[Crazyprepper]

Thank you for the thorough answere. It helps a lot, very good info.
Will order some exciters and start a build.

Seems like the comercially available Göbel 2.1 system use a 150hz xo point with single subwoofer. I might try something simmilar but with a tapped horn woofer or ob woofer.

[sedge]

Crazyprepper
It's not easy ,trying to recommend panels when the size and thickness you can obtain is not known.
What size room ,how you will xo,what's the size you really want and so on.
If you are building a LF unit ,I would make sure it can go up to at least 300hz without colorations,the panels can sound a bit thin because of room,panel,problems below this,this would have to be stereo of course.
I have used 2mm to 5mm xps for small panels and eps up to25mm max for the larger panels.
A 10 watt exciter will easily drive a poly type panel to very, very loud volumes.
Too many choices.
Steve

[Odal3]

Sedge & OB - thanks for posting all the good info.

Can't remember if I posted here or over at Parts Express, but I wonder if we should establish a common, easy and quick to build reference panel with a widely available exciter.  This will be a panel that we can all compare against different panel designs.  We have difficulty explaining differences because we have no reference to compare to.

Curious what others on this forum think about this idea?

Sounds like a good idea, but not really sure how to do it in practice since the access to material depends on where you live plus the standard impact of room and other equipment. What's your thoughts on how to actually do it? I even struggle getting the exact same sound if I buy ply from two different vendors - not counting the natural difference in wood. 
In a similar fashion, establishing a panel play list for testing would be nice to have as well with songs that emphasize different characteristics of the panels. Here are three songs that I often use to test the sound quality of the panels:

Bach - Unaccompanied Cello Suite No. 1 - Yo-Yo Ma
- The vibrating sound of a solo cello with both deep and high notes really showcase how closely the panels can reproduce the natural sound of the instrument

Trilobita Solo2 - Uakti from the movie Blindness
- Drums going back and forth between left and right channels lets you hear all the nuances and the impact of the hits.

From Gagarin's Point of View - Esbjorn Svensson Trio
- jazz trio that tests the LF of the bass combined with a nice flowing piano - Most smaller panels (sounds thin) or panels standing or leaning against something fails this song (rattle)  and if the panel can't vibrate freely and go both deep and high it will sound thin, compressed and not "alive". But if the panel can go low, this is a very impact full and immersive song on the panel.

Solo Piano is also something I always play to test. Will add that later since I have too many to choose from + the rest of my test playlist that includes everything from acoustic, jazz, classic, rock, alternative to electronic. Piano is tough to get right on regular box speakers but good panels gets both the dynamic, clarity, the mid-range harmonics and the air of the piano. It is mainly the piano I struggle with on the XPS panels since I can't get the XPS clear enough. BTW: If you think about it, a piano with its large sound board is perhaps one of the instruments closest to our panels.

So what songs do you play and why?

I'm a big fan of free floating panels as well - always creates the cleanest output across and sound IMO the best.

1. Rigidly mounting the panel to a frame results in more low frequency output?  Makes sense to me as the overall weight of the panel now includes the wood frame.

This is interesting since every time I tried to stiffen the panels on the sides it has moved up the roll-off point creating less bass. I never tried the exact layout as Sedge so what I did maybe can't be compared. My result is perhaps due to the fact my panels are so thick & heavy even before the frame, so I maybe would need an even more powerful exciter to get the LF in a framed config???? 

My latest panels I finished today are little bit larger squares - 2.5 x 2.5'. Still trying to get some smaller panels for the living room. Sound is really promising so far. I haven't measured them yet, but I only need a little bit extra sub help at the lowest octave to get the dynamics and punch. If music is not bass heavy, I can't really hear a difference if I have the sub on or off.

