[rhing]

Have you considered a Silicone RTV compound rather than a hot melt compound? The Silicone will be more elastic and not creep, whereas the hot melt adhesive will behave more like an extremely thick rubbery viscous material.

BTW, your woodworking looks great!

[Donka]

Sorry guys I wasn't very clear there.  I built the frame so there is a .200" gap around the panel when placed inside the frame, and plan on testing some different adhesive foam I have lying around and other material as a "gap filler" or means of suspension within the frame.  I'm going to use the hot melt to attach the exciters to the back rib.  I want to eventually test a rounded corner version a la Podium, as well as possibly 5 or 6 exciters on the same size panel, hence using potting glue so I can cut through it easier to make modifications. 

I remember in the 6moons Podium repair article about the fussing getting the panel aligned properly.  But honestly by taping a few shims in place I don't see it being difficult at all. 

Rich, I believe I have some rapid set 100% silicone that I could test.

[bobloblob]

Might want to check and see if the exciters heat up like voice coils can.  If these things get too hot, they could loosen the hot -melt glue.  Not a disaster in this case, however, since they would still be attached to the panel, but it would be a good idea to check on them to make sure they don't heat up too much, loosen the glue, and then slide on the spine - at least to the extent the panel would let them.  Should be easy enough to check by playing something loud for a time,  feeling to see whether the exciter is giving off heat, and then physically trying to move the exciter on the spine.  I think for this instance I would use the higher-temp hot-melt glue rather than the low-temp stuff, unless I were absolutely sure the exciter won't give off enough heat to start to melt the glue.  Even then, I would check.

I may be wrong about this, but I believe that as long as the glue bond is not too thick, I don't think there would be any creeping on the panel to frame attachment with hot-melt glue, if you decide to use that instead of the foam, but I'm not sure about using it with the exciters.

[usp1]

I made two test panels ( again 2x4 with 4 exciters each and with temporary 2-sided tape) and spent a few hours listening over the weekend. Overall the panels sound very good. I had to hi-pass at 60hz and keep the volume in check to avoid rattling and violent shaking. This should get fixed when I add 2 more exciters. Currently one of my panels is louder than the other. And since I don't have a balance knob on the pre or individual level controls for the two amp channels, it is hard to comment on the imaging. I don't know if this difference will go away after break-in or if it is important to precisely make the panels identical. Currently the exciter locations are just a tad off between the two panels.

[Donka]

Okay so I spent many hours testing these panels during the weekend, pausing football to take measurements.

A few comments before the graphs:

-I measured the temp of a few exciters after they had been playing at 70db for at least an hour with a IR laser thermo, the highest reading was 88.2deg so I don't think there is any worry using hot melt glue.
-I ended up using the 3M tape to adhere the exciters to the spine, after testing which adhering method would be easier to remove, popping a hot-glued exciter off required much more force hence the tape method for final mounting.
-After seeing some drastic dips in sweep measurements I went ahead and measured individual frequencies and verified the nulls.
-I am new to using REW so I may have screwed something up
-Afraid that a reflection from the wall 5ft behind was causing measurement anomalies I moved a panel out into the open room, and the measured response was nearly identical, so I continued measuring with my current setup.
-All the test panels beside the oblong are 21.3" x 48" with 4 Exciter spaced 12" from top and bottom w/ 8" in-between.
-No rounded corner testing yet, though observing the panel within the frame with no edge retention I could visibly see the corners moving more drastically then the rest of the panel edge.  The deflection was much easier to observe because the frame gave me a fixed point of reference which to view the movement against.
-In music listening the Framed and spidered version have a tighter bass response, though a slightly more reserved sound especially in the highs.  I don't have a trained ear so I am unsure whether this is a positive result due to reduced distortion or whether it's taking away from the sound.  My gross observation is that the framed/ spine version is a cleaner sound, and with some treble boost (needed for all configs) sounded good.
-The last panel setup I tried was 5 exciters with one in the center, and while the measurements didn't differ much, the vocals were really reduced when playing music.
-In removing some of my 5 point glued exciters to re-arrange one panel from 4 exciter to 5 I found the glue to have properly spread the circumference of the foot and had soaked well into the top layer for a very strong bond. 
-Except for the one brief adhesive taped test panel to test tape vs glue, all panel were tested with glued exciters.  It was much easier and I feel better surface mating.  Though it is definitely more permanent and probably the reason the manufacturers don't use it because future repairs would be difficult without damaging the panel, though you could use a glue dissolver. 
-After testing a panel w/ capacitors vs w/o I desoldered the caps and re-measured the 2 panels w/o against each other and they measured very close so the differentiation between exciters and panel was limited.

