NXT.......rubbish??....THINK AGAIN!

jeffac · « **Reply #560 on:** 19 Dec 2009, 04:10 am »

Hey Donka,

If only some of us here were as cleaver as you to put on blinkers and 'just do it' as per Ziggy's recipe.

I hope the art shop stll has some of those 6 sheets of black Gatorfoam board they said they had however long back it was now.

if the don't.

cheers..jeffac

jeffac · « **Reply #561 on:** 20 Dec 2009, 06:52 am »

Yep ... based on how lacquered cardboard sounds scratched and tapped, I indeed think it could make one hell of a dynamic NXT panel. aa Unfortunately no playing with Tung Oil lacquer as its been stormy and raining here most of the weekend so my time was better spent indoors building my new Silicon Chip DAC kit.

However, just to satisfy the curious, here's what the 'naked' and Tung Oil lacquered 3 mm cardboard test pieces look like, as well as my large 4 mm cardboard panels with folded-back side wings that completely prohibit the panel from wanting to sag vertically.

On my dinky test panels with a single exciter, its quite surprising just how much vibrational energy makes it around the crease to the wings. And as with my winged Visaton B200 OB panels, the wings might also partially explain the surprisingly low bass I get from these tiny panels.

cheers.. jeffac

jeffac · « **Reply #562 on:** 20 Dec 2009, 09:04 am »

Don't know about that, but I'm slowly getting there with panels that haven't cost me a cent..YET.

If you troll back to Reply #715 I've tried to explain changes I can perceive in corrugated cardboard properties after a single Tung Oil inside/surface lacquer treatment, and when done for real, I'd be tempted to at least give the panel outer surfaces a second coat to be sure of an even coating. Certainly it does become stiffer without any significant increase in weight. And with hitting the surface with a fingernail with your ear close to the opposite side, the crack transient must be something like placing your ear to the skin of a snare drum when its whacked, ie. bloody dangerous to your hearing.

As I have access to 60 mL syringes and the like, hopefully I can devise some system of getting good internal treatment right through the large cardboard panels with suitably diluted Tung Oil. And as I've now got some idea what 'naked' cardboard panels sound like, and how much different lacquered cardboard tests aa, I'm reluctant to stick exciters to the large panels until they're treated. Until then...

cheers.. jeffac

Voncarlos · « **Reply #563 on:** 20 Dec 2009, 03:01 pm »

I've read this thread from the beginning, although I may have skimmed over a few posts so I could get to the most recent, and there are a few notes I would like to contribute.

Regarding the stiffening of corrugated cardboard, I might suggest making a batch of very thinned epoxy and then applying it with a roller to the outside layers. It should readily accept a thinning agent like Acetone or Toluene. Successive coats should create a glass like hardness.

And on the thoughts of exciting a vibration in a panel, I am reminded of similar principals in musical instruments, in particular those of the violin family and to some extent the soundboard of a piano.
Chladni's Law would probably be a good place to start: http://www.phy.davidson.edu/StuHome/derekk/Chladni/pages/history.htm
Here is an interesting page showing some of the dominant modes of violin plates, including some Flash movies. http://www.phys.unsw.edu.au/jw/chladni.html

I could go on and on about soundboard vibrations but will stop at this teaser in hopes that someone may find some use in it.
It would be interesting to hear what an exciter would do to an unstrung violin top, or even a piano soundboard. Piano soundboards can be had for $600.00 to $1000.00, same for a double-bass soundboard, well out of reach for experimentation.
Another thought would be to glue up some Sitka Spruce or fine grained Redwood or Cedar in the thickness of 2.5mm and the perimeter dimensions of the current Gatorboard test panels. Although unbraced, this would be very sensitive to humidity. ???
Or even cutting the panels to the shape of a violin. ???
To the experimenters here, remember, Stradivari, Guarneri and even C.F. Martin did not have modern test equipment!

jeffac · « **Reply #564 on:** 21 Dec 2009, 01:29 am »

Not sure about glass-like hardness and epoxy being the ideal direction with cardboard

, mother-of-tone NO NO ...but...

