[bytheway]

Well, I have two 2x5 and two 2x3 pieces of gatorfoam now.  The daytons are in the mail and I just did the hardest part of this whole thing: ordered the tape.

Man that stuff is expensive.

Seriously, I'll need like a foot of this stuff, not 60 yards.  Too bad its too hard to cut pieces off the roll and sell them, or I'd be happy to pass along little strips for cost so others could build their NXTs without giving up that nice chunk of change.

[zobsky]

Well, you could sell the  left over tape roll when done. I'll buy it next month if the exciters are still on sale at that time. Let me know by PM if that's fine with you.

Thanks

[bytheway]

Perhaps I'll do that.  Of course, if my first 2 panels are good enough, I'll be building more for a surround system 

Its too bad it isn't easy to sell foot-long strips of tape, start a tape co-op or something.

[bobloblob]

Does this mean that maybe a suspended panel, and the exciters mounted on a spline/brace, will be the way to go?  A shame if it is, since part of the beauty of your speaker is the simplicity.  The suspension and spline wouldn't be really complex, but still more work and aligning than what you have begun with.  Dang it.

[Copperhead]

Unfortunately, this was always going to be a problem. Thinking you could just hang the exciters off the panel was asking for trouble.
A spine, or spine and frame was mandatory to properly finishing the speakers. I for one, was never going to be allowed to lean two
huge sheets of gatorfoam in the corners of the room anyway. So, this isn't any sort of a setback to my way of thinking.

[bytheway]

I've been pouring over this thread the past week or so making sure I was absorbing as much as I could before proceeding. Can I just summarize my understanding of the mounting/framing issue?

To avoid voice coil creep, the backs of the drivers must be supported, and can't just hang off the back of panel. At the same time the drivers, when supported shouldn't bear the weight of the panel alone, which also must have supports of its own.

Currently, podium supports the panel by using some sort of special marshmellowey material at four points of the panel, but what that substance is we don't know.

Double-sided foam doesn't work because of the poor shear strength.

One thing I think has been mentioned is using some sort of fishing line to suspend the panel from a frame or other support. I don't remember I've seen any thoughts on how to attach the line to the panel on the least intrisive way. This approach appeals to me because or seems to keep the panel as free as possible while still giving the needed support. Obviously as was mentioned above, this extra step requires some careful aligment, though fishing line is much easier to adjust than wood, foam, etc. 

[bobloblob]

You will need to be careful with the term "fishing line".  That covers a lot of territory.  Most monofilaments that I know of have some stretch to them, so they will eventually put more weight on the exciters, and they can degenerate with age.  Some lines, like braided dacron or kevlar, stretch much less and may age more gracefully.  There is also steel, like piano wire, and plastic-coated steel.  The ones that don't stretch will probably support a panel better over time.  The down-side is that they - the non-stretchy ones - will transmit  vibrations to whatever they are attached to more easily.

If you are looking for a somewhat soft substance to mount the exciters to the spline with, poster-tac may work.  It holds well, stretches and returns to shape somewhat, and damps well also.  Plastic clay that someone mentioned earlier is not elastic in that sense.  I've used plastic clay for years to damp speaker baskets, and quite often it falls off after a couple of years.  Also, since sheer strength is not so much a factor in holding the exciters to the spline, double-sided foam tape may work here - it the panel is suspended so that the exciter and the foam are supporting no weight.  Don't know whether the foam would absorb too much of the sound though.  Maybe a solid mount would be better?

Just some thoughts I thought I should toss into the mix.  I'm anxious to see what Ziggy comes up with here.  Maybe there will be a simple way through this.

[bobloblob]

For what it's worth, there may be a catalyst-activated silicone sealant.  I know there are catalyst-activated silicones for making molds - which also may work.  These may be good for those short on patience, like me.  From what I remember, the cure time is an hour or so.  They cost a bit, though, in the quantity I bought.  Maybe they are also sold in smaller quantities which would be more affordable.  Some of the new flexible hot-melt glues may be an even better alternative.

[jeffac]

Exactly when my OEM exciters arrive after their long trip from the US, the waters muddy and what looked straight forward has, as I should have expected, become a little more complicated.

