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polydome midrange help

jamset

jamset

Active Member
hi

i could really use some advice and help

will a dented polydome midrange (picture) affect sound and performance?

i m planning on getting infinity kappa 6 speakers so i went and audition them today. one of the polydome midrange is dented. i could perceive more presence of mid and high frequencies on the speaker with no dent on its polydome, so i guess it does affect the sound? i think i just answer my own question but i would like to have some advice form somebody who has had prior experience with the speakers. bass is sounding nice by the way!

sorry for the crappy picture (good camera, bad photographer)
 

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In this case the pressed in dome will propogate a very different wavefront than the dome that hasn't been damaged, so yes the difference you hear is likely real. Also, if there is a form behind the dome that the pressed in dome center has come into physical contact with, that would really cause sonic hijinks!

Another issue is that the various forms of ploydome mids used by Infinity speakers during the 1980's were often prone to dome cracking and disintegration. The Kappa 6 is a fine sounding speaker when driven by a powerful amp that can handle unusual loads, but the poly-dome midrange driver problem is endemic to all the Infinity models that used them. If Infinity fans have figured out a suitable replacement that's readily available, that's something I would want to know before buying a pair.

Also, be sure to look on Fleabay for people parting out these types of speakers, and if you buy a used driver unit make sure it will be packed and shipped properly! That is always a risk with exposed, protruding dome drivers that have no protective shield.
 
sounds like stickman has the technical aspects of your predicament well covered, and, though I own and love 6 Kappas myself, I've never had to deal with a dented dome, so I'll defer to his knowledge. I couldn't agree more with the statement that these are amazing speakers when properly powered..I drive mine with a Kenwood Basic M2 (+/- 220 wpc @ 8 ohms, and the ability to dig deep at lower than 8), and I couldn't be more pleased. Superbly full and balanced speakers when properly fed. I'd find OEM replacement domes were I you, but that's just me. Enjoy
 
stickman:thanks for your help, i think i will pass on those, since replacement midranges cost around 100 us dolars each and asking price for the speakers was already in the high zone...

kneeohfight: what is OEM replacement?
 
Their is no foam behind the polydome driver, and it is not diffuclt to remove the diaphram and very carefully using your finger to push that dent out. The main problem will be with time it might start cracking where the dome meets the edge of the diaphram. I would just carefully push the dent out and then use them and keep an eye for a a used replacement off an auction site. That being said, you will probably never find a fresh set of OEM replacements as they are all getting pretty old and all of them that I have seen have turned a yellowish cooler and are getting brittle with time. Vifa make a bolt in replacement driver only the diaphram is black and you probably should replace them both since they will probably sound slightly different then the orginals so you would want them to both sound equally slightly different. But in my experince I have not noticed a big difference in sound by having a dent in a diaphram's dome, maybe your ears are better then mine. I found a pair of replacements from an auction site, to replace a pair for my Kappa 8's and for now they sound great, but the time will come when they to will crack and at some point I will have to replace them with a non OEM driver as at some point all the used ones will fall to the test of time. And I would be patient as some people list the used ones with a buy it now price that is IMO to high for a driver that will just fail sooner or later. I just waited until I found a pair at a reasonable price.
 
OEM is Orginal Manufactors replacement, of which their are not OEM's left as Infinity discontinued making replacement diaphrams for the Kappa line. The Vifa is a non OEM bolt in replacment, and a lot of people say they sound just fine. But they cost around 100 dollars apiece if I recall correctly. I would only buy a Kappa 7 if it was very cheap, if it needs repair, or save a bit more and at least move up to the Kappa 8's, as they would be more worthy of spending a few hundred dollars to replace the polydomes and maybe refoaming the bass drivers. I have not heard a pair of the Kappa 7's but do have a pair of the Kappa 8's and I think they sound very good.
 
Ken Boyd said:
Their is no foam behind the polydome driver, and it is not diffuclt to remove the diaphram and very carefully using your finger to push that dent out. The main problem will be with time it might start cracking where the dome meets the edge of the diaphram. I would just carefully push the dent out and then use them and keep an eye for a a used replacement off an auction site. That being said, you will probably never find a fresh set of OEM replacements as they are all getting pretty old and all of them that I have seen have turned a yellowish cooler and are getting brittle with time. Vifa make a bolt in replacement driver only the diaphram is black and you probably should replace them both since they will probably sound slightly different then the orginals so you would want them to both sound equally slightly different. But in my experince I have not noticed a big difference in sound by having a dent in a diaphram's dome, maybe your ears are better then mine. I found a pair of replacements from an auction site, to replace a pair for my Kappa 8's and for now they sound great, but the time will come when they to will crack and at some point I will have to replace them with a non OEM driver as at some point all the used ones will fall to the test of time. And I would be patient as some people list the used ones with a buy it now price that is IMO to high for a driver that will just fail sooner or later. I just waited until I found a pair at a reasonable price.
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What he said. Use a large ball-bearing to smooth out the dome from the inside. Or Yin-Yang ball if you have one.
 
I would generally agree with others who would suggest removing the the diaphram and reforming the dome shape, on most drivers...except the Kappa Polydome midrange.
The denting has occurred for for some physio/chemical:) reason and will not appreciate helping but meddling nudging fingers and will at best eventually return to dented state or if prodded too often will crack along the dentline.
At least that's been my experience.
 
Seems there is a treatment to avoid brittle and faded domes.
 

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you can repair the dome. take it out and on the back you see a green circle. cut in there with a cutter knife a cross. Use a stoft stick to get in the dome and press very softly against it till the dome does have its orginial form
 
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