What is very interesting is the nodal sand patterns on a centre-excited rectangular panel. Simply from that picture of one of the experiments to validate Chladni's Law, I wonder whether this method (or the math) could be used to provide clues to the ideal spacing of multiple exciters on a large panel that would avoid cancellations, particularly at higher frequencies.

cheers.. jeffac

jeffac · « **Reply #565 on:** 21 Dec 2009, 10:28 am »

Found this great little web page this arvo with a Java applet that quote - demonstrates the mode patterns of vibrating circular and rectangular plates, usually called "Chladni Plates" -

http://webphysics.davidson.edu/alumni/jimn/Java/modes.html

I haven't completely come to grips with exceptional maths skills of Mr Chladni and how nodes/modes vary with frequency, but as I was going to "guess" at where to mount 4 exciters to the front 500 x 1200 mm sections of the large winged cardboard panels, I think I'll use the applet simulation as a guide. Exciters positioned at points of maximum vibration vertically down the centre. Obviously where the exciter is mounted generates the maximum vibration anyway so this should be sympathetic to their cause - I think

not the sharpest tool in the shed here

.

If I also use a through panel mounted piezo cone, it would go at a low vibration node, maybe middle vertical position and off centre toward the panel inside. The less vibration here might/should minimize the panel distorting the piezo cone, kind of makes sense.

What do you guys think? Straitjacket

pic - exciters (green circles) potential piezo cone (yellow circle)

cheers..jeffac

zobsky · « **Reply #566 on:** 21 Dec 2009, 04:46 pm »

Who's going to be the first to try and generate Chladni patterns on an NXT panel at various frequencies?

http://www.youtube.com/watch?v=GtiSCBXbHAg&NR=1

captainjack115 · « **Reply #567 on:** 22 Dec 2009, 07:14 pm »

Quote from: zobsky on 21 Dec 2009, 04:46 pm

Who's going to be the first to try and generate Chladni patterns on an NXT panel at various frequencies?

http://www.youtube.com/watch?v=GtiSCBXbHAg&NR=1

I will not be the first!

I currently have a pair of panels with 8 exciters mounted vertically on foam board. The exciters are mounted 3.25 inches apart center to center. The actual tone quality has not changed much from when I started with one exciter per panel for stereo. Sensitivity and loudness has changed considerably. A stereo pair of panels adds up to 16 exciters and they play loud, "very" loud. 106 db is no sweat and the exciters don't get the slightest bit warm, they're rated for 40 watts RMS. I wore hearing protection while checking exciter temperature with a laser sensor.

Bass is decent down to 55 or 60 Hertz, with readings to low 30's. The low 30's is down 15 db or so.

Two things bother me. The spoken voice, such as an announcers voice, has a ringing sound. This phenomenon has "always" been noticed regardless of number of exciters, panel size, exciter position and panel material. I have never heard Podium's and most likely will never have the chance.
At first I thought it was the wall behind the speakers causing early reflections, so I tried heavy drapes. It was no help and I also don't recall my ESL's doing this occupying the same position........Curious!!!!!! Still a lot of kinks to be worked out, but that's half the fun of it.

The Aussies on this forum have just started summer, we in North America are getting snow and cold weather.

On a lighter note, I told my better half I wanted a DVD re-winder for Christmas.
I told her to make sure it was compatible for Blu-Ray as well. I expect to hear about my little joke quite soon.

Jack

mkstat · « **Reply #568 on:** 23 Dec 2009, 01:25 pm »

Finally available:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-377

-m

captainjack115 · « **Reply #569 on:** 23 Dec 2009, 02:38 pm »

Quote from: mkstat on 23 Dec 2009, 01:25 pm

Finally available:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-377

-m

Interesting!!!!

It doesn't say too much about the mounting bracket.

Jack

xyr · « **Reply #570 on:** 24 Dec 2009, 03:36 am »

Can these panels rock?

Can they translate the musical energy and the impact of a rock concert well? I mean macro-dynamics, the mojo... How do they compare to a OB with classic dynamic drivers?

irishpatrick33 · « **Reply #571 on:** 24 Dec 2009, 03:40 am »

Ziggy and friends,

I just want to double check on the double sided 3M tape. Which model is it, I assume there are different types?

And has anybody tried a more permanent solution, like superglue for instance?

Thanks

el`Ol · « **Reply #572 on:** 24 Dec 2009, 07:51 am »

Conventional cyanacrylate super glue is not vibration resistent. Moray James who has developed a commercial bending wave transducer recommends Black Max, a cyanacylate glue with rubber as filler in the other forum. I believe (seen in an Araldite ad) that the speaker industry usually uses methacrylate glue. Epoxy is probably not used because of long hardening times. I used Pattex Repair Extreme,because I didn't find thin double sided tape in the local stores, advantage is that you get the RE in in very small quantities in construction stores (at least in Germany). The manyfacturer claims it is vibration resistent. It was quite hard to get the exciter off the panel (of course it was destroyed by doing this.

