[CLS]

to every panel builders,

How far is it from your panels to the rear wall? How do you feel the significance of this? Anyone tried absorption/diffusion on the back of panels? 

I'd like to hear your opinions. 

[pol_bct]

Both have bass....................framed has more bass

hello all
I think we should not let bass resonance interfere with bass production

an unframed panel has a very low resonance, under 10Hz, this is what we need
the same panel fully framed has resonance often in the 40/80Hz, not needed.
at first listening this may look appealing, but we will soon feel that
unpleasant one-note caracter, we already know from boomboxes.
regards
POL

[pol_bct]

Hello TOMMUS

maybe you will find me severe, but I have a couple of questions about this design
I think the transducers are the 4 ohm model, maybe I am wrong
how do you get 6 pieces to work as a 4 ohm load, with equal load on each of them?
if the load is not equal on all transducers expect to fry a couple of them soon.

another question is about the fins, does they touch the central backbone?
this is a possible source of noise & distorsion, as well as the wires glued ou touching the fins
this one is clearly a not-so-good good-idea.
We absolutely want nothing to interfere with panel, especialy wires, or any other fix or moving elements.
To be convinced do a frq sweep (log or lin) even at a moderate level, you will get bad noises.

another possible flaw is the well centered disposition of transducers,
this will excite the panel in the same way in any directions,
possibly rising peak resonance or dips at the same frequencies.
the equalization shows this quite clearly.

If I built something in the same style I would dispose the fins at semi-random
not like good soldiers marching on a parade. This design is more pistonic than chaotic.

POL

[pol_bct]

to every panel builders,

How far is it from your panels to the rear wall? How do you feel the significance of this? Anyone tried absorption/diffusion on the back of panels? 

I'd like to hear your opinions. 

I think 2 or 3 feet is mandatory, I already try to cutdown to 1/2 foot but the sound was not so open, lack of "air" 

POL

[bobloblob]

POL-

I saw the one picture of your panel from the front.  Is there any chance of posting a picture from the rear too?  I understand basically how you have the panel set up, but a photo is always nice if you can do it.

Any changes to your panel since your earlier description?

Thanks

[pol_bct]

POL-

I saw the one picture of your panel from the front.  Is there any chance of posting a picture from the rear too?  I understand basically how you have the panel set up, but a photo is always nice if you can do it.

Any changes to your panel since your earlier description?

Thanks

Hello
I have done some new panels since the last pictures posting
but I am not at home at the moment (in Madagascar)
all I can show is a dirty phone-picture of a pair of el-cheapo
set at random on a thin plywood board.

but my rules stay the same, zero contact wires - board
minimalist suspension to avoid any possible noise and no frame when it is possible for the same reason.


I know, it does not look HiEnd but it WORKS ! 
POL

[bobloblob]

Pol-

I appreciate the photos.  If it's possible and when you have time, could you post a photo of the whole panel from behind?  And the "dirty phone-pictures" are just fine.  I am curious about how the set-up looks from the rear.  I have a good picture in my mind from the description you posted some time ago, but, as the saying goes, a picture is worth a thousand words.  Fine detail is not necessary.

So you have gone from a  single floor-standing curved cardboard panel to a hung panel? What differences have you noticed?

Hope all is going well for you in your travels.

[CLS]

   Rubber bands, one of my favorites!

I saw there're shallow "battlements" along the edge of the panel. Hmmmm, would that be.... ?

And, again, those excitors come without their feet. Don't they rock at high level LF? 

Last but not least, how does the sound of thin plywood compare to CC?

[pol_bct]

hello all

as I am on a 3 month travel to Madagascar, I was in need for a little music but did not wanted to waste too much money on this
because everything I bring to this place will stay there and probably not last very long time due to the weather conditions.

