[Squibby]

Hi guys,

the reason i went down the wooden path was to try and emulate the resonance encountered in musical instruments such as guitars, violins and cellos. the tonal properties are well known, but various woods will give better or worse results.

i dont fully agree that birch plywood is the ideal wood to use (sorry Vlad)....most if not all violins/cellos/guitars have top soundboards made of solid spruce with bodies in maple, and the density of spruce varies but remains lower than the average for most other woods. birch has a similar density to maple and hence my "settling" on using birch plywood for the prototype speaker. If i were to build another, i would try and obtain solid spruce boards (not plywood) and brace them on the back as is done with vioin construction, either with thin strips of another wood in an opposing direction to the grain or thin aluminium L profiles (have yet to test the latter, but i am hopefull it will increase the clarity of the highs).

voids in the plywood shouldnt pose a significant problem (most modern panels use honeycomb structures with many voids), but i think the panel is dampened significantly by the adhesives used in producing the plywood which is undesirable and may hinder the clarity and loudness of the panel.

In the prototype build i used the monacor placement with 4 visaton EX 60 S tactile transducers wired in series and parallel (8ohm). the panel is then hooked up to the left channel of a cheap chinese amp (modded lepai) which is fed with a mono (summed stereo signal). I didnt think stereo imaging was necessary with such a wide field of dispersion as is encountered with DMLs...correct me if i'm wrong.

the dimensions of the panel are 122cm * 61cm (curved). i made the stand merely for testing...it will in all likelihood, end up on my wall.

again....i am super happy with the reult of this "little" experiment and should people enjoy what they hear and want one, then i will be happy to build one for them!

[zygadr]

Squibby and all..............................

I now have two panels of standard(it's actually called ''project ply, high quality'') 2.7mm thick, 1220X810 mm plywood sheets working in stereo mode. Believe me, you can notice a BIG difference in stereo mode as opposed to dual mono.

Interestingly, the edge of this plywood looks like three identical layers of wood.............weird!

The sound of this ordinary (?) ply is nothing short of phenomenal..............especially with brass and wind instruments, percussion, cymbals. It requires a bit more volume boost compared to CC, but it's worth it.

BTW Squibby, you are correct in what most musical string instruments use (spruce and maple), however, I have played many cheaper string instruments that had a great sound such as the guitar and cello and were made partly of..................................... ............................PLYWOOD!!!!...................hmmmmmmmmmmmm????

[Squibby]

Hi Zygadr...

i have seen a few instruments which have used plywood, and personally i think the difference in sound is so negligible as to be insignificant (purists disagree and would undoubtedly love to lecture me on the benefits and historical bla bla bla). the only real reason i would prefer to use solid wood and not plywood is that plywood is not as forgiving as solid wood. even sanding the surface down on plywood has to be done so carefully, so as to avoid taking too much off and revealing the adhesive layer (which tends to be brightly coloured to demonstrate coverage) or heaven fobid, the underlying wood layer.

with this particular panel, i came very close to the adhesive layer and didnt get the panel as silky smooth as i would have liked before applying the shellac layer (again to resemble a stringed instrument) as much as possible. I also noticed that alot of plywoods contain cracks which are not visible to the human eye (due to the compression involved when making the plywood), but become noticeable after sanding and treating the wood. in order to counter that i put a slight bend in the panel in order to compress the slightly cracked side. again, these problems could have been avoided by using solid wood.

I know that both will work and plywood will be infinitely cheaper than solid wood, but the work involved with plywood is  significantly increased (at least if aesthetics are an important factor to you).

as for the signal to the panel, i summed the stereo channels and output 2 mono (identical) signals to the amp, of which i am only using one. the reason for this is that i didnt want to make more than one panel at a time, especially for a prototype where there is no hard and fast solution. once the science of these dml panels is found and confirmed i will be happy to build various panels and output stereo, but until then its gonna be one at a time and summed stereo to mono I'm afraid!

I will most likely start building another panel from solid spruce next year (purchase of a new house is hindering my tinkering time), and will let you know how it compares to the plywood.

all i can say is that we all need to keep on experimenting, sharing our discoveries and learning from our collective mistakes...it makes a huge difference to the design and outcome of each of our projects. thanks for the motivation which enables us to keep on doing so!

p.s. the exciters i used were the most powerful i could obtain for a reasonable price in europe....for the next one i will undoubtedy use some high shove ones imported from the US.

[zygadr]

Hi Squibby,
I too am in the process of building a brand new home of considerable size and have my hands full.........so to speak.

I understand your quest for solid wood instead of ply...........makes sense to me.

What I will be attempting shortly is a 3 ply Balsa wood  panel. I have been thinking about this for some time. The cost will not be overly great and the construction method of the panel is well detailed on the net.
How will it sound????............who knows. It may be quite good or it may be a disaster due to poor internal self damping (however, it is a multi layer crossed grain composite with glue)?