[sedge]

Odal 3
The frame spreads the output across the panel,but also smooths the low end response ,getting rid of peaks and troughs,it also dampens the low end boom resonance.
The frame is not there to produce sound itself,I'm not making a piano !
The plain 3mm panel will shake and vibrate wildly in the low end ,the  thick heavy frame not only stops this but also gives the panel a more rock solid sound.
I don't know what thickness your ply panels are ,but as you say, your panels sound like they are already heavily into dml mode,extra bracing might not help?
Am a little puzzled why you are using square panels ,is there a reason for this?
What position do you place the exciter to help prevent the stronger standing wave resonances caused by square  panels?
Steve

[mildperil]

Hello All,

I introduced my self in November, got side tracked and have been struggling to catch up with the thread, but managed to get to the most recent post last night, after another evening of playing around with panels in the workshop.

So to recap, when I last posted, I had befriended a man with an EPS and cardboard packaging factory, experimented with many EPS panels, was making a EPS panel sound system for a bike pannier rack, but had fallen in love with the sound of 5mm Re-Board.

As for the Pannier sound system, it used 2 exciters on 1 panel of high density of EPS (25mm thick, sanded, PVA treatment both sides), approx 650 x 400mm, with cut out on one corner to avoid clashing with the heel of a foot while pedaling. The panel was suspended by rubber bands from a 3 point frame that clips onto a rack.
The first test ride ended, rather predictably, with the Dayton DAEX25FHE-4s falling off, despite extensive epoxy gluing. Great as these exciters are, they are just too fragile for what I was asking of them in this application, and trying to support the back of the exciter with a frame was not going to work. To survive bumps, the exciter would have to move as one with the panel, so I dug out some old exciters I had with plastic feet, epoxied the feet and to make double sure, screwed through the feet into the high density EPS panel. They clearly didn't sound quite as good, but reliability gets priority in this application.

This version was just ready in time to join a mass protest bike ride from London to Paris for the COP21 climate talks. I cycled the Brighton to Newhaven ferry leg, but passed the sound system on to friends to use for the journey from Dieppe to Paris. Well it performed brilliantly, the whole system weighed around 1kg, and you wouldn't know it was there while cycling. The sound was loud, very clear and omindirectional, although obviously lacking in the lowest frequencies. Music is a big part of these communal rides, turning the whole thing into a kind of mobile party. Systems to date have generally been a pair of cheap boxed speakers lashed together and powered by a Lepai class d amp and a small SLA 12V battery, and can tip the scales between 10-20kg, so you really notice that weight on a hill.


There were a lot of quizzical looks from fellow cyclists, who couldn't understand where the sound was coming from, and I have had a number of enquiries from guys who want to build their own. I think that the DML approach could revolutionise portable sound systems and there is the making of a niche product here. Unfortunately I was so caught up in it and my very sore knee that I forgot to take pictures of the sound system before it departed to France, and it has yet to make its way back to me. I will post some pics when it does.

Meanwhile, I am still stunned by how good 5mm Re-Board is in its raw state. It seems to have detail and clarity that brings voices to life. I contacted the UK distributor of Re-Board to see if they could sell me some sheets larger than 800 x 600mm, only to hear back from them that they had stopped making the 5mm version . I have managed to order 4 more sheets from a supplier this week. Perhaps I should buy up all the remaining stock, and preserve it for future audiophile generations. 2 sheets are ear marked for a local community hall in need of a PA system. We plan to test them out there in the next couple of weeks to see if they could work instead of traditional speakers.

I have been trying to find alternative honeycomb cardboard materials, and found a company called Dufaylite, and ordered some of their 6mm Ultraboard. It is much cheaper than Re-Board, has thicker skins, and a much more sparse fill of honeycomb in the middle, but it just doesn't have the stiffness of Re-Board, and sounds dull in comparison, the bass plays quite low and warm though. They have 2 types, one finished in white and one with brown raw recycled paper. The white one sounds much better with the raw paper sounding harsh. I have just added a coat of PVA to the raw paper version to try and damp it down, but it wasn't properly dry when I went home last night.



The 10mm brown honeycomb board in the picture is very stiff but sounded harsh. I have also tried to damp with PVA, and it now sounds good on axis, but horrible off axis, which I don't really understand.