OK, tentative thoughts on panel to frame mounting and exciter support.

I was planning large Gatorfoam (GF) panels 200 x 176 cm with 8 exciters per panel 200 mm apart. For support to a frame, I was thinking poster mounting 'Velcro' dots stuck to the 4 panel corners front and back to allow attachment to ~1" Velcro strips fixed to whatever frame I can hash-up. Easy, low resonance, non-damaging to the panel, hopefully 2 spots per corner will be strong enough, and all will be reversible if they don't work as planned.

Beyond the worry of exciter coil former/suspension deformation due the unsupported magnet weight, use of a spine to attach the magnets should afford sonic benefits similar to those reported from magnet mounting of conventional drivers. So my thoughts on something easy, functional and reversible. As I'll have GF off cuts to spare, I was thinking of a thin GF strip maybe 40 mm wide and the length of the panel, or slightly longer, depending on 'the frame' to which it could be attached. As vertical support is what's needed, this might work OK and as being of the same stuff as the panel, hopefully it won't adversely affect its resonance characteristics. Magnet fixing to the GF strip would use the same 3M tape endorsed for exciter to panel fixing. Small holes would be drilled through the GF strip aligned with the vent of each magnet. If not fixed to a frame, the GF strip might be fixable to the GF panel top and bottom 'somehow' without grossly affecting panel sonics.

As I have a couple of T-amps with ~20 K ohm input impedance that I'll test for driving the panels, a low value cap of 0.033 uf could used as a PLLXO to gradually drop off amplifier LF output below ~240 Hz, thus helping amp efficiency, protecting against exciter over excursion and avoiding any need for a cap at the exciter.  At this low values, cheap Russian teflon or PIO caps should work well. Bass ?..we'll have to see what augmentation is needed.

This is going to be a fun project aa and comments welcomed before I get to panel building as these ideas might be way off course.

[bobloblob]

I'm not sure I quite grasp how you will use the Gatorfoam strip as a mounting spline, if that's what you meant.  If the exciters are mounted to something that flexes too easily, that spline may radiate sound in opposite phase to the large panel.  I don't know whether that would have a large enough effect to be concerned about, though.  Maybe I'm misunderstanding here.  Seems like one wants the frame/spline as rigid as possible, so that all the exciters' energy is transferred to the panel.

I mentioned hotmelt glue above, and I think it may be a good choice for panel-to-frame mounting, but not for the exciters, which themselves may heat up enough to re-melt the glue, or at least soften it.  Velcro seems like it may work for the panel-to-frame, but it can be sort of wonky too.  Some of the dots may use adhesive that lets the dots slither downward, and I think they can also sag initially as the weight pulls down on the nylon hooks and loops.  I think it's worth investigating, though.  Low-temp hot-melt glue would be reversible also, as the heat used to soften it shouldn't be enough to damage the panel.  I would test all of these on scrap first.

[usp1]

One thing I think has been mentioned is using some sort of fishing line to suspend the panel from a frame or other support. I don't remember I've seen any thoughts on how to attach the line to the panel on the least intrisive way. This approach appeals to me because or seems to keep the panel as free as possible while still giving the needed support. Obviously as was mentioned above, this extra step requires some careful aligment, though fishing line is much easier to adjust than wood, foam, etc.

One thought is to attach, with the same 3M tape, picture hangars to the back of the panel. You can get very light weight picture hangers such as the ones in the picture below. You can then attach fishing line to the hook.

[jeffac]

Yep.... some experimenting will be required for sure . I got a few extra exciters exactly for that and will have GF panel offcuts. After birthing my first exciter from its case  , I'll think I'll leave the plastic attached to the magnet back by that double-sided foam tape to see whether this might retain enough stickness for spine attachment duties.

The Gatorfoam strip idea for exciter magnet mounting was more to avoid exciter sagging and stressing the voice coil/suspension. Something simple to try, like the Velcro panel-to-frame attachemnt idea.

The picture hook - fishing line attachemnt idea just posted looks interesting too. 

