markus76 said:
Worst case its a hypothetical problem with no data to support your claim and best case it isn't a problem at all. So what if there is bass on only one of the channels, I don't see how that affects anything at all. Two of the three front channels don't have bass, but there wasn't any in the mix on those channels anyways - what's the problem? I don't get it.
gedlee said:
There's also no data to support the best case, right? And as long as there's no such data there'll always be a potential flaw in your solution.
gedlee said:
The use of multiple subs makes only sense if ALL low frequency sources emit the SAME signal at ALL times. I really don't understand why you would want to challenge that.
Best, Markus
markus76 said:
Markus,
I am using a computer as a source, with a sound card that has balanced outputs. It's an Echo Audio MIA, which is considered a "pro" sound card.
Do you think it would be a good match for the Behringer gear?
Here's the problem that I am experiencing with my current set up:
I am using a Y-Cable to split the signal, and one side is going to a sub amp, the other is going to a second amp for the Summas.
When I run the Summas alone, it's as clear as a bell.
When I run both the subs and the Summas, the subs have a hum at about 60hz.
My guess is that a ground loop is being introduced, and it's introducing the hum into the subs?
Also, do you use amplifiers with balanced inputs?
markus76 said:
Correct, there is no data either way, so the best we have is logic and analysis and neither favors you claims.
Your last sentence is not one that I agree with, which is perhaps, the issue. I see no reason to assume that the signals need to be identical. In fact, I have said many times that, in theory, the signals to each sub should be decorrelated, meaning NOT identical.
You seem to be digging in your heals and grabbing at straws just to "be right".
This isn't always possible and not always effective. Cutting the ground lug is not such a big deal, because the equipment is still grounded, just not through that lug. Its grounded through the signal wire shield. If a short to ground occurs it will conduct the current through the signal wires and then to ground, but this should still blow the fuse before any damage is done.
gedlee said:
"You seem to be digging in your heals and grabbing at straws just to "be right". "
gedlee said:
No signal, no modal problems—I can understand that
In order to decorrelate a signal there needs to be a signal in the first place. For example, if there's a low frequency event in the left channel only, then your setup won't have that signal in the center channel and the right channel. But your optimization is based on the assumption that there IS that signal in the center and right channel.
Now I don't only sound like a broken record, I feel like one. Next time I'll just link one of my last posts randomly.
Best, Markus
markus76 said:
No signal, no modal problems—I can understand that
In order to decorrelate a signal there needs to be a signal in the first place.
No need to be sarcastic.
markus76 said:
As it should be.
markus76 said:
No system could do what you are expecting, not the JBL, not anything. I make the assumption that the LFs are mono or nearly mono, which, as I said, everyone assumes since it's correct virtually all of the time. You CAN assume anything that you like about the signal (left only, right only, etc.), but you have to assume something, and no matter what you assume it is always possible that the assumption will be wrong. Assuming what I do is not an error, to assume anything else would be.
Marcusmarkus76 said:
Grounding for safety in audio equipment is not necessary and its often not even done. My AVR is not grounded, perfectly legal and reasonable. Grounds are mostly for power equipment (drills, table saws, etc. that take lots of current and have a tendancy to short to the case which is often metal. Audio equipment is very low amperage and the internal circuits are always issolated from the mains by a transformer. The only failure in equipment like this that could be a danger is a short to the case BEFORE the transformer, but this is VERY unlikely. As such its really overkill to use a power line ground. Albeit the equipment should be grounded somewhere just for noise and hum rejection, but this need be and only should be done at one place.
gedlee said:
I've had the same issue with the DEQX. I'm using RCA connections. There's nothing wrong with the unit, but I had to work out a "star" grounding routing, as ground loops are easy to create with multiple pieces of gear. The more you have, the more likely it will be an issue. Sometimes connecting all pieces to the same earth circuit, or even the same power strip, does not eliminate all the loops. As someone mentioned, this is less of an issue with pro gear (balanced connections), but that's not usually what we are dealing with.
Earls method of using a single earthing point will work to sort out the hum, but might increase risk, primarily because not all users are knowledgeable enough to understand if there will be a safety issue for that particular set up.
One way around the safety issue is to securely wire all the chassis together with 14 gauge wire and lift all ground lugs with an adaptor, except for the main receiver.
Another way, if you have the knowhow (this is a DIY forum, after all), is to lift the internal chassis/circuit connections with about a 10 Ohm resistor. In parallel with the resistor, add a pair of antiparallel 25A diodes (a 25A bridge will work fine too - tie +/- together, and run the resistor across the AC connections). You might want to add 3nf or so, also in parallel, for RF ground. If your RCA connectors are directly connected to the chassis you will have to lift between the chassis and earth connection. If that helps, but not completely, you can try omitting the resistor and just use the diodes and cap.
Sheldon
randybes said:
Hum is a huge issue in the car stereo world. I've used a cheap $10 isolation transformer from Radio Shack and it seems to work well.
At first I didn't like the idea, since a cheap transformer will be bandwidth limited. But if it's only used on the sub channels, it seems acceptable.
The use of a transformer on the RCA inputs to the sub would eliminate the hum, wouldn't it?
(just thinking out loud - I'm working right now and can't test it one way or the other.)
Sheldon said:
This would be my recommendation as well. I'm in the process of doing my final testing and tweaking of an amplifier I built with a switchmode power supply, and careful grounding is proving to be very crucial. I'm forced to lift the ground on these using just this method, and finding that the RF cap is really a good idea. I think RCA connections should not be star grounded though, I do not find this to reduce hum. Grounding signal leads (both in and out) in a star configuration is good, but it's been my experience that star grounding everything made things worse.
With it being only on the subs, probably hiss will be a non-issue, and really only the hum would be the problem. This is why I was promoting active conversion from balanced to unbalanced. I would suggest doing this all the way to the subs including changing the input to a balanced input and mounting the circuit on the plate amp, so grounds can be properly isolated.
gedlee said:
I have a small amount of hum in my subwoofers, which have no earth grounds on them. I've been able to reduce the hum in my system overall by lifting the ground via the diode/resistor/cap method, but had to do so at various places. I also had to make sure the RCA inputs on the plate amps werent directly tied to the chassis ground I was lifting.