CS250 turned noisy

yoni

Hello,

I have old stuff i bought a decade ago that i use once a trimester.

Among those a Yamaha DPSA-1 using what "look like" a Polk Audio CS250 center speaker (i see that it used to be a sticker/serial that is gone with the time).

All of a sudden this speaker sounds bad and noisy.

I tried it on other output still sound bad.
I replace it with another speaker and the new speaker sound good.
So for sure the speaker is the problem.

I have check the 3 unit inside, 2 MW4801 (BD4801) and 1 SL5001 (BD0111-A), they all sounds noisy and bad.

Could it be all three together went down ?

I can see inside the box hooked to the input socket REO250-1 (CS250s) a round part with wired rounded on (bobinage), a ceramic resistor (5W09...) and a condenser. I can't read anything more cause all is covered with glue.

I have tools (voltmeter, iron molder) i know how to use them but i need someone to tell me what to do step by step so i figure what can be done to repair the speaker.

Thanks in advance
Yoni

PS: English is not my mother tongue.

[Deleted User]

Hello Yoni,
First of all, welcome to Club Polk. Sorry you are having a problem with your center channel speaker. From your description I would believe that the tweeter and both of the midrange drivers have become damaged. This causes a scratchy or noisy sound. The circuit you see, inside the cabinet, is called a crossover and is probably not causing the bad sound. This means that all three of the speaker's components would need to be replaced.
Regards, Ken

20hz

Your voltmeter should have impedance on it , dissconect one speaker at a time and hook up the voltmeter leads just as the speaker wires WERE hooked on .
Each driver will have a stabile reading around 6 ohms , any polkie here can tell you the exact number .
Its possible rust developed on the speaker magnet and is touching the voice coil , you can also try pushing in EVENLY AND SLOWELY on the cone of the 4801 and if you feal any grinding or rubbing or if its frozen the speaker is gone , what usually brings this on is if the speakers are stored in a shed outside and the humidity is higher than being stored inside .
Its rare the crossover network went bad .

yoni

20hz wrote: »

Your voltmeter should have impedance on it , dissconect one speaker at a time and hook up the voltmeter leads just as the speaker wires WERE hooked on .
Each driver will have a stabile reading around 6 ohms , any polkie here can tell you the exact number .
Its possible rust developed on the speaker magnet and is touching the voice coil , you can also try pushing in EVENLY AND SLOWELY on the cone of the 4801 and if you feal any grinding or rubbing or if its frozen the speaker is gone , what usually brings this on is if the speakers are stored in a shed outside and the humidity is higher than being stored inside .
Its rare the crossover network went bad .

First, tks for your answers !

The 2 4801 cone are moving smoothly.
I set my voltmeter in place of the 4801 and set it to 20k.

Where was hooked the first 4801 connected to the amplifier with no music it show 0.34 stable.

Where was hooked the second 4801 connected to the amplifier with no music it show 0.49 stable.

Where was hooked the tweeter connected to the amplifier with no music it show 0.05 stable.

I realize that i could test the two 4801 by hooking them on my bike stereo (like a car stereo but on 2 wheels ) to test. They booth sound quite alright.

Do i have the "rare" case ?

Yoni

20hz

disconnect both wires going to that speaker ( nothing hooked up not even the x/o ) .

If you dont you will read the resistance in that item also , all you want is the resistance in that speaker .
have you tried another speaker on the yamahas center ch output ?

yoni

20hz wrote: »

disconnect both wires going to that speaker ( nothing hooked up not even the x/o ) .

If you dont you will read the resistance in that item also , all you want is the resistance in that speaker .
have you tried another speaker on the yamahas center ch output ?

Sry i don't get it (x/o ?).

You want me to remove the 2 wires cable that goes from the amplifier to the cs250 ?

Sorry but i really need a step by step explanation.

Yes i have tried another HP and it work fine.

Note : I have unplug each unit to test. While the voltmeter was set to 200ohm it show 7.1 for the 4801 (both of them) and 6.6 for the tweeter.

20hz

yoni wrote: »

Sry i don't get it (x/o ?).

You want me to remove the 2 wires cable that goes from the amplifier to the cs250 ?

Sorry but i really need a step by step explanation.

Yes i have tried another HP and it work fine.

Note : I have unplug each unit to test. While the voltmeter was set to 200ohm it show 7.1 for the 4801 (both of them) and 6.6 for the tweeter.

To test you want only the speaker in your hand .
X/O is crossover thats the circuit on the back with the glue all over it .
But it looks like you got 7.1 and 6.6 ohms on the voltmeter readings they should be fine .
Whats the HP thing you tried I dont understand ?
I another thing if your crossover has some sort of protection in there it may be the problem , do you have another crossover to try in place of the one that came on your cs250?

20hz

have you tried putting the cs250 on the speaker wires for either the right and left ( remove from the center location ) ?

yoni

20hz wrote: »

To test you want only the speaker in your hand .
X/O is crossover thats the circuit on the back with the glue all over it .
But it looks like you got 7.1 and 6.6 ohms on the voltmeter readings they should be fine .
Whats the HP thing you tried I dont understand ?
I another thing if your crossover has some sort of protection in there it may be the problem , do you have another crossover to try in place of the one that came on your cs250?

20hz wrote: »

Whats the HP thing you tried I dont understand

Well i hooked the volmeter on the 4801 themself and got the 7.1 value.

