Well, as I said before, I don't give up easy on experiments even though I stated that this one was dead
I have discovered some interesting facts that may have misled my conclusive last official post on the performance of the panels
The buzzes and rattles were not the actual panel assembly - they were that damned wiring that interconnects all the drivers!
How could I have missed this MOST IMPORTANT aspect??
I came across this realisation when I had one of the panels in my study at the far end of the room, hooked up to a cheap Kenwood receiver, playing FM radio.
I heard the buzzes in one particular jazz recording that had great lows coming through. Walked up to the panel and suddenly noticed that I had not taken in to consideration that even floppy(but not touching the panel normally) wires would oscillate violently until they hit the panel!
On top of that, some wires were buzzing and rattling against the exciters also.
Had a private email from a New Zealand guy that threw some light on the dampening/mounting of the panels and how to retain output levels. So, there is more work to be done.
In the area of the reproduction of highs - in my study, no problem, lots of highs, even bright but this is a totally different sized room and the panels were just thrown in for fun.
Since then, I have discovered that they will vary their output including the high frequencies like night and day depending on where they are positioned in a particular room.
I read in many reviews that the Podium speakers are VERY sensitive to placement but never really paid any attention to this - I should have.
Another scary find - it's true, they are music dependant and WILL show up what's being fed to them down the line.On some recordings, the highs sound absolutely fantastic - classical string sections sound amazing. Yet, in other recordings,that had normal sounding highs on my horn system(if a bit lite on), the highs are simply awful - go figure
Where to from here?.............more experimenting, positioning,research and possibly trying some different panel materials as suggested by el'OL.
I have discovered some interesting facts that may have misled my conclusive last official post on the performance of the panels
The buzzes and rattles were not the actual panel assembly - they were that damned wiring that interconnects all the drivers!
How could I have missed this MOST IMPORTANT aspect??
I came across this realisation when I had one of the panels in my study at the far end of the room, hooked up to a cheap Kenwood receiver, playing FM radio.
I heard the buzzes in one particular jazz recording that had great lows coming through. Walked up to the panel and suddenly noticed that I had not taken in to consideration that even floppy(but not touching the panel normally) wires would oscillate violently until they hit the panel!
On top of that, some wires were buzzing and rattling against the exciters also.
Had a private email from a New Zealand guy that threw some light on the dampening/mounting of the panels and how to retain output levels. So, there is more work to be done.
In the area of the reproduction of highs - in my study, no problem, lots of highs, even bright
but this is a totally different sized room and the panels were just thrown in for fun.Since then, I have discovered that they will vary their output including the high frequencies like night and day depending on where they are positioned in a particular room.
I read in many reviews that the Podium speakers are VERY sensitive to placement but never really paid any attention to this - I should have.
Another scary find - it's true, they are music dependant and WILL show up what's being fed to them down the line.On some recordings, the highs sound absolutely fantastic - classical string sections sound amazing. Yet, in other recordings,that had normal sounding highs on my horn system(if a bit lite on), the highs are simply awful - go figure
Where to from here?.............more experimenting, positioning,research and possibly trying some different panel materials as suggested by el'OL.
The honeycomb panels have many open sections just like honeycomb from bees wax.The material is phenolic resin coated paper formed in to a honeycomb pattern.
This structure is then covered in a strong plastic/mylar and in some variations, fiberglass and aluminum.
So, it's not really something that is easy to DIY. The Gatorfoam can not be modified to anything like this.
This structure is then covered in a strong plastic/mylar and in some variations, fiberglass and aluminum.
So, it's not really something that is easy to DIY. The Gatorfoam can not be modified to anything like this.
Thanks for that link el'OL. Here's another:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-375
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-375
Looking back on this thread and visiting the the sites of some commercial offerings, I have a strong temptation to try 1/4 inch thick (or less) planks of balsa wood.
The idea is to join these end to end, side by side, in effect making a large lightweight sheet to form a panel for the exciters.
As far as information on this technology goes, it seems that any soft medium whether it be whole, in the middle of or laminated to, will stuff up the high frequencies.Then there is the problem of rigidity - any lack of, and the output takes a dive,so too if mass or weight is excessive.
Simple rules?......YES...........BUT,..........how to overcome them with a DIY alternative? Making a honeycomb, phenolic coated fine paper structure is obviously beyond a home build.
A large balsa wood sheet made from numerous sections can also be strengthened with cross beams at the rear of the structure and still not interfere with the exciter positioning.
Anyone care to comment?
Perhaps the total weight may end up being too high?
