Tube Radio
Super Member
If an amplifier introduces noise into a powered sub through the plate amp's speaker level inputs, there's something wrong with the main amp.
The truth about subwoofers
- Thread starter JoeESP9
- Start date
This thinking is why I'm done with this, have fun.
Tube Radio
Super Member
That thinking is true though.
However if connecting it that way somehow produces a ground loop yes there will be hum.
So what kind of noise will the amp introduce into the subwoofer amp?
Oh I run a setup like that and I hear NO noise whatsoever in the sub.
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kevintomb
Well-Known Member
This has to be a first.
Trying to justify something worse (High level inputs on a sub) to claim they make it sound better......
High level inputs were only made to cater to those amps that lack a proper low level crossover, to boost sales of subs to those potential users.
Trying to justify something worse (High level inputs on a sub) to claim they make it sound better......
High level inputs were only made to cater to those amps that lack a proper low level crossover, to boost sales of subs to those potential users.
Tube Radio
Super Member
So exactly how are high level inputs on a sub worse?
I'm not going to get into a back and forth discussion with you because I know how that turns out.
What you state above has no relevance because the internal sub amplifier is a given -- there is no way to eliminate it. The sub amps are designed to be as neutral as possible so they will blend with whatever mains you happen to use it with. How perfect that internal sub amp is is also irrelevant -- the only thing you have under control is how to feed you feed it . You want to feed it with the best signal possible for a given set of circumstances. For a 2-channel system, from the perspective of wanting the sub to act like an extension of the mains, feeding it with the exact same signals that the mains see is unquestionably going to be more uniform than feeding it with a preamp that is decoupled from what the mains see. From a "minimizing noise/distortion" perspective, feeding it with the preamp is unquestionably slightly lower noise due to bypassing the 2-channel amp in the signal chain, though none of that noise or distortion will be audible at all in any decent system, and that signal is decoupled from what the mains are using to produce almost all of the audible sound (except for the tiny portion the sub fills in at the lowest frequencies).
The fact that the sub has its own amp is irrelevant because it can't be removed from the equation, but you still have the obligation of feeding the best signal possible. Again, I will not at all suggest my preference for speaker-level is the answer for all 2-channel systems (that has been in my personal experience though), it's just important to state the plusses and minuses of both approaches instead of talking about one and ignoring (and/or denying) the other.
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Tube Radio
Super Member
Most regular subwoofer plate amps have phase shift closer to 20Hz due to a high pass filter and may have phase shift due to an LFE low pass filter.
However higher end subs may not have that phase shift. I don't know as I've never really owned a real high end sub.
The best way to see what if any phase shift a subwoofer plate amp has is with a dual channel oscilloscope and audio frequency generator.
The audio generator goes to the subwoofer input and scope channel 1.
The speaker output (if one side of the speaker wiring is grounded) goes to the second scope channel.
Both are adjusted so the traces are on top of each other. Set the plate amp to a decent output and adjust the V/div on the second channel to where the waveform at 50Hz very nearly fills the screen. Then adjust the input V/div and variable control until the input signal waveform is the exact same amplitude as the output.
Set the crossover to its highest frequency then vary the input frequency from 20Hz until your normal crossover frequency setting.
If one waveform leads or lags the other closer to 20Hz then you have phase shift and must eliminate it.
If you can bypass the crossover or the plate amp has a separate LFE input use that instead.
If the waveform leads or lags the other at your desired crossover frequency, the LFE filter will need to be removed.
The high pass filter is usually a couple caps in an OP-AMP stage that need to be much larger in value. The LFE filter is usually a couple caps in an OP-AMP stage that need to be removed completely.
Do that and the sub will integrate much better.
Stating preference is useful but arguing preference is fruitless.
Arguing preferences is definitely useless. Arguing the plus and minus tradeoffs of each approach is not fruitless (though it definitely should be a simple discussion and not an argument). Just about every "option" in audio has concrete plusses and minuses. It's important to understand them. Those concrete plusses and minuses don't dictate which will work better in a given real-world situation -- that will almost always be situational based upon equipment and preferences, but it is always beneficial to know the benefits and detriments of every approach.
never heard of a passive sub?