We shall see. Anyone have any thoughts on Balsa plywood???

[Squibby]

Hi Zygadr,

The balsa wood experiment sounds very interesting for a number of reasons.....primarily the weight of the panel should be greatly reduced, but also there have been a couple of luthiers who have experimented with balsa violins and the results have been surprising to say the least....

"Doug Martin, an always-interesting free-lance genius who's already had major impacts on the designs of racing sculls and hang gliders. #Doug also builds boats and fiddles - he built his first violin when he was 12.
 
Now Doug's experimenting with balsa wood violins - maple neck, balsa body. #First, they sound wonderful - full, rich, and powerful. #They've been played by a number of concert violinists who have been very impressed. #And these are raw wood instruments, without finish.
 

They have a wildly unconventional appearance. #The bodies are asymmetrical, with more than half of each body's volume on the bass side. #The top and back of each fiddle is a single sheet of balsa arched by bending and gluing and braced with dozens of short braces glued to the OUTSIDE of the instrument.
 
That way experiments in the effects of certain bracing patterns can be conducted immediately by popping off or whittling down any combination of braces and immediately hearing the resulting change in sound. #Perhaps when the experimenting yields a final pattern he'll put that bracing inside."

"Michigan violinmaker and genius grant recipient Joseph Curtin has also built some violins with balsa, and at the Vancouver ASA meeting last May, he said that it was frightening how good they sounded."

given this info, you may well be on to something...if anything they should be considerably louder and cleaner in terms of sound. the fact that you're going to use 3 ply balsa should do away with much of the bracing done on the violins and offer sufficient support to the panel without weird resonances and end vibrations.

good luck with the house and the associated (wife-induced)stress...look forward to hearing how the balsa works out.

all the best,

Squibby.
 

[zygadr]

Hey Squibby, thanks for that great information on Balsa violins...................fascinating to say the least!!

I am looking forward to giving this a go and many thanks for your encouragement!.

Cheers, 

Rob.

[oldschoolVlad]

Hey guys,

have read some smart articles on DML, Plate theory, etc. Well, now it’s clear for me what happens with the upper highs.
Let’s assume the driving point as a coupling of the voice coil, its former and the connection to the panel, where dDrv is the driving point diameter. At high frequencies, where the wavelength is comparable to the size of the connector, the so-called aperture effect of the driving point produces an additional mass reactance. At high frequencies the local stiffness of the panel goes into resonance with the mass-type reactance, produced by the driving point aperture effect and nearby mass of the voice coil assembly (Mms). In general, the resonance frequency rises with higher stiffness of the voice coil former, the type of connection to the panel and the stiffness of the panel material in transverse direction. Higher dDrv and Mms values lower the resonance frequency. 



In the above diagram the effect of resonance is displayed.

So, for the particular panel the certain combination of the exciter’s dDrv, Mms and the connection stiffness is needed.
Dissatisfied with the highs? Just get rid of that sticky tape and epoxy the exciter finally! 

Some notes on exciters.

Due to those new circumstances, for good upper highs I suggest to use exciters with the lower Mms and dDrv (see exciter’s datasheet). The higher motor strengths BL remain a common demand. Take a look at the Impedance vs. frequency diagram. The lowest impedance rise at 20 kHz means higher voice coil current at high frequencies. HIAX25C10-8/HS is the winner from this point of view.

Vlad

[zygadr]

Thanks Vlad.  I agree with your findings.
We need to  use the best exciter available at the moment. I am even considering using only One !

I am sitting here typing this post listening to two tall ,but narrow VH polystyrene panels that do not sound that bad at all??????.
Perhaps we have been over critical of the lighter and MUCH LOUDER panel materials ???

Damn .................. what is the way to beat this mongrel???????

[oldschoolVlad]

...Meanwhile, I continue to simulate and play with different materials. Here is some experience on the upper highs. Lighter materials like XPS have aperture-effect resonance freq. peak to the right of 10kHz, but it moves to the left immediately if we add some mass to the panel like the paper skins to increase overall bending stiffness and damping. To bring the peak back is possible only by increasing the core stiffness, i.e. to use another, stiffer material. Besides, XPS naked has the response as toothy as the hell smile.    As for the plywood, I have managed to get the response as flat as the skyline up to 15 kHz, but the plywood is TOO stiff and dumb for audio - the driving point diameter must be less than 1/2” and the overall SPL is only 83dB with 8 (!) best exciters.    How to beat that all?....... It turns out that we have to use something more stiff than CC or XPS, but less stiff than plywood. So what’s that???......... Exactly!!!........... That’s the Nomex honeycomb...    ...Or, Maybe, the balsa plywood.... We'll see....
To be continued…

[zygadr]

I'm thinking of what has been raised on this forum once before.................a Balsa lattice frame with Mylar stretched over both sides .................what do you think?????

