Monitor 7A's rescued from the basement...

DaveOrAstroDave

Hi Everyone,

I discovered this forum while trying to find out more information about my Dad's old speakers. I've just rescued a pair of Monitor 7A's from less than ideal conditions in my Dad's basement, and I had a few questions about cleaning and care.

1) The radiators, woofers and tweeters all appear to be in good shape, if a bit dirty. There's a grimy film on them that I'd like to clean off. Any suggestions on the best way to go about it? I'm a little hesitant to clean the tweeters, as they look pretty delicate.

2) After having been stored in the basement for a few years, the speakers have a bit of a musty smell that's probably mold/mildew related. Any cleaning suggestions for the cabinets?

And now for the tricky ones...

3) The bottoms of the cabinets, as well as some of the corners, are a bit swollen from moisture damage... One of the edge seams on the bottom has also split open a little. Is there anything that can be done about this, or am I out of luck?

4) The front speaker grilles are also a bit warped/moisture damaged, and for some reason, the pre-velcro ball-headed pin pads that are supposed to hold the grilles on don't seem to be engaging. I think it might be because of the strain of trying to attach them against the warping of the wooden frame, but I'm not sure. Is it possible to de-warp the grille frames, or perhaps obtain new ones?

Thanks for any help you can provide, and happy listening!

-Dave

pablo_rodz

Hello Dave,

Welcome to the forum....

I've seen very impressing recontitioning done by the guys here. You should be able to get great info and help. Good luck!

skrol

Welcome to the forum and great rescue.

As far as cleaning the passive radiator and the mid-woofer, most folks recommend a little (believe it or not) Windex on a cloth. I wouldn't tough the tweeter dome. Maybe use a little compressed air to gently dust it off.

The cabinets are particle board with vinyl laminate. Usually water is used to clean the cabinets. Might use a little very dilute dish soap if really bad. I am not sure what to recommend for the swollen cabinet parts. If you are handy and ready for a project, you could remove the vinyl, dig out the rot, fill with wood filler and re-laminate with something nice.

You might want to remove the passive radiator and check the interior seams to make sure that they are still sealed well. If they are not sealed, caulk the seams.

For the grills, you might try flattening them by sandwiching them between a flat surface and a large flat object for a while. If they spring back to the warped position, might try misting the frames with a little water, let it soak in and sandwich them again.

Sounds like a fun project but well worth it. Post some pics.

jimbo1421

Hi Dave.

Nice find. I have a pair and they are good speakers.

I had a similar problem with the bottom mitre joints on a pair of Monitor 10Cs. It is important that the cabinet be airtight since the mid woofer and passive bass radiator is designed to work against a certain amount of back pressure. Try this: press on the bass radiator and hold it. The mid woofer will push out, then slowly return to position. If it takes 2 seconds or more, you are good; 1-1/2 seconds-not so good. A certain amount of air leakage through the speakers themselves is normal, but not through the speaker seals, cabinet or holes in the rubber surrounds.

I couldn't get the mitre joints on the M10s to draw together with clamps, probably because internal fasteners prevented it. So I filled the mitre joints with epoxy using the System Three T-88 mixer/syringe available from Woodcraft. I masked off all the vinyl, but still was a messy job. I also used black caulk where the bottom had pulled away from the black soundboard.If I had it to do over again I think I would just caulk all the joints. Another tweak would be to remove the old speaker gaskets and reset the drivers in Moretite. See this thread:
http://www.polkaudio.com/forums/showthread.php?t=74524

Warped frames are hard to get back to flat. One other thing to try is set them out in the sun for a while, convex side up. Keep an eye on them and when they are flat, put them back on the speakers. They might stay flat. If they dont try some Velcro.

Enjoy,
Jim

AudioGenics

been looking at different speaker repair sites.

I remember throwing away lots of speaker baskets, magnets, etc.
just didn't take the time to repair.