[FullRangeMan]

Hi boys,
I sorry to read about this loose suspension problem.........Now I understand why these exciters are sell with a case.
I think we must use the exciter with the case or maybe just removing the legs, this could extend the suspension useful life.
Reseach and made a spine colunm is too work for me, mainly in the precision final mounting.  But if any one have a good sound spine project I think it yet worth a try.     I really wish to use the exciter with the original case, mainly the generic 0805 that is vented for cooling.
Regards

[usp1]

So I got my gatorfoam panels today. Because of zygadr's post about sagging voice coils I am trying to figure out how to do a good spine so I decided not to mount with the 3M tape as yet. I used some double sided tape I have, which I can remove easily, and mounted 4 exciters on a 2X4 panel. Everything seemed to work very well...except bass. Soon as there was a bass line in the music the panel seemed to make farting sounds. I did not have this problem with cardboard. Note that this is not particularly deep bass....for example the Robert Plant-Allison Kraus album Raising sand seemed to distress the panel quite a bit. So I decided to raise the panel off the ground. I stuck two pencils in the two corners and "hey presto" no more problems. It appears that the edge in contact with the floor was causing the problem!

Currently the panel looks quite ghetto...it has two pencils stuck on two sides and I am bracing it against a stick which goes from the lower most exciter to the ground. In this configuration though, other than the bottom two contact points, the panel is free of contact on all edges.

Update: I spoke too soon. The problem persists only at higher volume and a little less severe. Perhaps I am driving them too hard.

[bytheway]

Just got my first panel build (only one, its partner is still in parts).  Couldn't wait to try it.

Can't believe it works.

As for the sound, its probably unfair to judge mono, but so far so good.  I'm very sure there's some break in required that hasn't happened yet.  Surprised so far at the amount of bass.  Wondering a bit if I'm missing high end.

Need to get the other one built so I can listen in stereo again.  Then on to the frames.

[usp1]

What is a safe amount of power to feed these speakers? I have the cheapo $5/pr exciters.

[Donka]

Hey guys, been busy with other stuff, but have time to do some more testing this weekend with the NXT panels.  I ripped some 3/4" poplar I had lying around yesterday evening and made a simple frame that will come out of the clamps this evening.  I built it with a .200" gap around the panel.  Overall the rigidity may be lacking a bit, but this is for a 22x48" test panel so I can at least gather some good info. 

USP1,

For max power handling just multiply however many exciters you have in series or parallel X 10W.  That is MAX power handling though so I would suggest trying to stay under that to avoid damaging the exciters considering once out of their spider there is nothing supporting it and acting against it from over-extending.  I am going to use my third test panel to test them with their spiders.  The weight of the housing is pretty minimal compared to the exciter, and it may provide a viable option for people don't want to build a spine, we'll have to wait and see.

Zygadar,

I'm happy to hear you found the cause of the buzzing, and that it wasn't a blown VC. However are you not concerned about what you described as loose extension when you compared to the new exciters?  Do you think this was part of break-in, and something that is to be expected, or potentially a serious problem.  It was also interesting that NXT had told you that bracing the exciters would improve the sound, it looks like a spine may be ideal.  I didn't know if by chance you had maintained correspondence with someone at NXT and could ask them about the long-term effects of free-hanging. 

Thanks

[Donka]

Here is the frame I shot together real quick, it has a 2 deg. back-sweep.  Before attaching the spine I routed a 17/32" relief where the exciters attach so the panel will be centered front-to-back within the frame.  Then I overlayed the whole frame over the panel and marked the centerline of each exciter, then I used a carbide burr I already had setup in a rotary tool and relieved the front of the spine so the vents on the exciters could breathe.   When I'm ready to test the panel in the frame I plan to use some hot melt potting glue, it's softer than standard hot glue and will be easier to remove the panel if necessary.

[usp1]

Very nice work Donka!

[bytheway]

Looks great!   I had similar ideas on building such a frame, its nice to see someone has done it.

So, from what I see, you are planning on mounting the panel to the frame by putting the glue on the panel's edge, right (not on the panels face).

Is this the way podium does it as well?