Using other tweeter instead of RD0198-1 to replace SL2500 in Monitor 7 series 2

xenonsky · April 5

The SL2500 tweeters on my Monitor 7 series 2 are sounding dull and dim.
I realize the RD0198-1 are the replacements for SL2500, but they cost $61.50 each (https://reconingspeakers.com/product/polk-sl2500-tweeter/) with shipping to Hong Kong it'll run me close to $150 or more. (and I only paid around $100 for the speakers)

I just purchased and installed an alternative set of tweeter same as this one here http://www.kasun.com.cn/product/p86.html which run me only $25 a pair included shipping. So far they sounded really great, and brings back the high frequency airiness.

The Kasun brand SPC-1341 tweeter above are 6ohm (like the RD0198-1) and 91db sensitive rated at 70 Watts (I couldn't find sensitive or watts rating of the RD0198-1). Frequency response 1250Hz to 20kHz (it does not go as high as RD0198-1 I think, and SL2500 goes up to 25kHz). So they're similar enough given the price it's worth a try. (although I had to make custom bracket faceplate to mount it)

The Monitor 7 series 2 rated at 89db sensitivity, and the alternative tweeter above rated at 91 db sensitivity, seems it may play somewhat louder than the 6.5" woofer (assuming the 6.5" woofer also rated at 89db) then?

Want to see if there're any pitfall or potential problem I might run into using the above replacement tweeter instead of RD0198-1? Thanks guys.

Tony M · April 5

If you're happy, that's all that should matter.

Do you have any pics?

What are you going to do with the old tweeters?

xenonsky · April 5

@Tony M Just took some pics, the edge & circular cutouts (done with handheld jigsaw) on the ABS plastic edges are not as smooth or aligned perfectly but it works and out of sight with grill cover on.

For the old sl2500 tweeter one side was blown and I already replaced with a new silk dome coil, I may just do the other sl2500 as well (since the original one is the dimmer sounding one.)

slow_polk7 · April 5

Please stand by:

F1nut will be along shortly to properly berate you.

Gardenstater · April 5

Proof is in the listening, which only you can do

If you can work with 1/8" aluminum alloy plate, it would be better to use that than the ABS plastic because the material is much much stiffer and should be less likely to disturb the minute tweeter voice coil movements by its vibrations triggered by the midwoofer. Will stiffen the speaker baffle better than a 1/8" plate of ABS too.

Heck, maybe even use a non magnetic stainless steel like 316L.

F1nut · April 5

Want to see if there're any pitfall or potential problem I might run into using the above replacement tweeter instead of RD0198-1? Thanks guys.

You've already identified them.

xenonsky · April 5

Gardenstater wrote: »

Proof is in the listening, which only you can do

If you can work with 1/8" aluminum alloy plate, it would be better to use that than the ABS plastic because the material is much much stiffer and should be less likely to disturb the minute tweeter voice coil movements by its vibrations triggered by the midwoofer. Will stiffen the speaker baffle better than a 1/8" plate of ABS too.

Heck, maybe even use a non magnetic stainless steel like 316L.

Yeah the ABC plastic is 3mm thick and it does flex a little bit when it mount the 4 screws to the cabinet. Will see if I can source a place to fabricate a metal based plate for me, but likely it'll be expensive to paid for custom metal works. Or perhaps go with thicker 5mm harder plastic without flex may also work? Thanks.

xenonsky · April 5

F1nut wrote: »

Want to see if there're any pitfall or potential problem I might run into using the above replacement tweeter instead of RD0198-1? Thanks guys.

You've already identified them.

Possible anything in the tweeter crossover circuit I might be able to tweet to volume match the tweeter 91db sensitivity to the 6.5" woofer's 89db sensitivity?

F1nut · April 5

xenonsky wrote: »

F1nut wrote: »

Want to see if there're any pitfall or potential problem I might run into using the above replacement tweeter instead of RD0198-1? Thanks guys.

You've already identified them.

