Still havivg low frequeny distortion problems with my RTA-12s

rdozz

I am driving my RTA-12s with a harmond kardon AVR20 50watts per channel. I mentioned this problem a couple of weeks ago in a thread on this site. I did all that was suggested like insuring the cab was sealed,etc.

The question which was left, was the amplifier capable of drving the 12s without distorting. I found a cheap but big set of DCM KX10s for $30.00 on CL. I am becoming a horder. 8ohm impedance, not sure of the wattage. I connected the speakers to the HK AVR20 cranked it full volumne and they sounded loud and clear no distortion. Both of my RTA-12s distort at about 1/2 volumne.

When I first got the RTA-12s the the baskets on the PRs were wore out, completly dry rotted. The rubber surounds were fine but they just flopped around. I picked up 2 replacement PRs off ebay where someone parted out a set of RTA-12s. My question is, how can I tell if the basket on the MW6500s are wore out or just not up to spec. The wire baskets on the PRs were gone no tension. With all the MW6500 speakers being in the same boxes/cabnets as the dry rotted wire baskets on the PRs, I suspect the MW6500s my not be up to spec tension wise, even though the they visually look fine?

Does anybody live near chattanooga, TN....lol

Thanks in advance,
Rob D

F1nut

It's possible you have one or more bad drivers. It's also possible that the caps on your crossovers are shot.

You can listen to each driver separately by disconnecting one of the two. Leave the other speaker disconnected for the time being. Play some music listening up close to the driver. Repeat. If at the end of the experiment all four drivers distort, you either have 4 bad drivers or it's the crossovers.

BTW, the baskets are the stamped steel frames, they don't dry rot or wear out. The part of the driver you're referring to is called the spider.

Shacky

You could also try the finger push test. Using three fingers like a tripod push in gentle on each mid driver. You may be able to feel a VC rub on the driver causing the problem.

The active drivers are more likely to have voice coil or shifted magnet as problem than a rotted spider, I would think.

20hz

try what shacky said on the 6500 if they have no tension they are worn out but those rta12 are not to effeciant and that 50wpc may not drive it properly , I sugest trying a amplified sub that will free up more power for the polks since the sub amp drives the bass and has has a lot more than 50 watts in it .

rdozz wrote: »

I am driving my RTA-12s with a harmond kardon AVR20 50watts per channel. I mentioned this problem a couple of weeks ago in a thread on this site. I did all that was suggested like insuring the cab was sealed,etc.

The question which was left, was the amplifier capable of drving the 12s without distorting. I found a cheap but big set of DCM KX10s for $30.00 on CL. I am becoming a horder. 8ohm impedance, not sure of the wattage. I connected the speakers to the HK AVR20 cranked it full volumne and they sounded loud and clear no distortion. Both of my RTA-12s distort at about 1/2 volumne.

When I first got the RTA-12s the the baskets on the PRs were wore out, completly dry rotted. The rubber surounds were fine but they just flopped around. I picked up 2 replacement PRs off ebay where someone parted out a set of RTA-12s. My question is, how can I tell if the basket on the MW6500s are wore out or just not up to spec. The wire baskets on the PRs were gone no tension. With all the MW6500 speakers being in the same boxes/cabnets as the dry rotted wire baskets on the PRs, I suspect the MW6500s my not be up to spec tension wise, even though the they visually look fine?

Does anybody live near chattanooga, TN....lol

Thanks in advance,
Rob D

westmassguy

I suspect your receiver is running out of steam very quickly. The 12s have a sensitivity of 87 db, are rated for 4 ohms, and drop below that in the 100 to 1500 Hz range, according to a Stereo Review article I read. Like the Monitor 10s, the RTA 12's drivers are wired in parallel, which is a difficult load for any receiver. Your HK AV Receiver is rated 60 watts/channel @ 8 ohms. It's not even rated for 6 ohms, much less 4 ohms or less. The DCM KX10s in contrast, have a sensitivity of 97 db, which is several orders of magnitude higher, and more efficient than the 12s.

rdozz

I will try experimenting with the individual drivers. I did try the three finger test. If the pressure was not perfectly equal the voice coil would rub.

I bit the bullet and bought a real amplifier (Onkyo TX-SV727). I should receive the amplifier next week. It is 100 wpc. If the amplifier does not help, I will replace the drivers.

