[OB_Newbie]

I like the stands. Nice job! Now you just have to paint them pink and call it a day.

Whaaaaaahaaaaa...   Good for testing and better than the damn chairs I've been using for months!  All future panels shall be black... no more pink for this man.   

[OB_Newbie]

Did some experimenting last night with smaller panels and for ease of testing I glued the back of the exciter to a wood spine and used VHB between panel and exciter. Realized that in this setup the spine also makes sound and that having the back fixed creates a little bit of vibration problem for <130hz since the forced pushed back has nowhere to go than forward

Hey Odal, this is good to confirm... thanks!  I was assuming this as one of the guys over at PE TechTalk was mentioning "bass rattles" with his panels and the need to solidly mount them to a wood frame to stop said rattles.  He uses spline mounting.  Was hard to believe since I have little damping with my panels and no rattles with my panels.

Not only would the spline vibrate but so to would the wood frame.  The panel and wood frame become the speaker in the situation where the exciter is spline mounted and the panel solidly joined to the frame.

He really likes his DML's so that is all that counts...

[OB_Newbie]

Did some experimenting last night with smaller panels and for ease of testing I glued the back of the exciter to a wood spine and used VHB between panel and exciter. Realized that in this setup the spine also makes sound and that having the back fixed creates a little bit of vibration problem for <130hz since the forced pushed back has nowhere to go than forward

Hey Odal,
Was this on ply or XPS.  I assume ply but want to confirm. 

Also, how did the panel sound with the spline mounting other than introducing panel rattle at low frequencies?!?  I assume it also adds panel noise and resonance through the mid-range as well yes?  When I went back and listened to my first 2'x2' panel with the Dayton Audio DAEX25FHE-4 exciter I noticed that it adds a resonance through the mid-range so assumed that stiff suspensions, spline mounting or even more powerful exciters that transfer more energy to the panel will place more noise on the panel as well.  This on light weight panel material like XPS... should not be as bad on heavier panels like your ply.  If you get it on ply I can't imagine how noticeable it will be on XPS.

What say you?!?  Any additional insight would be way cool...
   

[Odal3]

Whaaaaaahaaaaa...  

Sorry - couldn't resist !

Actually it was very small foam boards I stole from my wife. Not exactly sure about the mtrl composition since it was from the craft store. Large plywood is too heavy to hang directly on the exciter themselves. It might have been OK if I had glued them on properly, but the VHB tape only lasted for a little bit before the rattling started. Normally the same VHB tape lasts for a very long time. The rattling is due to the exciter slightly comes loose - can't see it at first. Sounds good once I figured out how to cross it properly and apply some eq on the mid-range.

If I put my bigger birch ply panels on the floor and lean them against something with no special arrangement, I get a lot of vibration rattling between panel and whatever it leans agains or floor. But it can be fixed by letting the panel stand on something that can move slightly. Since you cross your panels pretty high, there is probably not as much vibration, plus you have the fleece to support (nice idea btw).

One thing to try out for people that uses stands is to put two nails with a round head on the bottom and then put it so the round nail head can move freely on fleece, etc. This will help with the LF 'ratteling'

[Squibby]

Hi Guys,

I'm glad to see that everyone is still experimenting and that the interest demonstrated by all is infectious and bringing in new people and their ideas!

just wanted to let you know what I'm currently working on (especially after seeing everyones efforts so far)....

I recently purchased some xps panels of varying thicknesses and types (open cell and paper backed)....the open cell panels are by far the better sounding material, so much so that the high frequencies sound almost too sharp and are almost a little harsh on the ear....it was lacking a little warmth, something I had in abundance with the birch ply panel.

so as a result of that little experiment I decided to glue three 5mm thick xps panels together with a slight curve in them (as I did with the birch panel, mostly to create tension across the front of the panel and hence maintaining rigidity, and compression on the back). I have since tried veneering a 0.8mm thick maple veneer on the sides and front...I will most likely also do the back but after a few quick listening tests which involved holding a single exciter to the rear of the panel, it already sounds a lot better than the birch ply panel.....high frequencies are crystal clear and I even have some bass, something which was almost completely absent from the birch panel.

the panel itself is super lightweight (i'll post exact weight and measurements once its finished) and only requires one exciter as opposed to the 4 exciters I used on the birch panel. It still needs some work (sanding, shellac, etc). There are a few wrinkles in the veneer due to my vacuum press bag failing, but I hope to get rid of most of those after some sanding and some more glue on the edges that require it.

here are a few pics to whet your appetites in the meantime....

