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Crackie welcome to the this thread........What I want to know is what is the definition of the word pistonic?.... Dont all drivers have moving coils and or move/vibrate in and out in a pistonic fashion to varying degrees? IF not, when EXACTLY does a driver become pistonic, what excursion levels of Xmax is required for a driver to be labeled as pistonic? A sub driver aspires to be highly pistonic because it needs that excursion to produce a good amount of bass, while a mid range driver and or tweeter does not aspire nor requires to have a high degree of pistonic/excursion movement, since they are only reproducing the high frequencies.
In all honesty, I do not think graphenes are the way to go at present. There are too many unanswered questions.It may have load bearing strength, as a monocrystalline monolayer, but what happens to it in the form as a 'bulk' material? What happens to it if you drop it?How does it respond to changes in temperature & humidity?Is it resistant to chemical "attack" (ie: glue)In short, how does it respond to "home" environment?Now I am SURE there must be a material scientist out there with the answers to all these questions, and the answers may well show that graphene is indeed ideal for DML panels but my pragmatic view is that easily 'pretty damn good' speakers can be made from 'pretty damn cheap' materials.Even if one wants to go super exotic, then a 2foot x 4foot carbonfibre/nomex honeycomb sandwich can probably be had for about £500 or less: this would still be pretty much The Bleeding Edge.Maybe as I get older I hear less (but listen more...?) - and so get less bothered about chasing the tiniest % differences 'fancy' kit/wires/DACs etc bring.That being said: semitransparent, impossibly thin, rigid floorstanding panels would be insanely cool. Especially if we could use LASERs to drive them.Ben
Thanks for the welcome(s). Apologies for the delay responding.For the sake of discussion, we can think of a moving coil driver's voice coil and an exciter's voice coil behaving in the same way and responding faithfully to the AC applied at its input. The cone motion on an 'ideal' moving coil driver would faithfully reproduce the input AC signal and apply pressure ( or not ) to the air in front of the cone. State of the art moving coil drivers from people like Accuton, Raidho, SEAS, etc variously use metal alloys, ceramics diamond and are notionally pistonic at the lower end of their bandwidth; they all cease to be pistons at the high end and become non linear. The point at which this happens is easy to determine by reviewing their CSD or distortion characteristics. A good old impedance curve also gives away many clues about non linearity.Regarding your point about bass drivers needing to be pistonic and midranges/tweeters not needing to be pistonic, I think each transducer should behave pistonically ( over the chosen operating bandwidth ). IMHO the primary reason that different driver materials sound the way they do is due to their breakup behaviour when they are no longer behaving like pistons. When they are not pistonic they become modal, like a DML.Regarding best panel materials; internal damping is the killer of HF so softer cores are poor. The best foam cores, such as Rohacell, have very high compressive strength and work well. Honeycombe cores ( aluminium and Nomex ) are better still. Amina and Podium use honeycombs for a reason; I've met Shelley Katz from Podium several times and did some work for him early in the 'layered sound' project; the big Podium products sound great and have received some great reviews. They are very simple things though. High quality Nomex honeycomb cored panels and 4 decent tulip exciters; exciter technology has since moved on and, with a little research, its possible to source similar quality panel materials too. DMLs modal panel behaviour cause them to be very labour intensive to measure. Small microphone position and/or distance changes can have significant changes in the measurement. It is conventional to measure a moving coil at 1W/1m somewhere between HF and mid driver axes, this will only give you a small snapshot of a DMLs true output. A polar plot or some form of averaging is needed to really see how a panel is behaving.
I understand the DML concept thanks for your explanation.....Rohacell seems to be pretty expensive like the nomex honeycomb materials hence why a lot of people wont use it to experiment on....There are 12 types of Rohacell listed on there site ,which one is the best suited for DML panels?Also since you have worked at Amina, what is the frequency response of the Amina honeycomb panels? Any NXT or Amina white paper/ariticles you care to share with us? Thanks.
For a DML the standard industrial grade (IG ) is fine; the numbers in their product range identify are the material's density. 31 IG is the lowest density and therefore the highest sensitivity for 'our' application. IG51 would fine too. There are many other low mass thermal insulation foams which can work extremely well too.......unfortunately it is often difficult to find them in the optimum thicknesses though. 4-6mm is optimal for large full range panels. There are alternative honeycomb panels which cost less than similar Nomex and Aluminium alternatives.http://www.coretexgroup.co.uk/Honeycombcore.htmlAmina's panel standard panel size dictates the response at the low end. There is a high pass to protect the panels and improve power handling; low end is deliberately limited to -3dB at 90Hz. The exciters used are Amina's own designs, are assembled in-house and they aren't available to the public. The specific HF exciter extends HF to above 40Khz. As I mentioned in earlier, excessive internal damping i.e soft cores are the killer of HF.http://aminasound.com/file-directory/product/loudspeakers/mobius/datasheet/Mobius5_Datasheet.pdfI don't have any white papers, sorry.
So how does rohacell panel sound compare to that of nomex or aluminum honeycomb panels? Which one do you think sounds better?How does those cortex honeycomb panels compare with the nomex/aluminum panels in terms of sound quality? Which one do you think sounds better?So amina panels are more like sat speakers which require a sub for the low end?....wow a exciter that extends to 40khz, now that is the type of exciter I want and need.
Hey Crackie thanks for all the info appreciate it.....I have a few more questions what is the best adhesive to use and what or where can one purchase the type of mylar skin used on the podiums, thanks.