captainjack115 · « **Reply #573 on:** 24 Dec 2009, 07:23 pm »

Quote from: el`Ol on 24 Dec 2009, 07:51 am

Conventional cyanacrylate super glue is not vibration resistent. Moray James who has developed a commercial bending wave transducer recommends Black Max, a cyanacylate glue with rubber as filler in the other forum. I believe (seen in an Araldite ad) that the speaker industry usually uses methacrylate glue. Epoxy is probably not used because of long hardening times. I used Pattex Repair Extreme,because I didn't find thin double sided tape in the local stores, advantage is that you get the RE in in very small quantities in construction stores (at least in Germany). The manyfacturer claims it is vibration resistent. It was quite hard to get the exciter off the panel (of course it was destroyed by doing this.

[/b]

I've used ordinary gel C.A. super glue with excellent results, no breaks in the bonding whatsoever. I have also used double-sided tape with equally good results. In an earlier post, I mentioned using "Terrifically Tacky Tape". I found this tape in a craft shop, it's 1 1/16 inches wide. This tape is thin and very tenacious, it cures to a permanent bond overnight, but can be used right away with no deleterious effects or failures.

Speaking of Moray James, has anyone heard from him? We chatted on the phone quite often and about a year ago he said his phone would be off for an extended period of time. His email is not working either, unless he has a cable modem. In most cases: No phone, no internet, no brainer!

Jack

el`Ol · « **Reply #574 on:** 24 Dec 2009, 07:46 pm »

Quote from: captainjack115 on 24 Dec 2009, 07:23 pm

Speaking of Moray James, has anyone heard from him? We chatted on the phone quite often and about a year ago he said his phone would be off for an extended period of time. His email is not working either, unless he has a cable modem. In most cases: No phone, no internet, no brainer!

His latest post on diyaudio is from today. Try to contact him there.

captainjack115 · « **Reply #575 on:** 24 Dec 2009, 08:03 pm »

Quote from: xyr on 24 Dec 2009, 03:36 am

Can these panels rock?

Can they translate the musical energy and the impact of a rock concert well? I mean macro-dynamics, the mojo... How do they compare to a OB with classic dynamic drivers?

[/b]

At the moment it would seem that the goal of this thread would be to develop a full range speaker with no crossovers.
That being said, I have found that using several of the cheap exciters from Parts Express will in fact produce a great deal of "impact". I am experimenting with 8 exciters per channel and they play loud, very loud!

Your term "macro-dynamics seems a bit contradictory. I'm going to assume that you're looking for subtle detail and loudness. In this case, IMHO I'm going going to say that the two are not necessarily inclusive. Until we find the right panel material and or exciters along with proper placement of the exciters we have not as yet hit on the "ultimate" speaker. The bass is decent, but will not break kidney stones or nail you to the wall by any stretch of the imagination.
Highs are still a bit shy and lack subtle detail. Again, this is only "my" opinion, others on this forum are quite happy with their findings, loudspeakers are a very subjective subject.

I have found and again this is only "my" opinion, the magical 3D imaging of these panels is best with one exciter per channel.

Jack

zobsky · « **Reply #576 on:** 24 Dec 2009, 08:22 pm »

where did you find this tacky tape locally. I finally found the time to go buy a sheet of black gator foam yesterday.

captainjack115 · « **Reply #577 on:** 25 Dec 2009, 02:46 am »

Quote from: zobsky on 24 Dec 2009, 08:22 pm

where did you find this tacky tape locally. I finally found the time to go buy a sheet of black gator foam yesterday.

[/b]

Michaels.

They're also on the web.

This tape works great, it's probably made by 3M. It sure is powerful stuff!

http://www.michaels.com/art/online/displayProductPage?productNum=gc0393

Jack

el`Ol · « **Reply #578 on:** 25 Dec 2009, 09:22 am »

http://www.audioasylum.com/forums/MUG/messages/14/147314.html

zobsky · « **Reply #579 on:** 26 Dec 2009, 04:19 am »

Any new progress on mounting methods

On another note, I can confirm that the bare freed exciters sound less compressed and have better efficiency and HF extension than the encased exciters . This is quite literally the result of less resistance / compression on the voice coils of the bare exciters compared to the encased exciters where the legs pull them towards the panel

Does the tacky tape mentioned inthis thread cure rigid or is it permanently supple. I'd think the ideal adhesive should tend towards rigid ( not completely though) in order to facilitate efficient energy transfer to the panel
Another thing I plan to try is thin vertical ribs of GF to limit the wild panel oscillations I see with bass heavy electronica tracks