Time to be more environmentally aware and renew the old gear.

DaveOrAstroDave

Thanks for the advice, Skrol and Jim. It's been pretty useful so far! I've been able to spend some time on clean-up, and also further assessed the situation. Both speaker cabinets have compromised seals - the bottom panels are actually loose! As you can see in MitreGap1.jpg and MitreGap2.jpg, the side panels and bottom panel have swollen and separated pretty far.

Other than that, I think one of the speakers looks pretty good (Mon7A-1.jpg).
As for the other one, well, both the radiator and the tweeter have some wrinkles/creases in them (radiator-1.jpg, and tweet-1.jpg). How likely is this to adversely affect performance?

As far as the cabinets go, I'm wondering if I should have some fresh particle board cut to size, at least for the sides and bottoms, but then again, would the density of the particle board have to match the original to maintain the original sound characteristics? I suppose the quick and easy solution is caulk...

Oh - one more thing - I've seen an 'upgrade kit' for these speakers on ebay, and it looks like a couple of replacement capacitors for the crossovers:

Kit Link

Does anyone know if this a worthwhile upgrade?

Thanks again!
Dave

comfortablycurt

Welcome to Club Polk!

Congrats on the new speaks...the 7A's are some excellent sounding speakers, I've got a pair of them myself. For the price they can be had for, they're very hard to beat for 2 channel speakers IMO.

Skrol was right about the Windex. I've used it to clean my drivers several times, and it works great.

A lint free cloth is preferable. Spray about 7-9 squirts of Windex onto the cloth, and gently wipe the drivers in a circular motion. Depending on how dirty they are, it may be necessary to make a couple applications. The drivers themselves naturally have a somewhat tacky/sticky feel to them, so you don't need to try and get all of the stickiness off. It's normal.

As far as cleaning the tweeter goes...BE VERY CAREFUL!!! These tweets are extremely delicate. I wouldn't use compressed air on them myself...I'd be too worried about damaging the dome. I used a Q-tip to clean mine...just be very VERY gentle with them.

Here's another test you should perform to check for airtightness. It will tell you if the cabinet has any air leaks. The cabinets must be air tight to perform optimally, due to the Passive Radiator design.

Push in on the Passive Radiator and hold it in. The mid-woofer should become fully extended, and retract slowly over a period of 3-5 seconds. If they retract real quickly, you've got air leaks.

As far as the upgrade kit on ebay goes, I'd pass on it. Many people have done crossover upgrades on their vintage Polk's, but you're much better off going with higher quality components, than what's included in those ebay kits. Those kits don't really offer much of an upgrade, it's more of a refreshing for the old worn out caps/resistors.

jimbo1421

Hi Dave,

If you can pull the joints together with some pipe clamps, I would inject some of that epoxy into the open joint and clamp it. Then caulk the interior. If you want to rebuild the boxes I would try to salvage the front & back panel and cut all new sides and bottoms from a half sheet of veneered MDF or particle board. Trying to fit new mitred pieces to old warped ones is more trouble than it is worth. Check your local hardwood supplier for prices and veneer choices.

Hey CC: Is the press test three seconds or more for smaller speakers?

Jim

comfortablycurt

jimbo1421 wrote: »

Hey CC: Is the press test three seconds or more for smaller speakers?

Jim

Generally, yes. They should stay extended on the Monitors for a longer period than they would on SDA's. On my M7A's, when I push the PR's in, the MW's extend completely, and will stay completely extended for 2-4 seconds before they even start moving back in. It then takes another 5-6 seconds for them to return to the resting position.

On my SDA2A's, they only stay extended for about a second or so, and then slowly move back in over about 3 seconds. I'd imagine the Monitor 10's would behave more similarly to the SDA2A's than the Monitor 7's, due to having dual MW's, like the 2A's.

jimbo1421

Thanks, CC. I still need to do some work on my 10Cs and 7As. Oddly, my
10Bs take 15 seconds + to return. Either that is very good or very bad. But that is another thread.

