Is this possible?
I'm using a pair of Radian 745PB compression drivers, a 3" aluminium dome diaphragm with mylar suspension and coil wound on a Kapton former. They supposedly play from 500Hz to 20kHz but I've always thought they had a bit of peaky breakup around 10-12kHz. I've hade to take one apart due to a terminal being broken off and noticed while I was playing with the bits:
1) the domes are filthy is there anything that should be used to clean the aluminium dome, will a light covering of dirt actually reduce their performance?
2) If you tap the dome (gently
with a finger-nail) it seems to resonate about 12kHz where this breakup is apparent in the sound! can I do anything like dope the diaphragm to reduce this breakup?
any help guys and girls???
I'm using a pair of Radian 745PB compression drivers, a 3" aluminium dome diaphragm with mylar suspension and coil wound on a Kapton former. They supposedly play from 500Hz to 20kHz but I've always thought they had a bit of peaky breakup around 10-12kHz. I've hade to take one apart due to a terminal being broken off and noticed while I was playing with the bits:
1) the domes are filthy is there anything that should be used to clean the aluminium dome, will a light covering of dirt actually reduce their performance?
2) If you tap the dome (gently
with a finger-nail) it seems to resonate about 12kHz where this breakup is apparent in the sound! can I do anything like dope the diaphragm to reduce this breakup? any help guys and girls???
The cold shoulder
You can have someone local cryo treat the diaphragms. While this will not remove the resonant peak it will yield improvements all round. If You can't find a local service I would be happy to treat them for you but its a fair way away. Air post before Christmas is not so bad though. Regards Moray James.
You can have someone local cryo treat the diaphragms. While this will not remove the resonant peak it will yield improvements all round. If You can't find a local service I would be happy to treat them for you but its a fair way away. Air post before Christmas is not so bad though. Regards Moray James.
Thanks for the responses guys:
I have used notch filters and while I can get the response to look flat on a RTA I still feel there is a 12kHzish ringing there, voices are still showing a bit of siblance.
I have a friend with epoxy powder coating gear so that is a possible, will the kapton and mylar stand up to the temps required to cure the epoxy.
I work at a university so I can relatively easily find a polystyrene tub and flask of liquid nitrogen! I did try and cryo treat some cables a few years ago but I cracked them taking them out of the bath! any advie on how to go about this?
I have used notch filters and while I can get the response to look flat on a RTA I still feel there is a 12kHzish ringing there, voices are still showing a bit of siblance.
I have a friend with epoxy powder coating gear so that is a possible, will the kapton and mylar stand up to the temps required to cure the epoxy.
I work at a university so I can relatively easily find a polystyrene tub and flask of liquid nitrogen! I did try and cryo treat some cables a few years ago but I cracked them taking them out of the bath! any advie on how to go about this?
powder coating
If I were to try this I would want to do so on a dead diaphragm first. The mylar will be the material of concern here as the kapton and aluminum will not have a problem with the heat. Yo would want to use a powder coat with the lowest possible flow temperature. I would be more inclined to simply spray on a layer of Acrylic high gloss at a time and see how things progress. You might also consider having someone hard anodise the diaphragms. Both these options appeal to me more than powder coating.
Re the cryo you need to soak the parts for a good long while and so need a dewar pot. A dip into the bath will not get the job done. Things need to go down slowly then soak 24 hrs min then come back up slowly. Find a local shop or like I said send a set to me.
Have you considered attempting to stiffen the diaphragm with a patern of ribs and circles to help damp out modes? This could be done with crazy glue or with masking tape as a patern mask (with light adhesive) and spray Acrylic high gloss paint. I am surethat there are other ideas but these come to mind first. Why not play around with this an see what happens. Best regards Moray James.
If I were to try this I would want to do so on a dead diaphragm first. The mylar will be the material of concern here as the kapton and aluminum will not have a problem with the heat. Yo would want to use a powder coat with the lowest possible flow temperature. I would be more inclined to simply spray on a layer of Acrylic high gloss at a time and see how things progress. You might also consider having someone hard anodise the diaphragms. Both these options appeal to me more than powder coating.
Re the cryo you need to soak the parts for a good long while and so need a dewar pot. A dip into the bath will not get the job done. Things need to go down slowly then soak 24 hrs min then come back up slowly. Find a local shop or like I said send a set to me.
