[scorpion]

Thanks Guys for doing all this investigation. Myself have been too occupied with my normal OB-speakers and their improvment to do any exciter work.
But I remember stating that Re-Board although good on paper probably would turn out to stiff (sic!) to let through any sound waves. But then I also stated that double well, at least this is kind of a Swedish terminology for two layer cardbord, that I thought worth examining. AND that is what has happened here now for all our benefit. We will come off very cheap with exellent speakers ! 

/Erling

[bobloblob]

I am curious about whether anyone is still using the Terrifically Tacky Tape mentioned by captainjack115 for mounting the exciters.  I like the price and availability - $8 US vs $50 to $60 a roll for the 3M, and in craft stores.  Though the goal of the builders in this thread has not been to create cheap speakers, the surprising part is that seems to be what has happened, incidental to chasing down great sound.  So - anyone having good luck with the less expensive tape?

[zobsky]

My TT tape came unglued from the gator foam in a week on one panel. The other panel held up longer, .. though at that point, I started to see one of the exciters separating. Maybe I should've cleaned the board better (the exciters were cleaned with denatured alcohol prior to mounting).


This time, I'm going to try rubberized superglue. It's as cheap and available at any of the hardware stores.

http://www.dickblick.com/products/gorilla-super-glue/?wmcp=google&wmcid=products&wmckw=23629-1015-11083

[BowerR64]

The best double sided tape you can get is from an R/C hobby store its called "servo tape" its black and you wont find anything better. Ive been into R/C for years and ive tried all types.

[cometarossa]

Wow it's a line transmission system?

[zobsky]

NXT tapped horn, ... do I laugh or cry?

[BowerR64]

You can go ahead and laugh i wont be offended. I should do the crying because i spent all the time to build this thing.

It was fun though

[pol_bct]

Hello all,

I have followed this thread from a few months and I give my experience about these transducers.
First, the cheapest are best for experimenting, if you burn a couple of them you don't care.

Then, the panel, the bigger gives more bass, but if we want more than one driver on that big panel
we have to put them in a close row along the smallest length of the board, not the longest as many people do.

Why this? because of the chaotic behavior of these transducers. One driver built a circle of wave aroud himself
more drivers built interferences and if we aim at big bass, we have to get the "positives" interferences
in the same direction on the longest path of the panel to reach the lowest frq.

Should we put drivers very close or as far as possible from each other?
If we need bass, the closest implantation give the biggest sollicitation, 4 drivers very close work like a big one
on the other side if we want high frq we have to put each driver alone or as far as possible from his fellows.
The worst situation is when drivers are only few inches appart, they interfere in the range of 7 to 2kHz, this is bad.

The corners of the panel must be rounded or cut a 45°, I think round is better.
the way the panel is suspended is VERY important, my best choice would be rope from the ceiling
Coton rope is my fist choice, NO fishing rope who resonate like crazy.
A wooden frame can be used instead of ceiling supension BUT it must be acousticaly neutral.
If the driver are leightweight they can be plucked on the panel without further help
heavier driver need a "backseat".

Where should we put the drivers on the panel? my best implantation is at one third/two third of panel
Why? because it gives at the same time one quarter wave and one half wave in opposite directions
this may be good for controlling impedance radiation.

How many drivers? we should try to keep impedance and electrical load equal on any combination of drivers
this means 4 or 9 drivers are best choice, others combinations like 2, 6 or 8 give unbalanced power on drivers
or heavy load as viewed from the amplifier.

Why do we need two panels to get stereo? It is just a bad habit, NOW we can built a coherent stereo dipole
with all drivers on a same row, for example a 1.40m x 1m vertical pannel can give very good stereo effect up to 5 or 6 meters.

we can implement a 2x4 drivers on an horizontal line centered at 2/3 of total heigh (93cm from floor)
three very close on each side of center line to act as one big bass driver and the two last drivers
at the far sides, only a few inches before the left and right end of panel.
http://img259.imageshack.us/img259/4148/coherentstereo.jpg

By doing this we have a COHERENT system, drivers are in phase in any way we look at them
left to right, up and down, in depth, and stereo with no center hole
imaging stay the same from a few centimeters up to few meters.

a coherency test can be made by switching from an in_phase to out_of_phase pink noise
a standard configuration, IE two multiways loudspeakers, will show 3 to 9dB of delta IN/OUT
this is very poor, a coherent stereo dipole built like I told, can reach 20dB of delta.

POL

[jonners]

Why do we need two pannels to get stereo? It is just a bad habit, NOW we can built a coherent stereo dipole
with all drivers on a same row, for example a 1.40m x 1m vertical pannel can give very good stereo effect up to 5 or 6 meters.

POL

Pol -

Your ideas are interesting. Are you saying that a single panel will give a good stereo effect at a listening distance of up to 5 or 6m, or do you mean that it will give a stereo image that is wider than the width of the panel?

