different dust cover

leftwinger57

If you guys remember a few weeks ago a guy blew a driver and replaced it and most of you spotted some inconsistencies. 1. was the surround and the other was the sheen or dope on the speaker and whether the leads were exposed or not. I blew a 6503 stereo
driver on my right 2B and bought one off E-Bay for $19 and free shipping. Now I just noticed the dust cover is smaller has a matte finish and no sheen to it. The speaker itself is doped and sounds correct and all the markings on the back were correct except a year newer than my '87s. Any concern here or just possibly a worked on speaker or a crushed dust cover that was used just because?

westmassguy

The woofer on the left has a solid, pressed paper dust cap, which is not original, and will affect the T/S parameters of the woofer. Polk used mesh dustcaps back then.

leftwinger57

That's amazing looking at the left speakers they are both the same as the one I bought a few months ago w/ that matte grayish finish. All had the SDA logo and year stamped on it which means the right dimensional driver is the odd duckling.Mesh or not that's how I got them that way with the one not not similar probably replaced by the original owner. Maybe like some say they used what they had on hand.

westmassguy

There's more to it than that Lew. Manufacturers use mesh or screen dust caps for a reason, it keep the voice coils cooler. As the cone moves in, air moves out through the dust cap, and vice versa. By using a paper dust cap, the air displaced by the cone/voice coil movement must now travel through the spider, which is less permeable. The entrapped air is now either slightly pressurized or under a slight vacuum. This changes the compliance of the woofer. The suspension is now stiffer than the original design.

leftwinger57

Dave, any guesses on why they are not the original. To me and I know nothing about internals the throw of the speakers seem fine and equal the sound after the mods is awesome, w/o any air leaks. I find it very hard to believe the original owner had all 4 drivers replaced . A real mystery here. Do you or any one have a close up shot of this mesh design dust cover ? Another what I call used what they had is one cross-over had a quick disconnect to the tweeters and the right x-over was hard wired to them. I did have that changed when they went out but I have heard of things like that before. The company notorious for doing things that was DCM back in the '70s in using what ever they had that was available at the time off their shelves.Thanks for the info ,this has me scratching my head....

pongshi

Not a mystery to me why he might have replaced polk midwoofers. The magnets probabably shifted due to mishandling of the speaker. I had to replace 7 MW6503s in my SDA SRS speakers.

leftwinger57

Not to debate the issue but here's the history of my 2Bs as I know it. I bought them bone stock(I presume) at a moving sale for $50 in 2013. The woman was down sizing and the husband passed away some 17/20 years prior. These were dormant for all that time. There was no E-Bay or any other source that I know of other than Polk themselves so it must be in my estimation Polk drivers with or w/o the mesh dust covers.

westmassguy

leftwinger57 wrote: »

Dave, any guesses on why they are not the original. To me and I know nothing about internals the throw of the speakers seem fine and equal the sound after the mods is awesome, w/o any air leaks. I find it very hard to believe the original owner had all 4 drivers replaced . A real mystery here. Do you or any one have a close up shot of this mesh design dust cover ? Another what I call used what they had is one cross-over had a quick disconnect to the tweeters and the right x-over was hard wired to them. I did have that changed when they went out but I have heard of things like that before. The company notorious for doing things that was DCM back in the '70s in using what ever they had that was available at the time off their shelves.Thanks for the info ,this has me scratching my head....

Lew, all your other woofers have the screen/mesh dust covers. The one you showed in the photo, has what appears to be a pressed paper dust cover. Very early Polk woofers ( late 70s) I've seen, had treated felt caps. Those were semi permeable.

edit
Close inspection of the odd looking woofer, shows an after-market paper dust cap. The original mesh was probably pushed in or damaged. If you look closely, you'll note its about 1/8" larger in diameter with a "lip up" . Original Polks, whether mesh or felt did not have a lip around them.

leftwinger57

That ends it. The one dust cover was replaced by the original owner I assume w/that larger dust cover and I was lucky just to get an original on E-Bay. Thanks for clearing it up. Even the cut outs on the surrounds are matching. I'm going w/ your explanation..

PolkieMan

Back in 94 I had a MW6510 in warranty go bad and Polk sent me a replacement. But they sent me a MM6510. Being native back then I figured that they knew what they were doing and it was correct. I recall the cone was a lot stiffer than the MW this reminds me of that.