[oldschoolVlad]

...First of all, some good news. The balsa wood is stiffer than XPS and can be of great interest. As for the lattice frame, there is no prediction cause it certainly is not a bending plate... Sorry, it's a plate, but the standard set of the parameters is useless here. It seems to me that there will be no damping at all. SPL strong peaks are expected.

Suggest to take a look on the exciter connection of the Wharfedale LoudPanel (XPS core).
A way to overcome aperture effect???... 

[oldschoolVlad]

…Leaving for vacation, so let me make some last suggestions that might be helpful for your next panels. All of them are based on my experience in DML simulation.
Please read carefully an article below if you haven’t done it yet. It explains a lot, especially on materials.

http://www.daytonaudio.com/media/resources/understanding-and-using-dayton-audio-exciters-revised.pdf

Some notes on the material parameters. These are the core stiffness and self-damping. The higher the core stiffness is, the higher is the upper highs level. Note the stiffness parameter E in the material properties called Modulus of Elasticity (Young's, tensile modulus). For the acceptable results E must be  > 25 Mpa, for the audiophile grade > 100 Mpa. But the plywood’s 1…16 GPa is way too much for audio. The self-damping of each component is crucial to smooth out the SPL response of an assembled panel. In general, synthetic polymer materials have poor self-damping and might cause too bright and colored sound. Natural materials, such as wood and paper, have much better self-damping. Paper has the most.
Some notes on the exciters placement. Use exciters with the voice coil diameter of 25mm. Reducing slightly the driving point diameter might be useful to get more upper highs on some stiffer panels.
Note the Amina’s placement:



It gives the MOST even response on some panels under 1m in size. Trust me.
For some taller panels you can try modified Monacor placement:



It might smooth the response in range of 5 – 10 kHz. The exciters should be placed side by side on the same line. It appears, the larger the panel is, the more bending modes it takes and the more even and smooth the SPL response is. With larger panels the response is better with no edge suspension. Some panels under 1m in size have better response with the Supported edge suspension like this:



The details you can dream up by yourself.
Hope my input was useful. Good luck in your future endeavors!..

[emailtooaj]

Hello again!

Sorry I've been inactive of recent, but I love popping in once in a while and see whats new on the best NXT thread!!

Dissatisfied with the highs? Just get rid of that sticky tape and epoxy the exciter finally! 

I agree 100% Vlad! I've been mounting my exciters with this method for some time now and never turned back. In my mind it's ALL about wave propagation! The key is being able to transfer the sound/wave energy from the exciter to the panel without loss or colorization. And epoxy makes that happen.

I see you guys been doing trials with plywood, various wood species and XPS. Of course individually they each have their own characteristics and results.
I have yet to experiment with my 40 sheets of CC  I was planning to mess around with   but I'll be honest, I wasn't digging the thought of using shellac to help stiffen the CC. Even though I've already bought all the supply's to try it out.

After reading your recent comments about various material you've used, I'm now starting to think about my next build; maybe trying out an idea that I've pondered over in the past few months.
So what is the best way to get that "natural" sound without using heavy, but thin plywood or Shellac'd CC?
Well... out of the wood species, Birch would be the go to candidate IMO. It's used a lot for instruments and can reproduce the most natural and pleasing sounds. There's plenty of papers out there to verify that fact.
Obviously there are other great wood species to choose from that have the same effect, but birch is probably the most cost effective and versatile when it comes to being able to reproduce a wider Hz spectrum.

XPS is, and has been, my go to panel material. I've built other panels for friends using XPS and I'm still using my same'ol  XPS panels (pics in my photo gallery).  I STILL LOVE and appreciate it's sound reproduction!
Now, I do apply a thin coat of epoxy to all the backs of the XPS panels to where the exciters get mounted.
So that's maybe why I don't hear the "harsh" highs that a lot of people talk about when using XPS panels without epoxy, don't know for sure?
But I do feel XPS could use help to get a more natural sound from it.

So all that being said, my thought is to make a layered/sandwich panel consisting of a thin Birch veneer and XPS. See pic below.




As you can see in the drawing there are 2 ways to go about this and I don't know which would work best. My guess would be the Veneer on the one side only (right side of the drawing). If that's the case, the question becomes, which side is optimal for the exciter placement?
Do you mount them on the XPS side or Veneer side?
I would guess mounting on the Veneer side should be best. I say this because if the exciters are located on the veneer side it would give you the natural sound everyone's looking for and the XPS would basically act as a stiffener and amplifier for the sound coming from the veneer; without changing or loosing the natural sound characteristics of the veneer to much.
If you mount the exciters on the XPS side, well... the sound is then going through the XPS first, then it would hit the veneer as like hitting a brick wall. I don't see this producing a desirable result. 

