dopeing the aluminium diaphragms of compression drivers?

[Puggie]

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???

[Puggie]

Anyone, can I do anything to tame the breakup in these drivers?

[woody]

You might try asking Bruice Edgar. I seem to recall that he has
done some work with using epoxy power coating on some compression diaphrams.


Good luck!

[MBK]

You'll be better off if you carefully measure the FR and using the data, build a notch filter to take out the peak. That will be much more predictable than using some coating, and will likely work better too.

[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.

[Puggie]

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?

[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.

[woody]

On second thaught the mylar sure wouldn`t like the heat
used with epoxy power coating. Perhaps a safer thing to
try is a light coating af Damar varnish. If you were realy careful
with this it could probably be removed later if it didn`t
have the results you were after.

[owen]

How about thick anodising?

The dome will have to be exposed to heat, but could be do-able.

You could anodise in layers - thicker in the middle, and thinner towards the edges....

Owen

[dnsey]

How about grease of some sort to start with - easy to apply and lsten to the effect, and reversable.