On the crossover i just see what i have say before.
The rounded bronze wire thing (what is the english name for that part) a resistor and a capacitor. No to my knowledge i don't have a spare crossover.

As the 4801 them seams ok connected without the crossover i suspect this part is defective.

Can't it be tested ?

Yoni

yoni

20hz wrote: »

have you tried putting the cs250 on the speaker wires for either the right and left ( remove from the center location ) ?

You mean connect the cs250 to the right or the left output of the amplifier ?
Yes noisy sound.

20hz

yoni wrote: »

Well i hooked the volmeter on the 4801 themself and got the 7.1 value.On the crossover i just see what i have say before.
The rounded bronze wire thing (what is the english name for that part) a resistor and a capacitor. No to my knowledge i don't have a spare crossover.
As the 4801 them seams ok connected without the crossover i suspect this part is defective.Can't it be tested ?
Yoni

Oh the rounded bronze wire thing that looks like a bunch of wire glued together would be a coil .
I am sure the crossover can be tested if you cut all the glue off and tested the individual parts as you figure that is a pain in the neck requires other testing equipment , so as far as testing it you did it .
Polk sells crossovers cheap like 25$ for yours and if you tell them you are on the polk forumn you get a discount .
You can try ebay for the crossover but polk is probebly cheaper and the knowlege there plus having a new part makes going to polk the best solution .
Did you try that cs250 on some other speakers locations other than the center ?

yoni

20hz the $25 look to me the best solution...

I will try with my local distributor (i live in Israel).

Many thanks all of you for the invaluable help you provided !

Yoni

[Deleted User]

Hello Yoni,
A few things to consider. By measuring the resistance of the voice coils of the tweeter and drivers you have determined that the coils are intact. But that doesn't mean they are not the source of the distortion. The best way to test them is to, at a very low playing volume, try playing them directly powered by your receiver. In other words, with the volume set low, try touching your speaker wires, of either the right or left channel, directly to the terminals of the tweeter and each of the mid-range drivers. Resist the temptation to increase the playing volume, they should make sound at even low volumes. While not impossible, it is difficult for a nonworking crossover to produce distortion. It is usually the last speaker component to suspect if there is a problem.
Regards, Ken

20hz

Kenneth Swauger wrote: »

Hello Yoni,
A few things to consider. By measuring the resistance of the voice coils of the tweeter and drivers you have determined that the coils are intact. it is difficult for a nonworking crossover to produce distortion. It is usually the last speaker component to suspect if there is a problem.
Regards, Ken

Hi Ken
I wish I could have given yoni a better awnser but without the parts in my hand it makes it difficult , I have never seen a dead crossover unless something is burnt up on it .
I have got drivers that played but the cone was frozen (sonded real bad) , I figured rust on the walls where the tight clearances were because if it was overpowered it it either wont play or would grind upon press test and I think the DCR would be way off than ..

[Deleted User]

Hi 20Hz,
At Polk we would do an autopsy, every-so-often, on blown tweeters and drivers and woofers. We could see the results of high temperature on voice coil windings, you could see the discoloration of the enamel coating. Also, there would be blistering and deformation of the voice coil former. The coil remains intact, but there's lots of severe distortion caused by voice coil rubbing. Better tweeters and drivers have small voice coil gaps and, as a result, can be damaged from excessive distortion.
Cheers, Ken

SDA1C

Just a quick idea to narrow down the problem.

The cs250 has 3 speakers correct? 2 on the mid and 1 tweet.

Try disconnecting the tweet and see if the "bad" sound goes away.

Then disconnect the mids and plug in the tweet. Then the same for each of the mids. At least you'll know if its a specific driver or one side or the other of the x-over or both.

By disconnecting one at a time you might narrow down the source path

20hz

SDA1C wrote: »

Just a quick idea to narrow down the problem.
The cs250 has 3 speakers correct? 2 on the mid and 1 tweet.
Try disconnecting the tweet and see if the "bad" sound goes away.
Then disconnect the mids and plug in the tweet. Then the same for each of the mids. At least you'll know if its a specific driver or one side or the other of the x-over or both.
By disconnecting one at a time you might narrow down the source path

good point but if the mids are in series disconnecting 1 will dissconnect the other ..
I had a driver in my ls50 that had a intermitant gargle noise , the driver felt fine probebly tested fine it took a long time to track it down , I wonder if the driver was always bad ?
Someday I will replace the needed drivers , I got some other models of the mw drivers in now ..

SDA1C

I hear ya there on the series thing. I know the 350 is that way. I had a scratchy driver so I hunted for a bit and got lucky. When I went to install it I noticed the magnet had shifted in the plastic locks on the existing driver. I fiddled with it for a bit and got it straightened out. It turns out that's all that was wrong and I now have a spare.

20hz

SDA1C wrote: »

I hear ya there on the series thing. I know the 350 is that way. I had a scratchy driver so I hunted for a bit and got lucky. When I went to install it I noticed the magnet had shifted in the plastic locks on the existing driver. I fiddled with it for a bit and got it straightened out. It turns out that's all that was wrong and I now have a spare.

great , I just built up a cs350 had 4 extra ?4850? drivers , I got taken sold the center for $30 on ebay , I should have listed here on the classified section .
I should see if that ls50 driver is fixable ..