All the best,

Squibby.

[Gregory Roig]

Wow, Squibby! Really anxious to hear how they sound. Looks like some real potential...

[OB_Newbie]

Hi Guys,

I'm glad to see that everyone is still experimenting and that the interest demonstrated by all is infectious and bringing in new people and their ideas!

just wanted to let you know what I'm currently working on (especially after seeing everyones efforts so far)....

I recently purchased some xps panels of varying thicknesses and types (open cell and paper backed)....the open cell panels are by far the better sounding material, so much so that the high frequencies sound almost too sharp and are almost a little harsh on the ear....it was lacking a little warmth, something I had in abundance with the birch ply panel.

so as a result of that little experiment I decided to glue three 5mm thick xps panels together with a slight curve in them (as I did with the birch panel, mostly to create tension across the front of the panel and hence maintaining rigidity, and compression on the back). I have since tried veneering a 0.8mm thick maple veneer on the sides and front...I will most likely also do the back but after a few quick listening tests which involved holding a single exciter to the rear of the panel, it already sounds a lot better than the birch ply panel.....high frequencies are crystal clear and I even have some bass, something which was almost completely absent from the birch panel.

the panel itself is super lightweight (i'll post exact weight and measurements once its finished) and only requires one exciter as opposed to the 4 exciters I used on the birch panel. It still needs some work (sanding, shellac, etc). There are a few wrinkles in the veneer due to my vacuum press bag failing, but I hope to get rid of most of those after some sanding and some more glue on the edges that require it.

here are a few pics to whet your appetites in the meantime....

All the best,

Squibby.

Hello Squibby and welcome back!
Are you able to compare the birch veneered panel to the straight XPS panel?  I'm very curious as to how the sound quality compares as the panel skin seems to be such an important element to a good sounding panel.

btw - I too have been thinking about curving the panel as well but my initial thoughts were that the panel would still need to be tensioned physically like CLS's wood contraptions.  If even so slightly.  After switching from my KEF Q500s back to the magic panels I can hear more of a constant resonant/vibrational signature... if that makes sense.  I hope that a slight amount of tension would reduce some of that resonant character.   

Cheers!

[Squibby]

Hey OB,

the xps panels in their raw state were too harsh a sound....too high and difficult to listen to for long periods of time (hence the maple veneer, the same wood used in violin and guitar construction for their inherent resonant qualities).

not sure if the curvature/tension makes a huge difference with the random vibrations, in theory it should...however it also serves another purpose (aesthetics mostly) in that it will hide the exciter and rear of the panel when its hanging on the wall. the veneer definitely dampens the high frequencies slightly but also gets rid of any weird vibrations on the edge (hence no need to round them), particularly with bass heavy songs.

so far I've only held the exciter up to the xps veneered panel during tests, its not fixed yet and hasn't had the break in time that the birch panel has had, which has been hanging on my wall for the last year.... but even so it sounds considerably better. once I've ironed out the veneer issues (glueing, sanding, shellac, etc) i'll post some measurements.....I'm currently trying to get my hands on a calibrated mic to do the tests with a certain degree of accuracy as opposed to  using the mic on my iphone!

another issue I encountered with the birch panel which I'm hoping to get rid of with this version is the number of suspension points...in theory, the lower the number of suspension points, the better the sound will be. I'm considering using a maximum of 4 suspension points but its also dependent upon the stability of the panel (which shouldn't be a major issue considering how lightweight the panel is).

I promise to post measurements and pics of course, once its all done.

not sure if we'll ever stumble across the holy grail of DML panel specs but its definitely getting closer....atleast to my untrained ear!

All the best,

Squibby.

[osssyvan]

Ben,

Any more to share on the reboards? To me they sound very interesting but would like have more info before trying to source.

So the LF comes mostly from size? Has anyone idea what else contributes to that? I am wondering if I have to get super sized panels at some point. Portability becomes an issue then. I wonder if around 1,8mx0,6m would be enough (close to podium model 1 size).

I slowly building my xps panels but work travel and flu chewed two weeks off. I also ordered some more exciters for further experiments. The birchply shall be the panels for the time being.

I am also thinking of wall mounted painting type. I guess there a test for closed back boxed type would be ok.I just have no idea if you can model those.

Squibby, hurry up!

