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post #121 of 146 Old 05-02-2012, 06:12 AM
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Originally Posted by Digital_Chris View Post

Ok, understood. Now, can anyone recommend new ways to tame this bass?

I was experimenting with Chris Whealy's spread sheet and came up with a design for an absorber that was appreciably effective at 50 Hz. 6" of 703 with a 6" air space between the 703 and the wall. Absorption @ 50 Hz is about 0.40 so it would have to be large - covering a significant part of wall(s).

I'm actually considering building one of these later on this year, as the back wall of a media booth that is currently experiencing a lot of bass build up in this range.

An alternative would be a resonant bass trap, for which a possibly useful design guide exists at
http://www.iperf.org/IPRF_ACUSES.pdf
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post #122 of 146 Old 05-02-2012, 06:14 AM
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Originally Posted by Digital_Chris View Post

One last question for now that seems to have many different outlooks on... Is EQ'ing not recommended for nulls? Some says that EQ'ing nulls is a big no no or even can't be done, others say it's ok if you have the headroom. What are your thoughts?

The problem with eqing nulls is that they can often absorb impractical amounts of power, and still not be effectively dealt with.

Generally, its a well-known no-no.
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post #123 of 146 Old 05-02-2012, 06:39 AM
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Quote:
Originally Posted by arnyk View Post

I was experimenting with Chris Whealy's spread sheet and came up with a design for an absorber that was appreciably effective at 50 Hz. 6" of 703 with a 6" air space between the 703 and the wall. Absorption @ 50 Hz is about 0.40 so it would have to be large - covering a significant part of wall(s).

if utilizing 6" absorber with 6" air-gap for LF absorption, light fibre is still the way to go. you're not gaining or losing much with such thin traps at 50hz, but the rest of the LF will see much better performance -

OC703:
(and performance is even worse if utilizing NASAs GFR values of ~28,000)





Pink Fluffy loosely filled insulation (uncompressed):




lower gas-flow-resistivity via sufficiently thick/large traps for LF absorption, as stated numerous times.

and even better as the porous trap gets thicker (spacing the insulation into areas of higher particle velocity for the lower/longer wavelengths):

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post #124 of 146 Old 05-02-2012, 07:17 AM
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Quote:


Thanks a lot for the reply

I do plan on trying out the BFD in a the next couple of days, I just learned how to calculate corrections in REW and apply them to the BFD

I have thought of running subs in the back, briefly I might add, but for a couple reasons I don't want to... One reason being that it's not recommended to run box subs with IB subs, forgot the reason but it's been talked about. Two, If I did that, I would have to run another amp for the extra subs and running wiring won't be an easy task... Also, giving up even more floor space is not on the top of my list. So, idk :/

Did your 4" panels make a big noticeable difference on the back wall? I'm willing to line my back wall with FG if a sound ifference is a given.

Did you have any serious nulls in your room that you were able to treat with absorption or EQ?

Running sub boxes with IB is not a problem with the proper orientation. Often folks will say you cant mix different types of sub types (delay and mixing issues), but with the plan of attack I was suggesting, this is most certainly OK. The Geddes approach only suggests using your main and most powerful subs up front, with "filler" subs at the halfway points of each side wall and one in the rear, optimally mounted near the ceiling (pipe dream for most). all of these said "filler" subs dont need to match the performance of your main sub rig, and actually only need to play around 10db below ref, so a small capable sub is plenty. These filler subs are simply there to help tame your main modes. I will stop there but just thought it might bear a little explaining.

My 4" panels definitely took some of the ringing out of the rear of the room. The performance benefits was well worth the installation of them. If I had a graph I would post it, but I dont, sorry!!



Quote:
Originally Posted by Digital_Chris View Post

One last question for now that seems to have many different outlooks on... Is EQ'ing not recommended for nulls? Some says that EQ'ing nulls is a big no no or even can't be done, others say it's ok if you have the headroom. What are your thoughts?