More thoughts later.

L= Left, R=Right, B=Bottom, T=Top

Base Panel = common size with 4 exciters no caps or resistors wired with the top and bottom exciters in series, and the middle 2 in series, then parallel'd.
Base Frame = equivalent base panel taped to spine with no edge retention.

Base Panel Test Setup


Purple Glue vs. Green Tape Exciters to Panel


Teal Base Panel vs Magenta Exciters w/ Spiders


Oblong Test Panel  (dimensions top 18"W, base 30"W, height 48", note the center mounted exciter)


Purple Base vs Oblong narrow side down


Purple Base vs 5 Exciter Panel (w/ center placed exciter)


Purple Base vs Base Frame (panel within frame w/ No edge support)


Teal Base Panel vs. Blue Base Frame vs. Multiple variations of foam edge support (graphs w/ separation)


Blue Base Frame vs. Magenta LRB wedges vs. Purple LR Wedges


Blue Base vs. Magenta LRB Wedges vs. Teal LR wedges and TB adhesive foam straps




Well from those graphs you can see the effect of the spine/frame and edge retention helps to reduce the sinusoidal response in the bass and high frequencies.  Clearly these exciters have major roll-off in the higher frequencies, and I want to experiment with testing through a receiver with high frequency compensation to see how much I can bring up the top end.

The Oblong panel was the best sounding of the various free-standing panels I tested, with better bass response when used upside-down, it also had new exciters on it vs. the base panel that had been run at least 15 hours up until the point of testing.  So possibly it will loosen up and become even more lively.  Surprisingly it did not suffer from the center mounted exciter like the 5 exciter panel tested.  As you can see from the layout marks I plan to test a staggered 5 exciter layout, though I wanted to baseline test it with 4 exciters so it had equivalent output of the other panels. 

There is really an endless amount of variations that can be tested, with offset exciters, more exciters, different panel shapes, different edge retention placement and materials in framed versions, the list goes on. 

If I have time this evening I hope to test rounded corners and also the 5 exciter oblong panel config..

[FullRangeMan]

Great post, Congratulations for the good work.

[bytheway]

Great work, thanks for the posts.

Unfortunately those verify what my ears have been telling me,  these things don' have much high end above 8k.

[Donka]

Bytheway,

I am thinking this is where the ultra stiff and lightweight resin impregnated nomex honeycomb comes into play.  I think the foam and the paper pulp are damping those ultra high frequencies.

I almost forgot I bought 4 of the Dayton version exciters when I ordered another batch of the cheapos, if I have time I will throw those on one of the panels and run some sweeps as well.



I dug out an old Technics 7 band EQ when I got home this evening and did a quick tweek, here is what I got after a little fiddling.

Panel with Foam wedges 2 per side at 1/3 and 2/3 height


Same EQ setting with varying foam wedge placement, Black = LR x 2 1/3's, Blue = LRB middle spacing, Red = LR only mid spacing


Haven't had a chance to listen to music yet, game's on.

[Donka]

Well, I had time to test multiple panel variations this evening.  I took test panel 3 which originally had the exciters with spiders and 5 exciter configurations yesterday.  This time, though the glue shows more promising sonic results, I used the 3M tape so I was able to remove the exciters with a knife and rub the adhesive off the panel.  You can see from the photo all the different Mods I tried as designated by the M#'s. The most promising proved to be Mod 4 with its more balanced LF and controlled HF roll-off.  Surprisingly it closely resembled the new oblong configuration. 

After 9 different Mods, I returned it back to Mod 0 and used glue so that I could use it for comparison testing vs test Panel 2.  After taking a reading, I rounded the corners off, and the measurements show little change, though I did notice less LF 'flap' during the sweeps and assume it will make the most difference when actually listening to music due to decreased distortion.

