Please give me some feedback on some old Polks I have

zuke8675309

I have a pair of Polk RT12s that I bought new 24 or 25 years ago. They were used and enjoyed for a long time but the past 8 or so years they've been little used as part of a sytem in our basement because over time our living pattern has changed in our house as our kids have taken over the basement and my wife and I watch TV & listen to music on our main floor.
We recently upgraded our TV and receiver (Yamaha TSR700) where my wife and I watch TV and I decided to reclaim these R12s and move them to our main listening/viewing area.

I hadn't really listened to them for a while but now listening to them at lower volume I feel like they sound...dull and kinda muffled or muted. Blech. At first I thought maybe there was a problem with a tweeter. After playing some various test tones, the tweeter is not damaged. When I turn up the volume quite a bit they are definitely MUCH better and seem to come alive.

I don't remember them sounding like that at low volume. Am I maybe misrembering? Anyone know if these speakers just need to be played loud? Is there some way to measure and/or fix what I'm describing in EQ?
Or is there a part that's gone bad after 25 years contributing to what I'm describing?
Or am I just crazy?

pitdogg2

You have an HT AVR
1. Not much power (weak)
2. Check make sure you're in 2ch mode
3. Did you run the calibration program?
4. Make sure all parameters are set to flat and balanced between front 2 speakers

audioluvr

What @pitdogg2 said plus
1. Old crossovers needing refreshed
2. Corroded connections inside speakers and between them and source components
3. Possibly comparing them to a bright pair of HT speakers?

boston1450

Did they sound like that when in basement ? Double check your Pos/Neg wires to rec & speakers & make sure they are + - hooked up correctly.

zuke8675309

Hmm, the ends of the speaker wire showed some oxidation. I suppose I should/could clean them up.

I did run the receiver's calibration program and was running it in 2 channel mode. And yes, they sounded dull when I played them in the basement, but that was the first time in a long time (maybe a few years) that I listened to music on them.

I didn't know that crossovers could go bad over time, but I suppose it makes sense because I've seen components on computer motherboards go bad. Do crossovers needing to be refreshed/replaced have a specific effect or is it rather random?

audioluvr

I have a pair of RTA 11T's that had a tweeter circuit not working. After redoing the crossovers everything worked again. I didn't bother isolating the bad component because I was planning on replacing them regardless.

RTally

zuke8675309 wrote: »

I didn't know that crossovers could go bad over time, but I suppose it makes sense because I've seen components on computer motherboards go bad. Do crossovers needing to be refreshed/replaced have a specific effect or is it rather random?

Crossovers include capacitors, inductors, and resistors. Capacitors, in particular, are susceptible to failing as they age. Electrolytic caps have an expected lifetime of 20 to 25 years. As they age, their capacitance values will change, often drifting upwards. The higher capacitance lowers the crossover frequency for high pass filters. Sometimes they fail catastrophically, resulting in an open circuit (and no sound from the tweeter).

The equivalent series resistance (ESR) also increases as electrolytic caps age. For caps in high pass filters, high ESR is audible as a loss of highs, and, in bad cases, the speaker sounds muffled, as if a blanket is thrown over the speaker. The change in ESR is often more noticeable than the change in capacitance value.

Recapping is when only the capacitors are replaced. The caps can be replaced like-for-like using electrolytics. I only do this for low quality speakers that have low value. As the speaker quality/value goes up, so too does the cost of caps.

I replace the caps in one speaker and then compare the recapped to the original speaker. Generally, the difference is audibly significant, but not always.

The inductors and resistors are not always replaced when recapping. Inductors do not age. Resistors will age if they have been subject to excess power. Look for signs of heating around the resistor. Generally, higher quality inductors and resistors are available and those wishing to spend the time and money often replace them. This is often worthwhile for the better quality/valuable speakers.

zuke8675309

Thanks for the education! I learned quite a bit. I think I'm going to replace the capacitors as this seems like a pretty straightforward and beginner friendly project. I've been looking at some speaker building projects and this is a way I can get my feet wet on the electronics part.

The schematic I was able to find shows 2 caps needed for each crossover. A 2.2 uF and 10uF both +/- 10%, 100v, mylar, DF <=5%.

When I look on Parts Express for crossover caps, it looks like I can choose an electrolytic with the exact same specs for 75cents or metalized polypropelene with better specs +/-5% tolerance, 250v for $2.
Is it important to choose one over the other and if so, why?

Again, thanks for the education!

rooftop59

@westmassguy @VR3 @F1nut

These guys, among many others here, can help you. I cannot 😂

pitdogg2

If you can I'd swing for the metalized polypropelene caps. I'd also look for some clarity caps instead of the dayton caps.
Polypropylene are better caps than the Mylar IMHO.

https://www.madisoundspeakerstore.com/claritycap-caps/?gclid=CjwKCAiAudD_BRBXEiwAudakX-qA7mlknp5PfdODMRTtT8EdD4BTMMxG-QPgZSCtONVwZFJhkHJ4EhoCm_gQAvD_BwE

The CSA are better than dayton caps. You can go up more if you have the cash. Sonic caps are very well regarded and they have all the correct values. Do not worry about the 250v rating as that is pretty standard. They will be MUCH larger in size so you will need to be creative when placing on the board. I'd also recommend vashay-mills resistors to replace the ceramic installed by factory. Use same ohm rating but step up to 10 or 12 watt. They higher voltage has better heat dissipating ability.

http://www.soniccraft.com/index.php/sonicap-gen-c-301_49_50

They'll have all you need but they are more expensive than CSA caps.

F1nut

^ What he said ^