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Originally Posted by hjones View Post

You won't accomplish much trying to EQ room mode nulls. You will "run out of speaker" before you accomplish much. 3-4 db, yes. But one of these 20-30db suck outs - no way.

agreed 100%, but in your graph I see absolutely no nulls in your sub response at the mlp, only two peaks that could easily be pulled down a shade and bring you right in line with your 100hz and up readings. Boosting anywhere more than 3-4 db's is a no-no and more than likely you wont run out of speaker, you'll run out of amp to do it. just think a 6db boost is QUADRUPLE the power needed to get you there over the rest of the Freq response. I learned this the hard way. I eq with cuts ONLY, if at all possible.

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Originally Posted by HopefulFred View Post

Something else that occurred to me: is it possible to adjust the phase of the signals to some of the IB drivers? This may be a total non-starter of an idea for any number of practical or scientific reasons (like it wouldn't be effective even if you could do it), but what do I know?

Phase of the entire sub system, definitely!! The individual drivers, since they are for the most part co-located wouldnt have much of an effect, and in almost all cases would be detrimental to the sound. Even if OP had the capability to adjust each sub's individual phase, they are of one system essentially and need to be treated as such. Now an additional sub in the room? This would be QUITE important to address.

I like this thread has gotten back on track, there are some excellent points being made here.

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post #125 of 146 Old 05-02-2012, 11:59 AM
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Unfortunately the OP has taken away two very useful tools. Multiple subs - and varying sub and listener positions. He also does not want anything complicated (i.e. tuned absorbers, which may not be appropriate in a small room anyway - there are just so many modes). So what we have left is thick broadband porous absorbers - but apparently no space for them.

You have "super traps" in two wall-wall corners (I'd increase the flow resistance of them, but I'll leave it up to others to determine what the optimum is). Have you considered other "corner" locations? i.e. wall-ceiling and wall-floor.
Do you need the headroom above the rear seats? If not, I'd put panels above the rear seats. Ideally 12" thick, the width of the room, and 4 feet wide into the room. Make sure you leave the face toward the screen open - you are trying mostly to absorb front to back resonances - and perhaps some top to bottom - with four subs up front side to side should not be too much of a problem.
The 4' depth front to back will really help with the primary room mode, and the large volume will help with almost all modes.

Can you put in a few porous benches? If you could find a place to put 16"x24"x4' benches along the wall/floor corner you might get some real benefit. Or even 16"x24x24" this would help - again align the long dimension front to back if possible.
Cover these big traps with a thin plastic membrane if required to reduce excessive high frequency absorption.

Are your rear seats elevated? If so, open up the front of that cavity and stuff it.
Your subs are IB - what else is up there? Can you perhaps divide the front wall space - devote some to making bass, and some to absorbing excess? What about behind your rear wall?

Are your side wall panels framed in on the sides? If so, redo them. Open the sides up so they can absorb bass.

I've never understood the appeal of air spaces - better IMO to fill all available space with absorber. The cost is not much higher, and construction is easier. And if you leave the sides open you have more surface area (and a deeper absorber) to do the job.

Basically you are going to have to be creative. And consider this a learning experience.

When you have treated the room as well as you can. Use room correction eq to optimize your favorite seats. When guests come - give them the best seats.
Anyway that is my $.02

Edit: as others have said - don't bother trying to eq a null
Edit 2: go ahead and try if you like - you might have the umph - and it might be a good learning experience

Everything I say here is my opinion. It is not my employers opinion, it is not my wife's opinion, it is not my neighbors opinion, it is My Opinion.
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post #126 of 146 Old 05-02-2012, 12:22 PM
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A couple points re: boosting nulls:

Whether its worth trying depends on your headroom and SPL output goals - if your output goals leave you with headroom to spare, you can put some of it to use (modest) to boost nulls. In my case, I listen at -10, I don't need reference - and I have dual THTs, so I was able to do some boosting without too much risk of blowing stuff up.

If peaks and dips are very narrow, they might not be worth touching, since program material may not expose them to any significant extent.
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post #127 of 146 Old 05-02-2012, 02:06 PM
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My experience has been peaks are easier to hear than nulls, and easier to correct. But my experience is limited. YMMV - only one way to find out - try it.

