch and got a new model, and that new model doesn't have the means to substitute the regular 3 prong plug to the the orange color +ve/-ve plug, so w/ that new sub-woofer, I've been stuck w/ the problem since

5) did try to include the powered sub-woofer in the same circuitry as the AVR in my room, and also did try to have the AVR and the power sub-woofer in 2 separate circuitry (current setup). No difference, both setup yields the humming sound, this is why I lean on a passive sub-woofer in the future.

6) didn't buy the Denon yet. But I have this model in mind, Denon is good, this is their med end product, but still made in Japan

AVR-X4800H | Home Theater Receiver

The Denon AVR-X4800H is a 9.4 Ch. 125W AV receiver for breathtaking home theater with Dolby Atmos, 8K Ultra HD, DTS:X Pro, and Powered by HEOS™

www.denon.com

 

[Golfx]

Ground Loops - Eliminating System Hum and Buzz

Got an annoying hum or buzz in your audio system? You likely have a ground loop. This article helps you diagnose the problem so it can be eliminated. Don't put up with hum. Read this article!

www.audioholics.com

4 Effective Ways to Eliminate Ground Loop Hums | SC&T

Ground loops can cause video/audio hums and interference. With this tutorial, you might not necessarily need a ground loop isolator to fix the irritating noise.

www.sct.com.tw

Try these suggestions

 

[jcmccorm]

I use a Yamaha AVR (A8A) and for the last 10 years or so have taken to building my own subs. You *can* buy a plate amp to put into these (there are lots to choose from) but most people in the DIY sub community just buy rack-mount class D amps top power the subwoofers.

So the signal chain is: Yamaha sub out -> amp -> subwoofer

A lot of people, (also including myself) add a miniDSP (or the like) in the signal path between the AVR and the AMP. The miniDSP has RCA inputs and outputs. The DSP is used to shape the subwoofer output and adjust delays when using multiple subwoofers that need to be aligned with each other to add constructively.

Yes, the amplifier does add some delay but the AVR's room correction will account for it. It's probably the same amount of delay that is present with a normal commercial sub that has a built-in plate amplifier.

Here's a couple of examples of amps. I've used the Behringers for many years and just switched to the CVR amps.

Here's one of the Behringers. They have models with less power output.
NX6000

Here's a CVR (cheaper of you buy direct from them)
CVR D-2004

Both of the above company's have the same model of amplifiers that have built-in DSP if you want it. There lots of company's that make these amps. Crown and Behringer amps are probably the most affordable.

I should add that almost all of these amps are stereo. Some let you bridge the two channels into one for double the power, making it a monoblock.

Ground loop hum is not an issue if you use balanced interconnects (XLR). I do not, I have unbalanced RCA interconnects but I've been really lucky and not had any hum issues. If I did have an issue, I'd use an isolated audio transformer like this one.
Jensen ISO MAX

I think it's cool that Focal is offering a passive sub. I wondered why I've never seen any. I know the idea seems odd because the residential AV industry is used to built-in amplifiers for the subs while the pro-audio folks always use rack-mount amps (like the ones I linked). I've gotten used to the external rack-mounted amps and wouldn't have it any other way. It's really not a big deal, just a different way to hook up your subs. Don't be intimidated by it and try that Focal if you're interested in it.

Here's a recent pic of my media room with 21" drivers up front (LaVoce SAN214.5). You wouldn't know that those are passive subs unless you took a peek at the back of them; only speaker wires hooked up to them.

 

[happy hopping]

1) sub-woofer w/ XLR, now you are talking and that's a great idea. I just check those top 2 models from Focal, their sub-woofer doesn't have XLR option. As to AVR, you are absolutely right, Denon A series high end XLR does have balanced out.

2) I am always in favor of European brand name speaker, so I just have to do some research and see what other EU brand that has sub-woofer w/ XLR.

as to the

Behringer NX6000​

even the Focal active sub-woofer is only 600W, why would we need a 6kW power amplifier?

 

[Ruediger]

Before I spend 17k on that passive focal, I'd get a pair of these for 10k.

Dalis only model with XLR. Fully produced in Denmark, I assume.