Possible anything in the tweeter crossover circuit I might be able to tweet to volume match the tweeter 91db sensitivity to the 6.5" woofer's 89db sensitivity?

You could add a small value resistor in series to the positive circuit going to the tweeter. Maybe start with a 0.5 ohm/5 watt to establish if the value needs to go up or down.

Personally, I'd get the correct tweeters. In time, the money spent will be a distant memory.

Toolfan66 · April 5

You know, maybe someone around here has a set of the face plates from the 198 or 194 tweeters, I’m not sure if the hole to hole matches, but if it did, they would look better than what you have going look wise..

I am with Jesse, I would get the correct tweets..

DaveHo · April 5

I've rebuilt a couple SL-2500 tweeters using these domes from eBay:

https://ebay.com/itm/395318669766?_skw=Polk+SL-2500&itmmeta=01JR4GD94ZG3XSRE6DVFEN3BT7&hash=item5c0ad431c6:g:ke8AAOSwi4NlT5Ml&itmprp=enc%3AAQAKAAAA4FkggFvd1GGDu0w3yXCmi1ez6Rt2BYtu0qKZtq1Mw%2FGxQ7teUh7s%2FdVitUvfCyVj%2FvM9ge%2Bs5ksZ2o3oYO49nYZBvIt2geX%2FZsNGkG5LwXsUVEFH2bIrBAgan8tkckzdTremyix5MefwROstMNZysZn9QfYTp2xTh527W%2FU%2Bt4GEXcPaMswnQCoFxBs4NhFjzPQxZsi9O6QcRBuOP9oSkzYAIKu5edW5nlX5qS8HuHnZfWrHV%2FB2qMPILSh%2FDv1%2F5C%2FQ7djqZ33UN9j6jncuRPGZKAAjwe4N9d4dLj0o4ldV%7Ctkp%3ABFBM1pK1kMFl

Also replaced the ferrofluid at the same time. They currently reside in a pair of 8tl's. I also have a pair of series two 7s with SL-2500s. New ferrofluid in those also. I don't notice a difference between the two.

xenonsky · April 6

DaveHo wrote: »

I've rebuilt a couple SL-2500 tweeters using these domes from eBay:

https://ebay.com/itm/395318669766?_skw=Polk+SL-2500&itmmeta=01JR4GD94ZG3XSRE6DVFEN3BT7&hash=item5c0ad431c6:g:ke8AAOSwi4NlT5Ml&itmprp=enc%3AAQAKAAAA4FkggFvd1GGDu0w3yXCmi1ez6Rt2BYtu0qKZtq1Mw%2FGxQ7teUh7s%2FdVitUvfCyVj%2FvM9ge%2Bs5ksZ2o3oYO49nYZBvIt2geX%2FZsNGkG5LwXsUVEFH2bIrBAgan8tkckzdTremyix5MefwROstMNZysZn9QfYTp2xTh527W%2FU%2Bt4GEXcPaMswnQCoFxBs4NhFjzPQxZsi9O6QcRBuOP9oSkzYAIKu5edW5nlX5qS8HuHnZfWrHV%2FB2qMPILSh%2FDv1%2F5C%2FQ7djqZ33UN9j6jncuRPGZKAAjwe4N9d4dLj0o4ldV%7Ctkp%3ABFBM1pK1kMFl

Also replaced the ferrofluid at the same time. They currently reside in a pair of 8tl's. I also have a pair of series two 7s with SL-2500s. New ferrofluid in those also. I don't notice a difference between the two.

@DaveHo I used the exact same silk dome to replace one of the SL2500 which had blown coil, but I didn't have any ferrofluid around to fill in (I need to purchase some then). Even after I replaced the dome on the SL2500 the volume still sounded a bit not as loud enough (compare to the SL2000 on my 5jr+). Would it be due to dried up or evaporated ferrofluid? Thanks.

