I've been lurking around in this thread for a while now, and I must say that the results in your experiences are interesting! I might need to grab a pair of exiters and test myself.
I need to cut my projector screen smaller, which is made of KAPA board (is it the same foamcore you have used?), and I think that might be something to try also, since I will be left with couple large pieces of it. I'm not really sure what type of board I actually have, I think it might be the KAPA line, which has foam core and paper-like surfaces on each side. You can see the different boards here: KAPA(R) | Extremely efficient lightweight foam board
Is there a clear number 1 in the exiters? It would be nice to get a driver that has capability. But I was also thinking in testing some cheap drivers from aliexpress or ebay, or are those just a waste of money?
I need to cut my projector screen smaller, which is made of KAPA board (is it the same foamcore you have used?), and I think that might be something to try also, since I will be left with couple large pieces of it. I'm not really sure what type of board I actually have, I think it might be the KAPA line, which has foam core and paper-like surfaces on each side. You can see the different boards here: KAPA(R) | Extremely efficient lightweight foam board
Is there a clear number 1 in the exiters? It would be nice to get a driver that has capability. But I was also thinking in testing some cheap drivers from aliexpress or ebay, or are those just a waste of money?
Simplicity is beautiful. You are now going down the road of ideas I've had for awhile, but lack the $$$ to make happen. So if I may be so bold as to offer some ideas for further investigation.
1. Instead of the wood pedestal stand, lets make it even simpler. Just use a steel L-bracket on the bottom-middle of the panel backside. Let the panel itself rst on the floor/carpet (to provide bottom edge damping) and then the L-bracket provides the "tripod" effect to keep the panel standing upright. Of course you would again want to use some damping/adsorption material between the panel back and the L-bracket.
2. Another variation of this is instead of having the panel bottom resting directly on the floor, place some foam weather stripping along the bottom edge to provide even more damping.
3. Another idea is instead of using just one L-Bracket, try 2. One each on the back at the sides/corners instead of the middle. This will provide more stability and a bit more clamping effect. The you could also try, the same but this time raise the panel an inch or two off the floor so just the 2 L-brackets hold it up. Then the bottom edge won't be damped on the floor, but also you will tend to have some floor decoupling on the bass end as well.
4. Another variation maybe more for looks: Use variation #3, but instead of putting the exciter towards the middle of the panel, put it at the middle-bottom of the panel. The make a small box enclosure to "hide" the exciter that can also support the exciter and hide its cabling within the box and use some banana plugs on the box to connect the exciter wires and have a nice clean speaker connection. This would make the speaker look like just a single thin sheet of wood from front and back and people will be amazed at how it could possibly work
5. Yet another variation is instead of wood, try a sheet of acrylic or poly-carbonate or even glass so the panel is completely see-thru, with the exciter hidden at the bottom not to be seen. Of course then you could go overbaord and place some colored leds at the bottom of the panel that would make the speaker seemly glow, lol.
There are lots of other stand variations that could be used on this theme to really make a DML look like just a tall thin panel with nothing driving it for a really stunning look.
Hopefully, some day I will get to try these types of ideas out when I win the lottery...
geosand
Like I said before anything you put on the panel will change and take on that materials characteristics. Steel puts out harsh high frequency tones that ring because its to hard/stiff. Even with damping it wont stop it completely. These panels are very sensitive to what you put on them as anything you put on them can change the sound. This is the reason STEEL L brackets are not good. Anything hard like steel including nuts and bolts, washers, and even staples will change and effect the sound.
Wood is the best as its characteristics is all around best in tone. So wood material makes the best stand/support for floor standing DML panels.
And yes using some type of damping material underneath the stand works great, who would of thunk it. LOL
£181.00+VAT / m2 (=2 panels) is not to bad if we would know it to be the best panel.
CELPANEL - Tom Sold
The PP honeycomb panels (with polyesther top) are even lighter and stiffer then foam panels, but would they be better then foam?
0,65kg/M² - 10mm thickness - €36 + vat. (2500 x 1220 x 10 mm)
Gluing wood veneer on it instead of glass or carbon fibres, sounds like a good idea to me.
Think,
PP honeycomb looks very interesting indeed. The 10 mm stuff seems a bit on the thick side to me. The panels may have to be pretty large to get low frequencies, but it's worth a try.
I found this this:
PP Polypropylene Honeycomb - Plascore
This is supposedly available down to 6 mm, and with a scrim on the faces to facilitate adhesion of whatever skin you would want. The brochure also notes the high damping of PP honeycomb as you noted. Now I just have to ind out where I can get it...
Eric
Burnt,
One concern I would have about the tall blonds is that they would be pretty susceptible to warp with changes of season. That's an additional reason why I personally would lean towards a frame for a plywood panel.
Birch ply is probably the best plywood in that regard, but still even that warps. The more plies the better of course. I'm curious about your 4 mm birch, however. As far as I know, the typical versions of birch ply are 3 mm (3 ply) and 6 mm (5 ply). I haven't seen 4 mm at all. How many plies are yours? Did they come from a specialty source (model aircraft?).
Eric
One concern I would have about the tall blonds is that they would be pretty susceptible to warp with changes of season. That's an additional reason why I personally would lean towards a frame for a plywood panel.
