Kappa Seven: Replace the polydomes?

[jberger]

I have a set of Kappa Sevens with Polydomes in better than average condition (cloudy, but still flexible, with a 1/4" tear in one). Nevertheless, every potential buyer has tried to bargain them down based on this.

I'm considering replacing both of the Polydomes with this driver from Midwest Speaker Repair; the claim is that it was designed specifically as a replacement; they make both 4 and 8 ohm versions.

https://www.midwestspeakerrepair.co...o-mm-2150-3-inch-dome-infinity-copy-midrange/

I expect that I'll more than break even with the value of the polydomes; the question is, are these speakers better off for the upgrade?

 

[markuus3889]

http://audiokarma.org/forums/index.php?threads/polydome-replacement.789959/

 

[swechsler]

Thus far I haven't seen a thread on this forum indicating a Polydome replacement that sounds as good as the original (except possibly the RSDS polydome, which is rarer than the original). So, no, the speakers are probably not better with the replacements, but you may have difficulty convincing a buyer of that unless they're also a member here.

 

[Listnnthdark]

Seems right they would try to bargain down because of torn dome . BUT I would not be interested in purchase of any kappa with non original mid ) so no No don't replace it ( if it is working ) best option would be keep driver and have dome redone by millersound . anyone who knows will prefer this over non original mid driver . imho

 

[Tedrick]

The ONLY acceptable replacement for the Polydome is the Vifa/Scanspeak 3" dome midrange. It is a drop-in replacement, but is higher impedance (8 ohm) than the original (3-4 ohms). Not sure if this affects the sound, but should be considered. Probably the best option is to have them repaired by Bill LeGall at Millersound; they will be equal to or better than original.

 

[Archguy]

The ONLY acceptable replacement for the Polydome is the Vifa/Scanspeak 3" dome midrange. It is a drop-in replacement, but is higher impedance (8 ohm) than the original (3-4 ohms). Not sure if this affects the sound, but should be considered.

Now, this seems like a simple solution: the mfr should offer a 4-ohm version. Seems like there's enough demand for a simple tweak like that and this is a whole lot easier than starting almost from scratch, as others have proposed. They could even make the 4-ohm version white if not clear. Or am I underthinking this?

My polydomes are in perfect shape, knock wood, but it would be great to have a drop-in option and I'd happily buy a couple just to keep around for safety's sake.

Midwest Speaker Repair is selling a 4-ohm version, I know nothing about them though.

 

[slimpikkins]

Many have tried the vifa and is not acceptable as replacement. If anyone has gotten them to work with a tweek they are keeping it a secret. The new ones from midwest speaker were reviewed here but were to be found lacking. I would've put maybe fifty or so hours on those before I was too critical of them but thats me. New speakers sound different over time.

If you were keeping the kappa 7 I'd say buy a broken poly dome with a good vc, send that one and your broken one to Millersound, sell the good one on eBay before it cracks too.

If you are selling them and they work maybe hold out a little longer with the originals and tell prospective buyers about the above options. Personally I haven't been able to give speakers away lately.
Good luck.
Jim

 

[Sam1879]

Many have tried the vifa and is not acceptable as replacement. If anyone has gotten them to work with a tweek they are keeping it a secret. The new ones from midwest speaker were reviewed here but were to be found lacking. I would've put maybe fifty or so hours on those before I was too critical of them but thats me. New speakers sound different over time.

Jim

The ONLY acceptable replacement for the Polydome is the Vifa/Scanspeak 3" dome midrange. It is a drop-in replacement, but is higher impedance (8 ohm) than the original (3-4 ohms). Not sure if this affects the sound, but should be considered. Probably the best option is to have them repaired by Bill LeGall at Millersound; they will be equal to or better than original.

Hi there,

Tried the Scanspeak D7608/920010
https://www.scan-speak.dk/datasheet/pdf/d7608-920010.pdf

Bought from a local infinity repair service. They added a ceramic resistor in series to fix the volume difference.
Had just a little bit of burn in now. Sounds in my opinion (with neutral knobs on a Kappa 8.1) a bit more detailed, but less laid-back compared to an old original.
Sounded a little bit bright first, but i'm starting to appreciate it. I'll need some time listening to it to give it a recommendation / or not. But I like it so far.
Though did not fit exactly in to the driver hole.

Did some in room measurements, but don't take them too serious. Aren't made in a too exact way, and are in room.
Blue line is original driver.

 

[Bkphoto]

This is another rabbit hole,

there isnt any drop in that sounds as good as a properly functioning original....get them fixed by millersound and move on....

 

[Sam1879]

if „as good“ means same sonic signature, compared to this driver, you‘re right fore sure. for an very old man with 1 khz hearing loss maybe not

 

[Bkphoto]

Random scenarios aside, if you want them to sound like they are supposed to see my prior post...