-ossi

[sedge]

Osssyvan
The 3x2ft x3mm ply panel I am trying out at the moment with low powered exciters ,which has a fr of 40hz to 20k, is a very good full range speaker ,the LF below 40hz drops off like a brick ,so this is a good place to have a steep electronic cut off to save the exciter from excessive movement,if used with a powerful exciter you should end up with a very full bodied sound ,Voices and instruments sound very good and is very powerful in the low end ,this is a very easy and cheap panel to make no fussing about,I'm sure Lot's of people will love them.
Steve

[sedge]

As well as the DEAX 30HESF-4, there's the DEAX32QMB-4 which also looks like a good unit, if the feet hindered the sound too much I'd cut them off,as I have done with my low powered exciters,but would probably have to find some other way to support them as they are heavier,suddenly there's so much choice ,this has got to be good news
Steve

[OB_Newbie]

Hey Steve,
I got a few Tectonic Elements TEAX25C10-8/SP and the first exciter I've purchased with the "arms".  Do you cut off just the arms?  I expected and prefer to take the entire plastic housing off but not sure if there are any issues with doing so?  Any insights to removing this would be appreciated!

Thanks,
Rich

[sedge]

This looks very similar to the el cheapo units I use , the frog part is just glued on , I used a thin screwdriver to gently prize it off, you have to slide the screwdriver in between the spider and the housing , try to get the screwdriver to the magnet at the back,so that you don't put pressure on the spider and slowly lever it off, the glue on the el cheapo models was quite soft and slowly popped off so don't rush things,hopefully these will be the same,if not you might have to use small wire cutters and slowly cut it up in sections,this should leave you with a basic exciter unit.
Good luck
Steve

[OB_Newbie]

Thanks Steve for the response.  I pried at them with light pressure but the plastic casing seemed sturdy and attached pretty well so may have to cut away slowly at the first one and see how it's attached and hopefully the others will be easier then. 

I'll report back when we get back to town and have time to play. 

[OB_Newbie]

btw... Has anyone listened to any of the Bertagni DML panels from the 70's?   Someone over at the Parts Express TechTalk forum  has a set and thinks highly of them.   Just curious if anyone else may have run across them in the past?!?

[OB_Newbie]

.

[Odal3]

Here's an inside of the old Bertagni sound panels: Note the shape of the panel and the triangular corners!

http://www.audioimprov.com/AudioImprov/Speakers/Entries/2012/6/15_Bertagni_SM-275_restoration.html

[OB_Newbie]

This is the most complicated design.  3 way with a piezo tweeter(????).

He knew what he was doing with channels cut into the panels to clip the corners.  Then round insets to further breakup/diffuse output within the tiangular corners!

The smaller SM100 is a single driver full range panel more similar to what we are listening too.  The feedback on sound quality reflects what we hear... room filling sound.

Kinda want to get a set for the novelty and historic value...

[sedge]

Squibby
Some years ago I did try bending a poly panel ,as you have ,but at the end of the day you are still restricting the movement of the panel and damping it at the same time, this may give you a slightly better presentation in one area but will also change the performance ,usually to the worse in other area's,swings and roundabouts.
I did go a bit further with this idea and had an 8ft panel jammed between the ceiling and the floor ,I had the panel bowed towards me and away ,I must say it looked very good,the panel was only 40cm width by 25mm thick ,I used foam sponges to stop the panel touching the ceiling and floor, to stop the buzzing,and a little bluetak to stop them walking along the room to the loud music ,restricting the LF helped this.
I even had them lightly held between the ceiling and the floor so they could freely vibrate as much as possible,no wood frame ,just the panel standing on its own,so easy.
having the mounting so far away from the exciter does help the sound as long as it's not too rigid a mounting,I  only have the small sponge in the middle , I  do not have the sponge damping the whole of the top and bottom, I let it ring freely,even sitting them on the floor will change the sound.
In the end I always come back to the( free floating panel) it just sounds so natural to me,as opposed to a forced sound you inevitably get if you manipulate the panel too much.
Steve

[osssyvan]

Steve,

I got 60 cm x 120 cm x 3,5 birch ply panel that I had in some previous post. They seem quite full range but the xps seems more detailed or airy. Do you know how big you would have to go with XPS to really get full range?

The birch is lacking a bit on LF volume though. They are incredible for HT use though. We watched a movie at our work, after work of course, as we had free room and projector to lend. You don't get the movie LF but it is still great. The panels were shaking like crazy sometimes but the insulation compliant fixture worked nice.

Only problem was that I managed to mishandle one panel and broke it just in front of office . Some quick fixes allowed to watch the movie but it was no means perfectly ok as it rattled sometimes. Gotta fix it for the next show.

Ossi