Here are the graphs and photos from the tests:

Purple base panel 3 vs. Red w/ rounded corners


Purple base panel vs. Orange Oblong 5 Exciter


Orange Oblong panel vs. Magenta Panel 3 Mod 4


New 5 Exciter configuration on Oblong Panel O(as tested above)


Panel 3 After 10 Mods and then Rounding the Corners off  (M4 is the location of the exciters graphed above vs. the oblong panel
)



All in all it looks like by moving the exciters you can help even-out and smooth the response however it does not help the HF Lulls.  I assume the more even slope vs. widely varying HF response would be easier to correct with EQ or possibly an active crossover.  As seen from my earlier post, the effects of EQ were very linear, shifting the graph evenly, I may purchase a Behringer 2496 to experiment with.  At this point I plan to do a little more testing by pairing down the dimensions of the panel, and testing the Dayton exciters, lastly testing various panel to frame damping materials.  Just need to find more time..

[jeffac]

In my search for Gatorfoam, local suppliers seem to be moving to Gilman Board for ease of cutting. There are other boards like Prime-Foam-X ? Board too.  Maybe the foamboard  descriptions here might help ID your sample.

http://www.trueart.info/foamcore_boards.htm

[HenryPercy]

I have a disturbing compulsion that the white piece of foamcore or whatever the sample is that I have here at home is a better material than Gatorfoam.
The reason for this is that the surface seems harder ......and the foam core is also harder........somehow different and more rigid than Gatorfoam's softish core.

We must have different materials, because the Gatorfoam I have is much stiffer and the surface is much harder than foamcore of the same thickness.  I also think the Gatorfoam is lighter, but I haven't weighted them yet.

[jeffac]

"Structa-Board" maybe, "the new big hitter in substrates" 

"dense polystyrene core" "tough lightweight bright white manmade wood-fibre veneer facers" 

3/16" thickness in standard 4' x 8' sheets

http://www.sgpweb.com/_datasheets/132_datasheet.pdf

[Donka]

Well,

I ran a few more options this morning before I tore down my testing setup.  The most surprising result was when I rounded off the corners on the oblong panel, I only rounded the corners on the wide side which I had at the top when standing.  Anyhow it sent the HF back into a sinusoidal wave response, at which point there was no going back, so I got out the TC gun and started gluing different gatorfoam ribs I cut out of scrap to different areas. of the panel, some traversing across between exciters, some extending out to the corners.  I was able to clean up the response some, but it was clear I couldn't get back to where I was before I lopped off the corners. 

Since I had the hot melt out I started trying different ribbing on test panel 3 which was a common size panel with rounded corners.  I triead ribbing across the back of all 4 exciters linking them, I then tried different strakes all over the place as on the oblong panel, the only setup i found to make a larger effect in measurement and sound was when I glued 2 short ribs (roughly 9" long) vertically spanning across the centerline, each a 1/2" to the left and right of the middle 2 exciters.  This configuration audibly cleaned up the lower end and greatly reduced panel distortion during low frequency sweeps. 

After that I started pairing down the panel, taking more and more off the length and width.   Ultimately I tapered the sides and then cut a relief slot and side wedges to try and isolate the upper exciter to see if it would promote HF transmission, I also tried ribbing out from around the uppermost exciter toward the edges, still no breakthrough. 

The one thing I was able to test before I lopped the corners off the oblong panel was my theory of applying EQ to a panel which had a better base response. The results seemed to back that up with a flatter HF response once boosted with EQ.  I went ahead and ordered a Behringer DCX2496,  I had been wanting to experiment with one for awhile and this project finally pushed me to buy.  Though I am wondering if the PEQ may be a better option since it is geared as an EQ only, and maye have more filter options.  The HF rolloff is pretty drastic so a better transmitting material would be ideal, but in the meantime EQ is my best bet even with heavy dB boosts.  I was thinking about a small square or rectangular panel of aluminum either above the main panel or suspended in a cutout in the center of the large NXT panel would maybe compensate for the highs, that is all of course if the aluminum measures appreciably better.

Lastly, while I don't have an overlayed graph ready (you can look back at my previous EQ post), with Panel 1 in the frame with optimized foam wedge placement actually ended up worse than the Oblong panel with varying offset exciters, that is before I rounded the corners off.  I am tempted to cut my full scale panels in oblong configuration considering I could square them up later on.  Overall the best base panel performance before any mods.