 

[swechsler]

there isnt any drop in that sounds as good as a properly functioning original....get them fixed by millersound and move on....

Or even better, get it repaired by our own @Bobbyd38 (website here)

Note that I have no affiliation with Bobby, and am not even a customer yet, but we've had good reports from others here.

 

[Bkphoto]

Of course, I’m just going from my own experience

 

[elnaldo]

Regarding the OP, to replace the original domes to sell a speaker, I think (same thing I'm telling to a KAppa owner who wants to sell them with broken domes), I'd leave the original part in, and leave the repair to the new owner, or do whatever repair he wants to do. There is a chance that you choose "x" repair service or "x" replacement speaker (probably quite expensive), and the buyer don't like it because he thinks that "z" repair is better, or "z" replacement driver is better.

Speakers to keep for yourself are different. In that case, I'd fix the original following a bit the reviews of people who already did it, and then you'll have your own experience.

 

[E.Man]

Or even better, get it repaired by our own @Bobbyd38 (website here)

Note that I have no affiliation with Bobby, and am not even a customer yet, but we've had good reports from others here.

This if you're in the US. From AU it's too expensive.

 

[swechsler]

This if you're in the US. From AU it's too expensive.

No surprise there, but you'd have the same problem with Millersound. I'm assuming that shipping to/from Europe is similarly expensive...

 

[Sam1879]

Regarding the OP, to replace the original domes to sell a speaker, I think (same thing I'm telling to a KAppa owner who wants to sell them with broken domes), I'd leave the original part in, and leave the repair to the new owner, or do whatever repair he wants to do. There is a chance that you choose "x" repair service or "x" replacement speaker (probably quite expensive), and the buyer don't like it because he thinks that "z" repair is better, or "z" replacement driver is better.
Speakers to keep for yourself are different. In that case, I'd fix the original following a bit the reviews of people who already did it, and then you'll have your own experience.

I agree technically. However in my interpretation of sales psychology probably many (not so technically informed) people might not go in to the risk of buying a speaker described as flawed/defect. Or they are only willing to pay much less for it. Caused by discomfort about not knowing how much effort it will be to fix it.


In my case changing the drivers to Scanspeak D7608/920010 (including new driver frame) led to good results; and i could keep the original domes. Is a little complex to implement by your self, but not a huge thing if you know what to do. -> need to work very exactly because the frame is a bit bigger than the original. Maybe other scews are needed and maybe something like sealing strip for the inside. Worked good for me. Probably it would also be possible or even better to cut the outer frame by ca. 3mm.
Recommended Resistor for matching: Ceramic Resistor, 20 Watt - 2.7 Ohm.

My Recommendation when you don't have time and tools and want to try with a D7608/920010 : Let it change by a Infinity repair service inclusive driver frame or maybe better: let the repair service implement the new driver in to the original driver frame if they offer doing this. But if you want to keep the original domes it's not possible to use the new dome in the original driver frame.

The former subjective "harshness" vanished after some burn-in time and after a unmounting and remounting the drivers again. (maybe my brain got burned in, too...) Don't know exactly what happened.

But yes, the "original sound" of the speaker seems to be altered a little bit with these replacements. Not harsh anymore but maybe less laid back than before. (New in-room measurements attached).

I dont have experience with results after changing the dome material on a original driver , but what i can say is i'm happy to have fixed the over 25 years old, yellow, detoriated polydome. Didn't notice it was detoriated so much, it was really at the end of its lifetime.
After this long time the old yellow dome on my speakers just really didn't perform anymore as could, especially at louder transients. May be that'ss different for better stored/threaded speakers of course.

So, if your polydome is old, yellow and performance might be lacking at certain points, repairing them is absoulutely worth it!




Lower part of picture is an older measurement.

 

[Bkphoto]

I would rather buy a speaker that is all original and needs a restoration over something modified with aftermarket parts...

 

[Kevinbigdog]

Hi there,

Tried the Scanspeak D7608/920010
https://www.scan-speak.dk/datasheet/pdf/d7608-920010.pdf

Bought from a local infinity repair service. They added a ceramic resistor in series to fix the volume difference.
Had just a little bit of burn in now. Sounds in my opinion (with neutral knobs on a Kappa 8.1) a bit more detailed, but less laid-back compared to an old original.
Sounded a little bit bright first, but i'm starting to appreciate it. I'll need some time listening to it to give it a recommendation / or not. But I like it so far.
Though did not fit exactly in to the driver hole.

Did some in room measurements, but don't take them too serious. Aren't made in a too exact way, and are in room.
Blue line is original driver.

What was the impedance of the resistor?

 

[Sam1879]

CeramicResistor, 10 Watt - 2.7 Ohm.
While i was installing the new drivers on one of the resistors a connection wire on the resistor broke away. (my fault) Changed them to Ceramic 20 Watt 2.7 Ohm. Should not make a difference. ( or does it?)