''

Experience epic subwoofer power and ultra-clean bass with the DALI SUB V-16 F – engineered for elite home cinemas and immersive audio precision.

dali-speakers.com

 

[jcmccorm]

1) sub-woofer w/ XLR, now you are talking and that's a great idea. I just check those top 2 models from Focal, their sub-woofer doesn't have XLR option. As to AVR, you are absolutely right, Denon A series high end XLR does have balanced out.

2) I am always in favor of European brand name speaker, so I just have to do some research and see what other EU brand that has sub-woofer w/ XLR.

as to the

Behringer NX6000​

even the Focal active sub-woofer is only 600W, why would we need a 6kW power amplifier?

A passive sub will just have speaker wire inputs. It *is* odd that these Focals need that "power supply". It seems to do some DSP work.

The XLR cable will go between the AVR and the amplifier (all these pro-audio amps have XLR connections for the inputs).

Yes, that Behringer NX6000 would be overkill. Behringer makes a 1000W version, NX1000.

I bet your sub is just fine. I'd address the issue with the sub you have.

You've got some good suggestions so far and some links to some good articles. Before going down the rabbit hole of fixing it, I'd try and verify that is is indeed a ground-loop issue. Have you tried just unplugging the subwoofer audio cable from the sub, at the input to the sub itself? Remove anything connected to the sub except for the power cable. With the input removed and the sub powered up, does the hum stop? If it stops, you have a ground-loop issue. If it doesn't, then something is wrong with your sub.

 

[john61ct]

Note that with such expensive gear, RCA vs XLR should not be much of a decision factor in selecting components.

Cleanly converting analog connections between the two is not too expensive. Aphex 124b does the job nicely, and without transformers.

If there needs to be detailed discussion on pro's and cons of how to accomplish this, I would welcome a new thread.

 

[jcmccorm]

Interesting. I assume that device yields a "true" balanced signal.

I just use rca-to-XLR cables from Monoprice. Inexpensive and they work. I am exposing myself to getting ground-loop hum in doing this since it isn't a real balanced signal but as I said, I lucked out and don't have any hum.

 

[john61ct]

Ground loops is just one issue, going long distances at line level and overcoming EMI/RF noise can be just as troublesome.

True Balanced (identical, symmetrical impedances) would require the transformer approach, which iirc colors the sound, and is over double the price

The Aphex 124b is an active two-way buffer, and its "servo-balancing" amplifier drives both the hot (Pin 2) and cold (Pin 3) lines, acting exactly like a True Balanced line in practice, giving you the same common-mode noise rejection and headroom.

No -6dB loss nor any chance of damage grounding either Pin 2 or Pin 3 to go into an unbalanced (single-ended) sink device.

 

[Ruediger]

5) did try to include the powered sub-woofer in the same circuitry as the AVR in my room, and also did try to have the AVR and the power sub-woofer in 2 separate circuitry (current setup). No difference, both setup yields the humming sound, this is why I lean on a passive sub-woofer in the future.

You have to check that the hum is not coming via the RCA cable. You could have the same issue with a passive sub and poweramp then. I don't think it's that, more likely something with the power. But before actually buying something expensive - check.

Maybe you already pulled the cable from the sub or used a different one to connect it to something else.

A possible reason for hum is also the RCA socket. Check that it's not loose. Try a different one.

 

[Redacted]

How many items in the complete audio chain are connected to mains power points?

 

[happy hopping]

A passive sub will just have speaker wire inputs. It *is* odd that these Focals need that "power supply". It seems to do some DSP work.

The XLR cable will go between the AVR and the amplifier (all these pro-audio amps have XLR connections for the inputs).

Yes, that Behringer NX6000 would be overkill. Behringer makes a 1000W version, NX1000.

I bet your sub is just fine. I'd address the issue with the sub you have.

You've got some good suggestions so far and some links to some good articles. Before going down the rabbit hole of fixing it, I'd try and verify that is is indeed a ground-loop issue. Have you tried just unplugging the subwoofer audio cable from the sub, at the input to the sub itself? Remove anything connected to the sub except for the power cable. With the input removed and the sub powered up, does the hum stop? If it stops, you have a ground-loop issue. If it doesn't, then something is wrong with your sub.

I re-think about what you talked about, it still won't work

The AVR is capped out at 140 W /chnl., most (if not all) of these power active sub-woofer is easily a few hundred W. So say the Focal gives you XLR, but that big box needs 500@ to 1K W of electricity as per the manual, how can a AVR w/ 140W/ chnl. works?