Blue Oblong Panel base vs. Purple Rounded Corners


Oblong Base Panel (before rounding) with EQ


Blue Base Panel 3 vs. Orange w/ Stiffener ribs between mid exciters


Orange Panel 3 w/ Stiffener Ribs (cut slimmer) vs. Purple Skeletor Mod


Skeletor Panel Front


Skeletor Panel Back (the torn paper spots were the 2 stiffener ribs between the mid exciters)


Zygadar, I do not disagree that the sound is very enveloping and quite detailed, however the HF lulls are audible, and once boosted using EQ the difference was pretty night and day, also measurably better.  I question whether it may be the exciters themselves, since you are operating a series different from our cheapos, it's possible yours perform better in this area.  It could also be that when playing music the mid-bass doesn't exactly keep up, therefore the low HF isn't as noticeable.  I have a pair of Yamaha professional near field monitors that have a very flat frequency response, sometime this week I will try and dig them out and do some level matched listening tests, including with EQ for the panels and see what's what against a known reference.

So are you going to tell us what the new material is??


Jeffac,

I had seen that chart before but never paid to much attention to it.  If the weight is low, that Structra looks promising, also maybe some Dibond for a HF inset panel. 

[jeffac]

Donka,

Fab stuff with your panel investigations, and I thought building a set of these would be a straight forward piece of cake  .

I can get Bainbridge foamboard locally, the Smooth Mount type with harder surface, greater rigidity looks interesting. Free sample packs available in the US. Like to request one and let us know whether it might be a good thing ?  aa

http://www.nielsen-bainbridge.com/Bainbridge/NB-BainbridgeQualityFoamboard.html

This Bienfang Mighty Core board looks interesting too, plus it comes in large sheets!

http://buz-line.com/p-1930-bienfang-mighty-core.aspx
http://www.usaframing.net/Bienfang/bnfngfoam.htm

and this supplier seems to stock all foamboard brands

http://qx4ao.69as5.servertrust.com/URLrewrite.asp?404;http://www.mmdistributors2.com:80/BIENFANG-Mightycore-1-4-by-the-SHEET-p/bien%2016%20mighty%20cor%201-fslash-4%20sht.htm&Redirected=Y

cheers.. jeffac

[jeffac]

 

[scorpion]

Well, I am home again after my Australian adventure. I havn't had regular Internet access, so I decided to wait until at home to write my comments.

I had the opportunity to visit zygadr, kindly invited to his home, and listen to the 'black monsters'.

Time was short so we had a good hour of listening and talking, which was both interesting and revealing. I didn't bring any of my own familiar records so what I say here is based on what I heard with zygadr's records and a bit of experience.

Conclusion first: These are very good loudspeakers.

Beeing first introduced to Hi-Fi by Stig Carlsson's, ( http://www.carlssonplanet.com/ , he still has a lot of followers around the world ), as a Swede, at that time revolutionary omnidirectional speaker theories and constructions, it was quite an experience to hear something that much more than his designs and any conventional dynamic directivity speakers could recreate a live performance as heard by an auditorium. I suppose that the Podium speaker isn't named Podium by chance.

Regarding the sound:

I agree with zygadr's points: No coloration, very detailed, accurate reproduction of instruments and that special omnidirectional effect that can produce very life like results.

What I considered best was definitively the high bass, midrange and low treble range where everything seemed to produce a glaring performance of the fundamental notes. The detail was quite revealing and the Tympani record zygadr was talking of really let you hear how the skins were worked to give sound.

/Erling

[FullRangeMan]

Thankyou Scorpion for this first hand report.

[j gale]

Zygadr,   Looking at the gatorfoam technical buletin, the white faced stuff seems to be significantly different than the black. It apparently has a much harder surface.

[HenryPercy]

Donka -

What kind of saw and blade did you use to cut the gatorfoam?

Also, could you give some details about making the frames - type of wood, saw, joining the pieces, etc?  I have no experience in woodworking, but I'd like to try it if feasible.  Also, I would use it for other projects in addition to speakers.  Thanks.

- Henry

[Donka]

Jeffac,

I will give those a look, I am sure someone here in SoCal carries the stuff.  I will do some investigating this evening and see if I can find technical specs, or at least the weight so we can roughly calculate the density.  I tried giving the framing supplier a call but they were already closed, I was going to see what their subjective opinion was. 

