monitor 5a information

buttercup

I found a pair of what I believe to be monitor 5a speakers at the goodwill for 2 bucks. The cabinets are rough, but the drivers appear to be in good shape. Both protection fuses were blown, but the drivers meter good.

These have almost zero bass response, I've metered the bass/mid driver and it has continuity and they are playing... both speakers sound about the same.

The tweeters are very detailed and airy and I'd love to restore these if possible. The only markings on the cabinet are serial numbers, they begin with 5B (06484). After some research I'm pretty sure these are 5a's... I'm wondering if they have the wrong x-over. All the drivers have a 1984 date stamp.

Any idea where I could find a diagram of the x-over and driver models for 5a's and 5b's?

phocion

http://www.polkaudio.com/forums/showthread.php?t=38755

Air leaks are probably your first stop on the quest for bass. Gently push in the passive and see if the driver returns to neutral quickly. If it is less than 2 seconds, you have leak that is robbing you of precious bass

buttercup

The passives are very slow returning...so they appear sealed.

The bass/mid have no push to them at all. It appears the spider has been damaged. The pleated material covering it is concave and has no movement.

When I got these it included 3 speakers, the third had no tweeter, but I discovered the bass/mid driver is not damaged... so I pulled it and swapped it out. The one speaker sounds pretty good.

I've rebuilt tweeters but, I've never disassembled a woofer before... does anyone know how, or am I better off buying a replacement. The driver is a MW6502

phocion

6502's are pretty common across the monitor line, but they are decently hearty unless dropped.

If the mid cone moves normally without scraping, and the passive also moves cleanly, you should take a look at the x-over, which you can jumper to test in the short term.

Not sure if you looked at this, but make sure you have good signal and power (speakers set to "large" or "full range" on a HT amp, for instance) Both speakers being blown seems odd, so I want to make sure that we don't have a system problem that would cause both to sound off.

As for the spider, pics would be helpful at this point

buttercup

The mid cones do not move easily... they don't move at all. I'm testing these using a G-7000 receiver that I've refurbished, it has gobs of clean power.

The drivers are definitely not working... the spider seems to be locked up somehow.

I was wrong in my original post, these are Monitor 5b's-

phocion

Well, failure of those drivers is occasionally magnet shift from falling shock, so you might try to gently move the magnets and see if they shift. If they do, you can try to realign them till the cone smoothly and silently operates, and then jb-weld them down. They might have shifted, which could have damaged the coil, and there is not a non-destructive method that I am familiar with to check the coils.

You can source these drivers from other monitors, ebay, or polk audio. Mention that you are a club polk member over the phone, and they will give you a discount.

buttercup

I think you're right... judging by the condition of the cabinets these have been handled roughly.

I can spin the magnet assembly by hand, which is odd.

How would I attempt to realign the magnet assembly?

phocion

Well, you sound pretty familiar with the design of speakers, so you know how the coil goes through the basket and sits between the magnet post and ring without touching either the magnet or the basket. Basically, it sounds like you might be pinched between this post and the basket, so I would gently try to center the magnet on the basket, and then gently press on the cone to see if there is any travel. If you can get it to travel freely, without any scratching or other friction, jb weld that sucker, and hope that the coil was not damaged in the process.

Polkersince85

http://www.polkaudio.com/forums/showthread.php?t=102923

buttercup

I'll see what I can do... I appreciate the info and expertise.

skrol

Great find. Based on your quoted serial number, they are Monitor 5B. You will find that Polk tended to make tweaks to the design without changing the name. Hence, some were 4 ohm and others were 6 ohm. If yours were made in 1984, then they were the earlier 5B. I have a pair of 5A from 1983.

Here are the specs for the 5B:

Subwoofer 1 - 8" Diameter fluid coupled subwoofer (sub bass radiator)
Midrange 1 - 6-1/2" Diameter (16.51cm) drivers
MW6502
Tweeter 1 - 1" Diameter (2.54cm)
Polk SL2000 silver coil dome tweeter

Overall Frequency Response 28Hz - 26kHz (30Hz – 26KHz)
-3 dB Limits (43Hz – 20KHz)
Crossover Frequency 60Hz and 3000Hz
Nominal Impedance 4 ohms (6 ohms)
Recommended Amplifier Power 10-125 w/channel
Efficiency 91 dB (90 dB)
Max Output Level 116 dB

Dimensions Cabinet Size 21.5" H x 10.5" W x 8.5" D
Weight 29. lbs.

phocion

Polkersince85 wrote: »

http://www.polkaudio.com/forums/showthread.php?t=102923

Unmitigated Badass, great find