Everything I say here is my opinion. It is not my employers opinion, it is not my wife's opinion, it is not my neighbors opinion, it is My Opinion.
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post #128 of 146 Old 05-03-2012, 05:09 AM
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Quote:
Originally Posted by dknightd View Post

My experience has been peaks are easier to hear than nulls, and easier to correct. But my experience is limited. YMMV - only one way to find out - try it.

I believe that for equal sized and shaped peaks and dips, particularly those that are relatively narrow and have substantial amplitude, your statement agrees with generally accepted experience and wisdom.

Hearing a relatively narrow dip falls prey to what we know about proving a negative hypothesis. This is particularly true if we have no close correct or significantly different alternative to compare to.

How do you know that are not hearing something if you have no way to know that it exists? Answering this this question leads to a more reliable means for discerning peaks and dips, which is to compare two different things as closely as possible.

Of course, making close comparisons of speakers and particularly room treatments is very difficult. Speaker comparisons can be facilitated with quick-acting positioning devices, but room treatments tend to be quite a bit larger.
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post #129 of 146 Old 05-14-2012, 12:19 AM - Thread Starter
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Thanks for the replies guys. As of right now, my main issue is the HUGE peak followed by a HUGE dip at my rear seats. If I can tame the peak at least (not sure how I'm going to do that yet), I think I'll be ok with the dip because like you said, it's easier to live with something that I can't hear vs something that I can.

If you guys have any ideas on how to tame that peak/null combo without moving subs or seats, I'm all ears.
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post #130 of 146 Old 05-14-2012, 03:59 AM
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Quote:
Originally Posted by Digital_Chris View Post

Thanks for the replies guys. As of right now, my main issue is the HUGE peak followed by a HUGE dip at my rear seats. If I can tame the peak at least (not sure how I'm going to do that yet), I think I'll be ok with the dip because like you said, it's easier to live with something that I can't hear vs something that I can.

If you guys have any ideas on how to tame that peak/null combo without moving subs or seats, I'm all ears.

You seem to be oblivious to every post on this thread. :-(

The short answer is that you can probably address your situation with a combination of:

(1) Equalization of peaks. An approach was recommended.

(2) Sound absorbers that are actually large enough to actually be effective at these low frequencies. A detailed design was proposed.

(3) Multiple subwoofers. Their usage was proposed.

It's all about space, money and WAF. Only you really know about those.
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post #131 of 146 Old 05-22-2012, 12:44 AM - Thread Starter
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Originally Posted by arnyk View Post

You seem to be oblivious to every post on this thread. :-(

The short answer is that you can probably address your situation with a combination of:

(1) Equalization of peaks. An approach was recommended.

(2) Sound absorbers that are actually large enough to actually be effective at these low frequencies. A detailed design was proposed.

(3) Multiple subwoofers. Their usage was proposed.

It's all about space, money and WAF. Only you really know about those.

Sorry, I'm not trying act oblivious, there's just so much going on in every thread I post that I lose track of what suggestions are not repeats and ones that can't apply. I understand about EQ, I can tame peaks at one position but they will affect the other in a negative way so I'm looking for ways to fix the problems as much as I can before EQ. Like you said, it's just part of the equation but I figure that was the "easiest" of the options so I figured I'd leave that for last.

Multiple subs was out of the question for the most part, I just didn't want to add more to the back of the room because wiring for it/them would be a PITA, but I'm going to try that next, I'll temporarily add a 2nd sub to see what that does... I'm just not sure how to set the gain or xo freq on the 2nd sub, any suggestions for that?

And for sound absorbers, the only detailed approach that was suggested was making a few bench style absorbers... I'm not going to lie, I did miss that post. See, I lost track

So, bottom line is, space is an issue with the room being so small at 18 x 10.5, money can be an issue but if I pace myself for the right corrections, it's not a problem, and WAF is NA, just me and my craziness to deal with
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post #132 of 146 Old 05-22-2012, 04:23 AM
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Originally Posted by Digital_Chris View Post

...there's just so much going on in every thread I post that I lose track of what suggestions are not repeats and ones that can't apply.

I feel your pain. There was a silly war in this thread started by people who were overplaying the superior knowledge card for their fun at everybody else's expense.