Jim

comfortablycurt

I'd imagine that's probably a good thing.

Actually, when doing the pressure test on my 7A's, they won't even return to their resting position until you take the pressure off of the PR's. They'll return most of the way, but still stay slightly extended. They'd probably return the rest of the way if I continued holding them in for another 15-20 seconds...not sure though. I'll have to check them sometime.

skrol

They will return eventually. If nowhere else, there is a leak path through the spider, around the voice coil and through the dust cap (unless the dust cap happens to be sealed). The more MW's you have, the more leak paths. My RTA11TL's hold for about 5 sec after applying Moretite while my Monitor 5A's hold for at least 10 sec with the original gaskets.

nooshinjohn

I would also remove all the drivers and check them out with an ohm meter. Also look at the cross-over/ binding posts for corrosion damage. From the pictures you posted, it looks like there is enough moisture in your dad's basement to take a nice swim at times, so taking a peek inside is probably a good idea.

John

zombie boy 2000

Hey Dave...
I'm just wondering if your screen name is a reference to one of the greatest bands of all time. Man or Astro-man?

DaveOrAstroDave

Greetings Zombie Boy 2000,

It is indeed a reference to Man or Astro-man. Nothing but the best in retrofuturistic space-surf. I also use the screen name on some import videogame forums, where it doubles as a reference to the Sega Astro City arcade game cabinet. Restoring that thing was a pain, but well worth it!

Hopefully the speakers will turn out as well :cool:

DaveOrAstroDave

nooshinjohn wrote: »

I would also remove all the drivers and check them out with an ohm meter. Also look at the cross-over/ binding posts for corrosion damage. From the pictures you posted, it looks like there is enough moisture in your dad's basement to take a nice swim at times, so taking a peek inside is probably a good idea.

Excellent point. I'll have to take a look.

By the way, is there anything I have to be careful of when removing/reinserting the foam sheeting inside the cabinets?

zombie boy 2000

Beyond super-sweet!! I've had the glorious distinction of seeing them over twenty times. Best show in the galaxy, bar none. Here's to Coco, Star Crunch and Birdstuff making a comeback. Welcome to the Forum and good luck with your speaks.

kcoc321

Hey Dave,
I read of your plight the other day and remember you when I came across this thread.
http://www.polkaudio.com/forums/showthread.php?t=84993&highlight=monitor

Don't know how much shipping would run, but it would get yo up and running.
Good luck

DaveOrAstroDave

Nice catch! I've just posted a reply, so we'll see...

Now for the status update - The moisture damage looks pretty extensive, but I might try stripping the cabs, filling, sanding, and putting on a fresh veneer.

There's an odd white grit on the back of the tweeters, and on the frames of the woofers - it looks like the metal casings might have corroded a bit. As for the crossovers, one of the inductors has a broken lead, and the 12uF caps have green leads, so I wonder if they leaked a bit. I'm trying to find the value of the inductor, but all the schematics I've found so far seem to be for a different revision, because I have an additional 4.7ohm resistor in my crossover that doesn't appear in the 3 schematic revisions I've found on the forum. I'm assuming the difference is that I've got the old peerless tweeters, so if anyone has the schematic for the old late 70's crossovers, please let me know.

Thanks!
Dave

DaveOrAstroDave

Well, I've rebuilt the crossovers, and successfully filled in/resealed the cabinets.
I've got one of them covered in Parts Express Walnut Melamine, and I think it turned out pretty good. She sounds great too!

Now I just have to finish the second one.. and replace the old cheesy Sony bookshelf system I'm using to power them

skrol

Hey that looks pretty nice and unique. I like the color.

Off topic but I was wondering about your user name DaveOrAstroDave. Are you in the space biz?
Stan

comfortablycurt

That looks weird with wood grain on the baffle...I'm not sure if I like that or not. I kind of prefer the black baffle myself.