So I found two panels of 3mm plywood 1.25m x 0.90m, (1€ each!), I put a set of 4 transducers on each of them, around the 1/3  - 2/3 locations. They are suspended from the ceiling, lying "barefoot" on the wood floor, (gives some bass extension).



they are good from 100Hz up to 14kHz, with a resonance around 4-8kHz, the contact to the floor give some output into the infra regions,but with a lack of level in the 60/180Hz. I put a pair of cheap chinese boxes with 2 x 12" in the center of the setup to fill the low-mids hole, no filtering.  dirty cheap and simple...



this set up lacks the magic low-mids of the C.C. but it is listenable, the output level is decent with a kind of T.amp (chinese false Akai) about 20W. To avoid distorsion on the amp, the transducers are wired in serie (4x4) 16 ohm left and right channels, feeding the center bassboxes set in the return path, wired in //, so 2x16 ohm plus common path 4ohm/2.



The sound is quite good, considering the overall cost who does not exceed 100€, amplifier included !!!
I would caracterize the sound of plywood as very live, voices have an interesting presence.


Bobloblob

"So you have gone from a  single floor-standing curved cardboard panel to a hung panel? What differences have you noticed?"

no big difference because both are lying on the floor, but I feel usefull to let them touch the floor.
this damp them partialy and it give some acoustic load to the panel.


CLS

"I saw there're shallow "battlements" along the edge of the panel. Hmmmm, would that be.... ? "

it looks like, but it is not, traces of previous metal fasteners.


POL

[bobloblob]

POL-

Nice, and thanks for the photos and description.  I assume then that you still feel your earlier cc single panel to be your first choice.

[pol_bct]

"I assume then that you still feel your earlier cc single panel to be your first choice."

single stereo panel, YES

CC, not 100% , wood has something magic as sygadr noticed earlier
we may find many other good material, but I would avoid any "plastic"
maybe with an exception for teflon composite.

POL

[CLS]

Hi Pol,

Thanks for sharing. With panel touching the floor, isn't there noise cuased by the vibration?

About material(s), I had some interesting findings recently in the experiments of thin foam panel with wooden ribs and fabric damping. I'll post them here once I get them more organized. (the experiments are still on going.... ) 

[zygadr]

Very good pol!!

I'm glad you have noticed that real wood has something special to offer!

The plywood is a great start to begin to understand the sonic qualities possible. Plywood is heavy of course, but we are only playing around with the cheapest and most ready material aren't we?

I am speaking to our wood working department next week on what can be done with pine -  sliced across the widest parts in to thin long sheets and glued together at the edges to form a larger sheet.

This will be an interesting exercise as spruce/pine is quite light as is easily worked with.
I propose to make a sheet with ''cut line'' edges all the way around the sheet which will form the suspension.

 As I have mentioned, this has been done before by a commercial company.........I'm only following their ideas

[pol_bct]

.....
 only one cheapo on each panel, at the crossover point of the ribs:
.....
Preliminary setup, wired by the method mentioned by Pol, with an exception that my center has only one driver:

Hello CLS

I dont get how the transducers push on the panel, via the ribs or direct? and if it is on the ribs, the suspensions are also on the ribs !? 

with this wiring , currents of both channels L & R are going in only one central transducer. this means you do not get much L&R informations but mainly out of phase signals. it may sound from "outer space". 

POL

[CLS]

Pol,

Its VC is attached on the rib at the crossover point by 3M adhesive tape. The feet are also attached on the ribs, but by screws. I thought this is OK since the feet are quite soft, should be compliant enough. And it's just like how it's designed to be used on any surface. Now the surface is the rib, that's all.

I did encounter a problem by such configuration, but I guess it's not caused by the feet, though... I think it's the ribs, or between the rib and panel.

Oh, you didn't answer one of my previous question: securing the transducer by its VC alone (without feet or external frame), would it rock at high SPL?

And about the 3-ch connection, I don't understand. Isn't the center seeing the sum of L&R?

[pol_bct]

Pol,

Its VC is attached on the rib at the crossover point by 3M adhesive tape. The feet are also attached on the ribs, but by screws. I thought this is OK since the feet are quite soft, should be compliant enough. And it's just like how it's designed to be used on any surface. Now the surface is the rib, that's all.

I did encounter a problem by such configuration, but I guess it's not caused by the feet, though... I think it's the ribs, or between the rib and panel.

Oh, you didn't answer one of my previous question: securing the transducer by its VC alone (without feet or external frame), would it rock at high SPL?