Hey F1nut, thanks I meant the spider, it would be tough to dry rot the metal basket!

I am looking foward to hearing the speakers when they are working as they were designed. They sound great as they are now but at low volumes.

Thanks again...

TennMan

rdozz wrote: »

I am looking foward to hearing the speakers when they are working as they were designed. They sound great as they are now but at low volumes.

I don't think any speaker was ever designed to have the amplifier turned to maximum volume as you described in one of your post above without the possibility of hearing distortion or possibly doing damage to the one of the components. You have to use common sense with any speaker/amplifier combination or you're just asking for problems. If you want to listen at volumes that high you should buy a system that has horns that aren't as easily damaged.

Here is a photo of what you need. :biggrin:

rdozz

TENNMAN, really, what is your problem. You made many asumptions about me and what i did without very much information. Not very nice. I only turned the volume up for a moment, and as I said it was a cheap set of speakers.. Common sense,really?

TennMan

Sorry you were offended. That was not my intent. I was trying to make a point that would be helpful to you in preventing damage to your speakers. I didn't realize you would be so thin skinned or I wouldn't have replied.

Below you will find a quotation of what you said. From that I think my comments were appropriate. The photo was intended to add a little humor to my post but it appears you would rather gnash your teeth instead of smile. That's fine. I won't make the mistake again of trying to be helpful.

rdozz wrote:

The question which was left, was the amplifier capable of drving the 12s without distorting. I found a cheap but big set of DCM KX10s for $30.00 on CL. I am becoming a horder. 8ohm impedance, not sure of the wattage. I connected the speakers to the HK AVR20 cranked it full volumne and they sounded loud and clear no distortion. Both of my RTA-12s distort at about 1/2 volumne.

F1nut

westmassguy wrote: »

I suspect your receiver is running out of steam very quickly. The 12s have a sensitivity of 87 db, are rated for 4 ohms, and drop below that in the 100 to 1500 Hz range, according to a Stereo Review article I read. Like the Monitor 10s, the RTA 12's drivers are wired in parallel, which is a difficult load for any receiver. Your HK AV Receiver is rated 60 watts/channel @ 8 ohms. It's not even rated for 6 ohms, much less 4 ohms or less. The DCM KX10s in contrast, have a sensitivity of 97 db, which is several orders of magnitude higher, and more efficient than the 12s.

Excellent points!

westmassguy

F1nut wrote: »

Excellent points!

Thanks F1nut, I just call it as I see it.

tonyb

Translation is, your Polks distort at half volume because your receiver doesn't have the juice they need to play louder. Your other speakers, being easier to drive will naturally play louder on less power.

Moral of the story is, know what your speakers require to sound good. If you can't match that, then expect less.

rdozz

Sorry for posting twice like this but, I forgot to ask if the (Onkyo TX-SV727) amplifier is capable of driving the RTA-12s properly? I looked at the specifications but I am new to this and appreciate advice/ help. I want to get the best out my system with-in my limited budget.

rdozz

Thank you for the responses. I will update when the new amplifier comes in.

westmassguy

rdozz wrote: »

Sorry for posting twice like this but, I forgot to ask if the (Onkyo TX-SV727) amplifier is capable of driving the RTA-12s properly? I looked at the specifications but I am new to this and appreciate advice/ help. I want to get the best out my system with-in my limited budget.

As long as you keep it in two channel (stereo) configuration, it may power them adequately, but JUST adequately. Your 12s should play a little bit louder than they do now, but don't expect them to shake the walls. It should be an improvement over the much older HK, but the Onkyo will hit a wall just like the HK does. It too is only rated for 8 ohm loads. How it behaves when it's approaching that wall is anyones guess. Your HK distorts, the Onkyo's protection circuits may just shut it down. It does have a full compliment of pre-amp outs, so a separate power amp could easily be added.

westmassguy

TennMan wrote: »

Sorry you were offended. That was not my intent. I was trying to make a point that would be helpful to you in preventing damage to your speakers. I didn't realize you would be so thin skinned or I wouldn't have replied.

Below you will find a quotation of what you said. From that I think my comments were appropriate. The photo was intended to add a little humor to my post but it appears you would rather gnash your teeth instead of smile. That's fine. I won't make the mistake again of trying to be helpful.