Birch ply is probably the best plywood in that regard, but still even that warps. The more plies the better of course. I'm curious about your 4 mm birch, however. As far as I know, the typical versions of birch ply are 3 mm (3 ply) and 6 mm (5 ply). I haven't seen 4 mm at all. How many plies are yours? Did they come from a specialty source (model aircraft?).
Eric
I got the sheet from here Eric
Russian Birch Plywood Cut To Size
The specification was BB/BB, EN 636-1, EN 314-2 Class 1
Not a lot of help where you live I am afraid but perhaps the supplier could put you in touch with the Mill to see if they ship to the USA?
On warping I will wing it and see. The loft room goes through some major changes in heat and humidity over the year so it will be interesting to see what shape my bigger panels are in when I get back to France in a couple of weeks time.
You could always try Gaboon Marine Ply which is highly moisture resistant.
Russian Birch Plywood Cut To Size
The specification was BB/BB, EN 636-1, EN 314-2 Class 1
Not a lot of help where you live I am afraid but perhaps the supplier could put you in touch with the Mill to see if they ship to the USA?
On warping I will wing it and see. The loft room goes through some major changes in heat and humidity over the year so it will be interesting to see what shape my bigger panels are in when I get back to France in a couple of weeks time.
You could always try Gaboon Marine Ply which is highly moisture resistant.
Oh, yeah, I don't find the 1.5 or 4 mm versions here in the US, except maybe from the model aircraft suppliers, and they only have small pieces like 6" x 24" and smaller as I recall.
How many plies in your 4 mm panels?
Eric
Three layers Eric. I have attached an image of the layers. It was an interesting question in that I had not paid much attention to the board build. It looks very similar to the board construction for the panels in France which are still my favorite panels in terms for frequency balance and bandwidth.
The larger panels here in London have a different construction, three equal thickness and same density ply. The French panels have a softer core ply than the outer plys.
Burnt
The larger panels here in London have a different construction, three equal thickness and same density ply. The French panels have a softer core ply than the outer plys.
Burnt
Attachments
Hello Group,
I have been following this Thread for awhile it seems quite active.
The latest recordings BurntCoil sounds very similar to what I was hearing with gator boards. I am attributing the sound quality to being a chromatic effect rather than damping. With the layered ply's the sound frequencies have different speeds and does not appear to be a constant so it shows up as a doppler shift. I am trying to come up with a experiment to confirm my suspension of doppler shift by using REW sonograph and multiple frequencies.
Cheers
Steve
I have been following this Thread for awhile it seems quite active.
The latest recordings BurntCoil sounds very similar to what I was hearing with gator boards. I am attributing the sound quality to being a chromatic effect rather than damping. With the layered ply's the sound frequencies have different speeds and does not appear to be a constant so it shows up as a doppler shift. I am trying to come up with a experiment to confirm my suspension of doppler shift by using REW sonograph and multiple frequencies.
Cheers
Steve
Burnt, What I am trying to wrap my mind about is the tone quality that the Gator Board and thin plywood produce. I am thinking along the line of optics since that is my physics background and the chromatic dispersion that one has when passing light through glass. If I am not mistaken each ply is at a different grain so in my model it would be like different index of glass and has the wave "sound"propagates through it would either speed up or slow down thus having a "dispersion" of acoustic frequencies.
To explore this I am thinking that one sends a 440Hz tone for 23 milliseconds and record the sonograph "Spectrograph" of the response it should only see the 440Hz tone if the time resolution can approach the tone burst of the 2.3 milliseconds.
One could do this for several frequencies to get a dispersion response
DMLBES does your foam panels have a similar tone quality?
To explore this I am thinking that one sends a 440Hz tone for 23 milliseconds and record the sonograph "Spectrograph" of the response it should only see the 440Hz tone if the time resolution can approach the tone burst of the 2.3 milliseconds.
One could do this for several frequencies to get a dispersion response
DMLBES does your foam panels have a similar tone quality?
I think doing a swept tone FFT in REW will give you the info you seek. The excitation swept from say 20Hz to 20kHz. The 2nd through 9th harmonics are displayed as a function of frequency. This would reveal the dominant order of harmonic distortion and the relative levels of each one over the whole frequency band.
Then just plot the sonogram and that will tell your where the energy is stored/decays.
Then just plot the sonogram and that will tell your where the energy is stored/decays.
Any panel material that does not have some sort of damping will result in that same type of hollowish reverb diffused type of sound that you heard from Burnt's sound clip.
It seems people forget the simple steps of DML 101. Two beginner damping techniques is the water/glue mixture and or paint. For wood though I wouldn't use the water/glue mixture instead I would use Latex acrylic paint.
Understood. One of the aspects about DMLs to bare in mind is that what you hear is a bending wave on the surface of the panel. Bending wave velocity is frequency dependent, high frequencies have a higher velocity than lower ones, so DML’s are naturally dispersive. I think what you are proposing is well worth a try but would not the velocity differential swamp any difference you might measure?
The other factors to consider are that these recording were not made to represent any quality factor, they were just a quick and dirty recording to answer DM’s request for the same tracks I had used on a framed and damped version a few days ago. The focus was actually on bass reproduction from tall panels, not overall quality. I have a way to go before I would say I was happy with these panels from a quality perspective. The discussion has veered from ‘how low can they go’ to tonality. That might be a little premature.
Burnt.