And about the 3-ch connection, I don't understand. Isn't the center seeing the sum of L&R?

Hi CLS,
the reason why I removed anything but the transducer itself is to reduce the possibilities of parasitics vibrations. this is the main problem I have encountered with this kind of loudspeakers.  this is also why I do very basic designs, no frame , no suspension , no nothing...

About the Hi-SPL on voicecoil , I always use 4 transducers where you only put one, so I have no problems on this side, my ears get saturated before the system.

about the 3 ch connection, what you get depends of the impedance ratio L&R to center. The current flow from L& R channels is supposed to run into a lower (or <=) impedance for the central channel. My config is 16 ohms on L & R, but only 2ohms in the center. If you invert this situation , you get a strong mono center but tiny L&R signals. Pushing to the limits you get only outofphase signals on L&R channels.

hope this help

POL

[CLS]

Thanks for the explanation for 3-ch connection. I understand better now, will look for improvement....

Nevertheless, now my 3 panels are sounding pretty good, actually. Better than the previous 2 floppy ones in almost every aspect. Soundstage is wider and deeper with better image definition. 

Of course it's not perfect and I'm still working on some problems. About the ribs, I got something to share. Just let me catch my breath....

[pol_bct]

CLS

> Bad thing is, what a surprise, there's a broad HF peak above 10kHz !! In
the top octave, it's more than 15dB higher than average on my central panel, and more than 10dB on L/R panels.

have you evaluated the depth & width of ribs and the 1/4, 1/2 wave band of resonance...

POL

[zygadr]

CLS ...................you're putting in a lot of hard work in to this which I take my hat off to you.........well done!

The problem is...............the bracing................no secrets here - THAT is the cause of your problems .
 I found that braces using EPS started to create all sorts of weird things to happen .
Sometimes, simple is best..............believe it or not .

Yes, you can dampen the panel at certain spots until you find an area where the most difference is heard, BUT!............damping all around the panel can cause problems depending on what you use for damping.

You may like E.Q. to fix frequency anomalies, but I hate it with a passion.............unecessary garbage in the signal path!

Here's an idea : I was in a locksmith shop the other day and saw a cut away view of the inside of a door for display purposes.
What did I see?..................two sheets of thin plywood with vertical corrugated cardboard strips, standing on edge and arranged and positioned as snakes glueing and reinforcing the front panel to the rear panels of the door.
 The corrugated cardboard was just strengthened with some sort of glue/resin/paint.........not sure really? Anyhow, this arrangement made the panels feel exremely solid and rock hard. If there was no C.C. bracing inside, the door panels would bend like crazy!

What I propose is that we should perhaps look at making a ''sandwich'' panel of no more than 3/4 inch thickness.
The front and back can be C.C as thin sheets are easily available and the snake like bracing that bonds the two panels together can be C.C. also.The panels and internal bridges or bracing can be hardened with Shellac perhaps?

If you look at Nomex honeycomb material you will see that the small honeycomb shapes are actually hundreds of small braces connected together and hold the mylar front and back sheets like a vice - extremely rigid yet lightweight.

It's good to remember that this honeycomb materail is actually ''PAPER'' based and hardened with a resin (yeah, yeah, a synthetic resin ).It's structure is so as mentioned above AND when rapped on the surface, it ''RINGS'' like a bell............which is good according to the designer of the Podiums.

I think that bracing problems so far have been due to overly large, ''symmetrical'' (instead of random)braces that have somehow impacted negatively on the working of the exciters and the NXT/DML principle.

Having examined many NXT speakers and the panel materials they use, NONE have used any form of braces such as the types tried here on this forum.
Here we are mixing foam with wood, we are using equal or near equal spacing of these braces and are positioning exciters all over the place.
 I have yet to hear exciters sound better than when they are placed equally along the central axis of a tall rectangular panel. This method, as used by Podium speakers is yet to be bettered and is done so for a reason.........I'm sure of it!! 

[el`Ol]

This paper honeycomb look lighter than usual and is available from 5 mm up.
http://orientflex.en.alibaba.com/product/364624057-212563567/honeycomb_panel.html