Monitor 5B scratchy audio from tweeter

AudioToaster100

Hello folks!

I have had an issue with my vintage Monitor 5B speakers for a long time, so I shelved them for about 10 years. Now I took them out again and want to fix them.

Here is my issue:
The sound emitted from the tweeter is not clear. It sounds kind of distorted. This is occurring on both speakers and happened at the same time.


When it started:
Stupidly, I used an audio splitter cable to have two audio inputs: One input from an ipod for music, one input from an Xbox. These were connected to the amplifier input. After this, the phenomenon happened with the tweeters.
Subwoofer and midrange speaker are crystal clear.


What I tried:
Ohm test on the tweeters reads 6.4 ohms.
Different amplifier results in the same issue.
Re-seating the coil on the tweeter didn't fix it. Unless it's worth trying again.


Other notes:
The amplifier this happened on is a Panasonic RE8140 which says "8 ohms only" on the output.
Both amplifiers tried are for 8 ohm speakers.
Speaker wire was unknown. I inherited the whole set.

What I'm blaming:
Could both amps be bad?
Could I have fried some component in the speakers? I only see two large capacitors, one small one, a coil, and a large 2 ohm resistor which was reading 2 ohms.
Could the tweeter coil need replacing?

I have no background in audio, but I do have a background in electronics and soldering. Perhaps someone more seasoned would know exactly what to do next to troubleshoot. I do miss the clear sound from these speakers and am hoping to get them back on track. Much thanks for any help.

Please let me know if this is in the wrong forum. I picked this over vintage.

SeleniumFalcon

Hello, welcome to Polk's forum. The most common cause of your problem is damaged tweeter voice coils, which means both tweeters will need replacing. If you contact Polk's CS department at 1-800-377-7655 they can sell you replacements. If you mention that you've joined Club Polk you should get a reduced price.

Gardenstater

Since you have a background in electronics, maybe you try installing a temporary jumper wire bypassing the polyswitches and see what happens to the sound quality. If they get tripped too many times maybe they can become faulty and produce distortion.

AudioToaster100

Gardenstater wrote: »

Since you have a background in electronics, maybe you try installing a temporary jumper wire bypassing the polyswitches and see what happens to the sound quality. If they get tripped too many times maybe they can become faulty and produce distortion.

Thanks George. I never heard of a polyswitch before this post. I guess that is what I erroneously called a "small capacitor" in my original post. I'll verify and give that a try as it seems to be the easiest thing to do before placing an order for another set of tweeters.

Thanks for the welcome and the response @SeleniumFalcon. I may end up resorting to that if I can't fix these by trying above. Glad to know that this is common behavior for tweeters that are damaged. Great advice too for the "Club Polk" mention. Never knew that either!

Can the following damage the voice coils? I want to make sure I don't repeat my mistake when I put in new tweeters.

• too high volume
• mismatching amp impedance

SeleniumFalcon

Like most things in audio there isn't a simple cause for damage in tweeters. In very general terms an excess of heat builds up in the tweeter's voice coils and this heat can cause a failure in the voice coil's wire and stop the tweeter completely. Other times the excessive heat can cause a warping of the voice coil's former and the resultant bulging can scrape against the inside of the voice coil's gap. Most good quality tweeters use a thick liquid in the interior to help drain off excess heat. Sometimes just turning down the playing volume after a loud session can help lower the temperature before resuming.
A good idea is to always make sure the power amplifier is being used within its capabilities and if you start hearing any harshness or brittleness in the way high frequencies sound to lower the volume. Any tone controls or loudness compensation should be set neutral or off when playing at higher volumes.

AudioToaster100

Thanks for the additional info @SeleniumFalcon. I think I did everything wrong then:

• Too much audio input (loud)
• Equalizers high
• Mismatched amplifier

I will be testing the polyswitch jumper this weekend when cables arrive for an input source. I tried with FM radio and the signal was too poor to determine if anything was happening.

SeleniumFalcon

Good luck with your project!

AudioToaster100

Thanks @SeleniumFalcon!

I jumped the polyswitch @Gardenstater, and I am having the same issue. But thanks for the recommendation, that was a good idea.

I am testing on a friend's amp tomorrow who also has monitor 5Bs. I hear hissing/noise when the speakers are hooked up and the amp is on, so I am going to verify whether my amp is bad.

If the speakers don't sound good on the other amp tomorrow, I'm going to place an order for Polk's replacement tweeters.

F1nut

Hissing from the tweeters when you ears are up close and personal to the tweeters is not uncommon. It's not the tweeters though, it's from the power source, which doesn't mean the power source has a problem.

AudioToaster100

Thanks @F1nut, I appreciate it. That gave me some peace of mind. I also came across a lot of your answers in other topics during my research. Much thanks for contributing on this thread too.

Test Results:
I tested the speakers this weekend on a friend's amp that he uses for his Monitor 5Bs. My speakers are clear as day on his setup. Side-to-side when compared to his Monitor 5s, they sound excellent and about the same (his mids are re-coned and the speakers may be re-capped). Man I missed that sound!

I also did a "crossover test" to see what frequencies will play through the tweeter. By playing single tone sine waves, I found that 1200 Hz was playing through the mid and tweeter with harmonic interference, but above 1500 only played through the tweeter while 1000 and below only played through the mid.

I am going to conclude that the speakers are actually fine, and my source of bad sound is from the amplifiers I have (strangely enough, both amplifiers).


The receiver/amp is from the 70s, and it has never been opened up for a repair. I may try and re-cap it and/or buy a new receiver.

It's possible that I'm getting "clipping" on the treble frequencies. It's hard to notice unless I turn up the volume. Especially noticeable are strings in orchestral pieces. Violins sound distorted enough to make you frown a little.


Thank you all for helping me determine what to look at, what to try, and options for replacement parts for my speakers. Beyond helpful. Now I know what I have to do to fix my setup.