Zyagadar,

It sounds like you may have some of the Bainbridge foamboard in front of you based on the clay coating as described in the link Jeff provided.  Though Clay and other Baryta style coatings are common amongst photography printing papers, so I assume they are as well with foamcore's designed for mounting. 

Since my Oblong panel is pretty much destroyed after cutting the corners off I may cut it down to rectangular and then try the Dayton exciters on it to see if that makes a difference.  Do you possibly have another source for the units you used, I could see if I could acquire some cheap to test as well so we can definitively say it's the panel material vs exciters.  The gluing and then removing of the ribs has torn up the back of the test panels pretty good, so I may sacrifice one of my remaining 4x8' sheets to cut some fresh test panels, I want to leave #1 that's mounted in the frame, and #2 which is my freestanding untouched for now so I can maintain a reference.   I also need to fix-up another batch of exciters.  I have had about 9 crap out so far from removing and re-taping/gluing, stress testing, pressing too hard to seat them with the tape, and what not to see what they can take.   

Regarding the sound, I agree EQ'ing them is not ideal, and though I was the first to measure the roll-off, Bytheway audibly heard it before I posted my results.  The DCX2496 that I have arriving tomorrow is more of a digital crossover, and supposedly has high quality dac's and adc's in it, and is touted by many as pretty transparent.  We shall see. 


Scorpion,

Thanks for the 1st-hand review.  I agree, with just these roughly 2' X 4' test panels playing side by side in stereo, the sound is quite enveloping.  They have a more open and laid back sound, which I think may be partly due to the HF roll-off.  I believe much contributes to this overall aural sound including the fact that they're dipole, without the sound level rapidly trailing off with distance as in other speaker designs.


HenryPercy,

For cutting the panel I used whatever was setup in my tablesaw at the time, which I believe was a 72T TCG (triple chip grind) because I was cutting MDF before that.  However I rough dimensioned the board with just a straight edge and blade, and got very clean edges, I only used the saw because it was setup and I wanted a faster method to get precisely equal panel sizes.  I figure any blade thats sharp and is 36T or more should cut fine, as long as you don't feed it unreasonably fast.   For the frame I used a 48T Raker that I use as a combination blade for general ripping and crosscutting on non critical parts.  For joining I used loose tenon joinery from the stiles into the rails, via a Festool Domino.   However, woodworking has been one of my main hobbies for years so this is all equipment that I have accumulated over time and use often, I just entered the foray of speaker building 2 months ago and have found it to be very rewarding already.  I get to hear what I build, instead of giving it away to family/friends or staring at it. 

I don't know what you have already, but if you have a miter saw saw you could build the frame by purchasing pre-dimensioned lumber.  HD or Lowes carries 1x3 or 1x4 poplar, oak, and sometimes birch.  Or you if you wanted to go heavier you could call around to local lumber houses or hardwood suppliers and  ask for 6/4 (1.25" actual thickness) or 8/4 (1.75") dimensioned S4S (all 4 sides finished).  This way you won't have to do any ripping or planing.  The easiest strong joint is going to be a half-lap, you could use a skil saw and make many shallow cuts, a router with a rabbeting bit, or a tablesaw with a dado stack to cut these, then just glue and clamp.  However if you're using thicker wood that isn't too wide you could do a butt joint and use long #14 screws as long as you pre-drill, however this is not ideal since you are screwing into end-grain.  For the spine and support again just use pre-dimensioned lumber that you cut to length w/ a miter saw, and you could use the same full lap joinery that I did, by gluing or screwing the leg supports to either side of the spline, and using a butt or filler block at the end as shown on mine.  For the rebate on the spine to inset the exciters, you could go about that 3 ways, one with a router and flush trimming bit bearing on an inset guide underneath the spine, with a saw and straight edge, plunging and then stopping short of your marks and finishing w/ a handsaw; or last and probably easiest is using a spacing block between the frame and the spine top and bottom to offset it's depth.  The last thing I did on mine, that I don't think shows in the photo, is to cut some 2.5" x 6" pieces that T off the spine at the top between it and the frame to give it additional support from twisting since I was using thin stock. 

Overall I would say thee heavier you build it the better, so that it doesn't start to rattle an impart it's own vibrations on the panel.