[jeffac]

Welcome POL,

You have some exceptional ideas here….fantastic… 

bigger panels give more bass – confirmed by many of us

panel corners need to cut at 45 degrees/rounded as harsh sound seems to emanate from them - confirmed by jgale and now me (Oh so smooth and relaxed yet dynamic sound I’m getting now from my treated panels  )

ceiling hanging of panels – I have thread jute-based string though the corrugations of my largish cardboard panels, a large knot tied at the bottom to stop it pulling though the hole, with excess hanging down to fix the string to the floor with something heavy – brick , to see whether this might work OK, and it could, I was just so keen to get my panels playing, I just propped them up.. and haven’t gotten back to this….yet. Certainly worth revisiting though.

exciter spacing – I think you’re on to something here … and I have been thinking along similar lines from watching all the Chladni vibrating pate videos on youtube. The exciter is never at a null at any frequency, it’s always at a seriously vibrating mode, and you can tell this by placing your ear against a panel where an exciter is attached, where it appears louder at all frequencies. This little Java app demonstrates quite well some of what you’re proposing.
http://webphysics.davidson.edu/alumni/jimn/Java/modes.html
for example… try an M=1 N=1 square and maximum vibration, and I assume maximum bass (probably at the expense of HF due to mechanical issues with exciter movement being compromised) occurs in the centre, where you’re proposing several exciters should be positioned close together. Other M and N dimensions will show resonating mode and null patterns… unfortunately you seem to have to go back to the equations at the linked site to manually calculate the frequency at which any mode pattern will occur (although patterns shown are not to scale, you can see what its getting at).

Exciter panel positioning – need to get my head around the 1/3 2/3 panel physics with quarter wave/half wave in the opposite directions and the effects of this on impedance. I’m sure others here can comment on this.

Exciter number – sounds like you know what you doing.

Single panel for stereo – great idea as described with 2 x 4 exciters for each channel grouped or spaced as suggested (everything on the same plane, no panel cutting, I gotta give this a try)

Keep feeding us your great ideas POL, and post more pics of your NXT panels if you can,  these are always worth a 1000 words.

cheers.. jeffac

[j gale]

Pol, Is the vertical dimension 1 meter or 1.4 meter. If the exciters are along the smallest length the vertical dimension would be 1.4 meter or do I misunderstand? Your picture seems to indicate the opposite. Have you tried cardboard for a panel? I am very interested in comparing the image etc. from a single panel to what I have from 2 separate panels. I'm always happy to see new ideas. Thanks

[jeffac]

Hi Jim,

If the exciters are positioned horizontally, rather than vertically, at a 2/3 position on the panel, and this is 0.93 m above the floor, then its vertical height must be 1.4 m and its width 1.0 m. Obviously you were thinking what I was thinking, that the wider the panel is, within reason, the better the stereo image. I'm sure these are only POLs test mules.. but gee he's got some interesting ideas.... , hopefully which he'll expand on in the next little while.

cheers.. jeffac

[jeffac]

Winding maybe... thicker maybe... but lost... not yet

POL has some very interesting ideas and lets face it.... there still is a few (albeit less than a couple of weeks ago) areas where don't have a clue YET what's BEST PRACTICE to optimized these beasts..

Although great results are being obtained without knowing why, my hat gets tipped to all here providing input on their experiences. And zydadr, keep the enthusiasm, it motivated me to have a play.... and got me 'laughable looking' speakers made of ordinary quality 4 mm cardboard, with the best midrange I've ever heard..  for peanuts... Bass and HF are not to be sneezed at either.

Couple of headphone nuts are coming over for a listen tonight, and these things do have headphone-like sound qualities , I'll let you know what they think.

cheers.. jeffac

[pol_bct]

Hello all,

>> Your ideas are interesting. Are you saying that a single panel will give a good stereo effect at a listening distance of up to 5 or 6m, or do you mean that it will give a stereo image that is wider than the width of the panel?

both are correct, a 1m wide panel with drivers set horizontally in stereo mode gives an image which depend only of the quality of the recording, a two mic stereo gives sound far away from the panel, a multimic mixing gives garbage...
I suggest you start listening "Oscar PETERSON, you look too good to me", you will get what I mean


for Jeffac
http://img41.imageshack.us/img41/3479/p280709oeillets.jpg

>> Single panel for stereo – great idea as described with 2 x 4 exciters for each channel grouped or spaced as suggested (everything on the same plane, no panel cutting, I gotta give this a try)

maybe I was not clear, I apologize, I meant 2x4 drivers (L&R) on one single stereo board in serie/parallele wiring

for j gale
I am located in the middle of nowhere and different panels are not avaiblable here
I am stucked with carton&polystyrene composite, plays very loud but nasty resonances

and yes, actual board is 1.4m vertical and 1 m horizontal, pictures  are rather old and does not fit this.

about stereo effect, our ears are 17cm to 19 cm appart, this means,  at a short distance any source which spans more than  20cm is clearly detectable in direction
a 1 m wide source gives easily horizontal localization up to 10 meter, IF the recording is of decent quality

for example a simple stereo pair on a single board
http://img203.imageshack.us/img203/476/p280709daex25.jpg
and last but not least a single stereo big board can be used as a screen for hometheater
that's all for the moment

