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Is the Infinity polydome replaceable with any IMG midrange?

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BSEYE

New Member
Guys, I need your help with the infamous polydome issue.

as expected the polydome yellowed out and cracked.
I tried the Midwest driver drop-in replacement and it sounded horrible.. too bright. (Millersound not an option due to no international service policy that they have..)

Soo.. i tried ordered these replacement diaphrams with the voice coil.. had my usual refoamer replace them.. something sounded off so i ran a frequency sweep, the whole midrange area from crossover to crossover point had a drop of about -10db..
Also some distortion at loud levels in the 1khz region, audible with some music, and definitely with any piano piece.

honestly my two other Infinity's both have a 4" and a 5" midrange and sound glorious, so the question is, is there an IMG midrange that is 4 ohm (the kappa 6 is spec'd at 4-6 ohms..) and would fit and sound okay with the current crossover spec of 800, 3800 hz..

Thanks for reading and appreciate any input.
 

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BSEYE said:
Guys, I need your help with the infamous polydome issue.

as expected the polydome yellowed out and cracked.
I tried the Midwest driver drop-in replacement and it sounded horrible.. too bright. (Millersound not an option due to no international service policy that they have..)

Soo.. i tried ordered these replacement diaphrams with the voice coil.. had my usual refoamer replace them.. something sounded off so i ran a frequency sweep, the whole midrange area from crossover to crossover point had a drop of about -10db..
Also some distortion at loud levels in the 1khz region, audible with some music, and definitely with any piano piece.

honestly my two other Infinity's both have a 4" and a 5" midrange and sound glorious, so the question is, is there an IMG midrange that is 4 ohm (the kappa 6 is spec'd at 4-6 ohms..) and would fit and sound okay with the current crossover spec of 800, 3800 hz..

Thanks for reading and appreciate any input.
Click to expand...
I also have a IMG variant that will probably fit in my parts collection. I can get the number. If you are going to go black, the new sartori would be fantastic and better than any of the original infinity drivers
 
jefferylhenr said:
I also have a IMG variant that will probably fit in my parts collection. I can get the number. If you are going to go black, the new sartori would be fantastic and better than any of the original infinity drivers
Click to expand...
I would prefer to use an Infinity IMG or the polydome you mentioned. The part number would be great so I can fish for one, im not familiar with sartori but will look it up, thanks for the information!
 
This is what I put in my last set. I have had a number of the Kappa 6’s both with working polydomes and with this driver as well. It sounded great.
 

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jefferylhenr said:
This is what I put in my last set. I have had a number of the Kappa 6’s both with working polydomes and with this driver as well. It sounded great.
Click to expand...
Cant find those on ebay but thanks ill keep looking,
Are these the polydomes you're talking about?
 

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The Polydomes (in the above pic) from the RS4b will not work properly in the Kappas as they do not go low enough. You didn't say which speaker you wanted to use them in, but if it's a Kappa 8, 8.1, 9 or 9.1, theoretically you could modify the crossover to get the midbass coupler to play higher to cover that range; however, I wouldn't recommend that since Infinity's crossovers are pretty complex and you're basically talking about reengineering the whole speaker at that point (ETA: I see you have a Kappa 6, which wouldn't be a good candidate for that anyway).

The only IMG midrange that I'm aware of that is a drop-in replacement for the Kappa Polydome is the RSDS Polydome, originally designed for automotive use, but they are extremely rare these days. @BSEYE are those the silicone replacement diaphragms you tried? They've been discussed here before as not being good. Correct replacement diaphragms should be transparent or very close to it. One of our members was at one time making replacements but he stopped because it was too labor intensive to do the repairs and he wasn't comfortable selling the domes by themselves.
 
swechsler said:
The Polydomes (in the above pic) from the RS4b will not work properly in the Kappas as they do not go low enough. You didn't say which speaker you wanted to use them in, but if it's a Kappa 8, 8.1, 9 or 9.1, theoretically you could modify the crossover to get the midbass coupler to play higher to cover that range; however, I wouldn't recommend that since Infinity's crossovers are pretty complex and you're basically talking about reengineering the whole speaker at that point (ETA: I see you have a Kappa 6, which wouldn't be a good candidate for that anyway).

The only IMG midrange that I'm aware of that is a drop-in replacement for the Kappa Polydome is the RSDS Polydome, originally designed for automotive use, but they are extremely rare these days. @BSEYE are those the silicone replacement diaphragms you tried? They've been discussed here before as not being good. Correct replacement diaphragms should be transparent or very close to it. One of our members was at one time making replacements but he stopped because it was too labor intensive to do the repairs and he wasn't comfortable selling the domes by themselves.
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Its kappa 6's yes. I know about the RSDS and gave up on trying to find a pair. Although, theres a pair installed on Kappa 7's for sale now at ebay.. im not sure if these are silicone but they do feel like that, and they're from a different seller than that famous one that was selling them, it comes with a VC attached, anyway, a failure to implement.
I have no experience with crossovers so thats a no-go. Im mainly looking for an IMG Cone that is the same ohm as the polydome and can play 800-3800hz well.. so maybe a 4".. i don't mind modifying the cabinet because at this point its either this solution or they end up in the trash as they're useless.
 
