SL2500, RDO-198, Original vs Series 2 MW6502s

mascab

I would like to know how the SL-2500's are supposed to sound, and how the RDO-198's sound compared to them? I know the RDO-198's are deemed better sounding, but what are the differences, how are they better, does the sound depend on what speaker they are in? I saw xchops thread.
http://forum.polkaudio.com/discussion/171202/xschops-modded-5jr
Would a newer SL tweeter be even better?

Are there any sonic differences between the series 2 MW6502's and older ones? Is there a difference between 4 and 8 ohm versions? Do they vary? The drivers in my M5Jr+'s look, and may sound different than the ones my M4A's.

I am asking because my 4A's sound pretty good, but a pair 5jr+s I recently picked up sound like crap, and I am not sure if it only this pair, or replacing the tweeters or crossovers or both would help. $200 for RDO-198's and a crossover rebuild is more than I paid for the speakers, and way more than I planned on spending. I don't think I could get that back. If the MW drivers are that different or bad, then its a waste.

TLDR history below.

This is a carryover from a thread I resurected
http://forum.polkaudio.com/discussion/162973/opinions-monitor-4-or-5jrs

I have a pair of Monitor 4A's from the 80's and recently got a pair of 5jr+s Series 2 that have the SL2500 tweeter. Everything is working fine on the 5's, but the very high frequencies are barely there and much of the mids to highs are muddy and blurred. There is little detail. My 4s s have much more detail and better highs. I have heard Montor 5's and RTA 11T's with the SL-2000 tweeter. I don't like the tweeter, but there was much more clarity, detail, and highs above the peak.

I borrowed a single spare SL-2000 and crossover that I think came from a 5jr to try a comparison with. The highs were there. There was much more high end detail, but the mids still sounded a little muddy but were better. The RTA11's and my 4's have much more detail overall. I did notice my 4's might be lacking a little in the upper mids. It might be worth a crossover upgrade for them.

My go to track was RUSH, Clockwork Angels, Track 4, about 1 minute in when the vocals kick in. With the SL-2500 in the 5's there was very little high hat or upper cymbals, and once he starts singing the guitar gets lost and the voice is not well defined. With the SL-2000 and crossover for it, the high hat and upper cymbals are there and there is more detail over all. It was still a bit muddy when he starts to sing, and muddy over all. My 4's and the RTA11's had much more separation of detail with the RTA's being the best aside from the SL-2000 sound.

westmassguy

The RDO-198-1 Silk Dome, was designed by Polk as a drop-in replacement for the SL2500 and SL3000. It's light years ahead of both. There is no difference between older and newer 6502s from that era. The replacements available now do have a different appearance, but are functionally the same. 6502s are 4 ohm, there is no 8 ohm version. If your 5s sound like crap, and the tweeters are functioning, it's most likely the cheap NP Electrolytics Polk used in the late model crossovers.

westmassguy

If the NP Electrolytics in there now are shot, then replacing them with new NP Electrolytics, may make them sound better.
Two 6.8uf Claritys will work just fine, I do it all the time.
Sonic Craft will match 13.5ufs for an additional fee. I would call or email them for a quote.
Use the Mills 10 or 12 watt, or Mundorf MOX 10 watt in place of the existing 5 watt sand-cast Resistor. I've replaced many 5 watt resistors that were burned out, or overheated to the point where the circuit board was burned.
When you install the new resistors, make sure they're about a 1/4" or more above the circuit board. This allows air to circulate, and keeps them cooler.

Gunther16

Can't argue with westmassguy..............only listen/read and be educated.

mascab

Not arguing, only trying to be more sure something isn't completely wrong and wasting money on the caps.

Would two 6.8 uF 50V +/- 10% inexpensive electrolytics have a shot at sounding better, or even a 12 uF? I think I can get some from work, or from an electronics shop near by for ~$5 total.

If I go big, get custom 13.5 uF 200V Gen1 Sonicaps? Should they be matched? I haven't seen that Clarity makes custom caps. I've gathered from this thread http://forum.polkaudio.com/discussion/158701/crossover-question-monitor-5jr and some other posts that a custom cap would be better and probably less expensive than two 6.8's.

Could a bad resistor throw the sound off? They should be easy to check if they are way off. If get the caps I might as well get the mills resistors two? 1.0 Ohm, 5W? Is there a benefit to getting the 12W resistors?

mascab

I see now not to click yes to answering the question more than once. It messes with the thread order.

Thanks for the cap info. Are matched caps beneficial for left and right speakers or mainly when you have a pair of caps together?