As for exciters, my current favourite is the Dayton Audio DAEX30HESF-4. It can managed high SPL without distortion on Re-Board, has plenty of shove for the bass and seems a lot less prone to wobbling and voice coil droop than the DAEX25FHE-4. It is a bit over bright on the ReBoard, but that might EQ out when I get my MiniDSP working again. I must try the Dayton Ultra on the new ReBoard panels.

The DAEX32Q-4 was a real disappointment as I think others have mentioned here. I like the idea of having screwable feet, but they need to supply at least 3 feet to try different materials and positions, and then the sound is awful on anything anyway.

I'll leave it there for now, Ben

[sedge]

Mild peril
If you look back to page 136 you will see a pic of my 50-50 ply panel ,this frame was pulled off of an eps panel.
The eps panel was far more efficient than the ply but had a similar performance,if I remember correctly,also the cross brace was used to support the exciter,I accidentally dropped the panel  a few times and the exciter didn't rip off,even when my large dog jumped all over it,smashing a large hole through it,the exciter was still firmly attached,so it can take a few bumps .
The only concern I'd have with using too large an eps panel on a bike would be strong side winds ,you might find yourself sailing across the road at speed,I had a similar experience in the car park when I bought my first 8x4ft eps panel    not to be repeated!
Steve

[OB_Newbie]

Sedge... I have a terrible image in my head with you flying across the lot, fighting the panel all the way to your car... I laughed with you... not at you! 

Terrible... just terrible...   

[Odal3]

I don't know what thickness your ply panels are ,but as you say, your panels sound like they are already heavily into dml mode,extra bracing might not help?
Am a little puzzled why you are using square panels ,is there a reason for this?
What position do you place the exciter to help prevent the stronger standing wave resonances caused by square  panels?

Hey Steve - I was a bit hesitant to buy square panels as well but that's the only thing they had pre-cut...and I have to say that close to <10F temperatures with my saw in an unheated garage made my decision easy

I haven't really had time to play them or optimize them much, but I ran a quick sweep before my computer decided to do an automatic upgrade that froze the computer. It follows about the same profile as the 4 x 2 panels which is my favorite size but cuts off the LF little bit higher: ~40Hz, and high end for the 30HESF starts to drop little bit over 10k Hz, and then dips down 10db. The only exciter I have managed to consistently get flat to 20hz on wood is the 25FHE, which has a smaller mount ring. I really think the larger mounting rings on the 40W exciters cuts the HF. I didn't have them free-floating so I had some of the typical dips and peaks in the LF.

I currently have the exciter mounted in monacor position 1 so I can do like for like comparisons, but I have found that the position on wood requires a bit more fine-tuning by ear/mic to get right due to the woods areas with different densities.

I tried a square panel in XPS before like the early ones OB made, and those were not too bad either.

[Odal3]

Mildperil - that sounds like a fun ride! I need to put some panels on my bike too - if I do it right it should be more aerodynamic right?

As for exciters, my current favourite is the Dayton Audio DAEX30HESF-4. It can managed high SPL without distortion on Re-Board, has plenty of shove for the bass and seems a lot less prone to wobbling and voice coil droop than the DAEX25FHE-4.

Yeah - agree, the 30HESF has a tendency to come in a bit hot in the 4k-8k range, but I think it can be tamed some with positioning of exciter and strategic dampening of areas of the panel/edges.