Of course epoxy (applied thinly and evenly)  would be used to "glue" the XPS and veneer together and would have to sit through a full cure period before using it.
The other nice bonus of this method though is you could easily use a jig saw to cut/trim the panel to match the size and/or shape you desire, without fear of damaging or splitting the panel.

This sandwich panel would obviously weigh in heavier than just XPS on its own, but if you mount a small rubber cord to the top of the panel and then secure it to the top of the panels "framing";  this will help support the panel weight while also relieving stress to the exciters, in turn helping to eliminate any future coil drops.

I wish I had time to try out this method myself, but I'll just have to get to it when I can get to it 
If anyone else would like to give this method a shot... give me a PM and I'll be more than happy to help with some directions/suggestions to what I think would be best to get the optimal results AND help save you some time hopefully. 

Peace!

[zygadr]

There is one particular exciter available that does not need to be bolted to any frame work in addition to the panel material and has a metal spider rather than the traditional cloth type.

I will be ordering this powerful exciter  and will mount it(one only!!) directly to the panel without the usual B.S.

I have found some crucial information on sandwiched XPS and will attempt to try this method to see if there is any improvement.
I agree that XPS is in many ways the ideal material due to the light weight and free transmission of upper frequencies and above all AND most importantly with this technology...................EFFICIENCY/SPL.

There has been too much deviation towards panel materials that are too heavy...............this is NOT the way to go.....................neither are materials that ''soak up'' the high frequencies, making the panels ''mid-fi''.

I can not give up the sound that VH XPS gives...............''air'' and ''micro dynamics'' that make them sound ''electrostatic like''................this is of utter importance!!!!!................let us not forget the target we wish to obtain.

[b2m]

Hey guys, long time no talk. I wasn't at home a lot so I neither had time to build speakers nor to use them afterwards. As this is chaning a bit, I'm back!
I thought of using Finnboard ( http://www.modulor.de/en/Paper-Cardboard-Paperboard/Cardboard-and-Paperboard/Finnboard/Finnboard-wood-pulp-beige.html ) as a material, which is halfway between wood and cardboard. I'd harden it with either epoxy or shellack. What do you think? Ever heard or used the material?

[zygadr]

Hi b2m.
I have not heard of or seen this material.
I would hazard a guess that it would be most likely too flimsy to be useful as a panel material.
I think you would be better off using corrugated cardboard or VH polystyrene in 5mm thickness?

[b2m]

How thick is the veneer the wood guys use?

I have to use a halfway non-ugly material or my girl won't allow I use it in the living room anyways and I don't count cardboard or polystyrene as on-ugly. That's why I'm looking into alternatives, even if if may be a little worse on the sound reproduction side, although i tried Re-Board and it was way to heavy for listening to it.

[b2m]

I wish I had time to try out this method myself, but I'll just have to get to it when I can get to it 
If anyone else would like to give this method a shot... give me a PM and I'll be more than happy to help with some directions/suggestions to what I think would be best to get the optimal results AND help save you some time hopefully. 

Peace!

Hey AJ, how big did you plan to do this? I normally opt for 700*1000mm but it seems hard to find veneer in that size. What's your plan there?

edit: Which thickness do you guys use in XPS?

edit: I would guess so, but is XPS better when it has a higher compressive strength? I find that all manufacturers offer up to 700 kN/qm, which requires more thickness (normally 50mm). Any pointers?

[jeffac]

Featherlight.... local possibilities for me.... including 9 mm hardwood veneer-faced 'rigid' end-grain balsa core.... but no doubt a lotto win required to experiment.... 

http://duflex.com.au/files/products.featherlight/fl_brochure_new.pdf
http://duflex.com.au/files/products.featherlight/featherlight.pdf

[raptorman]

Hi all,

I am working on an idea to create flat panel surround and centre speakers which I can hide with photos/paintings (to keep the wife happy) and do away with my measly satellite speakers.

I was wondering whether anyone has tried mounting a Monacor AR-50 or Visaton EX60S onto 1mm steel or aluminium sheet?

My thoughts so far are (very loosely):
1. to use 250mm x 500mm sheet metal for the rear surrounds and a 250mm x 1000mm sheet for the centre.
2. build a box frame with a 30mm rebate all round and line with neoprene
3. set the metal sheets onto the rebate and line again with neoprene around the edges.
4. Fit a front frame, screwed through the 4 corners to maximise compression at these points but allow some movement along the edges of the metal sheet.
5. work out some way of fitting a canvas???

This is all in my head and thus far have not brought anything or made any drawings.

I have built speaker enclosures in the past and the alternative to above is to build similar sized speakers with low profile drivers but this would be an expensive build. I quite like the idea of trying something a bit different but until I've played, have no idea how this might sound.

Any thoughts would be great