POL

[jonners]

http://www.boxline.co.uk/grades_and_styles.htm

[Tinnitus]

I've been following this thread for a while with great interest.
It's now beginning to go way over my head, but that's no bad thing.
I've just purchased a  tripath 2020 chip amp off 'the bay' and eagerly await it's delivery.
My home speakers are Spendor S6's and the T-amp probably wont drive them,so I have been googling NXT transducers as an alternative.
I've come across inflatable speakers on several occasions and although they're clearly not hi-fi the principles which transform a saggy bag of polyprop (or whatever the hell they're made from) into a structure which will propagate sound may be applicable to better designs/materials.
I'd like to propose an idea, I can't try this out myself as it will be some time before I can get hold of transducers, but I offer my idea here for your appraisal/scorn/amusement.
Structures stiffened by inflation:
When inflated to around 120psi a bicycle tyre can ring like a bell when flicked with a finger, this pressure also stiffens this, very flexible rubber structure with no structural strength into something capable of carrying the weight of even a heavy adult over rough surfaces for hundreds or thousands of miles before the tyre wears out.
Flicking the tyre as you deflate it reveals a widely changing acoustic response.
My plan is to (eventually) get a sheet of corrugated plastic (the kind used by conservatory manufacturers as opposed to the really thin flimsy stuff), use a bradawl or similar to puncture holes through the walls which divide each individual channel so that they are all 'connected' together for the purpose of even inflation across the surface of the board.
The open ends of the board will be sealed by using silicone sealant.
A bead of sealant could be laid on a flat surface with the aid of a board edge to keep it straight, and the open edge of the panel lowered into the silicone.
This would ensure the ends of the channels were evenly/minimally plugged with sealant, I don't want to make the edge too heavy.
A strong and wide strip of duct-tape of similar should also be folded over the edge of the board to prevent the plugs of silicone from simply blowing out under pressure.
One of the channels (probably a central one?)would have a presta valve from a bicycle inner-tube fitted instead of a silicone plug to allow inflation.

What do you think? dumb or dumber?.
If anyone can think of a lighter solution that would allow for a pressurised 'sheet' please let me know.
Has anyone heard the inflatable speakers?, any better that the cardboard pyramids that we all laughed at before listening?.
One good thing would be that testing would be pretty conclusive as you could alter the pressure 'on the fly' as you listened to a test tone.
If anyone's interested enough in my idea to try it out I'd be fascinated to hear their results.
Sorry if this seems like an attempted thread hijack.

[Tinnitus]

By the way, to permanently affix the 'ducers to a board why not simply mix up some 2 part epoxy putty such as araldite, spread it flat on a surface, dip the ring of the 'ducer into the layer of glue before applying it to the panel?.

Sorry that should read 'epoxy glue', not putty.

[BowerR64]

Glue? do you guys have the same units i have? 

Maybe this is why mine scream 

[Tinnitus]

Another possible method for making a pressurised panel could be to lay down a sheet of very thin self adhesive veneer (like: http://www.woodveneeruk.co.uk/proddetail.php?prod=flexipeel )onto which a tube of around 5mm dia could be laid in either a zig-zag or spiral pattern to cover the entire panel before terminating in a pressure valve (other end sealed!).
It would probably be best if the tube were lightweight but capable of containing a fairly high pressure without stretching much (or at all).
A second sheet of veneer could then be laid on top before a hardening agent such as  thinned shellac is applied to both surfaces.
I don't think that a little pressure leakage over time would be a deal-breaker, think of the novelty of pumping up your speakers so that visitors could best appreciate the sound!, and opens new territory for hi-fi bling:
http://www.bromleybike.co.uk/shop/accessories/pumps/mini-pumps/lezyne-micro-floor-drive-hp-723372.html
And DIY!:
http://blog.makezine.com/archive/2008/05/diy_manual_vacuum_pump.html

What do you think guys?, is the whole concept too much like hanging a pair of beach mattresses on the wall?.

[Tinnitus]

Glue? do you guys have the same units i have? 

Maybe this is why mine scream 

Scream bad? or scream good?
Bolts eh? who'd have thought?.

If you mean "scream" bad, I once worked in the stained-glass restoration biz and was occasionally required to dismantle broken panels which had been 'repaired' by sticking pieces of glass/plastic/wood/you name it over holes with silicon sealant, this crap was often almost impossible to remove in most cases, even after years, and I don't mean that it was just difficult to remove the last traces, I mean the 'patches' were nearly always a total b@5tard to get off AT ALL.
Slightly stretchy (vibration resistant?) but tough as hell.
I appreciate that anything compliant between the exciter and panel may reduce/alter the sound but perhaps a very thin layer would be ok?
I'm convinced that it wouldn't take much to stick good and strong, has anyone already tried silicone?
Does glue fail because of its rigidity?, or some other reason?.

Can anyone tell me how many exciters I should be able to drive with a 2020 tripath amp?.
I think I'm going to order some of these (unless someone has prior knowledge that they're crap):

http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=309-148&scqty=6