But...I suppose they aren't my speakers.;) Looks like you did a great job on them!


Skrol...

zombie boy 2000 wrote: »

Hey Dave...
I'm just wondering if your screen name is a reference to one of the greatest bands of all time. Man or Astro-man?

DaveOrAstroDave wrote: »

Greetings Zombie Boy 2000,

It is indeed a reference to Man or Astro-man. Nothing but the best in retrofuturistic space-surf. I also use the screen name on some import videogame forums, where it doubles as a reference to the Sega Astro City arcade game cabinet. Restoring that thing was a pain, but well worth it!

Hopefully the speakers will turn out as well :cool:

That was already discussed earlier in the thread.;)

skrol

Oops.

DaveOrAstroDave

Skrol - I think Curt beat me to it, but no, I'm not in the space program, as awesome as that would be

Curt - yeah, I can understand that. I had considered repainting the baffle, because I had to sand it extensively to get the bottom of it back into square, but I thought I'd try the melamine since I had to recover the sides anyway. I wasn't sure how I'd feel about it, but the more I look at it the more I like it.

In any case, thanks for the compliments!

kcoc321

Wow, Dave, those have come along way.

Nice job.:D How do they sound?

One thing that was recommended to me was to recess the MW into the baffle like the PR is. I am not sure exactly why, but it is supposed to improve the sonics. If you need I can measure the depth on my 7c's, that have it already done.

Just an added idea, adding the same thickness (or minimally thicker) filler under the tweeter would bring it out flush again and hide the edge of the melamine. Easy to trim the inside with a flush cut router bit.

skrol

Recessing the MW would serve to reduce turbulence around the edge. The grill frames should be shaped to help reduce this turbulence. If you recess the MW, the shape of grill frame may then create more interference.

My Monitor 5A's are the same way.

kcoc321

Valid concern Skrol, so I did checked all my "current" speakers and the interior grill frame clear width is as follows:
The 7b's I have are 11 wide at the MW location (originally non-recessed MW)
The 7c's I have are 10.75" wide at the MW location (recessed MW)
The 5jr's I have are 5.75" wide at the MW location (recessed MW)
The RTA-8TL's I have are 6" wide at the MW location (recessed MW)

Since the 7's grill frames are already sized to accommodate the PR's he should be fine, at least based on the 'production specs' of frames made by Polk.
IMHO

DaveOrAstroDave

Hi kcoc321,

The one that's finished sounds great! As for the second one, well, I've been a little lazy and haven't finished re-forming the corners of the box. That's an interesting thought about recessing the mid. I don't really have the appropriate woodworking tools, but I'll give it some thought as a future upgrade.

Oh - I think you were asking in another thread about the inductor upgrade. Unfortunately, I can't really tell you what the difference was because when I tested the speaker initially, the original inductor was already busted. Maybe I can compare for you once I get the second one back together, as I haven't modified that crossover yet.

I've also just discovered that one of the MWs had been replaced back in the '90s, and it was replaced with the wrong part, so I've got a 6500 and a 6502. I'll probably have to get a couple of 6503's so I have a matched pair...

kcoc321

It's kindof fun renovating those, huh?

The MW6502's seem to be pretty available in the F/S section pretty regularity, as they were used in most of the Monitor speakers.
Then you could just get one and save the $30 (MW6502's seem to run around $20)

Or you could just watch for a pair of M-'X' speakers on CL and pick them up.
I bought a second pair of 7c's on CL here a couple of weeks ago for $60..still $$ ahead from (2) MW6503's which would run you $96 +/- from Polk.
you can always sell off the extra parts to recoup your costs.
Unless yo want to have 'new' drivers....so they will last another 20 years.

PS: actually I just saw this from Ricardo...dunno if the same applies but worth a PM to him.
(post #5)
http://www.polkaudio.com/forums/showthread.php?t=86414