Quote:


I understand about EQ, I can tame peaks at one position but they will affect the other in a negative way so I'm looking for ways to fix the problems as much as I can before EQ. Like you said, it's just part of the equation but I figure that was the "easiest" of the options so I figured I'd leave that for last.

Speaking as a person who has been solving tough technical problems professionally for over 40 years, one important rule of thumb is that you almost *always* implement the easiest solutions *first*.

For one thing, cleaning up the obvious easy problems clarifies your view of what is left over. For another thing, you get quick gratification and confidence building.

That means EQ! ;-)
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post #133 of 146 Old 05-22-2012, 11:20 PM - Thread Starter
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Thanks Arny, now for a little good news...

Well, as many of you could have predicted, it worked!!!

I decided to throw a 2nd sub into the mix and well, what do you know? It helped

I disconnected two of my 18's, wired the outer two to one channel on my amp and hooked up my table tuba from upstairs to the other channel on the amp, set my gains so that both "subs" separately put out the same spl and voila! Out came more even response across both rows!!

Again, most of you are like, yeah, uhh, Duhh!

But, I had to see for myself and see what it could actually do. So, what does this mean? It means that I'm wiring in one or two subs in the back of the room!!! Haha, some light finally peeped it's way through the crack

Here are few graphs to show what happened...

Front Center no TT...



Front Center w/TT...



Overlayed...



Rear Center no TT...



Rear Center w/TT...



Overlayed...



WOOHOO!!

Now, I still have some funkiness going on above 80hz, any ideas?

I did try a few different crossovers, 60hz/80hz, 80hz80hz, 100hz/100hz, 120hz/120hz. Out of all the above, 120hz/120hz worked best, is this odd?
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post #134 of 146 Old 05-23-2012, 06:37 AM
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Looking great! Odds are your >80hz situation is still integration issues with your mains. have you messed with the phase of your subs?

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post #135 of 146 Old 05-23-2012, 08:17 AM
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Also, give this quick article a read, Im discussing this a bit in another thread, but it is good to know what SBIR is, and if it is affecting you in regards to your speaker placement...

http://gikacoustics.com/education_sbir.html

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post #136 of 146 Old 05-24-2012, 03:23 AM - Thread Starter
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I actually messed with the phase last night. Fist I swapped + - on the second sub I added and it was almost like the sub disappeared, response graph was similar to when there was no second sub. Switched that back and swapped + - for the IB's and same result, large peak then dip. So, then swapped both + - and even worse result, lol. Looks like normal polarity is the way to go for this setup

Also, I just read about SBIR. With my speakers flush mounted, about 1" off the wall anyway, maybe I'm getting some interference. I have the 3" fiberglass panels that I can put on the wall but I'm not sure if it's ok for the fiberglass to stick past the LCR's, will that hurt the speakers' response?
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post #137 of 146 Old 05-24-2012, 01:44 PM
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Quote:
Originally Posted by Digital_Chris View Post

I actually messed with the phase last night.


You could also experiment with the sub distance setting on your AVR and watch what happens with the frequency response. Also, if your subs have more than two ports each - you could try plugging one port on each sub and see what that does to the frequency response as well.

I use 3 subs in my room. Placed around my room that still all puts them at the same physical distance from my main LP. I can then adjust sub distance on the AVR to fine tune phase with the speakers.

Apart from a 90hz null, I have managed to get things reasonably flat from 25hz...

Attachment 247543
LL
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post #138 of 146 Old 05-25-2012, 12:57 AM - Thread Starter
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I don't have any ports in my subs, the front subs are IB while rear is a horn loaded sub that I borrowed from upstairs. I will play with the distance settings and see what that yeilds
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post #139 of 146 Old 05-25-2012, 08:13 AM
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yea, switching the polarity and the phase of the subs with the rest of the system are two different things as well. To adjust the polarity like you did is always going to cause one sub to cancel with the other. Adjusting the polarity of the entire sub system is what you need to look for in an eq, but delay is also a key point.

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post #140 of 146 Old 05-30-2012, 10:58 PM - Thread Starter
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Ok, here's where I get frustrated and deterred...