[sedge]

OB_NEWBIE


This was the first eps panel I ever bought,as you can see there is a chunk missing from the bottom right side ,this was the part that broke off as I was flying across the car park,away from my car!
This turned out to be lucky,as I had missed running into the parked car's so far,but was running out of space.
I had now managed to stop but I was now flying a 6x4ft Kite above my head ,I managed to walk backwards towards my car dragging the panel with me.
The fun really started when I got back to my car ,as I had to land the panel like a plane by the side of my car and cut it up
I had to slide across the panel to hold it down while I opened the car and get out the knife ,measuring tape and wood,for a straight edge.
You know that moment after you've managed to finally get it all cut up and in the car,where you stop and nonchalantly look round to see if anyone was watching,I couldn't see anyone ,but always will be a little suspicious,there could have been person's crouching behind  car's clutching their stomachs in need of medical attention 


This was the panels setup in my living room,notice the missing piece glued back in place bottom right
I'm showing this as the one on the right was large and square,I played a recording of big Ben over these panels and it sounded fantastic , I seem to remember that the larger the panel the less importance the shape made, but we are talking large.
I certainly wouldn't recommend using a small round or square panel as this would cause problems,and if used,offsetting the exciter is a must !


To me,the sound came mainly from the centre of the panel and gave a strong image even when walking between and around the panels,the rest of the panel seemed to disappear,these days I tend to forget this and regard this as the norm,that is until I listen to NORMAL speakers ,even very ,very expensive ones at that,but they just don't sound REAL anymore !!!!
I'd sit in front of my speakers and say wow listen to that sweet treble or midrange ,cool,NOW ,with the panels I listen to the music and the instruments,no hifi,no amps,no cables,just live music.
Nowadays when I go to audio shows I just sit there thinking ,oh dear ,what have they done!!!!
Steve

[sedge]

Have just finished the frame on the ply panel,will wait a few days before measuring to see if anything out of the ordinary happens,not yet used a cross brace to support the exciter,but don't expect much to change in the low end as I roll them off heavily below 50hz anyway,but we will see.
Seem to remember the 50-50 eps panel rolled off heavily at about 50hz when the cross brace was installed.
Steve

[OB_Newbie]

Hey Steve - I was a bit hesitant to buy square panels as well but that's the only thing they had pre-cut...and I have to say that close to <10F temperatures with my saw in an unheated garage made my decision easy

I haven't really had time to play them or optimize them much, but I ran a quick sweep before my computer decided to do an automatic upgrade that froze the computer. It follows about the same profile as the 4 x 2 panels which is my favorite size but cuts off the LF little bit higher: ~40Hz, and high end for the 30HESF starts to drop little bit over 10k Hz, and then dips down 10db. The only exciter I have managed to consistently get flat to 20hz on wood is the 25FHE, which has a smaller mount ring. I really think the larger mounting rings on the 40W exciters cuts the HF. I didn't have them free-floating so I had some of the typical dips and peaks in the LF.

I currently have the exciter mounted in monacor position 1 so I can do like for like comparisons, but I have found that the position on wood requires a bit more fine-tuning by ear/mic to get right due to the woods areas with different densities.

I tried a square panel in XPS before like the early ones OB made, and those were not too bad either.

You would think that a square panel is bad, but I don't hear any issues with the square panels... well not at least the 24"x24" XPS panels.  They sound very similar to the 24"x30"... just do not go quite as low as the larger panel.  In one of the DML white papers, they mention that nearly square is optimal for getting the most nodes in a given panel area.  Not that this is critically important... surely most folks would prefer smoother frequency response. 

I'll have to go back and try to find the measurements, but I am fairly sure there were no FR anomalies nor anything that stood out in the distortion measurements with the square panel.  Only thing that was interesting... after I rounded the corners and edges the HF response around 10KHz and up dropped by about 2db due to the square edged panel being less rigid.  The loss in rigidity was very noticeable.

Odal, how did the 25FHE measure on ply??  Just as smooth as on XPS?

