New to me Monitor 7 and 5

DeRod

Hi guys new to the forum. Just picked up a pair of 1978 monitor 5s and a 1980 pair of monitor 7s. I was so surprised at how good they sounded that I am now upgrading the crossovers. The photo is of the 7s crossover will do the 5s next.

pitdogg2

What is the bypass cap for? The original may of had one, when we add better caps the bypass is no longer needed.

DeRod

I was trying to make a 34ohm ...33+1=34 ... should I remove the 1ohm? They sound way better with the new caps and I ordered a pair of Mills 4.5 resistors to change to one remaining old resistor.

pitdogg2

DeRod wrote: »

I was trying to make a 34ohm ...33+1=34 ... should I remove the 1ohm? They sound way better with the new caps and I ordered a pair of mill 4.5 resistors to change to one remaining old resistor.

When you do that it is better to divide by as close to half as possible 2x17 would have got your value. It is now acting as a bypass cap and may bring some anomalies along with it. The 33 would have been fine if the new caps had closer tolerances than the old. I would have went with Vishay-Mills 10 or 12 watt for both resistors. Another tidbit is to raise the resistors off the board a bit for air circulation around them.
Other than that looks very good !

DeRod

Thank you very much for the knowledgeable advice. Ok so now I have questions. Should I just remove the 1 ohm? Do the resistors make that big a difference in the sound? The capacitors 100% for sure did. I have more bass and way more sound stage now.

Also why does the woofer on my 5 look warped? it plays fine just looks a little weird.

pitdogg2

Yes, the resistors can make a difference. I have used the Vishay-Mills resistors in all my builds. I switched out the Vishay-Mills for Path resistors in my 2.3tl's and did notice a difference. I would leave the 1 ohm for now, most caps take a few hundred hours to settle in so get your playing time on and listen. If you like what you have leave well enough alone. In the future just keep this in mind to try and keep as close to half as you can to make your value.
The monitor 5 midwoofer does have some "funky-ness" to it in the picture. Have you removed it to look at the back side?
IF you have not done so yet get some JB-Weld metal epoxy and glue your magnets on the midwoofers, slipped magnets is VERY real and those MW6500 drivers are not very common on the used market anymore. I'm guessing they are MW6500 due to the silver basket and cone gasket on the flange of the driver and passive.

DeRod

Yes, both pair of speakers have MW6500s, but they are different. The MW6500s from the 5s (dated 1978) have 2 single terminals and the basket is shorter than the 2 double terminal 6500s on the 7s (dated 1980).

I'll post photos of the 2 different MW6500s this evening.

You think gorilla glue epoxy will work for the magnets or JB weld better?

Gardenstater

DeRod wrote: »

Thank you very much for the knowledgeable advice. Ok so now I have questions. Should I just remove the 1 ohm? Do the resistors make that big a difference in the sound? The capacitors 100% for sure did. I have more bass and way more sound stage now.

Also why does the woofer on my 5 look warped? it plays fine just looks a little weird.

That is pretty suspicious of some sort of negative event having occurred. I wouldn't be too quick to epoxy them up until you confirm that there is absolutely no voice coil scraping/rubbing.

Looking forward to seeing pics especially of those 1978 ones. Both speakers look really clean.

Gardenstater

By the way, guess what, no joke.......Happy Veteran's Day!

DeRod

Yes Happy Veteran's Day to everyone!

Ok, so here are photos of the 2 different MW6500s

Also check out the backside of the rubber surround on my weird woofer. Could that have been mis-glued from the factory? Cone moves freely and no rubbing on the voice coil.

Gardenstater

I think I see what you are saying, where the surround is almost glued behind the cone in one area or something. Hard to tell from one photo.

Do you have any way of measuring magnet and pole piece dimensions? Are they different on the earlier one?

pitdogg2

JB weld, the two part grey stuff.
Popsicle/craft sticks are your friend.

DeRod

The magnets both measure appox 85mm across and 19mm thick. The magnets look the same as do the pole cap piece, but the baskets are totally different. Notice the newer one is taller/deeper than the older one.

I tried to get a better photo of the back of the surround, but the weird spot is right underneath one of the spokes. It looks like it was slightly mis glued. Maybe the cone looked perfect initially but over time with the mis-glued surround it developed that wave in the front?

pitdogg2

If it plays fine run with it. You could save a search for mw6500 on ebay and hope for the best with a pair.
I've glued up many surrounds, the hardest I've ever done has been the smaller 6.5" speakers. There's not much room behind there to get your fingers in there and get things correct.