OK, well the midrange in the Reference Four, Five and Six might work; possibly also the mid from the Crescendo CS3007/8/9 (they look pretty similar to the mids in the Reference models, but with different trim), as well the mid from the Kappa 5.1 (may be the same as the Crescendo mids). But I don't know if any of those models were sold outside the US.

Also look out for the mids used in the Delta series (not the Gamma/Delta, that's a whole different beast that uses EMIMs). Those were made in Denmark and I believe sold around the world. There are a few other Infinity models such as the Reference 51/61/71/81 and Kappa 70/80/90 that were not sold in the US, that have midranges that might work, but I'm not too familiar with those.
 
Funny that my other two Infinity speakers are Ref 6 and Kappa 5.1.. i have a spare pair of kappa 5.1 midranges, might give those a go.
Although, the kappas are spec'd at 8 ohms and the ref six 6 ohms..
4" in the kappa,
5" in the ref
 
BTW, there's a reason that the Polydomes are larger than other Infinity domes or most other midrange domes: they were designed to play lower frequencies so they could be crossed over from the 12" Infinity woofer in the Kappa 7 without a midbass coupler.

If the actual impedance of the Kappa mids is 8Ω you might be able to get away with putting a 3 or 4Ω resistor in parallel with it to avoid changing the crossover frequencies too much...But you'll need something that can handle a few watts (doesn't need to be as much as the speaker can handle, as most of the power goes to the bass anyway). Probably 20W would be sufficient. And since the resistor is going to absorb half the power going to the mid, you'll probably need to bump up the level control for it. No matter what value you use it's not going to be an exact match since impedance of a speaker driver is a curve, not a single number, and a simple resistor's impedance is going to be constant along the entire frequency range.
 
I wish they just used a cone midrange instead, I actually prefer the cones.. I feel it has a narrower dispersion and therefore more forward sounding.
this should be the Kappa 6 manual.. i know it says RS-6 kappa, but those RS-6 came with an 8" woofer, and the midrange partnumber here corresponds to the eggyolks.
swechsler said:
BTW, there's a reason that the Polydomes are larger than other Infinity domes or most other midrange domes: they were designed to play lower frequencies so they could be crossed over from the 12" Infinity woofer in the Kappa 7 without a midbass coupler.

If the actual impedance of the Kappa mids is 8Ω you might be able to get away with putting a 3 or 4Ω resistor in parallel with it to avoid changing the crossover frequencies too much...But you'll need something that can handle a few watts (doesn't need to be as much as the speaker can handle, as most of the power goes to the bass anyway). Probably 20W would be sufficient. And since the resistor is going to absorb half the power going to the mid, you'll probably need to bump up the level control for it. No matter what value you use it's not going to be an exact match since impedance of a speaker driver is a curve, not a single number, and a simple resistor's impedance is going to be constant along the entire frequency range.
Click to expand...
 

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BSEYE said:
Soo.. i tried ordered these replacement diaphrams with the voice coil.. had my usual refoamer replace them.. something sounded off so i ran a frequency sweep, the whole midrange area from crossover to crossover point had a drop of about -10db..
Also some distortion at loud levels in the 1khz region, audible with some music, and definitely with any piano piece.
Click to expand...
The most likely cause of the lower than expected output is the voice coil is not properly located in the magnet gap. If these are based on the same soft dome that I've been able to get here in the US., the shape of the dome material is slightly less convex than the originals and is dropping the voice coil down too far into the gap. A shim is required between the magnet frame and the plastic ring the dome is glued to. This will lift the voice coil up into the correct position.

The distortion is likely due to the voice coild not being centered properly and rubbing on the magnet or the pole piece.
 
@seifreit I've linked to you in the past regarding replacement polydomes. Is the version you get cloudy like the OP's? Or clear like the version that AVA used to sell?
 
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seifreit said:
The most likely cause of the lower than expected output is the voice coil is not properly located in the magnet gap. If these are based on the same soft dome that I've been able to get here in the US., the shape of the dome material is slightly less convex than the originals and is dropping the voice coil down too far into the gap. A shim is required between the magnet frame and the plastic ring the dome is glued to. This will lift the voice coil up into the correct position.

The distortion is likely due to the voice coild not being centered properly and rubbing on the magnet or the pole piece.
Click to expand...

I did not have much hope in my refoamer anyways, not the best in the world but for simple tasks he does the job done. This on the other hand im sure he has never dealt with before and was his first time.

These are what I ordered.. recommended by someone that installed them himself and said they sounded amazing and "a little warmer",

1x Diaphragma Polydome 3" + coil kompatibel für Infinity Kappa

A suitable IMG midrange will fix all my issues.. 4 ohm, 88 db, handles 800-3800, so 3-4" would be suitable

EDIT: ive sent them back to the refoamer to check them.. but i assume any proper check or fix will have the new diaphrams damaged.
 
Tried the 902-6770 kappa 5.1 midrange and a mountain style peak in FR of about +8db from/to crossover points, Unusable without crossover modification.
 
swechsler said:
@seifreit I've linked to you in the past regarding replacement polydomes. Is the version you get cloudy like the OP's? Or clear like the version that AVA used to sell?
Click to expand...
It's semi-translucent like AVA. I had Bob do a set for me before he stopped and they look comparable.
 
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