Hey TennMan, I got the joke. That's some horna-a-palooza

TennMan

westmassguy wrote: »

Hey TennMan, I got the joke. That's some horna-a-palooza

Thanks. It's good to know some people here still have a sense of humor. Seems a lot of folks have lost their sense of humor lately. Here's an example of one of them. I'm not sure if he's on CP or not.

[video=youtube_share;C-okDJA5CVw]http://youtu.be/C-okDJA5CVw[/video]

Mystery

Hmmm...
Sounds like I have to check mine for worn out basket on the PR's.
They sound fine even at loud volumes playing music but test tone of 30 hz or below make some flapping sound.
http://www.polkaudio.com/forums/showthread.php?137952-Lookie-what-I-got-RTA-12C&p=1832101&viewfull=1#post1832101

PolkieMan

I had a speaker wire that got in between the cone and the baskets one time. How loud are you playing them?

http://www.hearforever.org/quiz/fact-or-fiction-hearing-loss


maybe we should all have one of these.

http://www.newegg.com/Product/Product.aspx?Item=9SIA0U00BK5217&nm_mc=KNC-GoogleMKP&cm_mmc=KNC-GoogleMKP-_-pla-_-NA-_-NA

westmassguy

Mystery wrote: »

Hmmm...
Sounds like I have to check mine for worn out basket on the PR's.
They sound fine even at loud volumes playing music but test tone of 30 hz or below make some flapping sound.
http://www.polkaudio.com/forums/showthread.php?137952-Lookie-what-I-got-RTA-12C&p=1832101&viewfull=1#post1832101

Baskets don't wear out, they're steel. The spider may be loose or separated.

rdozz

Thanks again, not very loud. I only turn the volmue up loud for a very brief moment. I don't want to damage my speakers or the amplifier. Not to mention at 51 I would like to protect what hearing I have left. The best way to describe my listining level is; FM soft rock at 1/4 volume. The amplifier is 50wpc with loudness on. If I turn the amplifier up much past that the drivers distort. Another example, 1/4 volume and increase the bass to 3/4 posistion the speaker distorts.
I will post an update when I get the new amplifier. If it continues to distort I am going to replace the MW6500s.

Mystery

westmassguy wrote: »

Baskets don't wear out, they're steel. The spider may be loose or separated.

Hmmm... I see. I was confused by OP's post mentioning basket rot... so what was worn out and rotted if rubber surrounds were okay? :idea:

rdozz wrote: »

...
When I first got the RTA-12s the the baskets on the PRs were wore out, completely dry rotted...

phocion

What happens when loudness is off? That button can cause a lot of problems

westmassguy

Mystery wrote: »

Hmmm... I see. I was confused by OP's post mentioning basket rot... so what was worn out and rotted if rubber surrounds were okay? :idea:

Basket is short for Basket Frame. It's the metal part or frame of a Speaker or Passive Radiator. Unless they are physically damaged or abused in some way, the Basket Frame will remain unchanged. The moving parts are susceptible to wear and tear, fatigue, and rot. The rubber surround can dry out, become brittle and crack. The speaker cone can also dry rot, and in the case of the passive radiators, the plug or disc that's glued to the face of the cone can also rot, become loose or even fall off. The last item is the spider, which sits between the cone and the basket frame. It's attached to both, and is one of two points that keep the cone in proper alignment (the surround being the other). The spider is normally made from treated cloth, and has accordion like ribs in it for flexibility. The spider can tear, separate from the cone or the basket frame, or rot. It's also subject to fatigue from constant motion.

rdozz

The spider was completely gone on one of the PRs and almost gone on the other PR. I am sorry for the wrong terminology. The rubber surrounds look ok on the MW6500s. No signs of rot.

I will disengage the loudness button and try it when I get home.

Thanks again for the help.

westmassguy

rdozz wrote: »

The spider was completely gone on one of the PRs and almost gone on the other PR. I am sorry for the wrong terminology. The rubber surrounds look ok on the MW6500s. No signs of rot.

I will disengage the loudness button and try it when I get home.

Thanks again for the help.

You've had the Loudness on all this time? Oh my....................

TennMan

westmassguy wrote: »

You've had the Loudness on all this time? Oh my....................

Be careful so you don't get a tongue lashing. He got upset with me for suggesting he use common sense.

rdozz

Hey TENNMAN give it a rest, it is getting old and I really don't see the point. It is not very helpful.