Regarding filler subs, some people mention that small filler sub(s) don't need to be nearly as powerful as my main subs, but others say that my rear subs need to be able to output same amount of power as my main subs... why the two different opinions? Are they two different approaches for two different problems and some people don't realize that?
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post #141 of 146 Old 05-30-2012, 11:27 PM
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Yep there are certainly two different approaches. Geddes' approach basically states to put your big firepower up front and each "filler" sub should be operating purely to help cancel nulls in your response. This is assuming you get enough bass from your "main" subs up front.

The other approach is to just have separately located subs of all the same performance around the room with perhaps less firepower from your "main" sub. In this case all subs would be identical just not mutually located. If you are happy with the output of your main sub, sans fr issues elsewhere in the room, geddes approach will suffice. If not, start building identical doubles of your main sub and locate them where they help with the room modes the most (or where is conventient, or a combo of the two).

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post #142 of 146 Old 06-01-2012, 12:09 PM - Thread Starter
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I know the main subwoofers are definitely capable of producing plenty of SPL in my little room.

One problem that I just realized last night, is that no matter what the second sub is that I add to the mix, I will never be it able to adjust the distance setting in the receiver separate from the main subs. I only have one subwoofer output, so that part of the tuning will be out of the question. So, all I'm really going to be able to adjust is level and possibly phase depending on the amp I get.

I'm not sure if you posted in my other dedicated thread about my filler sub issue, but some people are still recommending that I put a high output subwoofer in the back that's capable of reproducing what my mains produce, but don't understand that I have plenty of power up front and I just need a filler sub in the back to, like you said, cancel out nulls and peaks. Is that really all the filler sub does? And isn't there to actually add, let's say, 15 dB to a 50 Hz dip?
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post #143 of 146 Old 06-01-2012, 12:13 PM - Thread Starter
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Sorry beast, I just skimmed through the other thread and noticed you DID post in there, I forgot, my bad :P
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post #144 of 146 Old 06-06-2012, 07:21 AM
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Do you have the ability to get the filler sub to AROUND the same distance as you are from your main sub? Just try that or try reverse polarity in other positions not equidistant to see if that helps instead.

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post #145 of 146 Old 06-06-2012, 10:58 AM
 
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Quote:
Originally Posted by beastaudio View Post

Do you have the ability to get the filler sub to AROUND the same distance as you are from your main sub? Just try that and reverse polarity to see if that helps too smile.gif


Stop and think about what has been proposed for a moment....

If the distance between acoustical origins and the listening position are indeed identical, and if the originating signal polarity is indeed reversed (effectively 180 degrees out of phase), how will this ONLY "correct nulls"?

It will effectively restore all of the arriving energy to the ambient state, thus effectively canceling all of the energy, as all of the energy from the two sources will effectively be 180 degrees out of phase. It result will be nothing but a "null" with reference to the energy sourced by the two subs. This process is commonly referred to as 'active noise cancellation'.

A simpler 'solution', if this is imagined to be a solution: Get rid of the subs and do not stimulate the frequencies in question at all.


It is critical that folks establish a very clear grasp of the fundamental concept and behavior of superposition.
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post #146 of 146 Old 06-06-2012, 11:47 AM
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Originally Posted by dragonfyr View Post

Stop and think about what has been proposed for a moment....
If the distance between acoustical origins and the listening position are indeed identical, and if the originating signal polarity is indeed reversed (effectively 180 degrees out of phase), how will this ONLY "correct nulls"?
It will effectively restore all of the arriving energy to the ambient state, thus effectively canceling all of the energy, as all of the energy from the two sources will effectively be 180 degrees out of phase. It result will be nothing but a "null" with reference to the energy sourced by the two subs. This process is commonly referred to as 'active noise cancellation'.
A simpler 'solution', if this is imagined to be a solution: Get rid of the subs and do not stimulate the frequencies in question at all.
It is critical that folks establish a very clear grasp of the fundamental concept and behavior of superposition.

Edited for clarity, I meant try having it at the same distance from LP OR try reversing polarity in other positions, my bust, and thanks, I have a low turbidity grasp on "superposition" not exactly clear.

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