And you're right, the plate amps in $100 subs are so awesomely neutral. And speaking of neutral, isn't that the goal of all amplifiers, to add nothing to the signal, but sadly nothing is perfect.
It's useless, again, done here.
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With a passive sub- either you're going to be running it from the main amp (in which case, it will inherently get the same signal as the main speakers), or with a separate amp (in this case, you have the potential of using the same type amp as the mains- which would definitely be superior, in terms of matching transfer function). It's still got to have power from somewhere... and unless you're going to do one of the two options above, then you're back to the same situation as you would be with a built-in plate amp in an active sub.
Regards,
Gordon.
That's the nice thing about the amp in the Von Schweikert sub shown above- there IS no LFE filter. It's designed to be a 2-channel-system sub.
And, with the continuously adjustable phase control- matching phase with the mains at the crossover point, is a cinch.
I don't think many people realize, how downright useful a continuously adjustable phase control is, in a situation like this. If you really want a good blend, it's probably the most elegant way of doing it...
Regards,
Gordon.
Tube Radio
Super Member
Agreed GordonW.
Usually the phase shift in a plate amp is minimal provided there is no LFE filter and no high pass at 20Hz or lower.
At what frequency does the variable phase control work or is it at the crossover frequency or the whole frequency range of the amp?
What kind of noise?
Usually the phase shift in a plate amp is minimal provided there is no LFE filter and no high pass at 20Hz or lower.
At what frequency does the variable phase control work or is it at the crossover frequency or the whole frequency range of the amp?
What kind of noise?
And my high end sub without high level inputs has not only variable phase, but also variable high pass, you get what you pay for.
One more time, manufacturers of high end subs eschewed high level inputs for a reason, they're inferior. In recent yrs some have been adding them to reach a wider market for more sales, period.
Rel started this mess to set themselves apart by eschewing line level inputs and starting the rumor it was somehow superior, some drank the coolaid, others didn't.
For those interested, start reading this thread from the beginning, you'll see this was already hashed out here at least once before, it's a waste of time going around in this circle again.
Tube Radio
Super Member
And that high pass filter will introduce an undesirable phase shift.
I have a plate amp that had a 20Hz high pass filter and the phase shift from that filter started at about 40Hz.
Then again who needs a high pass filter on a sub unless it is to protect the sub from frequencies that would damage it if it is a design where the driver can unload from the cabinet below a certain frequency and destruct itself due to over excursion.
Isn't the idea for a sub to reproduce frequencies the mains cannot reproduce?
I have a plate amp that had a 20Hz high pass filter and the phase shift from that filter started at about 40Hz.
Then again who needs a high pass filter on a sub unless it is to protect the sub from frequencies that would damage it if it is a design where the driver can unload from the cabinet below a certain frequency and destruct itself due to over excursion.
Isn't the idea for a sub to reproduce frequencies the mains cannot reproduce?
Tube Radio
Super Member
And your sub is crossed over where the mains start to roll off, right?
Does your amp for the mains have any phase shift at all?
Does your amp for the mains have any phase shift at all?
kevintomb
Well-Known Member
Think about it some. List off in order all the chain of stuff it has to go through, and the inherent shortcomings of each chain.
You are taking a high level amplified signal that has been through several stages, then trying to drop that signal down to line level again, then amplifying that signal yet again.
Stuff we used to do with 70s/80s car audio. There is always a loss, a gain in noise, and added complexity.
I thought this was an obvious no brainer. Maybe not.
I would only use it as a last resort if I had no preamp level line out.
I guess maybe the simplest explanation, is to question, would you do this 10 times in a row? Daisy chain 10 power amps together this way.? The answer is Hell no. For the same reason it is worse to do it just one time.
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This has been my experience also.
Many of my friends and I had been using speaker level inputs long before we ever heard of REL and before the internet became a thing.
REL started using and promoting speaker level in 1990 (not sure when they started being sold in the US), but I never heard of them until several years later.