[OB_Newbie]

OB_NEWBIE


This was the first eps panel I ever bought,as you can see there is a chunk missing from the bottom right side ,this was the part that broke off as I was flying across the car park,away from my car!
This turned out to be lucky,as I had missed running into the parked car's so far,but was running out of space.
I had now managed to stop but I was now flying a 6x4ft Kite above my head ,I managed to walk backwards towards my car dragging the panel with me.
The fun really started when I got back to my car ,as I had to land the panel like a plane by the side of my car and cut it up
I had to slide across the panel to hold it down while I opened the car and get out the knife ,measuring tape and wood,for a straight edge.
You know that moment after you've managed to finally get it all cut up and in the car,where you stop and nonchalantly look round to see if anyone was watching,I couldn't see anyone ,but always will be a little suspicious,there could have been person's crouching behind  car's clutching their stomachs in need of medical attention 


This was the panels setup in my living room,notice the missing piece glued back in place bottom right
I'm showing this as the one on the right was large and square,I played a recording of big Ben over these panels and it sounded fantastic , I seem to remember that the larger the panel the less importance the shape made, but we are talking large.
I certainly wouldn't recommend using a small round or square panel as this would cause problems,and if used,offsetting the exciter is a must !


To me,the sound came mainly from the centre of the panel and gave a strong image even when walking between and around the panels,the rest of the panel seemed to disappear,these days I tend to forget this and regard this as the norm,that is until I listen to NORMAL speakers ,even very ,very expensive ones at that,but they just don't sound REAL anymore !!!!
I'd sit in front of my speakers and say wow listen to that sweet treble or midrange ,cool,NOW ,with the panels I listen to the music and the instruments,no hifi,no amps,no cables,just live music.
Nowadays when I go to audio shows I just sit there thinking ,oh dear ,what have they done!!!!
Steve

This post I enjoyed... very similar to what I had in my head as I read your original post.  But the inclusion of the "where you stop and nonchalantly look round to see if anyone was watching, I couldn't see anyone..." was a fantastic addition.   

This looks like the el' cheapo EPS I have now.  I am still surprised how good it sounds... or at least the potential I hear in even this low grade stuff.  Mine are just to small; they saturate and have to much resonances with the powerful Ultra attached.... even at low levels... they are just so light!!  Case in point... when I walk pass the 24"x64" (untreated) panels propped against a wall, they would often fall away from the wall just from the little air turbulence from my body as I walked by.   I do hear the promise of EPS!!!

For the cheap EPS, I started with 2 PVA treatments on the back and only 1 on the front.  But with the resonances and panel noise I am tempted to do 2 coats front and back on this low grade stuff?!?!     

[OB_Newbie]

Have just finished the frame on the ply panel,will wait a few days before measuring to see if anything out of the ordinary happens,not yet used a cross brace to support the exciter,but don't expect much to change in the low end as I roll them off heavily below 50hz anyway,but we will see.
Seem to remember the 50-50 eps panel rolled off heavily at about 50hz when the cross brace was installed.
Steve

Let us know how this goes Steve... very interested to hear the results!!!

[sedge]

OB_NEWBIE
The eps I use has no holes in the surface and the surface is quite hard,I haven't a clue what grade it is ,at a guess I'd say probably a medium?
I can only find the low grade in the shops at the moment ,too many holes in the surface for my liking,that's why I'm playing around with others materials at the moment ,so hope they bring back the good stuff as ordering from the manufacturer is expensive.

Mmmmmmm as I'm typing this ,I just thought I could buy the 6x2ft  3mm ply ,and solidly mount in a frame,if it doesn't perform well I can easily saw it in half,then I will still have two 3x2ft panels that I know perform well.
Solidly mounting them on the floor might help the low end performance, the only worry would be that the larger panel might cause a bit of low end boom.
My memory is getting sooooo bad,I just remembered some more  mods I was going to try out on the ply ,I will get there eventually ,just too much going on in my life at the moment

How much pva you apply to the panel is always going to be a personal choice,it's a very much like the light delicate paper cone choice or the doped paper cone or any of the other types of cones ,which do you prefer,all of these cones have their champions,and usually perform well in certain area's ,I think it usually comes down to which annoys you the least,I have used many ways to damp the self noise of panels and cones , but usually you end up damping the sounds you love too
Steve

[OB_Newbie]

OB_NEWBIE
The eps I use has no holes in the surface and the surface is quite hard,I haven't a clue what grade it is ,at a guess I'd say probably a medium?
I can only find the low grade in the shops at the moment ,too many holes in the surface for my liking,that's why I'm playing around with others materials at the moment ,so hope they bring back the good stuff as ordering from the manufacturer is expensive.