The idea is to join these end to end, side by side, in effect making a large lightweight sheet to form a panel for the exciters.
As far as information on this technology goes, it seems that any soft medium whether it be whole, in the middle of or laminated to, will stuff up the high frequencies.Then there is the problem of rigidity - any lack of, and the output takes a dive,so too if mass or weight is excessive.
Simple rules?......YES...........BUT,..........how to overcome them with a DIY alternative? Making a honeycomb, phenolic coated fine paper structure is obviously beyond a home build.
A large balsa wood sheet made from numerous sections can also be strengthened with cross beams at the rear of the structure and still not interfere with the exciter positioning.
Anyone care to comment?
Perhaps the total weight may end up being too high?
Sorry, I don't quite understand. If you mean the heavier or greater the mass of the panel = less output/sensitivity, then yes, I confirm this from my findings.
The material needs to be very light but stiff. ........easier said than done(unless you spend big bucks on the honeycomb panels which defeats the purpose of the whole effort).
The material needs to be very light but stiff.
........easier said than done(unless you spend big bucks on the honeycomb panels which defeats the purpose of the whole effort).We use stiffer plate for low critical frequency. In my example softer plate (PVC+PUR plate) is 0,086 kg and heavier and much stiffer aluminum (Alucobond) is 0,13 kg but difference in sound output is large. As mu at around 5,6 kg/m2 is too high then which material is cheap, light and stiff enough? What about balsa wood? Goebel says critical frequency being 600Hz. Here in Poland double side vakuum aramid honeycomb plate 2500x1250x15mm costs EUR 225,00.
There's an interesting phenomenon with Stradivarius wood called "Abete della val di Fiemme". Its non-linear behaviour, anisotropy makes it very efficient radiator even when accelerometer says that other similar woods produce comparable vibration. No one knows why - it simply couples difefrent to the far field. This topics requires very basic research so bending wave is still mysterious.
Check:
http://www.operesonore.it/
Check:
http://www.operesonore.it/
Very interesting jzagaja.Thank you for the link.
It seems to me that their product suffers the same problems as most other wood based DML speakers - low sensitivity and limited bandwidth.
Of particular interest is the ''TRANSDUCER'' (picture attached).Seems to be a piezoelectric ?
It seems to me that their product suffers the same problems as most other wood based DML speakers - low sensitivity and limited bandwidth.
Of particular interest is the ''TRANSDUCER'' (picture attached).Seems to be a piezoelectric ?
Attachments
Di fiemme is known for its superb efficiency that's why violin and piano makers use them for ages. It differs from usual wood as longitudinal wave speed is almost 6000 m/s and strong anisotropy of parallel fibers. Second trick for efficiency in piano are the transversal beams and pre-stress. What causes the audible sound happens between solid and air in hydroacoustic nearfield about 1mm thick. Turbulences, whirlpools and their interference define the far field we hear - hard to analyze experimentally but can be modeled using CFD/CAA methods.
My piezo exciter taken from 3$ horn tweeter has nasty resonances regardless membrane material and no bass. Wish to find cheap and usable alternative for dynamic exciters.
My piezo exciter taken from 3$ horn tweeter has nasty resonances regardless membrane material and no bass. Wish to find cheap and usable alternative for dynamic exciters.
has anyone heard or had any experience with the ROLEN AUDIO STAR TRANSDUCERS used as speakers ONLY?
http://www.rolen-star.com/
http://www.rolen-star.com/
Went to a local hobby shop and collected a bunch of balsa wood of various thicknesses and weighed them in batches(in the shop with their kind permission) enough to make a large panel when glued together - similar sized panel to what I have at the moment.
Result?.........WAAAAAAAAY TOO HEAVY!... There is no way that wood of any kind will be light enough for the job(as far as I'm concerned).
MY next step towards the panels is to mount a piezo cone at the top with a impedance matching transformer.
This may increase the top end output I suspect?
At present, I have found the correct positioning so that highs are quite adequate, but could be a bit more pronounced.
Result?.........WAAAAAAAAY TOO HEAVY!...
There is no way that wood of any kind will be light enough for the job(as far as I'm concerned).MY next step towards the panels is to mount a piezo cone at the top with a impedance matching transformer.
This may increase the top end output I suspect?
At present, I have found the correct positioning so that highs are quite adequate, but could be a bit more pronounced.
Attachments
Ziggy said:
Result?.........WAAAAAAAAY TOO HEAVY!...
I built a DML with magnetostatic drive some months ago. It had a double diaphragm made of 0.8 mm balsa boards. I didn´t measure beyond 20 kHz, but the 20 kHz were there. I also tested a 1 mm balsa board with piezo. Worse transparency than the corrugated cardboard.