Have you considered attempting to stiffen the diaphragm with a patern of ribs and circles to help damp out modes? This could be done with crazy glue or with masking tape as a patern mask (with light adhesive) and spray Acrylic high gloss paint. I am surethat there are other ideas but these come to mind first. Why not play around with this an see what happens. Best regards Moray James.
Blimey lots of options!!!
right, replacement diaphragms are £100 ea so I'm more inclined to start on the simply reversible options. there is a reasonable ammount of space in the compression chamber above the dome so glue etc is a possible, I would have expected some form of acourtic damping above here but their isn't, I have thought about some wool to dampen HF reflections, do you think this may help?
With the acrylic or Damar varnish (where do you get Damar Varnish?) would the added mass to the dome not impede the Hf response somewhat?
should I be looking at stiffening the dome to reduce break up or should ?I be trying to dampen the modes of the dome? the compression drivers will eventually be used in a car audio system so grease is something that may melt and move around with the heat and movement.
right, replacement diaphragms are £100 ea so I'm more inclined to start on the simply reversible options. there is a reasonable ammount of space in the compression chamber above the dome so glue etc is a possible, I would have expected some form of acourtic damping above here but their isn't, I have thought about some wool to dampen HF reflections, do you think this may help?
With the acrylic or Damar varnish (where do you get Damar Varnish?) would the added mass to the dome not impede the Hf response somewhat?
should I be looking at stiffening the dome to reduce break up or should ?I be trying to dampen the modes of the dome? the compression drivers will eventually be used in a car audio system so grease is something that may melt and move around with the heat and movement.
should I be looking at stiffening the dome to reduce break up or should ?I be trying to dampen the modes of the dome? the compression drivers will eventually be used in a car audio system so grease is something that may melt and move around with the heat and movement. [/B][/QUOTE]
I think that what you want to do is both. You cannot make the dome stiff enough to not resonate but you can stiffen it enough to shift some modes and you can damp/break up what is there. That's the main thrust behind the idea with the ribs and circles. You can build them up to two layers thick with a bit of masking work and then you can give a third overall coat which will add some damping while at the same time providing your third coat to the ribs. At that point you are on your own as to wether or not you spray anymore coats.
I don't think that increased mass will be too much of a concern. The two main reasons why I suggested high gloss Acrylic over other compounds (like Damar) are this. High gloss has the highest solids content. Acrylic goes on fully cured you only wait for the solvents to dispurse. Other compounds will take considerable time to cure to achieve full hardness. The average time for cure ie about 21 days and can range as far as 30 plus. While the vast majority of the cure comes in the first week it is still a long time to wait to determine results.
The suggestion of hard anodise coating I think is a good one as the process will leave the dome lighter and yet stiffer as a result of the hard anodised layers on either side of the dome. That in itself will provide constrained layer damping. This will push resonances upward and make them easier to damp with the rib and paint ideas. Good luck have fun. I bet you never thought that one hundred pounds could buy so much fun. Keep us posted. Trgards Moray James.
I think that what you want to do is both. You cannot make the dome stiff enough to not resonate but you can stiffen it enough to shift some modes and you can damp/break up what is there. That's the main thrust behind the idea with the ribs and circles. You can build them up to two layers thick with a bit of masking work and then you can give a third overall coat which will add some damping while at the same time providing your third coat to the ribs. At that point you are on your own as to wether or not you spray anymore coats.
I don't think that increased mass will be too much of a concern. The two main reasons why I suggested high gloss Acrylic over other compounds (like Damar) are this. High gloss has the highest solids content. Acrylic goes on fully cured you only wait for the solvents to dispurse. Other compounds will take considerable time to cure to achieve full hardness. The average time for cure ie about 21 days and can range as far as 30 plus. While the vast majority of the cure comes in the first week it is still a long time to wait to determine results.
The suggestion of hard anodise coating I think is a good one as the process will leave the dome lighter and yet stiffer as a result of the hard anodised layers on either side of the dome. That in itself will provide constrained layer damping. This will push resonances upward and make them easier to damp with the rib and paint ideas. Good luck have fun. I bet you never thought that one hundred pounds could buy so much fun. Keep us posted. Trgards Moray James.
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