Mmmmmmm as I'm typing this ,I just thought I could buy the 6x2ft  3mm ply ,and solidly mount in a frame,if it doesn't perform well I can easily saw it in half,then I will still have two 3x2ft panels that I know perform well.
Solidly mounting them on the floor might help the low end performance, the only worry would be that the larger panel might cause a bit of low end boom.
My memory is getting sooooo bad,I just remembered some more  mods I was going to try out on the ply ,I will get there eventually ,just too much going on in my life at the moment

How much pva you apply to the panel is always going to be a personal choice,it's a very much like the light delicate paper cone choice or the doped paper cone or any of the other types of cones ,which do you prefer,all of these cones have their champions,and usually perform well in certain area's ,I think it usually comes down to which annoys you the least,I have used many ways to damp the self noise of panels and cones , but usually you end up damping the sounds you love too
Steve

Hey ya Sedge!
Ahhhh, I thought I could see the EPS "holes in the surface"; I was wrong.      I was hoping it was the low grade stuff just to see what you did.      I like the sound of 2 coats back, 1 in front but on the smaller panels, there are still to many resonances... could probably put another light coat on the front.  This low grade EPS is SOOoooo light and appears that more damping is needed.

I am considering building a 24" x 60" ply panel using 2 - 1/8" 24" x 30" panels... a common cut size at woodworker stores here in the states.  Its hard to imagine a 6x2ft ply is effective with a single exciter.  That is a lot of surface area and the far reaches of the panel can't be generating much output.  And even a 24"x36" panel is easily reaching down to 50Hz where you would be cutting it anyway?!?  Just a thought! 

[Odal3]

I tried a 2.5 x 5 ft ply in 1/8 thickness. It was too woobly to play any bass properly without adding a frame or support beams to make it stiffer. Using 2 separate panels is probably a much better idea. I did try the same size but in 1/4. It sounded great but the size and weight made them hard to hang up freely. With a sub, the smaller sizes sounded just as good if not better.

[OB_Newbie]

Hey Odal!
What smaller panels did you make Odal... any details would be great... very interested in your smaller panels. 

I would solidly mount the panels to a frame gould be as Steve did.   

[Odal3]

By smaller I meant smaller than the 2.5 x 5 ft. My favorite is 4 x 2ft but I got to say the square 2.5 x 2.5 is growing on me - especially after I made a free hanging stand. Took down some of the hot character of the 30 exciter, not to mention the better WAF amd living room factor... not to be discounted in my house  .

Since we are talking smaller, I have had some success with small Al and Cu looking plates. 3" x 4". Of course only for the upper frequencies. I havent had a chance to integrate them with bigger panels yet

[sedge]

OB_NEWBIE
a 2x6ft 3mm ply panel is the cheapest way to buy the material ,this was the original size I had for years ,the 10watt exciter just wasn't powerful enough to drive it to the levels I wanted,more powerful exciters on the market could change this.
The reason I make the cut off at 50hz is mainly because the exciter is under powered ,and will overheat badly even with the extra dbs from framing,also the exciter bounces wildly,not only back and fourth but wobbles from side to side,mainly because of the imbalance caused by the terminal and incoming wire's .
I will have a 6x2ft panel so it makes sense to me to compare the straight large panel with the 3x2ft framed panel.
The next thing would be to frame the larger panel and once again compare.
There is also another option before cutting the panel in half,I could place the frames across the centre of the panels and have two joined panels,then compare the two joined panels with the two separate panels
I could also use different exciter positions for the top and bottom panel areas to spread the resonances and dropouts for a more even response,I could go on ,but that's the start.
This is the way I work ,comparing any changes to make sure I'm on the right track.

I'm listening to the 3x2 panels as I type and am very pleased with the sound,there seems more life in them than before,getting closer to the eps sound,will have to do more listening ,but so far it's going well
Steve