I have asked someone to manufacture penels to my specs on Thursday. I hope the answer will be positive. I also have a sheet of Rohacell left (probably massively overdamped).
Ziggy
Don't spend money on piezo tweeters - just buy piezo elements alone. You need many of them at least ten to get 16 Ohms in parallel (monomorphs), overall capacitance around 200-500nF. To get anything below 2kHz you need to add mass on the back side of them and chose plate fundamental resonance low enough (100Hz). Use wood that is for musical instruments and couples better to the air.
Don't spend money on piezo tweeters - just buy piezo elements alone. You need many of them at least ten to get 16 Ohms in parallel (monomorphs), overall capacitance around 200-500nF. To get anything below 2kHz you need to add mass on the back side of them and chose plate fundamental resonance low enough (100Hz). Use wood that is for musical instruments and couples better to the air.
Interesting.......thanks for your comments and recommendations.
el'OL yes, it seems balsa wood is both too heavy yet soft as well - no good for NXT sound principles.
jzagaja, I already have the piezos and with transformers, they reach 100db on horn flares attached!
Without horns, they are around 95 db, so only two are required.
Also, they will only be tried as TWEETERS ONLY so there is no need for full range operation.
On the subject of NXT high frequencies, there are some very interesting things that I need to inform everyone on:
1. positioning of the panels can make or break the highs - especially the room dampening(curtains, furniture and distance from the rear walls).
2. The panels configured as I have them are unforgiving of the what is feeding them ( In other words, if you have a warm sounding system, that's exactly how it will sound through the panels - warm, with ''warm'' highs.
3. I have been using a high end Pioneer receiver all along while developing and testing the panels.
What I did not realize, is that the top end of this receiver is far from abundant in the high frequency department. In fact the highs are a bit lacking, or at least appear to be as indicated by the reviews I have read on the net. This has not helped at all and has probably given me a false impression of exactly how much highs should be or could be coming through the panel material.
When listening to this receiver on my horns, they appear to be more prominent - BUT..........that's because you need to sit in a sweet spot to hear them AND,besides the fact that they are firing directly at you as most speakers do, the mid/top drivers are made from Titanium which has a bright tonal balance anyway(no matter what amplifier or system used).
4. Last night I connected a simple two stage single ended mosfet amplifier that I built over the last few days(about 10 watts per channel)
The difference was like night and day!
on some music, there was almost too much highs!.
As I said, this NXT technology can be ruthless in showing up system deficiencies - believe me!.
The biggest surprise apart from the high frequency thing was also the fact that this ten watter could drive the panels with ''sensible music'' to quite loud levels......I did not expect that
So, is there a need for piezo tweeters?.........only time will tell
el'OL yes, it seems balsa wood is both too heavy yet soft as well - no good for NXT sound principles.
jzagaja, I already have the piezos and with transformers, they reach 100db on horn flares attached!
Without horns, they are around 95 db, so only two are required.
Also, they will only be tried as TWEETERS ONLY so there is no need for full range operation.
On the subject of NXT high frequencies, there are some very interesting things that I need to inform everyone on:
1. positioning of the panels can make or break the highs - especially the room dampening(curtains, furniture and distance from the rear walls).
2. The panels configured as I have them are unforgiving of the what is feeding them ( In other words, if you have a warm sounding system, that's exactly how it will sound through the panels - warm, with ''warm'' highs.
3. I have been using a high end Pioneer receiver all along while developing and testing the panels.
What I did not realize, is that the top end of this receiver is far from abundant in the high frequency department. In fact the highs are a bit lacking, or at least appear to be as indicated by the reviews I have read on the net. This has not helped at all and has probably given me a false impression of exactly how much highs should be or could be coming through the panel material.
When listening to this receiver on my horns, they appear to be more prominent - BUT..........that's because you need to sit in a sweet spot to hear them AND,besides the fact that they are firing directly at you as most speakers do, the mid/top drivers are made from Titanium which has a bright tonal balance anyway(no matter what amplifier or system used).
4. Last night I connected a simple two stage single ended mosfet amplifier that I built over the last few days(about 10 watts per channel)
The difference was like night and day!
on some music, there was almost too much highs!. As I said, this NXT technology can be ruthless in showing up system deficiencies - believe me!.
The biggest surprise apart from the high frequency thing was also the fact that this ten watter could drive the panels with ''sensible music'' to quite loud levels......I did not expect that
So, is there a need for piezo tweeters?.........only time will tell
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