By the way I noticed the origin silk dome on SL2500 the height of the coil itself is shorter than the replacement silk dome in the ebay picture. So the original SL2500 coils has less number of coils, does that make the dome with less coils more efficient or easier to drive than a coil with more winding? Below is the silk dome coil I've taken out from my SL2500 for reference.

xenonsky · April 6

I tried to do a 20hz to 20khz frequency sweep track and held my iphone's mic about 3 feet in front of the tweeter/woofer and it seem I'm getting pretty even volume or gain to the left and right of ~1200hz.

Does this suggest the tweeter is not playing particularly louder than the woofer? (assuming the woofer has 89db sensitivity and the tweeter has 91db sensitivity)

Gardenstater · April 6

3 feet away you are going to be getting room effects. That's why, if you can't do a gated response with a sweep tone (throws out the room delayed reflections that come back to the mic), it is best to hold the mic an inch or so from the tweeter's dome. You could then do the same thing with the woofer, maybe 6" away from the dust cap.

I like to use a sweep tone (which you did?) instead of a steady pink noise or white noise signal. Also, you should disgregard everything below 200 Hz or so. That's what Danny Richie does.

xenonsky · April 6

Gardenstater wrote: »

3 feet away you are going to be getting room effects. That's why, if you can't do a gated response with a sweep tone (throws out the room delayed reflections that come back to the mic), it is best to hold the mic an inch or so from the tweeter's dome. You could then do the same thing with the woofer, maybe 6" away from the dust cap.

I like to use a sweep tone (which you did?) instead of a steady pink noise or white noise signal. Also, you should disgregard everything below 200 Hz or so. That's what Danny Richie does.

Thanks will use your suggestion to do another sweep tone test to see the results tomorrow.
I used the below sweep tone from Tidal earlier and I think it should work ok.

skipshot12 · April 6

Hey Dave,

This may be a dumb question….
Does the RD0-194 have ferro-fluid?

Also, how difficult is it to replace ferro-fluid on a tweeter like the SL2000?
Are there different weight fluids?

pitdogg2 · April 6

Not all tweeters use ferro fluid. I do not believe the sl2000 had any. It's not difficult if you can remove the VC and diaphragm. Yes there are different viscosities/weight. You should remove the old best you can. Usually an index card will work to soak it up if it still has some liquidity. It not maybe the index card will be stiff enough to break it up to blow out.

skipshot12 · April 6

Tanks

xenonsky · April 7

@Gardenstater I've done another frequency sweep test below per your suggestion.
Looking at the dark green color frequency peak bars. For tweeter graph > 1250 hz and woofer graph < 1250 hz sweep seems to have similar peak sound energy level.

Here's one with iPhone mic one inch in front of tweeter play 20 to 20K sweep.

And this one done with iPhone mic about 4-6 inch from woofer dust cap

Toolfan66 · April 7

skipshot12 wrote: »

Tanks

Gardenstater · April 7

Cool. Well one observation is that you have a couple pretty major dips in the response between 8 and 16kHz where the response they measure is pretty smooth with 1/3 octave smoothing. Not sure which it is; on axis or 30deg off axis or both averaged together? Your response could be from diffraction. You cut the hole for the dome with a jigsaw and they have a very smooth beveled edge on theirs.

As far as detecting a difference between 89dB and 91dB sensitivity I think your graphs are tough to do that because of the scale of your graphs being 20dB per division. Does your app allow adjustment of that? 5dB per division would be more like it.

xenonsky · April 7

@Gardenstater Thanks, I'll try to clean up and smooth out the opening edge a bit to see if any improvements.

DaveHo · April 7

skipshot12 wrote: »

Hey Dave,

This may be a dumb question….
Does the RD0-194 have ferro-fluid?

Also, how difficult is it to replace ferro-fluid on a tweeter like the SL2000?
Are there different weight fluids?

No ferrofluid in the 194 or SL2000 tweeters.

skipshot12 · April 7

Tanks again

Using other tweeter instead of RD0198-1 to replace SL2500 in Monitor 7 series 2

Answers