Gardenstater

Hmm. Looks to me like the older one looks like it has a larger, deeper basket. The windows look larger, not only because they don't have the unnecessary unused tabs.

DeRod

I asked about the gorilla epoxy because I have some here and wanted to start gluing these up right away but I’ll wait till I pick up some JB Weld.

Do you guys know or have any experience replacing the MW6500 with a MW6503? Or even with the newer Chinese ones from Midwest ?

Just curious if either of these would be good replacement options ?

F1nut

Do you guys know or have any experience replacing the MW6500 with a MW6503? Or even with the newer Chinese ones from Midwest ?

The MW6503 is close, so is the MW6510.

Those are a one size fits all that fits none.

DeRod

It’s the newer one that’s deeper you can see a bit better in that photo

Gardenstater

That photo didn't reveal that, for me anyways Can you measure the basket windows W x L, and the basket spoke W x H, along with overall depth of the driver? Not to give you homework but it is of interest to see how the design changed as the supplier of the midwoofer changed.

Maybe if they were both on a very flat surface and you put a straightedge on top of them it would show what you are trying to show better.

F1nut

They are both MW6500 drivers. So what if one basket looks different than the other. Good lord!!!

DeRod

DeRod

F1nut wrote: »

They are both MW6500 drivers. So what if one basket looks different than the other. Good lord!!!

Sorry it’s my OCD

Gardenstater

DeRod wrote: »

F1nut wrote: »

They are both MW6500 drivers. So what if one basket looks different than the other. Good lord!!!

Sorry it’s my OCD

Not at all. Don't pay any heed. So basket looks largely the same but there is less air space underneath the spider above the front plate and the voice coil was shorter. Plating looks different on the pole piece.

One of the reasons I was interested is because the very early MW6500 had copper plated pole piece. I think they would've had to plate nickel over that to keep the copper from corroding but it is just a guess on my part. Perhaps they would've done a thin nickel plating underneath as well. I am curious how thick the plating was and if they had to have a stronger magnet to compensate for the fact that reduction of gap would mean less magnetic flux (lower BXL). Also, knowing how backwave reflections off the frame and magnet effects sound clarity due to the fact that they come back through the cone, I was interested in the spoke and window sizes.

DeRod

I’ll measure the spokes and windows this evening. I didn’t do it last night because just by eyeballing it they look the same. The only difference I noticed was the newer MW had the little tabs. Where I did notice a difference is between the magnets and baskets. Also the older ones had a factory gasket whereas the newer one has the white hand placed gasket. I put one of each in the 7s and they sound the same.

Gardenstater

At some point they switched from a die cut one piece gasket to the light gray/whitish foam tape from a roll and then later went back to the one piece ones. Very early ones used mortite instead of foam.

Yours may not have been early enough to have the copper plated pole pieces. Good that they all sound the same.

Gardenstater

"reduction of gap" in my post above was confusing. Too late to edit. The reduction of physical gap that would happen with the plating would have to be compensated for by making the pole piece magnetic piece smaller in diameter so that voice coil clearance is maintained, resulting in an increase in the effective magnetic gap but the same physical gap.

@SeleniumFalcon Would any of your contacts at Polk be able to tell us about the Copper Plated Pole Piece in the early MW6500?

F1nut

It's copper

DeRod

Got some tweeter pads .. I didn’t actual glue them on yet. Just got them resting on top of the woofers but doing an a/b test I think the highs are crisper and more focused with the pads around the tweeters.

Gardenstater

The thing to keep in mind is that lots of incremental improvements will add up to a huge difference.

PS: I don't know of anybody that glued them on. Only people who have used the hook half of the hook and loop adhesive backed fasteners. Not a perfect system but it worked well enough. What type of adhesive will you use? I could see "possibly" using that type of temporary adhesive that they use when they mail you a card or something where you can peel it off assuming it will stick to the wool.

DeRod

I not sure yet haven't really given it much thought. I was actually hoping you guys had some ideas.

I don't like the idea of Velcro. I am thinking maybe the Aleenes glue like for the grill fabric but just on the edges between the screws? This would keep it flush to the tweeter rather than sandwiching some velcro in there. Just thinking.

I agree with you about improvements. The crossovers - huge improvement. Tweeter pads - noticeable improvement.

I've been listening to my new 7s for a couple of weeks now and I couldn't be happier. I own many more expensive speakers but these little guys are awesome and can definitely compete with newer pricier speakers.

F1nut

3M 300LSE