I see that my 4A use two caps per speaker instead of a cap and inductor. Would it be beneficial for the caps in each speaker to be matched? If wanted to save some money and go with cheaper caps in the 4A, are their any recommendations? Is there much sonic difference between "good" caps, or is it mostly tolerance and life span? Due the cheaper brands offer matching? Would having them all be near the same value, but all off by 6 or 7% be better than all varying but varying withing a +/- 3 or 5% range?

westmassguy

It's always best practice to match the value of the original caps, and from right to left as well.
The conservatively priced MP Caps I use, are Daytons, and Clarity PX.
Daytons come in 5% and 1% tolerance. It's the same cap, they're just binned separately, and you pay a premium for the tighter tolerance.
Clarity PX are 5% Tolerance.
Sonic Craft is the only vendor I use that will hand match for an additional fee.
The difference in sound quality can be very dramatic between the lower priced caps and the higher end.
Lifespan is not an issue with metalized polypropylene caps.

mascab

Thanks, good to know about the different caps. So metalized polypropylene caps will last the speakers or my lifetime?

How does the sound quality differ? Why would it differ?This part is new to me.

westmassguy

As with many things, the quality of materials, the manufacturing process, and quality control all play a role in the end product. With passive components in the audio signal path, you want as much of the original signal to pass through un-molested as possible. Everything alters the original signal to some extent. The key, is finding the component that does the least. What's most important, is how they sound to your ears.
As for life expectancy, as long as the seal on the cap is intact, and the rated voltage is never exceeded, MP caps should last indefinitely in a crossover.
MP caps, when used in other applications, can fail over time however.

Schurkey

No electrical part is "pure". Capacitors have some amount of resistance. Resistors can be inductive. Inductors have resistance. All electrical parts have some amount of resistance, capacitance, and inductance; although one of these traits is dominant. All electrical parts create some amount of noise, too.

In the case of capacitors, electrolytics have high resistance. Film caps tend to have much lower resistance. More signal gets through the film capacitor than the electrolytic, and that signal provides more power to the driver. The film cap tends to have lower noise than electros, too--although there's still some noise even in the best cap.

There are folks who refuse to replace an electrolytic cap with a "superior" film cap, they say it changes the voicing of the speaker. The rest of the speaker was designed to be used with the crappy electrolytic cap. In other words, the speaker designer INTENDED the crossover to have all that "extra" resistance, and noise.

I say "bullsh!t", the speaker designer either didn't have a source of better caps, or the design was compromised to hold the price down. HOWEVER, speaker voicing does change when crossover parts are substitued--and the general consensus with SDA speakers is that dumping the electrolytics for film caps makes a substantial improvement.

Old electrolytic caps degrade. The rule of thumb is 20--25 years is the expected service life of an electrolytic cap. It may be that they are audibly degrading long before that. Replacing old electrolytics with fresh electros of similar quality should improve speaker performance...but...sh!!t-canning the electros in favor of film caps is even better.

mascab

Great information. I guess the added resistance in the electrolytic caps does not change the crossover points otherwise resistors would be added to the circuit.

I read about the poly fill in another thread. Where is the poly supposed to be in the 5jr+? Mine is all stuffed up behind the tweeter. There is none behind the MW. It feels like there is some missing. If I were to pull it down it would be a thin sheet and not stay in place so I pushed it back up. I noticed this when I tried different caps.

I picked up some cheap electrolytic caps to test out the sound. I got 4 6.7uF 50VDC caps that are supposed to be +/- 10%, but one guy said 15% would be more correct. They had a machine to check them, but it was not functioning, and I was told it is not that accurate for these lower values. I got two 11.7uF 100VDC that are supposed to be +/- 3 to 5%. They were super cheap and not labeled except for the plastic bag they were in. The leads came out the same end. They had a plus and minus like the inline ones and was told they were the same. Total cost was less than $10.

I sniped the original caps, and at first clipped the new 6.7's in place in parallel. They sounded better, but still not very clear or close to my 4's. I clipped in the 11.7's and it sounded better yet. Cymbals sounded better, but the midrange was still not clear. My 4's still sounded better.

I went to solder the leads instead of clipping them, and the + sides of both the 11.7s broke right at the base. this explains the extreme low price. Would soldering make a big difference? I was hoping to find out with the 11.7s, Trying to solder the two 6.7's is more work and not likely permanent if I keep the speakers. I want to see if I need more poly fill first.

There were some 35VDC caps. Could I try those as long as I don't play the speakers too loud? If I do play them too loud will the cap fail and open the circuit, or could I damage the speakers? Would two identical 35VDC caps in parallel be close to a 70VDC cap, or is 35VDC still the weakest link?

mascab

I found out the 35VDC is the weakest link